Differential minimum mean squared error communication signal compensation method

This invention reformulates the MMSE criterion to apply to systems in which the desired data to be tracked is the ratio of the data appearing in successive observation intervals. The resulting differential MMSE criterion leads to a number of novel algorithms for adaptive implementation of the MMSE receiver. Applications include equalization for single user systems, and multiuser detection, or interference suppression, for direct sequence CDMA with short spreading sequences (i.e., the period of the spreading sequence equals the symbol interval). The invention also provides blind (i.e., without the requirement of a training symbol sequence for the user of interest) equalization and beamforming (using a receive antenna array) for direct sequence CDMA systems with long spreading sequences (i.e., systems in which the spreading sequences are aperiodic, or have period much larger than the symbol interval). The invention enables recovery of the desired symbol sequence up to an unknown phase. The invention is therefore well suited to the demodulation of differentially modulated data, in which information is encoded in the phase differences of successive transmitted symbols. Assuming that the channel amplitude and phase is approximately constant over two successive symbol intervals, the demodulator can use the differences in phases of two successive received symbols to recover differentially encoded data. The invention may also be used in conjunction with a separate phase recovery method to demodulate data without differential modulation.