A Study Of Anti-shortmultipath In Pseudo-random Code Ranging System Between Spacecrafts

Pseudo-random code ranging method is widely used in various aerospace measurement and control systems. There are two factors that can determine the precision of Pseudo-code ranging system. One of factors is the width of Pseudo-code and the other is tracking precision of receiver. The limitation of code width can be solved by adjusting the Pseudo-code clock but the tracking precision of receiver, which is restricted by the structure of hardware, is vulnerable to be affected by the interferences in external environment. Generally, the random error caused by the accidental factors in the channel environment, such as frequency interference, multipath effect, is difficult to eliminate. Moreover, the conventional multipath mitigation methods are not effect to cope with short multipath (smaller than 1 chip). Therefore, this dissertation focuses on reducing short multipath error from the aspects of signal processing and signal system designing. The contributions of the thesis are listed as follows:1. According to the principle of producing the code tracking error and on the base of analyzing the traditional discriminator output, this dissertation proposes an improved discriminator. The improved discriminator can ensure the zero of discriminator function without deflection. The proposed method fundamentally eliminates the code tracking error. Finally, the simulation results show better performance than the conventional methods.2. Based on the content of signal system designing, to select appropriate code type and modulation method under the scene of measuring the distance between two spacecrafts. But the modulation method which we choose has an ambiguous problem. To solve this problem this dissertation proposes two stages unambiguous multipath suppression scheme. The conventional schemes of solving the ambiguous problem will lower the correlation peak, which reduces the tracking loop sensitivity. The proposed scheme can solve the ambiguous problem, while keeping the value of correlation peak and reduce the width of correlation peak to improve the anti-shortmultipath performance. Finally, the simulation results show the superiority of proposed scheme.