Research On QC-LDPC Decoding Technology In Weak Turbulence Channel

Applying laser technology to the wireless communication field can satisfy high directionality,confidentiality and other applications.Therefore,laser wireless communication research has long-term research value and wide application prospects.The laser propagates in the atmospheric channel.Due to the disturbance of turbulence in the atmospheric channel,it will affect the intensity,phase and amplitude of the transmitted beam and reduce the stability and effectiveness of information transmission.Channel error correction coding technology can provide a certain coding gain.To some extent,a "good" code can ease or effectively eliminate the impact of the situation above.The LDPC code,which is a linear block code based on a sparse parity check matrix,has excellent performance approaching the Shannon limit and has advantages almost suitable for all channels and suitable hardware implementation,making LDPC code bring higher coding gain for wireless optical communication system.The QC-LDPC code,which is called quasi-cyclic LDPC code,is an important subclass of LDPC codes.Its sub-matrices in the check matrix is circular matrices or a zero matrices.This special structure makes the code coding and decoding relatively simple,consumes less resources,and also has excellent decoding performance.In this paper,the characteristics of near-Earth atmospheric turbulence are theoretically analyzed and studied,and the influence of near-ground weak turbulence on the light beam of wireless optical communication equipment is analyzed.In this paper,author choose IEEE802.16 e standard QC-LDPC code with length of 2304 bit and rate of 5/6 as the research foundation.This paper studied the near-surface turbulence channel,LDPC coding scheme and soft decoding scheme theoretically,and the coding and decoding applications are simulated and implemented.Specific work as follows:In this paper,the generation matrix of IEEE802.16 e is analyzed in detail and encoded by the sparsity of parity check matrix.At the same time,we use the characteristics of generator matrix to optimize the encoding process,select the Xilinx XC7 A series chips and build the hardware platform,and complete the hardware implementation of the encoder while reducing the consumption of chip resources.In this paper,LDPC code decoding algorithm is analyzed theoretically.With BP iterative algorithm as the theoretical core,the chip resource consumption,decoding performance and the difficulty of hardware implementation are integrated.As an implementation of soft decoding,an improved minimum decoding algorithm is adopted.The paper analyzes the soft decoding,verifies the correctness of the scheme,and chooses Xilinx XC7 A series chip to realize the decoder.In this thesis,the designed codec is verified by simulation;A hardware test circuit was set up to perform board-level functional verification of the decoder.The near-field long-distance test link was set up.Under the conditions of this paper,the designed LDPC decoder has reduced the bit error rate by an order of magnitude to the laser communication system under weak turbulence channel.