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.