GNSS position-aided delay-locked loops for accurate urban navigation

In urban environments, when GNSS signals are weakened, blocked, and interfered with by multipath, the tracking accuracy and continuity of scalar delay-locked loops (SDLL) deteriorate seriously. Vector delay-locked loops (VDLL) can improve the tracking performance by estimating each channel’s control information from positioning, but it requires reconstruction of the receiver baseband and has a heavy processing load. We propose a position-aided delay-locked loop (PA-DLL) with its numerically controlled oscillator (NCO) controlled by a local loop filter and position jointly. Compared with SDLL and VDLL, PA-DLL can be implemented with minor adjustments to the SDLL and brings the superiority of VDLL. NCO control by position is composed of an extended Kalman filter-based positioning algorithm and an aiding information estimation module. The performance of PA-DLL is fully tested in our software receiver i2xSNR and compared with SDLL and VDLL in urban environments. Compared to SDLL, the pseudorange and positioning accuracy of PA-DLL are improved by at least 20%. Test results show that PA-DLL performance significantly improved over SDLL and is comparable to VDLL with a high enough update rate. The processing load test illustrates that, compared to SDLL-based receiver, PA-DLL has only a little increase in processing load, while VDLL needs more than 10 times of computation load to ensure comparable performance.