In order to produce a valid position, a GPS receiver must know (among other measurements) the position of its reference points: the GPS satellites. The GPS satellite position can be accurately reconstructed starting from a set of data called ephemeris that is periodically broadcasted by each GPS satellite. In good GPS signal conditions ephemeris are typically decoded by the receiver directly from the satellite signal and maintain their validity for about 4 hours.
To overcome the fact that in difficult signal conditions, such as urban environments, downloading the ephemeris can take a very long time, in recent years ephemeris ‘extensions’ techniques have been developed to extend the validity of the data beyond the 4 hours, thus eliminating the need of a new download after their expiration. The first generation of extensions techniques are based on a small file periodically made available by the GPS chipset manufacturer on a server, which once downloaded on the GPS receiver can lead to an extension of the ephemeris validity period up to 14 days. Such solution being unpractical for unconnected devices (first of all PNDs), a second generation of ephemeris extension has been developed, that is able to produce the extensions directly on the GPS receiver (eliminating the need to connect to a server) achieving a typical extension period of 3 days.
Such TTFF acceleration technology is nowadays available also from third party, GPS chipset independent providers. It is technically possible to develop a TTFF ‘booster’ technology that can be applied to almost any existing PND (independently from the underlying GPS chipset) and obtain the same level of acceleration effect and end user benefits available on PNDs that natively come with such feature.