Semi-blind decorrelating multi-user detectors for CDMA: subspace methods

We consider the problem of multi-user detection for CDMA systems where the codes of some users are known while others are unknown, semi-blind multi-user detection. 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. We develop a number of decorrelating, semi-blind multi-user detectors, using a subspace approach. One of the detectors has a computationally efficient structure of a subspace estimation common to all known users, followed by a simple processing specific to each user. The performance of the detectors is compared to that of the purely blind decorrelating detector and the non-blind decorrelating detector, and the semi-blind detectors are seen to have the best performance.