# Improving the Design of MEMS INS-Aided PLLs for GNSS Carrier Phase Measurement under High Dynamics
## 1 Introduction  
With the development of global navigation satellite systems (GNSS), precision positioning is gradually being applied in dynamic environments, including mobile mapping, autonomous driving, seismic surveying, precision weapon guidance, and other areas [1; 2; 3; 4]. GNSS carrier phases, observations of precision positioning, are measured by phase locked loops (PLLs). The PLL bandwidth design suffers a dilemma with accuracy and dynamic stress tolerance [5]. To reduce the noise and improve accuracy, the tracking bandwidth should be narrow [6]. However, to be better suited for dynamic stress, a wider tracking bandwidth is ideal [7; 8]. Therefore, in a stand-alone GNSS receiver, a trade-off design of PLL bandwidth is required to adapt various scenarios [9]. The carrier phase accuracy is worsened in dynamic environments.  
External sensor aiding is considered as an alternative to improve carrier phase tracking performance. The inertial navigation system (INS) has a superior dynamic characteristic, which is highly complementary to GNSS. Therefore, GNSS/INS integration is widely studied and applied [10; 11; 12; 13; 14]. When the INS is used to assist the GNSS receiver baseband, the structure is named deeply coupled system [15; 16; 17]. The INS information assists PLLs based on the concept of feed-forward [18; 19]. In INS-aided PLLs, with the aiding of the INS feed-forward branch, PLLs only need to tolerate the errorfrom the aiding information, instead of vehicle dynamic stress. Therefore, INS-aided PLLs do not need to increase loop bandwidth to tolerate dynamics, and the carrier phase tracking performance is better than that of stand-alone PLLs [20; 21].  
The concept of INS-aided PLLs has been proposed and studied in the GNSS community. [PERSON] et al. proposed the INS-aided tracking loop architecture, but its advantage was not fully shown due to simple implementation [18]. [PERSON] et al. tested the sensitivity of INS-aided PLLs, with the same design as [PERSON]'s [21]. [PERSON] et al. adjusted the aiding information update rate by extrapolation of the INS velocity, and realized the carrier phase tracking under an acceleration of 40G [4]. However, INS-aided PLLs were not optimized to improve carrier phase accuracy. [PERSON] et al. tested the INS-aided GPS tracking performance under strong ionospheric scintillations, without purposeful design for high dynamics [17]. Therefore, the tracking error caused by aiding information needed to be analyzed in detail, and INS-aided PLLs needs to be optimally designed to improve the carrier phase accuracy under high dynamics.  
To obtain accurate GNSS carrier phase under dynamics, we focus on improving the design of INS-aided PLLs. First, micro-electro-mechanical systems (MEMS) INS-aided PLLs were implemented in our software GNSS/INS deeply-coupled system, and tracking errors caused by aiding information were tested and analyzed under a jerk of 2000 m/s\({}^{3}\) using hardware simulator. Then, INS-aided PLLs were improved to reduce tracking errors caused by aiding information. Finally, the performance of improved MEMS INS-aided PLLs was evaluated under a jerk of 300 m/s\({}^{3}\) through field tests.