Communications through time-varying subspace channels

We consider the problem of communicating through a time-varying channel whose parameters (gains, impulse response coefficients) are unknown, but have known statistics. Several detection schemes are developed for the signals received at the channel output. The performance of these detectors is evaluated as a function of the rank of the channel covariance matrix. It is demonstrated that effective communication can be achieved provided that the channel covariance matrix has a low rank.