Estimation and Compensation of Frequency Selective TX/RX IQ Imbalance in MIMO OFDM systems

The influence, digital estimation and compensation of IQ mismatch at both transmitter (TX) and receiver (RX) side of a direct-conversion based multiple antenna OFDM system are presented in this paper. The resulting IQ imbalance can be split into a frequency independent and a frequency selective part. For estimation and compensation a two-step approach is presented, combining a data-aided and decision directed approach. First the frequency independent IQ imbalance is estimated using a preamble and, subsequently, the frequency selective IQ imbalance is removed using adaptive filtering. A numerical performance analysis reveals that the presented approach effectively mitigates the influence of IQ mismatch in OFDM-based space division multiplexing systems experiencing both TX and RX IQ imbalance.