KR100881869B1 - Methods and apparatuses for using mobile gps stations to synchronize basestations - Google Patents

Abstract

The present invention relates to various methods and apparatuses for synchronizing base stations in a cellular network. One example method performs time synchronization between two or more base stations, such as a first base station and a second base station, of a cellular communication system. In this exemplary method, the first time and first geographic location of the first mobile cellular receiver station (MS) is determined from a first satellite positioning system (SPS) located with the first mobile station (MS), and The first time and the first position are transmitted by the first MS to the first base station that determines the time of the first base station from the first time and the first position and the known position of the first base station. Also, in this exemplary method, the second time and second geographic location of the second MS is determined from a second SPS located with the second MS, the second time and the second location being determined by the second time. It is transmitted from the second position and the known position of the second base station to the second base station which determines the time of the second base station. Further methods and apparatuses are described for synchronizing base stations in a cellular network.

Description

METHODS AND APPARATUSES FOR USING MOBILE GPS STATIONS TO SYNCHRONIZE BASESTATIONS

Background of the Invention

The present invention relates to the field of cellular communication systems, and more particularly to the field of cellular communication systems for determining the location of a mobile cellular communication station (MS).

In order to perform position measurement in a cellular network (e.g., cellular telephone network), several methods of performing triangulation using timing information transmitted between each base station of several base stations and a mobile device such as a cellular telephone can be used. come. In one method, the time of receiving a signal from a mobile station, known as a Time Difference of Arrival (TDOA), is measured at several base stations, which calculate the location of the mobile station and locate the location server (location). sent to a positioning entity called server). When performing this method, times-of-day at several base stations are required to coordinate to provide the correct location. In addition, there is a need to accurately know the location of the base stations. 1 is an example of a TDOA system in which the reception times TR1, TR2, and TR3 for the same signal from the mobile cellular telephone 22 are measured by the positioning server at the cellular base stations 12, 14, and 16. It is shown. Positioning server 24 is coupled to receive data from base stations via a mobile switching center 18. The mobile switching center 18 provides a signal (e.g., voice communication) to / from a land-line public switched telephone system (PSTS), so that other telephones (e.g., Signals may also be sent to land-line phones or other mobile phones via PSTS.

Also, in some cases, the location server may communicate with a mobile switching center via a cellular link. In addition, the location server monitors transmissions from several base stations, trying to determine the relative timing of these transmissions.

Another method, called EOTD, measures the arrival time of a signal transmitted from each base station of multiple base stations at the mobile station. In FIG. 1, if the arrows of TR1, TR2, and TR3 are reversed, this is the case. This timing data may then be used to calculate the position of the mobile station. When the timing information so obtained by the mobile station is transmitted to this server via the link, the calculation may be performed at the mobile station itself or at the positioning server. In addition, base station times must be adjusted to accurately assess their location. In both methods, the location of the base station is determined by standard surveying methods and may be stored in a server, which is a base station or some sort of computer memory.

However, a third method of performing position measurement is to use a Global Position Satellite System (GPS) or other satellite positioning system (SPS) at the mobile station. The method may use a fully autonomous or cellular network to provide assistance data or share location calculations. Examples of such methods are described in US Pat. No. 5,841,396; No. 5,945,944; And 5,812,087. Briefly, these various methods are called "SPS".

The combination of either the EOTD and the TDOA and the SPS system is referred to as a "hybrid" system.

As is apparent from the above, for EOTD or TDOA, the time coordinates between the various cellular base stations are required for accurate location calculation of the mobile station. The visual accuracy required at the base station depends on the details of the positioning method used. In one method, a round trip delay (RTD) is found for the signals returned after being sent from the base station to the mobile station. In a similar but alternative method, a round trip delay is found for signals returned from the mobile station to the base station. Each of these round trip times is divided into two, to determine an estimate of one-way time delay. Awareness and one-way delay for the location of the base station limits the location of the mobile station to a circle on the earth. Another measurement with the second base station then creates a two-way intersection, which in turn constrains its location to two points on the earth. The third measure resolves ambiguity. In round trip timing, measurements with several base stations are adjusted in seconds, no matter how bad, so it is important that when the mobile station moves quickly, the measurements correspond to what happens at the same location.

In other situations, it is not possible to perform round trip measurements for each two or three base stations, but only for one base station, which is the first base station to communicate with the mobile station. This is the case for the IS-95 North American CDMA cellular standard. Also, due to device or signaling protocol limitations, accurate measurement of round trip timing may not be possible at all. In this case, since only the time difference between the mobile station-base station paths is used, it is even more important to maintain accurate timing at the base station when performing triangulation operations.

Another reason for providing accurate timings to base stations is to provide time to mobile stations to assist in GPS based location calculations, the information may result in reduced time for the first location, and / or improved sensitivity. It may be. The accuracy required for this situation may range from a few microseconds to 10 milliseconds, depending on the desired performance improvement. In a hybrid system, base station timing serves two purposes of improving TOA or TDOA operation as well as GPS operation.

Conventional methods for network timing used a special fixed position timing system called a position measurement unit (LMU) or a timing measurement unit (TMU). Typically, the units have a GPS receiver that can determine the correct time. The location of the unit may be surveyed, which may be performed with a GPS based surveying device.

Typically, LMUs or TMUs observe timing signals such as frame markers, provide cellular communication signals transmitted from a base station, and provide these timing signals to local signals found through a GPS set or other time determining device. Try to time-tag with time. The message may then be sent to the base stations (or other subcomponents) to allow these entities to keep track of the elapsed time. Then, upon instruction, or periodically, special messages may be sent via the cellular network to the mobile station served by the network indicating the time associated with the framing structure of the signal. This is particularly easy for systems such as GSM where the entire framing structure is maintained for periods of more than three hours. The location measuring unit may serve other purposes, such as acting as a location server, that is, the LMU may actually perform arrival time measurements from the mobile stations to determine their location.

One problem with the LMU or TMU method is that they require the construction of new and special fixed devices at each site or other sites within the communication range of multiple base stations. This can be very expensive to install and maintain.

Summary of the Invention

The present invention provides various methods and apparatuses for synchronizing cellular base stations in a cellular network. One example method performs time synchronization between two or more base stations, such as a first base station and a second base station, of a cellular communication system. In this exemplary method, the first time and first location of the first mobile cellular station (MS) is determined from a first satellite positioning system (SPS) located with the first mobile station (MS), the first time And the first position is transmitted by the first MS to the first base station that determines the time of the first base station from the first time and the first position and the known position of the first base station. Also, in this exemplary method, the second time and the second position of the second MS are determined from a second SPS located with the second MS, the second time and the second position being equal to the second time. It is transmitted from the second position and the known position of the second base station to the second base station which determines the time of the second base station. These mobile stations can be used for normal communication operations and need not be fixed to buildings or other structures, so their use of timing networks prevents high real estate costs to maintain fixed timing devices. Further methods and apparatuses are described for synchronizing base stations in a cellular network.

Brief description of the drawings

The invention is illustrated by way of example and not by way of the accompanying drawings, like reference numerals denote like objects.

1 illustrates an example of a conventional cellular network that determines the location of a mobile cellular device.

2 illustrates an example of a mobile cellular communication station having a GPS receiver and a cellular communication transceiver, which may be used with the present invention.

3 illustrates an example of a cellular base station that may be used in various embodiments of the present invention.

4 is a flowchart illustrating one embodiment of a method according to the present invention.             

5a and 5b are flow charts showing yet another embodiment of the method according to the invention.

6A shows two signals processed according to one exemplary method of the present invention.

6B shows a representation of a signal at a base station illustrating how the base station updates its clock to synchronize with other base stations.

7 illustrates an example of a location server that may be used with certain embodiments of the present invention.

8 illustrates a framing structure of a GSM cellular signal.

details

 This article describes various methods and apparatus for determining time at a cellular base station and synchronizing the cellular base stations in a cellular network. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. For example, various configurations for base stations and mobile communication stations are provided for illustrative purposes rather than as limitations of the present invention. However, it will be appreciated that the invention may be practiced without these specific details. In another example, well-known configurations and devices are shown in block diagram form for ease of description.

One method described herein utilizes mobile communications stations that include (or couple to) a GPS receiver that determines both time and location. 2 shows an example of such a mobile communication station. Such GPS processing may be performed in autonomous mode if the received signal is large, or with the aid of the device in the infrastructure (servers) if the received signal-to-noise ratio is low. In addition, a server device (eg, a positioning server shown in FIG. 7 and described in more detail below) may contribute to vision and position determination in situations where improved performance is desired (eg, US Pat. 5,945,944; 5,841,396; and 5,812,087).

In a network such as GSM, visual information from a GPS receiver may be used to time-tag the framing structure of a received communication (eg, GSM) signal. For example, one may use the start of a particular GSM frame boundary that occurs every 4.6 ms (see FIG. 8). There are 2048 such frames per superframe that last for 3.48 hours. Thus, when this timing information is delivered to the base station (BS; for example, the cellular base station shown in FIG. 3) via normal cellular signaling, the largest error remaining in the transmission time is the mobile station (MS; Propagation time from the mobile cellular communication station in FIG. 2 to the BS. Of course, some of the other remaining errors, such as multipath delay and transmission delay through the MS hardware, may remain, and methods are described below that describe such remaining errors.

Various methods may be used to estimate the propagation delay between MS-BS described above. The first and most accurate method can be used when the MS and / or the server correctly determine the MS location via the GPS unit and are correctly aware of the BS location (eg, some perception through the survey). . In this case, the propagation time can be determined by dividing the BS-MS range by the speed of light (typically in some network entities). The BS may then determine the timing of its transmission frame marker by simply subtracting the propagation time calculated from the frame marker timing provided by the MS. This method is described in detail below with reference to FIGS. 5A, 5B, 6A and 6B.

A second and less accurate method of estimating propagation delay between MS-BSs can be achieved by “timing advance” information previously available within the MS and BS. The original intended purpose of that information is about intra-cell traffic coordination. However, the timing-advanced metric can be processed in a direct manner to yield these inter-MS-BS delay estimates. The accuracy achieved by these time alignment parameters is mainly determined by the time resolution of the relevant communication bit intervals. Thus, accurate propagation delay estimates can be obtained within a few microseconds or tens of microseconds. This second method, although less accurate than the first delay estimation method above, may be particularly advantageous in situations where privacy concerns preclude network processing of the correct MS location.

As mentioned above, in some applications, base stations do not need to be synchronized to microsecond type of accuracy, only to milliseconds or even second types. For these scenarios, it may be counterproductive to compensate for delays between MS-BSs, since small delays such as tens of microseconds are less important than the required timing accuracy. Thus, the coarse time obtained by the MS may simply be used by "time tagging" the signal from the BS. This is sent to the BS without the need for precise BS-MS range data. This situation involves coarse time tagging at a much lower signal level than GPS receivers can precisely tag (see, for example, U.S. Patent No. 5,812,087, and here on April 16, 1998). And US patent application Ser. No. 09 / 062,232, filed and co-pending. Furthermore, once the coarse time-tagging is performed, the accuracy may be maintained for a long time because the frequency of the base station transmission data is very stable.

4 illustrates an exemplary method according to an embodiment of the present invention. In operation 151, the mobile cellular system determines a representation of its time at the mobile cellular communication station. In one embodiment where a GPS receiver such as GPS receiver 52 is used within a mobile cellular communication station such as shown by 50 in FIG. 2, the GPS time is determined by reading the GPS time deviating from the GPS signal from the GPS satellites. It may also be obtained from. Alternatively, a technique for determining time may be used, as disclosed in US Pat. No. 5,812,087. In this method, a sample of GPS signals received at the mobile station may be sent to a location server or another server that processes this record to determine the reception time, as disclosed in US Pat. No. 5,812,087. In addition, the time in operation 151 may be optionally calculated using one of the various methods filed on April 16, 1998 and disclosed in co-pending application number 09 / 062,232. The method shown in FIG. 4 proceeds to operation 153 when determining the propagation delay between the mobile cellular communication station and a cellular base station, such as the cellular base station shown in FIG. In some embodiments described above, if the time determined in operation 151 has more errors associated with it than the propagation delay, this operation is optional. Also, as discussed above, this propagation delay may be determined by determining the location of the mobile station (processing the GPS signal) and determining the location of the cellular base station. In operation 153, the propagation delay is determined by dividing the distance between these two positions by the speed of light.

In operation 155, when using this optional operation, the time at the cellular base station is determined from the time at the mobile station (sent from the mobile cellular communication system) and the propagation delay determined in operation 153.

Each cellular base station in the network may use this procedure to synchronize all base stations with respect to one time standard, such as GPS time. In this manner, an improved triangulation or range may be obtained based on the use of timing information transmitted between each of several base stations and the mobile system. Many other uses for timing information may be possible. These include allowing more efficient "handoff" for the mobile station's communication from one base station to the next, and allowing clear time to be transmitted throughout the network for various purposes.

Next, FIGS. 5A, 5B, 6A and 6B will be described as another example of one embodiment according to the present invention. This method may be performed with a mobile cellular communication system such as the system 50 shown in FIG. 2 and the cellular base station 101 shown in FIG. 3.

The mobile cellular communication station 50 shown in FIG. 2 includes a GPS receiver 52 having a GPS antenna 51 and a cellular communication transceiver 54 having an antenna 53. Alternatively, the GPS receiver 52 may be included in another chassis (and not integrated into the chassis supporting components of the mobile station 50, such as the cellular communication transceiver 54), but the cellular communication transceiver Coupled to 54 and present near the transceiver 54; In this situation, the mobile station 50 does not have a GPS receiver and does not require it if the GPS receiver is coupled to the mobile station 50 and located together in the mobile station 50. GPS receiver 52 is a conventional hardware correlator based GPS receiver, a matched filter based GPS receiver, or a GPS receiver that uses a buffer to store digital GPS signals processed in fast convolution, or US Pat. No. 6,002,363 As disclosed in the call, it may be a GPS receiver that shares components of the GPS receiver with a cellular communication transceiver (see, eg, FIG. 7B of US Pat. No. 6,002,363, referred to herein). The cellular communication transceiver 54 is a well known cellular standard, including a GSM cellular standard, or a PDC communication standard, or a PHS communication standard, or an AMPS analog communication standard, or a North American IS-136 communication standard, or an asynchronous broadband spread spectrum CDMA standard. It may be a modern cellular telephone that operates either one. The GPS receiver 52 is coupled to the cellular communication transceiver 54 to provide the GPS time and location in one embodiment to the cellular communication transceiver 54 (then send this information to the base station). In addition, cellular communication transceiver 54 may provide assistance data, such as Doppler information or time information, to the GPS receiver disclosed in US Pat. No. 5,841,396 or 5,945,944. In addition, the coupling between the GPS receiver 52 and the cellular communication transceiver 54 may transmit a record to or from the cellular base station to determine the time at the GPS receiver disclosed in US Pat. No. 5,812,087. It can also be used to match the record with other records. The location server is used to provide assistance data to the mobile cellular communication station to determine location or time in system 50, or the location server shares processing of information (e.g., location server is time or mobile system 50 In the situation or embodiments, which determine the calculation of the final position of the position of the position), it can be seen that the location server shown in FIG. 7 and described further below is connected to a cellular base station via a communication link to assist in the processing of data. have. The position of the mobile station is usually not fixed and is not usually predetermined.

3 illustrates an example of a cellular base station that may be used with various embodiments of the present invention. The base station 101 is a cellular transceiver 102 having one or more antennas 102a for communicating with signals from and at a mobile cellular communication station present in the area served by the cellular base station 101. It is provided. For example, the mobile cellular communication station 50 may be one of the mobile stations served by the cellular base station 101, typically depending on the range of signals transmitted by the mobile system 50. The cellular transceiver 102 may be a conventional transceiver used to transmit and receive cellular signals, such as GSM cellular signals or CDMA cellular signals. Clock 103 may be a conventional system clock that maintains time at the cellular base station. The accuracy of this clock may be improved in accordance with the methods of the present invention to synchronize this clock with other clocks in other cellular base stations according to the methods disclosed herein. In many cases, this clock may be very stable, but over time periods the clock drifts significantly against the initial time setting. In general, as is well known in the art, the cellular base station 101 is a network that transmits data to and from the cellular transceiver 102 to couple the cellular transceiver to the mobile switching center. With an interface. In addition, the cellular base station 101 may include a digital processing system 105 that may be located remote to the cellular base station or at the same site as the cellular base station itself. The digital processing system 105 is coupled to the clock 103 to adjust or re-measure the clock's time, synchronizing the clock to other clocks at further cellular base stations in accordance with the methods of the present invention. In many cases, the clock is very stable but runs freely, affecting network operation to actually change the clock's time strokes. Instead, the time associated with the clock epochs can be adjusted. This is what is called "recalibrating". In addition, the digital processing system 105 is coupled to the network interface 104 to receive data or communications from the mobile switching center, and to synchronize the clock 103 with other clocks at other cellular base stations. Receive data from the cellular transceiver 102, such as a time-tagged frame marker transmitted from the.

The method shown in FIGS. 5A and 5B begins at operation 201 when the cellular base station transmits a cellular signal to a mobile cellular communication station. Optionally, this signal may include a request for synchronization information from the mobile system to cause the cellular base station to synchronize itself with other cellular base stations. The cellular base station provides time tags or markers in its signal transmitted to the mobile system. This marker may be a marker that is a unique part of the framing structure of the signal. This also means that base station 1 receives a signal having a framing structure that includes markers M1, M2, M3, M4, M5, M6, M7, M8, and M9 as shown in signal 301 of FIG. 6A. The transmitting is shown in FIG. 6A. The mobile system in operation 203 of FIG. 5A receives a cellular signal with markers. Also, as is well known in the art, at the same time as receiving the cellular signal, the mobile station receives the GPS signal from the GPS satellites including GPS time. The mobile station may then time-tag the marker in the cellular signal received from the base station with the GPS time representing the time when the marker is received in the mobile system in GPS time. This is also shown in Fig. 6A by a signal 303 representing a signal received by the mobile station 1 from the base station 1, which is delayed by the propagation delay 307. As shown in FIG. 6A, the time tag 305 can be applied to the marker M1, which represents the GPS time associated with the reception time of this marker in the mobile system. The mobile station in operation 205 determines its position simultaneously with the time tagging of the marker in the cellular signal. The GPS receiver at the mobile station may autonomously determine its position (e.g., a conventional hardware correlator based GPS receiver may read ephemeris data from GPS satellites to determine its own position), or It is also possible to determine its location with the help of a server, such as the location server, which is coupled to the cellular network and shown in FIG. In operation 207, the mobile station transmits to the cellular base station its GPS position associated with its location (or pseudoranges that cause the location server to determine its location) and a marker time tagged by the mobile station.

In operation 209, the cellular base station calculates its time using the location of the mobile station and its known predetermined location to determine the propagation delay between the mobile station and the base station. This propagation delay is subtracted from the GPS time associated with that marker to determine the GPS time at its transmission marker. This is shown in FIG. 6B where base station 1 receives time tag TR1 from the mobile system. This time tag TR1 represents the GPS time associated with the marker M1. The propagation delay 307 is subtracted from the GPS time TR1 to derive the time T1 associated with the marker M1. That is, time T1 is the time tag 309 associated with marker M1 at the base station. The current time at the base station is then updated by combining the GPS time at tag 309 with the current frame M9 to generate the current time 311 as shown in FIG. 6B. That is, there is a known time relationship given to the framing structure of the signal 301 between the marker M9 and the marker M1 in the signal 301. The time difference between these two markers given to the known framing structure is summed with time T1 to produce the current time 311. Thus, the current time at the cellular base station is updated from the GPS time associated with the transmission marker time tagged by the mobile station. This is illustrated by operation 211 in FIG. 5B. Then, in operation 213, the last time that the clock at the cellular base station is synchronized is optionally stored to determine when it is suitable to update the clock, so that the clock is different from other clocks at other cellular base stations. Motivate In operation 215, the cellular base station or a remote entity assisting the cellular base station may determine when to resynchronize. For example, a set time of minutes may automatically trigger another synchronization process. Alternatively, other techniques may be used to determine when to resynchronize the clock at the base station to other clocks of other cellular base stations.

7 illustrates an example of a location server 350 that may be used with various embodiments of the present invention. For example, as disclosed in US Pat. No. 5,841,396, the server may provide assistance data, such as Doppler or other satellite assistance data, to the GPS receiver of the mobile station 50, or the location server may provide more information than the mobile station 50. After performing the final position calculation (after receiving the pseudorange or other data for which the pseudorange may be determined), the position determination may be forwarded to the base station so that the base station can calculate the propagation delay. Typically, a location server includes a data processing unit such as a computer system, a modem or other interface 352, a modem or other interface 353, a modem or other interface 354, a mass storage device 355 (eg, software and Data storage) and, optionally, a GPS receiver 356. This location server 350 may be coupled to three different networks, shown as networks 360, 362, and 364. The network 360 includes a cellular switching center or multiple cellular switching centers and / or terrestrial based telephone system switches; Alternatively, modem 353 may be coupled directly to a cell site, such as cellular base station 101. In general, multiple cellular base stations are arranged to cover a geographic area with wireless coverage, and as is well known in the art, these different base stations are coupled to one or more mobile switching centers (see FIG. 1). Thus, multiple instances of base station 101 are geographically distributed but must be coupled together by a mobile switching center. The network 362 may be a network of reference GPS receivers that provide differential GPS information, and may provide GPS astronomical location data for use in calculating the location of the mobile system. This network is coupled to the data processing unit 351 via a modem or other communication interface 354. The network 364 includes network components, such as other computers, or the data processing system 105 shown in FIG. 3 (via optional wiring not shown in FIG. 3). In addition, the network 364 may have computer systems operated by emergency operators, such as Public Safety Answering Points (PSAPs), that respond to 911 telephone calls. Various examples of methods using location server 350 are described in US Pat. No. 5,841,396, filed April 16, 1998; 5,874,914; 5,874,914; No. 5,812,087; And US patent application Ser. No. 09 / 062,232, which is disclosed in a number of US patents and patent applications.

The methods described above determine the effective transmission time at the surface of the BS antenna. The use of multiple MSs may be easy to reduce errors through the averaging procedure. This assumes that system bias can be eliminated.

Concerns about sufficient MS activity to support timing (eg, early morning hours) can be improved by positioning and periodically invoking MSs at various locations.

Typical timing errors due to GPS processing in one MS may be on the order of 10 to 30 nanoseconds. Thus, other sources of error, such as multipath, may be suppressed.

The stability of the BS oscillator affects how often timing measurements are required and distributed. The drift vs. time of the BS oscillator can be modeled and this update can be reduced.

Next, several methods of measuring the error and the impact of the mobile station receiver are described. In some embodiments of the present invention, a mobile station (eg, mobile cellular communication station 50 of FIG. 2) has its location P _mobile = [x _m , y _m , z _m ] and the time T _mobile associated with that location. Decide By simply measuring the time delay from the positioning time (eg, GPS time) to the time of the framing marker, this time may be associated with the framing marker of the received cellular communication signal. Alternatively, positioning may be performed at the same time as this framing marker. Thus, without losing generality, it is assumed that T _mobile is equal to the time of the framing marker observed by the _mobile station.

It is also assumed that the mobile station has recognized the position P _base = [x _b , y _b , z _b ] of the _base station. Then, if the multipath delay is minor, the range from time base T _mobile to base station to mobile station

to be.

Next, if there is no delay in the receiving circuits, the range of propagation time delay between the base station and the mobile station is R _Tm / c, where c is the speed of light.

For clarity, the transmission time of the framing marker at the base station is the occurrence time of this marker at the surface of the transmission antenna of the base station. Therefore, if there is no multipath delay or delay of the receiver, the transmission time of the frame marker on the antenna surface of the base station is T _base = T _mobile -R _Tm / c.

Next, the GPS receiver may have a delay (referred to as b _GPS ) associated with its RF and digital signal processing. Similarly, there may be a delay (called b _comm ) associated with the RF and digital signal processing of the communication receiver. Thus, referring to FIG. 2, b _GPS is caused by a delay in the GPS receiver 52 and b _comm is caused by a delay in the cellular communication transceiver 54. In addition, due to the multipath there may be additional delays b _mult in propagation from the base station to the communication receiver. This assumes to suppress any multipath delay associated with GPS measurements. Thus, instead of providing an unbiased measurement of transmission time at the base station, it provides a measurement with a bias (measurement time _minus real time) of b _mult + b _comm -b _GPS . Typically, b _mult may suppress further sources of error, especially when performing a receiver measurement function (described below). Thus, in general, the estimation time for the transmission of the framing marker is later.

B _comm -b _GPS may be measured by simply using a base station simulator which transmits a cellular signal in a framing structure and is directly connected to the antenna port of the mobile station and measures the reception time of the frame marker at the mobile station. In this procedure, the mobile station's GPS receiver is used to time-tag (in time received by the mobile station's GPS receiver) frame markers. It is assumed that the base station simulator uses the GPS receiver to synchronize its transmission with the GPS time provided by this GPS receiver. Since the transmission delay from the base station to the receiver is zero, this method determines b _comm -b _GPS without error (except for a small amount of measurement noise). This measurement procedure can be fully automatic and is easily incorporated into the receiver testing procedure during manufacture. Some simple variations of this procedure are possible, such as transmitting the simulated signals from the simulator in close proximity to the mobile station.

Excessive multipath delay, b _mult , _leaves the dominant source of error in synchronizing the base stations. For line-of-sight paths, this delay has a bias that is zero average. For paths that combine a straight path and a reflected path or reflected paths, the average (measured straight path delay versus actual straight path delay) is greater than zero. In general, within a short time period, the base station receives multiple estimates of the time associated with each frame marker from several mobile units and each mobile unit. These visual estimates are D ₁ , D ₂ ,. It is called D _K. In general, the smallest of these estimates has an average bias much lower than any individual measurement, or the average of those measurements. If the number of measurements, K, is large, the measurements may be sorted from low to high, taking an average of at least 10% of the measurements, or some similar statistics. This significantly reduces the average bias and takes advantage of some of the averaging benefits.

If the base station has a very stable clock, it may use this clock to keep time between updates from remote mobile units. The clock may be used in a smoothing process to remove poor measurements from mobile stations due to multipath. In addition, measurements from the mobile station may be used to measure the long term stability of the base station clock, for example due to aging. For example, the GSM hyperframe is about 3.48 hours and the superframe is 6.12 seconds. Thus, the hyperframe is about 12528 seconds. A typical GPS time measurement without differential corrections should be accurate at about 100 nanoseconds. This accuracy results in measurements of the base station oscillator's long term frequency approximately 100 nanoseconds / 12528 seconds = 8x10 ^-12 . In addition, measurements over a period of 6.12 seconds allow for long-term frequency accuracy of about 1.6x10 ^-8 . This measurement of long term stability is best performed by measuring several times with the same mobile receiver. Thus, stationary or slow moving mobile stations are best suited for this purpose. Continuous measurements of mobile station location provide the required information about the dynamics of the mobile receiver.

If there is significant user motion, it is important that no Doppler related effects affect the timing measurement described above. In particular, if the mobile station measures time at one moment and predicts the time associated with the cellular signal frame boundary occurring at another moment, errors may be caused by the mobile station's motion. In particular, this is the case when the mobile station moves quickly or the difference in these time instances is large. There are many ways to deal with this type of problem. For example, if a mobile station can determine its speed, it may provide this data to a base station that can compensate for errors due to Doppler associated with a range rate between the mobile station and the base station.

Although the methods and apparatus of the present invention have been described with reference to GPS satellites, it can be seen that the techniques are equally applicable to positioning systems using pseudolites or a combination of satellites and pseudolites. In general, pseudolight is a ground based transmitter that broadcasts a PN code (similar to a GPS signal) that may be modulated onto an L-band carrier signal that is synchronized with GPS time. Each transmitter may be assigned a unique PN code to allow identification by the remote receiver. Pseudolites are useful in situations where GPS signals from orbiting satellites are not available, such as in tunnels, mines, buildings or other closed areas. The term "satellite" as used herein is intended to include pseudolites or equivalents of pseudolites, and the term GPS signals used herein is intended to include GPS-like signals from pseudolites or equivalents of pseudolites.

In the foregoing description, the present invention has described the application of the Global Positioning Satellite (GPS) system of the United States. However, these methods are equally applicable to similar satellite positioning systems and, in particular, the Glonass system in Russia. The Glonass system is essentially different from the GPS system in that emissions from different satellites are identified from another using slightly different carrier frequencies rather than using different pseudorandom codes. The term "GPS" as used herein encompasses another satellite positioning system, including the Russian Glonass system.

In the foregoing description, the invention has been described with reference to specific exemplary embodiments. However, various modifications and changes are possible within the scope without departing from the broader spirit and scope of the invention as set forth in the claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

Claims (34)

A method of performing time synchronization between two or more base stations, including a first base station and a second base station of a cellular communication system, the method comprising: Determining a time and location of the first mobile cellular station; Transmitting the time and location of the first mobile cellular station to the first base station via a first cellular communication link; Determining a time of the first base station from the time and the location of the first mobile cellular station, together with a known location of the first base station; Determining the time and location of the second mobile cellular station; Transmitting the time and location of the second mobile cellular station to the second base station via a second cellular communication link; And Determining, together with a known location of the second base station, the time of the second base station from the time of the second mobile cellular station and the location, The first mobile cellular station and the second mobile cellular station each use a satellite positioning system receiver co-located to determine the time and location of the first mobile cellular station and the second mobile cellular station. How to do motivation. The method of claim 1, Wherein the time of the first mobile cellular station is measured with respect to a frame synchronization epoch present in the cellular communication signal transmitted from the first base station and received by the first mobile cellular station. How to do it. The method of claim 1, And determining the time of the first base station is performed with respect to a frame synchronization period present in the cellular communication signal transmitted from the first base station. The method of claim 1, At least one of the first cellular communication link and the second cellular communication link is a GSM communication standard, a PDC communication standard, a PHS communication standard, an AMPS analog communication standard, a North American IS-136 communication standard, or an asynchronous broadband spread spectrum CDMA standard. A method of performing time synchronization using one standard. The method of claim 1, And the first mobile cellular station and the second mobile cellular station are the same mobile cellular station. The method of claim 1, And the first mobile cellular station and the second mobile cellular station are different separate mobile cellular stations. A system for performing time synchronization between two or more base stations including a first base station and a second base station of a cellular communication system, the system comprising: A first satellite positioning system (SPS) receiver capable of determining the time and location of a first mobile cellular station capable of conveying the time and location of a first mobile cellular station to the first base station via a first cellular communication link; A first measurement coupled to the first base station, the first measurement being capable of determining the time of the first base station from the time and the location of the first mobile cellular station together with a known location of the first base station; Device; A second satellite positioning system (SPS) receiver capable of determining the time and location of a second mobile cellular station capable of conveying the time and location of a second mobile cellular station to the second base station via a second cellular communication link; And A second measuring device coupled to the second base station, the second measuring device being capable of determining, with the known position of the second base station, the time of the second base station from the time and the position of the second mobile cellular station; , Wherein the first mobile cellular station is located with the first SPS receiver, and the second mobile cellular station is located with the second SPS receiver. The method of claim 7, wherein And the first SPS receiver is integrated with the first mobile cellular station in an enclosure. The method of claim 8, And the first SPS receiver and the first mobile cellular station share at least one common component. The method of claim 7, wherein Wherein the time of the first mobile cellular station is measured with respect to a frame synchronization interval present in a cellular communication signal transmitted from the first base station to the first mobile cellular station. The method of claim 7, wherein And the determination of the time of the first base station is performed with respect to a frame synchronization period present in the cellular communication signal transmitted from the first base station. The method of claim 7, wherein At least one of the first cellular communication link and the second cellular communication link is one of a GSM communication standard, a PDC communication standard, a North American IS-136 communication standard, a PHS communication standard, an AMPS analog communication standard, or an asynchronous broadband spread spectrum CDMA standard. A time synchronous performance system using one standard. The method of claim 7, wherein The first mobile cellular station and the second mobile cellular station are the same mobile cellular station, And the first SPS receiver and the second SPS receiver are the same receiver. The method of claim 7, wherein The first mobile cellular station and the second mobile cellular station are different separate mobile cellular stations, And the first SPS receiver and the second SPS receiver are different separate receivers. The method of claim 1, Further comprising a method of determining a mobile cellular station time bias at one or more of the first mobile cellular station and the second mobile cellular station comprising a co-located SPS receiver, The additional method is Placing at least one of the first mobile cellular station and the second mobile cellular station near a cellular base station simulator; Synchronizing the cellular base station simulator to a precise time reference; Determining, using the co-located SPS receiver, one or more times of view of the first mobile cellular station and the second mobile cellular station; Using the time to determine one or more time biases of the first mobile cellular station and the second mobile cellular station; And Storing one or more time biases of the first mobile cellular station and the second mobile cellular station in a memory added to one or more of the first mobile cellular station and the second mobile cellular station. How to do it. The method of claim 15, And the circuit of the first mobile cellular station and its SPS receiver and the circuit of the second mobile cellular station and its SPS receiver are contained in one enclosure. A method performed at a mobile cellular communication station and for establishing a time at a first base station in a cellular communication system, the method comprising: Determining location information of the mobile cellular communication station, wherein the location of the mobile cellular communication station is determined from the location information; Determining a time indicator indicative of the time at the mobile cellular communication station for a signal available at the first base station; And Transmitting at least one of the location information and the location, and transmitting the time indicator from the mobile cellular communication station to the first base station, wherein at least one of the location information and the location and the time indicator are cellular And a step of transmitting, used in establishing a time at the first base station such that the first base station is synchronized with other base stations in a communication system. The method of claim 17, The mobile cellular communication station includes a satellite positioning system (SPS) receiver for determining the location information including at least a pseudorange in an SPS satellite, The signal available at the first base station is a cellular communication signal transmitted from the first base station to the mobile cellular communication station, And the time indicator corresponds to a marker in the signal. The method of claim 18, And the time indicator comprises at least one of a sampling of an SPS signal received by the SPS receiver and a visual message in the SPS signal. The method of claim 19, A location server receives the location information, determines the location and provides the location to the first base station. A method performed remotely for a mobile cellular communications station, the method of establishing time at a first base station in a cellular communications system, comprising: Receiving a time indicator from the mobile cellular communication station, representing a time at the mobile cellular communication station, the time indicator being determined for a signal available at the first base station; And At the first base station, determining a time from the time indicator to synchronize the first base station with other base stations. The method of claim 21, And the signal is a cellular communication signal transmitted from the first base station to the mobile cellular communication station. The method of claim 22, Receiving a location of the mobile cellular communication station, Wherein the time at the first base station is also determined from the location of the mobile cellular communication station and a predetermined location of a known location of the first base station. The method of claim 23, The location is not predetermined that the mobile cellular communication station is not fixed, The location and the known predetermined location determine a propagation delay between the mobile cellular communication station and the first base station. The method of claim 24, The other base stations are synchronized to the first base station by receiving further time indicators from at least one of the mobile cellular communication station and another mobile cellular communication station, And the another time indicator and the time indicator are based on the same time standard. The method of claim 25, The same time standard is Global Positioning System (GPS) time. A base station apparatus used in a cellular communication system, Wireless cellular transceiver; A network interface coupled to the wireless cellular transceiver; And A clock coupled to the wireless cellular transceiver, The wireless cellular transceiver receives a time indicator from a remote mobile cellular communication station indicating a time at a mobile cellular communication station, the time indicator being determined for a signal available at the base station apparatus, wherein the time for the clock is And the base station apparatus is determined from the time indicator such that the base station apparatus is synchronized with other base stations. The method of claim 27, The signal is a cellular communication signal transmitted from the base station apparatus to the mobile cellular communication station. The method of claim 28, The network interface delivers terrestrial based communications to the mobile cellular communication station via the wireless cellular transceiver; The wireless cellular transceiver to receive a location of the mobile cellular communication station, The base station apparatus further determines a time with respect to the clock from the position and a predetermined predetermined position of the first base station. The method of claim 29, Coupled to the clock and coupled to at least one of the wireless cellular transceiver and the network interface to determine propagation delays from the location and the known location, using the propagation delay and the time indicator. And a digital processing system to set the time or provide correction to the clock. The method of claim 28, The other base stations are synchronized to the base station apparatus by receiving further time indicators from at least one of the mobile cellular communication station and another mobile cellular communication station, The another time indicator and the time indicator are based on the same time standard. An apparatus comprising a mobile cellular communication station, The mobile cellular communication station, Wireless cellular transceiver; A satellite positioning system (SPS) receiver coupled to the wireless cellular transceiver, the satellite positioning system (SPS) receiver indicating a time at the mobile cellular communication station and determining a time indicator determined for a signal available at a base station, The wireless cellular transceiver transmits the time indicator to the base station, the time indicator being used to establish a time at the base station such that the base station is synchronized with another base station capable of wireless communication with the mobile cellular communication station; A device comprising a mobile cellular communication station. The method of claim 32, The SPS receiver determines a location, the wireless cellular transceiver transmits the location to the base station, The signal is a cellular communication signal transmitted from the base station to the mobile cellular communication station, And the time indicator comprises a mobile cellular communication station corresponding to a marker in the signal. The method of claim 33, wherein And the time indicator is a mobile cellular communication station that is a visual message in an SPS signal received by the SPS receiver.

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