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GPS is fully passive. It operates by generating a CDMA PN sequence and adding it to signal below the noise level. It takes a fair amount of time for first fix as the bit pattern must be shifted repeatedly to make the signal copyable. Once achieved, a 50 characters per second stream is picked up with the initial almanac. That first acquisition plus a time stamp allows the received to guess the other PN sequences that should be visible. The time referenced is locked to the first satellite, then at least two more must be picked up. A precise time delay between the satellite and the receiver is then measureable. The "ephemeris" data is downloaded with fine corrections in satellite orbital details. With the orbital details in hand, time synchronization and time offsets to 3 or more satellites, a position is space can be calculated. That data is then correlated with an onboard map t produce something usable to the human operator.

Future fixes happen more quickly with the almanac, rough current location and current time already on board, the receiver knows exactly which "birds" should be visible. It often has 12 concurrent receivers on board. Each one is handed a PN sequence matching a desired satellite. The lockup can be as quick as 15 seconds on a "warm start".

Cell phone get a time stamp off the tower. You get that running start of general location and time. Some can even pass the almanac from the tower. CDMA phones have AGPS. They can leverage the known GPS coordinates of a tower to get a jump start on the positioning calculations or even ask for them to be done as "a service" using precise time offsets to the phone.

Back to the original point. GPS can be done purely passively. No transmissions required. If you have a cell phone, you can leverage the connectivity to save the lag time of the typical GPS cold start. GSM phones can perform a high resolution "ping" using 3 towers to get a pretty decent fix on your with the time offsets. Much of this technology exists per the E911 mandate. It is required to locate any cell phone within 100 meters to support law enforcement 911 services.

Stealing the cell phone was the criminal's mistake.

Actually I believe it is. I believe that it needs to be able to send a signal to the satellites in order for the whole system to figure out where you are.

That would be a monumental scalability problem. Given the rapid expansion of GPS usage, you'd basically have to launch Google into orbit, if the system required client-server interaction with the satellites.

GPS is way cooler than that. GPS is receive-only. It listens to the satellites as they transmit exact times and positions, and it calculates its position by correlating the readings from a minimum of four satellites. Four equations in four unknowns: latitude, longitude, elevation, and time. Actually, it could do with only three satellites, but the fourth is necessary if the GPS receiver lacks its own synchronized, miniaturized, dirt-cheap atomic clock (LOL) — it needs to work out its own time to the nanosecond in order for the concept to work. Additional satellites beyond the minimum of four add to accuracy.