This paper presents the results of a study carried out in the Greater London area to assess and characterise the performance of the Global Positioning System (GPS) for vehicle positioning in urban areas. The performance assessment addresses, in varying levels of detail, the issues of service coverage, positioning accuracy, integrity and availability of service. The project was supported by Racal Survey Limited and is part of the wider research at Imperial College in the area of architectural design and testing of Advanced Transport Telematics (ATT) systems. The results highlight the shortcomings of GPS as the sole means for in-car navigation in urban areas and details the temporal and spatial considerations to be taken into account in the process of designing an integrated positioning system capable of meeting navigation requirements placed on ATT systems.

Satellite Based Augmentation Systems are being developed in Europe (EGNOS), the USA (WAAS), and in Japan (MSAS). As part of their support to EGNOS, NATS and Racal have developed and deployed a prototype SBAS system called the Northern European Satellite Test Bed (NEST Bed). NEST Bed uses GPS L1/L2 reference stations at: Aberdeen, Rotterdam, Ankara, Cadiz, Keflavik, and Bronnoysund. Data is sent to the Master Control Centre at NATS Gatwick Services Management Centre for processing. The resulting 250 bits-per-second message is sent to Goonhilly for up-linking by BT to the Navigation Payload of either the Inmarsat AOR-E or F5 spare satellite. NEST Bed was deployed and commissioned during summer 1998, and flight tests were successfully demonstrated at the September 1998 Farnborough Air Show where approaches were flown to Boscombe Down on the DERA BAC1-11 aircraft. In October 1998, a NATS/FAA flight trial was held in Iceland involving NEST Bed and the FAA NSTB. NEST Bed is also being used for SARPS validation.

This paper describes selective tests performed in the areas of Gdansk and Gdynia VTS Centres. The main goal of the tests was to determine the accuracy of position, speed and course estimations measured by shore-based radar VTS tracking systems by using measurements of the same parameters available on board a tracked vessel equipped with GPS and GLONASS receivers. Six DGPS/GPS/GLONASS receivers were installed on board a survey vessel, and all of them recorded the vessel's route simultaneously with two different VTS radars – one at Gdansk and one at Gdynia (20 km apart). All DGPS receivers tracked the same reference station. Presented results show that the radar information can be used by VTS operators to provide navigation assistance within certain limits, but these limits must be understood. A more detailed description of the experiment was presented during the IALA Conference in Hamburg in June 1998.