Optimal Parameter Design of Continuous Phase Modulation for Future GNSS Signals

Continuous phase modulation (CPM) is a power and spectrum efficient modulation that intrinsically possesses constant envelope, phase continuity as well as less out of band (OOB) radiation, especially appropriate for stringently bandwidth-constrained systems employing non-linear power amplifiers. Such advantages render CPM as a promising modulation candidate with application to satellite navigation. CPM comprising of a few parameters has large amounts of modulation subclasses. This paper is devoted to optimal parameter design of CPM for future GNSS signals. Parameter design approaches endowing CPM with similar spectrum profiles as legacy binary offset carrier (BOC) and binary phase shift keying (BPSK) modulations are also proposed. Several optimal subclasses of CPM family are suggested as unimodal or bimodal GNSS signal solutions. The simulation results indicate that the designed CPM signals behave same or similar main lobes with BPSK and BOC signals, and proposed optimal subclasses of CPM family with high spectral efficiency are comparable or superior than legacy modulations, typical GMSK, and filtered multitone (FMT) signal using the squared root raised-cosine (SRRC) basic pulse in terms of tracking accuracy, multipath mitigation and compatibility. In addition, some constructive comments on CPM design are presented, which provides a reference for CPM applications in GNSS.