“…Even if assuming reasonably good antenna isolation in each device, there are always unavoidable frequency response (FR) mismatches between the transmitter (TX, containing, e.g., mixers, power amplifier and RF filtering) and receiver (RX, e.g., RF filtering, LNA, mixers, and lowpass filtering) chains implemented in the same transceiver, which, in turn, distort the reciprocal nature of the effective DL and UL channels. As shown in [5]- [10], if the CSIT at the BS is obtained by measuring the UL signals under transceiver non-reciprocity, inter-user interference (IUI) occurs at user equipment (UE) reception and thus causes severe performance degradation in TDD MU MIMO-OFDM DL transmission.…”