Microsoft Word - 7. OEP100301 LTE Radio Network Design ISSUE 1

LTE Radio Network Design Training Manual

Contents

Contents 1 LTE Architecture ................................................................................................................... 1-1 1.1 EPS Architecture ........................................................................................................................................... 1-2 1.1.1 User Equipment ................................................................................................................................... 1-2 1.1.2 Evolved Node B ................................................................................................................................... 1-4 1.1.3 Mobility Management Entity ............................................................................................................... 1-5 1.1.4 Serving Gateway .................................................................................................................................. 1-6 1.1.5 Packet Data Network - Gateway .......................................................................................................... 1-7 1.2 E-UTRAN Architecture and Interfaces ......................................................................................................... 1-8 1.2.1 Uu Interface ......................................................................................................................................... 1-8 1.2.2 X2 Interface ......................................................................................................................................... 1-9 1.2.3 X2 Interface - X2 Application Protocol ............................................................................................... 1-9 1.2.4 X2 Interface - Stream Control Transmission Protocol ......................................................................... 1-9 1.2.5 X2 Interface - GPRS Tunneling Protocol - User ................................................................................ 1-10 1.2.6 S1 Interface ........................................................................................................................................ 1-10 1.2.7 S1 Interface - S1 Application Protocol ............................................................................................... 1-10 1.2.8 S1 Interface - SCTP and GTP-U ........................................................................................................ 1-11 1.3 UE States and Areas .................................................................................................................................... 1-11 1.3.1 RRC State Interaction ........................................................................................................................ 1-12 1.3.2 Interaction with CDMA2000 States ................................................................................................... 1-13 1.3.3 Tracking Areas ................................................................................................................................... 1-14

2 LTE Air Interface ................................................................................................................... 2-1 2.1 LTE Access Techniques ................................................................................................................................. 2-2 2.1.1 Principles of OFDM ............................................................................................................................. 2-2 2.1.2 Frequency Division Multiplexing ........................................................................................................ 2-3 2.1.3 OFDM Subcarriers ............................................................................................................................... 2-3 2.1.4 Fast Fourier Transforms ....................................................................................................................... 2-4 2.1.5 LTE FFT Sizes ..................................................................................................................................... 2-4 2.1.6 OFDM Symbol Mapping ..................................................................................................................... 2-5 2.1.7 Time Domain Interference ................................................................................................................... 2-6 2.1.8 General OFDMA Structure .................................................................................................................. 2-8 2.1.9 Physical Resource Blocks and Resource Elements .............................................................................. 2-9 2.1.10 SC-FDMA Signal Generation .......................................................................................................... 2-10

Issue 01 (2010-06-01)

Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd

i


Contents

2.2 Channel Coding in LTE ............................................................................................................................... 2-13 2.2.1 Channel Coding ................................................................................................................................. 2-13 2.2.2 Modulation and Coding Scheme ........................................................................................................ 2-14 2.3 LTE Channel Structure ................................................................................................................................ 2-17 2.3.1 Logical Channels ............................................................................................................................... 2-17 2.3.2 Transport Channels ............................................................................................................................ 2-19 2.3.3 Physical Channels .............................................................................................................................. 2-19 2.3.4 Radio Channels .................................................................................................................................. 2-20 2.3.5 Channel Mapping ............................................................................................................................... 2-20 2.4 LTE Data Rates ........................................................................................................................................... 2-22 2.4.1 Physical Data Rates ............................................................................................................................ 2-23 2.4.2 Downlink Overheads.......................................................................................................................... 2-25 2.4.3 Uplink Overhead ................................................................................................................................ 2-28 2.4.4 Total Physical Overhead .................................................................................................................... 2-33 2.5 UE Categories ............................................................................................................................................. 2-34

3 LTE Traffic ............................................................................................................................. 3-1 3.1 Traffic Types Carried by LTE Networks ....................................................................................................... 3-2 3.2 Transport Layer Protocols ............................................................................................................................. 3-2 3.2.1 User Datagram Protocol ....................................................................................................................... 3-3 3.2.2 Transmission Control Protocol ............................................................................................................. 3-3 3.3 Protocols used in Support of Various Traffic Types ...................................................................................... 3-5 3.3.1 Real Time Services .............................................................................................................................. 3-5 3.3.2 Web Browsing ...................................................................................................................................... 3-7 3.3.3 File Transfer ......................................................................................................................................... 3-7 3.4 Issues Surrounding Voice over LTE .............................................................................................................. 3-9 3.4.1 PDCP ROHC........................................................................................................................................ 3-9

4 Radio Planning Process ........................................................................................................ 4-1 4.1 Radio Planning Process ................................................................................................................................. 4-2 4.1.1 Pre-Planning ......................................................................................................................................... 4-2 4.1.2 Detailed Planning ................................................................................................................................. 4-3 4.1.3 Optimization ........................................................................................................................................ 4-6 4.2 Frequency Deployment Options .................................................................................................................... 4-6 4.2.1 LTE Bands............................................................................................................................................ 4-6 4.2.2 Spectrum Refarming ............................................................................................................................ 4-8 4.2.3 Advanced Wireless Services ................................................................................................................ 4-8 4.2.4 700MHz Deployment ........................................................................................................................... 4-8

5 LTE Link Budget ................................................................................................................... 5-1 5.1 Cell Coverage and Range .............................................................................................................................. 5-2 5.2 Link Budget ................................................................................................................................................... 5-2 5.2.1 Tx Parameters ...................................................................................................................................... 5-2 5.2.2 Rx Parameters ...................................................................................................................................... 5-3 ii


Issue 01 (2010-06-01)


Contents

5.2.3 Rx Sensitivity ....................................................................................................................................... 5-4 5.2.4 Propagation Margins ............................................................................................................................ 5-4 5.2.5 Maximum Allowable Path Loss ........................................................................................................... 5-4

6 Coverage and Capacity Planning ........................................................................................ 6-1 6.1 Coverage Planning ........................................................................................................................................ 6-2 6.1.1 Radio Propagation ................................................................................................................................ 6-2 6.1.2 Radio Channel ...................................................................................................................................... 6-2 6.1.3 Propagation Models ............................................................................................................................. 6-4 6.1.4 Cell Range and Coverage ..................................................................................................................... 6-5 6.2 Capacity Planning ......................................................................................................................................... 6-6 6.2.1 Cell/ Site Capacity ............................................................................................................................... 6-6 6.3 Optimization .................................................................................................................................................. 6-7 6.3.1 Pre-Launch Optimization ..................................................................................................................... 6-7 6.3.2 Post-Launch Optimization ................................................................................................................... 6-7

7 Huawei LTE Tools................................................................................................................. 7-1 7.1 Huawei Tools................................................................................................................................................. 7-2 7.1.1 U-Net - Professional Radio Network Planning Tool ............................................................................ 7-2 7.1.2 Probe & Assistant - Drive Testing & Data Analysis Tool .................................................................... 7-3 7.1.3 Nastar - Network Performance Analysis Tool ...................................................................................... 7-3 7.2 GENEX U-Net for LTE ................................................................................................................................. 7-4 7.2.1 Product Overview ................................................................................................................................ 7-4 7.2.2 U-Net LTE Planning Functions ............................................................................................................ 7-4 7.2.3 Simulation ............................................................................................................................................ 7-8 7.2.4 Neighbor Cell and PCI Planning .......................................................................................................... 7-9

8 Glossary .................................................................................................................................. 8-1

Issue 01 (2010-06-01)


iii


Contents

iv


Issue 01 (2010-06-01)


Figures

Figures Figure 1-1 LTE Reference Architecture ............................................................................................................. 1-2 Figure 1-2 User Equipment Functional Elements .............................................................................................. 1-3 Figure 1-3 Evolved Node B Functional Elements .............................................................................................. 1-4 Figure 1-4 MME Functional Elements ............................................................................................................... 1-6 Figure 1-5 S-GW Functional Elements .............................................................................................................. 1-7 Figure 1-6 PDN-GW Functional Elements......................................................................................................... 1-7 Figure 1-7 E-UTRAN Interfaces ........................................................................................................................ 1-8 Figure 1-8 Uu Interface Protocols ...................................................................................................................... 1-8 Figure 1-9 X2 Interface Protocols ...................................................................................................................... 1-9 Figure 1-10 S1 Interface Protocols ................................................................................................................... 1-10 Figure 1-11 RRC States .................................................................................................................................... 1-12 Figure 1-12 E-UTRA RRC State Interaction .................................................................................................... 1-13 Figure 1-13 Mobility Procedures between E-UTRA and CDMA2000 ............................................................ 1-13 Figure 1-14 Tracking Areas .............................................................................................................................. 1-14 Figure 2-1 Orthogonal Frequency Division Multiple Access ............................................................................. 2-2 Figure 2-2 Use of OFDM in LTE ....................................................................................................................... 2-2 Figure 2-3 FDM Carriers .................................................................................................................................... 2-3 Figure 2-4 OFDM Subcarriers............................................................................................................................ 2-3 Figure 2-5 Inverse Fast Fourier Transform......................................................................................................... 2-4 Figure 2-6 Fast Fourier Transform ..................................................................................................................... 2-4 Figure 2-7 OFDM Symbol Mapping .................................................................................................................. 2-5 Figure 2-8 OFDM PAPR (Peak to Average Power Ratio) .................................................................................. 2-6 Figure 2-9 Delay Spread..................................................................................................................................... 2-6 Figure 2-10 Inter Symbol Interference ............................................................................................................... 2-7 Figure 2-11 Cyclic Prefix ................................................................................................................................... 2-8 Figure 2-12 OFDMA in LTE .............................................................................................................................. 2-9

Issue 01 (2010-06-01)


v


Figures

Figure 2-13 Physical Resource Block and Resource Element .......................................................................... 2-10 Figure 2-14 SC-FDMA Subcarrier Mapping Concept ...................................................................................... 2-11 Figure 2-15 SC-FDMA Signal Generation ....................................................................................................... 2-12 Figure 2-16 SC-FDMA and the eNB ................................................................................................................ 2-12 Figure 2-17 Summary of LTE Transport Channel Processing .......................................................................... 2-13 Figure 2-18 Using the TBS Size ....................................................................................................................... 2-15 Figure 2-19 Modulation and Coding Scheme Options ..................................................................................... 2-16 Figure 2-20 LTE Channels ............................................................................................................................... 2-17 Figure 2-21 Location of Channels .................................................................................................................... 2-17 Figure 2-22 BCCH and PCCH Logical Channels ............................................................................................ 2-18 Figure 2-23 CCCH and DCCH Signaling ........................................................................................................ 2-18 Figure 2-24 Dedicated Traffic Channel ............................................................................................................ 2-18 Figure 2-25 LTE Release 8 Transport Channels ............................................................................................... 2-19 Figure 2-26 Radio Channel .............................................................................................................................. 2-20 Figure 2-27 Downlink Channel Mapping ......................................................................................................... 2-21 Figure 2-28 Uplink Channel Mapping.............................................................................................................. 2-22 Figure 2-29 PRB with Normal and Extended CP ............................................................................................. 2-25 Figure 2-30 Reference Signals for 2 Antenna ( Normal CP) ............................................................................ 2-25 Figure 2-31 Synchronization Signal Overhead................................................................................................. 2-26 Figure 2-32 PBCH Overhead ........................................................................................................................... 2-27 Figure 2-33 Control Region Overhead ............................................................................................................. 2-27 Figure 2-34 DRS Overhead .............................................................................................................................. 2-29 Figure 2-35 PUCCH Control Regions .............................................................................................................. 2-29 Figure 2-36 Example PRACH Configuration (Format 0) ................................................................................ 2-30 Figure 2-37 PUSCH Control Signaling ............................................................................................................ 2-32 Figure 2-38 SRS Overhead............................................................................................................................... 2-32 Figure 2-39 Uplink and Downlink Physical Overheads ................................................................................... 2-34 Figure 3-1 UDP Header Format ......................................................................................................................... 3-3 Figure 3-2 TCP Session Establishment .............................................................................................................. 3-4 Figure 3-3 TCP Header Format .......................................................................................................................... 3-4 Figure 3-4 RTP / RTCP Protocol Stack .............................................................................................................. 3-5 Figure 3-5 RTP Key Features ............................................................................................................................. 3-6 Figure 3-6 RTCP ................................................................................................................................................ 3-7

vi


Issue 01 (2010-06-01)


Figures

Figure 3-7 Web Browsing Using HTTP ............................................................................................................. 3-7 Figure 3-8 TCP Connections Required for FTP ................................................................................................. 3-8 Figure 3-9 FTP Data Connection Establishment ................................................................................................ 3-9 Figure 3-10 Overheads Associated with a Voice Packet ..................................................................................... 3-9 Figure 3-11 ROHC Feedback ........................................................................................................................... 3-10 Figure 4-1 Radio Planning Process .................................................................................................................... 4-2 Figure 4-2 Pre-Planning Dimensioning .............................................................................................................. 4-3 Figure 4-3 Model Tuning ................................................................................................................................... 4-4 Figure 4-4 Site Selection .................................................................................................................................... 4-5 Figure 4-5 Cell and Site Coverage Planning ...................................................................................................... 4-5 Figure 5-1 Path Loss and Cell Range ................................................................................................................. 5-2 Figure 6-1 Radio Channel Propagation .............................................................................................................. 6-2 Figure 6-2 Impact of Shadowing and Multipath................................................................................................. 6-3 Figure 6-3 LTE Site Dimensioning..................................................................................................................... 6-6 Figure 7-1 LTE Tools ......................................................................................................................................... 7-2 Figure 7-2 U-Net LTE Planning Procedure ........................................................................................................ 7-4 Figure 7-3 RF Results......................................................................................................................................... 7-5 Figure 7-4 U-Net Traffic Parameters .................................................................................................................. 7-6 Figure 7-5 Example U-Net Coverage Predictions .............................................................................................. 7-7 Figure 7-6 U-Net Monte Carlo Statistics ............................................................................................................ 7-8 Figure 7-7 PCI Planning ................................................................................................................................... 7-10

Issue 01 (2010-06-01)


vii


Figures

viii


Issue 01 (2010-06-01)


Tables

Tables Table 2-1 LTE Channel and FFT Sizes ............................................................................................................... 2-5 Table 2-2 Downlink PRB Parameters ............................................................................................................... 2-10 Table 2-3 Transport Channel Coding Options .................................................................................................. 2-14 Table 2-4 Control Information Coding Options................................................................................................ 2-14 Table 2-5 Modulation and TBS index table for PDSCH................................................................................... 2-14 Table 2-6 LTE Channel and FFT Sizes ............................................................................................................. 2-23 Table 2-7 LTE FDD Downlink Peak Rates (FDD using Normal CP)............................................................... 2-23 Table 2-8 LTE FDD Uplink Peak Rates (FDD using Normal CP) ................................................................... 2-24 Table 2-9 PUCCH Overhead ............................................................................................................................ 2-30 Table 2-10 PRACH Configuration Index ......................................................................................................... 2-31 Table 2-11 Downlink Physical Channel Overhead ........................................................................................... 2-33 Table 2-12 Uplink Physical Channel Overhead ................................................................................................ 2-33 Table 2-13 UE Categories ................................................................................................................................. 2-34 Table 3-1 ............................................................................................................................................................. 3-2 Table 3-2 Port Allocations .................................................................................................................................. 3-3 Table 4-1 Business Model Inputs........................................................................................................................ 4-3 Table 4-2 LTE Release 8 FDD Frequency Bands ............................................................................................... 4-7 Table 4-3 LTE Release 8TDD Frequency Bands ................................................................................................ 4-7 Table 5-1 LTE Downlink and Uplink Link Budget ............................................................................................ 5-3 Table 6-1 Example of Cost 231 Hata Cell Ranges.............................................................................................. 6-5

Issue 01 (2010-06-01)


ix


Tables

x


Issue 01 (2010-06-01)


Issue 01 (2010-06-01)

Tables


xi


1 LTE Architecture

1

LTE Architecture

Objectives On completion of this section the participants will be able to: 1.1 Describe the structure of the Evolved Packet System. 1.2 List the nodes and interfaces that make up the Evolved UTRAN. 1.3 Explain the LTE UE states and area concepts.

Issue 01 (2010-06-01)


1-1


1 LTE Architecture

1.1 EPS Architecture The term EPS (Evolved Packet System) relates to the Evolved 3GPP Packet Switched Domain. In contrast to the 2G and 3G networks defined by the 3GPP, LTE can be simply divided into a flat IP based bearer network and a service enabling network. The former can be further subdivided into the E-UTRAN (Evolved - Universal Terrestrial Radio Access Network) and the EPC (Evolved Packet Core) whereas support for service delivery lies in the IMS (IP Multimedia Subsystem). This reference architecture can be seen in Figure 1-1. Figure 1-1 LTE Reference Architecture

Whilst UMTS is based upon WCDMA technology, the 3GPP developed new specifications for the LTE air interface based upon OFDMA (Orthogonal Frequency Division Multiple Access) in the downlink and SC-FDMA (Single Carrier - Frequency Division Multiple Access) in the uplink. This new air interface is termed the E-UTRA (Evolved - Universal Terrestrial Radio Access).

1.1.1 User Equipment Like that of UMTS, the mobile device in LTE is termed the UE (User Equipment) and is comprised of two distinct elements; the USIM (Universal Subscriber Identity Module) and the ME (Mobile Equipment). The ME supports a number of functional entities including:

1-2

RR (Radio Resource) - this supports both the Control Plane and User Plane and in so doing, is responsible for all low level protocols including RRC (Radio Resource Control), PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control) and the PHY (Physical) Layer.

EMM (EPS Mobility Management) - is a Control Plane entity which manages the mobility management states the UE can exist in; LTE Idle, LTE Active and LTE Detached. Transactions within these states include procedures such as TAU (Tracking Area Update) and handovers.


Issue 01 (2010-06-01)


1 LTE Architecture

ESM (EPS Session Management) - is a Control Plane activity which manages the activation, modification and deactivation of EPS bearer contexts. These can either be default EPS bearer contexts or dedicated EPS bearer contexts.

Figure 1-2 User Equipment Functional Elements

Registration Tracking Area Update Handover

Control Plane

User Plane

Bearer Activation Bearer Modification Bearer Deactivation

EPS Mobility & EPS Session Management

IP Adaptation Function

Radio Resource

RRC, PDCP, RLC, MAC & PHY Layer Protocols

In terms of the Physical Layer, the capabilities of the UE may be defined in terms of the frequencies and data rates supported. Devices may also be capable of supporting adaptive modulation including QPSK (Quadrature Phase Shift Keying), 16QAM (16 Quadrature Amplitude Modulation) and 64QAM (Quadrature Amplitude Modulation).

UE Identities An LTE capable UE will be allocated / utilize a number of identities during operation within the network. These include:

IMSI (International Mobile Subscriber Identity) - this complies with the standard 3GPP format and is comprised of the MCC (Mobile Country Code), MNC (Mobile Network Code) and the MSIN (Mobile Subscriber Identity Number). This uniquely identifies a subscriber from within the family of 3GPP technologies - GSM, GPRS, UMTS etc.

IMEI (International Mobile Equipment Identity) - is used to uniquely identify the ME. It can be further subdivided into a TAC (Type Approval Code), FAC (Final Assembly Code) and SNR (Serial Number).

GUTI (Globally Unique Temporary Identity) - is allocated to the UE by the MME (Mobility Management Entity) and identifies a device to a specific MME. The identity is comprised of a GUMMEI (Globally Unique MME Identity) and an M-TMSI (MME Temporary Mobile Subscriber Identity).

S-TMSI (Serving - Temporary Mobile Subscriber Identity) - is used to protect a subscriber’s IMSI during NAS (Non Access Stratum) signaling between the UE and

Issue 01 (2010-06-01)


1-3


1 LTE Architecture

MME as well as identifying the MME from within a MME pool. The S-TMSI is comprised of the MMEC (MME Code) and the M-TMSI.

IP Address - the UE requires a routable IP address from the PDN (Packet Data Network) from which it is receiving higher layer services. This may either be an IPv4 or IPv6 address.

1.1.2 Evolved Node B In addition to the new air interface, a new base station has also been specified by the 3GPP and is referred to as an eNB (Evolved Node B). These, along with their associated interfaces form the E-UTRAN and in so doing, are responsible for:

RRM (Radio Resource Management) - this involves the allocation to the UE of the physical resources on the uplink and downlink, access control and mobility control.

Data Compression - is performed in both the eNB and the UE in order to maximize the amount of user data that can be transferred on the allocated resource. This process is undertaken by PDCP.

Data Protection - is performed at the eNB and the UE in order to encrypt and integrity protect RRC signaling and encrypt user data on the air interface.

Routing - this involves the forwarding of Control Plane signaling to the MME and User Plane traffic to the S-GW (Serving - Gateway).

Packet Classification - this involves the “marking” of uplink packets based upon subscription information or local service provider policy.

Figure 1-3 Evolved Node B Functional Elements

Security in LTE is not solely limited to encryption and integrity protection of information passing across the air interface but instead, NAS encryption and integrity protection between the UE and MME also takes place.

eNB Identities In addition to the UE identities already discussed, there are a number of specific identities associated with the eNB. These include:

1-4

TAI (Tracking Area Identity) - is a logical group of neighboring cells defined by the service provider in which UEs in LTE Idle mode are able to move within, without needing to update the network. As such, it is similar to a RAI (Routing Area Identity) used in 2G and 3G packet switched networks.


Issue 01 (2010-06-01)


1 LTE Architecture

ECGI (E-UTRAN Cell Global Identifier) - is comprised of the MCC, MNC and ECI (Evolved Cell Identity), the latter being coded by each service provider.

Femto Cells In order to improve both network coverage and capacity, the 3GPP have developed a new type of base station to operate within the home or small business environment. Termed the HeNB (Home Evolved Node B), this network element forms part of the E-UTRAN and in so doing supports the standard E-UTRAN interfaces. However, it must be stated that HeNBs do not support the X2 interface. The architecture may include a HeNB-GW (Home Evolved Node B - Gateway) which resides between the HeNB in the E-UTRAN and the MME / S-GW in the EPC in order to scale and support large numbers of base station deployments.

1.1.3 Mobility Management Entity The MME is the Control Plane entity within the EPC and as such is responsible for the following functions:

NAS Signaling and Security - this incorporates both EMM (EPS Mobility Management) and ESM (EPS Session Management) and thus includes procedures such as Tracking Area Updates and EPS Bearer Management. The MME is also responsible for NAS security.

S-GW and PDN-GW Selection - upon receipt of a request from the UE to allocate a bearer resource, the MME will select the most appropriate S-GW and PDN-GW. This selection criterion is based on the location of the UE in addition to current load conditions within the network.

Tracking Area List Management and Paging - whilst in the LTE Idle state, the UE is tracked by the MME to the granularity of a Tracking Area. Whilst UEs remain within the Tracking Areas provided to them in the form of a Tracking Area List, there is no requirement for them to notify the MME. The MME is also responsible for initiating the paging procedure.

Inter MME Mobility - if a handover involves changing the point of attachment within the EPC, it may be necessary to involve an inter MME handover. In this situation, the serving MME will select a target MME with which to conduct this process.

Authentication - this involves interworking with the subscriber’s HSS (Home Subscriber Server) in order to obtain AAA (Access Authorization and Accounting) information with which to authenticate the subscriber. Like that of other 3GPP systems, authentication is based on AKA (Authentication and Key Agreement).

Issue 01 (2010-06-01)


1-5


1 LTE Architecture

Figure 1-4 MME Functional Elements

1.1.4 Serving Gateway The S-GW terminates the S1-U Interface from the E-UTRAN and in so doing, provides the following functions:

1-6

Mobility Anchor - for inter eNB handovers, the S-GW acts as an anchor point for the User Plane. Furthermore, it also acts as an anchor for inter 3GPP handovers to legacy networks - GPRS and UMTS.

Downlink Packet Buffering - when traffic arrives for a UE at the S-GW, it may need to be buffered in order to allow time for the MME to page the UE and for it to enter the LTE Active state.

Packet Routing and Forwarding - traffic must be routed to the correct eNB on the downlink and the specified PDN-GW on the uplink.

GTP/PMIP Support - if PMIP (Proxy Mobile IP) is used on the S5/S8 Interfaces, the S-GW must support MAG (Mobile Access Gateway) functionality. Furthermore, support for GTP/PMIP chaining may also be required.


Issue 01 (2010-06-01)


1 LTE Architecture

Figure 1-5 S-GW Functional Elements

1.1.5 Packet Data Network - Gateway The PDN-GW is the network element which terminates the SGi Interface towards the PDN (Packet Data Network). If a UE is accessing multiple PDNs, there may be a requirement for multiple PDN-GWs to be involved. Functions associated with the PDN-GW include:

Packet Filtering - this incorporates the deep packet inspection of IP datagrams arriving from the PDN in order to determine which TFT (Traffic Flow Template) they are to be associated with.

IP Address Allocation - IP addresses may be allocated to the UE by the PDN-GW. This is included as part of the initial bearer establishment phase or when UEs roam between different access technologies.

Transport Level Packet Marking - this involves the marking of uplink and downlink packets with the appropriate tag e.g. DSCP (Differentiated Services Code Point) based on the QCI (QoS Class Identifier) of the associated EPS bearer.

Accounting - through interaction with a PCRF (Policy Rules and Charging Function), the PDN-GW will monitor traffic volumes and types.

Figure 1-6 PDN-GW Functional Elements

Issue 01 (2010-06-01)


1-7


1 LTE Architecture

1.2 E-UTRAN Architecture and Interfaces As with all 3GPP technologies, it is the actual interfaces which are defined in terms of the protocols they support and the associated signaling messages and user traffic that traverse them. Figure 1-7 illustrates the main interfaces in the E-UTRAN. Figure 1-7 E-UTRAN Interfaces

1.2.1 Uu Interface The Uu Interface supports both a Control Plane and a User plane and spans the link between the UE and the eNB / HeNB. The principle Control Plane protocol is RRC in the Access Stratum and EMM (EPS Mobility Management)/ ESM (EPS Session Management) in the Non Access Stratum. In contrast, the User Plane is designed to carry IP datagrams. However, both Control and User Planes utilize the services of the lower layers, namely PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control) and MAC (Medium Access Control), as well as the PHY (Physical Layer). Figure 1-8 Uu Interface Protocols

1-8


Issue 01 (2010-06-01)


1 LTE Architecture

1.2.2 X2 Interface As previously mentioned, the X2 interface interconnects two eNBs and in so doing supports both a Control Plane and User Plane. The principle Control Plane protocol is X2AP (X2 Application Protocol). This resides on SCTP (Stream Control Transmission Protocol) whereas the User Plane IP is transferred using the services of GTP-U (GPRS Tunneling Protocol User) and UDP (User Datagram Protocol). Figure 1-9 illustrates the X2 User Plane and Control Plane protocols. Figure 1-9 X2 Interface Protocols

1.2.3 X2 Interface - X2 Application Protocol The X2AP is responsible for the following functions:

Mobility Management - this enables the serving eNB to move the responsibility of a specified UE to a target eNB. This includes Forwarding the User Plane, Status Transfer and UE Context Release functions.

Load Management - this function enables eNBs to communicate with each other in order to report resource status, overload indications and current traffic loading.

Error Reporting - this allows for the reporting of general error situations for which specific error reporting mechanisms have not been defined.

Setting / Resetting X2 - this provides a means by which the X2 interface can be setup / reset by exchanging the necessary information between the eNBs.

Configuration Update - this allows the updating of application level data which is needed for two eNBs to interoperate over the X2 interface.

1.2.4 X2 Interface - Stream Control Transmission Protocol Defined by the IETF (Internet Engineering Task Force) rather than the 3GPP, SCTP was developed to overcome the shortfalls in TCP (Transmission Control Protocol) and UDP when transferring signaling information over an IP bearer. Functions provided by SCTP include:

Reliable Delivery of Higher Layer Payloads.

Sequential Delivery of Higher Layer Payloads.

Issue 01 (2010-06-01)


1-9


1 LTE Architecture

Improved resilience through Multihoming.

Flow Control.

Improved Security. SCTP is also found on the S1-MME Interface which links the eNB to the MME.

1.2.5 X2 Interface - GPRS Tunneling Protocol - User GTP-U tunnels are used to carry encapsulated PDU (Protocol Data Unit) and in-band signaling messages between endpoints. Numerous GTP-U tunnels may exist in order to differentiate between EPS bearer contexts and these are identified through a pair of TEID (Tunnel Endpoint Identifier). GTP-U is also found on the S1-U Interface which links the eNB to the S-GW and may also be used on the S5 Interface linking the S-GW to the PDN-GW.

1.2.6 S1 Interface The S1 interface can be subdivided into the S1-MME interface supporting Control Plane signaling between the eNB and the MME and the S1-U Interface supporting User Plane traffic between the eNB and the S-GW. Figure 1-10 S1 Interface Protocols

S1-MME

S1-U

Control Plane

User Plane

S1AP

GTP-U

SCTP

UDP

IP

IP

Layer 2

Layer 2

Layer 1

Layer 1

1.2.7 S1 Interface - S1 Application Protocol The S1AP spans the S1-MME Interface and in so doing, supports the following functions:

1-10

E-RAB (E-UTRAN - Radio Access Bearer) Management - this incorporates the setting up, modifying and releasing of the E-RABs by the MME.

Initial Context Transfer - this is used to establish an S1UE context in the eNB, setup the default IP connectivity and transfer NAS related signaling.

UE Capability Information Indication - this is used to inform the MME of the UE Capability Information.


Issue 01 (2010-06-01)


1 LTE Architecture

Mobility - this incorporates mobility features to support a change in eNB or change in RAT.

Paging.

S1 Interface Management - this incorporates a number of sub functions dealing with resets, load balancing and system setup etc.

NAS Signaling Transport - this is used for the transport of NAS related signaling over the S1-MME Interface.

UE Context Modification and Release - this allows for the modification and release of the established UE Context in the eNB and MME respectively.

Location Reporting - this enables the MME to be made aware of the UEs current location within the network.

1.2.8 S1 Interface - SCTP and GTP-U The S1-MME and S1-U lower layer protocols are similar to the X2 interface. As such, they also utilize the services of SCTP (discussed in Section 1.2.4 ) and GTP-U (discussed in Section 1.2.5 ).

1.3 UE States and Areas There are three LTE mobility states, namely: LTE Idle, LTE Active and LTE Detached. The initial EMM Attach procedure enables a UE to transition into the LTE Active State from the LTE Detached State. In LTE, RRC has two main states, namely:

RRC Idle - this provides services to support DRX (Discontinuous Reception), broadcast of SI (System Information) to enable access, cell reselection and paging information.

RRC Connected - in this state the UE has state information stored in the eNB and has an RRC connection, i.e. SRB (Signaling Radio Bearer). The eNB can track the UE to the cell level and RRC provides services to support cell measurements in order to facilitate network controlled handovers.

Figure 1-11 illustrates the different LTE states, as well as some of the key functions performed by RRC in these states. In addition to having a GUTI (Globally Unique Temporary Identity) and S-TMSI (Serving Temporary Mobile Subscriber Identity), whilst in the RRC Connected mode, the UE is also allocated an E-UTRAN identifier(s). The most common is the C-RNTI (Cell - Radio Network Temporary Identity), however other forms of RNTI (Radio Network Temporary Identity) also exist.

Issue 01 (2010-06-01)


1-11


1 LTE Architecture

Figure 1-11 RRC States

PLMN Selection Broadcast of System Information Cell Selection RRC Connection (SRB) RRC Context in eNB UE Known in a Cell Send and/or Receive Data to/from UE Network Controlled Mobility Measurement Control UE Monitors Scheduling Control Channel UE Reports Channel Quality UE can send Feedback Information DRX can be Configured

LTE Detached

LTE Active RRC Connected

LTE Idle RRC Idle

DRX configured by NAS Broadcast of System Information Paging Cell Reselection Mobility GUTI Allocated Located in Tracking Area(s) No RRC Context Stored in the eNB

1.3.1 RRC State Interaction In addition to RRC Idle and RRC Connected there are various transitions to and from UTRA (Universal Terrestrial Radio Access) and GERAN (GSM/EDGE Radio Access Network) States. Figure 1-12 illustrates the main states and inter-RAT mobility procedures. In contrast to the GERAN and UTRA states, the E-UTRA (Evolved - Universal Terrestrial Radio Access) state is simplified. This is mainly due to the fact that it is an optimized packet system.

1-12


Issue 01 (2010-06-01)


1 LTE Architecture

Figure 1-12 E-UTRA RRC State Interaction

GSM Connected Handover

Cell_DCH

Cell_FACH

GPRS Packet Transfer Mode

CCO with NACC

Cell_PCH URA_PCH

Connection Establishment/ Release



UTRA_Idle

Handover

E-UTRA RRC Connected

CCO, Reselection

Reselection

Reselection

E-UTRA RRC Idle

Reselection CCO, Reselection

GSM Idle/GPRS Packet Idle

1.3.2 Interaction with CDMA2000 States In addition to interworking with UMTS and GERAN, the LTE system is also able to interwork with CDMA2000 1xRTT CS (Circuit Switched) and HRPD (High Rate Packet Data) based systems. Figure 1-13 illustrates the main mobility transitions for CDMA2000 interworking. Figure 1-13 Mobility Procedures between E-UTRA and CDMA2000

Issue 01 (2010-06-01)


1-13


1 LTE Architecture

1.3.3 Tracking Areas Cells are divided into TA (Tracking Areas). These are similar in concept to the Location and Registration Areas used in GSM/GPRS and UMTS. The number of cells within a tracking area will be dependent on aspects such as traffic throughput, geographical restrictions etc. A cell can only be a member of one Tracking Area. In addition, it is worth noting that the eNB may have multiple cells which belong to different TAs. Figure 1-14 illustrates the basic concept of Tracking Areas. The UE performs TAU (Tracking Area Update) procedures based on crossing Tracking Area boundaries or on the expiry of the Tracking Area Periodic Timer, namely the T3412 timer. By default this is set to 54 minutes in the 3GPP specifications. Figure 1-14 Tracking Areas

1-14


Issue 01 (2010-06-01)


2 LTE Air Interface

2

LTE Air Interface

Objectives On completion of this section the participants will be able to: 2.1 Explain the principles of OFDMA and SC-FDMA. 2.2 Explain the coding and modulation adaptation used in LTE. 2.3 List the LTE logical, transport and physical channels. 2.4 Explain how the LTE downlink and uplink data rates are achieved. 2.5 List the LTE UE category capabilities.

Issue 01 (2010-06-01)


2-1


2 LTE Air Interface

2.1 LTE Access Techniques OFDMA (Orthogonal Frequency Division Multiple Access) is the latest addition to cellular systems. It provides a multiple access technique based on OFDM (Orthogonal Frequency Division Multiplexing). Figure 2-1 illustrates the basic view of OFDMA. It can be seen that the bandwidth is broken down to smaller units known as “subcarriers”. These are grouped together and allocated as a resource to a device. It can also be seen that a device can be allocated different resources in both the time and frequency domain. Figure 2-1 Orthogonal Frequency Division Multiple Access

2.1.1 Principles of OFDM The LTE air interface utilizes two different multiple access techniques both based on OFDM (Orthogonal Frequency Division Multiplexing):

OFDMA (Orthogonal Frequency Division Multiple Access) used on the downlink.

SC-FDMA (Single Carrier - Frequency Division Multiple Access) used on the uplink.

Figure 2-2 Use of OFDM in LTE

OFDM (OFDMA)

OFDM (SC-FDMA) The concept of OFDM is not new and is currently being used on various systems such as Wi-Fi and WiMAX. In addition, it was even considered for UMTS back in 1998. One of the main reasons why it was not chosen at the time was the handset’s limited processing power and poor battery capabilities. LTE was able to choose OFDM based access due to the fact mobile handset processing capabilities and battery performance have both improved. In addition, there is continual pressure to produce more spectrally efficient systems.

2-2


Issue 01 (2010-06-01)


2 LTE Air Interface

2.1.2 Frequency Division Multiplexing OFDM is based on FDM (Frequency Division Multiplexing) and is a method whereby multiple frequencies are used to simultaneously transmit information. Figure 2-3 illustrates an example of FDM with four subcarriers. These can be used to carry different information and to ensure that each subcarrier does not interfere with the adjacent subcarrier, a guard band is utilized. In addition, each subcarrier has slightly different radio characteristics and this may be used to provide diversity. Figure 2-3 FDM Carriers

FDM systems are not that spectrally efficient (when compared to other systems) since multiple subcarrier guard bands are required.

2.1.3 OFDM Subcarriers OFDM follows the same concept as FDM but it drastically increases spectral efficiency by reducing the spacing between the subcarriers. Figure 2-4 illustrates how the subcarriers can overlap due to their orthogonality with the other subcarriers, i.e. the subcarriers are mathematically perpendicular to each other. As such, when a subcarrier is at its maximum the two adjacent subcarriers are passing through zero. In addition, OFDM systems still employ guard bands. These are located at the upper and lower parts of the channel and reduce adjacent channel interference. Figure 2-4 OFDM Subcarriers

Issue 01 (2010-06-01)


2-3


2 LTE Air Interface

The centre subcarrier, known as the DC (Direct Current) subcarrier, is not typically used in OFDM system due to its lack of orthogonality.

2.1.4 Fast Fourier Transforms OFDM subcarriers are generated and decoded using mathematical functions called FFT (Fast Fourier Transform) and IFFT (Inverse Fast Fourier Transform). The IFFT is used in the transmitter to generate the waveform. Figure 2-5 illustrates how the coded data is first mapped to parallel streams before being modulated and processed by the IFFT. Figure 2-5 Inverse Fast Fourier Transform

Subcarrier Modulation

Coded Bits

Serial to Parallel

Inverse Fast Fourier Transform

IFFT

RF Complex Waveform

At the receiver side, this signal is passed to the FFT which analyses the complex/combined waveform into the original streams. Figure 2-6 illustrates the FFT process. Figure 2-6 Fast Fourier Transform

2.1.5 LTE FFT Sizes Fast Fourier Transforms and Inverse Fast Fourier Transforms both have a defining size. For example, an FFT size of 512 indicates that there are 512 subcarriers. In reality, not all 512 subcarriers can be utilized due to the channel guard bands and the fact that a DC (Direct Current) subcarrier is also required. Table 2-1 illustrates the LTE channel bandwidth options, as well as the FFT size and associated sampling rate. Using the sampling rate and the FFT size the subcarrier spacing can be calculated, e.g. 7.68MHz/15kHz = 512.

2-4


Issue 01 (2010-06-01)


2 LTE Air Interface

Table 2-1 LTE Channel and FFT Sizes Channel Bandwidth

FFT Size

Subcarrier Bandwidth

1.4MHz

128

1.92MHz

3MHz

256

3.84MHz

5MHz

512

Sampling Rate

7.68MHz 15kHz

10MHz

1024

15.36MHz

15MHz

1536

23.04MHz

20MHz

2048

30.72MHz

The subcarrier spacing of 15kHz is also used in the calculation to identify the OFDM symbol duration.

2.1.6 OFDM Symbol Mapping The mapping of OFDM symbols to subcarriers is dependent on the system design. Figure 2-7 illustrates an example of OFDM mapping. The first 12 modulated OFDM symbols are mapped to 12 subcarriers, i.e. they are transmitted at the same time but using different subcarriers. The next 12 subcarriers are mapped to the next OFDM symbol period. In addition, a CP (Cyclic Prefix) is added between the symbols. Figure 2-7 OFDM Symbol Mapping

LTE allocates resources in groups of 12 subcarriers. This is known as a PRB (Physical Resource Block).

In the previous example 12 different modulated OFDM symbols are transmitted simultaneously. Figure 2-8 illustrates how the combined energy from this will result in either constructive peaks (when the symbols are the same) or destructive nulls (when the symbols are different). This means that OFDM systems have a high PAPR (Peak to Average Power Ratio).

Issue 01 (2010-06-01)


2-5


2 LTE Air Interface

Figure 2-8 OFDM PAPR (Peak to Average Power Ratio)

2.1.7 Time Domain Interference The OFDM signal provides some protection in the frequency domain due to the orthogonality of the subcarriers. The main issue is with delay spread, i.e. multipath interference. Figure 2-9 illustrates two of the main multipath effects, namely delay and attenuation. The delayed signal can manifest itself as ISI (Inter Symbol Interference), whereby one symbol impacts the next. This is illustrated in Figure 2-10. Figure 2-9 Delay Spread

ISI (Inter Symbol Interference) is typically reduced with “equalizers”. However, for the equalizer to be effective a known bit pattern or “training sequence” is required. However, this reduces the system capacity, as well as impacts processing on a device. Instead, OFDM systems employ a CP (Cyclic Prefix).

2-6


Issue 01 (2010-06-01)


2 LTE Air Interface

Figure 2-10 Inter Symbol Interference

1st Received Signal

Delayed Signal

Interference Caused

Cyclic Prefix A CP (Cyclic Prefix) is utilized in most OFDM systems to combat multipath delays. It effectively provides a guard period for each OFDM symbol. Figure 2-11 illustrates the Cyclic Prefix and its location in the OFDM Symbol. Notice that the Cyclic Prefix is effectively a copy taken from the back of the original symbol which is then placed in front of the symbol to make the OFDM symbol (Ts). The size of the Cyclic Prefix relates to the maximum delay spread the system can tolerate. As such, systems designed for macro coverage, i.e. large cells, should have a large CP. This does however impact the system capacity since the number of symbols per second is reduced.

Issue 01 (2010-06-01)


2-7


2 LTE Air Interface

Figure 2-11 Cyclic Prefix

Frequency CP

CP

CP

CP

CP

CP

CP

CP

CP

CP

CP

CP

Symbol Period T(s)

Cyclic Prefix

Time

Bit Period T(b)

T(g)

Symbol Period T(s)

LTE has two defined Cyclic Prefix sizes, normal and extended. The extended Cyclic Prefix is designed for larger cells.

2.1.8 General OFDMA Structure The E-UTRA downlink is based on OFDMA. As such, it enables multiple devices to receive information at the same time but on different parts of the radio channel. In most OFDMA systems this is referred to as a “Subchannel”, i.e. a collection of subcarriers. However, in E-UTRA, the term subchannel is replaced with the term PRB (Physical Resource Block). Figure 2-12 illustrates the concept of OFDMA, whereby different users are allocated one or more resource blocks in the time and frequency domain, thus enabling efficient scheduling of the available resources.

2-8


Issue 01 (2010-06-01)


2 LTE Air Interface

Figure 2-12 OFDMA in LTE

Frequency Device is allocated one or more PRB (Physical Resource Blocks)

Channel Bandwidth E.g. 3MHz

OFDMA

PRB consists of 12 subcarriers for 0.5ms

Time It is also worth noting that a device is typically allocated 1ms of time, i.e. a subframe, and not an individual PRB.

2.1.9 Physical Resource Blocks and Resource Elements A PRB (Physical Resource Block) consists of 12 consecutive subcarriers and lasts for one slot, i.e. 0.5ms. Figure 2-13 illustrates the size of a PRB. The NRBDL parameter is used to define the number of RB (Resource Blocks) used in the DL (Downlink). This is dependent on the channel bandwidth. In contrast, NRBUL is used to identify the number of resource blocks in the uplink. Each RB (Resource Block) consists of NSCRB subcarriers, which for standard operation is set to 12. In addition, another configuration is available when using MBSFN and a 7.5kHz subcarrier spacing. The PRB is used to identify an allocation. It typically includes 6 or 7 symbols, depending on whether an extended or normal cyclic prefix is configured. The term RE (Resource Element) is used to describe one subcarrier lasting one symbol. This can then be assigned to carry modulated information, reference information or nothing.

Issue 01 (2010-06-01)


2-9


2 LTE Air Interface

Figure 2-13 Physical Resource Block and Resource Element

Radio Frame = 10ms 0

1

2

3

4

5

6

7

8

9

Subframe Slot 9

NSCRB Subcarriers = 12

Slot 8

NRBDL

Resource Element NSymbDL

The different configurations for the downlink E-UTRA PRB are illustrated in Table 2-2. Table 2-2 Downlink PRB Parameters Configuration Normal Cyclic Prefix Extended Cyclic Prefix

NSCRB ∆f = 15kHz

NSymbDL 7

12

∆f = 15kHz ∆f = 7.5kHz

6 24

3

The uplink PRB configuration is similar; however the 7.5kHz option is not available.

2.1.10 SC-FDMA Signal Generation The uplink in LTE, as previously mentioned, is based on SC-FDMA (Single Carrier Frequency Division Multiple Access). This was chosen for its low PAPR (Peak to Average Power Ratio) and flexibility which reduced complexity in the handset and improved power performance and battery life. SC-FDMA tries to combine the best characteristics of single carrier systems like low peak-to-average power ratio, with the advantages of multi carrier OFDM and as such, is well suited to the LTE uplink requirements.

2-10


Issue 01 (2010-06-01)


2 LTE Air Interface

The basic transmitter and receiver architecture is very similar (nearly identical) to OFDM, and it offers the same degree of multipath protection. Importantly, because the underlying waveform is essentially single carrier, the PAPR is lower. It is quite difficult to visually represent SC-FDMA in the time and frequency domain. This section aims to illustrate the concept. Figure 2-14 illustrates the basic structure of the SC-FDMA process. Figure 2-14 SC-FDMA Subcarrier Mapping Concept

0 0 0 0 DFT Symbols

Subcarrier Mapping

IDFT

CP Insertion

0 0 0

In Figure 2-14 the SC-FDMA signal generation process starts by creating a time domain waveform of the data symbols to be transmitted. This is then converted into the frequency domain, using a DFT (Discrete Fourier Transform). DFT length and sampling rate are chosen so that the signal is fully represented, as well as being spaced 15kHz apart. Each bin (subcarrier) will have its own fixed amplitude and phase for the duration of the SC-FDMA symbol. Next the signal is shifted to the desired place in the channel bandwidth using the zero insertion concept, i.e. subcarrier mapping. Finally, the signal is converted to a single carrier waveform using an IDFT (Inverse Discrete Fourier Transform) and other functions. Finally a cyclic prefix can be added. Note that additional functions such as S-P (Serial to Parallel) and P-S (Parallel to Serial) converters are also required as part of a detailed functional description. Figure 2-15 illustrates the concept of the DFT, such that a group of N symbols map to N subcarriers. However depending on the combination of N symbols into the DFT the output will vary. As such, the actual amplitude and phase of the N subcarriers is like a “code word”. For example the first combination represents the first set of symbols. Since the second set of symbols is different the amplitude and phase of the N subcarriers would then be different.

Issue 01 (2010-06-01)


2-11


2 LTE Air Interface

Figure 2-15 SC-FDMA Signal Generation

N symbols sequence produces N subcarriers

DFT Output

First N Symbols DFT Modulated and Coded Symbols Second N Symbols DFT

Different input sequence produces different output

The process at the eNB receiver takes the N subcarriers and reverses the process. This is achieved using an IDFT (Inverse Discrete Fourier Transform) which effectively reproduces the original N symbols. Figure 2-16 illustrates the basic view of how the subcarriers received at the eNB are converted back into the original signals. Note that the SC-FDMA symbols have a constant amplitude and phase and like ODFMA, a CP (Cyclic Prefix) is still required. Figure 2-16 SC-FDMA and the eNB

2-12


Issue 01 (2010-06-01)


2 LTE Air Interface

2.2 Channel Coding in LTE The term “channel coding” can be used to describe the overall coding for the LTE channel. It can also be used to describe one of the individual stages. LTE channel coding is typically focused on a TB (Transport Block). This is a block of information which is provided by the upper layer, i.e. MAC (Medium Access Control). Figure 2-17 summarizes the typical processes performed by the PHY (Physical Layer), these include:

CRC (Cyclic Redundancy Check) attachment for the Transport Block.

Code block segmentation and CRC attachment.

Channel Coding.

Rate Matching.

Code Block Concatenation.

Figure 2-17 Summary of LTE Transport Channel Processing

Transport Block

MAC Layer PHY Layer

Transport Block CRC Attachment Code Block CRC Attachment and Segmentation Channel Coding

Rate Matching

Code Block Concatenation

Additional Layer 1 Processes

The coding stages in Figure 2-17 are indicative of the LTE DL-SCH (Downlink Shared Channel) and the PCH (Paging Channel). Other channels, such as the UL-SCH (Uplink Shared Channel), BCH (Broadcast Channel) etc. are different but they can still utilize similar processes, e.g. they all have a “channel coding” stage.

2.2.1 Channel Coding Channel coding in LTE facilitates FEC (Forward Error Correction) across the air interface. There are four main types:

Issue 01 (2010-06-01)

Repetition Coding


2-13


2 LTE Air Interface

Block Coding.

Tail Biting Convolutional Coding.

Turbo Coding.

The actual method used is linked to the type of LTE transport channel (Table 2-3) or the control information type (Table 2-4). Table 2-3 Transport Channel Coding Options Transport Channel

Coding Method

Rate

Turbo Coding

1/3

Tail Biting Convolutional Coding

1/3

DL-SCH UL-SCH PCH MCH BCH

Table 2-4 Control Information Coding Options Control Information

Coding Method

Rate

DCI


1/3

CFI

Block Code

1/16

HI

Repetition Code

1/3

UCI

Block Code

Variable


1/3

2.2.2 Modulation and Coding Scheme One of the key parameters in the DCI messages is the MCS Index Parameter. Table 2-5 illustrates the mapping of the MCS index to the modulation and TBS (Transport Block Set) Index. Table 2-5 Modulation and TBS index table for PDSCH

2-14

MCS Index I MCS

Modulation Order Qm

TBS Index I TBS

MCS Index I MCS

Modulation Order Qm

TBS Index I TBS

0

2

0

16

4

15

1

2

1

17

6

15

2

2

2

18

6

16

3

2

3

19

6

17


Issue 01 (2010-06-01)


2 LTE Air Interface

4

2

4

20

6

18

5

2

5

21

6

19

6

2

6

22

6

20

7

2

7

23

6

21

8

2

8

24

6

22

9

2

9

25

6

23

10

4

9

26

6

24

11

4

10

27

6

25

12

4

11

28

6

26

13

4

12

29

2

Reserved

14

4

13

30

4

15

4

14

31

6

The modulation order parameter indicates whether the scheduled transmission is QPSK (2 bits), 16QAM (4bits) or 64QAM (6bits). The UE is able to use this information, in conjunction with the physical number of Resource Blocks, i.e. symbols, to receive all the bits. Figure 2-18 illustrates an example of a scheduled message with associated parameters. As previously mentioned the resource allocation, modulation order and precoding information enables the UE to determine the number and location of the physical bits. The TBS (Transport Block Set) parameter in the previous table enables the UE to identify the size of the transport block(s) using a mixture of a table and equation. Since the coding is all predefined, the UE is able to replicate the number of coded bits (pre puncturing) and therefore, using the RV (Redundancy Version) parameter, identify which bits the eNB would have punctured/rate matched. Using this it can now attempt to decoded the transport block and verify the CRC.

5MHz (25 Resource Blocks)

Figure 2-18 Using the TBS Size

Issue 01 (2010-06-01)


2-15


2 LTE Air Interface

Figure 2-19 illustrates an example of a transport block being coded and then scheduled using different modulation techniques. In so doing, it illustrates the efficiencies of using HOM (Higher Order Modulation) schemes. Figure 2-19 Modulation and Coding Scheme Options

The main issue when using higher order modulation schemes is the increased SINR (Signal to Interference plus Noise Ratio) required. The actual value required is based on link level simulations and the resultant “Look-Up Tables”. For example, MCS Index “12” for 5 RB (Resource Blocks) would typically require 5.6dB SINR. In contrast, MCS Index “23”, for 2 RBs would typically require 15.06dB SINR. It is also worth noting that different Look-Up Tables are typically generated for:

Different Channel Models, e.g. EPA (Extended Pedestrian A), EVA (Extended Vehicular A) and ETU (Extended Typical Urban) models.

Different Antenna Schemes, e.g. 2TX (Transmit) 2RX (Receive).

BLER (Block Error Rate), e.g. 10%.

MCS Decision The decision/choice of MCS is a trade-off between SINR and resource utilization, with the SINR impacting on the coverage and power utilization.

2-16


Issue 01 (2010-06-01)


2 LTE Air Interface

2.3 LTE Channel Structure The concept of “channels” is not new. Both GSM and UMTS defined various channel categories, however LTE terminology is closer to UMTS. Broadly there are four categories of channel. Figure 2-20 LTE Channels

2.3.1 Logical Channels In order to describe Logical Channels it is best to identify where Logical Channels are located in relation to the LTE protocols and the other channel types. Figure 2-21 shows Logical Channels located between the RLC and the MAC layers. Figure 2-21 Location of Channels

Logical Channels

RLC MAC

Transport Channels

PHY Physical Channels

Radio Channel

Logical channels are classified as either Control Logical Channels, which carry control data such as RRC signaling, or Traffic Logical Channels which carry user plane data.

Control Logical Channels The various forms of these Control Logical Channels include:

BCCH (Broadcast Control Channel) - This is a downlink channel used to send SI (System Information) messages from the eNB. These are defined by RRC.

PCCH (Paging Control Channel) - This downlink channel is used by the eNB to send paging information.

Issue 01 (2010-06-01)


2-17


2 LTE Air Interface

Figure 2-22 BCCH and PCCH Logical Channels

System Information Messages BCCH PCCH Paging Devices

CCCH (Common Control Channel) - This is used to establish a RRC (Radio Resource Control) connection, also known as a SRB (Signaling Radio Bearer). The SRB is also used for re-establishment procedures. SRB 0 maps to the CCCH.

DCCH (Dedicated Control Channel) - This provides a bidirectional channel for signaling. Logically there are two DCCH activated: −

SRB 1 - This is used for RRC messages, as well as RRC messages carrying high priority NAS signaling.

−

SRB 2 - This is used for RRC carrying low priority NAS signaling. Prior to its establishment low priority signaling is sent on SRB1.

Figure 2-23 CCCH and DCCH Signaling

Traffic Logical Channels Release 8 LTE has one type of Logical Channel carrying traffic, namely the DTCH (Dedicated Traffic Channel). This is used to carry DRB (Dedicated Radio Bearer) information, i.e. IP datagrams. Figure 2-24 Dedicated Traffic Channel

2-18


Issue 01 (2010-06-01)


2 LTE Air Interface

The DTCH is a bidirectional channel that can operate in either RLC AM or UM mode. This is configured by RRC and is based on the QoS (Quality of Service) of the E-RAB (EPS Radio Access Bearer).

2.3.2 Transport Channels Historically, Transport Channels were split between common and dedicated channels. However, LTE has moved away from dedicated channels in favor of the common/shared channels and the associated efficiencies provided. The main Release 8 Transport Channels include:

BCH (Broadcast Channel) - This is a fixed format channel which occurs once per frame and carries the MIB (Master Information Block). Note that the majority of System Information messages are carries on the DL-SCH (Downlink - Shared Channel).

PCH (Paging Channel) - This channel is used to carry the PCCH, i.e. paging messages. It also utilizes DRX (Discontinuous Reception) to improve UE battery life.

DL-SCH (Downlink - Shared Channel) - This is the main downlink channel for data and signaling. It supports dynamic scheduling, as well as dynamic link adaptation. In addition, it supports HARQ (Hybrid Automatic Repeat Request) operation to improve performance. As previously mentioned it also facilitates the sending of System Information messages.

RACH (Random Access Channel) - This channel carries limited information and is used in conjunction with Physical Channels and preambles to provide contention resolution procedures.

UL-SCH (Uplink Shared Channel) - Similar to the DL-SCH, this channel supports dynamic scheduling (eNB controlled) and dynamic link adaptation by varying the modulation and coding. In addition, it too supports HARQ (Hybrid Automatic Repeat Request) operation to improve performance.

Figure 2-25 LTE Release 8 Transport Channels

2.3.3 Physical Channels The Physical Layer facilitates transportation of MAC Transport Channels, as well as providing scheduling, formatting and control indicators.

Downlink Physical Channels There are a number of downlink Physical Channels in LTE. These include:

PBCH (Physical Broadcast Channel) - This channel carries the BCH.

PCFICH (Physical Control Format Indicator Channel) - This is used to indicate the number of OFDM symbols used for the PDCCH.

Issue 01 (2010-06-01)


2-19


2 LTE Air Interface

PDCCH (Physical Downlink Control Channel) - This channel is used for resource allocation.

PHICH (Physical Hybrid ARQ Indicator Channel) - This channel is part of the HARQ process.

PDSCH (Physical Downlink Shared Channel) - This channel carries the DL-SCH.

Uplink Physical Channels There are a number of Uplink Physical Channels in LTE. These include:

PRACH (Physical Random Access Channel) - This channel carries the Random Access Preamble. The location of the PRACH is defined by higher layer signaling, i.e. RRC signaling.

PUCCH (Physical Uplink Control Channel) - This channel carries uplink control and feedback. It can also carry scheduling requests to the eNB.

PUSCH (Physical Uplink Shared Channel) - This is the main uplink channel and is used to carry the UL-SCH (Uplink Shared Channel) Transport Channel. It carries both signaling and user data, in addition to uplink control. It is worth noting that the UE is not allowed to transmit the PUCCH and PUSCH at the same time.

2.3.4 Radio Channels The term “Radio Channel” is typically used to describe the overall channel, i.e. the downlink and uplink carrier for FDD or the single carrier for TDD. Figure 2-26 Radio Channel

2.3.5 Channel Mapping There are various options for multiplexing multiple bearers together, such that Logical Channels may be mapped to one or more Transport Channels. These in turn are mapped into Physical Channels. Figure 2-27 and Figure 2-28 illustrate the mapping options.

2-20


Issue 01 (2010-06-01)


2 LTE Air Interface

Figure 2-27 Downlink Channel Mapping

ESM

EMM

IP

Integrity

ROHC

RRC

Ciphering Ciphering

Issue 01 (2010-06-01)

TM

TM

TM

UM/AM

UM/AM

Logical Channels

BCCH

PCCH

CCCH

DCCH

DTCH

Transport Channels

BCH

PCH

Physical Channels

PBCH

PCFICH


DL-SCH

PHICH

PDCCH

PDSCH

2-21


2 LTE Air Interface

Figure 2-28 Uplink Channel Mapping

ESM

EMM

IP

RRC Integrity

ROHC

Ciphering

Ciphering

TM

UM/AM

UM/AM

Logical Channels

CCCH

DCCH

DTCH

Transport Channels

RACH

Physical Channels

PRACH

UL-SCH

PUCCH

PUSCH

In order to facilitate the multiplexing from Logical Channels to Transport Channels, the MAC Layer typically adds a LCID (Logical Channel Identifier).

2.4 LTE Data Rates There are various options and configurations that impact the actual LTE data rates. These include:

Channel Bandwidth.

Cyclic Prefix Size.

Scheduling Options.

Physical Channel Overhead.

MIMO/Diversity Configuration.

UE Capabilities.

In addition, depending on the location of the UE and the planning of the network other factors such as the:

2-22

Required MCS and required SINR based on UE location.

ICI (Inter Cell Interference) Issues.


Issue 01 (2010-06-01)


2 LTE Air Interface

2.4.1 Physical Data Rates Bandwidth Limitations The cell bandwidth is very important to the calculation of cell and UE data rates. Table 2-1 illustrates the channel bandwidth options available to LTE, as well as the FFT size and number of Resource Blocks Table 2-6 LTE Channel and FFT Sizes Channel Bandwidth

FFT Size

1.4MHz

Subcarrier Bandwidth

Sampling Rate

Number of Resource Blocks

128

1.92MHz

6

3MHz

256

3.84MHz

15

5MHz

512

7.68MHz

25

15kHz 10MHz

1024

15.36MHz

50

15MHz

1536

23.04MHz

75

20MHz

2048

30.72MHz

100

Downlink LTE Peak Rates It is possible to calculate the downlink peak rates for different combinations of bandwidth, MCS and MIMO. Table 2-7 illustrates typical quoted figures. Table 2-7 LTE FDD Downlink Peak Rates (FDD using Normal CP) Effective MCS

MIMO

QPSK ½

1.4MHz

3MHz

5MHz

10MHz

15MHz

20MHz

Single

0.85

2.21

3.71

7.46

11.21

14.96

16QAM ½

2x2

3.35

8.53

14.29

28.69

43.09

57.49

16QAM ¾

2x2

5.02

12.79

21.43

43.03

64.63

86.23

16QAM 1

2x2

6.69

17.06

28.58

57.40

86.18

114.98

64QAM ½

2x2

5.02

12.79

21.43

43.03

64.63

86.23

64QAM ¾

2x2

7.53

19.19

32.15

64.55

96.95

129.35

9

2x2

9.03

23.03

38.58

77.46

116.34

155.22

64QAM 1

2x2

10.04

25.59

42.87

86.07

129.27

172.47

64QAM 1

4x2

19.09

48.47

81.11

162.71

244.31

325.91

64QAM

Streams

10

The downlink peak figures assume that only 1OFDM symbol is allocated to the PDCCH.

Issue 01 (2010-06-01)


2-23


2 LTE Air Interface

Uplink LTE Peak Rates The uplink peak data rates are reduced when compared with the downlink. This is mainly due to the fact Uplink SM (Spatial Multiplexing) MIMO is not available in Release 8. Table 2-8 illustrates the various uplink peak rates. Table 2-8 LTE FDD Uplink Peak Rates (FDD using Normal CP) Effective MCS

MIMO Streams

1.4MHz

3MHz

5MHz

10MHz

15MHz

20MHz

QPSK ½

Single

0.72

2.02

3.46

7.06

10.66

14.26

16QAM ½

Single

1.44

4.03

6.91

14.11

21.31

28.51

16QAM ¾

Single

2.16

6.05

10.37

21.17

31.97

42.77

9

Single

2.60

7.26

12.44

25.40

38.36

51.32

16QAM 1

Single

2.88

8.06

13.83

28.22

42.62

57.02

64QAM ½

Single

2.16

6.05

10.37

21.17

31.97

42.77

64QAM ¾

Single

3.24

6.05

10.37

21.17

31.97

42.77

9

Single

3.88

7.26

12.44

25.40

38.36

51.32

Single

4.32

12.10

20.74

42.34

63.94

85.84

16QAM

64QAM

10

10

64QAM 1

The figures assume 1RB of PUCCH is allocated. In addition, support for 64QAM is optional.

It is also worth noting that the uplink also supports MU-MIMO (Multi-User MIMO) whereby multiple UEs are able to be allocated the same RB, differentiated by the DRS. This effectively doubles the peak uplink throughput at the eNB.

Impact of Cyclic Prefix Size One of the main physical attributes which affects the data rate is the choice of Cyclic Prefix size, i.e. Normal or Extended. Figure 2-29 illustrates the two options, as well as the total number of symbols per PRB for each. In essence, when the Extended CP is used, about 1/6 of the bandwidth is lost (when compared to using the Normal CP). In fact this ratio is dependent on the control region used over the subframe period, i.e. 1ms.

2-24

1 Symbol of control - is slightly better that 1/6 loss.

2 Symbols of control - equates to 1/6 loss.

3 Symbols of control – it slightly worse than 1/6.


Issue 01 (2010-06-01)


2 LTE Air Interface


84 Symbols


Figure 2-29 PRB with Normal and Extended CP

72 Symbols 7 Symbols Normal CP

6 Symbols Extended CP

2.4.2 Downlink Overheads There are various overheads which are independent from the system Bandwidth and Cyclic Prefix configuration.

Reference Signals The PRBs in the downlink each carry RS (Reference Signals). The amount of Reference Signals is dependent on the number of Tx Antennas:

1Tx Antenna - 4 Reference Signals per PRB.

2 Tx Antenna - 8 Reference Signals per PRB.

4 Tx Antenna - 12 Reference Signals per PRB.

Figure 2-30 illustrates an example of 2 TX Antenna Ports and the associated reference signals over the subframe (1ms). In total 8 RSs are used per PRB. This is effectively 8/84 Resource Elements which equates to 9.524% of the system bandwidth. This value is the same for Normal and Extended CP options. Figure 2-30 Reference Signals for 2 Antenna ( Normal CP)

Issue 01 (2010-06-01)


2-25


2 LTE Air Interface

Synchronization Signals LTE FDD and TDD systems both utilize PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal). Figure 2-31 illustrates the location of the PSS and SSS for both Normal CP and Extended CP. Each utilizes 72 subcarriers and is sent twice a frame. The overhead for the PSS is 144 Resource Elements per frame. The SSS has the same amount of overhead, i.e. 144 Res per frame. The percentage of overhead is dependent on the system Bandwidth and CP size (i.e. 84RE or 72RE per PRB), for example for the PSS the overhead would be:

10MHz and Normal CP: 144/(50 x 20 x 84) = 144/84000 = 0.17%

10MHz and Extended CP: 144/(50 x 20 x 72) = 144/72000 = 0.2%

5MHz and Normal CP: 144/(25 x 20 x 84) = 144/42000 = 0.34%

5MHz and Extended CP: 144/(25 x 20 x 72) = 144/36000 = 0.4%

It is worth noting that the PSS and SSS are only transmitted on one antenna port at a time, however the other antenna ports would not use the resource elements, i.e. the percentage overhead remains the same. Figure 2-31 Synchronization Signal Overhead

0 1 2 3 4 5 PSS (Primary Synchronization Sequence)

Bandwidth

0 1 2 3 4 5 6 62 Subcarriers

72 Subcarriers

Bandwidth SSS (Secondary Synchronization Sequence) Slots

0

1 2 3 4 5 6

7 8 9 10 11 12 13 14 15 16 17 18 19 Radio Frame Repeated in slots 0 and 10

PBCH The PBCH occupies 72 subcarriers for 4 OFDM symbols, i.e. 288 Resource Elements per frame. However, this value (288) also includes the Reference Signals in the PRB. In so doing, the actual number of Resource Elements used is 288 less “n”, where “n” is dependent on the number of transmit antenna:

2-26


Issue 01 (2010-06-01)


2 LTE Air Interface

1 TX Antenna “n” equals 12.



As a percentage overhead the PBCH is passed on the Bandwidth, CP size and Number of Antenna. Examples include:

10MHz, Normal CP and 1TX: (288-12)/(50 x 20 x 84) = 276/84000 = 0.32%




System Bandwidth

Figure 2-32 PBCH Overhead

PBCH (288 REs)

10ms Frame

Control Region The downlink control region is used to carry the PFICH, PHICH and PDCCH. Figure 2-33 illustrates the downlink control region. This can be 1, 2 or 3 OFDM symbols in duration and can dynamically change every 1ms based on scheduling requirements. It is worth nothing that the control region wraps around the existing Reference Signals. Figure 2-33 Control Region Overhead

Issue 01 (2010-06-01)


2-27


2 LTE Air Interface

4* OFDM symbols is only available when using a bandwidth of 1.4MHz. In this case the options are 2, 3 or 4 OFDM symbols.

The number of Resource Elements occupied by the control region in the Resource Block (i.e. two PRBs) can be calculated as: 12 x (A-B). Where “A” is the number of OFDM symbols assigned (1, 2, 3 or 4*) and “B” relates to the number of Resource Elements already reserved for Reference Signals. The values of “B” when using a Normal CP include:

B=2 for 1 TX.

B=4 for 2 TX.

B=4 for 4 TX (when A=1).

B=8 for 4 TX (when A= 2 or A=3).

With these values the control region overhead can be calculated for different permutations:

Normal CP, 1TX and A=1: (12 x 1 – 2) / (12 x 7 x 2) = 10/168 = 5.95%









Note for Extended CP options the figures are slightly different due to the Reference Signals being located in different places.

2.4.3 Uplink Overhead The uplink also includes various overheads which impact the performance of the system. These include the DRS (Demodulation Reference Signals), PRACH occurrences and the PUCCH.

Demodulation Reference Signal The overhead caused by the DRS is quite considerable. Figure 2-34 illustrates the uplink frame structure, as well as an enlarged view of a Resource Block (two PRBs). In each PRB the forth OFDM symbol (Normal CP) is used to carry the Demodulation Reference Signal. The DRS is therefore seen across the entire bandwidth, however it does not overlap the PUCCH region which is typically at the ends of the channel.The overhead is related to the channel bandwidth, CP Size and the number of PRB per slot for the PUCCH Control Regions. As an example:

5MHz, Normal CP and 4PRBs for PUCCH: ((25-4) x 12)/(25 x 84) = 276/2100 = 12%

10MHz, Normal CP and 8PRBs for PUCCH: ((50-8) x 12)/(50 x 84) = 552/4200 = 12%

Note that using an Extended CP the overhead is slightly greater for the same amount of bandwidth and PUCCH Control Regions.

2-28


Issue 01 (2010-06-01)


2 LTE Air Interface

12 Subcarriers

Figure 2-34 DRS Overhead

PUCCH Overhead Depending on the cell configuration the PUCCH also forms part of the physical layer overhead. Figure 2-35 illustrates the location of the control regions.

Uplink Carrier Bandwidth

Figure 2-35 PUCCH Control Regions

The number of control regions depends on higher layer configuration. Table 2-9 identifies the typical PUCCH overhead assuming various values for different bandwidths. Issue 01 (2010-06-01)


2-29


2 LTE Air Interface

Table 2-9 PUCCH Overhead Channel Bandwidth

PUCCH PRB used per Slot

PUCCH Overhead

1.4MHz

1

1/6 = 16.67%

3MHz

2

2/15 = 13.33%

5MHz

4

4/25= 16%

10MHz

8

8/50= 16%

15MHz

12

12/75= 16%

20MHz

16

16/100= 16%

PRACH Overhead The PRACH is very flexible in terms of when and how many times it occurs in a frame. The system also defines a number of PRACH Formats which last either 1, 2 or 3 subframes. To facilitate the overhead calculation a concept of PRACH density is used. Figure 2-36 illustrates a Format 0 PRACH. This occupies 6RB for a TTI (Time Transmission Interval) of 1ms. Figure 2-36 Example PRACH Configuration (Format 0)

The parameter “PRACH Configuration Index” is the key to identifying the format used and its occurrence. This is based on a table and can vary from 0 to 63. Table 2-10 illustrates the first part of the table.

2-30


Issue 01 (2010-06-01)


2 LTE Air Interface

Table 2-10 PRACH Configuration Index PRACH Configuration Index

Preamble Format

System Frame Number

Subframe Number

PRACH Density

0

0

Even

1

0.5

1

0

Even

4

0.5

2

0

Even

7

0.5

3

0

Any

1

1

4

0

Any

4

1

.

.

.

.

.

.

.

.

.

.

63

3

Even

9

1.5

Based on the PRACH density and the channel bandwidth the percentage of overhead can be calculated. For example if using PRACH Configuration Index = 3:

1.4MHz (6RB) and PRACH Density of 1: (6 x 1) / (60RB in the Frame) = 10%.

3MHz (15RB) and PRACH Density of 1: (6 x 1) / (150RB in the Frame) = 4%.

5MHz (25RB) and PRACH Density of 1: (6 x 1) / (250RB in the Frame) = 2.4%.




PUSCH Control Overhead The Resource Blocks used for the PUSCH include Demodulation Reference Signals. In addition, they can also carry UCI (Uplink Control information) in the form of CQI (Channel Quality Indicator), A/N (ACK/NACK), PMI (Precoding Matrix Indicator) and RI (Rank Indication). Figure 2-37 illustrates all the options that may be added, however the options sent depends on the configuration and transmission mode. The reason that the Uplink Control Information is included when sending the PUSCH is due to the fact UEs are not allowed to transmit the PUCCH and the PUSCH in the same subframe. As previously mentioned the PUSCH can carry the information normally carried on the PUCCH, however the eNB could ask for additional information, e.g. aperiodic CQI. The actual PUSCH control overhead it very hard to calculate. Even using simulations there are many variables and configuration options. Typical overhead figures range from 0.6% to 3%, however values of 5.5%, 11% and higher may be observed.

Issue 01 (2010-06-01)


2-31


2 LTE Air Interface

Figure 2-37 PUSCH Control Signaling

Sounding Reference Signals The eNB is able to configure SRS (Sounding Reference Signals) to be sent from UEs. There are various configuration options which determine the location and periodicity of the SRS. It is worth noting that whilst the SRS is being transmitted the PUCCH and PUSCH is not used. Assuming the worst scenario, SRS could be scheduled for every subframe, i.e. 1/14 OFDM symbols are used, effectively ~7%.

5MHz (25 Resource Blocks)

Figure 2-38 SRS Overhead

The SRS overhead is slightly different from other overhead since as a feature it may be deactivated.

2-32


Issue 01 (2010-06-01)


2 LTE Air Interface

2.4.4 Total Physical Overhead The total physical channel overhead in the downlink and uplink vary depending on the:

Bandwidth.

Cyclic Prefix Size.

Number of TX Antenna.

Size of the PDCCH Control Region (DL Only).

PRACH Format (UL Only).

Number of PUCCH Control Regions (UL Only).

PUSCH Uplink Control (UL Only).

SRS (UL Only).

Downlink Overhead Table 2-11 illustrates an example of the total physical channel and signals overhead for a 2 TX configuration using a Normal CP and 3 OFDM symbols for the PDCCH. Table 2-11 Downlink Physical Channel Overhead Overhead

1.4MHz

3MHz

5MHz

10MHz

15MHz

20MHz

Reference Signals

9.524%

9.524%

9.524%

9.524%

9.524%

9.524%

PSS and SSS

2.857%

1.143%

0.686%

0.343%

0.229%

0.171%

PBCH

2.619%

1.048%

0.629%

0.314%

0.210%

0.157%

PDCCH

19.048%

19.048%

19.048%

19.048%

19.048%

19.048%

TOTAL Overhead

34.048%

30.762%

29.886%

29.229%

29.010%

28.900%

This does not include the CRC (Cyclic Redundancy Check) and FEC (Forward Error Correction) effective coding rate which would be applied to the PDSCH.

Uplink Overhead Table 2-12 illustrates an example of the total physical channel and signals overhead for a 1 TX configuration using a Normal CP. In addition, the PRACH Density is assumed to be 1 and there is an average amount of PUSCH UCI overhead. Table 2-12 Uplink Physical Channel Overhead Overhead

1.4MHz

3MHz

5MHz

10MHz

15MHz

20MHz

DRSs

11.905%

12.381%

12.000%

12.000%

12.000%

12.000%

PUCCH

16.667%

13.334%

16.000%

16.000%

16.000%

16.000%

PRACH

10.000%

4.000%

2.400%

1.200%

0.800%

0.600%

PUSCH UCI

2.000%

2.000%

2.000%

2.000%

2.000%

2.000%

TOTAL Overhead

40.571%

31.714%

32.400%

31.200%

30.800%

30.600%

Issue 01 (2010-06-01)


2-33


2 LTE Air Interface

Figure 2-39 identifies a summary of the downlink and uplink overheads. Figure 2-39 Uplink and Downlink Physical Overheads

2.5 UE Categories In terms of the radio spectrum, the UE is able to support several scalable channels including; 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz and 20MHz whilst operating in FDD (Frequency Division Duplex) and/or TDD (Time Division Duplex). Furthermore, the UE may also support advanced antenna features such as MIMO (Multiple Input Multiple Output). Table 2-13 UE Categories

2-34

UE Category

Maximum Downlink Data Rate

Number of Downlink Data Streams

Maximum Uplink Data Rate

Support for Uplink 64QAM

1

10.3Mbit/s

1

5.2Mbit/s

No

2

51.0Mbit/s

2

25.5Mbit/s

No

3

102.0Mbit/s

2

51.0Mbit/s

No

4

150.8Mbit/s

2

51.0Mbit/s

No

5

302.8Mbit/s

4

75.4Mbit/s

Yes


Issue 01 (2010-06-01)


3 LTE Traffic

3

LTE Traffic

Objectives On completion of this section the participants will be able to: 3.1 Explain the protocols that support the various LTE traffic types. 3.2 Explain the transport layer protocols used for LTE traffic types. 3.3 Explain the operation of TCP, UDP, HTTP and FTP Internet Protocols. 3.4 Explain the issues surrounding Voice over LTE.

Issue 01 (2010-06-01)


3-1


3 LTE Traffic

3.1 Traffic Types Carried by LTE Networks LTE Default and Dedicated EPS bearers are capable of transporting a large variety of traffic types between the UE and the PDN. This could range from regular Internet browsing based on HTTP, through to real time voice services based on RTP. Table 3-1 outlines the traffic types which can potentially be encountered, including detail on the characteristics of the traffic and its associated QCI (QoS Class Identifier) value. Table 3-1 QCI

Type

Priority

Packet Delay Budget

Packet Error Rate

Service Example

1

GBR

2

100ms

10-2

Conversational Voice

2

GBR

4

150ms

10-3

Conversational Video

3

GBR

3

50ms

10-3

Real Time Gaming

4

GBR

5

300ms

10-6

Non Conversational Video

5

Non GBR

1

100ms

10-6

IMS Signaling

-6

Video (Buffered Streaming)

6

Non GBR

6

300ms

10

7

Non GBR

7

100ms

10-3

Voice, Video, Interactive Gaming

8

Non GBR

8

300ms

10-6

Video, TCP (HTTP, E-mail, FTP etc)

9

Non GBR

9

300ms

10-6

Video, TCP (HTTP, E-mail, FTP etc)

The QCI is a parameter associated with each EPS bearer which will determine the bearer level packet forwarding treatment e.g. scheduling weights, admission thresholds, queue management etc. The QCI value of an EPS bearer will be established during the Default or Dedicated EPS bearer setup procedure.

3.2 Transport Layer Protocols With regard to the OSI 7 layer model, there are two Transport Layer protocols associated with service delivery across LTE; namely UDP and TCP. Generally speaking, Transport Layer protocols are responsible for the delivery of IP datagram payloads to the correct higher layer application. This is achieved using port allocations. That is, where the Network Layer uses IP addressing for source and destination addressing, transport layer protocols use ports to distinguish where the application layer data should be sent when it reaches its network destination. Consequently, the use of ports provides a multiplexing/demultiplexing function for higher layer data. Note: SCTP (Stream Control Transmission Protocol) is also a Transport Layer

3-2


Issue 01 (2010-06-01)


3 LTE Traffic

protocol, however its use will be typically confined to the E-UTRAN and EPC rather than being utilized by the UE. The most popular application protocols use “well known” ports (such as HTTP on port 80) ranging from 0 to 1023. Other more user orientated protocols can use a “registered” port, ranging from 1024 to 49,151. Finally “dynamic” ports can be assigned and these are numbered from 49,152 to 65,535. This is shown in Table 3-2. Table 3-2 Port Allocations Port Description

Port Allocation

Well Known

0 - 1023

Registered

1024 - 49151

Dynamic

49152 - 65535

3.2.1 User Datagram Protocol UDP is considered to be a connectionless protocol, ideal for the transmission of real time applications such as voice conversations. That said, UDP is also used to carry a wide variety of other traffic, particularly when the services of TCP are not required. UDP is a relatively basic protocol, with the header fields defined as follows:

Source Port - this denotes the port at the source network node from which the payload was generated.

Destination Port - this denotes the port at the destination network node to which the payload must be sent.

Length - this specifies the length of the entire UDP datagram, including the UDP header and payload.

Checksum - an optional 16bit checksum calculated over the entire UDP datagram.

Accordingly, with such a basic header structure, transmission overheads are low and any processing at the transport layer is minimal. Figure 3-1 UDP Header Format

3.2.2 Transmission Control Protocol TCP and IP are ubiquitous across the Internet, with numerous applications specifically designed to run over TCP due to the services TCP can provide to a piece of application data. Where UDP is a connectionless protocol, TCP is connection orientated. This means that before payload data is delivered using TCP, a “3 way handshake” procedure is carried out between the two endpoints in order to establish a connection, shown in Figure 3-2. Data using the TCP connection will then be transferred in a reliable, sequential, flow controlled manner. As a result, a TCP header is fairly complex.

Issue 01 (2010-06-01)


3-3


3 LTE Traffic

Figure 3-2 TCP Session Establishment

In terms of reliable delivery, TCP uses a “sliding window” technique to acknowledge received data. In order to reduce signaling overhead, instead of every segment (TCP data unit) being individually acknowledged, TCP applies a sequence number to each octet of data and confirms the reception of contiguous blocks of sequence numbers. This sequence number can be seen in each and every TCP header, as Figure 3-3 shows. The Acknowledgement number is used to acknowledge received TCP segments and will refer to the sequence number that the source is next expecting the destination to send. Figure 3-3 TCP Header Format

0

16

32

Source Port Destination Port Sequence Number Acknowledgement Number Data Offset

Reserved

Control Bits

Checksum

Window

Urgent Pointer Data (Payload)

To illustrate the sliding window mechanism: if two segments are comprised of 1000 octets between them and the first octet has a sequence number of 200, for a transmitting endpoint to know the two segments have been delivered, the receiving endpoint must send an acknowledgement specifying that the next octet sequence number it expects is 1201 (the previous acknowledgement number would have been 200). If that acknowledgement arrives, the sliding window will slide to the next segments and drop the previous segments from its retransmit buffer. If the acknowledgement fails to arrive and a timeout occurs, the two segments must be retrieved from the retransmit buffer and retransmitted. In addition, the sequence number also ensures in sequence delivery of data. Other fields in the TCP header include the Window, which provides an indication to the destination endpoint of the amount of data that the source endpoint is willing to receive. This

3-4


Issue 01 (2010-06-01)


3 LTE Traffic

is used to provide flow control, ensuring that endpoints do not transmit too much data and overload the network. Although TCP is widespread, long established and very capable, the protocol does have a number of negative elements that should be noted:

Head of line blocking- this involves the dropping of data from the transmit buffer if too many retransmissions are occurring.

Security - due to the ubiquity of TCP, there has been lots of focus on the potential security flaws of the protocol. Well known TCP security flaws include “SYN Flooding” and “Man in the Middle” attacks.

Lack of robustness - if a TCP session between two endpoints is lost, a whole new session must be re-established using the 3-way handshake procedure.

3.3 Protocols used in Support of Various Traffic Types Depending on the service being utilized, there are various protocols which will be encountered in LTE. What follows is a brief synopsis of some of these protocols, including an overview of operation and appropriate usage scenarios.

3.3.1 Real Time Services Voice, in terms of a conversation, is quite tolerant to the loss of a packet, since packet sizes in VoIP tend to carry no more than 20ms of speech. Although dropping a packet is not ideal, if only one or two packets become corrupted or lost in delivery, the quality of the call should not degrade to a level perceivable by the human ear (providing the packet loss is not too frequent). The problem with transporting voice across an IP transport network is delay; voice conversations are extremely sensitive to excessive delay. If the delay between transmission and reception of voice exceeds 300ms, this will have an extremely detrimental effect on the service. Moreover, jitter is also a significant factor which could impair the Quality of Experience in a VoIP call. Accordingly, the characteristics of an EPS bearer carrying voice will include a low packet delay budget coupled with a relatively high packet error rate.

Real time Transport Protocol RTP (Real time Transport Protocol) is the defacto standard for transporting voice services in the majority of IP based transport networks, from private enterprise VoIP networks to carrier grade telecommunications networks. Figure 3-4 outlines the protocol stack, which includes RTCP (Real time Transport Control Protocol). RTCP is used to provide feedback and error reporting for RTP streams. Figure 3-4 RTP / RTCP Protocol Stack

Issue 01 (2010-06-01)


3-5


3 LTE Traffic

Each voice sample (typically in the region of 5, 10 or 20ms samples) will be encapsulated with an RTP header before delivery to UDP, which is providing a connectionless delivery service. RTP streams are demultiplexed using dynamic port allocations, which will be negotiated during call set up. It should be noted that RTP is only designed to transport real time media and as such, additional protocols are used to initially establish the RTP streams. Examples of these include SIP (Session Initiation Protocol) and RTSP (Real Time Streaming Protocol). The RTP header contains fields which are designed to provide a number of features:

Sequential Delivery - the RTP header contains both a sequence number and a timestamp. Either of these can be used to provide sequential delivery.

Jitter Correction - each RTP packet is given a timestamp in order for jitter to be corrected on reception. This process would involve the use of a jitter buffer.

Payload Identification - RTP is capable of carrying a variety of real time traffic which can be encoded in numerous ways. As such, the RTP header will specify the coding format of the real time payload.

Extensibility - if additional functionality is required, RTP Extension Headers can be created.

Security - with the use of SRTP (Secure RTP), each RTP packet can be transmitted with integrity protection and encryption, if required.

These features are listed in Figure 3-5. Figure 3-5 RTP Key Features

Real time Transport Control Protocol Each RTP stream can be associated with an RTCP stream in order to provide feedback on RTP packet delivery. It should be noted that the use of RTCP is not mandatory, since in some situations the bandwidth that RTCP requires is not readily available. Generally speaking, RTP streams are established on even ports, whilst the RTCP port for a given RTP stream is typically allocated the next highest odd port. RTP uses UDP at the Transport Layer, which means that there is no delivery assurance for RTP packets. This, coupled with the fact that QoS marking at the Network Layer may not be available, drove the development of RTCP as a feedback mechanism for RTP. RTCP uses reports to deliver statistical information to the sender of an RTP stream, as well as additional information which cannot be carried by RTP. Statistical information includes overall jitter, number of dropped packets and last sequence number detected. This is outlined in Figure 3-6.

3-6


Issue 01 (2010-06-01)


3 LTE Traffic

Figure 3-6 RTCP

RTP Stream RTCP Stream

Contains Reports providing statistical feedback on the associated RTP stream eg. jitter, dropped packets etc.

3.3.2 Web Browsing Web browsing is very tolerant to delayed packets, within reason. There are no real time requirements placed upon packet delivery however, integrity of the packets is extremely important. As such, the characteristics of the EPS bearer used to carry web browsing traffic include a relatively high packet delay tolerance, coupled with a low packet error rate. Browsing the World Wide Web requires the use of HTTP (Hyper Text Transfer Protocol). HTTP is the IETF standardized protocol used across the Internet for the request and transfer of web page content, files and other additional resources. HTTP version 1.1 is the current version in use and this employs a client/server based relationship. Consequently, requests and suitable responses are passed between client and server in order to acquire the appropriate content. A request requires the use of a HTTP “method” such as GET, and a URI (Uniform Resource Identifier) on which to carry out the method. A URI is effectively an address string which identifies the location of a particular resource; most users of the World Wide Web will be accustomed to typing a URI in the navigation bar of a web browser. To illustrate the process of browsing the World Wide Web using HTTP, we can use an example URI - www.Huawei.com/LTEtutorials. So, “GET www.Huawei.com/LTEtutorials HTTP/1.1” would be a request to retrieve information from that particular Huawei file location (Please note: this URI is an example only). The 1.1 at the end of the URI identifies the HTTP version. In order to actually download the content, HTTP uses the services of TCP (Transmission Control Protocol). The well known port for HTTP used by TCP is port 80. Figure 3-7 Web Browsing Using HTTP

TCP Session Establishment Procedure HTTP Request (GET www.Huawei.com/LTEtutorials HTTP/1.1) HTTP Response (HTTP/1.1 200OK) File Transfer and Acknowledgements TCP Session Shutdown

3.3.3 File Transfer The process of file transfer across a TCP/IP network has for many years been facilitated by FTP (File Transfer Protocol), which is one of the most widely used applications in the world. FTP allows the efficient, reliable transfer of files between any two devices that reside on a

Issue 01 (2010-06-01)


3-7


3 LTE Traffic

TCP/IP network. Moreover, FTP provides additional functionality which allows a user to browse the file structure of a particular directory and even delete files. Standardized by the IETF, FTP uses a Client / Server based model whereby the client will establish a connection to an FTP server in order to send and receive files from that server. TCP is used for reliable delivery, although it should be noted that in an FTP session, two TCP connections will be established. These are illustrated in Figure 3-8: Figure 3-8 TCP Connections Required for FTP

Control Connection - this will be established to allow the exchange of FTP control commands and replies and is not used to send files.

Data Connection - this is established each time data is exchanged between the client and server. Once the file exchange is complete, the data connection can be terminated.

FTP operation is achieved through the use of FTP commands sent between the client and the server. Although there is a large number of commands, three groupings are defined which encapsulate all of them:

Access Control Commands - this group contains the commands required for user login and authentication, in addition to resource access commands and general session control. An example would be the USER and PASS commands, which carry the username and password respectively.

Transfer Parameter Commands - this group of commands define how data transfer should occur, such as defining the data type of a file and whether passive or active data connections should occur (the former is client initiated whereas the latter is server initiated). An example would be the PORT command, which can be used by the client to notify the server of the port allocation for a particular data connection.

FTP Service Commands - this group contains the commands required for file operations, such as the actual sending and receiving of files, as well as deleting or renaming files. An example would include the RETR (Retrieve) command, which allows the client to request a file from the server.

Figure 1-6 outlines a typical FTP procedure, using what is termed a passive data connection. This means that the data connection is initially established by the client. The initial authentication procedure in FTP is very basic, with the username and passed word delivered in plain text. However, subsequent security extensions to FTP have made authentication much more secure.

3-8


Issue 01 (2010-06-01)


3 LTE Traffic

Figure 3-9 FTP Data Connection Establishment

3.4 Issues Surrounding Voice over LTE Voice is highly susceptible to delay and as such, one of the key issues for delivering voice over LTE is to ensure that end to end QoS requirements are met. This means that a suitable EPS bearer must be provided to the voice traffic, with characteristics which match the requirements of the voice service. This essentially equates to an EPS bearer that provides minimal delay, with a relatively high packet error rate (approximately 1-3% of total voice traffic; anything higher than this could result in an audible service degredation). For this, the 3GPP have recommended an EPS bearer with a QCI value of 1, a guaranteed bit rate, a packet delay budget of 100ms and a packet error rate of 10-2. Providing these requirements are met, the voice service should not encounter any problems. For the Service Provider, ensuring that there are enough resources in the network to accommodate the number of subscribers using voice services is a challenge. To address this challenge, the Service Provider is responsible for correctly dimensioning the network and putting into place appropriate priority and retention levels for the subscriber traffic. Moreover, bandwidth requirements for a given call may be reduced through compression techniques. Figure 3-10 outlines the associated overheads of a voice packet (this does not include the additional overheads added by the LTE transport network). Figure 3-10 Overheads Associated with a Voice Packet

3.4.1 PDCP ROHC ROHC works by enabling the sender and the receiver to store the static parts of the header, for example the IP addresses, whilst only updating the dynamic part. The sender is typically referred to as the compressor and the receiver the decompressor. VoIP (Voice over IP) is one of the most important usages for ROHC. This is due to the potentially high ratio between header and payload. For example, AMR 12.2Kbps packets are just over 30octets and typically 32octets with framing. The RTP/UDP/IPv4 header is 40 octets and is therefore bigger than the payload. In contrast, the RTP/UDP/IPv6 header is 60 octets.

Issue 01 (2010-06-01)


3-9


3 LTE Traffic

The addition of ROHC enables the RTP/UDP/IPv4 and RTP/UDP/IPv6 to be reduced to 4 or 6 octets.

ROHC States A ROHC compressor is in one of 3 main states:

IR (Initialization and Refresh) - In this state the compressor has just been created or reset, and full packet headers are sent.

FO (First-Order) - In this state, the compressor has detected and stored the static fields on both sides of the connection. The compressor is also sending dynamic packet field differences.

SO (Second-Order) - In this state the compressor is suppressing all dynamic fields such as RTP sequence numbers and sending only a logical sequence number and partial checksum to enable the other side to predict, generate and verify the headers of the next expected packet.

Figure 3-11 ROHC Feedback

PDCP Header VoIP

RTP UDP IPv4

VoIP Compressed

3-10


PDCP Header

First Order ROHC Feedback

Issue 01 (2010-06-01)


4 Radio Planning Process

4

Radio Planning Process

Objectives On completion of this section the participants will be able to: 4.1 Explain the process of LTE Radio Planning. 4.2 Identify the possible frequency bands for LTE deployment.

Issue 01 (2010-06-01)


4-1



4.1 Radio Planning Process The radio network planning process is designed to maximize the network’s coverage, whilst at the same time providing the desired capacity. In order to achieve this, there are a number of stages that are typically performed, these are illustrated in Figure 4-1. Figure 4-1 Radio Planning Process

4.1.1 Pre-Planning The first stage of the pre-planning process requires the gathering of information; the features of the network to be deployed, the desired coverage, the QoS (Quality of Service), capacity / coverage planning targets and the range of services to be provided, etc. The goal is to assess the minimum density of sites that would be required in order to meet these requirements. Broadly the initial stage is termed “dimensioning”.

Dimensioning The dimensioning is a part of the pre-planning phase. It is intended to provide a quick estimation of the number of sites required in various environments. It usually involves a nominal network plan or a simplified simulation in order to achieve the capacity and coverage estimates, as well as meeting the business model goals.

4-2


Issue 01 (2010-06-01)



Figure 4-2 Pre-Planning Dimensioning

An LTE business case typically involves meeting coverage requirements for customers, whilst at the same time supporting planned services and meeting network capacity thresholds, as well as identifying CAPEX (Capital Expenditure) and OPEX (Operational Expenditure) costs. In addition, the system must be designed to meet the necessary regulatory requirements. The process starts with the business model inputs. These usually include some high level subscriber data forecasts which review traffic and network coverage requirements. Table 4-1 illustrates some of the business inputs to the dimensioning model. Table 4-1 Business Model Inputs Business Model Input Population Penetration Rate Subscriber and Service Profiles

Description Enables the traffic calculation to be performed based on services and penetration rates

Geo Areas and Clutter Profiles

Dense Urban, Urban, Suburban, Rural.

Hierarchical Site Types

Percentage of Macro, Micro, Pico and Femto sites. In-building solutions.

Site Deployment

Site configuration and costs.

Based on these inputs, and the network configuration options, the radio planner can perform a link budget for the different geographical types. This identifies the maximum cell size and potential coverage area of the site for different geographical types. It is then compared to the capacity calculations, i.e. site capabilities, as well as the traffic requirements. The calculations are then adjusted to meet the capacity requirements, as well as the financial business model.

4.1.2 Detailed Planning Information gathered from the dimensioning stage, such as: estimated traffic / user density and distribution, existing base station sites, coverage predictions, capacity targets, etc, are required to provide effective detailed planning. It is also vital that the planned area has actual propagation data, as well as information on radio network requirements.

Issue 01 (2010-06-01)


4-3



Model Tuning The process of model tuning is required to modify the theoretical propagation model so that it closely meets the actual propagation environment. Most propagation models have several parameters within an equation which enables the system to correctly calibrate the model. The goal of model tuning is to get the predicted field strength in the planning tool as close as possible to the measured field strength. This process is typically performed in the planning tool by importing the CW (Carrier Wave) measurements. The planning software is then able to apply the corrections and therefore re-model how the signal propagates. Figure 4-3 Model Tuning

Site Selection In cellular radio systems, the issue of site selection is a common problem. The process involves identifying sites from a set of candidate sites while also meeting agreed criteria including:

Number of sites.

KPI (Key Performance Indicator) for coverage and capacity.

Close to traffic hotspots.

The site selection process can be done manually (time-consuming) or most planning tools now provide an automatic site selection algorithm. However, the reliability of these automatic systems depends on the accuracy of the propagation model. There are various methods for manual site selection (e.g. the site elimination method), however the planner needs to continually check that the eNB clusters are at a uniform height and spaced evenly. At the same time the signal blockage and spillage level must be monitored.

4-4


Issue 01 (2010-06-01)



Figure 4-4 Site Selection

Capacity and Coverage Planning In LTE the capacity planning and coverage planning processes are interrelated. The main goal of LTE capacity planning is to support the subscriber’s traffic requirements, whilst at the same time achieving low blocking and delay within the network. In contrast, the goal of LTE coverage planning is to ensure the availability of the network and its services in the desired service area. Figure 4-5 illustrates some of the basic information that must be identified, it includes:

Cell Range - this is derived from the link budget and the associated propagation model(s). Like other cellular systems the LTE link budget has many parameters and assumptions need to be made.

Cell Coverage Area - once the cell range is known it is then possible to estimate the cell area.

Site Coverage Area - this is a total site area. It may simply be three times the cell coverage area, however sometimes the equation can be more complex.

Figure 4-5 Cell and Site Coverage Planning

Site Coverage Area

Cell Coverage Area

Cell Range

Configuration Planning The overall goal of the configuration planning process is to enable the planning tool or planner to identify the E-UTRAN (Evolved - Universal Terrestrial Radio Access Network) configuration, which includes identifying the configuration of cells, eNB and possible features.

Issue 01 (2010-06-01)


4-5



Parameter Planning In this process, various system parameters need to be identified and configured. This enables the planning tool or planner to identify the maximum loading for cells, as well as various other thresholds.

4.1.3 Optimization Optimization is probably the most important stage when planning an LTE network. Typically it can be split into pre-launch and post-launch optimization. There are however a number of different areas that may be optimized, these include:

capacity.

coverage.

configuration and parameters.

cluster optimization.

interference.

The optimization process is fundamentally based on network analysis. This includes the gathering of statistics and measurement results from the network management system, as well as from field testing data, i.e. drive tests of the planned area. This information enables the optimization tool and / or optimizer to propose changes and in so doing, optimizes the network’s performance. As previously identified, traffic is a key issue in the planning process. It therefore has to be considered continuously during the dimensioning, detailed planning and optimization stages. Furthermore, since the coverage and capacity planning are also inter-related, interference needs to be also considered at all stages.

Continuous Optimization Since LTE facilitates a very flexible service delivery platform, it means that in the first few years after deployment, there will be continually changing services and subsequently the network must adapt. Consequently, the optimization process will be one of continual enhancements, ensuring network resources are used efficiently and KPI (Key Performance Indicators) are met.

4.2 Frequency Deployment Options Radio spectrum is a valuable and finite resource. The service provider’s requirement for more spectrum is being driven by the consumer’s demand for improved coverage, services and indoor penetration, as well as the increased availability and appeal of cheaper and more capable multimedia based devices.

4.2.1 LTE Bands There are many considerations which will influence a service provider’s decision for deploying LTE. These include:

4-6

spectrum availability and regulatory issues.

current deployments and existing infrastructure.

demand for services and service provider competition.


Issue 01 (2010-06-01)



There are several new frequency band options for LTE, some of which are available now or should be within the next few years. These include the 700MHz, AWS (Advanced Wireless Services) and 2.6GHz bands, as well as the re-use of existing GSM 900MHz and 1800MHz bands. In addition, due to poor harmonization, there are other spectrum bands available, including: 850MHz, 1500MHz, 1700MHz and 1900MHz. Table 4-2 LTE Release 8 FDD Frequency Bands LTE

Frequency Band

Uplink (MHz)

Downlink (MHz)

Name

1

2100

1920 - 1980

2110 - 2170

UMTS

2

1900

1850 - 1910

1930 - 1990

PCS (US)

3

1800

1710 - 1785

1805 - 1880

1800

4

1700

1710 - 1755

2110 - 2155

AWS (US)

5

850

824 - 849

869 - 894

850 (US)

6

800

830 - 840

875 - 885

Japan 800

7

2600

2500 - 2570

2620 - 2690

2600

8

900

880 - 915

925 - 960

900

9

1700

1749.9 - 1784.9

1844.9 - 1879.9

Japan 1700

10

1700

1710 - 1770

2110 - 2170

Extended AWS (US)

11

1500

1427.9 - 1452.9

1475.9 - 1500.9

Japan 1500

12

700

698 - 716

728 - 746

700 (US)

13

700

777 - 787

746 - 756

700 (US)

14

700

788 - 798

758 - 768

700 (US)

17

700

704 - 716

734 - 746

700 (US)

Band

The 2.6GHz band has been specified by the ITU (International Telecommunication Union) as a wireless broadband frequency. Most countries have or are planning to auction this band, with many service providers already affirming their interest in using it for LTE. Table 4-3 LTE Release 8TDD Frequency Bands LTE

Uplink (MHz)

Downlink (MHz) Name

33

1900-1920

1900-1920

UMTS TDD

34

2010-2025

2010-2025

UMTS TDD

35

1850-1910

1850-1910

PCS (US)

36

1930-1990

1930-1990

PCS (US)

37

1910-1930

1910-1930

PCS (US)

Band

Issue 01 (2010-06-01)


4-7



38

2570-2620

2570-2620

Europe Middle Gap

39

1880-1920

1880-1920

TDD (China)

40

2300-2400

2300-2400

TDD (China)

4.2.2 Spectrum Refarming Spectrum refarming is the process of deploying a different technology into a frequency band which previously had regulatory restrictions applied. For example there is great interest in deploying UMTS in the 900MHz frequency band. This process is attractive to service providers since it offers:

improved multimedia based services.

better rural deployment options.

enhanced in-building penetration (lower frequency).

If the service provider chooses to deploy UMTS 900MHz, there are a few issues which they and the regulators need to consider:

interference between GSM 900MHz and UMTS 900MHz networks, as such a guard band between systems needs to be identified.

minimizing dropped calls/sessions when mobiles move between the 900MHz and 2100MHz frequency bands.

4.2.3 Advanced Wireless Services In September 2006 the FCC (Federal Communications Commission) auctioned various AWS (Advanced Wireless Services) licenses. These are not reserved for specific technologies, therefore can be used for 2G, 3G or 4G. This spectrum uses 1.710-1.755GHz for the uplink and 2.110-2.155GHz for the downlink. There is a total of 90MHz FDD spectrum which is divided into six frequency blocks (identified as A through to F). Blocks A, B, and F are 20MHz each and blocks C, D, and E, are 10MHz each.

4.2.4 700MHz Deployment Many service providers are interested in the 700MHz band (Digital Television), with some countries like the US having already auctioned 62MHz of spectrum broken into 5 blocks:

Lower A (12 MHz) - 2 x 6MHz.

Lower B (12 MHz) - 2 x 6MHz.

Lower E (6 MHz unpaired).

Upper C (22 MHz) - 2 x11MHz.

Upper D (10 MHz) - 2 x 5MHz.

Note that there are other 700MHz frequency bands. Due to its low frequency, this band is very efficient for LTE roll-out due to providing better in-building penetration than the higher frequency bands.

4-8


Issue 01 (2010-06-01)


5 LTE Link Budget

5

LTE Link Budget

Objectives On completion of this section the participants will be able to: 5.1 Identify how path loss and the cell range/coverage are linked. 5.2 Explain the main attributes of the LTE Link Budget. .

Issue 01 (2010-06-01)


5-1


5 LTE Link Budget

5.1 Cell Coverage and Range Like all cellular systems the link budget is a key part of the dimensioning process. It is linked both to coverage and capacity planning. The main goal for coverage planning is the estimation of the site coverage area, i.e. identify the number of sites for a given area. This is achieved using a link budget calculation which provides an estimate on the maximum allowed PL (Path Loss) in the downlink and uplink. Once the maximum Path Loss is identified it can be used to calculate cell range, cell area and site area. Figure 5-1 Path Loss and Cell Range

5.2 Link Budget Table 5-1 illustrates a typical LTE Link Budget. Like any link budget various assumptions and configuration parameters are required. The parameters include:

5.2.1 Tx Parameters

5-2

Tx Power - this depends on the system and radio module. A typical value of 43dBm, i.e. 20Watts, is used. Note that when MIMO Transmit Diversity is active the power is split between the two antenna. To compensate the power could be increased by 3dB.

Cable Loss - the Cable Loss parameter may include feeder losses and jumper losses. Note that there are various Huawei eNB solutions, some of which are feederless.

Antenna Gain - like UMTS, the antenna gain is dependent on the antenna type, as well as the frequency band. For the downlink, most sectored directional antenna are ~18dBi, however various types exist. In the uplink the Tx antenna gain is related to the UE. Typically this is 0dBi.

Insertion Losses - depending on the deployment option, a MHA (Mast Head Amplifier) may be added to improve the Uplink. A typical value would be 0.5dB.

Other Gains - depending on the implementation, additional power gains may be used e.g. adding 3dBs to combat the losses associated with transmission across two antenna.

EIRP (Effective Isotropic Radiated Power) - this equates to the Effective Isotropic Radiated Power, i.e. EIRP = Tx. Power - Cable Loss + Antenna Gain – Insertion Loss + Other Gains.


Issue 01 (2010-06-01)


5 LTE Link Budget

Table 5-1 LTE Downlink and Uplink Link Budget

Units Tx Parameters Tx Power Cable Loss Antenna Gain Insertion Losses (MHA) Other Gains EIRP Rx Parameters Sub-carriers Cable Loss Rx Antenna Gain Number of Antennas Rx Antenna Diversity Gain Net Rx Antenna Gain Rx Sensitivity Thermal Noise Power Density Composite Thermal Noise Power Rx NF (Noise Figure) Required SINR Composite Rx Sensitivity System Gain Propagation Margins Fast Fade Margin Interference Margin Penetration Loss Body Loss Total Margin Required Maximum Allowable Path Loss

DL 43.0 0.0 18.0 0.0 3.0 64.0

UL 23.0 0.0 0.0 0.0 0.0 23.0

dB dB

300.0 0.0 0.0 1.0 0.0 0.0

72.0 0.0 18.0 2.0 3.0 21.0

dBm/Hz dBm dB dB dBm dB

-174.0 -174.0 -107.5 -113.7 7.0 2.2 -4.50 -1.8 -105 -113 169.0 157.3

dBm dB dBi dB dB dBm -dB dBi --

dB dB dB dB dB

6.0 0.2 15.0 0.0 21.2

2.0 0.2 15.0 0.0 17.2

dB

147.8

140.1

5.2.2 Rx Parameters

Sub-Carriers - this is related to the bandwidth and is used as part of the equation to ultimately identify the Composite Rx Sensitivity.

Cable Loss - this equates to the possible losses, e.g. feeder, in the receive direction.

Rx Antenna Gain - this is typically the same as the TX antenna gain, i.e. the downlink Tx antenna gain equals the uplink RX antenna gain. It is worth noting that the values could be different based on the antenna configuration.

Number of Antennas - this is used as part of the calculation for Rx antenna diversity gain.

Rx Antenna Diversity Gain - this is the calculated Rx antenna diversity gain, the equation is: 10*LOG (Number of Rx antennas).

Net Rx Antenna Gain - this is the total Rx Antenna Diversity Gain.

Issue 01 (2010-06-01)


5-3


5 LTE Link Budget

5.2.3 Rx Sensitivity

Thermal Noise Power Density - this is the Thermal Noise Density not considering the bandwidth impact. The value is -174dBm/Hz.

Composite Thermal Noise Power - this is the thermal noise for the used bandwidth. In the downlink it is calculated based on the full channel bandwidth, e.g. 300 subcarriers for a 5MHz channel. In contrast, the uplink calculation is based on the resource blocks allocated.

Rx NF (Noise Figure) - this is dependent on the receiver equipment design. For a UE it is typically 7dB, whereas for the eNB it is ~2.2dB.

Requirement SINR - the SINR (Signal to Interference plus Noise Ratio) requirement is the minimum ratio of the received signal “S” and sum of interferences, “I”, from the serving and neighboring cells plus the received noise power “N”.

SINR =

S I Serving + I neighboring + N

The 3GPP specifications provide various SINR values to meet BLER (Block Error Rate) requirements. However the value can depend on various attributes including the specific OFDM channel model, e.g. EPA05 (Pedestrian A 5Hz) or ETU70 (Enhanced Typical Urban), the throughput requirement, and Physical Layer Overheads.

Composite Rx Sensitivity - this is a summation of the previous three parameters.

System Gain - this equates to the EIRP + Net Receive Gain - Composite Rx Sensitivity.

5.2.4 Propagation Margins

Fast Fade Margin - the Fast Fade margin or PCH (Power Control Headroom) is dependent on the MCS (Modulation and Coding Scheme) and UE’s speed. Typical values can vary between 2dB and 6dB.

Interference Margin - the IM (Interference Margin) is added to the link budget to compensate for the loading of the cell, i.e. the higher loading allowed, the larger is the interference margin specified.

Penetration Loss - this is added based on the average building penetration loss.

Body Loss - this is the loss due to the user, i.e. proximity to the user’s head.

Total Margin Required - this is the summation of the various losses.

5.2.5 Maximum Allowable Path Loss In this link budget the maximum path loss allowed is calculated based on the “System Gain” less the “Total Margin Required”. This value can be utilized in other equations to determine cell size and ultimately system capacity.

5-4


Issue 01 (2010-06-01)


6

6 Coverage and Capacity Planning

Coverage and Capacity Planning

Objectives On completion of this section the participants will be able to: 6.1 Explain the process of Coverage Planning. 6.2 Explain the process of Capacity Planning. 6.3 Explain what is meant by optimization.

Issue 01 (2010-06-01)


6-1



6.1 Coverage Planning The process of coverage planning requires various attributes to be defined, these include:

Type of Service.

Link Budget including eNB Configuration and Capabilities.

Radio Propagation.

6.1.1 Radio Propagation An important requirement for assessing LTE planning requirements is to have an accurate description of the wireless channel. This is usually referred to as a “Channel Model” or “Propagation Model”. In systems that employ a scalable multi-cell architecture with NLOS (Non-Line-of-Sight) propagation, it becomes more important to model the effects and performance of Base Station locations. When planning, these parameters are random and therefore only a statistical approximation is usually possible. In a similar way to all other radio systems, LTE must provide acceptable levels of signal at the receiver. This is achieved through good radio and system planning.

6.1.2 Radio Channel The term “Radio Channel” refers to the connection between a Tx (Transmit) antenna and a Rx (Receive) antenna. The RF (Radio Frequency) characteristics in the Uplink and Downlink may be different, this depends on whether the system is FDD (Frequency Division Duplex) or TDD (Time Division Duplex) based. The different radio channel characteristics are illustrated in Figure 6-1. Figure 6-1 Radio Channel Propagation

Radio Channel

- Path Loss - Shadowing - Multipath Propagation - Fading Characteristics - Doppler Spread - Co-channel/Adjacent Channel Interference - Heights and Distances - Clutter - Antenna Configuration It is almost impossible to predict the radio channel propagation environment, since there are so many factors that influence how the signal will propagate between the transmitter and receiver. When radio planning the LTE system, a reasonably accurate prediction model is ideally required.

6-2


Issue 01 (2010-06-01)



In general, the received signal is based on the transmitted signal, which has then propagated over a radio channel, with a certain channel response. This “channel response” is typically described in terms of path loss, shadowing and multipath.

Path Loss The simplest path loss equation focuses on free space loss only. This assumes that an isotropic antenna is used, i.e. the power is radiated equally well in all directions. In this case, the propagated signal’s energy expands over a spherical wave front. Thus, the energy received at an antenna placed a certain distance away is inversely proportional to the sphere surface area. There are a few different versions of the free space path loss equation. Like UMTS and GSM, the LTE propagation environment is not “free space”. Thus, additional models and factors need to be considered.

Shadowing Shadowing is typically identified as additional attenuation due to objects, such as buildings or trees, along the radio path. It can include:

Absorption.

Reflection.

Scattering.

Diffraction.

Multipath Many wireless systems experience multipath propagation, whereby multiple radio paths are reflected, refracted or diffracted by objects. It is possible for some of these reflected waves to arrive at the receiver, in which case they usually have different amplitude and phase attributes. The combination of multipaths may increase or decrease the overall power received. In environments when there is a dominant LOS (Line of Sight) wave, the amplitude of the signal envelope has a Rician probability distribution, which means the receiver experiences less deep fades. In contrast, if there is no LOS wave, the envelope has a Rayleigh probability distribution. In this case, the receiver may experience deep fades. Figure 6-2 Impact of Shadowing and Multipath

Log (Pr/Pt)

Multipath+ Shadowing + Path Loss Shadowing + Path Loss Path Loss

Log (d)

Issue 01 (2010-06-01)


6-3



Doppler Spread In a mobile environment, the receiver can move relative to the source. When they move toward each other, the relative frequency at the receiver is higher than that at the source, and when they move away from each other, the reverse is true. This is known as Doppler Shift, or Doppler Spread, and can affect transmissions that are sensitive to carrier frequency offsets. The coherence time of the channel is the inverse of the Doppler spread, and is a measure of the speed at which the channel characteristics change. If the transmitter, receiver, or the intermediate objects move very fast, the Doppler spread is large and the coherence time is small, i.e. the channel changes fast.

6.1.3 Propagation Models In order to more accurately describe various propagation environments, most LTE planning is based on either empirical or deterministic models.

Deterministic Propagation Models - This method uses the radio wave propagation characteristics. In so doing, the tool simulates how a radio wave would interact with objects, i.e. the reflections, scattering, diffractions, etc between the transmitter and the receiver. These methods require accurate mapping data and involve a lot of computation time.

Empirical Propagation Models - In practice, actual radio environments are far too complex to model accurately. Therefore, planning tools and simulators use empirical models that have been developed based on measurements taken in various real environments, i.e. derived from actual data. Example of empirical models include: Okumura-Hata Model, COST 231 Extension to Hata Model and Erceg-Greenstein - SUI (Stanford University Interim). However there are various others which may be utilized, the final choice is typically dependant on the planning tools used, as well as the frequency of operation.

Okumura-Hata Model The Okumura-Hata model is a well-known propagation model, which can be applied for a macro cell environment to predict signal attenuation. Having one component, the model uses free space loss. The Okumura-Hata model is an empirical model, which means that it is based on field measurements. Okumura performed the field measurements in Tokyo and published the results in graphical format. Hata applied the measurement results into equations. The model can be applied without correction factors for quasi-smooth terrain in an urban area but in cases of other terrain types, correction factors are needed. The weakness of the Okumura-Hata model is that it does not consider reflections and shadowing. In addition, the Hata model approximates the Okumura model for distances greater than 1km. This model is intended for large cells when the Base Station is placed higher than the surrounding rooftops. Both models are designed for 150-1500MHz.

COST 231 Extension to Hata Model The European COST (Cooperative for Scientific and Technical) research extended the Hata model to 2GHz as follows:

L = A + B ⋅ log 10 (fc) - 13.82 ⋅ log10 (h BS ) - a(h UE ) + [44.9 - 6.55 ⋅ log10 (h BS )] ⋅ log(d) + Correction

6-4


Issue 01 (2010-06-01)



Where:

fc is the carrier frequency.

hBS is the height of the transmitting (base station) antenna.

hUE is the height of the receiving (mobile) antenna.

d is the distance.

In addition,

69.99 150 MHz < f < 1500 MHz  A=  46.30 1500 MHz < f < 2000 MHz  26.16 150 MHz < f 1500 MHz  B=  33.90 1500 MHz < f < 2000 MHz a(h UE ) = [1,1 ⋅ log10 (f) - 0,7] ⋅ h MS - [1.56 ⋅ log 10 ( fc) − 0.8] In this example a(hUE) is a correction factor for the mobile antenna height based on the size of the coverage area.

Erceg-Greenstein - SUI (Stanford University Interim) This has appeared in recent years as a suitable propagation model for WiMAX in the high frequency bands. It is therefore possible that it may suit some LTE deployments. This is designed for propagation loss calculations between 1.9GHz and 6GHz and can be utilized for cells from 100m to 8km. The Erceg-Greenstein (SUI) model is mostly adapted for suburban environments, using the terrain profile, diffraction and reflection attributes to calculate propagation. Like most propagation models, the Erceg-Greenstein (SUI) model can be adjusted with correction factors for different types of environments.

6.1.4 Cell Range and Coverage In order to identify the range and area of the cell the “Maximum Path Loss” parameter calculated in the link budget can be used in conjunction with the appropriate propagation modeling equation. Table 6-1 illustrates an example. If the figure of maximum path loss was 140.1dB then using the Cost 231 Hata formula, as well as other configuration parameters the cell range may be calculated. Table 6-1 Example of Cost 231 Hata Cell Ranges Max. Pathloss

2100MHz

2100MHz

2100MHz

2500MHz

2500MHz

2500MHz

Urban

Suburban

Rural

Urban

Suburban

Rural

140.1dB

0.330 km

0.640 km

1.571 km

0.293 km

0.580 km

1.422 km

These cell ranges quoted depend on other inputs such as: cell edge probability, the original carrier frequency, eNB antenna height, UE antenna height etc.

Issue 01 (2010-06-01)


6-5



6.2 Capacity Planning LTE, like W-CDMA, is an interference based system. As the number of active users in a cell increases the total loading and interference seen at the receiver will increase. What this means to the planning process is that coverage planning, capacity planning and interference analysis cannot be performed independently. Figure 6-3 illustrates how some of the inputs to the dimension process may be combined to estimate the number of sites required. Figure 6-3 LTE Site Dimensioning

Cell Range Cell and Site Area No. Of Coverage Sites Total Area (Geo)

Subscribers (Geo)

Cell/Site Capacity

Number of Sites (Largest Value)

No. Of Capacity Sites Services Traffic (BH) Once the range of each cell is identified, it can then be combined with the site configuration and the total areas to identify the number of coverage sites required. This is typically done per Geo (Geographical) type. At the same time, the subscriber density, as well as the forecasted services in the BH (Busy Hour) can be used to identify the number of capacity sites. This also requires information on cell and site capacity capabilities. In addition to achieving all the above, the costs must be kept within budget.

6.2.1 Cell / Site Capacity The process of defining “Cell/Site Capacity” as well as the “number of users” on a cell is an important part of the dimensioning process and related to the site configuration. This includes:

6-6

Channel BW (Bandwidth) - e.g. 5MHz, 10MHz etc.

Frequency reuse - this will impact the interference and possible bandwidth availability if fractional frequency re-use is chosen.

Downlink / Uplink Ratio - the LTE TDD system enables the network to configure different DL/UL configurations. This will have a huge impact on the throughput levels.

Physical Layer overhead - this is the overhead from Physical Channels and signals. Typically it is about ~30%.

Control overhead - this is the predicted amount of overhead caused by broadcast and control information. This is typically a percentage of the total symbols available, however in reality this will increase as more subscribers are on the system.

Data overhead - this is usually identified as the amount of header overhead for transferring application data. This varies depending on the application, e.g. VoIP (Voice over IP) or Internet browsing.

ICIC (Inter Cell Interference Cancelation) - this is related to the frequency reuse method, as well as the implementation of the X2 interface.


Issue 01 (2010-06-01)



6.3 Optimization Optimization of LTE typically falls into two parts, namely pre-launch and post-launch optimization.

6.3.1 Pre-Launch Optimization Pre-Launch Optimization is performed before and during the initial launch. It typically involves cluster level optimization to meet KPI (Key Performance Indicators) for both unloaded and loaded configurations. The size of a cluster typically depends on the site density and geo type, however other aspects such as subscriber mobility may also impact the size. The cluster level testing involves drive testing and measurements analysis. In so doing the eNB configuration and parameters can be checked and the site configuration confirmed. The results from the drive test may be used to:

Validate the initial planning design, i.e. compare the received RSRP and RSRQ against the actual network measurements.

Identify coverage issues.

Provide recommendations for changes - this can include site configuration changes, for e.g. antenna tilt and azimuth.

Identify areas of KPI degradations.

6.3.2 Post-Launch Optimization Once the network has been launched the optimization does not stop. Instead, ongoing cluster level optimization is typically performed. This includes analyzing KPIs, diagnosing problems and recommend solutions for capacity issues, dropped calls (sessions), mobility failures, etc.

Issue 01 (2010-06-01)


6-7



6-8


Issue 01 (2010-06-01)


7 Huawei LTE Tools

7

Huawei LTE Tools

Objectives On completion of this section the participants will be able to: 7.1 Identify the main Huawei LTE tools. 7.2 Explain the functions of U-NET for LTE planning.

Issue 01 (2010-06-01)


7-1


7 Huawei LTE Tools

7.1 Huawei Tools Huawei has developed a suite of tools that assist engineers, collectively known as GENEX (Generate Excellence). No matter what phase of network maturity, the GENEX solution can be utilized, from initial planning through deployment & optimization to network operation and future expansion, to increase network performance with cost-effective measures. Figure 7-1 LTE Tools

7.1.1 U-Net - Professional Radio Network Planning Tool Inheriting rich experience in network planning, the GENEX U-Net can be applied across a variety of networks. The U-Net integrates the functions of link budget and network dimensioning, coverage and capacity pre-planning and simulation, verification and planning based on the import drive test data from GENEX Probe, planning of the antenna parameters, and automatic site selection.

7-2

Advanced Network Design Features: −

Full support for multiple technologies including CDMA / GSM / GPRS / UMTS / HSPA+ / LTE.

−

Focusing on the accuracy of predictions and simulations.

−

Support for hierarchical networks and multi-service traffic modeling required for complex deployments.

Open and Flexible Architecture: −

Easily extended platform, integrating third-party products.

−

Multiple networking configuration solutions from standalone to company level.

Evaluate Costs & Benefits: −

Automatic cost and benefit evaluation.

−

Automatic RF optimization.

−

Automatic evaluation for the planning and expansion of several phases.

Make full use of existing 2G/3G resources: −

Prediction and simulation based on 2G/3G drive test data.

−

Traffic modeling based on 2G/3G traffic data.

Increase Efficiency: −

Parameter input template.

−

Propagation module - One-key correction.

−

Intelligent network planning report.


Issue 01 (2010-06-01)


7 Huawei LTE Tools

7.1.2 Probe & Assistant - Drive Testing & Data Analysis Tool Independently developed by Huawei, the GENEX Probe can be applied in the performance testing of wireless networks. As a professional tool for network trouble-shooting, verification, optimization, and maintenance, the GENEX Probe supports network architectures such as LTE, UMTS/GSM/GPRS, CDMA and WiMAX. GENEX Assistant is the post-processing software of the test data based on the Probe drive test data and eNB data.

Advanced Features: −

Support for LTE, UMTS/GSM/GPRS, CDMA and WiMAX.

−

Comprehensive service test.

−

Sharing of test plan to improve test standardization.

−

QoS test.

Low Cost & High Efficiency: −

Graphic test mode.

−

Indoor test conducted independently by test mobile.

−

Search for and record network information at any place and at any time.

−

Support for Bluetooth GPS.

Intelligent System: −

Complete solution to network optimization.

−

Integrated analysis of the uplink and downlink data.

−

UE event simulation based on scanner data.

−

Various types of intelligent network optimization reports.

7.1.3 Nastar - Network Performance Analysis Tool As the software for network performance analysis, the GENEX Nastar provides integrated analysis of variable types of performance data, such as traffic statistics, call tracing and configuration data. The GENEX Nastar monitors network quality, locates network problems, and predicts network trends, which helps the Operator in fault location and troubleshooting.

Issue 01 (2010-06-01)

Integrated Monitoring: −

Integrated data management and remote analysis.

−

Effective query of data.

−

Intelligent reporting system.

−

Multi-leveled management.

Identifying Problems & Service Distribution: −

Deep analysis of network problems.

−

Quality estimate of backbone services.

−

QoE (Quality of Experience).

Network Trends: −

Network trend analysis.

−

Evaluation of demand for expansion and new service.

−

UE compatibility analysis.


7-3


7 Huawei LTE Tools

7.2 GENEX U-Net for LTE 7.2.1 Product Overview GENEX U-Net is a component of the GENEX series and provides end-to-end support for radio network planning. It fully supports the planning of LTE FDD radio parameters and incorporates support for the following features:

ICIC and semi-dynamic simulation of frequency scheduling.

Planning of LTE neighboring cells, frequencies, PCIs, PRACHs, and TAs.

Auto-planning of the antenna azimuth, downtilt, and RS power.

Coverage prediction based on multiple KPI counters of LTE channels.

7.2.2 U-Net LTE Planning Functions The U-Net planning tool performs various functions. Figure 7-2 highlights the main U-Net LTE planning procedure. Figure 7-2 U-Net LTE Planning Procedure

Importing Map Data N

Adjusting RF

Importing NE Data

Y Planning RF

Planning Frequencies Creating Traffic Map

Calibrating Propagation Models

Simulating and Calculating

Adjusting Parameters

Calculating Path Loss

N

Predicting Coverage

Expected Result Achieved Y Providing Planning Result

During this procedure, various tasks and processes are performed. The following information describes some of these in more detail.

7-4


Issue 01 (2010-06-01)


7 Huawei LTE Tools

Data Preparation U-Net enables various parameters to be imported and managed. This includes NE (Network Element) parameters, antenna parameters, service parameters, traffic parameters, propagation mode etc.

AFP (Automatic Frequency Planning) LTE, like other cellular systems, is able to employ different frequency planning options. This includes both single and multiple frequency reuse scenarios. U-Net supports these different configurations.

Propagation Calibration U-Net supports a propagation model calibration based on CW (Continuous Wave) data and DT (Drive Test) data. It also supports automatic mapping between PCI (Physical Cell Identities) and transceivers. In addition, the mapping between PCIs and transceivers can be completed either manually or automatically.

RF Planning U-Net is a RF (Radio Frequency) planning tool. As such, a propagation model for each transceiver is configured. The tool is then able to calculate path loss matrices. U-Net also supports the auto-planning of parameters of antenna azimuth, downtilt, and RS (Reference Signal) power. Figure 7-3 illustrates one of the many outputs of the RF planning process. It also illustrates how multiple iterations may be different. This is due to the simulation method, e.g. “Monte Carlo” distribution. Figure 7-3 RF Results

Issue 01 (2010-06-01)


7-5


7 Huawei LTE Tools

During RF planning various parameters must be set, these include:

RSRP.

RS SINR (Signal to Interference Noise Ratio) proportion.

Coverage calculation precision.

Number of iterations.

Size of the population.

Downtilt adjustment range and steps.

RS power adjustment range and steps.

Azimuth adjustment range and steps.

Service/Traffic Model Establishment U-Net supports the service model structure of Environment, User Profile, Terminal, Mobility, and Service. It enables the planner to construct different user groups or scenarios by defining different combinations of service, mobility and terminal type. Figure 7-4 illustrates an example of the Traffic Parameters and their flexibility in the U-Net tool. Figure 7-4 U-Net Traffic Parameters

The U-Net tool has various options for defining the traffic model, these include:

7-6

Environment - this traffic model is based on the association between the polygon area and the service model.

Vector - this traffic model is based on the polygon. The terminal, service, and mobility proportion can be customized in this model.

Coverage - this traffic model is based on the best server range predicted according to the coverage. In this model, you need to specify the following items for each cell: number of


Issue 01 (2010-06-01)


7 Huawei LTE Tools

users associated with each service, terminal, mobility, and user proportion based on clutter.

Coverage U-Net enables various coverage predictions to be calculated. These include:

DL RSRP - this indicates the strength of the downlink reference signals on an RE.

Symbol RSRP - this indicates the strength of the reference signals on a downlink symbol.

Best Server - this indicates the best serving cell.

DL RSSI - this indicates the sum of useful power and interference noise received in the downlink.

Geometry - this indicates the valid power strength in the downlink.

Handover Area - this indicates whether an area is a handover area.

DL SCH RP - this indicates the signal strength of an SCH.

DL PBCH RP - this indicates the signal strength of a PBCH.

UL RSRP - this indicates the strength of the uplink reference signals.

PDSCH SINR - this indicates the SINR of the downlink traffic channel.

PUSCH SINR - this indicates the SINR of the uplink traffic channel.

PDSCH MCS - this indicates the bearer efficiency of the downlink traffic channel.

PUSCH MCS - this indicates the bearer efficiency of the uplink traffic channel.

Throughput - this indicates the throughput of the traffic channel. This parameter supports both MAC and application layers.

The U-Net provides abundant prediction effect pictures of reference signals, serving cells, uplink and downlink channel quality, bearer efficiency, and throughput. Figure 7-5 illustrates a selection of the key plots. Figure 7-5 Example U-Net Coverage Predictions

Issue 01 (2010-06-01)


7-7


7 Huawei LTE Tools

7.2.3 Simulation U-Net uses semi-dynamic simulation of the Monte Carlo algorithm together with the TTI (Time Transmission Interval) scheduling. There are various parameters which need to be set:

Number of snapshots.

Number of TTIs.

Warm-up period.

Correlation factor of shadow fading and sites.

Fixed user position.

Traffic map.

Polygon area.

Figure 7-6 illustrates some of the typical outputs from the simulation. These include overall statistics, as well as a breakdown for individual services, e.g. web browsing. Figure 7-6 U-Net Monte Carlo Statistics

The simulation results are also able to estimate the throughput of the MAC (Medium Access Control) layer and the application layer, as well as the throughput of each service on the basis of sites. Overall, U-Net simulations provide information about the following KPI parameters on the basis of cells:

7-8


Issue 01 (2010-06-01)


7 Huawei LTE Tools

Actual transmit power.

Uplink IoT (Interference over Thermal noise).

Actual uplink load.

Number of uplink RBs in use.

Number of downlink RBs in use.

Uplink/downlink service rate of the MAC layer.

Uplink/downlink service rate of the application layer.

Number of subscribers in each state.

Information about the actual transmit power, load, and IoT of cells can be synchronized to the NE data and this information provides a basis for analyzing coverage prediction.

7.2.4 Neighbor Cell and PCI Planning The U-Net tool is also equipped to manage other aspects of LTE, such as neighbor cell and PCI planning.

Neighbor Cell Planning Neighbor cell attributes can be managed in terms of basic parameters:

Maximum number of intra-frequency neighboring cells.

Maximum number of inter-frequency neighboring cells.

Number of bidirectional intra-frequency and inter-frequency neighboring cells.

Existing neighboring cells deleted.

Planning area.

In addition, advanced parameters can also be managed:

Planning algorithm - topology or coverage prediction.

Minimum receiver sensitivity.

Handover threshold.

Shadow fading considered.

Cell edge coverage probability.

Indoor user.

PCI Planning PCI planning is an important part of the LTE system. It is imperative that PCI re-use is maintained. U-Net includes various features and methods for planning PCI values and maintaining their re-use. Broadly, the parameters are split into general, control and advanced parameters. The general parameters include:

Reservation ratio.

PCI range.

Planning area.

The control parameters include:

Issue 01 (2010-06-01)


7-9


7 Huawei LTE Tools

Maximum interference distance.

Reset PCI.

Impact of neighboring cells considered.

Frequency offset of reference signals considered.

Existing PCI considered.

In addition, advanced parameters include:

Planning algorithm - topology or coverage prediction.

Minimum receiver sensitivity.

Handover threshold.

Shadow fading considered.

Cell edge coverage probability.

Indoor user.

Figure 7-7 illustrates an example of cells with different PCI allocated. In reality, it is important that the PCI values have a re-use distance, as well as monitoring the PCI with the same MOD3 or MOD6 offsets - since this too increases interference. Figure 7-7 PCI Planning

There are various methods the U-Net tool uses to validate PCI planning. These include checking the following parameters:

Re-use distance threshold.

Threshold number of re-use layers.

Threshold ratio of cells with the same MOD3 or MOD6.

Maximum interference distance.

Analysis area.

U-Net is then able to identify:

7-10

Cells that do not meet the requirement of the re-use distance threshold.

Cells that do not meet the requirement of the threshold number of re-use layers.

Cells that do not meet the requirement of MOD3 or MOD6 threshold.

Cells that are not allocated with PCIs.


Issue 01 (2010-06-01)


7 Huawei LTE Tools

TA (Tracking Area) Planning The LTE system utilizes Tracking Areas which consist of one or more cells. These are similar to Location and Routing Areas in W-CDMA networks and therefore are related to paging, as well as additional signaling on TA boundaries. As such, U-Net is able to configure the TA and its relationship to the cells and MMEs.

PRACH Planning The PRACH (Physical Random Access Channel) is an important channel in LTE. There are various configuration options which relate to how the channel works, as well as the mitigation of interference between different cell PRACHs. The PRACH is also a factor in calculating the maximum distance for initial access. U-Net includes various parameters relative to PRACH configuration, as well as the cell radius parameters. These enable it to perform various calculations which provide a reference to coverage and simulations.

Issue 01 (2010-06-01)


7-11


7 Huawei LTE Tools

7-12


Issue 01 (2010-06-01)


8 Glossary

8 Numerics

Glossary

C

16 QAM (Quadrature Amplitude Modulation) 64QAM (Quadrature Amplitude Modulation) 2G (Second Generation) 3G (Third Generation) 3GPP (Third Generation Partnership Project) 4G (Fourth Generation)

C (Conditional) CCCH (Common Control Channel) CGI (Cell Global Identifier) CQI (Channel Quality Indication) CRF (Charging Rules Function) CS (Circuit Switched) CSG (Closed Subscriber Group)

A

D

AAA (Access Authorization and Accounting) AC (Access Class) AES (Advanced Encryption Standard) AKA (Authentication and Key Agreement) AM (Acknowledged Mode) AMBR (Aggregate Maximum Bit Rate) AMD (Acknowledged Mode Data) APN (Access Point Name) APN AMBR (Access Point Name Aggregate Maximum Bit Rate) ARP (Allocation and Retention Priority) AS (Access Stratum)

D/C (Data/Control) dB (Decibels) DCCH (Dedicated Control Channel) DL-SCH (Downlink - Shared Channel) DRB (Dedicated Radio Bearer) DRX (Discontinuous Reception) DSCP (Differentiated Services Code Point) DTCH (Dedicated Traffic Channel) DTM (Dual Transfer Mode)

B BCCH (Broadcast Control Channel) BCH (Broadcast Channel) BH (Busy Hour) BI (Backoff Indicator) BSR (Buffer Status Report)

Issue 01 (2010-06-01)


E E (Extension) EARFCN (E-UTRA Absolute Radio Frequency Channel Number) ECGI (E-UTRAN Cell Global Identifier) ECI (Evolved Cell Identity) EIR (Equipment Identity Register) EMM (EPS Mobility Management) eNB (Evolved Node B) 8-1


8 Glossary

EP (Elementary Procedures) EPC (Evolved Packet Core) ePDG (evolved Packet Data Gateway) EPS (Evolved Packet System) E-RAB (E-UTRAN - Radio Access Bearer) ESM (EPS Session Management) ESM (Evolved Session Management) E-UTRA (Evolved - Universal Terrestrial Radio Access) E-UTRAN (Evolved - Universal Terrestrial Radio Access Network)

I

F

KPI (Key Performance Indicators)

FAC (Final Assembly Code) FDD (Frequency Division Duplex) FI (Frame Information) FO (First-Order)

L

G GBR (Guaranteed Bit Rate) Geo (Geographical) GERAN (GSM/EDGE Radio Access Network) GTP (GPRS Tunneling Protocol) GTP-U (GPRS Tunneling Protocol - User) GTPv1-U (GPRS Tunneling Protocol Version 1 - User Plane) GTPv2-C (GPRS Tunneling Protocol Version 2 - Control) GU Group ID (Globally Unique Group Identifier) GUMMEI (Globally Unique MME Identifier) GUTI (Globally Unique Temporary Identity) H HA (Home Agent) HARQ (Hybrid Automatic Repeat Request) HeNB (Home Evolved Node B) HeNB-GW (Home Evolved Node B - Gateway) HFN (Hyper Frame Number) HPLMN (Home Public Land Mobile Network) HRPD (High Rate Packet Data) HSS (Home Subscriber Server)

8-2


ICIC (Inter Cell Interference Cancelation) IE (Information Elements) IETF (Internet Engineering Task Force) IM (Interference Margin) IMEI (International Mobile Equipment Identity) IMS (IP Multimedia Subsystem) IMSI (International Mobile Subscriber Identity) IR (Initialization and Refresh) K

LCG ID (Logical Channel Group Identity) LCID (Logical Channel Identifier) LI (Length Indicator) LSF (Last Segment Flag) LTE (Long Term Evolution) M M (Mandatory) MAC (Medium Access Control) MAC-I (Message Authentication Code - Integrity) MAG (Mobile Access Gateway) MCC (Mobile Country Code) ME (Mobile Equipment) MIB (Master Information Block) MIMO (Multiple Input Multiple Output) MME (Mobility Management Entity) MMEC (MME Code) MNC (Mobile Network Code) MS (Mobile Station) MSB (Most Significant Bits) MSIN (Mobile Subscriber Identity Number) M-TMSI (MME - Temporary Mobile Subscriber Identity) N NAS (Non Access Stratum) non-GBR (non - Guaranteed Bit Rate)

Issue 01 (2010-06-01)


8 Glossary

NSAPI (Network layer Service Access Point Identifier)

QPSK (Quadrature Phase Shift Keying)

O

R

O (Optional) O&M (Operations and Maintenance) OFDMA (Orthogonal Frequency Division Multiple Access)

RA (Random Access) RACH (Random Access Channel) RAI (Routing Area Identity) RAN (Radio Access Network) RAPID (Random Access Preamble Identifier) RAR (Random Access Response) RAT (Radio Access Technology) RB (Radio Bearer) RLC (Radio Link Control) RLF (Radio Link Failure) RNC (Radio Network Controller) RNL (Radio Network Layer) RNTP (Relative Narrowband Tx Power) ROHC (Robust Header Compression) RR (Radio Resource) RRC (Radio Resource Control) RRM (Radio Resource Management) RSRP (Reference Signal Received Power) RSRQ (Reference Signal Received Quality) Rx (Receive)

P P (Polling) PBCH (Physical Broadcast Channel) PBR (Prioritized Bit Rate) PCCH (Paging Control Channel) PCFICH (Physical Control Format Indicator Channel) PCH (Paging Channel) PCI (Physical Cell Identifier) PCRF (Policy and Charging Rules Function) PDCCH (Physical Downlink Control Channel) PDCP (Packet Data Convergence Protocol) PDF (Policy Decision Function) PDN (Packet Data Network) PDSCH (Physical Downlink Shared Channel) PDU (Protocol Data Unit) PH (Power Headroom) PHICH (Physical Hybrid ARQ Indicator Channel) PHR (Power Headroom Report) PHY (Physical Layer) PL (Pathloss) PLMN (Public Land Mobile Network) PMIP (Proxy Mobile IP) PN (N-PDU Number) PRACH (Physical Random Access Channel) PRB (Physical Resource Block) PS (Packet Switched) PT (Protocol Type) PUCCH (Physical Uplink Control Channel) PUSCH (Physical Uplink Shared Channel) Q QCI (QoS Class Identifier) QoS (Quality of Service)

Issue 01 (2010-06-01)


S S (Sequence) S1AP (S1 Application Protocol) SC-FDMA (Single Carrier Frequency Division Multiple Access) SCTP (Stream Control Transmission Protocol) SDF (Service Data Flow) SDU (Service Data Unit) SGSN (Serving GPRS Support Node) S-GW (Serving - Gateway) SI (System Information) SIB 1 (System Information Block 1) SINR (Signal to Interference Noise Ratio) SMS (Short Message Service) SN (Sequence Number) SNR (Serial Number) SO (Second-Order) SO (Segment Offset)

8-3


8 Glossary

SPS (Semi-Persistent Scheduling) SRB (Signaling Radio Bearer) SRNC (Serving RNC) SRS (Sounding Reference Signal) SRVCC (Single Radio Voice Call Continuity) S-TMSI (Serving - Temporary Mobile Subscriber Identity) SUI (Stanford University Interim) T TA (Timing Advance) TA (Tracking Area) TAC (Tracking Area Code) TAC (Type Approval Code) TAI (Tracking Area Identity) TAU (Tracking Area Update) TB (Transport Block) TCP (Transmission Control Protocol) TCP/IP (Transmission Control Protocol, Internet Protocol) TDD (Time Division Duplex) TEID (Tunnel Endpoint Identifier) TFT (Traffic Flow Template) Thresh1 (Threshold1) Thresh2 (Threshold2) TM (Transparent Mode) TMD (Transparent Mode Data) TNL (Transport network Layer) TPC (Transmit Power Control) TTI (Time Transmission Interval) TTT (Time To Trigger) Tx (Transmit)

V VoIP (Voice over IP) VPLMN (Visited Public Land Mobile Network) W WCDMA (Wideband CDMA) X X2AP (X2 Application Part) X2AP (X2 Application Protocol)

U UDP (User Datagram Protocol) UE (User Equipment) UE AMBR (User Equipment Aggregate Maximum Bit Rate) UL (Uplink) UL-SCH (Uplink Shared Channel) UM (Unacknowledged Mode) UMD (Unacknowledged Mode Data) USIM (Universal Subscriber Identity Module) UTRA (Universal Terrestrial Radio Access) UTRAN (Universal Terrestrial Radio Access Network)

8-4


Issue 01 (2010-06-01)


8 Glossary

Cautioned Words

HTTP

There is security risk for HTTP and Huawei recommends to use HTTPS to replace it

2

FTP

There is security risk for FTP protocol and Huawei recommends to use SFTP or FTPS to replace it

3

IMSI/IMEI/IP Address

The privacy-related information may be anonymity for user's privacy protection

1

Issue 01 (2010-06-01)


8-1

Microsoft Word - 7. OEP100301 LTE Radio Network Design ISSUE 1

Recommend Documents