Method and apparatus for determining propagation delays for use in wide area networks
View Patent ↗A system and method for determining a signal propagation delay between a transmitter and a receiver, and for adjusting a transmission time based on the propagation delay. A central station inserts a marker into a transmitted signal at a time corresponding to a received timing signal. The MCT receives the signal from the central station and determines a time difference between receipt of the marker and the detection of the time interval event. A transmission by the MCT is adjusted by an amount of time proportional to the time difference.
1. A method for determining a propagation delay between a mobile communications terminal (MCT) and a network management center (NMC), comprising:
receiving a response from said NMC to a request by said MCT to transmit a message to said NMC at an expected time;
receiving a first signal from said NMC;
detecting an inverted pilot signal, which is inverted relative to a GPS signal, sent from said NMC, over a time interval during which said GPS timing signal is commonly received by said MCT and said NMC;
determining a signal propagation delay offset from a time difference between receipt of the commonly received GPS timing signal and receipt of the inverted pilot signal; and
transmitting said message from said MCT to said NMC at a time adjusted for said propagation delay offset to ensure receipt by said NMC at said expected time.
2. The method of claim 1 wherein said GPS timing signal comprises a one pulse-per-second signal from a global positioning satellite timing signal.
3. The method of claim 1 , wherein the inverted pilot signal is inserted into the first signal at a time relative to the time interval.
4. The method of claim 1 , wherein determining the signal propagation delay offset comprises:
starting a counter upon detection of the GPS timing signal;
stopping the counter upon receipt of the inverted pilot signal; and
determining the signal propagation delay based on a count of the counter when stopped.
5. A mobile communications terminal (MCT) operable to adjust the transmission time of a signal, comprising:
a receiver operable to receive a GPS timing signal commonly received by said MCT and a network management center (NMC), said receiver being further operable to receive a pilot signal from said NMC and an inverted pilot signal dispatched from said NMC at the time of the commonly received GPS timing signal; and
a central processing unit (CPU) operable to determine a signal propagation delay offset from a time difference between receipt of the commonly received GPS timing signal and receipt of the inverted pilot signal.
6. The MCT of claim 5 further comprising:
means for adjusting a transmission time of a second signal based on said signal propagation delay offset.
7. The MCT of claim 5 wherein the GPS timing signal comprises a one pulse-per-second signal from a global positioning satellite timing signal.
8. The MCT of claim 5 , wherein the inverted pilot signal is inserted into the first signal at a time relative to the time interval event.
9. The MCT of claim 5 , further including:
a counter, said counter being operable to start counting upon detection by said MCT of the GPS timing signal and being operable to stop counting upon receipt by said MCT of the inverted pilot signal, said CPU being operable to determine said signal propagation delay offset from an elapsed time between detection of said GPS timing signal and said receipt of said inverted pilot signal.