Performance Of Q-ary Low-Density Parity-Check Coded Continuous Phase Modulations

Low-density parity-check (LDPC) codes are a class of capacity-approaching error-correcting codes, which come to be one of the best coding technologies because of their low-complexity iterative decoding algorithms and good performance. Existing works have already showed that nonbinary LDPC codes have better performance than binary LDPC codes. A Fast Fourier Transform based q-ary SPA for decoding q-ary LDPC codes, called FFT-QSPA, is more effective than the q-ary SPA. The nonbinary LDPC codes are constructed using algebraic methods based on finite fields GF(q) (q>2), which have quasi-cyclic structure with low error-floors and their coding-gain exceeds that of Reed-Solomon (RS) codes with the same code length and rate. Continuous phase modulation (CPM) is a kind of constant-envelope digital modulation schemes with continuous phase which provides good spectral- and power-efficiency. The decomposition model shows that a CPM system can be decomposed into a continuous-phase encoder (CPE) and a memoryless modulator (MM), thus it can be used as an inner code combined with other codes in the serially concatenated coded-modulation system with interleaving and iterative decoding. To achieve high bandwidth- and power-efficiency, we proposed a serially concatenated coded-modulation system consisting of a nonbinary LDPC code followed by a CPM.In this thesis, the algebraic construction methods of nonbianry LDPC codes based on finite fields GF(q) (q>2) decoded using FFT-QSPA which have quasi-cyclic structure are described in detail. Using the decomposition model of a CPM system, the soft-input-soft-output detectors for MSK, M-ary CPM are investigated systematically. Based on these, we introduce a q-ary LDPC coded CPM system in which the decoder operates on the symbol likelihoods. Thus, the performance loss incurred in bit-interleaved coded-modulation (BICM) schemes by the conversion between symbol and bit likelihoods is avoided. Simulation results show that the coded modulation system based on q-ary LDPC codes, including LDPC-coded 16-QAM and M-ary CPM, can achieve better performance than binary LDPC coded systems with the same spectral efficiency. The proposed system is bandwidth- and power-efficient, and moreover it is able to against burst errors effectively.