Research On Underwater Wireless Optical Communication System Based On Polar Codes

Underwater Wireless Optical Communication(UWOC)systems are quite flexible,as well as confidential and interference-resistant.Therefore,they have received extensive attention in underwater communication.To solve the problem of huge attenuation,channel coding technology can improve communication performance.As an emerging coding scheme,polar codes have become popular because of their superior performance and channel adaptivity.However,there are few applied studies in practical scenarios.In this thesis,polar codes are applied to the turbulent channel and the UWOC system based on Monte Carlo(MC)simulation.In this way,the performance advantages of polar codes in different environments are verified.To further improve the transmission performance of the UWOC and satisfy the requirements of low latency,this thesis proposes an improved decoding algorithm.The specific work of this thesis is as follows:1.The causes and characteristics of underwater turbulence are analyzed,and several common turbulence models are introduced.Then two typical turbulence models,lognormal distribution for medium-weak turbulence and gamma-gamma distribution for strong turbulence,are simulated.Combining the pulse phase modulation to derive expressions for the bit error rate(BER)and transfer probability.Polar codes are constructed by the Monte Carlo construction method.The simulation results show that polar codes can achieve the advantage of 0.3d B～0.35 d B compared with the low-density parity-check(LDPC).Moreover,polar codes do not have the error floor under medium turbulence.The progressive performance advantage in underwater turbulent channels is verified.2.This thesis verifies the application limitations of the turbulence model based on the MC simulation algorithm.Subsequently,the channel impulse response under three typical water types was obtained.Combining with the advantages of orthogonal frequency division multiplexing(OFDM)to design the OFDM-UWOC system model,and the polar codes are constructed by the Monte Carlo construction method.It is demonstrated that polar codes can obtain the advantage of 0.15 d B ～0.55 d B compared with the LDPC.The effect of different parameters on the performance of the UWOC is also verified.The simulation results under three turbulence models and three typical water types can effectively illustrate that polar codes have competitiveness and development in UWOC.3.To further improve the communication performance of the UWOC and the reliability of data transmission,this thesis proposes the segmented WSCA-SCLF decoder based on the weighted sum code-assisted SCL decoder.The hardware implementation is simple,where each clock unit can process multiple bits.In addition,compared with the original decoder,the communication performance can be improved,and the decoding complexity can be reduced.The proposed decoder can improve the performance of the UWOC,and can effectively reduce the latency.