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Methods for determining a system latency of an audio call path of a voice communications network, and for synchronizing a remote unit ( 108 ) with a reference oscillator of a reference station ( 102 ) involve transmitting a reference signal ( 106 ) over the audio call path from the reference station

Methods for determining a system latency of an audio call path of a voice communications network, and for synchronizing a remote unit ( 108 ) with a reference oscillator of a reference station ( 102 ) involve transmitting a reference signal ( 106 ) over the audio call path from the reference station ( 102 ) to the remote unit ( 108 ), where a reply signal ( 112 ) is generated and transmitted back to the reference station ( 102 ) over the call path after a preselected reply delay interval (t det ). A round-trip time difference (t RT ) is used to determine total system latency, which is then taken into account in synchronizing the remote unit ( 108 ) with the reference oscillator. The reference and reply signals ( 106, 112 ) are generated as audio-frequency signals resembling human voice sounds to avoid destructive attenuation by the voice communications network. One embodiment includes a wireless telephone unit having an on-board SPS receiver. The SPS receiver includes an oscillator that can be synchronized using the method to improve performance of the SPS receiver. Convenient and efficient methods of synchronization and location data reporting within existing wireless communication network infrastructures are disclosed.

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1. In a voice communications network, a method for synchronizing a remote unit with a reference oscillator of a reference station, comprising:establishing an audio call path between the reference station and the remote unit;transmitting an audio-frequency reference signal from the reference station

1. In a voice communications network, a method for synchronizing a remote unit with a reference oscillator of a reference station, comprising:establishing an audio call path between the reference station and the remote unit;transmitting an audio-frequency reference signal from the reference station over the call path, the reference signal being transmitted for a predetermined reference duration;receiving the reference signal at the remote unit;generating an audio-frequency reply signal at the remote unit in response to the reference signal;waiting a preselected reply delay interval beginning at an observed time of receipt of the reference signal;transmitting the reply signal from the remote unit over the call path after waiting the reply delay interval, the reply signal being transmitted for a predetermined reply duration;receiving the reply signal at the reference station;measuring at the reference station a round-trip time difference between the transmission of the reference signal and an observed time of receipt of the reply signal;calculating a total latency based on the round-trip time difference, the reference duration, the reply duration, and the reply delay interval;selecting a synchronization reference time corresponding to a time mark output by the reference oscillator;defining a correction time preceding the synchronization time by one-half the total latency;transmitting a synchronization signal from the reference station over the call path at the correction time;receiving the synchronization signal at the remote unit; andin the remote unit, synchronizing the remote unit with the reference oscillator in response to the synchronization signal. 2. The method of claim 1 in which:the reference signal comprises first and second reference tones separated by a reference pause; andthe reply signal comprises first and second reply tones separated by a reply pause. 3. The method of claim 2 in which the first and second reference tones are of equal duration, the first and second reply tones are of equal duration, and further comprising:at the remote unit, averaging the observed times of receipt of the first and second reference tones and adjusting the observed time of receipt of the reference signal to thereby reduce errors inherent in the transmission and receiving of the reference signal; andat the reference station, averaging the observed times of receipt the first and second reply tones and adjusting the observed time of receipt of the reply signal to thereby reduce errors inherent in the transmission and receiving of the reply signal. 4. In a cellular telephone network, a method of synchronizing a mobile unit with a reference oscillator of a reference station, comprising:establishing an audio call path between the mobile unit and the reference station;transmitting an audio-frequency reference signal from the reference station over the audio call path, the reference signal having a predetermined reference duration;receiving the reference signal at the mobile unit and generating an audio-frequency reply signal in response to the reference signal, the reply signal having a predetermined reply duration;waiting a preselected reply delay interval beginning in response to receipt of the reference signal;transmitting the reply signal from the mobile unit over the call path after waiting the reply delay interval;receiving the reply signal at the reference station;measuring at the reference station a round-trip time difference between the transmission of the reference signal and the receipt of the reply signal;calculating a total latency based upon the round-trip time difference, the reference duration, the reply duration, and the reply delay interval;selecting a synchronization reference time corresponding to a to a time mark output by the reference oscillator;defining a correction time preceding the synchronization reference time by one-half the total latency;transmitting a synchronization signal from the reference station over the call path at the correction time;receiving the synchronization signal at the mobile unit; andin the mobile unit, synchronizing the mobile unit with the reference oscillator in response to the synchronization signal. 5. The method of claim 4 in which the reference and reply signals each includes a substantially Gaussian pulse. 6. The method of claim 5 in which each Gaussian pulse is characterized by a standard deviation of between 100 and 330 microseconds. 7. The method of claim 4 in which the reference and reply signals each has an amplitude of between −4 dBm and −10 dBm. 8. The method of claim 4 in which transmitting the reference signal includes repeating transmission of the reference signal until the reply signal is received by the reference station. 9. The method of claim 8 in which:the call path has an anticipated maximum one-way propagation latency; andrepeating the transmission of the reference signal includes repeating at repeat intervals that are greater than the anticipated maximum one-way propagation latency. 10. The method of claim 4 in which the reference and reply signals each includes a pulse train consisting of a series of audio-frequency pulses. 11. The method of claim 10 in which the audio-frequency pulses are irregularly spaced. 12. The method of claim 10 in which the audio-frequency pulses are modulated onto a voice frequency carrier signal. 13. The method of claim 10 in which the audio-frequency pulses are approximately 11.4 milliseconds in duration with a 3 dB bandwidth of 400 Hz and a roll-off of 1.0. 14. The method of claim 10 in which the pulse train has a total pulse train duration of between 143 milliseconds and 189 milliseconds. 15. In a voice communications network, a method for synchronizing a remote unit with a reference oscillator of a reference station, comprising:establishing an audio call path between the reference station and the remote unit;transmitting an audio-frequency reference signal from the reference station over the call path, the reference signal emulating human voice sounds to thereby avoid destructive attenuation of the reference signal by the voice communications network, the reference signal being transmitted for a predetermined reference duration;receiving the reference signal at the remote unit;generating an reply signal at the remote unit in response to the reference signal, the reply signal emulating human voice sounds to thereby avoid destructive attenuation of the reply signal by the voice communications network;waiting a preselected reply delay interval beginning in response to receipt of the reference signal;transmitting the reply signal from the remote unit over the call path after waiting the reply delay interval, the reply signal being transmitted for a predetermined reply duration;receiving the reply signal at the reference station;measuring at the reference station a round-trip time difference between the transmission of the reference signal and the receipt of the reply signal;calculating a total latency based on the round-trip time difference, the reference duration, the reply duration, and the reply delay interval;calculating a correction interval equal to one-half the total latency;transmitting a synchronization signal from the reference station over the call path, the synchronization signal representative of the correction interval;receiving the synchronization signal at the remote unit; andin the remote unit, synchronizing the remote unit with the reference oscillator in response to the synchronization signal. 16. The method of claim 15 in which the reference signal and the reply signal each includes a substantially Gaussian pulse characterized by a standard deviation (σ) of between 100 microseconds and 330 microseconds. 17. The method of claim 15 in which the reference and reply signals each has an amplitude of between −4 dBm and −10 dBm. 18. The method of claim 15, further comprising:generating an audio-frequency synchro nization reference signal corresponding to a reference time mark output by the reference oscillator and occurring after receipt of the reply signal;transmitting the audio-frequency synchronization reference signal from the reference station over the call path upon the output of the reference time mark. 19. The method of claim 15, further comprising determining a correction time preceding a synchronization time of the reference oscillator, and in which transmitting the synchronization signal includes an transmitting an audio-frequency synchronization correction signal from the reference station over the call path at the synchronization time. 20. The method of claim 15, further comprising determining a correction time preceding a reference time mark output from the reference oscillator, the correction time preceding the reference time mark by an amount equal to the correction interval; andin which the synchronization signal is representative of the correction time. 21. In a telephone network including a reference station positioned at a known terrestrial location and a mobile cellular telephone unit in communication with the reference station, an improved method of synchronizing a mobile oscillator of the mobile cellular telephone unit with an SPS oscillator of an SPS satellite system, comprising:synchronizing a reference oscillator of the reference station with the SPS oscillator;establishing an audio call path between the reference station and the mobile cellular telephone unit;transmitting from the reference station an audio-frequency reference signal over the call path, the reference signal being transmitted for a predetermined reference duration;receiving the reference signal at the mobile cellular telephone unit;generating at the mobile cellular telephone unit in response to the reference signal, an audio-frequency reply signal;transmitting from the mobile cellular telephone unit the reply signal over the call path at a reply time, the reply time occurring after a predetermined reply delay interval following receipt of the reference signal by the mobile cellular telephone unit, the reply signal being transmitted for a predetermined reply duration;receiving the reply signal at the reference station;measuring at the reference station a round-trip time difference between the transmission of the reference signal and the receipt of the reply signal;calculating a total latency based on the round-trip time difference, the reference duration, the reply duration, and the reply delay interval;transmitting from the reference station over the call path a synchronization signal at a correction time, the correction time being subsequent to the synchronization of the reference oscillator with the SPS oscillator and preceding a synchronization reference time by a correction interval, the correction interval equal to one-half the total latency;receiving the synchronization signal at the mobile unit; andadjusting the mobile oscillator in response to the synchronization signal and thereby synchronizing the mobile oscillator with the SPS oscillator. 22. A method of synchronizing a mobile wireless communications device having a local clock, comprising the steps of:establishing a voice call connection between the mobile device and the reference station;determining a specific time correction factor as between the reference station and the mobile device over the established voice call connection;in the reference station, maintaining a current Satellite Positioning System (SPS) time and generating a periodic SPS time mark signal associated with the current SPS time;transmitting data reflecting the current SPS time from the reference station to the mobile device over the established voice call connection encoded as audio frequency signals;forming a delayed SPS time mark by delaying the periodic SPS time mark by the time correction factor;transmitting the delayed SPS time mark from the reference station to the mobile device; andin the mobile device, synchronizing the local clock to the current SPS time responsive to the delayed SPS time mark thereby synchronizing the local clock to the SPS time maintained by the reference station. 23. The method of claim 22 wherein said determining a specific time correction factor includes determining a total latency time for transmission of signals between the reference station and the mobile device over the established voice call connection. 24. The method of claim 22 wherein determining the total latency time includes:transmitting an audio frequency reference signal from the reference station to the mobile device over the established voice call connection;transmitting a reply signal from the mobile device to the reference station over the established voice call connection in response to the reference signal; andmeasuring a latency time between said transmission of the reference signal and receipt of the reply signal at the reference station. 25. The method of claim 23 wherein the time correction factor is calculated as one-half of the total latency time. 26. A method of synchronizing a mobile wireless communications device having a local clock, comprising the steps of:establishing a voice call connection between the mobile device and a reference station;determining a specific time correction factor as between the reference station and the mobile device over the established voice call connection;in the reference station, maintaining a current Satellite Positioning System (SPS) time and generating a periodic SPS time mark signal associated with the current SPS time;transmitting data reflecting the current SPS time from the reference station to the mobile device over the established voice call connection encoded as audio frequency signals;transmitting the SPS time mark signal from the reference station to the mobile device;in the mobile device, forming a delayed SPS time mark signal by delaying the received SPS time mark by the time correction factor; and then synchronizing the local clock to the current SPS time responsive to the delayed SPS time mark thereby synchronizing the local clock to the SPS time maintained by the reference station. 27. The method of claim 26 wherein said determining a specific time correction factor includes determining a total latency time for round trip transmission of signals between the reference station and the mobile device over the established voice call connection. 28. The method of claim 27 wherein determining the total latency time includes:transmitting an audio frequency reference signal from the reference station to the mobile device over the established voice call connection;transmitting a reply signal from the mobile device to the reference station over the established voice call connection in response to the reference signal; andmeasuring a latency time between said transmission of the reference signal and receipt of the reply signal at the reference station. 29. A method according to claim 27 wherein the time correction factor is calculated as one-half of the total latency time. 30. The method of claim 26 wherein said determining a specific time correction factor includes:transmitting an audio frequency reference signal from the mobile device to the reference station over the established voice call connection;transmitting a reply signal from the reference station to the mobile device over the established voice call connection in response to the reference signal; andmeasuring a latency time between said transmission of the reference signal and receipt of the reply signal at the mobile station. 31. A satellite positioning system (SPS)-enabled mobile unit having a local SPS time clock and configured for assisted synchronization, the mobile unit comprising:an SPS antenna for receiving SPS signals from orbiting SPS satellites;an SPS receiver coupled to the SPS antenna for receiving the SPS signals to form SPS raw data and for maintaining the local SPS time clock;a microprocessor coupled to the SPS r eceiver and including software for processing the raw SPS data to form location data and for synchronizing the local SPS time clock;a multi-frequency controller coupled to the microprocessor for generating multi-frequency audio tones to encode the location data and for decoding received multi-frequency audio tones to form synchronization data;a wireless communications transceiver operable for sending and receiving voice communications over a call path of a wireless communications network, the wireless communications transceiver including an audio port coupled to the multi-frequency controller for sending the encoded location data over the call path and for receiving and decoding synchronization data received as audio-frequency tones over the call path;the software for synchronizing the local SPS time clock operable to adjust the local SPS time clock in response to the synchronization data received by the wireless communications transceiver over the call path and decoded by the multi-frequency controller. 32. The mobile unit of claim 31 wherein the multi-frequency controller is implemented in software executable on the microprocessor. 33. The mobile unit of claim 31 wherein the software for synchronizing the local SPS time clock is responsive to synchronization data received over the call path that includes a correction time for synchronizing the SPS local time clock, the correction time corresponding to a difference between the local SPS time and an actual SPS time as provided by the orbiting SPS satellites.