Study On Some Key Techniques For Serially Concatenated Continuous Phase Modulation Systems

Continuous phase modulation(CPM)is a class of constant envelope modulation technique with high spectral efficiency and power utilization,whose constant envelope characteristic can solve the problem that some modulation schemes like amplitude shift keying(ASK)and quadrature amplitude modulation(QAM)are not adaptive to the nonlinear amplifiers.Thus,the CPM is a good choice for some communications such as satellite communications,deep space communications and unmanned aerial vehicle(UAV)communications.In order to improve transmission reliability and achieve high spectral efficiency and power utilization,a serially concatenated CPM(SCCPM)scheme has become a popular research direction.This thesis mainly considers how to deal with large Doppler shifts and low signal-to-noise ratios(SNRs)environment with limited power and spectrum resources in wireless communications such as satellite communications and UAV communications.Although the SCCPM scheme can to some extent alleviate the mentioned problems,some key problems such as the design of low-complexity demodulation algorithms,the selection of outer codes,the construction of system models and the ability of anti-burst errors and anti-Doppler shifts are still worth deep study.In response to the above problems,three main contributions of this thesis are as follows.1.Based on a given SCCPM system model,basic principles of error correction codes as outer codes and CPMs as inner codes are illustrated,respectively.For error correction codes,the encoding and decoding principles of low-density parity-check(LDPC)code and polar code are introduced in detail.For CPMs,both expressions of the single-h and multi-h CPM signals,the Rimoldi's and PAM decompositions,and the coherent and non-coherent demodulation algorithms are specifically described.2.Considering a serially concatenated single-h CPM system based on the Rimoldi's decomposition,a non-recursive structure is proposed to weaken the error propagation caused by the recursive structure.Thus,the BER performance can be greatly improved and the modulation implementation can become easier.Then,with the non-coherent demodulation insensitive to channel state information and allowing imprecise synchronization,a pilot-aided quasi-coherent demodulation algorithm(PA-QCDA)is proposed.Using pilot symbols and sliding-window technique,the demodulation algorithm outperforms the non-coherent demodulation and achieves the performance similar to the coherent demodulation.Also,the proposed non-recursive structure and quasi-coherent demodulation algorithm are applied to the LDPC coded GMSK system and the polar coded MSK system.The parameters of the non-recursive GMSK signaling are optimized according to the trade-off of the power and spectral efficiency.Simulation results show that both the systems can achieve excellent performance even in the the presence of burst errors or frequency and phase offsets,which are suitable for wireless communications such as satellite communications.3.Considering a serially concatenated multi-h CPM system,taking the disadvantages of the Rimoldi's and PAM decompositions into account,a new decomposition method is designed,whose derivation process is also given.Based on the proposed decomposition method,the above PA-QCDA can be extended and applied to the demodulation of the multi-h CPM signals.From the demodulation complexity,demodulation performance and power spectrum,the multi-h CPM system and the single-h CPM system are compared.Although the non-recursive single-h CPM system has lower implementation complexity,its demodulation performance and power spectrum performance are not as good as the multi-h CPM system.Finally,simulation results show that the LDPC coded multi-h CPM system can perform well even when frequency and phase offsets happen,which makes it become a potential transmission solution in wireless communications such as satellite communications.