GNSS signal multi-frequency carrier phase asynchronous joint tracking

As demonstrated in numerous studies, jointly tracking global navigation satellite system (GNSS) multi-frequency signals transmitted from the same satellite can improve tracking sensitivity and robustness. To facilitate the application of this joint tracking technique in contemporary GNSS receivers with asynchronous signal reception structures, we propose a synchronous-input asynchronous-update mechanism for multi-frequency carrier phase joint tracking. To elucidate the joint-tracking mechanisms, a linearized mathematical model of the joint tracking loop is constructed. We derive an equation to calculate the thermal noise jitter of the loop. Additionally, we examine the dynamic stress response characteristics of the loop and clarify the loop design requirements for eliminating the influence of inter-frequency biases. The theoretical results are validated using Monte Carlo simulations and preliminary field tests, with the B1C and B2a pilot signals from the medium earth orbit (MEO) satellite within the BeiDou satellite navigation system (BDS). Experimental results show that the carrier phase tracking threshold of the B1C and B2a signals can be reduced by approximately 1 dB and 3.5 dB, respectively.