A reference symbol assisted interference cancelling hybrid receiver for an asynchronous DS/CDMA system
Oliver Nesper, Paul K. M. Ho · 2002
This paper focuses on a reference symbol assisted multiuser interference cancelling receiver for a quasi-synchronous DS/CDMA system using BPSK modulation. The channel is assumed Rayleigh and the propagation delay differences between the users are assumed to be a fraction of the symbol time. The receiver employs two structures: a decorrelator structure for channel estimation based on pilot symbols, and a successive interference cancellation scheme (SIC) for data detection. We refer to this receiver as a hybrid receiver and its performance will be compared with that of a pure SIC receiver for both channel estimation and data detection. To facilitate channel estimation in the presence of propagation delay differences, we shortened the correlation interval for the pilot symbols but increased the pilot power accordingly. The numerical results indicate that as far as the bit error rate is concerned, a one-stage hybrid receiver is as good as a two-stage pure SIC receiver. Although the decorrelation receiver has to perform matrix inversions, the matrix updates can be obtained by a computational efficient order recursive procedure. Moreover, the matrix calculations can be spread over a frame, allowing us to keep the computational load per symbol on a moderate level. Therefore, we believe our hybrid receiver scheme offers a good performance at an acceptable level of implementation complexity.