3GPP LTE Long Term Evolution

LTE, HSPA, EDGE

LTE (both radio and core network evolution) is now on the market. Release 8 was frozen in December 2008 and this has been the basis for the first wave of LTE equipment. LTE specifications are very stable, with the added benefit of small enhancements being introduced in Release 9, a Release that will be functionally frozen in December 2009.

LTE (Long Term Evolution) is the project name of a new high performance air interface for cellular mobile communication systems. It is the last step toward the 4th generation (4G) of radio technologies designed to increase the capacity and speed of mobile telephone networks. Where the current generation of mobile telecommunication networks are collectively known as 3G (for "third generation"), LTE is marketed as 4G. However, it does not fully comply with the IMT Advanced 4G requirements. Most major mobile carriers in the United States and several worldwide carriers have announced plans to convert their networks to LTE beginning in 2009. The world's first publicly available LTE-service was opened by TeliaSonera in the two Scandinavian capitals Stockholm and Oslo on the 14th of December 2009. LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) which will be introduced in 3rd Generation Partnership Project (3GPP) Release 8. Much of 3GPP Release 8 will focus on adopting 4G mobile communications technology, including an all-IP flat networking architecture. On August 18, 2009, the European Commission announced it will invest a total of €18 million into researching the deployment of LTE and 4G candidate system LTE Advanced.[1]

Motivation for 3GPP Release 8 - The LTE Release

Need to ensure the continuity of competitiveness of the 3G system for the future

User demand for higher data rates and quality of service

Packet Switch optimised system

Continued demand for cost reduction (CAPEX and OPEX)

Low complexity

Avoid unnecessary fragmentation of technologies for paired and unpaired band operation

LTE Release 8 Key Features

High spectral efficiency

— OFDM in Downlink, Robust against multipath interference & High affinity to advanced techniques such as Frequency domain channel-dependent scheduling & MIMO

— DFTS-OFDM(“Single-Carrier FDMA”) in Uplink, Low PAPR, User orthogonality in frequency domain

— Multi-antenna application

Very low latency

— Short setup time & Short transfer delay

— Short HO latency and interruption time; Short TTI, RRC procedure, Simple RRC states

Support of variable bandwidth

— 1.4, 3, 5, 10, 15 and 20 MHz

Simple protocol architecture

— Shared channel based

— PS mode only with VoIP capability

Simple Architecture

— eNodeB as the only E-UTRAN node

— Smaller number of RAN interfaces, eNodeB « MME/SAE-Gateway (S1), eNodeB « eNodeB (X2)

Compatibility and inter-working with earlier 3GPP Releases

Inter-working with other systems, e.g. cdma2000

FDD and TDD within a single radio access technology

Efficient Multicast/Broadcast

— Single frequency network by OFDM

Support of Self-Organising Network (SON) operation

LTE Release 8 Major Parameters

LTE-Release 8 User Equipment Categories

LTE Release 8 Specifications

LTE is specified in 36 series technical specifications

The latest version of the LTE Release 8 specifications (September 2009 version) can be found in On-line in the 36 series

LTE Historical Information

The technical paper UTRA-UTRAN Long Term Evolution (LTE) and 3GPP System Architecture Evolution (SAE) is a good starting point.

Initiated in 2004, the Long Term Evolution (LTE) project focused on enhancing the Universal Terrestrial Radio Access (UTRA) and optimizing 3GPP’s radio access architecture.

Targets were to have average user throughput of three- to four-times the Release 6 HSDPA levels in the Downlink (100Mbps), and two to three times the HSUPA levels in the Uplink (50Mbps).

In 2007, the LTE of the 3rd generation radio access technology – "E UTRA" – progressed from the feasibility study stage to the first issue of approved Technical Specifications. By the end of 2008, the specifications were sufficiently stable for commercial implementation.

Orthogonal Frequency Division Multiplexing (OFDM) was selected for the Downlink and Single Carrier-Frequency Division Multiple Access (SC-FDMA) for the Uplink. The Downlink supporting data modulation schemes QPSK, 16QAM, and 64QAM and the Uplink BPSK, QPSK, 8PSK and 16QAM.

LTE’s E UTRA uses a number of defined channel bandwidths between 1.25 and 20 MHz (contrasted with UTRA’s fixed 5 MHz channels).

4 x Increased Spectral Efficiency, 10 x Users Per Cell

Spectral efficiency is increased by up to four-fold compared with UTRA, and improvements in architecture and signalling reduce round-trip latency. Multiple Input / Multiple Output (MIMO) antenna technology should enable 10 times as many users per cell as 3GPP’s original W CDMA radio access technology.

To suit as many frequency band allocation arrangements as possible, both paired (FDD) and unpaired (TDD) band operation is supported. LTE can co-exist with earlier 3GPP radio technologies, even in adjacent channels, and calls can be handed over to and from all 3GPP’s previous radio access technologies.

In the same time frame as the development of LTE, 3GPP’s core network has been undergoing System Architecture Evolution (SAE), optimizing it for packet mode and in particular for the IP-Multimedia Subsystem (IMS) which supports all access technologies.