Turbo Equalization of Binary Continuous Phase Modulation: Convergence Analysis

In this paper, the convergence behavior of a doubly-iterative receiver, proposed for joint turbo equalization, modulation and decoding of coded binary continuous-phase modulation (CPM), is analyzed by using extrinsic information transfer (EXIT) charts. The doubly-iterative receiver consists of a central soft-input soft-output (SISO) CPM demodulator coupled with a front-end soft information aided minimum mean square error (MMSE) equalizer and a back-end SISO channel decoder. The EXIT chart analysis shows that performing a few back-end demodulation/decoding iterations per each equalization iteration improves the a priori information for the front-end equalizer, and provides faster convergence to low bit-error rates (BERs) with less computational complexity, as also illustrated in the BER simulations.