Various GPS launch options affect just how much time is normally needed to provide position.
GPS Hot Start is when the GPS enabled smartphone retains its last calculated location, the satellites that were in range at the time, together with the almanac information in memory, and tries to find the same satellites and calculate a brand new location based upon the previous data. This is generally the quickest GPS lock but Hot Start only works if the phone is generally in the same location as when the GPS was last turned off.
GPS Warm Start describes when the GPS enabled device recalls its last known position, and almanac used, but not which satellites were in range. It performs a reset and attempts to find satellite signals and calculates the latest position. The GPS receiver narrows the choice of which satellites tolook for since it saved its last known position and the almanac data helps determine which satellites are in range. The Warm Start will take longer than the Hot Start although not as much as a Cold Start.
With GPS Cold Start, the device deletes all the previous data, and attempts to locate satellites and obtain a GPS lock. This usually takes the longest since there is no known reference information. The GPS enabled handset receiver must attempt to lock onto a satellite transmission from any accessible satellites.
As a way to get improved GPS lock times (the period of time it takes in order to lock onto a GPS Satellite signal) cellular manufacturers and system providers developed Assisted GPS technology. This downloads the ephemeris helping triangulate the device basic position. GPS Receivers will get a faster lock at the expense of a few kilobytes of data transmission.
Assisted GPS, also referred to as A-GPS or AGPS, increases the performance of normal GPS in smartphones connected to the cell network. In the United States Sprint, Nextel, Verizon Wireless, and Alltel all use Assisted GPS. This is a means of utilizing the cell network to speed up finding of GPS satellites. A-GPS improves location tracking functions of cell phones (and other connected devices) in a couple of ways:
The first method is by helping to acquire a faster “time to first fix” (TTFF). AGPS gets and stores data about the location of satellites via the cellular network and so the position details does not require to be downloaded via the satellite.
A subsequent approach is by assisting position cell phones when GPS signals are weak or not available. Since GPS satellite signals may be interfered with by tall structures, and do not penetrate building interiors well A-GPS utilizes proximity to cellular towers to estimate location when GPS signals are not available.