Over the last couple of years, the term "Long Term Evolution" or "LTE" has been thrown around rather loosely. In fact, LTE technically refers to more of a 3.9G than fourth-generation (4G) technology. Yet the Third-Generation Partnership Project (3GPP) has now announced an evolved version dubbed LTE-Advanced (LTE-A).

According to the 3GPP, LTE-A will meet or exceed the requirements of the International Telecommunications Union (ITU) for the 4G communications standard known as IMT-Advanced. Initially, LTE-Advanced is being specified as part of Release 10 of the 3GPP specifications. To provide a comprehensive overview of LTE-A while introducing design and test solutions that are ready for early adopters, Agilent Technologies has introduced a 36-page application note titled, "Introducing LTE-Advanced."

Quite simply, LTE is considered incapable of meeting 4G's uplink-spectral-efficiency and peak-data-rate requirements. LTE-A addresses these higher requirements with wider bandwidths, which are enabled by carrier aggregation and higher efficiency. The efficiency is derived from enhanced uplink multiple access and multiple antenna schemes (advanced multiple-input multiple-output techniques). Although they are not critical to meeting 4G requirements, the following performance enhancements also are being considered for Release 10: coordinated multipoint transmission and reception (CoMP); relaying; support for heterogeneous networks; LTE self-optimizing-network (SON) enhancements; Home-enhanced-node-B (HeNB) mobility enhancements; and fixed wireless customer-premise-equipment (CPE) RF requirements.

Apart from a set of rather general purpose requirements provided by the ITU for IMT-Advanced, LTE-A is expected to provide enhanced peak data rates to support advanced mobile services and applications (in the downlink, 100 Mb/s for high mobility and 1 Gb/s for low mobility). In contrast, 3G specified a peak rate of 2 Mb/s for indoor low-mobility applications and 144 kb/s vehicular. To achieve the 1-Gb/s peak data rate required by the ITU in LTE-A, 4x4 MIMO and transmission bandwidths wider than roughly 70 MHz will be used.

The ITU has renamed its IMT-2000 spectrum as "IMT" spectrum, meaning that all spectrum previously identified for IMT-2000 (3G) also is applicable for IMT-A (4G). With just one pool of IMT spectrum, the deployment of specific technologies in specific bands will depend on local circumstances. From the outset, Release 10 has upwards of 30 bands defined. In addition, TR 36.913 states that targets for average spectral efficiency and cell-edge user-throughput efficiency should be given higher-priority targets than targets for peak spectral efficiency and other features, such as voice-over- IP (VoIP) capacity. As a result, the work of LTE-A should focus on the challenges of raising average and cell-edge performance.

In addition to the bands that are currently defined for LTE Release 8, TR 36.913 identifies these new ones: 450 to 470 MHz, 698 to 862 MHz, 790 to 862 MHz, 2.3 to 2.4 GHz, 3.4 to 4.2 GHz, and 4.4 to 4.99 GHz. LTE-A is designed to operate in spectrum allocations of different sizes, which includes allocations wider than 20 MHz in Release 8. IMTA permits aggregation from different bands to meet its higher-bandwidth requirements, although it is of course desirable to have bandwidths greater than 20 MHz deployed in adjacent spectrum. These fine points of LTE-A are just some of the vast information provided in this new application note, which provides an in-depth look at many of the facets of LTE-A and its impact on design.