Hybrid semi-blind multi-user detectors: subspace tracking methods

We consider the problem of multi-user detection for CDMA systems where the codes of some users are known while others are unknown, called semi-blind detectors. An example is at the base station of a cellular communication systems with interference from both in-cell users, with known codes, and out-of-cell users, with unknown codes. In this paper we develop a hybrid semi-blind detector, which is partly decorrelating, partly MMSE. Subspace tracking methods are developed for on-line implementation of the detector. The performance of the detectors is compared to that of the purely blind MMSE detector and the non-blind MMSE detector, and the semi-blind detector is seen to have a considerable better performance.