A Study On The LDPC Channel Coding Technology Of Wireless Optical Communciation Systems Based On The Exponentiated Weibull Model

Wireless optical communication(WOC) is a modern technology that can realize duplex communication. It is gaining more and more attention of researchers from different countries for its high bandwidth, low cost and outstanding anti-interference ability in recent years. The atmosphere is used as the transmission medium of wireless optical communication. It is filled with a variety of substances such as gas molecules, aerosols, etc. These substances are likely to induce light absorption and scattering in the transfer process, thereby affecting the performance of communication. Researchers have proposed many techniques such as channel coding, the aperture averaging and diversity techniques to reduce the effect of atmospheric turbulence to the wireless optical communication system. And great success has been achieved. Low Density Parity Check(LDPC) coding is a typical representative of linear block code which has the error rate performance of nearing Shannon limit in the high-speed data transmission and high-capacity storage channel. LDPC coding has been listed as the main error correction code by a number of international and domestic industry technical standards. Based on the exponentiated Weibull(EW) fading channel, this work has investigated the improvement of LDPC coding for the BER performance of FSO communication system. Additionally, aperture averaging and diversity has been studied. The main work is as follows:1、LDPC coding based wireless optical communication system model using EW distribution as the PDF of received intensity has been established. The expressions of logarithmic likelihood ratio using OOK and BPSK modulation have been derived. The average BER of different turbulence strengths, aperture sizes, LDPC codeword parameters and decoding algorithm against SNR has been achieved. Studies have shown that EW model works well in different turbulence strengths. It can describe the received intensity accurately when aperture averaging takes place compared with Gamma-Gamma(GG) model. Additionally, rate of parity check matrix, the maximum number of iterations and decoding algorithm can also affect the BER performance of the system.2 、 Based on the above work, LDPC-STBC coding based wireless optical communication system has been built, demodulation algorithm of LDPC-STBC coding system has been derived using maximum likelihood acceptance criteria, and then the likelihood ratio of LDPC decoder has been achieved. The effect of LDPC-STBC coding on system error oerformance under different atmospheric turbulence conditions has been studied. Simulation results show that better coding gain can be achieved for LDPC-STBC concatenated coding as the number of sub-sets increase. The channel coding and diversity techniques can improve the system performance well.The research results of this paper provide a theoretical reference for channel coding design of wireless optical communication systems.