Sameet Deshpande, Arun Raghupathy, NextNav Inc

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NextNav has developed a TerraPoiNT system, a terrestrial-based positioning, navigation and timing system which can complement navigation systems as well as serve as GNSS-backup. TerraPoint system is Time-Of-Arrival (TOA) multilateration system offering 3D positioning and timing through a dedicated terrestrial network of synchronized transmitters operating in the 920-928 MHz frequency band, using Code Division Multiple Access (CDMA) spread spectrum signals. The transmitters, beacons, are typically synchronized to absolute time through GPS but can also use other absolute time sources such as a disciplined Cesium clock, LEO satellite systems, eLoran or Time over Fiber. In the absence of an absolute time source or during extended outages the transmitters can maintain relative timing synchronization sufficient to provide position and navigation capability as well as relative timing without any significant loss in performance. TerraPoiNT transmitters can self-synchronize without the need for any absolute time system at each beacon allows the network to operate seamlessly in absence of GNSS making it ideal as an alternative to GNSS system. TerraPoiNT offers vertical positioning through integration with barometric and environmental reference information provided over the data payload. The beacons are designed to detect anomalies in position and timing. This capability enables TerraPoiNT to detect local anomalies in any absolute time system like GPS. TerraPoiNT’s innovative methods to address the near-far reception problem coupled with the short multipath resolution capability enables it to provide a robust performance in any environment. TerraPoiNT signals are 10000 times stronger than GNSS signals and can penetrate inside the building enabling TerraPoiNT receivers to conquer the frontier of indoor positioning. TerraPoiNT positioning receiver (LPRx) has been developed to track and demodulate TerraPoiNT signals, perform TOA measurements and compute a navigation solution. This receiver was used during the tests along with a highly accurate and precise GNSS-INS system to obtain the truth data and compute the navigation performance. A GNSS-free TerraPoiNT network of seven beacons was deployed in San Jose Downtown to demonstrate the navigation capability of the system. The network provided different environments from sub-urban to urban areas enabling to measure the system performance in different kinematic conditions. TerraPoiNT system was tested under various challenging environments including urban areas for automotive applications, aerial paths for UAVs and drones. Navigation drive tests performed from Valley Fair mall and San Jose downtown area showed the TerraPoiNT performance to be with 3m (50%) and 10m (95%) of the time. TerraPoiNT system was tested for avionics and UAM use-cases as well. In this case, the network covering the test route was deployed to ensure there is flight trajectory is within the boundary of the network. Flight tests were performed using a helicopter as the test vehicle flying from Oakland airport to the San Francisco downtown and returning to Oakland airport. TerraPoiNT was found to provide accurate performance during the entire flight even in segments when GPS receiver lost lock on GNSS signals. Tests were performed in the Baylands Park, Sunnyvale with the TerraPoiNT navigation receiver mounted on the drone and flown to an altitude of 200 ft. The drone and flight results demonstrated that TerraPoiNT system can have performance within the bounds of the avionics use-case. TerraPoiNT system demonstrated an accurate, reliable, and robust performance over different tests covering a variety of applications and serve to aid GNSS systems as well as work even when GNSS systems are compromised