Compensation of interference non-reciprocity in adaptive TDD MIMO-OFDM systems

In a time-division-duplex (TDD) system, the channel state information can be easily obtained at the transmitter side due to channel reciprocity and it can be used to dramatically increase the spectral efficiency of a MIMO system. However, the interference structure between transmission directions does not necessarily correlate at all. In such a case, the modulation/coding parameters assigned based on the reverse link measurements may lead to excessively high frame error rates. If the interference structure between transmission directions differs significantly, A simple closed-loop method to compensate the non-reciprocity between uplink and downlink interference structure is introduced. The simulation results clearly show that in the presence of non-reciprocal interference, some feedback to the transmitter is always needed in order to maintain the desired quality of service at the receiver. The gain from the fast feedback depends on the interference structure and the number of transmitter and receiver antennas.