GPS.... Hot, Cold, or Warm Start?

[President Fluid]

I use GPS Viewer and it gives those choices of Hot, Cold, or Warm start.

What is the difference in them?

[raven]

A few years back, I was involved in some development work that involved some GPS work. My memory is a bit fuzzy, but here are the basic principles.

Hot Start - The GPS receiver remembers its last calculated position and which satellites were in view, the almanac used, and the UTC Time. It then performs a reset and attempts to acquire satellites and calculate a new position based upon the previous information. This is the quickest re-acquisition of a GPS lock.

Warm Start - The GPS receiver remembers its last calculated position, almanac used, and knows the UTC Time, but not which satellites were in view. It then performs a reset and attempts to obtain the satellite signals and calculate a new position. The receiver has a general idea of which satellites to look for because it knows its last position and the almanac helps identify which satellites are visible in the sky. This takes longer than a Hot Start but not as long as a Cold Start.

Cold Start - The GPS receiver dumps all information and resets. It then attempts to locate satellites and then calculate a GPS lock. This takes the longest because there is no known information. The GPS receiver has to attempt to lock a satellite signal from all of the satellites, basically like polling, which takes a lot longer than knowing which satellites to look for. This re-acquisition of a GPS lock takes the longest.

While those options appear to be available in the GPS Viewer, I am not sure if you can actually perform those operations. I would have to look into the communications between the GPSone Chip that is embedded in our HTC devices. The GPSone chip is actually calculating the position and provides the information over a serial interface to the software on your device that wants to use the GPS information. What I don't know is if the GPSone Chip accepts commands back over that same serial connection.

Cheers!

[President Fluid]

Ok............ Thanks