Efficient semi-blind estimation of multipath channel parameters via a delay decoupling optimization approach

In this paper a parametric method for estimating the unknown multipath channel impulse response (CIR) in a semi-blind manner is proposed. The main trait of this method is that instead of seeking the whole CIR sequence, only the unknown time delays and attenuation factors of the physical channel multipath components are estimated. The technique is based on a suitable application of the sub-channel response matching (SRM) criterion. The resulting cost function is separable with respect to the two sets of unknown parameters, i.e., time delays and attenuation factors, and thus a two step optimization procedure can be applied. Concerning the first step, which is the most difficult one, it is proven that the resulting non-linear cost function can be decoupled in terms of the respective time delay parameters. Thus, only a small number of simple linear searches needs to be executed in order to estimate the time delays of the multipath channel. The new method offers significant computational savings and a lower mean square estimation error as compared to existing semi-blind channel estimation methods. It performs well even for closely-spaced delays and is quite robust to channel overmodeling.