Design and Optimize FQPSK Modulation Concatenated with LDPC Code for Space Information Network

Abstract

Because of the limited power and long propagation distance between spacecraft and Earth station, the high power efficiency is more important for space information system than others terrestrial communication system. Motivated by the potentially large gain achievable with iterative decoding, one novel coded modulation scheme based on LDPC code and FQPSK (Feher's QPSK) is designed and optimized in this paper, which can alleviate the challenge of signal power huge loss of communications path in space information system. The novel scheme improves power efficiency utilizing the property that LDPC code enables communication at very low signal noise rate and constant envelope property of FQPSK enables high power amplifier work at saturation states without nonlinear impact. At receiver, using iterative receive algorithm, large gain can be attained. The paper proposes concatenation scheme and optimizes it by computer assisted simulation. At last, the bit error rate performance of optimal scheme is confirmed.