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针对大气湍流引起的系统频带利用率下降的问题,研究了一种离散速率条件下的大气激光通信自适应调制编码系统。从信号层角度建立了湍流信道模型,给出了湍流信道下的瞬时信噪比概率密度函数,并采用外场实验验证了该信道模型。理论推导了系统频带利用率和误码率表达式,仿真结果表明大气激光通信自适应调制编码系统较传统单一传输模式系统具有优越性。研究了其频带利用率和误码率曲线特性,分析了误码率要求和湍流强度对系统性能的影响。结果表明降低误码率要求可大幅提高系统的频带利用率,且误码率要求越低,湍流强度越弱,频带利用率越高。
Aiming at the problem of decreasing the utilization of system frequency band caused by atmospheric turbulence, an adaptive modulation and coding system for atmospheric laser communication at discrete velocity is studied. The model of turbulence channel was established from the perspective of signal layer, and the probability density function of instantaneous signal to noise ratio under turbulent channel was given. The channel model was verified by field experiment. The theoretical derivation of the system bandwidth utilization and the error rate expression is given. The simulation results show that the atmospheric laser communication adaptive modulation and coding system is superior to the traditional single transmission mode system. The characteristics of the band and bit error rate curves are studied, and the effect of BER and turbulence intensity on the system performance is analyzed. The results show that the requirement of reducing the bit error rate can greatly improve the system bandwidth utilization, and the lower the bit error rate requirements, the weaker the turbulence intensity, the higher the band utilization.