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hi ,
i have N95 mobile .it is gps enable i am using it very well . but some one told me it work with A-GPS . i checked my phone specification which says " Built-in GPS receiver and A-GPS function ".what is this "A GPS" .can any body aware me better things about this ?
hi ,
you are looking enthusiastic about technology ,good .
Global positioning system is called GPS where AGPS is assisted global positioning system, while just regular GPS is non-assisted.
what is assisting ?
When you use a GPS system and you turn it on, it needs to find orbit and clock data for the relevant satellites, this in turn results in what is called TTFF, or Time To First Fix—how long before you get your location pinpointed. This initial TTFF is often called a “cold start” and on SiRF III systems (the latest GPS systems available), it can take anywhere from 30 seconds to a couple of minutes to acquire a signal. That time is dependent on your location, amount of interference and horizon information: open fields are faster than canyons or urban environments where buildings can interfere with the satellite-receiver line of site.
GPS cell phones will enable wireless location-based services (LBS), which are emerging as a new opportunity for mobile network operators to generate new revenues.AGPS is the most accurate of the methods, requiring only low infrastructure cost and allowing a direct migration path into 3G.
Assisted GPS describes a system where outside sources, such as an assistance server (Mobile Location Server) via a network, help a GPS receiver perform the tasks required to make range measurements and calculate position solutions. The assistance server has the ability to access information from the reference network and also has computing power far beyond that of the GPS receiver. In such a system, the assistance server communicates with the GPS receiver on the mobile phone on a cellular network. With assistance from the network, the receiver can operate more quickly and efficiently than it would unassisted, because a set of tasks that it would normally handle is shared with the assistance server. The resulting AGPS system boosts performance beyond that of the same receiver in a stand-alone mode.
Ordinarily, a standard GPS device needs to have a clear line-of-sight to at least four GPS satellites before it can calculate its position. In addition, it needs enough processing power to transform the data streams from the satellites into a position. In one mode of A-GPS, the mobile receiver takes a snapshot of the satellite signals and transmits these to a cell tower to relay the data to an assistance server that performs the necessary calculations for a position fix. The server may send the fix back to the mobile receiver or to a 911 dispatcher. Some mobile phones will accept converted data streams to compute a position themselves.
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One of the main purposes of A-GPS is to provide municipalities with location-based emergency phone service, such as E911 service. Another is to provide mobile carriers with end-user, location-based services such as a turn-by-turn navigation aid.
so when you use assisted GPS this whole process is much faster. Very often cellular network towers have GPS receivers (or a base station nearby) and those receivers are constantly pulling down satellite information and computing the data. This data is then passed on to the cellular phone (when requested) and acts like a “cheat” since the relevant satellites to your location are already identified and all that GPS computations is handled by 3rd party computers. This is the result of such a system, to you the end user:
* Faster location acquisition
* Less processing power is required by the device
* Saves battery life
* Location acquisition indoors or in non-optimal environmental settings
A cold start
From a cold start with typically older GPS receivers—where the receiver has never been turned on, has been off for several weeks, has lost a battery charge, or has been moved a few hundred miles since its last activation—the entire almanac has to be retrieved over 12.5 minutes. And that's outdoors with good overhead visibility. Jean-Michel Rousseau, a staff product manager in the group at Qualcomm that handles GPS technology, explained that that's "the maximum time that the user would get a position assuming it had absolutely no knowledge of the GPS constellation."
One of the phone's most innovative features is its ability to download topographical, street or city, nautical, or personal maps suitable for use at any time directly via a laptop computer, home PC, or from the Internet. The phone's user interface allows various operations, from waypoint navigation to locating a friend using SMS and MPTP to exchange location information.
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The Benefon Track, a sister product to Benefon Esc!, uses the same platform for communications and positioning but has a user interface tailored for professionals who work alone and individuals desiring personal security through location knowledge.
One of the most important features in the Benefon Track is a dedicated emergency button located clearly at the top of the phone. This button activates a procedure that instantly initiates a location message and a voice call to a user-definable number. This phone also features a wide range of special telematics functions such as tracking, condition check, and status messaging which all use position as a key element. Both of the phones have support for enhanced Cell ID-based network positioning which is combined with GPS to provide users a hybrid positioning capability.
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AGPS Performance
We have tested the performance of our AGPS approach for TTFF and position accuracy. We conducted the testing in both open and urban environments. TTFF was measured relative to the time when the assistance data was received at the phone and power consumption was monitored during the testing.
Special software was loaded into the phone to clear the memory of the GPS receiver prior to requesting a position solution. In these tests, the GPS receiver memory would be cleared and the assistance data requested. After the assistance data was converted to the format for the receiver, the position computation was requested. This test configuration used power directly from the phone battery and the built-in GPS antenna.
any phones with AGPS?
You can googled for such kind of phones using keywords "sony ericsson phones with the AGPS enabled" you will get the list of phone which has AGPS enabled.
:notworthy Thanks