An Adaptive Receiver Design for OFDM Systems Using Conjugate Transmission

In this paper, we propose an adaptive receiver for efficient intercarrier interference (ICI) cancellation in orthogonal frequency division multiplexing (OFDM) systems using two-path conjugate transmission. This receiver design is based on the phase rotated conjugate cancellation (PRCC) concept presented recently, where two individual phase rotations are employed on the two receive paths, rather than only one phase rotation is adopted for the two transmit paths in the PRCC scheme. We derive the optimal phase rotations using the criterion of maximizing the carrier-to-interference ratio, and then develop an adaptive normalized block least mean-squared algorithm to approach the optimal solutions. With such adaptive phase rotations in the receiver, the carrier frequency offset (CFO) variations due to the channel effect and the mismatch between oscillators at the transmitter and receiver can effectively be tracked without feeding back the CFO estimate to the transmitter as required in PRCC. Simulation results demonstrate that the proposed approach has better bit error rate performance than the PRCC and the conventional CC scheme for various time-varying channels, even when the CFO/channel estimation error is considered.