WO2010073210A1

WO2010073210A1 - Method and apparatus for establishing communication channels

Info

Publication number: WO2010073210A1
Application number: PCT/IB2009/055873
Authority: WO
Inventors: Lawrence Ka Keung Wong
Original assignee: Nokia Corporation
Priority date: 2008-12-22
Filing date: 2009-12-21
Publication date: 2010-07-01
Also published as: GB0823355D0

Abstract

Method and apparatus for establishing and maintaining two communications channels using respecting subscriber identity modules on a mobile telephone network such as a GSM network. The channels are chosen so that collisions due to drift of corresponding carrier waves are reduced or avoided. Embodiments of the invention find application where each communication channel corresponds to a different public land mobile networks which are not able to roam on one another's networks.

Description

METHOD AND APPARATUS FOR ESTABLISHING COMMUNICATION CHANNELS

FIELD OF THE APPLICATION

The present application relates generally to the field of establishing communication channels.

BACKGROUND

Communication channels such as cable connections or wireless connections may be used to enable multiple communications devices to send communications between each other using various protocols. This may be achieved by means of direct communications between the devices, or via intermediate communication stations.

SUMMARY

Various aspects of examples of the invention are set out in the claims.

An aspect of the invention relates to a method comprising: establishing, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; establishing, through said radio, a second communications channel for use with a second subscriber identity module; alternating between said first communications channel and said second communications channel to poll each communications channel for incoming communications ; wherein said radio, said first subscriber identity module and said second subscriber identity module form part of a single mobile communications device. Said first communications channel may correspond to a first physical communications channel and said second communications channel may correspond to a second physical Communications channel.

Said second communications channel may be established with said first base transceiver station or with a second base transceiver station. The method may further comprise: selecting said second communications channel to be spaced in time from said first communications channel. The method may further comprise: determining a timing for said first communications channel; determining a timing for a plurality of further communications channels; selecting one of said further communications channels as said second communications channel on the basis of said determined timings. Said second communications channel may be selected with reference to an expected frequency drift of said first communications channel relative to said second communications channel.

Said second communications channel may be selected so that a slot of said second communications channel is separated in time from a slot of said first communications channel by at least a predetermined offset. The method may further comprise: recording a timing of said first communications channel; recording a timing of said second communications channel; establishing, through said radio, a third communications channel for use with said first subscriber identity module or said second subscriber identity module based on said recorded timings. A carrier frequency of said third communications channel may be selected based on said recorded timings.

A carrier frequency of said third communications channel may be selected based on a minimum offset in time between a slot of either said first communications channel or said second communications channel and a slot of said third communications channel.

The method may further comprise predicting a collision between said first communications channel and said second communications channel based on said recorded timings.

Each of said communications channels may be established according to the GSM standard.

The first communications channel may correspond to a first public land mobile network and said second communications channel may correspond to a second public land mobile network where said public land mobile networks are unable to roam on each other's networks. The third communications channel may correspond to said first public land mobile network or said second public land mobile network.

A further aspect of the invention extends to an apparatus, comprising: at least one processor; and at least one memory including computer program code the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following: establishing, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; establishing, through said radio, a second communications channel for use with a second subscriber identity module; alternating between said first communications channel and said second communications channel to poll each communications channel for incoming communications ; wherein said radio, said first subscriber identity module and said second subscriber identity module form part of a single mobile communications device.

Said first communications channel may correspond to a first physical communications channel and said second communications channel may correspond to a second physical communications channel. Said second communications channel may be established with said first base transceiver station or with a second base transceiver station. The apparatus may further perform: selecting said second communications channel to be spaced in time from said first communications channel. The apparatus may further perform: determining a timing for said first communications channel; determining a timing for a plurality of further communications channels; selecting one of said further communications channels as said second communications channel on the basis of said determined timings. Said second communications channel may be selected with reference to an expected frequency drift of said first communications channel relative to said second communications channel.

Said second communications channel may be selected so that a slot of said second communications channel is separated in time from a slot of said first communications channel by at least a predetermined offset. The apparatus may further perform: recording a timing of said first communications channel; recording a timing of said second communications channel; establishing, through said radio, a third communications channel for use with said first subscriber identity module or said second subscriber identity module based on said recorded timings.

A carrier frequency of said third communications channel may be selected based on said recorded timings.

The apparatus may further perform: predicting a collision between said first communications channel and said second communications channel based on said recorded timings. Each of said communications channels may be established according to the GSM standard.

Said first communications channel may correspond to a first public land mobile network and said second communications channel may correspond to a second public land mobile network where said public land mobile networks are unable to roam on each other's networks.

Said third communications channel may correspond to said first public land mobile network or said second public land mobile network.

A further aspect of the invention extends to an apparatus, comprising: a processor configured to: establish, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; establish, through said radio, a second communications channel for use with a second subscriber identity module; alternate between said first communications channel and said second communications channel to poll each communications channel for incoming communications; wherein said radio, said first subscriber identity module, said second subscriber identity module and said processor form part of said apparatus, said apparatus being a single mobile communications device.

The processor may comprise at least one memory that contains executable instructions that if executed by the processor cause the apparatus to : establish, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; establish, through said radio, a second communications channel for use with a second subscriber identity module; and alternate between said first communications channel and said second communications channel to poll each communications channel for incoming communications .

A further aspect of the invention extends to a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer, the computer program code comprising: code for establishing, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; code for establishing, through said radio, a second communications channel for use with a second subscriber identity module; and code for alternating between said first communications channel and said second communications channel to poll each communications channel for incoming communications wherein said radio, said first subscriber identity module and said second subscriber identity module form part of said apparatus, said apparatus being a single mobile communications device. A further aspect of the invention extends to a computer program, comprising: code for establishing, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; code for establishing, through said radio, a second communications channel for use with a second subscriber identity module; and code for alternating between said first communications channel and said second communications channel to poll each communications channel for incoming communications; when the computer program is run on a processor; wherein said radio, said first subscriber identity module, said second subscriber identity module and said processor form part of a single mobile communications device.

A further aspect of the invention extends to a method comprising: recording a timing of a first communications channel, said first communications channel establishing communications through a radio with use of a first subscriber identity module; recording a timing of a second communications channel, said second communications channel establishing communications through said radio with use of a second subscriber identity module; establishing, through said radio, a third communications channel for use with said first subscriber identity module or said second subscriber identity module based on said recorded timings. wherein said radio, said first subscriber identity module and said second subscriber identity module form part of a single mobile communications device.

A further aspect of the invention extends to an apparatus comprising: at least one processor; and at least one memory including computer program code the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following: record a timing of a first communications channel, said first communications channel establishing communications through a radio with use of a first subscriber identity module; record a timing of a second communications channel, said second communications channel establishing communications through said radio with use of a second subscriber identity module; establish, through said radio, a third communications channel for use with said first subscriber identity module or said second subscriber identity module based on said recorded timings. wherein said radio, said first subscriber identity module, said second subscriber identity module and said processor form part of said apparatus, said apparatus being a single mobile communications device. BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of example embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which: Figure 1 is a schematic diagram of a mobile computing device in which an example embodiment of the invention can been implemented;

Figure 2 is a schematic diagram of hardware components of the mobile computing device of Figure 1;

Figure 3 is a block diagram representing aspects of the mobile computing device of Figure 1;

Figure 4 is a schematic illustration of an arrangement of a mobile computing device in a network;

Figure 5 is a schematic illustration of an alternative arrangement of a mobile computing device in a network; Figure 6 is a flow diagram of a process according to an example embodiment of the invention;

Figure 7 is a flow diagram of a process according to an example embodiment of the invention; and

Figure 8 is a schematic diagram of two carrier waves, illustrating an offset between a first communications channel and a second communications channel.

DESCRIPTION OF EXAMPLE EMBODIMENTS

A description of a number of embodiments of the invention follows, provided by way of example only.

Figure 1 is a schematic diagram of a mobile computing device 10 which represents an example of a device in which an embodiment of the invention may be implemented. The device has a casing 12 which encapsulates a keypad 14, a display 16, a speaker 18 and a microphone 20. The device 10 further includes an antenna 22. The device 10 illustrated in Figure 1 is a mobile device in that it may be held in a user's hand. It can be used to participate in communication sessions, in particular, telephone calls. During such sessions the device 10 may be utilised so that the speaker 18 is held to a user's ear and the microphone 20 is situated in proximity to a user's mouth.

Figure 2 is a schematic illustration showing the arrangement of certain of the hardware components of the device 10 of Figure 1. The keypad 14, display 16, speaker 18 and microphone 20 of this embodiment are connected to a system bus 42. The bus 42 is further connected to an application processor 24, a baseband processor 26, a digital signal processor (DSP) 38, a transmitter 28, a receiver 30 and a battery 40, in this embodiment. Transmitter 28 and receiver 30 of this embodiment are connected to antenna 22. The baseband processor 26 of this embodiment is concerned with the communication functions and to this end controls a telephony stack and communicates with the transmitter 28 and receiver 30 to establish communications by means of the antenna 22. The baseband processor 26, digital signal processor 38, receiver 30, transmitter 28 and antenna 22 of this example embodiment form a radio 58. The mobile computing device 10 of this embodiment comprises a single radio 58. It is to be realised that the layout and components of the radio 58 will depend on the type of wireless communications in which the device 10 is engaged. Further and alternative arrangements of the radio 58 are within the scope of this invention. Furthermore, the radio 58 of this embodiment includes components not illustrated or discussed.

The bus 42 is further connected to a memory controller 32 which is, in this embodiment, connected to a volatile memory 34 and a non-volatile memory 36. The application processor 24 of this embodiment processes instructions related to various software modules and operating system software which run on the device 10 and which provide various functionality of the device 10. The various processing elements of the device 10 such as the application processor 24 and baseband processor 26 may, in an alternative embodiment, be provided on a single processor or on more than two processors. Memory controller 32 of this embodiment controls the access to, and interaction with, volatile memory 34 and non-volatile memory 36. The application processor 24 of this embodiment is able to communicate with the various hardware elements as well as the memory controller 32 and thereby control the operation of the various hardware elements according to software instructions stored on volatile memory 34 or non-volatile memory 36. The mobile computing device 10 further comprises two subscriber identity module

(SIM) card readers 50 and 52 connected to bus 42. SIM card reader 50 is connected to SIM card 54 whereas SIM card reader 52 is connected to SIM card 56. The SIM cards 54, 56 are in this example removably located within the device 10. In this example the SIM cards operate according to the GSM standard, and each has an International Mobile Subscriber Identifiers (IMSIs). The card readers 50 and 52 of this embodiment have corresponding International Mobile Equipment Identifiers. In this embodiment, SIM card 54 is associated with a first public land mobile network (PLMN 1) and SIM card 56 is associated with a second public land mobile network (PLMN 2).

Only a single bus, bus 42, is illustrated in the example shown in Figure 2. It is to be realised that this bus may be replaced by two or more buses in alternative embodiments and that the topology of Figure 2 would vary accordingly. Furthermore, known computing devices include hardware components additional to those illustrated in Figure 2 which may be incorporated into embodiments of the invention.

Figure 3 is a diagram illustrating various hardware and software components of the example device 10. The software operating on the device 10 of this embodiment can be categorised in various ways. Certain software of this embodiment operates to manage the resources provided by the various hardware components and to establish an operational environment in which other software executes. This software is known as the operating system of the device of this embodiment and is partially represented in Figure 3 by a kernel 42. The kernel interacts with the memory controller 32 which, as previously described, is connected to volatile memory 34 and non- volatile memory 36 of this embodiment. The kernel 42 of this embodiment is further connected to a plurality of user programs 44 each of which may access the hardware components in a manner dictated by the kernel 42 of this embodiment. The kernel 42 is further connected to the keypad 14 by means of device driver 46, to speaker 18 by means of device driver 47 and to the baseband processor 26 by means of device driver 48, in this embodiment. Only certain of the hardware components have been illustrated but, generally, the kernel 42 of this embodiment controls the hardware resources of the device 10 through various device drivers. Furthermore, although the device drivers have been illustrated as separate to the kernel 42, it is possible for some or all of them to be incorporated into the kernel 42 in alternative embodiments.

The software components of Figure 3 are delineated by dashed area 41 in this embodiment. However, this distinction between software and hardware is not essential. Components depicted as software in Figure 3 may be rendered in hardware, and those depicted as hardware may, in certain circumstances, be rendered as software in further embodiments. Furthermore, some components may have a software portion as well as a hardware portion in further embodiments.

During operation of the device, software instructions stored in non- volatile memory 36 of this embodiment establish the kernel 42, the user programs 44 and the device drivers 46, 47 and 48. Through the use of the various components illustrated in Figure 3 a user is able to utilise the device 10 of this embodiment according to the functionality provided by the various user programs 44. For example, a user uses the keypad 14 of this embodiment to communicate with the kernel 42 by means of device driver 46 to cause one of the user programs 44 to access data stored on non- volatile memory 36 by means of memory controller 32. The kernel 42 of this embodiment then causes the data supplied by memory controller 32, together with instructions supplied by the user program, to be sent to the application processor 24 (Figure 2). The application processor 24 of this embodiment will return results from the data and instructions, generally utilising volatile memory 34 in the process, and these will be returned to the user program by the kernel 42. On further instructions from the user program, the kernel 42 will cause the results to be displayed to the user on display 16 by means of device driver 48.

The illustration of Figure 3 is presented merely by way of example. Devices on which example embodiments of this invention may operate comprise more or fewer components than those shown. Implementations of embodiments of the invention are not dependent on the precise arrangement and configuration of the components shown in Figures 1, 2 and 3. Therefore other components with similar functionality may be substituted and further components added thereto or illustrated components omitted therefrom without affecting the operation of example embodiments of the invention.

Figure 4 illustrates an arrangement of the mobile computing device 10 in a GSM network, according to an embodiment of the invention. The mobile computing device 10 of this embodiment communicates with base transceiver station 60 through a first connection 80 (denoted by a solid line). As described below, this first connection is established using the first SIM card 54. Furthermore, the mobile computing device 10 of this embodiment also communicates with the base transceiver station 60 through a second connection 82 (denoted by a dashed line). In this embodiment the first connection 80 is then extended from base transceiver station 60 to public land mobile network 1 62 by means of connection 84 whereas the second connection is extended from base transceiver station 60 to public land mobile network 2 64 by means of connection 86.

In this embodiment, the connection between mobile computing device 10 and PLMN 1 62 is denoted by the solid lines 80 and 84. This is the connection established in the manner described below with SIM card 54. Similarly, the connection between mobile computing device 10 and PLMN 2 64 of this embodiment is denoted by the dashed lines 82 and 86.

Figure 5 illustrates an arrangement of a mobile computing device 100 in a GSM network, according to an embodiment of the invention. The mobile computing device 100 of this embodiment communicates with base transceiver station 70 through a first connection 88 (denoted by a solid line). Furthermore, the mobile computing device 100 of this embodiment also communicates with base transceiver station 72 through second connection 90 (denoted by a dashed line). The mobile computing device 100 of this embodiment communicates with PLMN 1 62 through BTS 70 by means of connection 92 and with PLMS 2 64 through BTS 72 by means of connection 94. Therefore, Figure 5 illustrates the mobile computing device 100 of this embodiment involved with a first connection with PLMN 1 62 by means of BTS 72 which occurs over connections 88 and 92. The mobile computing device 100 of Figure 5 is further connected to PLMN 2 64 via BTS 72 over connections 90 and 94. As described below in greater detail, the connection with PLMN 1 62 of this embodiment is established with a first SIM of the mobile computing device 100 whereas the connection with PLMN 2 64 is established with a second SIM of the mobile computing device 100.

Figure 6 illustrates a process according to an embodiment of the invention wherein the mobile computing device 10 of this embodiment establishes a connection with PLMN 1 62 and with PLMN 2 64 as illustrated in Figure 4 or for the mobile computing device 100 of a further embodiment to establish a connection with PLMN 1 62 and PLMN 2 64, as illustrated in Figure 5.

The process of Figure 6 begins at block 102 where the power of the mobile computing device 10 of this embodiment is turned on. Thereafter, at block 104 of this embodiment, the mobile computing device 10 establishes the first communications channel with PLMN 1 62

(Figure 4). In this embodiment, this occurs according to the known manner of establishing a

GSM connection which involves the mobile computing device 10 establishing a control channel with the base transceiver station (BTS), sending a location updating request from the mobile computing device and, after a process of authentication involving the SIM card 54, establishing the first communications channel between PLMN 1 62 and the mobile device using SIM card 54. The procedure for SIM registration and authentication is detailed in the

European Telecommunications Standards Institute standard 04.08.

At block 106 of this embodiment, a determination is made as to whether the first communications channel was established at block 104. If no communications channel was established, the process of this embodiment will return to block 104 to try and establish the communications channel. If a communications channel is successfully established, the process of this embodiment will proceed to block 108.

At block 108 of this embodiment, the process will determine a timing for the first communications channel. This is done in this embodiment by determining the timing of leading and trailing edges of slots in which the data pertaining to the first communications channel appear (see below, with reference to Figure 8). In this embodiment, communications channels corresponding to different PLMNs are allocated different slots and the mobile computing device 10 determines the timing of the slots allocated to the first communications channel. At the following block of this embodiment, block 110, a minimum offset for the second communications channel is determined in the same manner as that for slots of the first communications channel. In this embodiment, the minimum offset will depend on the frequency of the carrier wave for the first communications channel and the frequency of the carrier wave for the likely second communications channel as well as the spacing of their respective slots. In further embodiments, the minimum offset may additionally or alternatively depend on other factors. In one example the offset is chosen to reduce the likelihood that drift of the frequencies of the two carrier waves will result in a collision between the first communications channel and the second communications channel. Once the chosen minimum offset for the second communications channel has been determined at block 110, the process of this embodiment proceeds to block 1 12 where a likely second communications channel is sought. In this embodiment, the timing of the second communications should be offset from that of the first communications channel by at least the minimum offset determined at block 110. At the following block of this embodiment, block 114, a determination is made as to whether a likely candidate has been found for the second communications channel. If no likely candidate has been found, the process of this embodiment will return to block 108 and re-establish the first communications channel. However, if a likely candidate has been found for the second communications channel, the process of this embodiment will proceed to block 116.

At block 1 16 the process of this embodiment will establish the second communications channel between the mobile communications device 10 and PLMN 2 64 using SIM card 56. At the next block, block 1 18, the process of this embodiment will determine whether the second channel had been successfully established at block 116. If, for whatever reason (e.g. authentication was unsuccessful), no second communications channel was established at block 116, the process of this embodiment will proceed from block 1 18 back to block 108 to again determine the timing for the first communications channel, determine the minimum offset and attempt again to establish the second communications channel which conforms to this determined minimum offset. In a further embodiment, if no second communications channel with the desired minimum offset can be found, the first communications channel is re-established.

If, on the other hand, it is determined at block 118 of this embodiment, that the second communications channel has been successfully established, the process will proceed to block 120 which represents an active communications state of the mobile communications device 10.

According to this embodiment of the invention, two communications channels are established with two different PLMNs involving two SIM cards. Furthermore, the timing of the second communications channel has been chosen to help avoid imminent collisions between the two communications channels. In the embodiment illustrated in Figure 4, the mobile computing device 10 communicates with BTS 60 when establishing both the first communications channel (the relevant connection being connection 80) and the second communications channel (the relevant connection being connection 82). However, the same process of establishing first and second communications channels is applicable to the mobile computing device 100 illustrated in Figure 5, but in this embodiment, the mobile computing device 100 communicates with PLMN 1 62 through BTS 1 70 and communicates with PLMN 2 64 through BTS 2 72.

Once the first and second communications channels have been established in the manner described above with reference to Figure 6, the mobile computing device 10 and the mobile computing device 100 will enter an active state. In this state, to help ensure that a clash between the first and the second communications channels does not occur, the mobile computing device 10 and the mobile computing device 100 follow the process described below with reference to Figure 7.

The process illustrated in Figure 7 is described with reference to the operation of the mobile computing device 10. However, it is to be realised that the mobile computing device 100 operates in an analogous manner.

Block 140 of this embodiment represents the active state once the first and second communications channels have been established. At the next block of this embodiment, block 142, the timings for the first communications channel are determined. In this embodiment, as the timings for this communications channel were determined at block 108 of the process of Figure 6, block 142 comprises maintaining the record of the timings for this communications channel. At the next block of this embodiment, block 144, the timings of the second communications channel are determined. As the timings for this communications channel were determined at block 110 of the process of Figure 6, the process at block 144 of Figure 7 comprises maintaining the record established earlier.

The process of this embodiment then proceeds to block 146 where the timings for the first communications channel determined at block 142 and the timings of the second communications channel determined at block 144 are used to calculate the drift of the second communications channel relative to the first communications. Furthermore, on the basis of the calculated drift, a time is predicted when the first and second communications will collide. At the following block, block 148 of this embodiment, a determination is made as to whether the predicted time of the collision is acceptable or not.

A number of criteria may be used to determine whether the predicted time of a collision is acceptable or not. In this embodiment, the acceptable time before a collision occurs will depend on the number and timings of other channels which are available. Therefore, a determination is made at block 148 whether a 'better' carrier wave is available. In this embodiment, a carrier wave is determined to be better if it provides a predicted time for a collision greater than the time for a collision calculated in block 146. In an alternative embodiment, the time predicted for a clash is determined to be acceptable if it is greater than a predetermined time period.

If it is determined at block 148 of this embodiment that the time period for a collision is acceptable, the process of this embodiment will return to block 142. In this manner the process of this embodiment will loop through blocks 142, 144, 146 and 148 testing the first and second communications channel to ensure that a collision between the two is not imminent.

If it is determined at block 148 that the predicted time for a collision between the first and the second communications channel is not acceptable, the process of this embodiment will proceed on to block 150 where a minimum offset for a third communications channel is determined. The minimum offset determined at block 150 is set according to the criteria used to determine the offset for the second communications channel at block 110 of the process of Figure 6. Once an acceptable minimum offset for the third communications channel has been determined at block 150, the process of this embodiment will proceed to block 152 where a search is conducted for a channel which will satisfy the determined minimum offset. It is to be realised that this search comprises searching for a replacement carrier for either the first communications channel (i.e. with PLMN 1 62) or the second communications channel (i.e. with PLMN 2 64). Therefore the third communications channel of this embodiment will replace the first or the second communications channel, depending on which PLMN has a corresponding carrier which satisfies the minimum offset determined at block 110.

At block 154 of this embodiment a determination is made as to whether a likely candidate has been found for the third communications channel to replace either the first or the second communications channels. If no likely third communications channel has been found the process of this embodiment will return to block 150 where the minimum offset is again determined. In this embodiment, the minimum offset will be determined with reference to whether a likely candidate for a third communications channel has previously been unsuccessfully sought. In other words, if the process of this embodiment enters block 150 after unsuccessfully seeking a third communications channel, the minimum offset will be reduced to increase the likelihood that a likely candidate will be found for the third communications channel. In this manner the process of this embodiment will loop through blocks 150, 152 and 154 until a likely candidate is found for the third communications channel. In this embodiment however, this looping will not continue indefinitely. If it is determined that it is unlikely that a third communications channel will be found, the process of this embodiment will terminate without establishing the third communications channel.

If, on the other hand, a likely candidate for the third communications channel is found at block 154, the process of this embodiment will proceed to block 156 where either the first or the second communications channel is replaced with the third communications channel to ensure that the resulting communications channels adhere to the determined minimum offset.

Thereafter, at block 158 of this embodiment, a determination is made to ensure that the third communications channel has been established. If it is determined that no communications channel was established, the process of this embodiment will return to block 150. However, if the third communications channel has been successfully established at block 156, the process of this embodiment will proceed from block 158 to block 160 which represents the active state. Once the active state 160 has been established, the mobile computing device 10 will employ the process of Figure 7 as and when required.

Furthermore, once the active state has been achieved in this embodiment, where two communications channels with corresponding SIM cards have been established, each communication channel is polled, in turn, for incoming communications. This involves polling the paging channels of the communication channels to determine whether incoming communications on these channels are being received.

Figure 8 illustrates a first carrier wave 160 at a first frequency which is divided into a number of slots 162. In this embodiment each of the slots 162 in a given time period corresponds to a different communications channel. Similarly, Figure 8 illustrates a second carrier wave 180 at a second frequency. The second carrier wave 180 is also divided up into a plurality of slots 182 each of which in a predefined time period corresponds to a different communications channel. One of the slots 166 of the first carrier wave 160 of Figure 8 is shown in detail.

Similarly, one of the slots 186 of the second carrier wave 180 is also shown in detail. Arrow 200 of Figure 8 represents time. Slot 166 of the first carrier wave 160 of this embodiment has a trailing edge 168 and a leading edge 170. Similarly, slot 186 of the second carrier wave 180 of this embodiment has a trailing edge 188 and a leading edge 180. In this embodiment, the slot 166 belongs to the first communications channel discussed above and the slot 180 belongs to the second communications channel discussed above. When the timings of the first and the second communications channels are determined and maintained, the timing of the leading and trailing edges of the slots of those communications channels are determined. Then the offset between the first and the second communications channel is the difference in time between the leading edge 170 of slot 166 of the first communications channel and the trailing edge 188 of slot 186 of the second communications channel. This time difference is represented by 175 in the embodiment of Figure 8. It is to be realised that the determination of timing for a third communications channel, as discussed above, may be carried out analogously. In the GSM standard, according to which the communications channels of this embodiment are implemented, the crystals used to generate the corresponding carrier waves have a permitted tolerance of 8 parts per million. As the first carrier wave 160 is distinct from the second carrier wave 180 and, in this embodiment, they are not synchronised with one another, the frequencies of each may tend to drift relative to one another. Eventually this may cause the slot 166 to overlap in time with the slot 186, thereby causing a collision. Therefore, the aforementioned processes of Figures 6 and 7 help to ensure that two communications channels having different carrier waves which are not synchronised (which may occur when the two communications channels correspond to different PLMNs) do not collide or clash with one another in a set time period.

In particular, example embodiments of the invention find application where both the first SIM card 54 and the second SIM card 56 relate to respective PLMNs which are both local to the country in which the mobile communications device 10 (or the mobile communications device 100) is being operated as, in this instance, the PLMNs are not able to roam across each other's networks.

Claims

1. A method comprising: establishing, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; establishing, through said radio, a second communications channel for use with a second subscriber identity module; alternating between said first communications channel and said second communications channel to poll each communications channel for incoming communications; wherein said radio, said first subscriber identity module and said second subscriber identity module form part of a single mobile communications device.

2. The method according to claim 1 wherein said first communications channel corresponds to a first physical communications channel and said second communications channel corresponds to a second physical communications channel.

3. The method according to claim 1 or claim 2 wherein said second communications channel is established with said first base transceiver station.

4. The method according to claim 1 or claim 2 wherein said second communications channel is established with a second base transceiver station.

5. The method according to any preceding claim further comprising: selecting said second communications channel to be spaced in time from said first communications channel.

6. The method according to claim 5 further comprising: determining a timing for said first communications channel; determining a timing for a plurality of further communications channels; selecting one of said further communications channels as said second communications channel on the basis of said determined timings.

7. The method according to claim 6 wherein said second communications channel is selected with reference to an expected frequency drift of said first communications channel relative to said second communications channel.

8. The method according to claim 6 or claim 7 wherein said second communications channel is selected so that a slot of said second communications channel is separated in time from a slot of said first communications channel by at least a predetermined offset.

9. The method according to any preceding claim further comprising: recording a timing of said first communications channel; recording a timing of said second communications channel; establishing, through said radio, a third communications channel for use with said first subscriber identity module or said second subscriber identity module based on said recorded timings.

10. The method according to claim 9 wherein a carrier frequency of said third communications channel is selected based on said recorded timings.

1 1. The method according to claim 10 wherein a carrier frequency of said third communications channel is selected based on a minimum offset in time between a slot of either said first communications channel or said second communications channel and a slot of said third communications channel.

12. The method of any of claims 9 to 1 1 further comprising predicting a collision between said first communications channel and said second communications channel based on said recorded timings.

13. The method according to any preceding claim wherein each of said communications channels is established according to the GSM standard.

14. The method according to any preceding claim wherein said first communications channel corresponds to a first public land mobile network and said second communications channel corresponds to a second public land mobile network and wherein said public land mobile networks are unable to roam on each other's networks.

15. The method according to claim 14, when dependent on claim 9, wherein said third communications channel corresponds to said first public land mobile network or said second public land mobile network.

16. An apparatus, comprising: at least one processor; and at least one memory including computer program code the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following: establishing, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; establishing, through said radio, a second communications channel for use with a second subscriber identity module; alternating between said first communications channel and said second communications channel to poll each communications channel for incoming communications ; wherein said radio, said first subscriber identity module and said second subscriber identity module form part of a single mobile communications device.

17. The apparatus according to claim 16 wherein said first communications channel corresponds to a first physical communications channel and said second communications channel corresponds to a second physical communications channel.

18. The apparatus according to claim 16 or claim 17 wherein said second communications channel is established with said first base transceiver station.

19. The apparatus according to claim 16 or claim 17 wherein said second communications channel is established with a second base transceiver station.

20. The apparatus according to any of claims 16 to 19 further performing: selecting said second communications channel to be spaced in time from said first communications channel.

21. The apparatus according to claim 20 further performing: determining a timing for said first communications channel; determining a timing for a plurality of further communications channels; selecting one of said further communications channels as said second communications channel on the basis of said determined timings.

22. The apparatus according to claim 21 wherein said second communications channel is selected with reference to an expected frequency drift of said first communications channel relative to said second communications channel.

23. The apparatus according to claim 21 or claim 22 wherein said second communications channel is selected so that a slot of said second communications channel is separated in time from a slot of said first communications channel by at least a predetermined offset.

24. The apparatus according to any of claims 16 to 23 further performing: recording a timing of said first communications channel; recording a timing of said second communications channel; establishing, through said radio, a third communications channel for use with said first subscriber identity module or said second subscriber identity module based on said recorded timings.

25. The apparatus according to claim 24 wherein a carrier frequency of said third communications channel is selected based on said recorded timings.

26. The apparatus according to claim 25 wherein a carrier frequency of said third communications channel is selected based on a minimum offset in time between a slot of either said first communications channel or said second communications channel and a slot of said third communications channel.

27. The apparatus of any of claims 24 to 26 further performing: predicting a collision between said first communications channel and said second communications channel based on said recorded timings.

28. The apparatus according to any of claims 16 to 27 wherein each of said communications channels is established according to the GSM standard.

29. The apparatus according to any of claims 16 to 28 wherein said first communications channel corresponds to a first public land mobile network and said second communications channel corresponds to a second public land mobile network and wherein said public land mobile networks are unable to roam on each other's networks.

30. The apparatus according to claim 29, when dependent on claim 24, wherein said third communications channel corresponds to said first public land mobile network or said second public land mobile network.

31. An apparatus, comprising: a processor configured to: establish, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; establish, through said radio, a second communications channel for use with a second subscriber identity module; alternate between said first communications channel and said second communications channel to poll each communications channel for incoming communications ; wherein said radio, said first subscriber identity module, said second subscriber identity module and said processor form part of said apparatus, said apparatus being a single mobile communications device.

32. The apparatus of claim 31, wherein the processor comprises at least one memory that contains executable instructions that if executed by the processor cause the apparatus to: establish, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; establish, through said radio, a second communications channel for use with a second subscriber identity module; and alternate between said first communications channel and said second communications channel to poll each communications channel for incoming communications .

33. A computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer, the computer program code comprising: code for establishing, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; code for establishing, through said radio, a second communications channel for use with a second subscriber identity module; and code for alternating between said first communications channel and said second communications channel to poll each communications channel for incoming communications wherein said radio, said first subscriber identity module and said second subscriber identity module form part of said apparatus, said apparatus being a single mobile communications device.

34. A computer program, comprising: code for establishing, through a radio, a first communications channel with a first base transceiver station for use with a first subscriber identity module; code for establishing, through said radio, a second communications channel for use with a second subscriber identity module; and code for alternating between said first communications channel and said second communications channel to poll each communications channel for incoming communications; when the computer program is run on a processor; wherein said radio, said first subscriber identity module, said second subscriber identity module and said processor form part of a single mobile communications device.

35. A method comprising: recording a timing of a first communications channel, said first communications channel establishing communications through a radio with use of a first subscriber identity module; recording a timing of a second communications channel, said second communications channel establishing communications through said radio with use of a second subscriber identity module; establishing, through said radio, a third communications channel for use with said first subscriber identity module or said second subscriber identity module based on said recorded timings. wherein said radio, said first subscriber identity module and said second subscriber identity module form part of a single mobile communications device.

36. Apparatus comprising: at least one processor; and at least one memory including computer program code the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following: record a timing of a first communications channel, said first communications channel establishing communications through a radio with use of a first subscriber identity module; record a timing of a second communications channel, said second communications channel establishing communications through said radio with use of a second subscriber identity module; establish, through said radio, a third communications channel for use with said first subscriber identity module or said second subscriber identity module based on said recorded timings. wherein said radio, said first subscriber identity module, said second subscriber identity module and said processor form part of said apparatus, said apparatus being a single mobile communications device.