The effect of out-of-synchronization on channel estimation and joint detection in downlink TD-SCDMA systems

摘要

In this paper, the effect of out-of-synchronization on channel estimation and then joint detection in downlink TD-SCDMA has been analyzed from both theory and simulations when different midambles are assigned to different user equipments (UE). The analysis shows that the maximum likelihood (ML) channel estimation using the specially designed midambles implemented with fast Fourier transform (FFT) will result in a circular shift of the actual channel impulse response (CIR) when downlink channel is in out-of-synchronization, and based on this, the shift deviation of downlink synchronization point along different direction of level axis (left or right) during some periods will cause quite different impact on joint detection.