MXPA01007086A - In-band signalling for synchronization in a voice communications network. - Google Patents

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

"SIGNALING IN BAND FOR SYNCHRONIZATION IN A VOICE COMMUNICATIONS NETWORK" TECHNICAL FIELD This invention relates to in-band signaling methods for measuring the latency of the system in wireless and wireline communications, in particular, with the use of latency measures for timing synchronization and synchronization error measurements between a clock of reference and a remote clock in communication through a wireless and / or wireline voice communication network.

BACKGROUND OF THE INVENTION Numerous signaling methods are known to accurately synchronize a synchronized oscillator with a distant master oscillator. One of these known methods uses SPS signals that are transmitted from the terrestrial satellites carrying the master oscillator of a satellite positioning system (SPS) such as the Global Positioning System (GPS) or GLONASS. An oscillator subordinated to a SPS master oscillator is synchronized in a normal SPS signal receiver mode called "latch". In a mobile unit including an SPS positioning receiver, the amount of ^ synchronization error between the SPS master oscillator in ^ a subordinate oscillator of the SPS positioning receiver collides with the ability of the positioning receiver SPS 5 to accurately determine its position from the SPS signals using ephemeris satellites data. For example, the synchronization error of a subordinate oscillator of a GPS receiver must be less than about +/- 500 · > . microseconds ^ sec) from a satellite master oscillator 10 GPS in order to get a fixed location from a cold start in less than 30 seconds. In the closing mode, the slave oscillator is typically synchronized up to +/- microseconds of the GPS satellite master oscillator. When the SPS signals are not available, for example 15 because the SPS satellites are out of sight, or when the mobile unit has not acquired a satellite signal f SPS, the mobile unit must be re-synchronized due to the drive of the oscillator subordinated through time. The re-synchronization requires a significant amount of time if the SPS signals should be read. SPS synchronization from a cold start is also delayed. Synchronization processing times of up to one minute or more from the cold start are not uncommon.

Other types of electronic equipment such as computer networking equipment, instruments, control systems, and devices also depend on synchronized internal clocks exactly. The patent American Number 5,510,797 by Abraham and others describes the use of an SPS receiver in connection with computers and time-controlled instruments to synchronize their internal clocks. U.S. Patent No. 4,368,987 to Waters describes a synchronization method for satellites wherein a master pulse is transmitted by a master clock station to a slave station where a slave pulse having a conjugation phase with respect to the master pulse is retransmitted. receipt through the master station. A measurement of the master station of a time difference between the master pulse and the received slave pulse is used to calculate a time phase difference between the master clock and the slave clock. The time phase difference is then used to synchronize the clocks. Waters requires cooperation between the satellite-based master station and the satellite-based subordinate station in order to determine the phase difference and for clock synchronization. In this way, the method described by Waters is not a substitute for the re-synchronization of a mobile unit trained by SPS. The SPS satellites, which were originally developed for military use, will not retransmit a subordinate impulse in response to a master impulse received from the mobile unit. Neither the SPS satellitesconversely, they will receive a conjugated subordinate impulse generated by the mobile unit or calculate a time difference in phase. For calls that originate from wireline telephones, the Automatic Number Identification (ANI) service allows a call receiving station, such as a Public Safety Answering Point (PSAP), to quickly find out the name and address of the caller (owner of the registered phone) in a database of the owner. The portable nature of the wireless communication devices eliminates the viability of this inquiry scheme in wireless networks. Wireless mobile telephone units incorporating the SPS receivers have been proposed as a way to generate the location data that can then be transmitted to a call receiving station. In theory, the generation and transmission of location data in this manner would be especially useful for locating a wireless caller who dialed 911 to publicize an emergency, but who is unable to verbally provide location information to a PSAP operator. Although wireless telephones trained by SPS can provide the ability to accurately determine and transmit location data, numerous practical realities present obstacles to the efficient and accurate generation and transmission of location data to a call receiving station. For example, the SPS receiver of the cordless telephone 10 trained by SPS may need to synchronize to the SPS time before it can generate usable location data. In an emergency situation involving a call to a PSAP, the amount of time required to synchronize the SPS receiver using the SPS satellite signals 15 can cost lives. Figure 1 shows a diagram of a network of r voice communications 10 of the prior art including V, a wireless communications network 12 coupled with a wired communications network (POTS network) 14. With Referring to Figure 1, the wireless communications network 12 includes one or more cellular base stations 16 each having an antenna 18 of the associated base station and a mobile switching center 20. The mobile switching center 20 dock the base station Cell 16 with the POTS network 14 to allow a wireline acceptor 22, such as a PSAP, to communicate with a mobile unit 24 of the wireless communications network 12. In operation, the mobile unit 24 transmits and receives signals that are received and transmitted respectively by the cellular base station 16 through two transmission channels 26. These transmission channels 26 include a voice channel 27 (which is also known such as a call path, voice call path, voice call connection, audio call path, audio traffic channel, and traffic channel] to transmit the radiofrequency signals representative of a voice, a control channel 28 (also known as an air channel and a non-call path) for transmitting call initiation and control signals In digital wireless communications networks, transmissions through control channel 28 consist of data packaged protocols The protocols for the control channel 28 and the type of data that can be carried in the control channel 28 are determined by means of The type of control channel communication protocol in use by the wireless communications network. Because each type of wireless network uses its own protocol, the control signals must be decoded at the cellular base station 16.

Other limitations inherent in the prior art will become apparent upon review of the following summary of the invention and detailed description of preferred embodiments.

COMPENDIUM OF THE INVENTION Wired and wireless line communication systems have some system latency, typically less than 500 milliseconds (ms), due to the propagation and processing of the signals that go on the call path. In wireless communications networks, differences in air interface protocols, base stations, device manufacturers and transmission distances vary the latency of the system. The present invention provides methods for determining a system latency of a voice communication network for the signals transmitted between a reference station and a remote station through an audio call path of the voice communication network. The latency system is then taken into account during synchronization of the remote unit with reference to the oscillator of the reference station. The measurement of the latency of the system is achieved by a signaling sequence that includes transmitting a reference signal through the audio call path from the reference station to the remote unit, where a signal is generated and transmitted. of response back to the reference station through the call path, after a preselected response delay interval. The reference signal and the response signal are transmitted for reference and response durations 10, which can be regulated by signal attenuation characteristics of the voice communications network. The response delay interval begins during receipt of the reference signal in the remote unit and must be preselected to allow sufficient time for the remote unit to process the reference signal and generate the response signal. A measure is made at the referral station to determine a round trip time difference less than the sum of the reference duration, the response duration and the response delay interval. In another aspect of the present invention, a correction interval is calculated as half of the total latency, and then a synchronization signal is transmitted which represents the correction interval from the reference station through the path N called for receipt through the remote unit. The remote unit is synchronized by itself with the reference oscillator in response to the synchronization signal. The synchronization can be effectively achieved in a number of different ways, for example by storing the synchronization signal in the remote unit and subsequently using it as a parameter to calculate the synchronized time, or by adjusting or re-starting the ^ 10 remote oscillator during the receipt of a synchronization mark of the synchronization signal. In a further aspect of the present invention, the remote unit is a mobile unit that includes an SPS receiver. In this aspect, the remote oscillator is coupled with or forms part of the SPS receiver and is used by the SPS receiver, together with the SPS satellite signals to determine a location of the remote unit. The synchronization of the remote oscillator can be achieved by any of the synchronization techniques 20 described above or by a modification in response to the synchronization signal, of the algorithms used by the SPS receiver to calculate the location of the remote unit. In still another aspect of the present invention, the reference signal, the response signal, and the synchronization signal are all audio-frequency signals that are adapted to pass freely through the voice communications network. These audio-frequency signals are necessary for transmission over a voice call path of an advanced communications network of the type using compression protocols and / or spread spectrum technology to maximize call traffic in a limited radio frequency bandwidth. Examples of protocols used in advanced communications networks include time division multiple access (TDMA), code division multiple access (CDMA), global system for mobile communication (GSM), and others. The reference, response and synchronization signals also transmit freely through analog wireless networks. These audio signals are specifically configured to emulate certain characteristics of the human voice such as, for example, frequency, amplitude and duration. By generating signals that resemble the sounds of the human voice, the present invention in this way prevents the destruction of signals by the voice communications network. In another aspect of the present invention, the signals are audio frequency signals that include one or more audio tones, multifrequency tones, or essentially Gaussian pulses generated by a multifrequency controller. The Gaussian impulses are characterized by a 3s (normal deviation x 3) of between ^ approximately 0.3 millisecond and 1 millisecond, and an amplitude of between -4 dBm and -10 dBm to avoid destructive attenuation 5 through the voice communications network. Single or multiple frequency tones have a duration of between approximately 5 milliseconds and 50 milliseconds and a frequency within the range of approximately 300 to ^ 3000 Hz. In a method that uses multiple pulses and tones ^ 10 per signal, the time of Receipt of tones and pulses (of a specific signal) can be averaged to improve the accuracy of latency and synchronization measurements. The signals may also comprise a pulse train created by concatenating a plurality of tones or pulses separated at regular and irregular intervals. The irregular separation of the tones or pulses facilitates the exact correlation of the response signal to the reference signal at the reference station for the calculation of the total time difference of the round trip. The use of these techniques allows synchronization of the remote unit up to within +/- 500 microseconds of the reference oscillator. In remote units enabled by SPS, the use of the method of the present invention significantly reduces the time it takes for the SPS receiver to achieve SPS closure.

In still another aspect of the present invention, the signaling sequence is initiated by the remote unit, which generates and transmits the reference pulse, the receipt of which causes the reference station to respond to a response pulse after an interval of response delay. Latency calculations they can then be carried out in the remote unit. The synchronization of the remote unit still requires that the remote unit receives a synchronization signal transmitted by the reference station during a timestamp output of the reference oscillator. The present invention presents particularly significant advantages in the context of a cellular telephone network wherein the remote unit comprises a wireless communication device such as a cellular phone. Unlike the known wireless data communication devices, which transmit data and synchronization signals through a control or "air" channel of the communication network, the present invention does not require special equipment or software that has to be installed at a site of the base station of the network wireless to handle the reference, response and synchronization signals. By preventing transmission through the control channel, the present invention lends itself to an efficient implementation in cost by preventing the modification of an existing wireless and wired telephone network (POTS) network infrastructure (POTS). On the contrary, the present invention operates transparently through the existing infrastructure. The "in band" signals in the voice call path can be received at any point in the wireless or wired line networks, for example in a location service controller or PSAP, which can also serve as a reference station. The present invention also provides advantages through wireless modem devices of the prior art, which completely occupy the voice call path during data transmission by switching the wireless communication device with the data mode. By keeping available the voice call path available to a wireless telephone user during the measurement of latency, synchronization and location data transfer, the present invention facilitates essentially simultaneous verbal communication between the wireless user and a call acceptor. Many additional aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments thereof which continues with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of a wireless communications network of the prior art that shows the components of a wireless communication network and its connection to a wireline communications network. Figure 2 is a diagram of a mobile unit s including an SPS receiver in communication with an acceptor v, 10 calling through a wireless communication network to implement a synchronization protocol in accordance with the present invention; Figure 3 is a diagram of a signal transmission sequence according to the present 15 invention; Figure 4 is a time limit diagram showing the time limit and the elements of a ^ reference signal as a response signal and a synchronization signal of the signal transmission sequence 20 of Figure 3; Figure 5A is a diagram of a first alternative modality of the audio frequency signal, comprising first and second reference tones; Figure 5B is a diagram of an audio frequency signal of the second alternative embodiment comprising a Gaussian pulse; Figure 5C is a diagram of an audio frequency signal of the third alternative mode comprising a train of reference pulses, overlapped with a train of observed response pulses; and Figure 6 is a schematic diagram of a mobile unit including an SPS receiver and a multifrequency controller implementing the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Figure 2 shows a diagram of a voice communication network 30 including a mobile unit 40 capacitated by SPS to implement a first embodiment of the present invention. With reference to Figure 2, the voice communication network 30 includes a wireless communication network 44 coupled with a public switched telephone network ("POTS") 48. The wireless communication network 44 includes a base station 52 for transmitting the radiofrequency signals 56 to the mobile unit 40 and to receive the radio frequency signals 56 from the mobile unit 40. The radio frequency signals 56 include a signal from the voice channel 58 to transmit an audio signal, and a signal 60 of control channel to transmit the control commands and digital data. A mobile switching center 64 couples the wireless communication network 44 with POTS 48. The mobile unit 40 is preferably a cellular telephone apparatus, but can be of any type of wireless communications device capable of transmitting through the wireless channel. voice 58. Mobile unit 40 includes a local oscillator (also referred to as a 10"mobile oscillator" or "remote oscillator") and an SPS 66 receiver to receive SPS signals 70 that are broadcast by SPS 72 satellites in the earth's orbit and to calculate a location of the mobile unit based on SPS signals 70. During normal operation, the receiver 15 SPS achieves a "close" with the SPS 70 signals to synchronize the local oscillator within +/- 10 microseconds ^ sec). However, if the SPS 70 signals are not available or the SPS 66 receiver has not acquired an SPS signal, the local oscillator will not maintain the 20 SPS time correct due to the local oscillator drive. In accordance with the present invention, the resynchronization of the SPS oscillator can be initiated automatically by the mobile unit 40, as necessary, or it can occur during the next call of 25 telephone received or made by the mobile unit 40.

To reduce the time required to resynchronize the local oscillator with the SPS time, the local oscillator can be synchronized with a reference oscillator placed at a known terrestrial location. This type of resynchronization procedure is known as "inseminating" the 66 SPS receiver because it results in synchronization to a wider tolerance than occurs during SPS locking or blocking. A processor 80 communicates with a reference SPS 82 receiver and the reference oscillator, which can be integrated with the SPS receiver 82. The processor 80 can be coupled with the wireless communication switch 64 with a POTS 48 call acceptor device 86, or both. Once an audio calling path has been established between the processor 80 and the mobile unit 40, the processor 80 initiates a signaling sequence 100 (Figure 3) to determine the latency of the system and for the synchronization of the local oscillator with the reference oscillator. Figure 3 is a diagram of the signaling sequence 100 for measuring the latency of the system. With reference to Figure 3, a reference station 102 such as the location services controller (LSC) 104 transmits a reference signal through the voice channel 58 (Figure 2). A remote unit 108 such as a cellular phone (HS) apparatus 110 receives the reference signal 106 after a reference latency t ^. Unit The remote 108 then responds to the receipt of the reference signal 106 by transmitting a response signal 112, 5 which is received at the reference station 102 after a reference latency t2- The reference latency t and the response latency t2 include both a signal propagation time as the time to process the ^ reference and respective response signals 106, 112"10 at the reference station 112 and the remote unit 108. The time elapsed between the transmission of the reference signal 106 and the receipt of the response signal 112 is measured in the reference station 102 to determine a round trip delay tR If the reference latency 15 ti and the response latency t2 are equal, the system is said to be symmetric. , exaggerates the asymmetry in Figure 3. However, the empirical measurements in CDMA, TDMA, GSM, and analog wireless telephone systems, confirm that the POTS network 20 48 in combination with the wireless communications network 44 (Figure 2) it is symmetric (and essentially invariable in time during each call session) up to within acceptable tolerances for the in-band signaling object for time synchronization within +/- 500 25 microseconds. Because the wireless communications and POTS networks are essentially symmetric, unidirectional latency can be calculated as half of the ^ round trip delay, or l 2tRx. Figure 4 is a timing diagram showing time regulation and elements of signaling sequence 100. With reference to Figure 4, the upper section of the time signaling diagram shows signals at the reference station 102, / ^ and the lower section shows signals on the remote unit ^ 10 108. The transmitted signals are shown in solid lines, while the received signals are shown in dashed lines. The signaling sequence 100 is shown in Figure 4 as having been initiated by the reference station 102, but may be initiated in an alternative mode (not shown) in the remote unit 108. To start the signaling signal 100, the signaling station 100 reference 102 transmits the reference signal ^ 106 which has a tref reference duration. For reasons of convenience, the reference signal 106 is transmitted 20 by the reference station 102 when a periodic time mark 120 of the reference oscillator having a period P occurs. The reference signal 106 is received in the remote unit 108 after of the reference latency t. During receipt of the reference signal 25 106, the remote unit 108 generates a response signal 112 and transmits the response signal 112 after a preselected response delay interval t iiei. The response signal 112 has a response duration trp and is received in a reference signal 102 after the response latency t2- A measurement of the round trip delay t¾T is made in the reference station 102. A latency is then calculated total ??, as: TL = RT "(tref + tdel + trp) Because the communications network is essentially symmetric, the system's unidirectional latency (calculated as 1/2?) can then be used as a range of Tc correction A synchronization signal 124 representative of the correction interval ??; is transmitted from the reference station 102. The synchronization signal 124 is transmitted during the next tender mark 120, and the correction interval Tc is transmitted as a data to the remote unit 108, either as part of the synchronization signal 124 or as part of a separate data signal (not shown) Alternatively, the synchronization signal 124 'is transmitted hard nte a correction time 126 in advance of a future time stamp 120 'by an amount equal to the correction interval Tc. The remote unit 108 then uses the correction interval Tc and / or a reception time 127 of the synchronization signal 124 ', to synchronize with the reference oscillator. Those skilled in the art will appreciate that synchronization can be achieved in a variety of ways, based on the receipt in the remote unit 108 of one or more signals representing the correction interval Tc, and a timestamp 120 of the oscillator of reference. For example (not shown), the synchronization signal 124 can be generated by forming a delayed time stamp that is delayed by an amount equal to the period P minus the correction interval Tc. Voice communication networks and, particularly, digital cell phone networks use signal compression, spectrum spread signal transmission, and other signal manipulation protocols to maximize call traffic in the transmission medium of signals. These signal processing protocols tend to remove signals in the call path that do not resemble the human voice. To improve the transmission of signals through the voice communication network 30 (Figure 2) and to improve the accuracy of the latency measurements, the reference signal 106, the response signal 112, and the synchronization signal 124 all they are generated as audio signals in the audio call path. Those skilled in the art will recognize that audio frequency signals are converted numerous times between the shape of the analog signal, the shape of the digital signal, and the shape of the radio frequency signal during coding, transmission and decoding, as normally occurs in the audio call path of a wireless telephone network. The term "audio-frequency signals" as used herein describes any audio representative signal as it proceeds in the path of the call, regardless of its shape. The reference signal 106, the response signal 112, and the synchronization signal 124 are generated to have characteristics that have been found empirically passing through the voice communication network 30. Figures 5A, 5B and 5C show the first, second and third respective alternative modes of an audio signal 128a, 128b and 128c that can be used for the reference signal 106, the response signal 112, and the synchronization signal 124. With reference to Figure 5A, an audio signal 128a of the first alternative mode includes a first audio tone 130 and a second audio tone 132 separated in time by a reference pause 134. The first and second audio tone 130, 132 each is characterized by a frequency between 300 Hz and 3000 Hz, a predetermined duration between 5 ms and 50 ms, and an amplitude between -4 dBm and -10 dBm. The reference pause 134 is characterized by a pre-selected duration, which for reasons of convenience may be the same as the duration of the first and second audio frequencies 130, 132, but may be selected to be shorter or longer. The use of multiple tones allows the remote unit 108 and the reference station 102 to averand the first and second audio tones 130, 132 as they are received and thus more accurately determine the time at which the signal is received. of audio 128a. With reference to Figure 5BX, an audio frequency signal 128b of the second alternate embodiment comprises an essentially Gaussian pulse represented as a time function (t) by the equation: 2 where A is the amplitude of between about -4 dBm and -10 dBm and s (normal deviation) is between approximately 100 microseconds and 330 microseconds. Figure 5C shows a third alternative mode of the reference signal 106 ', overlapped with a corresponding response signal 112. Referring to Figure 5C, an audio frequency signal 128c of the third alternative mode comprises a reference pulse train. 140 which includes ^ eight essentially Gaussian reference pulses 144 separated at predefined intervals a, b, c, d, e, f and g 5 Similarly, the response signal 112 '(shown in Figure 5C as received at the station) reference 102) comprises a pulse train of response that includes eight pulses 148 of essentially Gaussian response ^ ^ separated essentially identical to the pulses 144 of 10 reference. The intervals a-g are irregular to improve the correlation at the reference station 102 when the round trip delay tR-p is determined. Using the irregular intervals a-g, the correlation can be carried out mathematically, even if they are not All Gaussian impulses 144, 148 received. Those skilled in the art will recognize that the widths and ranges of the reference pulses 144 can be selected such that only one of the response pulses 148 needs to be received to correlate the 20 pulse trains and determine the total delay of the round trip t ^ T * even if less accurately than if more impulses are received. Preferably, the audio frequency signal 128c of the third alternative embodiment comprises an analog filtered pulse train modulated in 25 a voice frequency carrier signal, with pulses of 11.4 ms long with 3 dB of bandwidth of 400 Hz and of roll of 1.0. A total duration tp of the pulse train 140 is between approximately 143 ms and 189 ms. The voice frequency carrier signal may be the signal in the speech frequency spectrum (300 Hz to 3000 Hz), but preferably it is a 1800 Hz signal. Figure 6 shows a schematic diagram of the speech processing components of the speech. selected signal from the mobile unit 40. With reference to Figure 6, the mobile unit 40 includes an audio bridge 200 connected to a multifrequency controller 204 and a modem transceiver 208. The multifunction controller 204 and the modem transceiver 208 are connected to an interface processor 212 through, for example, a RS-232 connection number 214. The interface processor 212 is connected to an SPS receiver 216 which includes an SPS 220 antenna. Both the multifrequency controller 204 as the modem transceiver 208 actively listens to the call path during the signaling sequence. Ideally, the functions of the multifrequency controller 204, the modem transceiver 208, the interface processor 212 and the SPS 216 receiver are integrated into the existing components of the mobile unit 40, such as a CODEC a digital signal processor (DSP) , and an ARM microprocessor found in known cell phones. For prototype and test purposes, the multifrequency controller 204 can be a personal computer including a sound card and running the MATLAB software available from Mathworks, Inc., Natick, Massachusetts, USA, or any other commercially available multifrequency driver. To synchronize the mobile unit 40 to within +/- 500 mierseconds of the reference oscillator, the interface processor 212 and the multifrequency controller 204 work ideally so that the root mean square root error of the entire signaling sequence 100 is less than 0.1 ms. The reference station 102 (not shown) includes the signal processing components that are similar to those of the mobile unit, including a reference multifrequency controller, a reference modem transceiver, and a reference interface processor. It will be apparent to those skilled in the art that many changes can be made in the details of the above-described embodiments of this invention without departing from the underlying principles thereof. The scope of the present invention should therefore be determined only by the following claims.

Claims (1)

1. CLAIMS: 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 reference signal from the reference station through the call path, the reference signal being transmitted through a predetermined reference duration; receive the reference signal in the remote unit; generate an audio response signal in the remote unit in response to the reference signal; expect a preselected response delay interval that begins during an observed time of receipt of the reference signal; transmitting a response signal from the remote unit through the call path after waiting for the response delay interval, the response signal being transmitted for a predetermined response duration; receive the response signal at the reference station; measuring at the reference station a difference of the round trip time between the transmission of the reference signal and an observed time of receipt of the response signal; calculate a total latency based on the difference of the round trip time, the reference duration, the response duration, and the response delay interval; selecting a synchronization reference time corresponding to an output of the time stamp by the reference oscillator; define a correction time that precedes the synchronization time by half the total latency; transmitting a synchronization signal from the reference station through the call path during the correction time; receive the synchronization signal in the remote unit; and on the remote unit, synchronize the remote unit with the reference oscillator in response to the synchronization signal. 2. The method of claim 1, wherein: the reference signal comprises first and second reference tones separated by a pause of reference; and the response signal comprises first and second 5 response tones separated by a response pause. 3. The method of claim 2, wherein the first and second reference tones are of duration ^ same, the first and second answer tones are from 10 equal duration, and further comprising: in the remote unit, averaging the observed times of the receipt of the first and second reference tones and adjust the observed time of receipt of the reference signal in order to reduce the errors 15 inherent in the transmission and receipt of the reference signal; and r, at the reference station, averaging the observed times of receipt of the first and second response tones and adjusting the observed time of receipt of the response signal in order to reduce the inherent errors in the transmission and reception of the response signal. the answer signal. 4. In a cell phone network, a method of synchronizing a mobile unit with reference to the oscillator of 25 a reference station comprising: establishing a so-called audio path between the mobile unit and the reference station; transmitting an audio reference signal from the reference station through the audio call path, the reference signal having a predetermined reference duration; receiving the reference signal in the mobile station and generating an audio response signal in response to the reference signal, the response signal having a predetermined response duration; expect a preselected response delay interval that begins in response to receipt of the reference signal; transmitting the response signal from the mobile unit through the call path after waiting for the response delay interval; receive the response signal at the reference station; to measure at the reference station a round trip time difference between the transmission of the reference signal and the receipt of the response signal; calculate a total latency based on the round trip time difference, the reference duration, the response duration, and the response delay interval; selecting a synchronization reference time corresponding to a timestamp output by the reference oscillator; defining a correction time that precedes the synchronization reference time by mitt of the total latency; transmitting a synchronization signal from the reference station through the call path during the correction time; receive the synchronization signal in the mobile unit; and in the mobile unit, synchronize the mobile unit with the reference oscillator in response to the synchronization signal. The method of claim 4, wherein the reference and response signals each include an essentially Gaussian pulse. The method of claim 5, wherein each Gaussian pulse is characterized by a normal deviation of between 100 microseconds and 330 microseconds. The method of claim 4 wherein the reference and response signals each have an amplitude between -4 dBm and -10 dBm. 8. The method of claim 4, wherein the transmission of the reference signal includes repeating the ^ transmission of the reference signal until the response signal is received by the reference station. The method of claim 8 wherein: the call path has a maximum unidirectional propagation latency; and repeat the transmission of the reference signal ^ 10 includes repeating at repetition intervals that are greater than the anticipated maximum unidirectional propagation latency. The method of claim 4, wherein the reference and response signals each include 15 a pulse train consisting of a series of audio frequency pulses. The method of claim 10, wherein the audio frequency pulses are irregularly separated. 12. The method of claim 10, wherein the audio frequency pulses are modulated in a voice frequency carrier signal. The method of claim 10 wherein the audio frequency pulses are approximately 11.4 milliseconds in duration with a 3 dB bandwidth of 400 Hz and an unwinding of 1.0. The method of claim 10 wherein 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 a reference signal of audio frequency from the reference station through the call path, the reference signal emulating the sounds of the human voice in order to avoid the destructive attenuation of the reference signal by means of the communication network of voice, the reference signal being transmitted through a predetermined reference duration; receive the reference signal in the remote unit; generating a response signal in the remote unit in response to the reference signal, the response signal emulating the sounds of the human voice in order to avoid the destructive attenuation of the response signal by means of the voice communications network; expect a preselected response delay interval that begins in response to receipt of the reference signal; transmitting the response signal from the remote unit 5 through the call path after waiting for the response delay interval, the response signal being transmitted through a predetermined response duration; ^ ^ receive the answer signal at the station 10 reference; measuring at the reference station a time difference of the round trip between the transmission of the reference signal and the receipt of the response signal; calculate the total latency based on the round trip time difference, the reference duration, the response duration, and the response delay interval; calculate a correction interval equal to half the total latency; 20 transmitting a synchronization signal from the reference station through the call path, the synchronization signal representative of the correction interval; receive the synchronization signal in the unit 25 remote; and on the remote unit, synchronize the remote unit with the reference oscillator in response to the synchronization signal. 16. The method of claim 15 wherein the reference signal and the response signal each include an essentially Gaussian pulse characterized by a normal deviation (s) of between 100 microseconds and 330 microseconds. 17. The method of claim 15 wherein 10 the reference and response signals each have an amplitude between -4 dBm and -10 dBm. The method of claim 15, further comprising: generating an audio frequency reference reference signal 15 corresponding to an output of the reference time stamp by the -|N reference oscillator and occurring after receipt of the answer signal; transmitting the reference signal of 20 audio frequency synchronization from the reference station through the call path during the output of the reference time stamp. 19. The method of claim 15, further comprising determining a correction time that 25 precedes a synchronization time of the reference oscillator, and wherein the transmission of the synchronization signal includes a transmission of a sound synchronization correction signal from the reference station through the call path in the synchronization time. . The method of claim 15, further comprising determining a correction time preceding a reference time stamp output from the reference oscillator, the correction time preceding the reference time mark by an amount equal to the correction interval; and wherein the synchronization signal is representative of the correction time. 21. In a telephone network that includes a reference station placed at a known land location and a mobile cell phone unit in communication with the reference station, an improved method of synchronizing a mobile oscillator of the mobile cell phone 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 cell phone unit; transmitting from the reference station a reference signal of audio frequency through the call path, the reference signal being transmitted through a predetermined reference duration 5; receive the reference signal in the mobile cell phone unit; generate in the mobile cell phone unit in response to the reference signal, a response signal 10 of audio frequency; transmitting from the mobile cell phone unit the response signal across the call path during a response time, the response time occurring after a predetermined response delay interval followed by receipt of the reference signal by the mobile cell phone unit, the response signal being transmitted through a predetermined response duration; receiving the response signal at the reference station; measuring at the reference station a difference of the time of the round trip between the transmission of the reference signal and the receipt of the response signal; calculate a total latency based on the difference of the round trip time, the reference duration, the response duration, and the response delay interval; transmitting from the reference station through the call path a synchronization signal during 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 being equal to half of the total latency. receive the synchronization signal in the mobile unit; and adjusting the mobile oscillator in response to the synchronization signal and in this way synchronizing the mobile oscillator with the SPS oscillator. 22. A method of synchronizing a mobile wireless communication 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 such as between the reference station and the mobile device through the connection of the established voice call; at the reference station, maintain a time of the current Satellite Positioning System (SPS) and a periodic SPS time stamp signal associated with the current SPS time. transmitting the data reflecting the current SPS time from the reference station to the mobile device through an established voice call connection encoded as the audio frequency signals; forming a delayed SPS timestamp by delaying the periodic SPS timestamp by the time correction factor; transmitting the delayed SPS time stamp from the reference station to the mobile device; and on the mobile device, synchronize the local clock to the current SPS time in response to the delayed SPS timestamp by synchronizing the local clock to the SPS time maintained by the reference station. The method of claim 22 wherein a specific time correction factor is determined that includes determining a total latency time for the transmission of signals between the reference station and the mobile device through the voice call connection. established 24. The method of claim 22 wherein determining the total latency time includes: transmitting an audio reference signal from the reference station to the mobile device through the established voice call connection; transmitting a response signal through the mobile device to the reference station through the voice call connection established in response to 10 the reference signal; and measuring a latency time between the transmission of the reference signal and the receipt of the response signal at the reference station. 25. The method of claim 23 wherein the time correction factor is calculated as half the total latency time. 26. A method of synchronizing a mobile wireless communication device having a local clock, comprising the steps of: establishing a voice call connection between the mobile device and a reference station; determine a specific time correction factor such as between the reference signal and the mobile device through the voice call connection 25 established; at the reference station, maintain a time of the current Satellite Placement System (SPS) and generate a periodic SPS time stamp signal associated with the current SPS time; transmitting the data reflecting the current SPS time from the reference station to the mobile device through the established voice call connection encoded as audio frequency signals; transmitting the SPS time stamp signal from the reference station to the mobile device; in the mobile device, forming a delayed SPS timestamp signal by delaying the SPS time stamp received by the time correction factor; and then synchronize the local clock to the current SPS time in response to the delayed SPS timestamp by synchronizing the local clock to the SPS time maintained by the reference station. The method of claim 26 wherein determining a specific time correction factor includes determining a total latency time for the transmission of round trip signals between the reference station and the mobile device through the call connection. of established voice. The method of claim 27 wherein determining the total latency time includes: transmitting an audio reference signal from the reference station to the mobile device through the established voice call connection; transmitting a response signal from the mobile device to the reference station through the voice call connection established in response to the reference signal; and measuring a latency time between the transmission of the reference signal and the reception of the signal in response at the reference station. 29. A method according to claim 27, where the correction time factor is calculated as the same as the total latency time. 30. The method of claim 26, wherein determining a specific time-lapse factor includes: transmitting an audio frequency reference signal from the mobile device to the endorsement station through the established voice call connection.; transmitting a response signal from the reference station to the mobile device through the voice call connection established in response to the reference signal; and measuring a latency time between the transmission of the reference signal and the receipt of the response signal in the mobile station. 31. A mobile unit trained by the satellite positioning system (SPS) that has a local SPS time clock and is configured for assisted synchronization, to the mobile unit comprises: an SPS antenna to receive the SPS signals from the SPS satellites. orbit; an SPS receiver coupled with the SPS antenna to receive the SPS signals to form the SPS data and to maintain the local SPS time clock; a microprocessor coupled with the SPS receiver and including software to process the SPS data to form the location data and to synchronize the local SPS time clock; a multi-frequency controller coupled with the microprocessor for generating multifrequency audio tones for encoding the location data and for decoding the received multi-frequency audio tones to form the synchronization data; a wireless communications transceiver capable of operating to send and receive voice communications through a call path of a wireless communications network, including the wireless communications transceiver an audio hole coupled with the multifrequency controller to send the data of encoded location through the call path and to receive and decode the received synchronization data as audio tones through the call path; the software to synchronize the local SPS time clock is capable of. operate to set the local SPS time clock in response to the synchronization data received by the wireless communication transceiver through the call path and which is decoded by the multi-frequency controller. 32. The mobile unit of claim 31, wherein the multifrequency controller is implemented in software executable in the microprocessor. 33. The mobile unit of claim 31 wherein the software for synchronizing the local time clock SPS responds to the synchronization data received through the call path which includes a correction time to synchronize the local time clock SPS, corresponding to the correction time to a difference between the local SPS time and a current SPS time as provided by the SPS orbital satellites. SUMMARY OF THE INVENTION Methods for determining a system latency of a so-called audio 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) through the audio call path from the reference station (102) to the remote unit (108), where a response signal (112) is generated and transmitted back to the reference station ( 102) through the call path after a preselected response delay interval (tiei). A round trip time difference (t¾T) is used to determine the latency of the total system, which is then taken into account when synchronizing the remote unit (108) with the reference oscillator. The reference and response signals (106, 112) are generated as audio signals similar to the sounds of the human voice to avoid destructive attenuation by the voice communications network. One mode includes a wireless telephone unit having an SPS receiver on board. The SPS receiver includes an oscillator that can be synchronized using the method to improve the operation of the SPS receiver. Suitable convenient methods of synchronization and location data disclosed within the existing wireless communication network infrastructures are disclosed. V r