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多脉冲位置调制(MPPM)是基于脉冲位置调制(PPM)的改进形式,已成为卫星光通信中高效调制方式。针对存在背景辐射、大气湍流、热噪声的卫星光通信信道,研究了远场激光脉冲展宽机理和时钟抖动对系统的影响。提出基于格雷码的MPPM联合编码调制方式减小时钟抖动和码间干扰影响,应用星座图设计了基于格雷码(7,2)MPPM映射方法,在相同传输带宽下(7,2)MPPM的传输效率超过16PPM的2倍。分析泊松信道下基于格雷编码的(7,2)MPPM字符错误概率和比特错误概率(BEP)。结果表明,采用格雷编码MPPM可以有效抵御定时误差并降低系统比特错误概率。
Multi-pulse position modulation (MPPM) is an improved form based on pulse position modulation (PPM) and has become an efficient modulation method in satellite optical communications. Aiming at satellite optical communication channel with background radiation, atmospheric turbulence and thermal noise, the influence of far-field laser pulse broadening mechanism and clock jitter on the system is studied. The MPPM joint coding modulation scheme based on Gray code is proposed to reduce the effects of clock jitter and intersymbol interference. The MPPM mapping scheme based on Gray code (7,2) is designed by using constellation. The MPPM transmission under the same transmission bandwidth (7,2) 2 times more efficient than 16PPM. The (7,2) MPPM character error probability and bit error probability (BEP) based on gray coding under Poisson channels are analyzed. The results show that Gray coded MPPM can effectively resist the timing error and reduce the systematic bit error probability.