Evaluation of encoded MU-MISO-OFDM systems in TDD mode with non-ideal channel reciprocity

In multi-user orthogonal frequency division multiplexing (MU-OFDM) systems operating in time division duplex (TDD) mode downlink pre-equalization can be applied relying on channel state information (CSI) from the uplink direction. Unfortunately, the prerequisite of channel reciprocity is usually not fulfilled due to non-reciprocal transceivers. Hence, this paper deals with a comparison of robust pre-equalization schemes and a calibration approach to enhance the necessary uplink-downlink link equivalence for MU-MISO-OFDM systems applying linear and non-linear pre-equalization techniques and strong forward error correction (FEC). Performance evaluations concerning coded bit error rate results show that robust pre-equalizers exclusively improve the performance in moderate non-reciprocity conditions. In contrast, only calibration helps in dealing with severe transceiver mismatch.