Performance analysis of LDPC codes in the gamma-gamma channel

In order to improve the performance of wireless optical communication, the low density parity check (LDPC) code is used for the channel coding. When the channel state information is known, the performance of system LDPC+binary pulse position modulation(BPPM) and system LDPC+on-off keying(OOK) was compared respectively in additive white Gaussian noise(AWGN), weak, medium and strong turbulence channels. The result shows that the performance of LDPC+BPPM is better than that of LDPC+OOK, and with the increase of the turbulence intensity, the advantage of LDPC+BPPM becomes more apparent. The coding gain of OOK and BPPM was studied in various strength turbulence channels, both of the BPPM's and OOK's in AWGN, weak and medium turbulence channel, increase with the increase of the turbulence intensity. The difference is OOK coding gain in medium turbulence channel is bigger than that in strong turbulence, However, BPPM coding gain and OOK's are opposite. When coding, from 4PPM to 256PPM, when the number of binary is doubled, there is about 1dB loss than the original system. Therefore, system LDPC+PPM has a large coding gain in turbulence channel, and low complexity, and a certain application prospect in optical wireless communication.