Serially Concatenated Continuous Phase Modulation System Based On LDPC Codes

Continuous phase modulation (CPM) is a kind of constant-envelope digitalmodulation schemes which provides good spectral utilization. It is shown that anycontinuous phase modulation (CPM) system can be decomposed into acontinuous-phaseencoder(CPE)andamemorylessmodulator(MM),theformerisalinear time-invariant sequential circuit and the latter is also time invariant. The CPE isequivalent to a convolutional encoder; therefore, there is no need of inner code inserially concatenated system based on continuous phase modulation (SCCPM).Compared with the memoryless modulation schemes, the power-efficient of seriallyconcatenated system based on CPM is outstanding, and the complexity is alsoachievable.LDPC codes combining CPM is a new research topic that might achieve highbandwidth transmission capacity. It is possible to satisfy us with both high spectralefficient and low decoding complexity when a new reduced-complexity decodingalgorithm of Q-ary LDPC codes is used. In addition, because the parity-check matricesarerandomlyconstructedinLDPCcodes,theinterleaverisnotnecessaryfortheseriallyconcatenated system with Q-ary LDPC codes if the parity-check matrices are designedreasonable.To exploit the advantages of both CPM and LDPC codes, we propose ContinuousPhaseModulationSystembasedonLDPCschemes.Alltheworkcanbesummarizedasfollows:1. The principle of the iterative decoding for the LDPC codes are described based onthediscussionofthesum-productdecodingalgorithmsonTannerbipartitegraphs.2. Based on the principle of the CPM singles, a decomposition approach to CPM isdeveloped. A posteriori probabilities (APP) algorithm applied to the demodulationofCPMsinglesisintroduced.3. Aserial concatenation of the binary LDPC codes combining minimum shift keying(MSK) is investigated. In terms of the analysis of the error correlation, we show agreatimpactontheperformanceoftheiterativesystem.4. Anew reduced-complexity decoding algorithm of Q-ary LDPC codes is developed.Thenthesimulationresult ofQ-aryLDPC codes withQPSKsystem is given.Basedon the system model of a serially concatenated of Q-ary LDPC codes with CPM,simulationresultsandanalysisaregivenunderdifferentmodulationindexes.