An Improved Adaptive Receiver for OFDM Systems Using Conjugate Transmission

In this paper, we propose an improved adaptive receiver in order to overcome the performance degradation problem encountered by the existing conjugate transmission schemes due to a time-varying frequency offset. We apply two different phase rotations on the two receiving paths instead of employing only one common phase rotation for both paths in the previous work. The two phase rotations are chosen properly based on the derived optimization results, such that an additional phase distortion on the detected symbol could be completely removed. For practical use, the block least mean-squared algorithm is applied to adaptively update the two phase rotations with the frequency offset variation. Computer simulation results show that the proposed scheme outperforms the existing works in terms of bit error rate performance, especially when a rapid frequency offset variation is considered.