Comparison of noncoherent detectors for SOQPSK and GMSK in phase noise channels

Abstract

Shaped offset quadrature phase-shift keying (SOQPSK) and Gaussian minimum shift-keying (GMSK) are highly bandwidth efficient continuous phase modulation (CPM) schemes that are closely related when viewed as OQPSK-type modulations at the receiver. For both of these modulation schemes, coherent detectors are available with good performance in additive white Gaussian noise (AWGN). However in many applications noncoherent receivers are preferred as they are more robust, easy to synchronize and can recover input bits in the presence of phase noise. In this work we provide a comprehensive set of numerical performance results for SOQPSK and GMSK noncoherent detectors in phase noise channels. Since highly bandwidth efficient CPMs such as SOQPSK and GMSK require extremely complex receivers, we also address this problem with several complexity reduction procedures that have been proposed in literature. In particular, these are done for noncoherent detection of GMSK for the first time. We also provide results for serially concatenated (SC)-SOQPSK and SC-GMSK as SC systems with CPM as recursive inner codes have high coding gains at low power and are widely used.