GB2420471A - Method and location server for reporting the location of a user - Google Patents

Abstract

Method and location server for reporting the location of a user in a network. Location information relating to the user within an area is received from the network. If the location information indicates a location of a wireless transmitter or a base station and the location information can be used to predict the location of the wireless transmitter or the base station, the location information is randomised to disguise the location of the wireless transmitter or the base station.

Description

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METHOD OF REPORTING THE LOCATION OF A WIRELESS USER

FIELD OF THE INVENTION

This invention relates to methods and apparatus for reporting location of wireless users. The invention also relates particularly to methods of concealment of information relating to cell tower locations when reporting location of a wireless user in a cellular network.

BACKGROUND TO THE INVENTION

Location based services are offered in some current wireless networks and the provision of such services is anticipated to increase in future networks. These location based services provide services which are tailored to the location of a user within the network. There are several techniques which are known to enable the network to determine the location of a user, who is likely to be mobile,

for example:

* Cell-ID positioning technology returns the approximate geographical location of a mobile station (MS) such as a mobile phone, based on the ID of the cell site in which the MS is located.

Timing Advance/Network Measurement Report (TNNMR) positioning uses timing advance (TA) and network measurement report (NMR) information in combination with the known positions of base transceiver stations (BTS) in the network. Each BTS transmits on a set of frequencies at a known power and each MS periodically scans these frequencies and records the strongest received levels which it reports back to the BTS. This enables the distance between each MS and its closest BTSs to be calculated and if information from a minimum of three BTSs is available, the position of the MS can be determined with a reasonable level of confidence. TA/NMR is commonly used in GSM (Global System Mobile) networks.

* Round Trip Time (RU) positioning makes use of the round trip time for transmissions from the BTS to the MS and back to the BTS. RU is commonly used in UMTS (Universal Mobile Telecommunication System) networks. * . S

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* S S S -2- * * * 1 S * Time Difference of Arrival (TDOA) positioning uses the time difference of arrival of signals between the MS and the BTS to estimate the location of the MS.

* Assisted GPS (A-GPS, GPS = Global Positioning System) uses the network of GPS satellites to determine the location of a MS, with the MS including a GPS receiver.

In nearly all positioning methods, except A-GPS, the positioning technique relies on knowing the position of each BTS. This means that the reported position of a MS enables the position of the BTS to be calculated by the location based service provider. In some circumstances, however, a network operator may not wish to disclose the location of its expensive infrastructure due to threats from theft, terrorism etc.

OBJECT TO THE INVENTION

The invention seeks to provide an improved method of reporting the location of a wireless user which mitigates at least one of the problems of known methods.

A further object of the invention is to ensure that the locations of cell towers are not disclosed when reporting the location of a wireless user.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a method of reporting location of a user in a wireless network, the method comprising the steps of: receiving location information relating to the user from the network, said location information comprising a reported location within an uncertainty area; determining whether said location information indicates a location of a wireless transmitter within the network; determining whether said uncertainty area can be used to predict a wireless transmitter location; if both the determinations are positive, randomising the location information; and reporting the randomised location information to a network entity.

Advantageously, this ensures that true location information which can enable a third party to locate expensive network infrastructure is not reported.

Furthermore, it ensures that where the location information is not sufficient to enable a third party to locate the equipment, the location information is not affected.

*.. * * * . : a II * * S * S S S I S I a * * * * a I III * * * * * 3 *** * S The step of determining whether said uncertainty area can be used to predict a wireless transmitter location may comprises determining whether said uncertainty area is one of a circle and an arc-band.

The step of reporting may comprise: determining whether the entity is permitted to receive actual location information; and reporting the actual location information if the entity is permitted and reporting the randomised location information if the entity is not permitted.

Advantageously, this enables a network operator to decide which entities are allowed to receive true location information and which are not. This permission may be granted on the basis of whether the network operator trusts the entity.

Where the uncertainty area is an arc-band, the step of randomising may comprise: maintaining the reported location unchanged; and converting the uncertainty area from an arc-band to another shape, centred on the reported location and covering the arc-band.

Advantageously, this does not add any error to the reported location whilst disguising the location of the transmitter and the method by which the location information was obtained.

The another shape may be a circle.

Where the uncertainty area is a circle, the step of randomising may comprise: moving the reported location by a distance R and an angle 9, wherein said distance R is selected at random between an upper and a lower limit, and wherein said angle 0 is selected at random; and defining a new uncertainty area centred on the modified location.

Advantageously, this keeps the additional error on the randomised location within predetermined limits, whilst hiding the true location of the wireless transmitter.

According to a second aspect of the invention there is provided a location server comprising: means for receiving location information relating to a mobile subscriber, said location information comprising a reported location within an uncertainty area; means for determining whether said location information indicates location of a wireless transmitter and whether said uncertainty area can be used to predict wireless transmitter location; and means for randomising said location information where both said determinations are positive. e S

S.. * . S * * * * , : : . . * * S S * S S *** * * : : . * * * * 555 * The means for receiving may comprise an input.

The means for determining may comprise a processor.

The means for randomising may comprise a processor.

According to a third aspect of the invention there is provided a computer program embodied on a computer readable medium and capable of being executed by a processor, the computer program comprising computer readable code for performing the method described above.

This acknowledges that software can be a valuable, separately tradable commodity. It is intended to encompass software, which runs on or controls "dumb" or standard hardware, to carry out the desired functions, (and therefore the software essentially defines the functions of the register, and can therefore be termed a register, even before it is combined with its standard hardware). For similar reasons, it is also intended to encompass software which "describes" or defines the configuration of hardware, such as HDL (hardware description language) software, as is used for designing silicon chips, or for configuring universal programmable chips, to carry out desired functions.

The preferred features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of parts of a network which may be involved in reporting or sharing location information; Figure 2 is a flow diagram of a method of reporting location information; Figures 3 and 4 describe the process of arc-band conversion; and Figures 5 and 6 describe the process of circle randomisation. * * *

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DETAILED DESCRIPTION OF INVENTION

Embodiments of the present invention are described below by way of example only. These examples represent the best ways of putting the invention into practice that are currently known to the Applicant although they are not the only ways in which this could be achieved.

Figure 1 shows a schematic diagram of parts of a network which may be involved in reporting or sharing location information, by way of example only. The diagram shows two Location Services (LCS) clients 102, 104. These LCS clients, which may also be referred to as Location Based Applications (LBA), are entities which require location information from a network in order to be able to provide location specific services to enabled users within the network. The LCS clients request this information from a location server 106 such as a Gateway Mobile Location Centre (GMLC). The GMLC can either determine the location of a mobile station (MS) itself or request the information from the network. In figure 1, the GMLC is shown logically connected to a network node 108 which is able to determine the location of a MS within its area. A Mobile Switching Centre (MSC) is one example of such a network node 108 which can determine the location of a MS / user equipment (UE) / terminal in question. A second example is a Serving GPRS Support Node (SGSN, GPRS = General Packet Radio Service) which is the packet-switched analogue of the MSC. The network node 108 may obtain the location information for a particular MS (not shown) by consulting a Serving Mobile Location Centre (SMLC, not shown).

The location information reported to the network node 108 may be determined by one of many different location technologies, for example TNNMR, A-GPS, Cell- ID, RU and TDOA. Some of the location technologies will provide a MS location which is cell-based i.e. one which is related to the location of a cell tower or base transceiver station (BTS), e.g. Cell-ID. Other location technologies will provide a MS location which is independent of the location of a cell tower or BTS, e.g. A- GPS. When the location information is reported to the network node 108, the information may include an indication of what location technology was used to obtain the position information, e.g. a field identifying the location method. In the 3GPP (3rd Generation Partnership Project) standard, this field is called "position source".

The location information reported may also include, in addition to the location estimate of the MS and any technology identifier, an indication of the uncertainty *.. . * * . : * * . : : : * * * * * . * S S I S S *55 * S S * * * S * -6- * S S S of the position estimate. The purpose of the uncertainty information is to define an area in which there is a very high probability (e.g. 90%) that the MS is located.

Such uncertainty information may describe an area which is an ellipse 109, an arc-band 110, a circle 111 or other regular or irregular shape 112. Where the location information does not include a technology identifier, it may be possible to infer the likely technologies used by the shape of the uncertainty area provided.

Having received the location information from the network (via network node 108), the location server 106 can determine whether it is permitted to provide the location information to the LCS client which requested the information. The network operator may deem that some LCS clients e.g. LCS client A 102 is a trusted client and is therefore permitted to receive true location information whereas LCS client B 104 is not trusted to the same extent so the network operator is not prepared to provide the LCS client with location information which might disclose the position of its network infrastructure such as the location of the cell towers or BTSs. In such a situation, the location server 106 needs to determine if the location information it has received from the network could reveal, or be used to predict, the location of a wireless transmitter and if it does, the location server must randomise the location information prior to reporting such that the LCS client B cannot calculate cell tower location information from the randomised location information, but the LCS client B can still provide location services to the MS which are appropriate.

This method of reporting location information can be described in more detail with reference to the flow diagram of figure 2.

The location server receives a request for location information relating to a particular MS from a LCS client (202). As a result, the location server sends a request to the network (204) and receives the required location information in response (206). The location server then determines whether the location information it has been provided with is cell-based (208). This determination may be made from a location method field (or technology identifier) in the information message provided or by inferring the likely answer from the actual location information (position and uncertainty) provided. In the latter case, it may be necessary for the location server to err on the side of caution and assume that the information is cell-based unless the actual location information is such that it could not have been determined using a cell- based technology.

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* * U: : : * * * * e U * * a e U 1 1 S -7- **S ** Si. * 0 S One method of inferring the location method from the actual location information may include assessment of the shape of the uncertainty area. Alternatively the location server may determine whether the location information is cell-based by comparing the location information that it has been provided with a list of the positions of all the cell towers within the network. Where the location information and cell tower location are the same or similar (to within a predetermined amount), the location server can infer that the information is cell-based.

If the location server determines that the information is not cell-based, then it can report the actual location information to the LCS client (214) . If however, the location server determines that the location information was determined using a cell-based technology, the location server then determines whether the location information can be used to predict the location of a wireless transmitter. One method of achieving this is to determine whether the uncertainly area is in the form of either an arc-band or a circle (210). This is because if the area reported is an arc-band or a circle, the location information may provide sufficient information to enable a recipient to calculate the location of the cell tower, whereas other shapes do not usually indicate a cell tower location. If the uncertainty area cannot be used to predict wireless transmitter location (e.g. is not the shape of an arc-band or a circle), the location server can report the actual location information to the LCS client (214).

If the information is cell-based, and the uncertainty area can be used to predict wireless transmitter location (e.g. the uncertainty area is a circle or an arc-band), then the location server needs to determine whether the LCS client that requested the location information is one that the network operator allows to receive actual location information or not (212). This may be determined by way of a list which is stored on the location server or stored elsewhere but accessed by the location server. If the LCS client is a trusted client and therefore allowed to receive the actual information, then the location server can report the actual location information to the LCS client (214). However, if the LCS client is not allowed to receive such information, the location server must first perform a randomisation process on the information before reporting the randomised location (224).

The first stage of the randomisation process is to determine whether the reported uncertainty area is an arc-band or a circle (216). If the area is an arc-band, then the location server performs arc-band conversion (218) which is described in more detail with reference to figures 3 and 4. If the area is a circle, then the S * S * S S IS I S I S I S * * * * : : : 0. S S * S 0- U * *S S location server performs circle randomisation (222) which is described in more detail with reference to figures 5 and 6. In some circumstances, where the area is an arc-band, and the arc angle (marked a in figure 3) exceeds a predetermined angle X, which may be set at a value approaching 1800 (220), arc-band conversion may not disguise the location of the cell tower sufficiently and in this case it is beneficial to apply circle randomisation (222) to the results of the arc-band conversion (218) . The output of the randomisation process (steps 216-222) is a randomised location which can then be reported to the LCS client (224).

As an alternative to comparing the arc angle a to the predetermined angle X in order to determine if arc conversion has not sufficiently disguised the cell tower location, the reported uncertainty and the new uncertainty area may be compared.

The flow diagrams described herein and shown in figures 2, 4 and 6 are by way of example only and are not limiting to the precise steps described or the order of those steps. It will be apparent to a person skilled in the art that some of the steps can be performed in a different order to that shown without affecting the overall objective. The randomisation process (steps 21 6-222) is additionally just one example of a randomisation process that can be applied to location information in the circumstances that the location information is cell-based and also that the uncertainty area can be used to predict the location of a wireless transmitter.

Arc-band conversion (218) can be described with reference to figures 3 and 4.

Arc-band conversion is applied in certain circumstances when the reported uncertainty area is an arc-band 302 which includes the reported location 304.

The arc-band 302 is such that it forms part of a circle which is centred on the location of the cell tower 306. This means that it is easy to calculate the location of a cell tower from an arc-band shaped uncertainly area. One example of where an arc-band shaped uncertainty area may be obtained is when the base station or cell tower has a sectored design, and then the angle of the arc, a is defined by the angle of the sector.

In arc-band conversion (218), the reported location of the MS is unchanged (402), i.e. the position 304 remains the reported position, however, the uncertainty area is converted into a circle 308 (step 404) which covers all of the

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In arc-band conversion, the accuracy of the reported location is not degraded (it is not changed) however, the conversion of the uncertainty area hides the location of the cell tower and does not disclose the method by which the location information was obtained. The uncertainty area is increased considerably by arc- band conversion, as can be clearly seen in figure 3 by comparing the areas of the arc-band 302 and circle 308.

Although arc-band conversion is described above as the conversion of the uncertainty area from an arc-band to a circle, it would alternatively be possible to convert the arc-band to shapes other than a circle, with the shapes being centred on the reported location 304. By converting the uncertainty area from an arc- band to another shape, the information contained in the arc-band which identified the true location of the cell tower, and which therefore enabled the prediction of wireless transmitter location, is lost. Furthermore, by converting the shape from an arc-band to another shape, the ability to infer the technology used for location determination is also lost.

Circle randomisation (222) can be described with reference to figures 5 and 6.

Circle randomisation is applied in certain circumstances when the reported uncertainty area is a circle 502 centred on the reported location 504. In many cases this reported location is actually the location of the cell tower. This means that it is not necessary to calculate the location of a cell tower from a circular uncertainty area because the reported location is the location of the cell tower.

One example of where a circular uncertainty area centered on the cell tower may be obtained is when the base station or cell tower is omnidirectional.

In circle randomisation (222) the reported location is moved by a distance R where R lies between a predetermined minimum and a predetermined maximum (step 602) to a randomised location 505. The randomised location 505 therefore lies an annulus 506 centred on the original position 504. The annulus preferably lies totally within the original uncertainly area 502 such that the accuracy of the location information is not too seriously degraded, such that the location based services provided by the LCS client are worthless to the user of the MS in question. In addition to moving the reported location by a distance R, the location is also moved by an angle 9. The angle 0 is selected randomly (step 604) and defined with respect to an arbitrary coordinate system. The * . - * ." : * *: : : * . * I I S, * * * I * S S -10- ** . *:. * randomised location 505 is therefore determined (step 606) from the random selection of the value of R within predefined limits (step 602) and the random selection of the value of 0 (step 604). Unlike arc-band conversion, circle randomisation affects both the accuracy of the location (moved by a distance R) and the uncertainty.

Having defined the randomised location 505, the new uncertainty area (or modified uncertainty area) 508 is defined (step 608) such that it is a circular area which includes all of the original uncertainty area 502 and which is centred on the randomised location 505. If R is selected to be large then the area of the modified uncertainty area is increased considerably compared to the original uncertainty area and the accuracy of the location information is degraded by the large amount R. If R is selected to be small there is a smaller increase in uncertainty area but these results in the randomised location 505 being closer to the actual cell tower location 504.

By setting a predetermined minimum value of R, this ensures a minimum separation between the randomised location 505 and the cell tower location 504, which ensures that the cell tower location is hidden by a given minimum distance.

By setting a predetermined maximum value of R, this ensures that the randomisation process maintains the accuracy of the location information within a set limit which can be selected by the network operator. Setting predetermined minimum and maximum values for A therefore provides a number of advantages, however the process could be adopted without setting such constraints.

As described above, in some circumstances, for example when the arc-band defines an angle of approaching 180 or more, arc-band conversion may not adequately disguise the location of a cell tower. In this case, circle randomisation (222) may be performed on the output of the arc-band conversion process (218). The description of circle randomisation above is still applicable, using the reported location 304 as the unmodified location 504 and the new uncertainty area 308 as the original uncertainty area 502. By combining arc- band conversion and circle randomisation, the uncertainty is increased considerably and the accuracy of the location is degraded by distance A. In some circumstances, the network may convert all uncertainty areas to circles prior to reporting the location information to the location server, for example this may occur in the MCS / SGSN. In this case the method above will perform circle

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Although the above description is described in terms which reference a wireless network, for example a cellular network, the invention is not limited to wireless networks. The invention is also applicable to other types of network, such as IP networks.

It will be understood that the above description of a preferred embodiment is given by way of example only and that various modifications may be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims (11)

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1. A method of reporting location of a user in a wireless network, the method comprising the steps of: receiving location information relating to the user from the network, said location information comprising a reported location within an uncertainty area; determining whether said location information indicates a location of a wireless transmitter within the network determining whether said uncertainty area can be used to predict a wireless transmitter location; if both the determinations are positive, randomising the location information; and reporting the randomised location information to a network entity.

2. A method of reporting location according to claim 1, wherein said step of determining whether said uncertainty area can be used to predict a wireless transmitter location comprises determining whether said uncertainty area is one of a circle and an arc-band.

3. A method of reporting location according to any of claims 1 and 2, wherein said step of reporting comprises: determining whether the entity is permitted to receive actual location information; and reporting the actual location information if the entity is permitted and reporting the randomised location information if the entity is not permitted.

4. A method of reporting location according to any of claims 1-3, wherein said uncertainty area is an arc-band and wherein said step of randomising comprises: maintaining the reported location unchanged; and converting the uncertainty area from an arc-band to another shape, centred on the reported location and covering the arc-band.

5. A method of reporting location according to claim 4, wherein said another shape is a circle.

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6. A method of reporting location according to any of claims 1-3, wherein said uncertainty area is a circle and wherein said step of randomising comprises: moving the reported location by a distance R and an angle 0, wherein said distance R is selected at random between an upper and a lower limit, and wherein said angle 0 is selected at random; and defining a new uncertainty area centred on the modified location.

7. A location server comprising: means for receiving location information relating to a mobile subscriber, said location information comprising a reported location within an uncertainty area; means for determining whether said location information indicates location of a wireless transmitter and whether said uncertainty area can be used to predict wireless transmitter location; and means for randomising said location information where both said determinations are positive.

8. A location server according to claim 7, wherein said means for receiving comprises an input.

9. A location server according to any of claims 7 and 8, wherein said means for determining comprises a processor.

10. A location server according to any of claims 7-9, wherein said means for randomising comprises a processor.

11. A computer program embodied on a computer readable medium and capable of being executed by a processor, the computer program comprising computer readable code for performing the method according to any of claims 1- 6.