Realization of a Deeply Coupled GPS/INS Navigation System Based on INS-VDLL Integration

摘要

Many applications of navigation systems have high demands on reliability and robustness of the navigation solutions. Integrated GPS/INS systems make use of the complementary properties of different sensors and reach an accurate short- and long-term solution. Recent research is conducted on the field of deeply coupled GPS/INS integration systems. Deeply coupled systems enhance the reliability and robustness of a GPS receiver by improving the overall tracking performance. The dynamics of the antenna are estimated by a navigation filter and the output is used to control the tracking loops. This makes the system acceleration-resistant and enables tracking of satellites in poor signal conditions. rnThis paper describes the design of a deeply coupled GPS/INS integration system. In contrast to loosely and tightly coupled systems, where only the received satellite signals are used for controlling the tracking loops and each channel is controlled separately, in a deeply coupled system the tracking loops of each channel are stabilized and controlled by the output of the navigation filter. The tracking via the C/A code phase and the carrier frequency is replaced by direct tracking via the position and the velocity solution, respectively. For the code tracking a Vector Delay Lock Loop (VDLL) is used, which uses the position estimation to feed the numerically controlled oscillators (NCO) of each DLL, see [4]. For carrier tracking two methods are proposed. The VFLL works similar to the VDLL while a stabilized PLL approach uses single channels for tracking. This structure can be run isolated, or extended by an inertial navigation system (INS) to a deeply coupled system. While the vector based tracking is only operable if at least four satellites are available, the presence of an INS enables the tracking of satellites even if no signal is received. Furthermore the proposed GPS/INS structure results in a significant reduction of the required minimal signal power.