Binary Coded Symbol Modulations for GNSS

As next-generation signals are designed for Global Navigation Satellite Systems (GNSS), there is continuing interest in providing even higher performance while also ensuring compatibility with already-existing signals and services. A signal.s modulation is critical in establishing performance and compatibility. First-generation modulations for GPS used binary phase-shift keying with rectangular symbols (BPSK-R), while binary offset carrier (BOC) modulations were subsequently introduced as alternative binary phase-shift keyed (BPSK) modulations for GPS and Galileo, offering additional degrees of freedom in achieving both performance and compatibility. This paper shows that binary-coded symbols (BCS) generalize BPSK-R and BOC modulations, retaining BPSK and constant modulus while offering additional degrees of freedom for shaping the signal.s spectrum and thus its correlation function. Different binary coded symbols can be multiplexed in phase (using orthogonal spreading sequences) or in time, providing further opportunities for designing the modulation.s characteristics. This paper summarizes BCS modulations and their multiplexed variants, describing their properties and performance. Special emphasis is placed on BCS-based modulations that offer better performance in multipath than BPSK-R and BOC modulations having comparable spreading code rates.