LIMITER-DISCRIMINATOR DETECTION OF CONTINUOUS-PHASE MODULATION (CPM) TOMLINSON FILTERING

Limiter-discriminator detection of Continuous Phase Modulation (CPM) p artial response signals is of special importance in systems in which p hase coherence is very difficult to establish and/or maintain (eg., mo bile communications systems). We propose a Tomlinson-based approach wh ich copes with the intersymbol interference (ISI) introduced by the ba seband partial response frequency modulating pulses of the CPM schemes , (e.g., GTFM, GMSK, Raised Cosine (RC)). In this approach, the ISI eq ualization is divided between the transmitter and the receiver. We inv estigate, through simulation, the detectability performance and spectr al properties of a number of CPM signals and receiver structures with special emphasis on the Tomlinson approach. It is shown that this nove l application of the Tomlinson configuration allows the use of relativ ely simple receivers which exhibit almost the same performance as more complex Viterbi structured receivers. It is shown that a bandwidth-ef ficient narrow-band quaternary CPM-2RC modulation with either a Viterb i, a DFE or a Tomlinson receiver structure outperforms classical binar y FSK (discriminator -Integrate and Dump detection) by approximately o ne db. It is pointed out in the paper that in general it is also possi ble to achieve detectability results similar to that of classical disc riminator (Integrate and Dump) detection of binary CPFSK, for a number of bandwidth-efficient binary CPM schemes (e.g., GMSK) using the afor ementioned receiver structures.