Joint Data Detection and Channel Sounding for TDD Systems with Antenna Selection

Antenna subset selection is a cost-effective way of exploiting the spatial dimension by only using a subset of the available antennas and thereby reducing the number of RF chains. A simple but effective way of precoding signals in multiantenna OFDM systems using antenna subset selection is per-tone antenna selection, which can be applied to the chosen subset. In a TDD system, estimates of the strength of the antennas can easily be obtained from the uplink and then used for the downlink precoding. However if only a subset of the antennas is active, no information is available for the remaining antennas; this may result in poor downlink performance. In this paper we propose a simple modification to the uplink reception which allows channel sounding of inactive antennas; this will aid the per-tone selection process in the downlink. With simulations we show that this scheme outperforms other alternatives, such as switch-and-stay.