Indoor precise point positioning with pseudolites using estimated time biases iPPP and iPPP-RTK

The global navigation satellite system (GNSS) provides outstanding positioning services for outdoor activities with sufficient accuracies, but it has poor indoor performance. Indeed, indoor positioning is also expected to achieve the outdoor positioning level to cater to an even higher volume of user demands. A pseudolite (PL), also called a pseudosatellite, is a ground-based positioning system that offers flexible deployment and accurate “orbits”. The PL system can carry on the role of the GNSS to provide precise positioning for indoor users. The clock differences originating from ground-based transmitters cause unsynchronized timing issues and impede attempts to fix the integer ambiguity. Numerous studies have been conducted with an emphasis on time synchronization to obtain this ambiguity-fixed solution by employing multiple transceivers in transmitter-receiver combinations for self-calibration inside a regional network of the ground-based system. However, this process requires a large investment and complicates the positioning owing to its intricate implementation. Actually, time synchronization can easily be achieved with a transmitter-only PL system at a low cost once the clock bias between transmitters is properly handled. Thus, we propose and present indoor precise point positioning (iPPP) and indoor PPP-real-time kinematic (iPPP-RTK) to handle the PL clock bias efficiently. Experiments demonstrate that the transmitter-only PL system can be time-synchronized without high cost or complicated operations and that centimeter level indoor precise positioning can be reliably achieved with our proposed methods.