GPS vs AGPS
The acronyms GPS and AGPS stand for Global Positioning System and Assisted Global Positioning System respectively. As the names indicate, GPS and AGPS are used for the purpose of locating or positioning or tracking a location. This technology is used in almost all fields of science and others for hi-tech purposes, and by individuals for driving, exploring, running, fishing, etc. GPS technology was developed by the USA defence ministry for military purposes, and made available to public during 1994.
GPS
Simply, the GPS is a satellite based navigation system, which can send and receive data from satellite. NAVSTAR (NAVigation Satellite Timing And Ranging) is the formal name used for GPS. The GPS operation uses data from satellites to calculate the location; usually, it requires data from at least three satellite as to triangulate the position. There is another concept known as Time To Fix First (TTFF). TTFF is the lapse of time required to download the data before the commencement of calculations. It depends on when the chip was used last. If the chip has not been used for a long time the TTFF will be long, as it has to download the data from satellites. Usually, the transmission rate of data from satellite is around 6bytes per second. It takes for a GPS receiver about 65 to 85 millisecond to receive a radio signal from GPS satellite. If the device is used frequently, then the TTFF will be small as the data have already been downloaded. The main advantage of GPS is that, it can be used in a place where the net work coverage is not available, and to some extent the calculations are more accurate as the data are obtained from more reliable sources (that is satellite) and calculations are made from radio signals. However, any intrusion or disturbance to radio signals may question the accuracy.
AGPS
AGPS is a system developed to enhance the start up performance of GPS by allowing to use the data not only from satellite, but also from the local network so the time required to fix, that is TTFF, is very small compared to the TTFF in the GPS. AGPS uses the network sources to download data and calculate the required location. The main drawback of this method is if there is no network coverage it can’t be used as intended. The assistance is given in two ways; one is to allow to use the information to acquire satellite quickly, and the other is to allow to calculate the position by the server using the information from GPS receiver.
What is the difference between GPS and AGPS?
Though GPS and AGPS are used for the same purpose of positioning a location, there are some differences between them.
The TTFF in GPS is much higher than that of AGPS, because they operate little differently as discussed earlier. In some circumstances like, one is trying to locate a position where there are some obstacles like huge buildings to radio signals, which are to/from satellite, then the accuracy of GPS may be compromised as signals are deflected. On the other hand, AGPS uses data from the server, which was already fed through local networking. So it may be more accurate than the result obtained from GPS. AGPS depends on the satellite and assistance server, while GPS depends only on the satellite. In the real life, AGPS facility is embedded in some other equipments like mobile phones while stand alone GPS are used not frequently.
Some AGPS can work as normal GPS when there is no networking coverage, however, vice versa is not at all possible for a GPS
It is important to those, who are interested in purchasing a device for positioning purpose, to understand what is GPS, what is AGPS, and what are the differences between them, in order to choose the appropriate device that suits to their purpose.