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LTE-Advanced: An introduction

Posted: 04 Jul 2011 ?? ?Print Version ?Bookmark and Share

Keywords:LTE-Advanced? 3GPP? 4G?

An evolved version of LTE that is being developed by 3GPP. It's project name is LTE-Advanced (LTE-A). It is expected to meet or exceed the requirements of the International Telecommunication Union (ITU) for the fourth generation (4G) radio communication standard known as IMT-Advanced. LTE-Advanced is being specified initially as part of Release 10 of the 3GPP specifications. The LTE specifications will continue to be developed in subsequent 3GPP releases.

In October 2009, the 3GPP Partners formally submitted LTE-Advanced to the ITU Radiocommunication sector (ITU-R) as a candidate for 4G IMT-Advanced [1]. Publication by the ITU of the specification for IMT-Advanced is expected by March 2011. As more and more wireless operators announce plans to deploy LTE in their next-generation networks, interest in LTE-Advanced is growing.

What's new in LTE-A?
In the feasibility study for LTE-Advanced, 3GPP determined that LTE-Advanced would meet the ITU-R requirements for 4G. The results of the study are pub- lished in 3GPP Technical Report (TR) 36.912. Further, it was determined that 3GPP Release 8 LTE could meet most of the 4G requirements apart from uplink spectral efficiency and the peak data rates. These higher requirements are addressed with the addition of the following LTE-Advanced features:- Wider bandwidths, enabled by carrier aggregation
- Higher efficiency, enabled by enhanced uplink multiple access and enhanced multiple antenna transmission (advanced MIMO techniques)

Other performance enhancements are under consideration for Release 10 and beyond, even though they are not critical to meeting 4G requirements:

Coordinated multipoint transmission and reception (CoMP)
- Relaying
- Support for heterogeneous networks
- LTE self-optimizing network (SON) enhancements
- Home enhanced-node-B (HeNB) mobility enhancements
- Fixed wireless customer premises equipment (CPE) RF requirements

System performance requirements
The system performance requirements for LTE-Advanced will in most cases exceed those of IMT-Advanced. The 1Gbit/s peak data rate required by the ITU will be achieved in LTE-Advanced using 4x4 MIMO and transmission bandwidths wider than approximately 70MHz [8]. In terms of spectral efficiency, today's LTE (Release 8) satisfies the 4G requirement for the downlink, but not for the uplink.

The table below compares the spectral efficiency targets for LTE, LTE-Advanced, and IMT-Advanced. Note that the peak rates for LTE-Advanced are substantially higher than the 4G requirements, which highlights a desire to drive up peak performance in 4G LTE, although targets for average performance are closer to ITU requirements. It's worth noting that peak targets, because they can be met in ideal circumstances, are often easier to demonstrate than average targets. However, TR 36.913 states that targets for average spectral efficiency and for cell-edge user throughput efficiency should be given higher priority than targets for peak spectral efficiency and other features such as VoIP capacity5. Thus the work of LTE-Advanced should be focused on the very real challenges of raising average and cell-edge performance.

Spectrum flexibility
In addition to the bands currently defined for LTE Release 8, TR 36.913 identifies the following new bands:
- 450每470MHz band
- 698每862MHz band
- 790每862MHz band
- 2.3每2.4GHz band
- 3.4每4.2GHz band
- 4.4每4.99GHz band

Some of these bands are now formally included in the 3GPP Release 9 and Release 10 specifications. Note that frequency bands are considered release- independent features, which means that it is acceptable to deploy an earlier release product in a band not defined until a later release.

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