An Adaptive Receiver Design for OFDM-Based Cooperative Relay Systems Using Conjugate Transmission

In this paper, we propose an adaptive receiver design for OFDM-based cooperative relay systems using two-path conjugate transmission to achieve both diversity reception and intercarrier interference (ICI) cancellation. Considering that the relayed signals are affected by statistically independent channel fading gains and different frequency offsets, the proposed receiver applies not only phase rotations but also an amplitude scaling factor, whose values are optimized based on criteria of maximizing the carrier-to-interference ratio and minimizing the ICI power, respectively, on the two receiving paths to improve ICI cancellation performance. In order to track the channel and frequency offset variations under time-varying environments, we further develop an adaptive normalized block least mean-squared algorithm to update the phase rotations and the amplitude scaling. Simulation results demonstrate that the proposed adaptive receiver provides significant performance improvement over related works for OFDM-based cooperative relay systems.