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

This page compares GPS vs A-GPS and mentions difference between GPS and A-GPS. It describes A-GPS (Assisted GPS) Modes viz. MSA and MSB.

Introduction: 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.

What are GPS and A-GPS ?

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.

Assisted GPS Modes | MSA and MSB

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

Difference between GPS and A-GPS

Following table mentions comparison between GPS and A-GPS with respect to various parameters.

Parameters GPS A-GPS
Full name Global Positioning System Assisted Global Positioning System
Source Radio frequency signals from GPS satellites Radio frequency signals from GPS satellites via assistance servers e.g. mobile network cell sites
Location accuracy More accurate (Within 1 meter) Less accurate than GPS
Speed GPS devices require some time to lock with GPS satellites A-GPS devices find positions faster due to better internet connectivity
Cost Using GPS incurs cost on devices but low on services Costs money to use A-GPS devices on continuous basis as they use mobile data for connectivity.
Usage or application Cars, aircraft, ships Mobile phones and WiFi

GPS related links

GPS vs AGPS   GPS Frame Structure   GPS vs GPRS   GPS Basics Tutorial   GPS Antenna   GPS Receiver Module   GPS Satellite   GPS Tracking System  

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