无源互调对直扩系统伪码捕获性能的影响

无源互调干扰信号会对无线通信系统造成不同程度的影响，轻则干扰无线通信系统，严重时阻塞无线通信系统信号传输通道。为了定量分析无源互调干扰信号对直扩系统伪码捕获性能的影响，建立了无源互调干扰下直扩系统模型，考虑卫星接收机中噪声的影响，采用修正柯西分布概率密度模型，分别对平方律检波器捕获方法和平方检波累积器捕获方法在无源互调干扰下的捕获性能进行了理论推导和仿真验证。仿真结果表明，高信干噪比下无源互调干扰对通信系统的影响比噪声小，90%捕获检测概率下相差2.92dB；采用平方检波累积方法可获得一定的累积增益，90%捕获检测概率下的累积增益为2.36dB。

Effect of passive intermodulation on peudo noise code acquisition performance in direct sequence spread spectrum systems

The satellite communication systems can be jammed by passive intermodulation (PIM) interference signals，and the transmission channel may be blocked at worst. In order to analyze the performance of peudo noise (PN) code acquisition with the passive intermodulation interference quantitatively，the model of direct sequence spread spectrum (DSSS) systems with interference was established. The common methods of PN code acquisition were square law detection and square accumulation detection. The modified Cauchy distribution model was proposed to describe the statistical property of PIM. In consideration of PIM and the receiver noise，the acquisition performances of both detection methods were derived and simulated. The simulation results show that in the case of high signal to interference plus noise ratio(SINR)，the noise has a worse effect on PN acquisition performance than PIM. When the detection probability is 90%，the difference is 2.92dB. The performance of detection method with accumulation is better than that without accumulation，and achieves an accumulation gain. When the detection probability is 90%，the accumulation gain is 2.36dB.