Adaptive Channel Quantization on TDD Reciprocity Performance of Relative Antenna Calibration

This paper studies a relative antenna calibration scheme for time division duplex (TDD) systems, which relies on user equipment (UE) for the estimation of transceiver response via multiple forward and reverse link channel measurements. Since the downlink channel knowledge at the base station (BS) needs to be accurate, UE feeds the quantized channel coefficients back to BS. Once accurate channel estimation is available at BS within a calibration phase, the transceiver response can be approximated by total least squares method. We propose an adaptive quantization method for downlink channel state information, which selects the number of feedback bits based on the estimation quality of the instantaneous uplink channel. We also discuss two reference UE selection methods based on channel quality indication feedback and UE-BS channel signal-to-noise ratio measurement.