Blind joint equalization of multiple synchronous mobile users using oversampling and/or multiple antennas

We consider multiple (p) users that operate on the same carrier frequency and use the same linear digital modulation format. We consider m>p antennas receiving mixtures of these signals through multipath propagation (equivalently, oversampling of the received signals of a smaller number of antenna signals could be used). We consider conditions on the matrix channel response for the existence of a zero-forcing equalizer (ZFE) (which cancels intersymbol and inter-user interference). In the noise free case, we show how a ZFE can be obtained from linear prediction and the channel matrix itself can also be determined as a byproduct. The problem is one of signal and noise subspaces and we show a convenient way of solving the deterministic maximum likelihood problem using a minimal linear parameterization of the noise subspace. This parameterization is found as a byproduct in the linear prediction problem