Prediction of Time-Varying Multipath Fading Channel for Pre-equalization of Signal in Uplink Mobile MC-CDMA Communication

摘要

MC-CDMA has been considered as one of the promising transmission techniques for the next generation of mobile communication systems, because of its efficient usage of frequency bandwidth, robustness to the multi-path fading and efficient accommodation of multiple users. However, MC-CDMA has a difficulty to be employed in the uplink communication where the transmitted signal from each user propagates through the different multi-path fading channel, and the received multiplexed signal is not orthogonal anymore at the base station. From this fact, the BER performance of uplink MC-CDMA would be degraded relatively due to the occurrence of multi-user interference (MUI). To solve the MUI problem in the uplink MC-CDMA, the pre-equalization method was proposed in which the uplink signal is pre-equalized at the user terminal by using the channel response estimated in the downlink. Although the pre-equalization method is very effective for the stationary uplink channel with fixed users, it is hard to be employed in the time varying fading channel with mobile users because there is a big difference in the channel response between downlink and uplink. This paper proposes the prediction method for the uplink channel impulse response based on the ML time domain spectral decomposition of the downlink channel impulse response. The proposed prediction method can be used in the pre-equalization of uplink MC-CDMA even in the time varying fading channel. The computer simulation results show that proposed method can achieve much better BER performance in the uplink MC-CDMA communications as compared with static pre-equalization method.