Abstract
The ephemeris data format of legacy GPS receivers is improper for positioning stationary pseudolites on the ground. Therefore, to utilize pseudolites for navigation, GPS receivers must be modified so that they can handle the modified data formats of the pseudolites. Because of this problem, the practical use of pseudolites has so far been limited. This paper proposes a pseudolite-based positioning system that can be used with unmodified legacy GPS receivers. In the proposed system, pseudolites transmit simulated GPS signals. The signals use standard GPS ephemeris data format and contain ephemeris data of simulated GPS satellites, not those of pseudolites. The use of the standard format enables the GPS receiver to process pseudolite signals without any modification. However, the position output of the GPS receiver is not the correct position in this system, because there are additional signal delays from each pseudolite to the receiver. A post-calculation process was added to obtain the correct receiver position using GPS receiver output. This re-estimation is possible because it is based on known information about the simulated signals, pseudolites, and positioning process of the GPS receiver. Simulations using generated data and live GPS data are conducted for various geometries to verify the proposed system. The test results show that the proposed system provides the desired user position using pseudolite signals without requiring any modifications to the legacy GPS receiver. In this initial study, a pseudolite-only indoor system was assumed. However, it can be expanded to a GPS-pseudolite system outdoors.
Highlights
Over the past few decades, there have been a number of studies on Global Navigation SatelliteSystems (GNSS)
This paper proposes a new positioning system for pseudolite signals that does not require any modification of legacy GPS receivers
This study proposed a pseudolite-based positioning system that can be used by unmodified legacy GPS receivers
Summary
Over the past few decades, there have been a number of studies on Global Navigation Satellite. The receiver modification problem refers to the need to modify GNSS receiver hardware or firmware to acquire accurate data using a pseudolite-based positioning system. Legacy GNSS receivers such as those in smartphones or mobile devices cannot be used with pseudolite signals. To overcome this problem, a study was done that suggested a modified navigation message to deliver a pseudolite‟s position information [8]. This paper proposes a new positioning system for pseudolite signals that does not require any modification of legacy GPS receivers. The proposed system uses pseudolites which generate each channel signal of the GPS simulator and legacy GPS receiver without any modification. The results show that an accurate position can be obtained using the proposed algorithm without any receiver modification. The GPS L1 signal with C/A code was assumed during the study
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