Detection of CPFSK signals using per survivor processing

The use of per survivor processing (PSP) is considered in the detection of a continuous phase frequency shift keying (CPFSK) signal. It is shown that PSP can enable the use of a trellis structure for the demodulation that is different from the trellis structure used to generate the CPFSK signal. This allows one to select a receive trellis structure with fewer phases, resulting in a reduced state sequence estimation algorithm. Results are presented using a receive trellis of 3 states to receive binary CPFSK signals with a modulation index, h, of 7/10. The complexity of the receiver is reduced by a factor of 3.3 with minimal performance degradation. An application of this PSP technique is also discussed which enables one to perform maximum likelihood sequence estimation (MLSE) of a digital FM signal, where the modulation index is only approximately known. Results presented for the binary case show this technique to provide a significant detection efficiency advantage over conventional techniques such as limiter-discriminator detection or non-coherent detection.