HK1042389A1

HK1042389A1 - In-band signalling for synchronization in a voice communication network

Info

Publication number: HK1042389A1
Application number: HK02104123.0A
Authority: HK
Inventors: 丹‧A‧普雷斯顿; 丹‧A‧普雷斯頓; 约瑟夫‧普雷斯顿; 罗德‧L‧普罗克特; 約瑟夫‧普雷斯頓; 羅德‧L‧普羅克特
Original assignee: 爱尔比奎特公司; 愛爾比奎特公司
Priority date: 1999-01-15
Filing date: 2000-01-18
Publication date: 2002-08-09
Also published as: CA2360973A1; AU761918B2; BR0007520A; WO2001003344A1; EP1145468A1; AU2509600A; JP4482258B2; TR200102405T2; CN1340254A; MXPA01007086A; JP2003503942A

Abstract

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 (tdel). A round-trip time difference (tRT) 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.

Description

In-band signaling to achieve synchronization within a voice communication network

Technical Field

The present invention relates to an in-band signaling method for measuring system latency during wireless communication and during wired communication, and more particularly, to using a latency measurement procedure for time synchronization and a synchronization error measurement procedure between a reference clock and a remote clock during communication through a wireless voice communication network and/or a wired voice communication network.

Background

Various signaling methods are known to synchronize the slave oscillator with the remote master oscillator. One known approach is to employ SPS signals transmitted from the master controlled oscillator of an artificial earth satellite of a satellite positioning system, such as the Global Positioning System (GPS) or GLONASS. In a normal SPS signal reception mode, referred to as "locked", the slave oscillator is synchronized with the SPS master oscillator. In a mobile unit that includes an SPS position receiver, the amount of synchronization error between the SPS master oscillator and the slave oscillator of the SPS position receiver may affect the ability of the SPS position receiver to accurately determine its position from SPS signals using satellite ephemeris data. For example, in order to obtain position coordinates within 30 seconds after a cold start, the synchronization error between the slave oscillator of the GPS receiver and the GPS satellite master oscillator must be less than about +/-500 microseconds (μ S). In the locked mode, the slave oscillator is typically synchronized to the GPS satellite master oscillator within +/-10 μ S. When the SPS signals are invalid, for example because the SPS satellites are not visible, or when the mobile unit is not acquiring the SPS satellite signals, the mobile unit must be resynchronized because the slave oscillator can drift over time. Resynchronization takes a significant amount of time if SPS signals must be used. Achieving SPS synchronization after a cold start is also time consuming. It is not uncommon for the synchronization processing time to reach one minute or more after a cold start.

Other types of electronic equipment, instruments, control systems and ranging devices, such as computer networking equipment, also rely on precisely synchronized internal clocks. U.S. patent No. 5,510,797 to Abraham et al describes a method of synchronizing their internal clocks using an SPS receiver in conjunction with a computer and a time-controlled instrument.

Us patent 4,368,987 to Waters describes a satellite synchronization method in which a master clock station transmits a master pulse to a slave station where the slave station retransmits a slave pulse having a conjugate phase to the received master pulse for reception by the master station. The time phase difference between the master clock and the slave clock is calculated by measuring the time difference between the master pulse and the received slave pulse at the master station. Then, clock synchronization is achieved using the time phase difference. Waters requires cooperation between a satellite-based master and a satellite-based slave station in order to determine phase differences and to achieve clock synchronization. Thus, the method described by Waters does not replace SPS-activated resynchronization of mobile units. SPS satellites originally developed for military purposes are not able to retransmit slave pulses from master pulses received from mobile units. In contrast, SPS satellites also do not receive conjugate slave pulses generated by the mobile unit or calculate phase time differences.

For calls placed from wireline telephones, Automatic Number Identification (ANI) services allow call receiving stations, such as Public Safety Answering Points (PSAPs), to quickly check their databases for the name and address of the calling subscriber (the registered telephone owner). In a wireless communication network, mobility of wireless communication devices may eliminate the survivability of such checking methods. A wireless mobile telephone unit incorporating an SPS receiver may be considered as a method of generating position data for subsequent transmission to a call receiving station. Theoretically, generating and transmitting location data in this manner may be particularly useful for locating wireless calling subscribers who are 911 reporting an emergency, but who are unable to provide location information verbally to a PSAP operator.

While SPS enabled wireless telephones have the ability to accurately determine and transmit position data, various objective realities prevent timely, efficient generation of position data and timely, efficient transmission of position data to call receiving stations. For example, an SPS receiver of an SPS enabled wireless telephone needs to synchronize SPS time before generating available position data. In an emergency situation where a call is made to a PSAP, the time required to synchronize the SPS receiver with the SPS satellite signals may sacrifice life.

Fig. 1 illustrates a schematic diagram of a prior art voice communication network 10, the voice communication network 10 including a wireless communication network 12 connected to a wired communication network (POTS network) 14. Referring to fig. 1, the wireless communication network 12 includes one or more cellular base stations 16, each cellular base station 16 having an associated base station antenna 18 and a mobile switching center 20. A mobile switching center 20 connects the cellular base station 16 to the POTS network 14 to allow a wired caller 22, such as a PSAP, to communicate with a mobile unit 24 of the wireless communication network 12. In operation, signals transmitted by mobile unit 24 are received by cellular base station 16 via transmission channel 26, and signals received by mobile unit 24 are signals transmitted by cellular base station 16 via transmission channel 26. These transmission channels 26 include: a voice channel 27 (also referred to as a call path, a voice call connection, an audio call path, an audio traffic channel, and a traffic channel) for transmitting radio frequency signals representing voice; and a control channel 28 (also referred to as an overhead channel and a non-paging channel) for transmitting paging initiation signals and control signals. In a digital wireless communication network, the transmission over the control channel 28 comprises packetized digital data packets. The type of control channel communication protocol used by the wireless communication network determines the protocol of the control channel 28 and the type of data carried by the control channel 28. Because each type of wireless network uses its own protocol, the control signals must be decoded at the cellular base station 16.

Further limitations inherent in the prior art will become apparent from a study of the summary of the invention and the detailed description of the preferred embodiments.

Summary of the invention

Both wireline and wireless communication systems have some system latency, typically less than 50 milliseconds (ms), due to the propagation and processing of signals transmitted within the call path. In wireless communication networks, differences in air interface protocols, base stations, handset manufacturers, and transmission distances make system latency variable.

The present invention provides a method of determining system latency of a voice communication network for signals transmitted between a reference station and a remote unit over an audio call path of the voice communication network. System latency needs to be taken into account during synchronization of the remote unit with the reference oscillator of the reference station. System latency can be measured using a signaling sequence that includes a reference signal transmitted over an audio call path from a reference station to a remote unit that generates and transmits an answer signal back to the reference station over the call path after a preselected answer delay interval. The reference signal and the reply signal are transmitted during a predetermined reference duration and a predetermined reply duration, respectively, determined by signal attenuation characteristics of the voice communication network. The reply delay interval begins when the reference signal is received by the remote unit and must be preselected so that the remote unit has sufficient time to process the reference signal and generate the reply signal. Measurements are made at the reference station to determine the round trip time difference between the transmission of the reference signal and the reception of the reply signal. The sum of the reference duration, the response duration and the response delay interval is subtracted from the round trip time difference to obtain the total latency.

In accordance with another aspect of the invention, the correction interval is calculated as half of the total wait time and a synchronization signal representing the correction interval is transmitted from the reference station over the call path for receipt by the remote unit. In response to the synchronization signal, the remote unit synchronizes itself to the reference oscillator. There are several different ways in which synchronization can be effectively achieved, for example: by storing the synchronization signal at the remote unit and using it as a parameter thereafter for calculating the synchronization time, or by adjusting or restarting the remote oscillator after receiving the synchronization mark of the synchronization signal.

According to a further aspect of the invention, the remote unit is a mobile unit that includes an SPS receiver. In this regard, a remote oscillator is connected to or is part of the SPS receiver, and the SPS receiver uses the remote oscillator in conjunction with SPS satellite signals to determine the position of the mobile unit. The remote oscillator may be synchronized using any of the synchronization techniques described above or by adjusting the algorithm used by the SPS receiver to calculate the location of the remote unit based on the synchronization signals.

According to yet another aspect of the invention, the reference signal, the reply signal, and the synchronization signal are all audio signals adapted to freely pass through a voice communication network. It is necessary to transmit these audio signals over the voice path of advanced communication networks that employ compression protocols and/or spread spectrum techniques to maximize call traffic within a limited radio frequency bandwidth. Protocols used in advanced communication networks include, for example, Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), global system for mobile communications (GSM), and the like. The reference signal, the response signal, and the synchronization signal can also be freely transmitted through the analog wireless network. These audio signals are specially configured to simulate certain characteristics of human speech, such as: frequency, amplitude and duration. By generating signals that simulate the voice sounds of a human, the present invention can avoid these signals being corrupted by a voice communication network.

According to yet another aspect of the invention, the signals are audio signals including one or more audio tones, multi-frequency tones, or gaussian pulses generated by a multi-frequency controller. The gaussian pulse is characterized by an amplitude of between 3 σ (standard deviation x 3), -4dBm and-10 dBm between about 0.3ms and 1ms to avoid destructive attenuation by voice communication networks. The duration of a single tone or multi-tone is between about 5ms and 50ms, and its frequency is in the range of about 300Hz to 3000 Hz. In methods that use multiple frequency tones or pulses for each signal, the time of receipt of a tone or pulse (of a particular signal) may be averaged to improve the accuracy of the latency measurement process and the synchronization process. These signals may also include bursts generated by juxtaposing a plurality of tones or pulses spaced at regular and irregular intervals. The irregular spacing of the tones or pulses helps to achieve accurate correlation of the reply signal with the reference signal at the reference station to calculate the total round trip time difference. Using these techniques, the remote unit can be synchronized to the reference oscillator within a +/-500 μ s error range. In an SPS-activated remote unit, the time it takes for an SPS receiver to acquire an SPS lock may be significantly reduced using the method of the present invention.

In accordance with yet another aspect of the invention, a remote unit that generates and transmits a reference pulse initiates a signaling sequence, the receipt of which prompts the reference station to reply with a reply pulse after a reply delay interval. The latency calculation process is then completed at the remote unit. The synchronization process of the remote unit also requires that the remote unit receive the synchronization signal transmitted by the reference station when the reference oscillator outputs the time stamp.

The invention has particular advantage in the context of a cellular telephone network in which the remote unit comprises a wireless communication device such as a cellular telephone. Unlike known wireless data communication devices that transmit data and synchronization signals over a control channel or "overhead" channel of a communication network, the present invention does not require the installation of specialized equipment or software at the base station location of the wireless network to process the reference, reply and synchronization signals. The invention facilitates cost effective implementation by avoiding transmission over control channels and by avoiding adjustments to existing wireless telephone network infrastructure and wired telephone network infrastructure (POTS). In contrast, the operation of the present invention is transparent to existing facilities. The "in-band" signal within the voice call path may be received anywhere in the wireless or wireline network, such as at a location service controller or PSAP that is also used as a reference station. The present invention also has advantages over prior art wireless modem devices that fully occupy the voice call path during data transfer by switching the wireless communication device to data mode. By maintaining a voice call path available to a wireless telephone user during latency measurements, synchronization, and position data transfer, the present invention substantially facilitates parallel voice communications between the wireless user and a caller.

Many aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, which proceeds with reference to the accompanying drawings.

Brief description of the drawings

FIG. 1 is a schematic diagram of a prior art wireless communication network showing portions of the wireless communication network and its connections to a wired communication network;

FIG. 2 shows a schematic diagram of a mobile unit including an SPS receiver communicating with a caller over a wireless communication network for implementing a synchronization protocol in accordance with the invention;

FIG. 3 shows a schematic diagram of a signal transmission sequence according to the present invention;

FIG. 4 shows a timing diagram illustrating the timing of the reference signal, the reply signal and the synchronization signal and the individual signal elements of the signaling sequence shown in FIG. 3;

FIG. 5A is a schematic diagram of a first alternate embodiment audio signal including a first reference tone and a second reference tone;

FIG. 5B is a schematic diagram of an audio signal of a second alternative embodiment including Gaussian pulses;

FIG. 5C shows a schematic representation of a third embodiment audio signal comprising a reference burst overlapping with an observed response burst; and

fig. 6 shows a schematic diagram of a mobile unit including an SPS receiver and a multi-frequency controller implementing the present invention.

Description of The Preferred Embodiment

Fig. 2 shows a schematic diagram of a voice communication network 30, the voice communication network 30 comprising an SPS active mobile unit 40 for implementing a first preferred embodiment of the present invention. Referring to fig. 2, the voice communication network 30 includes a wireless communication network 44 connected to a public switched telephone network or ("POTS") 48. Wireless communication network 44 includes base station 52, and base station 52 transmits radio frequency signals 56 to mobile unit 40 and receives radio frequency signals 56 transmitted by mobile unit 40. The radio frequency signals 56 include a voice channel signal 58 for transmitting audio and a control channel signal 60 for transmitting control commands and digital data. The mobile switching center 64 connects the wireless communication network 44 to POTS 48. Mobile unit 40 is preferably a cellular telephone handset but may be any type of wireless communication device that can transmit over voice channel 58. The mobile unit 40 includes a local oscillator (also referred to as a "mobile oscillator" or "remote oscillator") and an SPS receiver 66, the SPS receiver 66 being operative to receive SPS signals 70 broadcast by SPS satellites 72 in earth orbit and to calculate a position of the mobile unit based on the SPS signals 70. During normal operation, SPS receiver 66 achieves a "lock on" with SPS signal 70 to synchronize the local oscillator within a range of +/-10 microseconds (μ s) of error. However, if SPS signal 70 is not available or SPS signal is not acquired by SPS receiver 66, the local oscillator does not maintain the correct SPS time because the local oscillator may drift. According to the present invention, mobile unit 40 may automatically initiate a SPS oscillator resynchronization procedure, if desired, or during the receipt or next telephone call by mobile unit 40.

To reduce the time required to resynchronize the local oscillator to the SPS timing, the local oscillator may be synchronized to a reference oscillator located at a known ground location. This resynchronization process is referred to as a process that causes SPS receiver 66 to generate a "seed" because it results in a wider tolerance than synchronization that occurs during an SPS lock. Seed processor 80 communicates with a reference SPS receiver 82 and a reference oscillator that may be integrated with SPS receiver 82. The seed processor 80 may be connected to the wireless communication switch 64 or the calling device 86 of the POTS48, or both. Once an audio call path is established between seed processor 80 and mobile unit 40, seed processor 80 initiates a signaling sequence 100 (shown in fig. 3) to determine system latency and synchronize the local oscillator with the reference oscillator.

Fig. 3 shows a schematic diagram of a signaling sequence 100 for measuring system latency. Referring to fig. 3, a reference station 102, such as a Location Service Controller (LSC)104, transmits a reference signal over the voice channel 58 (shown in fig. 2). At a reference waiting time t₁Thereafter, a remote unit 108, such as a cellular telephone Handset (HS)110, receives the reference signal 106. By sending an acknowledgement signal 112, the remote unit 108 responds to the received reference signal 106 at an acknowledgement latency t₂The reference station 102 then receives the reply signal 112. Reference waiting time t₁And a response latency t₂Both including signal propagation time and the time to process reference signal 106 and reply signal 112 at reference station 102 and remote unit 108, respectively. The time elapsed between the transmission of reference signal 106 and the receipt of reply signal 112 is measured at reference station 102 to determine the round trip delay t_RT. If the reference waiting time t₁And a response waiting time t₂And if the two are the same, the system is considered to be symmetrical. For illustrative purposes, FIG. 3 shows exaggerated asymmetry. However, empirical measurements made for CDMA, TDMA, GSM, and analog wireless telephone systems confirm that the POTS network 48 in conjunction with the wireless communication network 44 (shown in FIG. 2) is symmetric within acceptable tolerances for in-band signaling with time synchronization within +/-500 μ s of error. Since the wireless communication network and the POTS communication network are substantially symmetrical, the one-way latency can be estimated to be half the round-trip delay, 1/2t_RT。

Fig. 4 shows a timing diagram illustrating the timing of the signaling sequence 100 and the various signal elements. Referring to FIG. 4, the signals of the reference station 102 are shown in the upper portion of the timing diagram and the signals of the remote unit 108 are shown in the lower portion. The transmitted signal is shown in solid lines and the received signal is shown in dashed lines. Fig. 4 shows the signaling sequence 100 being activated by the reference station 102, but may also be at the remote unit in alternate embodiments (not shown)108 are activated. To begin the signaling sequence 100, the reference station 102 transmits a signal having a reference duration t_refThe reference signal 106. For convenience, the reference station 102 transmits the reference signal 106 after the occurrence of a period marker 120 of the reference oscillator having a period P. Passing of the reference waiting time t₁Thereafter, the remote unit 108 receives the reference signal 106. Upon receipt of reference signal 106, remote unit 108 generates an acknowledgement signal 112 and delays the transmission of a preselected acknowledgement delay interval t_delAnd then transmits an acknowledgement signal 112. The response signal 112 has a response time period t_rpAnd at a response waiting time t₂And then received by the reference station 102. At the reference station 102 for the round trip delay t_RTThe measurement is performed. Then, the total waiting time T is calculated_L：

T_L＝t_RT－(t_ref＋t_del＋t_rp) Since the communication network is symmetrical in nature, the one-way latency of the system (estimated at 1/2T) can be reduced_L) As correction interval T_C. Transmitting a representative correction interval T from the reference station 102_CThe synchronization signal 124. Sending a synchronization signal 124 at the next time stamp 120, correcting the interval T_CIs transmitted to the remote unit 108 as data, either as part of the synchronization signal 124 or as part of a separate data signal (not shown). On the other hand, the correction interval T is advanced at the future time marker 120_CThe correction time 126 of (2), the transmission synchronization signal 124'. Remote unit 108 utilizes correction interval T_CAnd/or the time of receipt 127 of synchronization signal 124' to synchronize with the reference oscillator. Those skilled in the art will appreciate that the correction interval T is based on one or more representative correction values received at the remote unit 108_CAnd the reference oscillator's time stamp 120 signal, may be synchronized using various methods. For example (not shown), by forming the delay amount thereof equal to the period P minus the correction interval T_CTo generate the synchronization signal 124.

Voice communication networks, and in particular digital cellular telephone networks, employ signal compression, spread spectrum signal transmission, and other signal processing protocols to maximize call traffic within the signal transmission medium. These signal processing protocols remove signals that are not close to human voice in the call path. To improve the signal transmission process through the voice communication network 30 (shown in fig. 2) and to improve the accuracy of the latency measurement, the reference signal 106, the answer signal 112, and the synchronization signal 124 are all generated as audio signals within the audio call path. Those skilled in the art will recognize that the audio signal is converted multiple times between analog, digital and radio frequency signal forms in the encoding, transmission and decoding processes as typically occurs in the audio call path of a wireless telephone network. The term "audio signal" as used herein describes any signal representing sound transmitted within a call path, regardless of its form. The generated reference signal 106, reply signal 112, and synchronization signal 124 are characterized as being empirically established to pass through the voice communication network 30.

Fig. 5A, 5B, and 5C show a first, second, and third alternative embodiment, respectively, of audio signals 128a, 128B, and 128C that may be used as reference signal 106, reply signal 112, and synchronization signal 124. Referring to fig. 5A, first alternate embodiment audio signal 128a includes a first audio tone 130 and a second audio tone 132 separated in time therefrom by a reference gap 134. The first and second audio sounds 130, 132 are each characterized by a frequency between 300Hz and 3000Hz, a predetermined duration between 5ms and 50ms, and an amplitude between-4 dBm and-10 dBm. The reference gap 134 is characterized by a preselected duration, which may be the same as the duration of the first and second audio sounds 130, 132 for convenience of duration, but may be selected to be longer or shorter. The use of multiple audio tones allows the remote unit 108 and the reference station 102 to average and more accurately determine the time at which the audio signal 128a is received when the first audio tone 130 and the second audio tone 132 are received.

Referring to fig. 5B, second alternate embodiment audio signal 128B comprises an approximate gaussian pulse represented as a function of time (t) of the equation:where A is an amplitude between about-4 dBm and-10 dBm, and σ (standard deviation) is between about 100 μ s and 330 μ s.

Fig. 5C shows a third embodiment of the reference signal 106 'overlapping the corresponding answer signal 112'. Referring to fig. 5C, third alternate embodiment audio signal 128C includes a reference pulse train 140, reference pulse train 140 including 8 approximately gaussian reference pulses 144 separated by predetermined intervals a, b, C, d, e, f and g. Likewise, the reply signal 112' (shown in FIG. 5C as received at the reference station 102) comprises a reply burst comprising 8 approximately Gaussian reply pulses 148 separated by approximately the same interval as the reference pulse 144. In order to determine the round trip delay t_RTThe correlation of the reference station 102 is enhanced, so the intervals a to g are irregular. By using irregular intervals a through g, the correlation can be mathematically achieved even if all of the gaussian pulses 144, 148 are not received. Those skilled in the art will recognize that the width and spacing of the reference pulse 144 may be selected such that only one reply pulse 148 need be received to correlate the bursts and determine the total round trip delay t_RTAlthough this is not as accurate as would be obtained if more pulses were received. Third embodiment audio signal 128c preferably comprises analog filtered bursts modulated onto an audio carrier signal, with pulses 11.4ms long, a 3dB bandwidth of 400Hz, and a roll-off factor of 1.0. The total duration t of the pulse train 140_PTBetween about 143ms and 189 ms. The audio carrier signal may be any signal within the audio spectrum (300Hz to 3000Hz), but is preferably an 1800Hz signal.

Fig. 6 shows a schematic diagram of selected signal processing components of the mobile unit 40. Referring to fig. 6, mobile unit 40 includes an audio bridge 200 coupled to a multi-frequency controller 204 and a modem transceiver 208. The multi-frequency controller 204 and the modem transceiver 208 are connected to the interface processor 212, for example, by an RS-232 connection 214. Interface processor 212 is connected to SPS receiver 216, which includes SPS antenna 220. During signaling sequence 100, multi-frequency controller 204 and modem transceiver 208 actively listen to the call path. Ideally, the functionality of multi-frequency controller 204, modem transceiver 208, interface processor 212, and SPS receiver 216 are integrated into existing components of mobile unit 40, such as CODECs, Digital Signal Processors (DSPs), and ARM microprocessors found in known cellular telephones. In typical applications and testing applications, the multi-frequency controller 204 may be a personal computer that includes a sound card and runs MATLAB software, available from Mathworks, inc. In order for the mobile unit 40 to synchronize to the reference oscillator within an error range of +/-500 mus, the interface processor 212 and the multifrequency controller 204 ideally operate such that the overall root mean square error of the entire signaling sequence 100 will be less than 0.1 ms. The reference station 102 (not shown) includes the same signal processing components as the mobile unit, including a reference multi-frequency controller, a reference modem transceiver, and a reference interface processor.

It will be apparent to those skilled in the art that variations may be made in the details of the above-described embodiments of the invention, in accordance with the principles of the invention. Accordingly, only the appended claims should determine the scope of the present invention.

Claims

1. A method of synchronizing a remote unit with a reference oscillator of a reference station in a voice communications network, the method comprising:

establishing an audio call path between the reference station and the remote unit;

the reference station transmitting an audio reference signal over the call path, the reference signal being transmitted for a predetermined reference duration;

the remote unit receiving the reference signal;

the remote unit generating an audio response signal based on the reference signal;

waiting a preselected reply delay interval from an observation time at which the reference signal was received;

after waiting an answer delay interval, the remote unit transmitting an answer signal over the call path, the answer signal being transmitted for a predetermined answer duration;

the reference station receives the response signal;

the reference station measures the round-trip time difference between the observation time of sending the reference signal and receiving the response signal;

calculating the total waiting time according to the round-trip time difference, the reference time length, the response time length and the response delay interval;

selecting a synchronous reference time corresponding to the time stamp output by the reference oscillator;

defining a correction time before the synchronization time to be half of the total waiting time;

at the correction time, the reference station transmits a synchronization signal through the call path;

the remote unit receiving a synchronization signal; and

within the remote unit, the remote unit is synchronized with the reference oscillator based on the synchronization signal.

2. The method of claim 1, wherein

The reference signal comprises a first reference tone and a second reference tone separated by a reference gap; and

the reply signal includes a first reply tone and a second reply tone separated by a reply gap.

3. The method of claim 2, wherein the first reference tone and the second reference tone have the same duration, the first reply tone and the second reply tone have the same duration, and the method further comprises:

calculating, at the remote unit, an average of the observed time of receipt of the first reference tone and the observed time of receipt of the second reference tone, and adjusting the observed time of receipt of the reference signal to reduce the inherent error of the reference signal during transmission and reception; and

the mean of the observed time of receipt of the first response tone and the observed time of receipt of the second response tone is calculated at the reference station and the observed time of receipt of the response signal is adjusted to reduce the inherent error in the transmission and reception of the response signal.

4. A method of synchronizing a mobile unit with a reference oscillator of a reference station within a cellular telephone network, the method comprising:

establishing an audio call path between the remote unit and the reference station;

the reference station transmitting an audio reference signal over the audio call path, the reference signal having a predetermined reference duration;

receiving the reference signal at the remote unit and generating an audible reply signal based on the reference signal, the reply signal having a predetermined reply duration;

waiting a preselected reply delay interval from responding to the received reference signal;

after waiting an answer delay interval, the remote unit sends an answer signal over the call path;

receiving a reply signal at the reference station;

measuring at the reference station the round trip time difference between the transmission of the reference signal and the receipt of the reply signal;

defining a correction time before the synchronization reference time as half of the total waiting time;

the remote unit receiving a synchronization signal; and

5. The method of claim 4, wherein the reference signal and the reply signal each comprise an approximately Gaussian pulse.

6. The method of claim 5, wherein each Gaussian pulse is characterized as having a standard deviation of 100 microseconds to 330 microseconds.

7. The method of claim 4, wherein the amplitude of the reference signal and the reply signal are each between-4 dBm and-10 dBm.

8. The method of claim 4, wherein transmitting the reference signal comprises repeatedly transmitting the reference signal until the reference station receives the reply signal.

9. The method of claim 8, wherein

The call path has an expected maximum one-way propagation latency; and

repeatedly transmitting the reference signal comprises repeatedly transmitting at a repetition interval greater than an expected maximum one-way propagation latency;

10. a method according to claim 4, wherein the reference signal and the reply signal each comprise a pulse train consisting of a series of acoustic frequency pulses.

11. The method of claim 10, wherein the acoustic frequency pulses are randomly separated.

12. The method of claim 10, wherein the audio frequency is pulsed onto an audio carrier signal.

13. A method according to claim 10, wherein the audio frequency pulses are pulses of approximately 11.4 milliseconds in duration, 400Hz in 3dB bandwidth, and 1.0 roll-off factor.

14. The method of claim 10, wherein the total burst duration of the burst is between 143 milliseconds and 189 milliseconds.

15. A method of synchronizing a mobile unit with a reference oscillator of a reference station within a voice communications network, the method comprising:

the reference station transmitting an audio reference signal over the call path, the reference signal simulating human voice thereby preventing the voice communication network from destructively attenuating the reference signal, the reference signal being transmitted for a predetermined reference duration;

the remote unit receiving the reference signal;

the remote unit generating a reply signal based on the reference signal, the reply signal simulating human voice thereby preventing the voice communication network from destructively attenuating the reply signal;

after waiting for an answer delay interval, the remote unit transmitting an answer signal over the call path, the answer signal transmitting a predetermined answer duration;

the reference station receives the response signal;

the reference station measures the round-trip time difference between the sending of the reference signal and the receipt of the reply signal;

calculating a correction interval equal to half of the total latency;

the reference station sends a synchronization signal through the call path, the synchronization signal representing a correction interval;

the remote unit receiving a synchronization signal; and

16. The method of claim 15, wherein the reference signal and the reply signal each comprise an approximately gaussian pulse characterized by a standard error (σ) between 100 microseconds and 330 microseconds.

17. The method of claim 15, wherein the reference signal and the reply signal each have an amplitude between-4 dBm and-10 dBm.

18. The method of claim 15, further comprising:

generating an audio synchronization reference signal corresponding to the reference time stamp output from the reference oscillator and appearing after receipt of the reply signal;

after outputting the reference time stamp, the reference station transmits an audio synchronization reference signal over the call path.

19. The method of claim 15, further comprising determining a correction time prior to a synchronization time of the reference oscillator, and wherein the act of transmitting the synchronization signal comprises the act of the reference station transmitting an audio synchronization correction signal over the call path at the synchronization time.

20. The method of claim 15, further comprising determining a correction time prior to a correction time stamp of the reference oscillator output, the correction time leading the correction time stamp by an amount equal to the correction interval; and is

Wherein the synchronization signal represents the correction time.

21. In a telephone network including a reference station at a known geographic location and a mobile cellular telephone unit in communication with the reference station, an improved method of synchronizing the mobile oscillator of the mobile cellular telephone unit with the SPS oscillator of an SPS satellite system, the improvement comprising:

synchronizing a correction oscillator of a reference station with an SPS oscillator;

establishing an audio call path between the reference station and the mobile cellular telephone unit;

the reference station sends an audio reference signal through a calling path and transmits the reference signal at a predetermined time reference duration;

receiving a reference signal by a mobile cellular telephone unit;

generating an audio response signal by the mobile cellular telephone unit based on the reference signal;

the mobile cellular telephone unit transmitting an answer signal through the call path at an answer time, the answer time occurring after a predetermined answer delay interval after the mobile cellular telephone unit receives the reference signal, the answer signal being transmitted for a predetermined answer duration;

the reference station receives the response signal;

the reference station measures the round-trip time difference between the sending reference signal and the receiving response signal;

the reference station transmitting a synchronization signal over the call path at a correction time after the reference oscillator is synchronized with the SPS oscillator and advanced by a correction interval from the synchronized reference time, the correction interval being equal to half the total wait time;

the mobile unit receives the synchronous signal; and

the mobile oscillator is adjusted and synchronized to the SPS oscillator based on the synchronization signal.

22. A method of synchronizing a mobile wireless communications device having a local clock, the method comprising the steps of:

establishing a voice call connection between the mobile device and the reference station;

determining a particular time correction factor through the established voice call connection as between the reference station and the mobile unit;

maintaining, within the reference station, a current Satellite Positioning System (SPS) time and generating a periodic SPS time marker signal related to the current SPS time;

the reference station transmitting data, reflecting the current SPS time, encoded as audio signals to the mobile device over the established voice call connection;

by delaying the periodic SPS time stamps by the time correction factor, delayed SPS time stamps may be formed;

transmitting a delayed SPS time stamp from the reference station to the mobile device; and

in the mobile device, the local clock is synchronized to the current SPS time based on the delayed SPS time stamp to synchronize the local clock to the SPS time maintained by the reference station.

23. The method of claim 22, wherein the process of determining a time-specific correction factor comprises a process of determining a total latency of sending signals between a reference station and a mobile device over an established voice call connection.

24. The method of claim 22, wherein determining a total latency comprises:

transmitting an audio 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; and

the latency between transmitting the reference signal and receiving the reply signal is measured at the reference station.

25. The method of claim 23, wherein the calculated time correction factor is half of the total latency.

26. A method of synchronizing a mobile wireless communications device having a local clock, the method comprising the steps of:

determining a particular time correction factor through the established voice call connection as between the reference station and the mobile device;

transmitting data representing the current SPS time, encoded as an audio signal, from the reference station to the mobile device over the established voice call connection;

transmitting an SPS time stamp signal from a reference station to a mobile device;

in a mobile device, forming a delayed SPS time stamp signal by delaying a received SPS time stamp by an amount of a time correction factor; the local clock is then synchronized to the current SPS time based on the delayed SPS time stamp, thereby synchronizing the local clock to the SPS time maintained by the reference station.

27. The method of claim 26, wherein the process of determining a particular time correction factor comprises the process of determining a total latency of a round trip transmission signal between a reference station and a mobile device over an established voice call connection.

28. The method of claim 27, wherein determining a total latency comprises:

the latency between the transmission of the reference signal and the reception of the reply signal is measured at the reference station.

29. The method of claim 27, wherein the calculated time correction factor is half of the total latency.

30. The method of claim 26, wherein the process of determining a particular time correction factor comprises:

transmitting an audio 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 unit in response to the reference signal over the established voice call connection; and

the latency between the transmission of the reference signal and the reception of the reply signal is measured at the mobile station.

31. A Satellite Positioning System (SPS) -enabled mobile unit having a local SPS 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 SPS signals to form SPS raw data and for maintaining a local SPS clock;

a microprocessor connected to the SPS receiver and including software for processing the raw SPS data to form position data and for synchronizing the local SPS clock;

a multi-frequency controller, coupled to the microprocessor, for generating multi-frequency audio tones for encoding the position data and for decoding the received multi-frequency audio tones to form synchronization data;

a wireless communication transceiver operable to transmit and receive voice communications over a call path of a wireless communication network, the wireless communication transceiver comprising an audio port coupled to a multi-frequency controller for transmitting encoded position data over the call path and for receiving and decoding synchronization data received as audio tones over the call path;

software for synchronizing the local SPS clock adjusts the local SPS clock in response to synchronization data received by the wireless communication 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 a microprocessor.

33. A mobile unit as in claim 31 wherein the software for synchronizing the local SPS clock is responsive to synchronization data received over the call path, the synchronization data including a corrected time for synchronizing the SPS local clock, the corrected time corresponding to a difference between the local SPS time and an actual SPS time provided by the orbiting SPS satellites.