Analysis of Combined Effects of Multipath and CW Interference on Coherent Delay Lock Loop

Multipath and continuous wave (CW) interference can cause severe performance degradation of global navigation satellite system receivers. Therefore, effects of multipath or CW interference have been analyzed separately in many papers. However, when multipath and interference exist at the same time, it hasn't been discussed whether their effects on code tracking performance are independent, and the combined effects of multipath and CW interference haven't been analyzed. This paper analyzes the combined effects of multipath and CW interference on the code tracking performance of coherent delay lock loop (DLL). An analytical expression of code tracking error envelope is suggested for coherent DLL and can be used to assess combined effects of multipath and CW interference. This analytical expression shows that multipath may change the slope of discrimination function, which causes the problem that effects of multipath and CW interference aren't independent. Therefore, multipath effects on the slope of discrimination function are discussed in this paper. It is shown that smaller correlator spacing can decrease the multipath effect on the slope of discrimination function. However, when the finite bandwidth is taken into account, the smaller correlator spacing can't suppress the multipath effect on the slope of discrimination function effectively. The combined effects of multipath and CW interference depend on many factors. The GPS C/A signal is taken as an example of the application of the derived expression to discuss how these factors affect the code tracking performance, and simulation validation shows the availability of theoretical results.