Precoding and Spatially Multiplexed MIMO in 3GPP Long-Term Evolution

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  • Author: Randall T. Becker
Multiple Input Multiple Output (MIMO) technology has been shown to provide higher data rates with increased spectral efficiency. The performance of a MIMO system is directly related to the received signal-to-interference-and-noise ratio (SINR) and the correlation properties that are characteristic of the multipath channel and antenna configuration. Although the wireless channel can deliver low SINR at some of the MIMO receive antennas, it is possible to improve system performance with the application of beamforming at the transmitter. Though often used together, it is important to differentiate here that beamforming is a signal processing technique, which is very different from beam steering where the direction of the main lobe of radiation is changed. Beamforming lends itself well to MIMO applications.The 3GPP Long Term Evolution (LTE) specification includes several transmitbeamforming techniques that may optimize system performance under various channel conditions. One technique, referred to as precoding, is designed to increase and/or equalize the received SINR across the multiple receive antennas.