GB2472832A

GB2472832A - Obtaining identity information using a virtual base station

Info

Publication number: GB2472832A
Application number: GB0914580A
Authority: GB
Inventors: Michael Kenyon
Original assignee: PRO SOLVE INTERNAT Ltd
Current assignee: PRO SOLVE INTERNAT Ltd
Priority date: 2009-08-20
Filing date: 2009-08-20
Publication date: 2011-02-23
Anticipated expiration: 2029-08-20
Also published as: GB0914580D0; GB2477919A; GB2472832B; GB201002600D0; WO2011021042A1

Abstract

An apparatus and method for obtaining identity information from at least one mobile station in a mobile telecommunications network, the method comprising receiving neighbour information (BA lists) broadcast by a plurality of base stations of the telecommunications system; selecting a channel for a virtual base station, VBTS, based upon the neighbor information received from the plurality of base stations; operating a virtual base station on the selected channel to cause at least one mobile station to reselect to the virtual base station such that the virtual base station receives identity information from the at least one mobile station. The virtual base station uses a location area code that will cause the mobile station to perform a location update. Identity information may include the mobile device's International Mobile Station Equipment, IMEI number, or its International Mobile Subscriber Identity, IMSI number.

Description

Apparatus and Method for Identifying Mobile Stations Embodiments of the present invention relate to a method and apparatus for identifying mobile stations in a telecommunications network.

EP1051053 discloses an apparatus for identifying a mobile telephone in a public cellular telecommunications network. The apparatus comprises a virtual base station (VBTS) connected to a test mobile telephone (TMS). In order to obtain an IMSI and/or IMEI number of the mobile telephone (MS), the VBTS and TMS are set up as spatially close as possible to the MS so that they are all in the same cellular environment (in a coverage area of a current base station). A BA list identifying broadcast control channel (BCCH) frequencies of one or more base stations adjacent to the current base station is then received by the TMS and a BCCH frequency of an adjacent base station is selected from the BA list. The VBTS then broadcasts on the selected BCCH frequency so as to be received by the MS at a greater power than the current base station on which the mobile telephone is inscribed or camped. This causes the mobile telephone MS to perform reselection to the VBTS so that its IMSI and/or IMEI number can be obtained.

However, the above method assumes that the MS and the TMS are camped onto the same current base station and therefore receiving the same BA list. This assumption is not always valid, resulting in the MS and TMS receiving different BA lists with the possibility of a frequency being selected for the VBTS which is not in the BA list received by the MS. Additionally, it is often desired to identify (to obtain the IMSI and/or IMEI numbers of) all mobile telephones within a certain area and, even when this one or a plurality of mobile telephones are located in a relatively small geographic area, they may be inscribed or camped on different base stations and thus receive different BA lists. It is not therefore possible, or it is at least difficult, to select a BCCH frequency applicable to all mobile telephones. Furthermore, it is frequently difficult, or at least very inconvenient, to locate the VBTS and TMS spatially close to the mobile telephone such that the two receive the same BA list.

Since such an apparatus is intended for use by security services e.g. police or intelligence agencies, it may be inconvenient or dangerous to locate the VBTS and TMS close to the mobile telephone.

It is an object of embodiments of the invention to at least mitigate one or more of the

problems of the prior art.

Summary of the Invention

According to a first aspect of the invention, there is provided an apparatus for determining identity information of a mobile station in a telecommunications system, comprising receiving means for receiving neighbour information broadcast by a plurality of base stations in the telecommunications system; a virtual base station; and a control unit arranged to select a channel for the virtual base station to operate on, wherein the channel is selected based upon the neighbour information received from the plurality of base stations; wherein the virtual base station is arranged to operate on the channel to cause one or more mobile stations to reselect to the virtual base station and to provide identity information to the virtual base station.

In contrast to the prior art, embodiments of the present invention select a channel for a virtual base station based upon neighbour information received from more than one base station. Advantageously, this increases a likelihood of all mobile stations reselecting to the virtual base station to provide identity information. For example, mobile stations which are camped on different base stations may still reselect to the virtual base station.

The telecommunications system may be a wireless telecommunications system, such as a mobile telephone system. The telecommunications system may be based upon GSM or UMTS/3G. The neighbour information may be a BA list broadcast by each base station.

The control unit may be arranged to select the channel according to a received signal level of each of the base stations broadcasting the received neighbour information.

The control unit may also consider a number of base stations whose broadcast neighbour information identifies each channel. Preferably, the control unit attempts to maximise the number of base stations identifiying the channel in their neighbour information whilst also selecting a channel having a lowest signal level to reduce interference. In some embodiments, the control unit attempts to select a channel identified by all base stations on which no signal is currently broadcast.

The control unit may be arranged to determine a base station having the greatest received signal level and one or more base stations having a signal level within a predetermined signal window of the base station having the greatest received signal level, and to select the channel according to the neighbour information broadcast by the base station having the greatest received signal level and the one or more base stations having a signal level within the signal level window. Preferably, the control unit attempts to select a sub-set of receivable base stations for consideration of the channel selection.

Preferably, the control unit is arranged to determine a normalised power for each of the base stations within the signal level window according to their respective received signal strengths.

The control unit may be arranged to determine, from the received neighbour information, a neighbour list identifiying a plurality of base stations and to select the channel as a channel of a base station identified in the neighbour list. The channel may be selected based upon a weighting factor. Preferably, the weighting factor is a sum of normalised powers of base stations whose neighbour information identifies each channel.

Preferably, the control unit is arranged to select the channel as a channel of a base station identified in the neighbour list according to, at least partly, a received signal power of each base station.

The receiving means may be a scanning receiver capable of scanning across a predetermined frequency range, such as a range of frequencies on which base stations in the telecommunications system broadcast. The frequency range may be that of a GSM telecommunications network.

According to a second aspect of the invention there is provided a method of obtaining identity information from at least one mobile station in a mobile telecommunications network, comprising: receiving neighbour information broadcast by a plurality of base stations of the telecommunications system; selecting a channel for a virtual base station based upon the neighbour information received from the plurality of base stations; operating a virtual base station on the selected channel to cause at least one mobile station to reselect to the virtual base station such that the virtual base station receives identity information from the at least one mobile station.

A further aspect of the invention may include computer-readable code stored on a storage medium which, when executed by a computer, causes the computer to perform a method according to an embodiment of the invention.

Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which: Figure 1 shows a schematic illustration of a cellular environment; Figure 2 shows an apparatus for identifying mobile stations according to an embodiment of the present invention; Figure 3 is a schematic illustration of a cellular communication environment including mobile stations and the apparatus; Figure 4 shows a method according to an embodiment of the invention; and Figure 5 shows a method of selecting a BCCH frequency according to an embodiment of the invention.

Detailed Description of Embodiments of the Invention Embodiments of the present invention utilise data received from a plurality of base stations in a telecommunications network to select frequency for a virtual base station.

Figure 1 a shows a schematic representation of a cellular telecommunications environment 110. The cellular environment 110 includes a plurality of base stations (BTS) llOa, liOb, hOc. Although Figure lashowsthreeBTSs llOa, 11Db, hOc the cellular environment 110 may comprise any number of BTSs. A coverage area of each BTS 1 lOa, 1 lOb, 1 lOc is represented schematically in Figure 1 as a hexagonal area with the coverage area of each BTS llOa, liOb, hOc interlocking so as to provide substantially continuous coverage for mobile stations in the cellular environment 110.

The schematic representation of the cellular environment 110 shown in Figure 1 a is somewhat misleading, however, in that it suggests that each BTS llOa, liOb, hOc has a unique coverage area which is distinct from that of the other BTSs 11 Oa, 11 Ob, 1 lOc. In reality there are considerable overlaps in coverage between adjacent BTSs llOa, liOb, hOc.

Figure lb shows a more realistic representation of a cellular environment 120 corresponding to the schematic cellular environment 110 shown schematically in Figure ha. An actual coverage area of each of the three BTSs h2Oa, h2Ob, h2Oc is shown. It will be noted that the actual cellular environment 120 includes areas of overlapping BTS coverage. Figure lb also includes a so called pico-cell 120d formed by a fourth base station BTS4 which may be deployed to provide additional coverage in a small area within the coverage area h2Ob of another BTS (in this case BTS2).

In addition to the overlapping coverage areas in the actual cellular environment 120 there may be considerable variation in received signal level within a coverage area of one or more BTSs h2Oa, h2Ob, h2Oc, h2Od. Figure hc shows a schematic representation of a coverage map 130 for a single BTS. The coverage map 130 illustrates a signal level in decibels (dB) received from the BTS h3Oa. Figure hc shows a general reduction in received signal level as a distance from the BTS h3Oa increases. Furthermore, the coverage map 130 illustrates areas which deviate from the general trend of signal level decreasing with distance, for example due to the effect of terrain, buildings or other obstructions causing locally variable i.e. reduced or increased signal levels. Therefore, a typical cellular environment may be more accurately represented as a plurality of at least partially overlapping coverage maps 130, such as that shown in Figure ic.

A significant variation in signal level from the BTS 1 30a can occur over a distance as short as one metre, or less. In an area of overlapping coverage from more than one base station (an area in which more than one base station can be received) this can cause a mobile station, such as a mobile telephone, to reselect BTSs if it is moved only a relatively short distance. A mobile station selects a BTS on which to camp according to one or more criteria, such as a BTS having the strongest signal at the mobile station's current location. First and second mobile stations only a short distance apart may be camped on to two different base stations due to their different received signal levels. As a consequence, it is not possible to be certain that all mobile stations whose identities it is desired to obtain will all be camped on to the same BTS and thus receive the same BA list. In other words, some or all of the mobile stations that it is intended to identify may not be camped on the same BTS.

A mobile station which is camped on a different BTS will receive a different BA list from one or more mobile stations camped on different BTSs. In this case, it is possible that the channel selected for use by a virtual base station (VBTS) may not be a channel that is in the BA list received by all of the mobile stations and is therefore not being monitored by all the mobile telephones. If a mobile station is not monitoring the BCCH channel used by the VBTS then it will not reselect to the VBTS and it will not be possible to obtain its IMSI or IMEI.

Referring to Figure 2, an apparatus 200 according to an embodiment of the present invention will now be described. The system 200 comprises a network survey receiver (NSR) 210 for receiving signals broadcast by base stations in a telecommunications system, and a virtual base station (VBTS) 220 for operating as a base station in the telecommunications environment. The NSR 210 and VBTS 220 are both connected to and controlled by a control unit 230. The control unit 230 may be a dedicated control unit, such as a dedicated microprocessor, or may be implemented by a general-purpose computer executing appropriate software. Also shown in Figure 2 are a plurality of network base stations 240 which form the telecommunications system to provide a mobile telecommunication service in a geographical locality, and a plurality of mobile stations in the form of mobile telephones 250 which receive the telecommunications service. It will be realised that, whilst mobile telephones are depicted in Figure 2, the mobile stations may be any device capable of interacting with the telecommunications system. The apparatus 200 is arranged to obtain identity information from one or more mobile stations, such as one or more of the mobile telephones 250. The identity information includes IMEI and/or IMSI numbers of at least some of the mobile telephones 250. In use, the apparatus 200 is deployed in the geographical area occupied by the mobile telephone or mobile telephones 250 from which it is desired to obtain the identity information.

This area may be in the coverage area of one or more of the network base stations 240.

Figure 3 shows the apparatus 200 deployed in an area having overlapping coverage from three network base stations 310, 320, 330, although it will be realised that the invention is applicable when there is coverage from more or fewer network base stations. The VBTS 220 which forms part of the apparatus 200 provides a coverage area 340 within which there is a plurality of mobile telephones (MS) 350, 351, 352, 353, 354, although the number of mobile telephones may be greater or fewer than this.

These are the target mobile telephones for which it is desired to discover their identities or obtain identity information.

Prior to activation of the apparatus 200, each of the mobile telephones 350, 351, 352, 353, 354 receives the telecommunications service supported by the base stations 310, 320, 330. Each mobile telephone 350, 351, 352, 353, 354 is camped onto one base station selected according to predetermined criteria, normally the base station 310, 320, 330 with the highest signal level at the location of the respective mobile telephone 350, 351, 352, 353, 354. Each base station 310, 320, 330 broadcasts a BA list which contains a list of the channel numbers (BCCH) used by other base stations in the area. Each mobile telephone 350, 351, 352, 353, 354 receives the BA list from the base station 310, 320, 330 on which it is currently camped. Each mobile telephone 350, 351, 352, 353, 354 monitors the channels in the received BA list and, if it detects a base station which it is receiving at a higher signal level than its current base station 310, 320, 330, it reselects onto the highest power base station 310, 320, 330 to camp on this new base station 310, 320, 330. Having reselected base stations, the mobile telephone 350, 351, 352, 353, 354 monitors the channels identified in a BA list broadcast by the new base station, such that each mobile telephone 350, 351, 352, 353, 354 continually seeks to camp on a base station 310, 320, 330 having the highest signal level at its current location.

This process of switching between base stations 310, 320, 330, termed cell reselection, is the means by which telecommunications network coverage is maintained while the mobile telephone moves through the coverage area. Cell reselection is normally a passive process meaning that the network has no knowledge of which base station on to which a particular mobile phone is camped. However the telecommunications network generally requires knowledge of a mobile telephone's location so that incoming calls can be routed to it. For this purpose the GSM system has a concept referred to as Location Area (LA) and each base station is allocated a Location Area Code (LAC) which it broadcasts on its BCCH channel. A group of base stations within a certain geographical area are allocated the same LAC but this differs from the LAC allocated to a group of base stations in a different but adjacent geographical area. When a mobile telephone wants to move from a base station in one LA to a base station in a different LA it performs a process referred to as Location Update which involves communication between the mobile and the new base station during which the mobile telephone identifies itself to the network and requests a transfer to the new LA. If the network accepts this request then the mobile telephone camps on to the new base station and the network is aware that it has moved to a new LA. When an incoming call is received for a particular mobile telephone a paging message is broadcast on all base stations within that mobile telephone's current LA so that the mobile telephone is aware of the incoming call and is able to respond.

A method 400 of operation of an apparatus according to an embodiment of the invention, such as the apparatus 200 shown in Figure 2, will now be described with reference to in Figure 4. In step 410 a plurality of BA lists, each received from one of a plurality of base stations 310, 320, 330, are received by the NSR 210. In step 420, a channel frequency is determined, based upon the plurality of received BA lists, by the control device 230. In step 430 the VBTS 220 broadcasts a signal on the determined channel frequency in order to cause one or more mobile telephones 350, 351, 352, 353, 354 to reselect the VBTS 220 as a current base station, such that identity information may be obtained from the one or more mobile telephones 350, 351, 352, 353, 354. Advantageously, by receiving BA lists from a plurality of base stations and selecting a channel frequency based upon the plurality of received BA lists, there is generally a high probability that a channel will be chosen that is being monitored by the one or more mobile telephones 350, 351, 352, 353, 354 or at least by a high proportion of them. This represents an improvement over the current art in which the channel selection is made from a single BA list, possibly resulting in the selection of a channel which is not being monitored by some or all of the mobile telephones 350, 351, 352, 353, 354. The consequence of selecting a channel not being monitored by a particular mobile telephone is that that mobile telephone will not reselect to the VBTS and it is therefore not possible to obtain the identity information from that mobile telephone.

Steps of the method 400 described with reference to Figure 4 according to embodiments of the invention will now be described in more detail. As noted above, in step 410 the NSR 210 is used to receive a plurality of BA lists broadcast by respective base stations. This may be achieved by the NSR 210 receiving data transmitted on a plurality of BCCH channels by the base stations 310, 320, 330 receivable at the location of the apparatus 200 and decoding received BCCH channel data. The NSR 210 may scan a range of frequencies on which base stations 310, 320, 330 broadcast in the system. The received data includes the BA list and LAC which is broadcast by each network base station 310, 320, 330. The data is read into the computer 230 for analysis in step 420 and selection of a suitable channel and LAC to be used by the VBTS 220 in step 430.

In embodiments of step 420 the channel on which VBTS 220 will broadcast is selected by means of a statistical analysis carried out on the received data from a plurality of BCCH. In particular, by analysis of the plurality of received BA lists.

Embodiments of step 420 aim to select a channel having a high probability of being monitored by as many as possible of the mobile telephones within the coverage area of the VBTS 220. An embodiment of a method of statistical analysis for selecting the channel on which the VBTS 220 will broadcast is described below. It should be understood that there may be differences in the BA lists transmitted by the base stations 310, 320, 330 with the result that mobile telephones camped onto different base stations 310, 320, 330 may be monitoring different channels and that choosing a channel for the VBTS 220 from a single base station's BA list may result in selecting a channel that fewer mobiles telephones are monitoring.

In step 430 the VBTS 220 is activated to broadcast on the selected channel. The VBTS 220 transmits at a power such that it will be received by the target mobile telephones at a level exceeding that of the respective base station on which they are currently camped and, as a result, the mobile telephones will reselect base stations to camp on to the VBTS 220. Moreover, the VBTS 220 broadcasts a LAC which differs from the LAC or LACs being broadcast by the network base stations 310, 320, 330, thus simulating a change in LAC for the mobiles telephones and triggering the location update process during which the mobile telephones send their identity information comprising IMSI and/or IMEI to the apparatus 200. The mobile telephones can then be returned to the network using one of several methods known in the current art.

A method 500 of performing a statistical analysis of the data received by the NSR 220 to select a channel frequency according to an embodiment of the invention will now be described with reference to Figure 5.

Figure 5 is a flowchart illustrating steps of the method alongside a simplified example for explanatory purposes. It should be noted that in a typical operational scenario there may be more channels and longer BA lists than are shown in this example. The method 500 may be performed for one cellular network, this being the telecommunications network used by the target mobile phones. In the event that the target phones are on multiple networks, e.g. different telecommunication service providers, then the following procedure is performed for each network in turn.

Step 510: From the data output of the NSR 220, determine all of the receivable BCCH channels for the target network and a received signal level of each BCCH channel.

The received signal level may be identified as an RxLev parameter used in GSM systems. In other words, in step 510 a list is assembled of all BCCH channel frequencies received at the location of the apparatus 200. In the example shown there are five channels receivable by the apparatus 200, these being channels 1, 2, 3, 6, 4 in order of decreasing signal strength.

Step 520: Determine one or more channels, according to predetermined criteria, whose BA lists are to be used to select a channel frequency for the VBTS 230. In a preferred embodiment of this step a signal level window is defined, for example 20dB, although other window widths may be used. A BCCH channel having a highest received signal level is then selected from the BCCH channels received in step 510. Any further BCCH channels are then selected which have a received signal level within the signal level window of the BCCH having the highest received power.

That is, BCCH channels which have a received signal level within the signal level range of the highest level BCCH channel. The purpose of this step is to allow for variations in signal level throughout the coverage area of the VBTS and to select a set of BCCH channels for analysis which includes all those BCCH channels likely to be monitored by mobile telephones within the coverage area of the VBTS. In the example BCCH channel 1 has the highest signal level of -60 dBm and BCCH channels 2 and 3 are within 20 dBm of the highest power channel i.e. greater than -80 dBm. Channels 1, 2 and 3 are selected according to the preferred embodiment of the invention. BA lists are then received from the BCCH channel having the highest power (channel 1) and any BCCH channels (channels 2 and 3) within the signal level window.

Step 530: A normalised power of each of the selected BCCH channels is determined.

In the preferred embodiment, the normalised power of each channel is determined by calculating a linear power P for each BCCH channel, summing all the linear powers of the channels to determine a total linear power S and dividing each of the BCCH channel powers by this sum to determine the normalised power N, as in Equation 1.

This results in a normalised power figure for each BCCH channel with the sum of these normalised powers totalling one. Figure 5 shows the calculation of the normalised powers for each channels 1, 2, 3 these being the channels selected in step 520.

N = -Equation 1

S

Step 540: A list of all base stations proximal to the location of the apparatus is determined based upon a plurality of BA lists. In the preferred embodiment of the invention the list of proximal base stations, known as a neighbour list (NEIGHBOUR_LIST), is determined as a union of the BA lists broadcast on the BCCH channels selected in step 520. A weight is then determined for each channel in NEIGHBOUR_LIST by summing the normalised powers of the BCCH channels which contain this channel in their BA List. For a channel that appears in the BA list of every selected BCCH channel the weight will be one. Channels that appear in only some of the BA Lists will have a weight of less than one. The example of Figure 5 shows that the union of the BA Lists contains channels: 1, 2, 3, 4, 5, 6 and 7. The weight for each of these channels is calculated by summing the normalised powers determined step 530 for each of the BCCH channels that contain the channel in their BA List.

Step 550: A VBTS transmission channel is selected for use by the VBTS 220. In the preferred embodiment the VBTS transmission channel is selected according to the weight determined in step 540 and the received signal level RxLev. The VBTS transmission channel is determined as a channel having a highest weight, or close to the highest weight, while also having a low value of RxLev so as to minimise interference to the transmissions from the VBTS 220. The weight is obtained from the results of step 540 while the RxLev is obtained from the results of step 510. If a particular channel is not recorded in the results of step 510 this indicates that the channel is effectively unoccupied and therefore suitable for use by the VBTS 220. An acceptable weight range (for example, within 5% of the maximum weight) is defined so as to provide a subset of channels that can be considered for use by the VBTS 220.

A channel is then selected from this subset, this being one within the acceptable weight range that has the lowest value of RXLev. In the example channels 1, 2, 3 and all have a weight within 5% of the maximum weight and channel 5 has the lowest value of RXLev (it is an unoccupied channel). Therefore channel 5 is chosen in the example of Figure 5 for use by the VBTS.

In the current art the channel for the VBTS is selected from the set of channels in the BA list of the BTS being received with the highest signal level at the location of the apparatus. Due to variations in signal level, some or all of the mobile telephones within the coverage area of the VBTS may be receiving a different BTS as their strongest and may therefore be receiving different BA lists which may contain different channels. It is therefore possible that they will not be monitoring the channel selected for use by the VBTS and therefore it will not be possible to obtain their identity information. The current invention uses a plurality of BA lists in the channel selection process, this plurality being chosen so as to include the BA lists from all those BCCH channels which mobile telephones within the coverage are likely to be monitoring. This increases the probability that the set of channels being considered for use by the VBTS contains some channels that are being monitored by all, or at least most of the mobile telephones within the coverage area. Furthermore, when selecting the VBTS operating channel from this set of channels more weight is given to channels in the BA lists from BCCH channels that are received by the apparatus at the highest signal levels as these BCCH channels are the ones on which mobile telephones within the coverage area are most likely to be camped. Finally, consideration is given to the interference level on the VTBS operating channel and the choice of channel is based on an acceptable compromise between the probability that mobile telephones are monitoring that channel and any other transmissions on that channel that may interfere with reception of the VBTS transmission by the mobile telephones.

Having activated the VBTS 220 on the chosen channel using a transmission power such that mobile telephones will receive it at a signal level exceeding that of their current BTS, the mobile telephones will perform a cell reselection and camp on to the VBTS. As the LAC chosen for use by the VBTS differs from the LAC used by the telecommunications network in the locality of the VBTS each mobile telephone will implement the Location Update process as specified in the standard GSM specifications. This process commences with the mobile telephone sending a message to the VBTS requesting permission to transfer to the new Location Area. In a normal mobile telecommunications network a BTS, before granting a Location Update request must establish the identity of the mobile telephone which is making the request. The VBTS 200 emulates this behaviour, using standard features of the standard GSM specifications and in this way is able to obtain the IMSI and/or IMEI from the mobile telephone. Finally, when the desired identity information has been obtained the VBTS can release the mobile telephone back to the normal network using one of the methods known in the current art.

It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program. Still further, embodiments of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims.

Claims

CLAIMS1. An apparatus for determining identity information of a mobile station in a telecommunications system, comprising: receiving means for receiving neighbour information broadcast by a plurality of base stations in the telecommunications system; a virtual base station; and a control unit arranged to select a channel for the virtual base station to operate on, wherein the channel is selected based upon the neighbour information received from the plurality of base stations; wherein the virtual base station is arranged to operate on the channel to cause one or more mobile stations to reselect to the virtual base station and to provide identity information to the virtual base station.
2. The apparatus of claim 1, wherein the control unit is arranged to select the channel according to a received signal level of each of the base stations broadcasting the received neighbour information.
3. The apparatus of claim 1 or 2, wherein the control unit is arranged to determine a base station having the greatest received signal level and one or more base stations having a signal level within a predetermined signal window of the base station having the greatest received signal level, and to select the channel according to the neighbour information broadcast by the base station having the greatest received signal level and the one or more base stations having a signal level within the signal level window.
4. The apparatus of claim 3, wherein the control unit is arranged to determine a weighting factor for each of the base stations within the signal level window according to their respective received signal strengths.
5. The apparatus of any preceding claim, wherein the control unit is arranged to determine, from the received neighbour information, a neighbour list identifying a plurality of base stations and to select the channel as a channel of a base station identified in the neighbour list.
6. The apparatus of claim 5, wherein the control unit is arranged to select the channel as a channel of a base station identified in the neighbour list according to a received signal power of each base station.
7. The apparatus of claim 5 or 6, wherein the control unit is arranged to select the channel as a channel of a base station identified in the neighbour list according to a weighting factor of each of the base stations.
8. The apparatus of any preceding claim wherein the control unit is arranged to select an area code for the virtual base station which is different from an area code selecting a channel for a virtual base station based upon the neighbour information received from the plurality of base stations; and operating the virtual base station on the selected channel to cause at least one mobile station to reselect to the virtual base station such that the virtual base station receives identity information from the at least one mobile station.13. The method of claim 12, wherein the channel is selected based upon a received signal level of each of the base stations broadcasting the received neighbour information.14. The method of claim 12 or 13, comprising determining one or more base stations having a received signal level within a predetermined signal level window of a base station having the greatest received signal level, and selecting the channel according to the neighbour information broadcast by the base station having the greatest received signal level and the one or more base stations having a signal level within the signal level window.15. The method of 13 or 14, comprising determining a weighting factor for each of the base stations within the signal level window according to their respective received signal strengths.16. The method of any of claims 12 to 15, comprising determining a neighbour list identifying a plurality of base stations from the received neighbour information and selecting the channel as a channel of a base station identified in the neighbour list.17. The method of claim 16, wherein the channel is selected to be a channel of a base station identified in the neighbour list based upon a received signal power of each base station.18. The method of claim 16 or 17, wherein the control unit is arranged to select the channel as a channel of a base station identified in the neighbour list based upon the weighting factor of each of the base stations.19. The method of any of claims 12 to 18, comprising selecting an area code for the virtual base station which is different from an area code used by a base station having the highest received signal power.20. The method of any of claims 12 to 19, comprising reselecting the channel for the virtual base station to operate on to cause one or more additional mobile stations to reselect to the virtual base station and to provide identity information to the virtual base station.21. The apparatus or method of any preceding claim, wherein the channel is a BCCH channel.22. A computer storage medium having computer-readable code stored thereon which, when executed by a computer, causes the computer to perform a method according to any of claims 12 to 21.23. An apparatus substantially as described hereinbefore with reference to the accompanying drawings.24. A method substantially as described hereinbefore with reference to the accompanying drawings.