Subspace tracking for group-blind multiuser detectors

This paper considers DS-CDMA systems with both inter- and intra-cell interference. The users inside the cell are assumed to have known codes, while the codes of the users outside the cell are unknown. To reduce the interference from both known and unknown users, a hybrid group-blind multiuser detector, derived in a previous paper, can be used. In the current paper we consider real time implementation using subspace tracking, and adapt the NA-CSVD (noise average cross-terms singular value decomposition) to the hybrid group-blind multiuser detector. The NA-CSVD algorithm is a new efficient QR Jacobi-type subspace tracking algorithm which has complexity O(Nd), where N is the processing gain and d is the number of out-of-cell users. It is shown that the NA-CSVD implementation of the hybrid multi-user detector has good performance, and that the performance considerably exceeds that of the purely blind detector, because of the sensitivity of the NA-CSVD to subspace dimension and the lower subspace dimension of the group-blind detector