Performance Analysis Of LDPC Codes Over Fading Channels

Multiple-input multiple-output (MIMO) antenna diversity techniques can be used to combat the adverse impact of the multipath fading. There are many kinds of implementation, such as transmit antenna selection/receive antenna selection (TAS/RAS), TAS/receive Maximal-ratio combining (TAS/MRC), MIMO MRC, and TAS/space time block codes(TAS/STBC), etc. Low-density parity-check (LDPC) code is an error control coding which can achieve good performance close to the Shannon limit. The randomness and sparseness of the parity check matrix suggest that LDPC codes have a built-in "interleaver", so LDPC codes have good performance in fading channels even if it doesn’t combined with interleaver. The MIMO spatial diversity techniques combined with LDPC codes can fully make use of the advantage of them and further improve the reliability of MIMO wireless communication systems. Therefore, this thesis investigates the performance of LDPC codes with MIMO antenna diversity techniques.Chapter1presents a brief review of MIMO antenna diversity techniques, LDPC codes and the state-of-art of LDPC codes in fading channels.Chapter2investigates the average bit-error rate (BER) performance of LDPC codes with MIMO MRC over Rayleigh fading channels, Maximal-ratio combining cascaded with selection combining (MRCS), TAS/RAS, and TAS/MRC over Nakagami-m fading channels, respectively. This thesis derives the closed form expression of the probability density function (PDF) of initial log-likelihood ratio (LLR) for LDPC decoding, stability conditions for density evolution (DE) and Gaussian approximation (GA), and the closed form expressions of average BER for LDPC codes based on GA approach. Numerical and simulation results show that the derived BER expressions can provide a good estimate for the performance of MIMO diversity systems with LDPC codes, thereby avoiding time-consuming DE analysis and computer simulation.Chapter3investigates the average BER performance of LDPC codes concatenated STBC/RAS or TAS/STBC over Nakagami-m fading channels, respectively. This thesis derives the closed form expression of the PDF of initial LLR for LDPC decode, stability conditions for DE and GA, and the closed form expression of average BER for LDPC codes based on GA approach. Numerical and simulation results show that the derived BER expressions can provide a good estimate for the performance of LDPC codes concatenated STBC/RAS or TAS/STBC, thereby avoiding time-consuming DE analysis and computer simulation.Chapter4finishes the thesis with concluding remarks.