Semi-blind downlink inter-cell interference cancellation for FDD DS-CDMA systems

We address the problem of downlink interference rejection in a DS-CDMA system. Periodic orthogonal Walsh-Hadamard sequences spread different users’ symbols followed by scrambling by a symbol aperiodic base-station specific overlay sequence. The point-to-point propagation channel from the cell-site to a certain mobile station is the same for all downlink signals (desired user as well as the intracell interference). The intercell interference (which can be seen as co-channel interference) degrades significantly the performance of the receiver when the mobile approaches the edge of its cell and the situation becomes more critical at the soft handover. We propose to simultaneously equalize the user of interest while cancelling (or reducing) the intercell interferers by the Interference Cancelling Matched Filter (ICMF) receiver which we introduced previously. We can get ride of the intracell interference by the maximum SINR receiver following the ICMF. The ICMF depends on the common channel for the cell of interest, to be estimated with a pilot sequence, and contains a blind interference cancellation part. The critical part is the channel estimation. The usual correlation method may lead to poor estimates in high interference environments. Significant improvements result from the exploitation of the sparceness of the propagation channel model.