What Is GPS Hotfix?by Fred Decker
Portable GPS devices are a boon to travelers, providing a reliable route to their chosen destination and a wealth of information about points along the way. However, the initialization of GPS can be delayed for several minutes while the device locates signals from any available GPS satellites. This can be maddening if you're in a hurry to be on your way, so manufacturers incorporate circuitry -- called "Hotfix" by Garmin -- to speed the process.
Your GPS navigation device uses a set of 24 satellites placed in orbit originally by the U.S. military for its own use. The satellites aren't "geosynchronous," meaning they don't hold a consistent location over one spot on the Earth's surface. Their orbits cover varying portions of the Earth, with several in the sky over any area at a given time. Your portable GPS receiver detects low-powered radio transmissions from these satellites. Each satellite's broadcast signals its own position and movement, so once your GPS locates three satellites it can triangulate your location. With five, it can also work out your elevation and speed.
Garmin equips some devices with Hotfix circuitry and other GPS manufacturers have created similar technology. This technology continues to download data from the satellites long after they've gotten their initial "fix" and triangulated your position. This additional data typically requires at least 30 minutes of operation after the satellites have been acquired. Once the GPS has received this data, it can calculate the positions of those satellites for the next three days. As long as you use your GPS again during that time, it will repeat the process and keep you up-to-date. This can dramatically shorten the time needed to get a fix from the satellites.
It's possible to give your GPS a similar head start through the use of a software utility, such as TomTom's "QuickGPSFix" program. With QuickGPSFix or similar third-party software, you can download current satellite positions and their expected positions for the next week. The data can then be transferred to your GPS by connecting it to your computer through Bluetooth or a USB cable. When you turn on your GPS and leave your home, the device will know where to find the satellites and be able to acquire them in seconds, even if the signal strength is poor.
There are other things you can do to speed your GPS' acquisition of a satellite signal. For starters, give your device the time it needs to get locked onto satellites before you start driving. A GPS that's in motion has more variables to track, and that will slow down the signal acquisition. Finding a location with a clear view of the sky also helps. If you've recently flown somewhere or left your GPS turned off during a long drive, neither Hotfix nor a software utility will help much when you turn it on again. Most GPS devices have a "New Location" feature to manually update your position and help the GPS determine where the satellites are.
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