Analysis and Study on the Influence of BDS TGD on Positioning

Abstract

With the development of BDS PNT (Positioning Navigation and Timing) services, the TGD (Timing Group Delay) parameters contained in the satellite navigation message become more and more important. In BDS, the spatial and temporal reference point of satellite clock error is the antenna phase center of B3 frequency, thus B3 channel delay of satellite is included into the clock error. Navigation message broadcasts the differential hardware delay of satellite B1-B3 frequency and B2-B3 frequency, and they are denoted as TGD1 and TGD2 respectively. Thus, both B1 B2 single frequency and all dual-frequency users need to pay much attention to TGD. If BDS want to be considered as the navigation system with high positioning service capability, it is necessary to study the impact of TGD on positioning further. The impact of TGD on UERE (User Equivalent Range Error) is studied based on theory at first. Then BDS TGD is monitored based on the absolute calibration of receiver hardware delay, and the effect of TGD on positioning is analyzed in quantity based on the monitored results. Meanwhile, the positioning performance is studied contrastively based on the different TGD conditions. Furthermore, the impact of TGD on single frequency positioning is compared with that on dualfrequency positioning. Finally, the monitored TGD is expanded to another receiver, and the application results reveal that the monitored TGD computed based on the proposed method has good applicability in other receivers. The analysis result shows that the precision of monitored TGD1 and TGD2 is better than 2 and 1 ns respectively. In the aspect of single frequency positioning of two receivers, 0.2 to 1.4 meters of positioning accuracy can be improved by using broadcast TGD, and 1.3 to 2.7 meters of positioning accuracy can be improved by using monitored TGD. In the aspect of dual-frequency positioning of two receivers, receiver 2 can not reach much better positioning performance even when broadcast TGD is used, but 2.4 to 5.1 meters of positioning accuracy can be improved in receiver 3 in the same condition. And 3.0 to 6.9 meters of positioning accuracy can be improved by using monitored TGD in both receivers dual-frequency positioning.