Test Results of Local Area Augmentation of GPS With an In-Band Pseudolite

The FAA is supporting a comprehensive evaluation of using pseudolites as a means of providing local area augmentation of GPS with improved accuracy, integrity and availability, and in particular to meet Cat II/III precision approach requirements. An in-band pseudolite (PL) signal design is being tested which includes special features to avoid any consequential interference to GPS throughout a terminal area. The concept is being evaluated for use as an additional ranging source (both code and carrier) and as a data link for the transmission of DGPS corrections and GPS integrity information at data rates up to 1 kbps. This paper presents results from a recent series of testing that was performed using a single PL transmitter broadcasting from the hangar roof-top at the FAA Technical Center (FAATC). A co-located GPS/PL reference receiver was used for signal monitoring and to support the generation of DGPS/PL correction data transmitted by the PL. An FAA Convair 580 test aircraft was outfitted with multiple antennas (high and low profile top-mounted antennas and a low profile bottom- mounted antenna) to enable a sensitivity assessment of aircraft antenna type and location. Various flight profiles were flown including straight-in approaches and holding patterns ranging up to 35 km from the PL. Aircraft positioning data as well as received PL messages and signal quahty.data (C/No) were recorded onboard during all segments. The results presented represent the first comprehensive test data for an in-band pseudolite used to augment GPS (with ranging and data) throughout an aircraft approach pattern. It also presents an initial comparison of different aircraft antenna configurations used to receive GPS and/or PL signals.