Blind identification with periodic modulation: a time-domain approach

We propose a method for blind identification of finite impulse response (FIR) channels with periodic modulation. The time-domain formulation in terms of block signals is simple compared with existing frequency-domain formulations. It is shown that the linear equations relating the products of channel coefficients and the autocorrelation matrix of the received signal can be further arranged into decoupled groups. The arrangement reduces computations and improves accuracy of the solution; it also leads to very simple identifiability conditions and a very natural formulation of the optimal modulating sequence selection problem. The proposed optimal selection minimizes the effects of channel noise and error in autocorrelation matrix estimation; it results in a consistent channel estimate when the channel noise is white. Simulation results show that the method yields good performance. It compares favorably with an existing subspace modulation-induced-cyclostationarity method, and it is robust with respect to channel order overestimation. The effect of modulation period and threshold of the modulating sequence are also discussed.