Assisted satellite positioning

Although standard satellite positioning provides unbeatable performance, compared with other available positioning methods it still suffers from many environment-related issues. One of them is disruption of continuity of positioning service, usually caused by temporal inability to collect navigation data due to poor satellite visibility. This problem is particularly noticeable in urban areas, where high buildings often considerably decrease the satellite visibility. A number of GPS-based systems and services (among them the location-based services - LBS) rely upon continuous provision of satellite positioning service. In order to decrease as much as possible the time to first fix (TTFF) after temporal unavailability of standard positioning service, auxiliary communications systems deploy the functionality of assistance data provision to satellite positioning receiver. This article examines the content of satellite positioning assistance, the impact of assistance data on position estimate calculation algorithm and the means for assistance data distribution. Special emphasis is given on satellite positioning assistance for LBS, and the mechanisms for assistance data delivery through the mobile communication network are presented. In conclusion, assistance data are identified as the major contributor to satellite positioning performance improvement, with a brief list of related future activities given