Proposal of spread spectrum MSK for BDS RDSS signal modulation

BPSK is the basis of current GNSS (Global Navigation Satellite System) signals. BDS (Beidou navigation satellite system) RDSS (Radio Determination Satellite Service) system also adopts BPSK to realize communication and ranging simultaneously. To realize higher system capacity, RDSS signals overlap in time and frequency domain. The signal performance is heavily determined by the MAI (Multiple Access Interference) between overlapping signals. In this paper, SSMSK (spread spectrum MSK) is proposed. The signal performance is investigated under four conditions considering the main lobe bandwidth and the receiver bandwidth. The maximum number of overlapping signals for SSMSK is 11.7% higher than BPSK when the receiver bandwidth is for the side subcarrier. And the value is 10.6% when the receiver bandwidth is. SSMSK can be received utilizing BPSK local signal. When the receiving bandwidth is 2 R c , the correlation peak of SSMSK_BPSK is identical to BPSK. The tracking accuracy of SSMSK is higher than BPSK when the correlation interval is between 0.2-1 chips. The accuracy of SSMSK_BPSK is higher than BPSK when the correlation interval is 0.5 chips. The disadvantage of SSMSK is larger quantization word length. SSMSK is a better modulation for RDSS based on the comprehensive performance.