Performance of space-time codes over a flat-fading channel using a subspace-invariant detector

Multiple-input, multiple-output (MIMO) communications has received considerable attention in recent years. The flat-fading channel, with identical, independently distributed gains between all transmitter and receiver pairs has been one of the MIMO channels studied extensively. Many studies have focused on channel capacity and coding in additive white Gaussian noise. When the noise background has an unknown spatial covariance due to interference, receivers that adapt to the noise background can be more robust. One way of achieving robustness builds invariances into the detector, creating a channel model that incorporates adaptive beamforming naturally into signal detection and coding. In the particular case of frequency-hopped waveforms with random fading and hop to hop white noise, the capacity of this channel can be evaluated. A family of space-time codes for the invariant detector is investigated and its performance compared with the derived capacity bounds. Theoretical predictions of performance in interference and in different fading conditions are presented and compared with simulation results for a concatenated coding architecture involving space-time inner codes and low density parity-check outer code.