Modeling and evaluation of MIMO systems exploiting channel reciprocity in TDD mode

The advanced knowledge of forward link channel information enables the optimal transmit waveform to be designed for a multiple input multiple output (MIMO) antenna system to exploit the channel´s characteristics fully. The reciprocal property of the radio channel makes time division duplex (TDD) an attractive air interface design since the forward link channel information can be derived from the reverse link signal without any explicit feedback. Among the many practical factors that may invalidate the channel reciprocity in TDD mode, this paper focuses on those that are associated with the mismatches among the radio frequency (RF) circuits in the many transmit/receive chains. With a simple model, the sources for the RF mismatches are identified and their calibration requirements are established using simulation.