Characterization of Code Tracking Error of Coherent DLL Under CW Interference

Characterization of the tracking error under continuous wave (CW) interference is the foundation of the interference detection and mitigation in receiver. It is helpful to select pseudo-random noise (PRN) codes with better code tracking performance under interference during the design of signal structure. Considering the effect of discrete spectral line of PRN code, we present a detailed analysis of tracking error of coherent delay locked loop (DLL) for the both situations that when the interference overlaps the spectral line and that when the interference is around the spectral line. In the first situation, the expression of the maximum tracking error for binary phase shift key (BPSK) modulated signal is obtained. The comparison of the tracking errors between finite and infinite frontend bandwidth cases in the first situation shows that the tracking error in the finite case is not like that in the infinite case and cannot be always reduced by narrowing the correlator spacing. The reason of this phenomenon is explained in detail. Further, we obtain the expression of the tracking error limitation as the correlator spacing tends to zero. It is more reasonable to take this limitation as the criterion of evaluating the code tracking performance for different PRN codes under interference. In the second situation, with the assumption of the infinite frontend bandwidth, we obtain the analytic expression of the tracking error. The analysis results show that the impact of the interference on tracking performance decays quickly when the interference leaves far away from the spectral line, and the diminution of correlator spacing and loop bandwidth both can reduce the tracking error efficiently.