The unbiased tracking for code phases in vector delay lock loop

For tracking the weak and high dynamic Global Positioning System (GPS) signals, the vector delay lock loop (VDLL) performs better than the traditional scalar based methods. The navigation states of the VDLL always converge to the biased solution when more than 4 satellites are available. In order to reduce the position bias caused by the code tracking bias, the modified VDLL with unbiased code tracking is proposed and implemented in the software defined receiver. The detector of the code phase is introduced to keep the unbiased code tracking adaptively. Simulation results show that the estimated code phase errors of the modified VDLL have zero mean when the redundant satellites are available.