Characterizing the Impact of Precision Time and Range Measurements from Two-Way Time Transfer Systems on Network Differential GPS Position Solutions

Precise positioning plays an important role for both military and civilian users, from cell phones and OnStar to precision munitions and swarms of UAVs. Many applications require precise relative positioning of a network of vehicles (such as aircraft, tanks, troops, etc). Currently, the primary means for performing precise positioning is by using the Global Positioning System (GPS), and although GPS has become commonplace in today’s society, there are still limitations affecting the system. Recent advances in dynamic Two-Way Time Transfer (TWTT) have potentially provided a means to improve precise relative positioning accuracy over differential GPS (DGPS)-only approaches. TWTT is a technique in which signals are simultaneously exchanged between users. This research investigates the impact of using Two-Way Time Transfer (TWTT) time measurements to augment differential GPS systems to improve the relative positioning solutions of vehicle networks. Incorporating the TWTT time measurement into the DGPS solution improves the 3-D relative positioning accuracy by up to 44% with pseudorange measurements and 35% with carrier-phase measurements. Normally, the TWTT measurements are used in a manner that cancels out the impact of the vehicle position in order to obtain a precise relative time measurement. The research also implements an innovative approach to using TWTT measurements to actually obtain a precise measurement of the vehicle position in addition to the time measurement. The results show that 3-D relative positioning solutions can be improved by up to 48% when using pseudorange measurements augmented with TWTT time and range measurements, and up to 40% when using carrier-phase measurements augmented with TWTT time and range measurements