Abstract
High-order modulations are necessary to improve the bandwidth efficiency of the satellite communication system. However, the non-linear characteristic of satellite channels limits the application of high-order modulations. In this paper, we propose a new 7-point constellation which is expected to be effectively applied to the satellite communication system, and combine it with non-binary low-density parity-check (NB-LDPC) codes over Galois field GF(7) to guarantee the reliability of the data transmission. The exact expression for the average symbol error probability (SEP) of 7-order quadrature amplitude modulation (7-QAM) over the Additive White Gaussian Noise (AWGN) channel is derived, and the non-linear distortion over satellite channels is also analyzed. Simulation results reveal that, compared with the traditional 8-order phase-shift keying (8-PSK), the 7-QAM method can achieve about 3 dB gain over the AWGN channel without channel coding at symbol error rate (SER) of 10 - 6 . Moreover, the proposed combined coded modulation scheme also has better SER performance than the NB-LDPC coded 8-PSK modulation scheme over the non-linear satellite channel.
Highlights
High-order modulations are important to improve the data rate and spectral efficiency of satellite communication systems [1]
The two non-binary low-density parity-check (NB-low-density parity-check (LDPC)) codes used to combine with the 7-order quadrature amplitude modulation (7-QAM) and the 8-order phase-shift keying (8-PSK) in the simulation are with the code rate of 1/2, the code length of 2304 symbols over GF(7) or GF(8), the row weight dc of 4, and the column weight dv of 2
The symbol error rate (SER) of 8-PSK, 8-QAM and 7-QAM are simulated over the Additive White Gaussian Noise (AWGN) channel without channel coding
Summary
High-order modulations are important to improve the data rate and spectral efficiency of satellite communication systems [1]. The NB-LDPC codes, often with better error correction performance than binary LDPC codes [21], could be better adapted to high-order modulations without considering the inter-conversion between bit probability and symbol probability These advantages of the 7-QAM constellation are verified through the calculating of PAPR, the derivation of an exact intuitive geometric infinite double series for its symbol error probability (SEP) over the Additive White Gaussian Noise (AWGN) channel using the similar derivation in [22,23,24,25,26,27,28,29,30] and the analysis of its sensitivity to the nonlinearity of HPAs. the demodulation threshold of 7-QAM and the symbol error rate (SER) performance of the proposed coded modulation scheme are simulated.
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