Limiter-Discriminator Detection of Continuous Phase Modulation (CPM) Tomlinson Filtering

Limiter-discriminator detection of Continuous Phase Modulation (CPM) partial response signals is of special importance in systems in which phase coherence is very difficult to establish and/or maintain (e.g., mobile communications systems). We propose a Tomlinson-based approach which copes with the intersymbol interference (ISI) Introduced by the baseband partial response frequency modulating pulses of the CPM schemes, (e.g., GTFM, GMSK, Raised Cosine (RC)). In this approach, the ISI equalization is divided between the transmitter and the receiver. We investigate, through simulation, the detectability performance and spectral properties of a number of CPM signals and receiver structures with special emphasis on the Tomlinson approach. It is shown that this novel application of the Tomlinson configuration allows the use of relatively simple receivers which exhibit almost the same performance as more complex Vlterbi structured receivers. It is shown that a bandwidth-efficient narrow-band quaternary CPM-2RC modulation with either a Viterbi, a DFE or a Tomlinson receiver structure outperforms classical binary FSK (discriminator - Integrate and Dump detection) by approximately one db. It is pointed out in the paper that in general it is also possible to achieve detectability results similar to that of classical discriminator (Integrate and Dump) detection of binary CPFSK, for a number of bandwidth-efficient binary CPM schemes (e.g., GMSK) using the aforementioned receiver structures.