Global Positioning System (GPS)
Global Positioning System (GPS) is a space based satellite system for direction-finding. The system was developed and is operated by the United States Department of Defense to determine current location, time and velocity of places. A cluster of 24 Earth-orbiting satellites and their ground stations are used in calculating accurate location and time information anywhere on the Earth. Three more satellites are available to be used in case of failure of functional satellites. The first GPS satellite was launched in 1974 and the 24th satellite, which is the latestworking station, was launched in 1994. With the advancement of technology, the cost of GPS devices has tumbled while the accuracy of location has been achieved and even the system has been incorporated in handheld devices.
A GPS receiver is a combination of an antenna – to tune frequencies transmitted by the satellites, receiver, processors, and a highly stable clock. It calculates position by accurately timing the signals sent by GPS satellite positioned above the Earth. Satellites continually transmit specific orbital information and the timing of the message transmitted. Receiver uses the messages to determine the transit time and computes the distance to each satellite to provide exact position of the receiver. The position is displayed on the receiver with a moving map or in form of latitude and longitude. Modern GPS units also derived information such as direction and speed, calculated from position changes.
GPS vs A-GPS
Global Positioning System (GPS) needs to find orbit and clock data for the relevant satellites, which is termed as the time to first fix” (TTFF) to pin point the accurate locations. It takes anywhere from 30 seconds to a couple of minutes to acquire a signal depending on your location, amount of interference and horizon information as satellite receiver is based on line of site mode. On the other hand, the whole process is very faster in assisted GPS (A-GPS) devices. Cellular network towers have GPS receivers or a base station in nearby location to pull down satellite information and compute the data constantly. The data is transmitted to the cellular phone on demand.
Thus, A-GPS improves the performance of the GPS. With a GPS, one can track location indoors or non-optimal environmental settings which cannot be done with a GPS device which is limited by line of sights.
A-GPS (Assisted GPS)
A-GPS boosts the reception signals of GPS receiver using assistance from other services. It is the technology, which is to be credited for introduction on GPS system in cellular devices such as mobile phone.
Here’s how A-GPS boosts the performance on an ordinary GPS receiver:
A-GPS helps GPS receiver to quickly obtain the time to first fix” (TTFF) – the measure of the time required for a GPS receiver to acquire signals and navigate data via the cellular network and avoid downloading the information via satellite, which is a slow process.
GPS uses an unobstructed line of sight to four or more GPS satellites to determine location. Signals may be obstructed by buildings as they cannot penetrate building interiors. In such cases, A-GPS uses proximity to cellular towers and calculate positions. It addresses signal and network problems by using assistance from other services such as GPRS and service provider network. Thus, A-GPS enhances GPS performance.