Posted Aug 6, 2009 12:11:52 PM by DecisionPoint Team & filed under

Standalone GPS is also known as autonomous GPS or native GPS. Time To First Fix (TTFF) is the time to pinpoint your present location. Initial TTFF is often referred to as “cold start”.

As its name implies, standalone GPS relies solely on the GPS satellites and a clear, unobstructed view of the skies to determine your present location.

satellite-gps1While standalone GPS can acquire your location without cell network coverage, TTFF can take anywhere from 30 seconds to a couple of minutes because it needs to search for satellites. Also, standalone GPS has difficulty providing reliable positions in poor signal conditions such as when the receiver is surrounded by tall buildings or trees. Standalone GPS also will not generally work inside buildings. However, standalone GPS is usually more accurate than A-GPS and there are no network-dependent downsides.

Assisted GPS (A-GPS) is intended to provide faster Time To First Fix and signal acquisition under poor signal conditions. A-GPS does not “triangulate” using cellular networks as is sometimes thought. Instead, A-GPS relies on projection of satellite orbital path data over a period of 2-10 days. A-GPS cell phones use a data connection to contact an assistance server and download A-GPS data which enables the device to quickly locate GPS satellites. Typically, an A-GPS device downloads a new “GPS Quick Connect File” every couple of days. When the file expires it takes about 2 minutes to get a fix on the satellites instead of the typical 20 seconds, but it still works.

It’s important to understand that Assisted GPS is a GPS with a full GPS, SIRF 3 or Globallocate chipset. The “Assisted” component is an additional or complementary function, rather than an enabling one. While some A-GPS solutions do not have the option of falling back to standalone or autonomous GPS, most systems will run fine and simply take longer for Time To First Fix.

Benefits of A-GPS are:

  • Faster location acquisition
  • Less device processing power required
  • Extends battery life
  • Location acquisition possible in non-optimal environments and indoors

All GPS solutions which DecisionPoint offer can run on either standalone GPS or A-GPS devices. Keep in mind though that Location-Based Services (GPS Tracking) solutions do require a data plan to transmit data real-time including current location, geofencing arrivals/departures and speed alerts. However, up to 3 weeks of historical data (breadcrumbing, geofencing and speed alerts) can be stored on some devices and transmitted when the unit is again within coverage.

Contact DecisionPoint Systems, Inc. to help you successfully navigate this complex topic and determine the best solution for you. (Admit it—don’t you like the way I worked the word ‘navigate’ into a sentence about GPS?)


Want to leave a comment?