New approach to fractionally spaced constant modulus blind equalization

TA new approach to fractionally spaced equalization of finite impulse response (FIR) channels is proposed based on the exact gradient expression of the square of the CM cost function. The new algorithm has a fast convergence rate in comparison with the other algorithms that use the constant modulus criterion such as fractionally spaced constant modulus algorithms FS-CMA and constant modulus equalization based on the exact gradient expression of Godard´s cost function (CME-GD). These two algorithms are used as a benchmark to test the proposed approach. Eventhough this latter uses the principle of the constant modulus criterion which penalizes the deviation of the magnitude of the received data from a desired amplitude level, it can be applied successfully to non-constant modulus sources such as M-ary quadrature amplitude modulation (M-QAM) and M-ary pulse amplitude modulation (M-PAM). These two cases are investigated.