Adaptive Coded Modulation Based on Continuous Phase Modulation for Inter-Satellite Links of Global Navigation Satellite Systems

The inter-satellite links (ISLs) will play an increasingly important role in improving the service performance and enhancing the survivability of global navigation satellite systems. The current signal transmission schemes in ISLs primarily employ constant coded modulation to guarantee a high reliable communication even for the worst channel status, and the adaptive coded modulation (ACM) schemes, such as binary low-density parity-check (LDPC) coded quadrature phase shift keying or M-ary quadrature amplitude modulation (MQAM) have been introduced to improve spectral efficiency over inter-satellite channels recently. However, the phase discontinuity of the above modulations will widen frequency spectrum and cause the high-voltage transient of transmitter, and the MQAM signal through high power amplifier onboard will result in non-linear distortion because of non-constant envelope. In this paper, the association between non-binary LDPC codes and high-order partial response continuous phase modulation with iterative detection is presented as the source of ACM schemes, which effectively inhibits information loss in the process of conversion between bit and symbol probabilities. According to the constellation of BeiDou navigation satellite system in 2020, an open loop ACM control mechanism based on inter-satellite distance is introduced, and implemented by the target bit error rate (BER) and the maximum ratio between the throughput and bandwidth algorithms. Simulation results show that the proposed ACM scheme can reduce the BER and improve the power efficiency in the requirement of target BER limit, and provide a higher spectral efficiency under the same transmitting power compared with the existing ACM scheme.