GPS is utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its location, speed and direction.
GNSS systems have a wide variety of uses:
Navigation, ranging from personal hand-held devices for trekking, to devices fitted to cars, trucks, ships and aircraft
There are two GPS communication standards, NMEA and SiRF. Although SiRF is the up and coming new boy on the block, NMEA is the acquired standard and one used by 95% of GPS applications.
And the North American Street & Trips. (currently at version 2008) Are both great PC applications for driving gudance. Autoroute currently at version 2007 has excelent coverage of western Europe, while estern Europe is very poorly covered even in comparison to many mobile devices such as the TomTom, it's surprising that Microsoft is not offering some free Map updating service.
Swiss GPS chip maker u-blox will be introduced a new GPS receiver chip called u-blox 5 it's a very promising chipset any devices using it will be lited here in the future.
SiRF star III chipset is currently the most popular, it's used by TomTom and other great devices.
SiRF recently introduced its SiRFDiRect technology, a portable navigation breakthrough that couples the SiRF star III chipset with acceleration sensors to tell where it's going when GPS signals are blocked. Employing sophisticated algorithms that take advantage of closely coupled GPS and dead-reckoning (DR) sensor measurements, SiRFDiRect technology delivers very high quality positioning, even in the worst GPS signal conditions, without the installation inconvenience and high cost of traditional in-dash navigation systems.
TomTom GO 720 with detailed maps of western and eastern europe comes on top of current GPS offerings. Comming with a windshield mount and a 5h battery it's a very good multi purpose GPS.
Ground reference stations monitor GPS satellite data, and master stations collect data from the reference stations and create a GPS correction message accounting for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere. The corrected differential message is then broadcast through geo-stationary satellites (satellites with a fixed position over the equator). Any WAAS-enabled GPS receiver can read the signal.
WAAS satellite coverage is available only in North America. Other governments are developing similar satellite-based differential systems - Europe's system is the Euro Geo-stationary Navigation Overlay Service (EGNOS). WAAS receivers are compatible with EGNOS.
