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GPS vs A-GPS | Difference between GPS and GPS-A

This GPS tutorial covers GPS system basics,applications and also provide link to GPS module/chip/components manufacturers.It covers difference between GPS vs A-GPS and GPS vs GLONASS.
GPS vs AGPS   GPS vs GPRS  GPS Basics Tutorial  GPS Frame Structure   GPS Antenna  GPS Receiver Module  GPS Satellite  GPS Tracking System 

This page on GPS vs A-GPS describes difference between GPS and GPS-A. Both the technologies help determine location on the earth. GPS is mainly employed in cars,planes and ships, while AGPS is employed in mobile phones. Though both have same application, let us see how both the features differ below. GPS stands for Global Positioning System and AGPS stands for Assisted Global Positioning System.

GPS devices determine location information by directly communicating with satellites moving around the earth. AGPS devices determine location information from network stations(BTS/NodeB/eNodeB) based on GSM,CDMA or LTE technology employed in the mobile terminal. Base station systems in the A-GPS technology in turn communicate with satellite and keep the information ready and provide the information to the mobile terminals upon request.

As GPS devices are communicating with satellite, it can get information only under clear sky conditions and when satellite is reachable without any interference. Due to this it is slower in responding the requested service. While A-GPS devices are communicating with network stations,it gets information even in cloudy atmosphere and worst network conditions,but it will have problem when network is not reachable. Under this conditions AGPS devices fall back to GPS feature if available to provide location information as per user request. A-GPS devices are faster as it need not have to go to satellite for information.

About GPS-A Modes-MSA and MSB

As mentioned GPS-A is the short form of Assisted GPS. There are two modes of operation in GPS-A. They are MSA and MSB. MSA is the short form of
MSA(Mobile Station Assisted):
In this mode MSA, GPS-A device gets reference time, acquisition help and other optional data information from mobile system operator. This operator obtains GPS information using GPS-A server from satellite and store in its database. From the information GPS-A server calculates the satellite position and provides the same to the GPS-A device. Hence in MSA mode it is server which calculates the position and not the GPS-A device.
MSB(Mobile Station Based):
In MSB mode, GPS-A device gets reference time and location, ephemeris and other data from the GPS-A server. With this data GPS-A device itself calculates satellite position. This is the difference between GPS modes MSA and MSB.

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