Study And Implementation On Error Correction Based On LDPC Codes In Wireless Optical Communication

Wireless optical communication (WOC) is a kind of communication carried by laser as an information carrier, transmitting in free-space, which have the advantage of wide bandwidth, anti-jamming, safety, low implementation cost, transparent protocol, etc. However, complex atmospheric environment seriously affect the quality of wireless of information transmission. In order to improve the wireless optical communication quality, and reduce the influence of attenuation, flicker, angle misalignment caused by atmospheric scattering, absorption, turbulence, beam expander, mismatch, we explored the feasibility of improving quality of atmospheric optical communication by error correction coding in modern communication theory and error correction coding techniques. Coding techniques for error control in wireless optical communication was researched into, and the improvement result of error rate by error correction coding in different SNR situations was obtained. Based on coding theory and simulation results, a hardware implementation was further proposed, and a high-performance encoder and a decoder hardware were implemented.Modeling and simulation are commonly used in communication research. In this paper, account for the atmospheric optical wireless communication channel, with the scattering, absorption, turbulence, the beam expander, mismatch loss, dark current thermal noise and many other factors, we build a channel model obeying the laws of distribution. We used low density parity check codes (LDPC, low density parity check codes) for error control which has a lower code complexity and a better error control performance. In hardware implementation, FPGA was used for encoder hardware implementation which has parallelly processing ability; DSP contains the hardware multiplier in the structure, for floating-point operations, it is more convenient. For that reason, it could be used in the decoding work.This paper focused on optical wireless communication coding error control method, and obtained corresponding result, the work mainly about: (1) Studying the channel optical wireless communication considering the weak turbulence of the atmosphere, combined with the mathematical and statistical properties of the impact of various factors, establishing a more comprehensive atmospheric channel model, and the module was verified through the system, in line with the laws of statistics;(2) Built a wireless optical communication transmission system, studied control performance of the LDPC error control and compared that in Gaussian channel. The results showed that the LDPC coding can significantly reduce the BER. For Gaussian channel, SNR can be reduced8dB when BER is10"6; For wireless optical communication, LDPC codes can make the error rate reduced by4-5orders of magnitude.(3)Building the H matrix based on the algebraic structure of the complete residue system. Using the linear complexity of approximate lower triangular coding method, and parallel processing ability of FPGA, using Altera’s EP304F484C6N to complete the implementation of the encoder. The single frame throughput was up to25Mb/s while resource is less than5%;(4)Adopting the belief propagation decoding algorithm, and using TMS320C6713DSP achieve the hardware implemention. The decoding results were consistent with the theoretical.