Integration and Testing of a Wide-Band Airport Pseudolite

The Federal Aviation Administration (FAA) baseline architecture for the Local Area Augmentation System (LAAS) includes Airport Pseudolites (APLs) as the preferred method for augmenting Differential Global Positioning System (DGPS) to achieve the availability required to support Category II/III operations. The FAA utilized a Cooperative Agreement with the Air Transport Association (ATA) to procure and test a prototype APL system. The specification for procurement of the APL system was the most current design specification developed by RTCA working group 4A. Key parameters in the APL signal in space format were implemented to be variable in the prototype unit to allow refinement of the standards. This paper first describes APL interference testing performed for the FAA by the ARINC SITE Laboratory. Tests were conducted on a selection of military and commercial GPS receivers. These interference tests explored the effects of the specified APL signal on the performance of standard GPS receivers. Additional tests were done while the APL parameters were varied over a wider range to allow flexibility during field tests. The interference tests concluded that the APL had minimal or no effect on the ability of GPS receivers to acquire and track the GPS satellite signal. Upon completion of the interference testing, the APL system was integrated into the LAAS Test Prototype (LTP). The FAA William J. Hughes Technical Center (WJHTC) is the primary test location for FAA LAAS testing and home to the LTP. This paper describes the integration of the APL system into the LTP. The paper provides initial results of a series of flight tests conducted using the LTP/APL system. United Parcel Service (UPS) provided a Boeing 767 to be used as a test vehicle that would represent a typical LAAS platform. A total of 39 precision approaches were conducted at the Atlantic City International Airport (ACY) using the LTP for guidance. Initial results have shown that the specified APL signal format required some modification before the APL could provide sufficient average power to allow the tested GPS receivers to acquire and track the signal in space. The APL signal was received by the top mounted antenna of the Boeing 767, but the expected coverage range was about half of what was expected. The body of the aircraft did at times prevent APL signal acquisition by blocking and attenuating the APL signal.