What can Assisted GPS do for you

More than 35 years have passed since some of us were fortunate enough to play a role in the design of GPS. Predecessor systems and designs, such as Transit, Timation, 621B, DNSS, and atomic clocks provided some of its foundations. Considered at first by some as a useless adventure of some technologists with little knowledge of real navigation, GPS has now become a household word and has many millions of users, mostly civilian, in aircraft, ships, surveying, construction, and most of all, cell phones and automobiles ( such as rearview mirror GPS, mirror GPS ). Assisted GPS (A-GPS) is one of the major contributors to the widespread use of GPS, especially for cell phones and other handheld units. A-GPS integrates GPS and communications, especially wireless and utilizes GPS chips with added low-cost processing power and many thousands of correlators. GPS satellites are limited in the amount of power they can provide to users on the ground many thousands of miles away. A-GPS provides important information, by means of these separate wireless communications channels, to substantially improve the processing power of the GPS receiver, so that they can operate successfully in disadvantaged locations and circumstances where buildings, trees, hills may partially degrade the GPS signals.

GPS was originally designed to guide bombs, aircraft, soldiers, and sailors. In all cases, the GPS receiver was expected to be outside with a relatively clear view of the sky. The system was designed to require a start-up time of approximately 1 min, and after that it would operate continuously. Today GPS is used for many more civilian than military purposes. Counterintuitively, the system demands of these civilian applications far exceed those seen before. GPS is now expected to work almost anywhere, even, sometimes, indoors; push-to-fix applications have emerged where a single position is expected almost instantly; and all of this must be delivered in a way that adds little or no cost, size, or power consumption to the host device.  You probably recognize the ways that your car's GPS rearview mirror and telematics system track you for your own good. Their tracking gives you directions. It means you will be found in the event of a crash. 

What can A-GPS do for you? The PLGR was the GPS receiver most widely used by the U.S. military. It is a five-channel, L1-only receiver, with a typical time to first fix of over a minute, and a cost of about $2,000. The PLGR receives encrypted P-code military signals, is waterproof, weighs three pounds and is far more robust than any modern mobile phone. But many of those mobile phones today have A-GPS, which can compute a position within a second and acquire satellites at signal levels 100 times lower than the PLGR, and adds less than $5 to the cost of the phone.  Nowadays, GPS enabled phones are widely available and are viable options for a dedicated handheld or an in-car GPS. These requirements are what drove the development of A-GPS. Assisted GPS (A-GPS) improves on standard GPS performance by providing information, through an alternative communication channel, that the GPS receiver would ordinarily have received from the satellites themselves.