Introducing LTE-Advanced

Moray Rumney, Agilent Technologies

February 5, 2011

Moray Rumney, Agilent Technologies

LTE-Advanced (LTE-A) is the project name of the evolved version of LTE that is being developed by 3GPP. LTE-A will 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, with a functional freeze targeted for March 2011. 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.

The following is an excerpt of the highlights from Agilent's application note on this topic. To view the entire article as a PDF, you can head here.

What's new in LTE Advanced
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 1 Gbps peak data rate required by the ITU will be achieved in LTE-Advanced using 4x4 MIMO and transmission bandwidths wider than approximately 70 MHz [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.


TABLE 1: Performance targets for LTE, Advanced LTE, and IMT Advanced

Spectrum flexibility
In addition to the bands currently defined for LTE Release 8, TR 36.913 identifies the following new bands:

• 450–470 MHz band
• 698–862 MHz band
• 790–862 MHz band
• 2.3–2.4 GHz band
• 3.4–4.2 GHz band
• 4.4–4.99 GHz 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.

LTE-Advanced is designed to operate in spectrum allocations of different sizes, including allocations wider than the 20 MHz in Release 8, in order to achieve higher performance and target data rates. Although it is desirable to have bandwidths greater than 20 MHz deployed in adjacent spectrum, the limited availability of spectrum means that aggregation from different bands is necessary to meet the higher bandwidth requirements. This option has been allowed for in the IMT-Advanced specifications.