Maximum Likelihood Implementation of a Constant Envelope, Quaternary Continuous Phase Modem

摘要

Continuous Phase Modulation exhibits constant envelope. A Minimum Phase Shift Key (MPSK) CPM signal is identical to Offset Quadrature Phase Shift Keying with a half-cycle sinusoid shaping filter. Most receiver designs revert to an OQPSK receiver structure to perform demodulation of MPSK CPM signals. System performance is reduced when an OQPSK process is used to receive a non-uniform phase profile CPM signal. Gaussian filtered CPM, or GMSK is an example of a mismatch between a shaped CPM modulator and an OQPSK demodulator. Maximum likelihood implementation of the general CPM receiver requires individual, complex weight, matched filters for each phase profile in the CPM signal set. An OQPSK receiver requires a single quadrature matched filter. We present a ML receiver implementation of a general CPM signal.