Simulation and design of MIMO algorithms for correlated wireless channels

Abstract

Spatial multiplexing and space-time codes are competing ways of extracting capacity from MIMO wireless systems. We present examples of both approaches and study their performance, in particular in the case of correlated channels. Next, we show that multiplexing and diversity oriented schemes (like STC) react differently to the correlation structure of MIMO arrays.

We address the problem of finding an optimal combination of multiplexing and diversity in a MIMO system. We develop a combining approach in the form of an optimal spatial assignment of antennas, in order to multiplex space-time coded symbol blocks. We call this scheme SMAL, and develop it in two versions, first for the case when instantaneous channel information is available at the transmitter, and second when only long-term correlation statistics are known. We investigate the performance of both versions in the practical case when correlation is not uniform across all antenna pairs (e.g. in linear arrays).

The SMAL scheme is tested for two levels of correlated fading between neighbouring antenna elements. A comparison between the two versions shows that the instantaneous SMAL is especially useful at low levels of correlated fading. Under conditions of heavily correlated fading the correlation-based approach performs just as well and is preferred because of its lower complexity.

We also vary the number of transmit and receive (N,M) antennas, and test the SMAL scheme for the two MIMO systems N=M=4 and N=M=6.

For the instantaneous version of SMAL and low correlation, we show improvements of over 2 dB over the case of random pattern selection , at a certain target bit-error rate, both for N=M=4 and N=M=6. With the statistical SMAL for high correlation, a performance gain of almost 5 dB is shown in the case of N=M=4.

The development and results of the SMAL scheme have also resulted in the submission of a conference article to NORSIG 2003.