建立了伪随机码测距的系统测距模型，从光子统计理论出发提出一种新的系统输出信噪比模型。蒙特卡罗算法模拟不同系统死时间下，系统输出信噪比和伪随机码码型的关系。理论模型与蒙特卡罗仿真基本吻合，结果表明信噪比随着伪随机码1的比例增大先增大再减小，选择最佳的发送码型可以获得最佳信噪比。根据新的模型，系统死时间的降低可提高信噪比，光子计数值增大，信噪比先增大再减小。引入系统高斯抖动，重构接收脉冲时间记录值，码速越高单点记录值出现误差的可能性越大，选取1 GHz的码发送速率可完全避免距离数值误差。

Pseudo-random bitstream ranging model is researched and a new output signal to noise ratio (SNR) model based on photon statistics model is proposed. The relationship between SNR and code pattern of pseudo-random bitstream with different dead time is studied by Monte-Carlo simulation. The theory model is almost consistent with Monte-Carlo simulation. The results show that with the fraction of randomly distributed 1-bits in transmitted pattern increased, the system SNR is getting better firstly and then getting worse. Best pattern of transmitted bitstream according to different dead time may lead to the best SNR. According to new output SNR model, lower dead time brings better SNR. The system SNR increases firstly then gets down with the growing signal photon counting. Gaussian distribution timing jitter is introduced to reconstruct received bitstream pattern formed from the arrival times of returning single photon. It is found that higher rate of bitstream brings higher possibility error of single time value. Suitable bits rate is restricted to 1 GHz to reduce the probability of ranging error.