Performance Analysis of LDPC Codes on Different Channels

This paper analyzes and simulates the performance of irregular Low Density Parity Check (LDPC) Codes on different channels. LDP Coding is a technique used in communication system for error correction of the information signal. This technology is also being used in telephone channel identification, modem echo cancellation and many other communication applications. LDPC codes reduce the noise closest to Shannon limit. This scheme has simpler decoding algorithm as compared to turbo codes. LDPC adds redundancy to the un-coded input signal to make it more immune to the channel impairments such as noise and fading. The impact of LDPC, (under BPSK, QPSK and QAM modulation schemes) over AWGN, Raleigh faded and Rician faded channels has been investigated and performed several computer based experiments. The procedure of each experiment would be divided into three phases. In the first phase LDPC encoder formed that includes the construction of parity check matrix and selection of modulation scheme for transmission. In the second phase, LDPC codes transmitted over channels, characterized with Additive White Gaussian Noise, Rayleigh and Rician Fading for checking the performance. In the third phase, modulated signal has been demodulated and decoded by using different decoding schemes. The results are reported using bit error rate (BER) versus ratio of bit energy to noise power spectral density (E_b/N_o) as a performance measure. The simulation models adopted in this research indicate that LDPC performs best on AWGN channel among the three models used. For Rayleigh, it shows worst results, requiring larger SNR values for decline of BER and for Rician research indicates intermediate results between AWGN and Rayleigh channels under different values of K parameter.