Abstract
In this paper, a non-binary low-density parity-check (NB-LDPC) coded high-order continuous phase modulation (CPM) system is designed and optimized to improve power and iterative efficiencies. Firstly, the minimum squared normalized Euclidean distance and the 99% double-sided power bandwidth are introduced to design a competitive CPM, improving its power efficiency under a given code rate and spectral efficiency. Secondly, a three-step method based on extrinsic information transfer (EXIT) and entropy theory is used to design NB-LDPC codes, which reduces the convergence threshold approximately 0.42 and 0.58 dB compared with the candidate schemes. Thirdly, an extrinsic information operation is proposed to address the positive feedback issue in iterative detection and decoding and the value of bit error rate (BER) can approximately be reduced by 5×10−3. Finally, iteration optimization employing the EXIT chart and mutual information between demodulation and decoding is performed to achieve a suitable tradeoff for the communication reliability and iterative decoding delay. Simulation results show that the resulting scheme provides an approximately 3.95 dB coding gain compared to the uncoded CPM and achieves approximately 0.5 and 0.7 dB advantages compared with the candidate schemes. The resulting NB-LDPC-coded high-order CPM for a given code rate and spectral efficiency converges earlier into a turbo cliff region compared with other competitors and significantly improves power and iterative efficiencies.
Highlights
Continuous phase modulation (CPM) has the advantages of a continuous phase, constant envelope, high spectrum utilization, and excellent bandwidth efficiencies [1,2]
The design of the continuous phase modulation (CPM) parameter, decoding delay, and the positive feedback problem in iterative decoding are the main factors that limit the development of the coded CPM system
A novel design method based on the minimum squared normalized Euclidean distance (MSNED) and B99% was introduced to explore a competitive CPM scheme using particular η and R under the constraint of implementation complexity
Summary
Continuous phase modulation (CPM) has the advantages of a continuous phase, constant envelope, high spectrum utilization, and excellent bandwidth efficiencies [1,2]. These characteristics are more notable for satellite systems with less power and fewer bandwidth resources, such as satellite navigation [3,4,5], satellite mesh networks [6,7], and satellite communication [8,9]. As the serially concatenated CPM schemes in terms of convergence threshold are difficult to approach the Shannon limit, the non-binary (NB)-LDPC [21] code is considered the outer code, which has been the subject of numerous studies due to its excellent error correction capability. Unlike the traditional bit-interleaved coded modulation (BICM) systems, the interleaver of a high-order CPM works at the symbol level, which always yields a lower convergence threshold than the bit level [22]
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