GB2370941A

GB2370941A - Error vector location of mobile unit by two measurements

Info

Publication number: GB2370941A
Application number: GB0022974A
Authority: GB
Inventors: John Graham King
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-09-19
Filing date: 2000-09-19
Publication date: 2002-07-10
Also published as: GB0022974D0

Abstract

A measurement to a first accuracy is corrected by use of an error vector determined by a second more accurate measurement. The measurements may be made by the same system or by GPS, wheel rotation and road map knowledge systems. A short message service text message may be sent from the mobile to the MSC, which analyses the message and returns the location co-ordinates to a service receiver which acknowledges receipt. The calculated error vector is used to determine the accurate location of mobile terminal 2.

Description

METHOD AND SYSTEM FOR MOBILE TERMINAL LOCATION The present invention relates to a method and system for locating a mobile terminal located within a land based mobile network.

Third generation (3G) and global system for mobile (GSM) mobile telecommunications systems are providing an increasing number of services to mobile phone users, above and beyond that of the traditional ability to make telephone calls. The provision of any service to a mobile terminal within a mobile network is dependent upon the network and network control elements such as the mobile services switching centre (MSC) having knowledge as to the actual location of the mobile terminal within the network. Within the GSM system, at any time an active mobile terminal (wherein active refers to a terminal which is not powered down) will be registered with a base station within a particular cell of the base station system. By base station system (BSS) we mean the radio equipment and base stations geographically distributed in order to provide network service across a wide geographical area. Typically one base station will serve one cell. A typical cellular deployment is shown in Figure 1, wherein a plurality of cells are geographically contiguous, each cell being defined by the coverage area of a base station 12 provided in the centre of the cell. Each base station 12 communicates via a communications link 20 to a mobile services switching centre (MSC) or short message services switching centre (SMSSC) 16 which is the gateway for the BSS into a wide area network or public switch telephone network.

In Figure 1, a mobile terminal 2 is registered with a particular base station 8 such that the mobile network has the knowledge that the mobile terminal is within the coverage area of the base station 8.

In addition to knowing that a particular mobile terminal is within a particular cell, various systems are known in the art which can provide for more accurate positioning of a mobile terminal by analysing a received message from the mobile to attempt to determine the radio conditions under which the mobile is

operating. By then correlating the detected conditions with known conditions across the network, a more accurate positioning can be acquired Other positioning systems which operate on other concepts are also known in the art, such as for example, simple direction-finding based systems However, whilst the mobile location systems discussed above make it possible to locate the position of a mobile to sub-cell resolution, the best accuracy which is known in the art is to an RMS (root-mean-square) error of 98 metres, with a 125 metre accuracy in 83% of cases (see http ://www cursorsystem. co. uk/), which is insufficient to direct services such as taxis, ambulances, rescue services or the like to the mobile location, and especially within a crowded urban environment.

Accurate positioning anywhere on Earth can also be obtained using the well-known Global Positioning System (GPS). Typically, a GPS receiver receives timing signals from a plurality of orbiting satellites, and from the timing signals the position of the receiver anywhere on Earth can be accurately determined to an accuracy of a few meters, or in best cases, sub-metre accuracy.

It has been known to combine a GPS receiver with a mobile telephone in order to allow for mobile telephone location (i. e. the mobile telephone merely transmits its location as determined by the on-board GPS receiver), but such combined systems are costly and can exhibit relatively short battery life due to the requirement to power both the GPS receiver as well as the mobile telephone.

It is an object of the present invention to provide a new method and system of mobile terminal location which allows a mobile terminal to be accurately located without providing any dedicated positioning system carried onboard the mobile terminal.

In order to meet the above object, from a first aspect the present invention provides a method of locating a mobile terminal comprising the steps of :- receiving a message transmitted from the mobile terminal to be

located ; and determining a first geographic location of the mobile terminal to a first accuracy; the method being characterised by further comprising the steps of :- determining the geographic location of a service receiver to the first accuracy to provide a first service receiver geographic location measurement; determining the geographic location of the service receiver to a second accuracy to provide a second service receiver geographic location measurement; calculating an error vector between the first service receiver geographic location measurement and the second service receiver geographic location measurement; and applying the error vector to the first geographic location of the mobile terminal to calculate a second geographic location of the mobile terminal to the second accuracy; wherein the second accuracy is greater than the first accuracy.

Preferably, the determination of the first geographic location of the mobile terminal to the first accuracy and the determination of the first service receiver geographic location measurement are performed using the same location method and system. The method and system for providing the first geographic location of the mobile terminal and the first service receiver geographic location measurement may be such method and systems which are already known in the art, such as, for example, those discussed previously in the preamble.

The second service receiver geographic location measurement is preferably performed using a different method and system to that of the method and system used to determine a first service receiver geographic location measurement. In one preferred embodiment, the second service receiver geographic location measurement is preferably determined using a GPS receiver, such that the second accuracy to which the second service receiver geographic location measurement is taken is a few metres, or in best case is submetre. In

another preferred embodiment, however, the second service receiver geographic location measurement is performed in advance, and the service receiver is fixed in place at the pre-determined location. Here, the location measurement may be performed using a GPS receiver, or by surveying of the location in the usual manner.

In another preferred embodiment the service receiver is co-located with a service user who is mobile, and the method preferably further comprises the steps of directing the service user to the first geographic location of the mobile terminal prior to determining the first service receiver geographic location measurement and the second service receiver geographic location measurement. The determination of the first and second service receiver geographic location measurements is then performed substantially at the previously determined first geographic location measurement of the mobile terminal. This has the advantage that the determination of the first service receiver geographic location measurement is undertaken in almost the same geographic location as the mobile terminal with an error corresponding to the first accuracy level, and therefore the determination of the first service receiver geographic location measurement is subject to the same error mechanisms as the determination of the first geographic location of the mobile terminal, and therefore the calculated error vector between the first service receiver geographic location measurement and the second service receiver geographic location measurement can be improved. That is, as the measurement of the first service receiver geographic location measurement is subject to the same error mechanisms as the measurement of the first geographic location of the mobile terminal to the first accuracy, a valid and accurate error vector can be determined.

In other embodiments of the present invention, a plurality of service receivers are provided geographically separated from one another, and an error vector is calculated for each service receiver. An appropriate one of the error vectors is then selected dependent upon the first determined position of the mobile

terminal, and is then used in the calculation of the location of the mobile terminal to the second accuracy. Where a plurality of service receivers are provided each is preferably fixed in position at a known location.

Preferably, the message transmitted from the mobile terminal is a short message service (SMS) message. In a preferred embodiment the message preferably comprises one of a plurality of predetermined code words or phrases, each particular code word or phrase indicating a particular requirement of the mobile terminal user. The SMS switching center (SMSSC) which receives the message is preferably then able to parse the message to determine the contents and meaning thereof, in order to direct the requested assistance to the mobile terminal user.

From a second aspect, the present invention also provides a system for locating a mobile terminal, the system comprising means for receiving a message transmitted from the mobile terminal to be located, and location means for determining a first geographic location of the mobile terminal to a first accuracy; the system being characterised by further comprising first location means arranged to determine the geographic location of a service receiver to the first accuracy to provide a first service receiver geographic location measurement ; second location means arranged to determine the geographic location of the service receiver to a second accuracy to provide a second service receiver geographic location measurement; and error calculation means arranged to calculate an error vector between the first service receiver geographic location measurement and the second service receiver geographic location measurement, and further arranged to apply the error vector to the first geographic location of the mobile terminal to calculate a second geographic location of the mobile terminal to the second accuracy; wherein the second accuracy is greater than the first accuracy.

The second location means for determining the second service

receiver geographic location measurement preferably comprise a GPS receiver arranged to calculate the second service receiver geographic location measurement to an accuracy of a few metres or in best case submetre. Alternatively, the second location means may be a dead-reckoning system based on wheel-rotation and road-map knowledge technology.

Furthermore, in one embodiment the service receiver is preferably located in a service user vehicle such as a taxi, ambulance or the like, and the second location means are also preferably located in said vehicle. In addition, the error calculation means are also preferably co-located with the service receiver in the vehicle In a preferred embodiment, the system further comprises interpretation means arranged to interpret the received message and to determine the meaning thereof. The provision of the interpretation means has the advantage that the message from the mobile terminal can be automatically processed, hence no confusion introduced by the misinterpretation of the message.

It is a feature of the present invention that the user of a mobile terminal may call for assistance merely by sending a predetermined message to the mobile network. In a preferred embodiment the message is automatically interpreted and the location of the mobile terminal is generally determined, the location then being transmitted to a service user using a known co-ordinate system thereby allowing the service user to locate the mobile terminal measurement by applying the error vector calculated in the service receiver's own position to the position generated for the mobile terminal. This arrangement has the advantage that the request for assistance on the mobile terminal may be automatically processed and hence no confusion introduced by misinterpretation of any instructions. Furthermore, it provides the further advantage that persons who have suffered an accident and who require rescue may call for assistance without having to know their specific location.

Further features and advantages will become apparent from the

following description of a number of embodiments of the present invention, presented by way of example only, and with reference to the accompanying drawings, wherein :- Figure 1 shows a block diagram of a mobile network in which the present invention is used; Figure 2 is a location chart to illustrate the method of a first embodiment of the present invention; Figure 3 is a system block diagram of system elements present in the mobile network in the embodiment of the present invention; Figure 4 is a system block diagram of system elements present in the service receiver system of the first embodiment of the present invention; Figure 5 is a flow chart of the method steps performed by the service receiver system of Figure 4; and Figure 6 is a location chart to illustrate the method of a second embodiment of the present invention.

A particularly preferred first embodiment of the method and system of the present invention will now be described with reference to Figures 1 and 2. The first embodiment is characterised by the service receiver being mobile and being provided within a service-user vehicle.

With reference to Figure 1, here a base station system (hereafter BSS) 10 comprises a plurality of base stations 12 geographically distributed across a network coverage area. Each base station 12 serves a particular network cell 13, network cells 13 being contiguous across the network coverage area. Each base station 12 is connected via a back haul channel 20 to a mobile services control centre/short message service switching centre 16 (hereafter SMSSC), which controls the base station system 10. Within the base station system 10, a mobile user 2 is registered with a particular base station 8 in cell 14. A service receiver 4 provided in a service user vehicle is registered with base station 9 in cell 15. It is of course possible for the mobile terminal 2 and the service receiver 4 to move

between cells In which case normal cell handover and registration procedures known in the art apply. The mobile services control centre/SMSSC 16 provides all standard network control functions and provides a gateway from the base station system 10 to one or more wide area networks or the public switched telephone network.

The operation of the method and system of the first embodiment of the present invention will now be described with reference to Figures 2 to 5.

First suppose that the user of the mobile terminal 2 requires some form of aid or assistance. In this case, the user may select one of a plurality of code messages or phrases pre-stored on the mobile terminal, and each of which specifies a particular type of assistance which is to be requested. The user then selects the appropriate code word for the assistance required, and sends the code word as a short messaging services (SMS) text message to the SMSSC via the BSS 10. More particularly, the SMS text message is sent to the base station with which the mobile terminal is presently registered, being the base station 8 of the base station system 10. The base station 8 then sends the SMS message to the SMSSC via the backhaul channel 20.

With reference to Figure 3, the SMS switching centre 16 preferably contains means for performing the standard SMS switching centre functions and which are denoted by block 32 in Figure 3. In addition, the system of the present invention also provides a locator module 34 which is arranged to receive signals from the SMSSC module 32, a parser module 36 arranged to receive SMS messages from the SMSSC, and an SMS generator arranged to receive location information from the locator module 34, and message information from the parser 36, and to generate SMS messages which are then passed to the SMSSC for transmission over the BSS. Functioning of the elements of the SMS switching centre 16 are described next.

When the SMSSC 32 receives an SMS service request message which has been transmitted by the mobile terminal 2 via the BSS and the back haul

channel 20 thereto, it passes the message to the parser unit 36, and the locator unit 34. The locator unit 34 is arranged to determine the location of the mobile terminal 2 to a first accuracy of n metres by any conventional method, such as those described in the preamble. The coordinates generated by the locator module 34 for the location of the mobile terminal are then passed to the SMS generator module 38, where they are incorporated as a first part of an SMS message which is to be generated by the SMS generator module.

The parser module 36 also receives the received SMS message from the SMSSC and acts to analyse the contents of the message to determine whether it is a valid request for assistance, and what assistance is in fact requested. This is preferably achieved by matching a received code phrase contained in the SMS message with a look up table of valid code phrases to determine the validity of the received code. If the parser determines that the received code phrase is not a valid request, then processing stops and no further action is performed. In this case, the user will not receive any assistance due to the fact that he has sent an invalid code phrase. If, however, it is determined that the received code phrase is a valid request for assistance, then the parser accesses the look up table again to determine the type of assistance requested, and passes information relating to the type of assistance requested to the SMS generator 38.

The SMS generator receives the mobile terminal location information from the locator module 34 and the requested assistance information from the parser 36 and assembles an SMS message containing the location information and the assistance information and passes the assembled message to the SMSSC for transmission onto the base station system network. The generated SMS is addressed to a particular service user 4 who is capable of rendering the assistance requested by the mobile terminal user. In this respect, the SMS generator may contain a look up table of service user addresses or mobile telephone numbers, indexed against the type of assistance which each service user can provide. The present invention envisages service users being such services as

taxis, ambulances, rescue vehicles, police vehicles, delivery vehicles, etc. The SMS generator uses the service user index to choose an appropriate service user based upon the assistance information passed thereto from the parser unit 36. Once the generated SMS message has been passed to the SMSSC, it is transmitted across the network to the addressed service user in the normal manner. In addition, preferably a confirmation SMS message is sent to the requesting mobile terminal to confirm that a valid assistance request has been received, and that the requested assistance will be arriving shortly.

Referring now to Figure 4, Figure 4 shows the system elements including the service receiver which are present within the service user vehicle 4. More particularly, the service receiver is provided with a location determination system 40 which comprises an SMS transceiver 42, a GPS receiver 44, a microprocessor 46 and a display 48. More particularly, the SMS transceiver 42 is arranged to send and receive messages to and from the base station system 10, and to pass received messages to the microprocessor 46, and also to receive messages to be transmitted therefrom. The GPS receiver 44 is arranged to receive signals from global positioning system satellites, and to calculate the accurate position of the service receiver anywhere on the earth, and to pass the calculated location to the microprocessor 46 upon command. The display 48 is provided to display images generated by the microprocessor to provide an interface into the system for the service user, who may, for example, be the driver of the service user vehicle. Operation of the service receiver location system 40 is described next with reference to Figures 2 and 5.

With reference to Figure 5, assume the user of the mobile terminal 2 has transmitted a request for assistance which has been analysed by the system elements located at the SMSSC, and an SMS message has been generated which has been transmitted to the service user vehicle 4. Therefore, at step Sl, the service receiver receives the generated SMS request from the network, the SMS message including the location coordinates of the mobile terminal as determined

by the conventional locator module 34 in the SM SC. That is, the SMS message contains coordinates (Xi, YmtL,)) as shown in Figure 2.

Having received the SMS request at the service receiver, the service receiver then acknowledges the SMS request at step S2, and from this acknowledgement the locator module 34 in the SMSSC determines the location of the service receiver in an identical manner as was previously used for the location determination of the mobile terminal, and the SMS generator 38 at the SMSSC generates an SMS message containing the location coordinates of the service receiver as determined by the locator module 34 which is transmitted by the SMSSC to the service receiver. Therefore, at step S3, the service receiver receives another SMS message containing location information corresponding to the coordinates of the service user vehicle as determined by the locator module, that is coordinates (XsuL1, YsuL1), as shown in Figure 2.

It should be noted at this point that both the determined locations of

the mobile terminal mt and of the service receiver suL, are subject to the accuracy of the conventional mobile terminal location systems known in the art, and therefore the measured locations will contain a large error. That is, the determined location mtn and sur will only be accurate to a first accuracy to within n metres.

In order to obtain a more accurate location of the mobile terminal, the service receiver measures its actual location to an accuracy of a few metres or submetre, using the GPS receiver 44. That is, at step S4 the service receiver

determines the coordinates (XsuL, YsuL2), of actual location su using the GPS receiver 44. Actual location SUL2 of the service receiver vehicle is therefore determined to an accuracy of b metres, wherein b is much less than n.

Having received the location as determined by the locator module 34 and the SMSSC and determined its own location using the GPS receiver 44, the service receiver is now in a position to calculate an error vector ev between the actual location as determined by the GPS receiver and the location as determined by the locator module 34 and the SMSSC. The error vector ev is calculated as

follows :ev (X) = X2-Xsi : and ev (Y) = YsuL2 - YsuL1.

The calculation of the error vector ev is performed by the microprocessor using the location information received from the SMS transceiver 42, and the location information from the GPS receiver 44. Therefore, calculation of the error vector ev is performed by the microprocessor at step S5.

Having calculated the error vector ev, the service user then applies the error vector as calculated for its own actual location to the location mtLl previously measured for the mobile terminal. The assumption is therefore made that the error in the location mtL1 as determined by the locator module 34 is both repeatable and translatable such that the error in the location mtLl is the same as the error in the location suL1. The actual location of the mobile terminal, milz, is calculated by the microprocessor by adding the error vector onto the already measured location mtL1 measured by the locator module 34, to arrive at the actual location milz That is, more specifically, mt is calculated as follows:

tL2-4 + ev M 'MtLI ie X 2 = X mtL1 +ev (X): and Y mILZ = Y mtLI + ev (Y) As shown, the microprocessor 46 calculates the mobile terminal location mt as step S6.

On determining the actual location of the mobile terminal mt, the service user vehicle can then travel to the determined location in order to render the requested assistance.

It will be apparent from the above discussion that although the mobile terminal's location mtL1 is determined by the locator module 34 at the SMSSC when the SMS request for assistance is received thereat, it is not essential for the service user location sun to be determined immediately upon receipt of the service request at the service user vehicle. Therefore, as a second embodiment of

the present invention, upon receipt of the SMS request at the service user vehicle at step Su stead of immediately acknowledging the SMS the service user vehicle can attempt to travel to the communicated mobile terminal location mtL, before acknowledging the SMS request at step S2. That is, as shown in Figure 6, the service user vehicle in the second embodiment after receipt of the SMS request containing the coordinates (Xmtu, Ymttu) attempts to travel to the location mtu defined by those coordinates or at least into the general vicinity of the location as defined by the coordinates before acknowledging the SMS request. In the second embodiment, the acknowledgement of the SMS request causes the locator module 34 in the SMSSC to measure the service receiver's location sun which is then transmitted back to the service receiver for use in the calculation of the error vector ev. It is thought that by having the service user vehicle travel either to the measured location mtLl of the mobile terminal, or at least into the vicinity of the mobile location mtLl within a radius defined, for example, by the RMS error present in location measurement of mtu, then a more accurate error vector ev should be calculated due to the fact that the SMS acknowledgement sent by the service user vehicle at step S2 should experience almost identical radio conditions to the original assistance request transmitted by the mobile terminal. Therefore, in the second embodiment of the present invention the service user vehicle carrying the service receiver first travels into the general vicinity of the mobile terminal as defined by both the mobile terminal location mtu and the known RMS error present in that measured location, before acknowledging the SMS request

and having the service receiver location SuLl measured by the locator module 34.

In addition, in a third embodiment instead of merely travelling to within the error radius of the mobile terminal location mtL,, the service user vehicle travels to that location before acknowledging the SMS.

Therefore, both the second and third embodiments allow for increased accuracy in the calculated error vector thereby providing increased accuracy of the finally calculated mobile terminal location mt.

Furthermore, within any of the first to third embodiments the error vector calculation and subsequent mobile terminal accurate positioning as described above can be continuously repeated by continuos transmissions between the service receiver and the SMSSC. Each calculation is performed in the same manner as described above, but merely repeated in order. As the service receiver approaches the actual position of the mobile terminal then the calculated error vector should tend towards the actual error vector in the mobile terminal initial position determination, thereby allowing the service user to accurately locate the mobile terminal.

Moreover, it is further envisaged that the service user can send an estimated time of arrival message to the SMSSC, which will be forwarded on to the mobile terminal.

While the first to third embodiments have described the invention with respect to the error vector being calculated using an accurate position of the service receiver being found using a GPS receiver, it will be understood that the invention is not limited to the use of a GPS receiver, and that any other accurate positioning system can be used. In particular, it is also envisaged that a dead reckoning navigation system using wheel-rotation and road-map knowledge could be used in place of or in addition to the GPS receiver. Furthermore, any other known navigation or positioning system could be used in place of or in addition to the GPS receiver, and the only requirement of such a system is that it is able to provide the position of the service receiver to a greater accuracy than that of the conventional mobile location system used to find the initial location of the service receiver i. e. SUn. Provided a more accurate location of the service receiver (SUL2) can be found than is found by the conventional mobile location system used, then a meaningful error vector can be found which can be applied to the determined mobile terminal location mt to give the more accurate location mtj.

Furthermore, while we have described the service receiver above as being co-located with a service user vehicle, it should be understood that the

service receiver itself may be hand-portable or vehicle-portable.

Whereas the first to third embodiments described above describe the invention in relation to the service receiver being mobile and co-located with the service user, in a fourth embodiment described next the service receiver is centrally located within the BSS, and fixed in position. The fourth embodiment is described next in relation to the differences that it presents with the first embodiment.

Here, within the fourth embodiment the service receiver comprises all of the elements shown in Figure 4 and described previously, except that there is no requirement for the GPS receiver 44, nor the display 48. Instead, as the service receiver is fixed in position, the precise location of the service receiver can be determined in advance, either by using GPS, or by conventional surveying techniques. A location memory is provided which the microprocessor can access which stores the pre-determined location of the service receiver for calculation of the error vector in the same manner as described previously in the first embodiment, but with the differences described next.

Within the fourth embodiment the purpose of the fixed service receiver is simply to calculate the error vector ev at regular intervals, and transmit the calculated error vector ev to the SMSSC for use in calculating the exact position of any mobile terminal which requests assistance. It is thought that the error vector ev will be time variant due to changes in radio propagation conditions across the region of the BSS, and hence the calculated vector must be updated on a regular basis for accurate mobile terminal location. The calculation of the error vector is performed as follows.

As in the first embodiment, the first step is that the service receiver transmits an SMS message to the SMSSC, and the conventional location system at the SMSSC calculates the position of the service receiver to the accuracy n using the conventional mobile terminal location methods (notwithstanding that the service receiver is now fixed). The calculated position (XsuLl, YsuLl) is then

communicated from the SMSSC to the service receiver in another SMS transmission.

Upon receipt of the SMS containing the SULI location, the service receiver then applies the received co-ordinates (i. e. (XsuL1, YsuL1)) together with the known co-ordinates of its fixed location stored in the location memory store (i. e. (X. Y to the equations described above in relation to the first embodiment, to calculate the error vector ev in the same manner as previously. The calculated error vector is then communicated to the SMSSC in a further SMS transmission from the service receiver.

It will be appreciated that the above described method steps are continuously repeated in order to allow for tracking of the error vector to the prevalent radio conditions in the BSS region. In addition, it will further be appreciated that the first SMS transmission from the service receiver to the SMSSC which causes the SMSSC to measure the location of the service receiver can contain the error vector information from the last error vector calculation, such that the error vector calculation and updating process occurs continuously in a looping manner, and with maximum spectral efficiency At the SMSSC, the received error vector is applied to the first determined location (XmtL1, YmtLi) (determined by the SMSSC using the conventional location methods) using the same equations as described in the first embodiment to calculate the actual location (Xmt, YmtL2) of the mobile terminal to the second accuracy of b metres. The actual location (xmtL2, YmtL2) can then be passed to the SMS generator for incorporation into the SMS to be transmitted to the service user who is to provide the requested assistance. In order to allow the SMSSC to perform the calculation, a calculation means such as the microprocessor of 46 of Figure 4 is provided at the SMSSC, and which is arranged : to receive the initial coordinates (Xmtu, Ymttu) from the locator module 34; to receive the error vector ev received at the SMSSC from the service receiver; and to pass the

calculated actual location coordinates (Xmt Ymt) to the SMS generator 38.

The generated SMS from the SMS generator 38 is then transmitted to the appropriate service user for action, the choice of the appropriate service user being performed in the same method as in the first embodiment.

It will be appreciated that the fourth embodiment removes the requirement for the actual service user who is to provide the requested assistance to possess a service receiver for calculation of the error vector, as the origmal SMS sent to the user will contain the accurate position (Xmt, YmtLZ) calculated in the SMSSC. Therefore, a more cost efficient deployment can be obtained, and in addition service users such as taxis, police, ambulances, can be requested without themselves requiring any specialist equipment other than a standard SMS transceiver.

A fifth embodiment closely related to the fourth embodiment will now be described with reference to the previously described fourth embodiment.

Whereas in the fourth embodiment the service receiver was provided with means for calculating the error vector ev locally, and then the calculated error vector was transmitted to the SMSSC to be used in the calculation for the mobile terminal location milz, in the fifth embodiment the service receiver contains no means for calculating the error vector, and instead merely acts as a beacon to repeatedly transmit SMS messages to the SMSSC. The SMSSC is then provided with the means (such as the microprocessor of the fourth embodiment) for calculating the error vector, together with a location memory store for storing the known location of the service receiver beacon.

More particularly, the service receiver merely acts to repeatedly send SMS messages, either on command from the SMSSC, or automatically. Upon receipt of each SMS from the service receiver at the SMSSC the location of the beacon is calculated using the conventional location techniques to the accuracy of n metres, and then, because the position of the beacon is known, the error vector can be calculated by the microprocessor provided at the SMSSC. Once the error vector has been calculated by the microprocessor, the actual position of the mobile

terminal to the accuracy of b metres, where b is less than n, can be found in the same manner as in the fourth embodiment. Once the mobile locatIOn mtL2 has been im I has been found, the processing of the method and system of the fifth embodiment proceeds as described previously for the fourth embodiment.

The fifth embodiment has the advantage that the service receiver may be a dumb terminal, as all it is required to do is to transmit SMS messages periodically, either automatically or on command from the SMSSC. Therefore, as no processing is required to be performed in the service receiver, the receiver can be produced at reduced cost with increased reliability.

A sixth embodiment of the present invention will now be described, which expands upon the previously described fourth embodiment.

In the sixth embodiment of the present invention a plurality of service receivers each arranged to calculate the error vector ev locally and transmit the error vector to the SMSSC are provided scattered throughout the BSS region.

Each of the plurality of service receivers are substantially identical to the single service receiver of the fourth embodiment. Preferably, one service receiver is provided in each cell of the BSS, although this not need be the case, and, for example, one service receiver may be provided for every three or four, or any other number of cells. Each service receiver calculates its own error vector independently of any other service receiver, and transmits it to the SMSSC.

At the SMSSC each error vector is received from each service receiver and an"error vector map"of the BSS region can be compiled illustrating the error vectors which should be applied in each part of the BSS geographic region. The map may be in any form, and need not be graphically represented, and may instead be a list of the location of each service receiver and the respective last error vector received from the particular service receiver at each location.

In the sixth embodiment when a request for assistance is received from a mobile terminal at the SMSSC, the SMSSC calculates the mobile terminal's position (Xrntu, Ymtu) using the conventional mobile location systems and then

selects the most appropriate error vector from the error vector map corresponding to the roughly calculated position of the mobile terminal. The selected error vector is then used to calculate the coordinates (Xmt, YmtL2) of the actual position of the mobile terminal. The calculated coordinates are then sent to the appropriate service user as described above for the service user to render the requested assistance.

The use of an error vector from a service receiver in the general calculated vicinity of the mobile terminal to calculate the actual position present the additional advantages as described in relation to the second and third embodiments above. That is, by using an error vector calculated for the area of the BSS local to the mobile terminal then the transmissions from the service receiver which calculated the particular error vector will have been subject to almost the same radio propagation conditions as the transmission of the request for assistance from the mobile terminal, and hence a more accurate or smaller error vector and hence final position of the mobile terminal can be found.

A seventh and final embodiment will now be described which combines various features of the previously described fifth and sixth embodiments.

In the seventh embodiment of the present invention a plurality of dumb terminals are scattered throughout the BSS region to act as the service receivers of the present invention. Each of the dumb terminals is substantially identical to the the service receiver of the fifth embodiment, and each acts merely as a beacon to repeatedly transmit a message to the SMSSC either automatically or on command from the SMSSC. Preferably, one service receiver is provided in each cell of the BSS, although this not need be the case, and, for example, one service receiver may be provided for every three or four, or any other number of cells.

At the SMSSC each transmission is received from each service receiver beacon and an error vector calculated at the SMSSC in the same manner

as described previously in relation to the fifth embodiment. As more than one error vector is being calculated corresponding to each service receiver throughout the BSS region, an"error vector map"of the BSS region can be compiled at the SMSSC illustrating the error vectors which should be applied In each part of the BSS geographic region. The map may be in any form, and need not be graphically represented, and may instead be a list of the location of each service receiver and the respective last error vector calculated for the particular service receiver at each location.

In the seventh embodiment when a request for assistance is received from a mobile terminal at the SMSSC, the SMSSC calculates the mobile terminal's position (Xmttu, Yrntu) using the conventional mobile location systems and then selects the most appropriate error vector from the error vector map corresponding to the roughly calculated position of the mobile terminal. The selected error vector is then used to calculate the coordinates (XmtL2, Ymt) of the actual position of the mobile terminal, and the calculated coordinates are sent to the appropriate service user as described above for the service user to render the requested assistance.

The seventh embodiment has the same advantages as the sixth embodiment regarding the increase in accuracy of the calculated mobile terminal position (XmtL2, YmtL2), but also possesses all of the advantages of the fifth embodiment in respect of the reduced cost of the service receiver, and that the actual service users rendering assistance do not have to be specially equipped.

The method and system of the present invention have many applications, but in particular it is envisaged that the assistance required could be such services as provided by Hackney carriages or car hire firms or by bus services such as Dial-a-Ride. That is, the service user vehicle is in fact a hire car or Hackney carriage, which is despatched to the location of the mobile terminal upon a request by the user of the mobile terminal. Alternatively, other uses of the method and system of the present invention are also apparent, such as for example,

for use by rescue services such as the police, ambulance of fire brigade services, or for the delivery of goods by delivery services. Here, the user requiring assistance from these services sends the appropriate message which is analysed by the parser unit, and the appropriate service is then called.

It should be appreciated that in the preferred embodiment we have described the service from the view point that it is to be provided by the mobile network operator network, however this need not be the case, and it may in fact be provided by a third party which receives the message from the mobile network.

In which case, however, the location determination of the mobile terminal is dependent upon information from the mobile network, and hence the co-operation of the mobile network operator is important.

Furthermore, whilst the preferred embodiment of the present invention has described the invention in relation to the user sending a SMS text message containing a coded phrase, this need not be the case, and in the case of a mobile terminal which is equipped to send and receive wireless application protocol messages, the coded phrases may be sent as e-mails or as hyper text compatible with wireless application protocol. Whatever message format is used, the SMSSC or MSC should be able to strip the network protocol headers and trailers, in order to process the message contents.

Claims

CLAIMS :

1. A method of locating a mobile terminal comprising the steps of : receiving a message transmitted from the mobile terminal to be located ; and determining a first geographic location of the mobile terminal to a first accuracy; the method being characterised by further comprising the steps of : determining the geographic location of a service receiver to the first accuracy to provide a first service receiver geographic location measurement; determining a geographic location of the service receiver to a second accuracy to provide a second service receiver geographic location measurement; calculating an error vector between the first service receiver geographic location measurement and the second service receiver geographic location measurement; and applying the error vector to the first geographic location of the mobile terminal to calculate a second geographic location of the mobile terminal to the second accuracy, wherein the second accuracy is greater than the first accuracy.

2. A method as claimed in claim 1, wherein the determination of the first geographic location of the mobile terminal to the first accuracy and the determination of the first service receiver geographic location measurement are performed using the same location method and system.

3. A method as claimed in claim 1, wherein the second service receiver geographic location requirement is determined using a GPS receiver.

4. A method as claimed in claim 1, wherein the second service receiver is performed in advance, and the service receiver is fixed in place at a pre determined location.

5. A method as claimed in claim 1, wherein the service receiver is co-located with a service user who is mobile.

6. A method as claimed in claim 5 which comprises the steps of : directing the service user to the first geographic location of the mobile terminal prior to determining the first service receiver geographic location measurement and the second service receiver geographic location measurement; and determining the first and second service receiver geographic location measurements at the previously determined first geographic location measurement of the mobile terminal.

7. A method as claimed in claim 1, wherein a plurality of service receivers are provided and an error vector is calculated for each service receiver.

8. A method as claimed in claim 1, wherein a plurality of error vectors of a geographic area are stored, one of the error vectors being chosen to be applied to the first geographic location of the mobile terminal to calculate a second geographic location of the mobile terminal.

9. A system for locating a mobile terminal, the system comprising: means for receiving a message transmitted from the mobile terminal to be located; and

means for determining a first geographic location of the mobile terminal to a first accuracy, the system being characterised by further comprising: first location means arranged to determine the geographic location of a service receiver to the first accuracy to provide a first service receiver geographic location measurement; second location means arranged to determine the geographic location of the service receiver to a second accuracy to provide a second service receiver geographic location measurement; and error calculation means arranged to calculate an error vector between the first service receiver geographic location measurement and the second service receiver geographic location measurement and further arranged to apply the error vector to the first geographic location of the mobile terminal to calculate a second geographic location of the mobile terminal to the second accuracy; wherein the second accuracy is greater than the first accuracy.

10. A system as claimed in claim 9, wherein the second location means for determining the second service receiver geographic location measurement comprise a GPS receiver.

11. A system as claimed in claim 9, wherein the second location means for determining the second service receiver geographic location measurement is based on wheel rotation and road-map knowledge technology.

12. A service receiver as claimed in all the above claims, wherein said service receiver is located in a service user vehicle.

13. A system as claimed in claim 9, wherein the second location means is located in a service user vehicle.

14. A system as claimed in claim 9, wherein the error calculation means are colocated with the service receiver in the vehicle.

15. A system as claimed in claim 9, wherein the system further comprises interpretation means arranged to interpret the received message.

16. A system as claimed in claim 1, wherein a plurality of error vectors of a geographic area are stored, one of the error vectors being chosen to be applied to the first geographic location of the mobile terminal to calculate a second geographic location of the mobile terminal.

17. A method of locating a mobile terminal substantially as hereinbefore described with reference to the accompanying drawings.

18. A system of locating a mobile terminal substantially as hereinbefore described with reference to the accompanying drawings.