Satellite Telemetry

sat telemetry is data transmission.

gps is acquiring information on your position by careful measurements of satellite signals, phase, timing etc.

http://www.google.ca/search?hl=en&q=%22global+positioning+system%22&btnG=Google+Search

glonass is the USSR similar system

http://www.google.ca/search?hl=en&q=glonass&btnG=Google+Search

among these will be some dateiled explanations

Telemetry is usually information about a vehicle itself, i.e. battery voltage, speed, etc. Some high-end race car teams have telemetry units aboard the cars that send information back to the pits - vehicle speed, engine rpm's, fuel status, etc. that allows the crew chief to make decisions regarding when to pit the car for fuel, etc. They can also analyze engine performance - the Honda team was thought to use the telemetry during the race by sending back to the home office in Japan and run it through the big computers during the race; they were usually after performance data, which was fed back into engine design, eventually making it's way into production cars. Good for autos, not much use in detirmining your position. Satellites send telemetry back to their control station(s) to let controllers know things like battery voltage, circuit temperatures, etc. - bird health stuff. Vehicle like the space shuttle orbiter send telemetry back such as location, speed, direction, thrust being produced, etc., as well as voice and other data being sent as well. The SRB's even send their own telemetry back as well - speed, direction, location, etc. - that's how NASA knew after the Challenger broke apart that the SRB's were still flying full thrust and where they were then headed, which led to the decision to self-destruct them to prevent futher catastrophe from their impact. So telemetry, though usually associated with satellites and space vehicles, can be used in any number of applications, most of them right here on the earth.

Like aurizon stated above, GPS is a constellation of satellites that transmit signals used by equipment to fix it's position by analyzing those signals - quite a bit of math going on here, especially with the 12 channel receivers picking up a lot of signals - more channels usually equals more accuracy, and at least more speed.

Hope this helps.