Closed-form blind channel identification with MSK inputs

Blind equalization of non-minimum phase FIR channels requires prior identification, for stability reasons. We present a novel algorithm that is able to identify a channel in the presence of an unknown MSK modulated input (which can be viewed as an approximation of the GMSK modulation used in GSM mobile systems), by resorting only to output second order moments. Blind identification is made possible because the input is not circular. It is shown that this approach leads to a system of L quadrics in L unknowns, if L denotes the number of taps of the unknown FIR channel. This system is then solved with the help of an original algorithm based on the resultant techniques. The performances in terms of bit error rates are also reported.