Experimental Comparison of Antenna Clustering Strategies in MIMO Distributed Antenna Systems

In this paper the effect of partitioning arrays of transmitting antennas into spatially separated clusters on the condition number and capacity of MIMO wireless systems is examined using experimental channel measurements of an indoor MIMO-enabled distributed antenna system (DAS). It is first shown for a 3×2 MIMO system that distributing the transmit antennas into spatially separated clusters provides an improvement in channel conditioning (~1dB) and hence capacity, in line with previous findings. Next, a configuration with transmit antennas and 2 receive antennas is examined and it is found that when it is operated as a 6×2 MIMO system, it makes negligible difference to the conditioning of the channel whether the transmit antennas are grouped into 3 clusters of 2 antennas or 2 clusters of 3 antennas. The capacity varies by only a small amount (~%1) between the two clustering schemes, which can be accounted for by environment-specific signal-to-noise ratio (SNR) effects. It is then concluded that for the two typical indoor DAS scenarios tested here, if sufficient transmit diversity is provided (i.e. there are a relatively large number of transmit antennas compared to receive antennas), greater spatial distribution through increased clustering provides diminishing performance improvements. Given the typically lower installation cost of less distributed arrangements, they may then be a preferred option in commercial DAS deployments.