Application and analysis of reduced state techniques on hybrid CPM demodulation
James A. Norris · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2008
Hybrid Continuous Phase Modulation (HCPM) is a variant of Continuous Phase Modulation that is optimized for low-power, wireless communications applications. Hybrid CPM uses either additional Amplitude or Phase pulses to create a higher order modulation without the increase in trellis complexity that normally accompanies higher order CPM modulation schemes. For standard CPM, an increase in the modulation order results in the increase of the symbol alphabet and a corresponding increase in the transmit bandwidth and exponential increase in the complexity of the decoder trellis structure. Hybrid CPM however achieves higher order modulation by adding parallel branches to the base CPM trellis structure thus reducing the receiver complexity. The novelty of this paper is the application of the techniques devised to reduce the demodulator complexity of standard modulation types like PSK and CPM and apply them to Hybrid CPM using a method that would not result in the loss of performance or require any sort of compromise. As an example, this paper provides an analysis of the power and spectral efficiency of the two hybrid CPM waveforms and gives specific examples of the application of reduced state techniques. Both set-partitioning and reduced-state sequence estimation with decision feedback techniques are analyzed and compared. The results will demonstrate that reduced-state sequence estimation can be coupled with Hybrid CPM demodulation without any loss in bit error rate performance.