Combined GPS/cellular data creates universal positioning data

eGPS provides a superset of the A-GPS aiding data to deliver fast and reliable positioning - anywhere, anytime - without necessitating upgrades to existing GSM/WCDMA network infrastructure. 

A-GPS (Assisted GPS) techniques are a popular method for reducing GPS's limitations when implemented on handsets.  A network-located server provides Ephemeris and Almanac data to shorten time to fix. However, A-GPS cannot help a handset to sense position when GPS signals are unavailable, and in these cases sometimes only the cell ID can be provided (which might mean an 'accuracy' of kilometres).

eGPS extends the aiding concept by supplementing Ephemeris and Almanac information with a database of GSM/WCDMA basestation locations and a timing model of the network, in order to generate fine time and frequency aiding to speed GPS fixes. It also provides positional information based on cellular network information alone, providing a fallback position accuracy of some 100m (CSR's real-world trials are currently demonstrating around 60m).

Satellite time information is maintained accurately and autonomously within the handset, which has the practical benefit of speeding time to fix in the poor GPS environments that most handsets operate in. This typically accelerates fix times by as much as three times compared with A-GPS.  Satellite time calibration can even be maintained autonomously by the handset alone for hours following a fix - allowing systems to operate with or without a network-located server - ensuring that users can sense position when roaming.

The impact on power consumption is almost negligible, as the cellular information is continuously derived via the handset's cellular modem, allowing the GPS subsystem to be powered up only when an accurate position fix is required. A typical eGPS push-to-fix will be available in less than 4 seconds, accurate to within 10m, and require the equivalent power of less than 1 second of handset talk time.