Assisted GPS

Assisted GPS, or A-GPS, is a system that concurs to pull down the necessary times to the first localization during the use of finishes them GPS. Extension its usefullness above all in "canyon" the city ones, which tight ways or remarkablly tree-lined tree-lined avenues, in which it is difficult to establish with precision the list of satellites in sight to finishes them. This system is showing a remarkable spread, and normally is associated to the systems of localization (LBS, Location System Base) bases to you on cellular telephony.

One of the main problems of finishes them to GPS classics is relative to the first localization ( the Fixing), in how much they finishes, to the ignition, must gain the list of the satellites in sight in that moment, for potervisi to couple and to try to find the own position. Such process is in somewhat expensive kind in terms of time and resources, and system A-GPS has been studied to the aim to pull down such costs, also in forecast of I use on finishes them with low abilities to elaboration or limited energetic resources, which the cellular telephones.

The main scope of this system is that one "to assist" receiver GPS in the calculation of the position, fornendogli information on the satellites in sight. Such methodology demands the support of the operator of mobile telephony.

The bottom idea is following: since every cell of present mobile telephony on the territory has a fixed position, it makes so that it is the cell to gain which are satellites GPS to it in sight, moment for moment. When A-GPS finishes them wants to know its position, it is connected through the cellular net to a Assistance Serveur (that it can also be managed from the same operator), to which comes sended also the information on the cell to which the customer it is coupled. Since the satellites in sight to the cell are famous, it can be assumed reasonably that also A-GPS finishes them sees the same satellites. Therefore the serveur elaborates a list with the satellites in sight, and it sendes it through the cellular net to finishes them, than in this way it can gain the own position immediately.

The reduced amount of data to send has suggested the employment of type messages cell broadcast, already wide uses you, as an example, in order to carry out various tariffazioni to second of the area in which the customer it finds, and that they appear on the screen of the customer under shape of indication of the province.

The protocol devised standard in order to comply with the own functionalities of A-GPS is the SUPL (Secure User Plane Location).