Adaptive blind equalization of time-varying channels

In mobile communications, often time-varying multipath is too rapid for a conventional adaptive algorithm to track. This motivates expansion of the time varying channel impulse response over a basis. Rather than estimating the time-invariant coefficients of this basis expansion, it is possible to equalize the channel output directly even when the input is not known. This requires multichannel data as well as a minimal persistence of the excitation condition on the input and a coprimeness condition on the multiple channels obtained via fractional sampling and/or multiple antennas. Since the coefficients of the basis expansion will not be constant due to noise and unmodelled dynamics, the equalizer coefficients may also change slowly with time. Adaptive algorithms to track this change are proposed and basis mismatch problems are also investigated.