Blind receivers for nonlinearly modulated signals in multipath

Classical blind channel equalization methods may not be suitable for systems with nonlinear modulation (e.g., continuous phase-modulated signals) because the input to the channel may not be i.i.d. due to the modulator´s memory. Moreover, the nonlinear characteristics of the modulator further complicate the channel estimation task. In this correspondence, we derive blind maximum likelihood channel estimation algorithms for nonlinearly modulated signals using a hidden Markov model (HMM) formulation. The proposed method implements a stochastic maximum likelihood approach and is well suited for short data records appearing in TDMA systems. Cramer-Rao bounds are derived, and some illustrative simulations are presented