National Satellite Test Bed (NSTB) communication network architecture and performance

The Federal Aviation Administration's (FAA) National Satellite Test Bed (NSTB) is the research development precursor system to the Wide Augmentation System (WAAS) for GPS based aircraft navigation. The NSTB currently consists of eighteen Testbed Reference Stations (TRSs) in the continental United States and three TRSs in Canada, all of which were deployed from the winter of 1995 to fall 1996. The TRSs consist of two threads of dual frequency GPS receivers, weather stations, DEC Alpha computers, and communication devices. Each TRS is connected to the Test Bed Integration and Test Facility (TBITF) at the FAA Technical Center (FAATC) in Atlantic City, NJ by a pair of dedicated 56 Kilobits per second (Kbps) lines. The TBITF uses the data from the TRSs to determine wide area differential corrections including fast, slow, and ionospheric grid correction terms. These corrections are formatted and transmitted to the Testbed Uplink Stations (TUS) on each coast for dissemination to the users through geosynchronous satellites. The system is scheduled to provide a continuous Signal In Space (SIS) after the network and the system software acceptance in the fall of 1997. Once completed, this wide area network has to meet stringent requirements for data latency (6.2 seconds). This paper describes the NSTB hardware architecture, the communication infrastructure, and the results of performance testing done to date. The NSTB communication backbone consists of two independent, continent spanning, dedicated networks that interface the processing components of the TRS, TBITF, and TUS. The NSTB uses an Internet Protocol(IP) multicast scheme facilitating the TCP/IP, Ethernet, and HDLC protocol suites; The FAATC has tested aspects of the network performance including the data latency from all TRS. These results are presented and compared to the NSTB network timing budget. Calculated availability for the TRS and TBITF are also presented. NSTB data is made available to approved recipients by several methods discussed in the paper.