Seamless handover of combined GPS/pseudolite navigation

The paper proposes and experimentally verifies a seamless handover algorithm for combined GPS/pseudolite positioning. With the advent of GPS technology, navigation practices have relied on the use of GPS signal extensively. To further enhancing accuracy, integrity, and coverage, pseudolites (PLs) which are ground-based transmitters that are capable of transmitting GPS-like signals have been proposed to augment GPS and, indeed, supplement GPS in an indoor environment. When a mobile navigator moves from an outdoor environment to an indoor environment, the GPS/PL receiver experiences changes in number, type, geometry, and quality of signal sources. The positioning problem becomes extremely challenging when the PL is not synchronized with the GPS system. In this paper, a positioning algorithm for successful handover from GPS positioning to combined GPS/PL positioning, and finally, to pure PL positioning is proposed. Essentially, the algorithm contains several modes. In the pure GPS mode, the GPS signals are used to provide position fixes. In the combined GPS/PL mode, there are two submodes: one is to estimate the clock characteristics of the PL and the other is to perform an integrated GPS/PL positioning. In the pure PL mode, the navigator relies on the PL signal solely. A high-level mode transition strategy is devised to monitor the number, geometry, and strength of each signal and adaptively handover the solution process. The algorithm relies on a filtering formulation so as to ensure a continuous position update. In addition to navigation computation, the filtering algorithm is also responsible for data integrity monitoring and fault exclusion. An experiment is then setup for the assessment of the handover algorithm. The PL used in the experiment is developed indigenously. The algorithm is demonstrated to be able to provide a position fix in the transition from pure GPS mode to pure PL mode. Overall, a seamless handover scheme from pure GPS to combined GPS/PL and eventually to pure PL navigation is experimentally demonstrated with an acceptable level of accuracy.