A CPM receiver based on the Walsh signal space

The optimum demodulator for CPM requires in general many matched filters, making it almost impractical. A sub-optimum coherent MLSE receiver for the AWGN channel is described. It needs only two projection filters each followed by sub-interval samplers. The receiver projects the received signal onto a receiver signal space specially chosen to make the projection operation easy to implement while keeping the error performance degradation small. Both the minimum projection distance in the receiver signal space and/or the loss compared with the corresponding free distance in the transmitter space are presented in the paper for some selected examples. For binary CPM schemes with modulation index h less than one, two samples per baud give a near-optimum error performance, while quaternary CPM with h less than 0.6 requires three or four samples