Claims:STATEMENT OF CLAIMS
We claim:

1. A method for sharing a Radio Resource Control (RRC) connection in a communication network, said method comprising:
establishing an RRC connection with a Universal Terrestrial radio Access Network (UTRAN) of said communication network, by one of a plurality of SIM cards in a User Equipment (UE) of said communication network;
sharing said RRC connection for establishing communication with said UTRAN, by said plurality of SIM cards, wherein sharing said RRC connection involves mapping signalling connection of said plurality of SIM cards to said RRC connection;
receiving at least one message for at least one of said plurality of SIM cards, through said RRC connection, from said UTRAN, by said UE; and
identifying said at least one message as a message that correspond to a specific SIM card of said plurality of SIM cards, based on value of a unique identifier associated with said message, by said UE.

2. The method as claimed in claim 1, wherein said RRC connection is shared for paging said UE, wherein said sharing of the RRC connection for paging further comprises:

setting value of a ‘neighbor SIM’ field in said paging message as ‘NULL’, if said paging message is for a single SIM UE, by said CN;
identifying a SIM card said paging message corresponds to, in a dual SIM UE, if said paging message belongs to said dual SIM UE, by said CN;
setting an International Mobile Subscriber Identity (IMSI) value of a neighboring SIM of said identified SIM card as value of said ‘neighbor SIM’ field in said paging message, by said CN, wherein said IMSI value of said neighboring SIM is identified from a reference database, by said CN;
identifying a SIM card said paging message belongs to, based on value of said ‘neighbor SIM’ field in said paging message, by said UTRAN; and
triggering at least one of a paging type 1 message and a paging type 2 message to said identified SIM card, by said UTRAN.

3. The method as claimed in claim 1, wherein said RRC channel is shared for signalling said UTRAN from said UE, wherein said sharing of the RRC channel for said signalling of the UTRAN from the UE further comprises of:
receiving a signalling connection request from said UE through a common RRC channel, by said UTRAN, wherein said signaling connection request is an Initial Direct Transfer (IDT) message;
identifying a SIM card that triggered said signalling connection request, by said UTRAN; and
sending an initial UE message to said CN, in response to said signalling connection request, through a signalling channel of said identified SIM card that triggered said signalling connection request, by said UTRAN.

4. The method as claimed in claim 3, wherein identifying said SIM card that triggered said signalling request further comprises of:
checking value of a unique identifier associated with said signalling connection request, wherein value of said unique identifier is pre-configured by said UE;
identifying a SIM1 as said SIM card that triggered said signalling request if said value of said unique identifier is ‘False’; and
identifying a SIM2 as said SIM card that triggered said signalling request if said value of said unique identifier is ‘True’.

5. The method as claimed in claim 1, wherein said RRC channel is shared for signalling said UE from said UTRAN, wherein said sharing of the RRC channel for signalling said UE from said UTRAN further comprises:
receiving a signalling request from said CN by said UTRAN, wherein said signalling request is a Direct Transfer Message;
identifying a SIM card to said received signalling request corresponds, by said UTRAN; and
sending a Non Access stratum (NAS) signalling message to said identified SIM card, through said shared RRC channel, wherein a unique identifier value corresponds to identified SIM card is associated with said NAS signalling message.

6. The method as claimed in claim 5, wherein identifying said SIM card that triggered said signalling request further comprises:
identifying a SIM1 as said SIM card said signalling request corresponds to, if said signalling request has been received from a signalling connection that belongs to said SIM1; and
identifying a SIM2 as said SIM card said signalling request corresponds to, if said signalling request has been received from a signalling connection that belongs to said SIM2.

7. The method as claimed in claim 1, wherein said RRC channel is shared for a Radio Access Bearer (RAB) signalling, wherein said sharing of RRC channel for the RAB signalling further comprises:
receiving a RAB assignment request from said CN, by said UTRAN;
identifying a SIM card said RAB assignment request corresponds to, by said UTRAN; and
triggering a setup procedure corresponding to said identified SIM card, by said UTRAN, wherein a unique identifier value corresponding to said identified SIM card is associated with message corresponding to said triggering setup procedure.

8. The method as claimed in claim 7, wherein identifying said SIM card to said RAB assignment request corresponds, further comprises:

checking a signalling connection from which said RAB assignment request is received by said UTRAN;
identifying a SIM1 as said SIM card to said RAB assignment request corresponds, if said RAB assignment request is received from a signalling connection that corresponds to said SIM1; and
identifying a SIM2 as said SIM card to said RAB assignment request corresponds, if said RAB assignment request is received from a signalling connection that corresponds to said SIM2.

9. The method as claimed in claim 8, wherein differentiating said RAB and corresponding Radio Bearer (RB) that belong to different SIM cards of said dual SIM mobile further comprises of:
collecting an RAB assignment request from said dual SIM UE, by said UTRAN;
differentiating between RAB that belongs to said SIM1 and said SIM2, wherein said differentiation is done at at least one of an RAB level and an RB level;
setting value of an information element ‘neighbor SIM message’ to ‘FALSE’ if said is received from said SIM1 of said dual SIM UE; and
setting value of said information element ‘neighbor SIM message’ to ‘TRUE’ if said is received from said SIM2 of said dual SIM UE.

10. The method as claimed in claim 1, wherein said RRC is shared for handling security mode procedures, said method comprises:
receiving a security mode command from said CN by said UTRAN;
identifying a SIM card in said dual SIM UE, said received security mode command corresponds to, based on a signalling connection from which the security mode command is received, by said UTRAN;
sending said security mode command to said UE, wherein a unique identifier corresponding to said identified SIM card is associated with said security mode command; and
processing said security mode command for said identified SIM card, by said UE, wherein said processing of the security mode command further comprises of:
performing at least one security mode procedure for said SIM card, based on said security mode command; and
sending at least one of a 'security mode complete' and 'security mode failure' as a response to said UTRAN using said UE, wherein said response indicates status of said performed security mode procedure.

11. A system for sharing a Radio Resource Control (RRC) connection in a communication network, said system comprising:
at least a User Equipment (UE) of said Communication Network (CN) establishing an RRC connection with a Universal Terrestrial radio Access Network (UTRAN) of said CN, wherein said RRC connection with said UTRAN is established by one of a plurality of SIM cards in said UE;
a plurality of SIM cards in said UE sharing said RRC connection for establishing communication with said UTRAN, wherein sharing said RRC connection involves mapping signalling connection of said plurality of SIM cards to said RRC connection;
said UE receiving at least one message for at least one of said plurality of SIM cards, through said RRC connection, from said UTRAN; and
said UE identifying said at least one message as a message that correspond to a specific SIM card of said plurality of SIM cards, based on value of a unique identifier associated with said message.

12. The system as claimed in claim 11, wherein said system is configured to share said RRC connection for paging said UE, wherein said system shares said RRC connection for paging by:

setting value of a ‘neighbor SIM’ field in said paging message as ‘NULL’, if said paging message is for a single SIM UE, by said CN;
identifying a SIM card said paging message corresponds to, in a dual SIM UE, if said paging message belongs to said dual SIM UE, by said CN;
setting an International Mobile Subscriber Identity (IMSI) value of a neighboring SIM of said identified SIM card as value of said ‘neighbor SIM’ field in said paging message, by said CN, wherein said IMSI value of said neighboring SIM is identified from a reference database, by said CN;
identifying a SIM card said paging message belongs to, based on value of said ‘neighbor SIM’ field in said paging message, by said UTRAN; and
triggering at least one of a paging type 1 message and a paging type 2 message to said identified SIM card, by said UTRAN.

13. The system as claimed in claim 11, wherein said system is configured to share said RRC channel for signalling said UTRAN from said UE, by:

receiving a signalling connection request from said UE through a common RRC channel, by said UTRAN, wherein said signaling connection request is an Initial Direct Transfer (IDT) message;
identifying a SIM card that triggered said signalling connection request, by said UTRAN; and
sending an initial UE message to said CN, in response to said signalling connection request, through a signalling channel of said identified SIM card that triggered said signalling connection request, by said UTRAN.

14. The system as claimed in claim 13, wherein said UTRAN is configured to identify said SIM card that triggered said signalling request by:
checking value of a unique identifier associated with said signalling connection request, wherein value of said unique identifier is pre-configured by said UE;
identifying a SIM1 as said SIM card that triggered said signalling request if said value of said unique identifier is ‘False’; and
identifying a SIM2 as said SIM card that triggered said signalling request if said value of said unique identifier is ‘True’.

15. The system as claimed in claim 11, wherein said system is configured to share said RRC channel for signalling said UE from said UTRAN, by:
receiving a signalling request from said CN, by said UTRAN, wherein said signalling request is a Direct Transfer Message;
identifying a SIM card to said received signalling request corresponds, by said UTRAN; and
sending a Non Access stratum (NAS) signalling message to said identified SIM card, through said shared RRC channel, wherein a unique identifier value corresponds to identified SIM card is associated with said NAS signalling message.

16. The system as claimed in claim 15, wherein said UTRAN is configured to identify said SIM card that triggered said signalling request by:
identifying a SIM1 as said SIM card said signalling request corresponds to, if said signalling request has been received from a signalling connection that belongs to said SIM1; and
identifying a SIM2 as said SIM card said signalling request corresponds to, if said signalling request has been received from a signalling connection that belongs to said SIM2.

17. The system as claimed in claim 11, wherein said system is configured to share said RRC channel for a Radio Access Bearer (RAB) signalling, by:
receiving a RAB assignment request from said CN, by said UTRAN;
identifying a SIM card said RAB assignment request corresponds to, by said UTRAN; and
triggering a setup procedure corresponding to said identified SIM card, by said UTRAN, wherein a unique identifier value corresponding to said identified SIM card is associated with message corresponding to said triggering setup procedure.

18. The system as claimed in claim 17, wherein said UTRAN is configured to identify said SIM card said RAB assignment request corresponds to, by:

checking a signalling connection from which said RAB assignment request is received;
identifying a SIM1 as said SIM card to said RAB assignment request corresponds, if said RAB assignment request is received from a signalling connection that corresponds to said SIM1; and
identifying a SIM2 as said SIM card to said RAB assignment request corresponds, if said RAB assignment request is received from a signalling connection that corresponds to said SIM2.

19. The system as claimed in claim 18, wherein said system is configured to differentiate said RAB and corresponding Radio Bearer (RB) that belong to different SIM cards of said dual SIM mobile by:
collecting an RAB assignment request from said dual SIM UE, by said UTRAN;
differentiating between RAB that belongs to said SIM1 and said SIM2, by said UTRAN, wherein said differentiation is done at at least one of an RAB level and an RB level;
setting value of an information element ‘neighbor SIM message’ to ‘FALSE’ if said is received from said SIM1 of said dual SIM UE, by said UTRAN; and
setting value of said information element ‘neighbor SIM message’ to ‘TRUE’ if said is received from said SIM2 of said dual SIM UE, by said UTRAN.

20. The system as claimed in claim 11, wherein said system is configured to share said RRC for handling security mode procedures, by:
receiving a security mode command from said CN, by said UTRAN;
identifying a SIM card in said dual SIM UE, said received security mode command corresponds to, based on a signalling connection from which the security mode command is received, by said UTRAN;
sending said security mode command to said UE, wherein a unique identifier corresponding to said identified SIM card is associated with said security mode command; and
processing said security mode command for said identified SIM card, by said UE, wherein said UE is configured to process said security mode command by:
performing at least one security mode procedure for said SIM card, based on said security mode command; and
sending at least one of a 'security mode complete' and 'security mode failure' as a response to said UTRAN using said UE, wherein said response indicates status of said performed security mode procedure.
, Description:FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules, 2005

COMPLETE SPECIFICATION
(SEE SECTION 10 AND RULE 13)

TITLE OF THE INVENTION

“UTILIZATION OF A SINGLE RRC CONNECTION IN A MULTI SIM MOBILE COMMUNICATION SYSTEM”

APPLICANTS:

Name Nationality Address
SAMSUNG R&D Institute India - Bangalore Private Limited India # 2870, Orion Building, Bagmane Constellation Business Park, Outer Ring Road, Doddanekundi Circle, Marathahalli Post, Bangalore-560037, India

The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed:-

FIELD OF INVENTION
[001] The present invention relates to the field of telecommunications and more particularly to facilitating RRC connection sharing in Multi SIM mobile communication system.

BACKGROUND OF INVENTION
[002] A Subscriber Identity Module (SIM) card is a portable memory chip used in mobile phones that operate on Global System for Mobile Communications (GSM) network. SIM cards are a key part of developing cell phone technology. A Multi-SIM mobile phone supports multiple SIM cards at a time, by providing different SIM slots. Dual SIM mobile phones that support two SIM cards at a time are generally used by many customers.
[003] Dual SIM mobiles are mostly classified into two types. First type, Dual SIM Dual Standby Mobiles (DSDS) wherein only one Radio frequency (RF) Transceiver is present. Second type, Dual SIM Dual Active Mobiles (DSDA) wherein two RF transceivers are present. DSDS mobiles support both SIM cards in Standby mode which means that when both the SIM cards are Idle (no Call or Data), then RF is shared by using different mechanisms to perform Idle Mode procedures for both the SIMs and when one of the SIM card is used for Call or Data purpose then the other SIM card is inactive. When one SIM is in use, a user who calls to the other SIM can hear a not-reachable message from the service provider of the other SIM card. There are also methods in DSDS device to perform Data in one SIM and other SIM will be listening to the paging channel for receiving the incoming call. DSDS mobiles use same RF transceiver for both SIM cards and thus consume less battery power compared to DSDA mobiles. In DSDS mobiles, both the SIM cards cannot remain in a connected mode at the same time.
[004] Dual SIM Dual Active mobiles keep both SIM cards active at all times. While the mobile phone user is busy on first SIM card, he/she will still receive calls and messages on second SIM card. The mobile phone user will have an option to put the first SIM card call on hold and attend the call on the second SIM card. Mobile phones that support DSDA use two separate RF transceivers and in some cases different processor cores for both SIM cards. This leads to more power consumption and has to be aided by use of larger battery capacity. Also, most of Radio Resource Control (RRC) procedures are duplicated.

OBJECT OF INVENTION
[005] The principal object of the embodiments herein is to allow sharing of a Radio Resource Control (RRC) connection for multiple SIM cards in a User Equipment to communicate with a UTRAN.
[006] Another object of the invention is to differentiate between messages that correspond to different SIM cards in a UE, based on value of a unique identifier associated with the message.

SUMMARY
[007] Accordingly the invention provides a method for sharing a Radio Resource Control (RRC) connection in a communication network. An RRC connection is established with a Universal Terrestrial radio Access Network (UTRAN) of the communication network, by one of a plurality of SIM cards in a User Equipment (UE) of the communication network. Further, the RRC connection is shared for establishing communication with the UTRAN, by the plurality of SIM cards, wherein sharing the RRC connection involves mapping signalling connection of the plurality of SIM cards to the RRC connection. Further, at least one message for at least one of the plurality of SIM cards is received through the RRC connection, from the UTRAN, by the UE. The UE then identifies the at least one message as a message that correspond to a specific SIM card of the plurality of SIM cards, based on value of a unique identifier associated with the message.
[008] Accordingly the invention provides a system for sharing a Radio Resource Control (RRC) connection in a communication network. At least a User Equipment (UE) of the Communication Network (CN) establishes an RRC connection with a Universal Terrestrial radio Access Network (UTRAN) of the CN, wherein the RRC connection with the UTRAN is established by one of a plurality of SIM cards in the UE. A plurality of SIM cards in the UE share the RRC connection for establishing communication with the UTRAN, wherein sharing the RRC connection involves mapping signalling connection of the plurality of SIM cards to the RRC connection. The UE receiving at least one message for at least one of the plurality of SIM cards, through the RRC connection, from the UTRAN, and then identifying the at least one message as a message that correspond to a specific SIM card of the plurality of SIM cards, based on value of a unique identifier associated with the message.
[009] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF FIGURES
[0010] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[0011] FIG. 1 is a block diagram illustrating RRC channel sharing based dual SIM communication system, according to embodiments as disclosed herein;
[0012] FIG. 2 is a block diagram illustrating different components of a User Equipment (UE), according to embodiments as disclosed herein;
[0013] FIG. 3 is a block diagram illustrating different components of an Universal Terrestrial Radio Access Network (UTRAN), according to embodiments as disclosed herein;
[0014] FIG. 4 is a block diagram illustrating different components of a Core Network (CN), according to one embodiment as disclosed herein;
[0015] FIG. 5 is a flow diagram depicting various steps involved in a method of handling paging in a Dual SIM mobile communication system, according to one embodiment as disclosed herein;
[0016] FIG. 6 is a flow diagram depicting various steps involved in a method of requesting signalling connection by a UE in a Semi-Connected Dual SIM mobile communication system that support RRC channel sharing, according to one embodiment as disclosed herein;
[0017] FIG. 7 is a flow diagram depicting various steps involved in a method of triggering signalling connection request by UTRAN, in a Semi-Connected Dual SIM mobile communication system that support RRC channel sharing, according to one embodiment as disclosed herein;
[0018] FIG. 8 is a flow diagram depicting various steps involved in a method of handling signalling connection request in an UTRAN, in a Semi-Connected Dual SIM mobile communication system that support RRC channel sharing, according to one embodiment as disclosed herein;
[0019] FIG. 9 is a flow diagram depicting various steps involved in a method of handling Non-Access Stratum (NAS) signalling messages in a Fully Connected Dual SIM mobile communication system that support RRC channel sharing, according to one embodiment as disclosed herein;
[0020] FIG. 10 is a flow diagram depicting various steps involved in a method of handling of Radio bearer management procedures in UTRAN in a Fully Connected Dual SIM mobile communication system that support RRC channel sharing, according to one embodiment as disclosed herein;
[0021] FIG. 11 is a flow diagram depicting various steps involved in a method of handling of security mode control procedures at UTRAN and at UE in a Fully Connected Dual SIM mobile communication system that support RRC channel sharing, according to one embodiment as disclosed herein;
[0022] FIG. 12 is a flow diagram depicting various steps involved in a method of triggering of Signalling Connection Release message from UTRAN and reception of Signalling Connection Release message at UE in a Fully Connected Dual SIM mobile communication system that support RRC channel sharing, according to one embodiment as disclosed herein; and
[0023] FIG. 13 is a flow diagram depicting various steps involved in a method of triggering of Signalling connection release Indication message from UE and reception of Signalling connection release Indication message at UTRAN in a Fully Connected Dual SIM mobile communication system that support RRC channel sharing, according to one embodiment as disclosed herein.

DETAILED DESCRIPTION OF INVENTION
[0024] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0025] The embodiments herein achieve RRC connection sharing in a Multi SIM mobile communication system for connection and communication procedures. A method for utilizing the single RRC Connection for protocol stacks of a Dual SIM mobile communication system, wherein the Dual SIM mobile communication system is in Fully Connected Mode (both SIMs are in connected mode) or Semi-Connected Mode (one SIM is in connected mode and the other SIM is in idle mode). The SIMs in the Dual SIM mobile communication system are registered on same Public Land Mobile Network (PLMN) and listen to same cell of the PLMN. It is to be noted that the system and method disclosed herein can be used for facilitating RRC connection sharing in a multi SIM communication system. However, for the ease of explaining the process, Dual SIM communication system is considered and explained. Referring now to the drawings, and more particularly to FIG 1 through FIG 13, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.
[0026] FIG. 1 is a block diagram illustrating RRC connection sharing system, according to embodiments as disclosed herein. The RRC channel sharing system 100 comprises of at least one User Equipment (UE) 101, a corresponding Universal Terrestrial Radio Access Network (UTRAN) 102, and a Core Network (CN) 103. The UE 101 is a Dual SIM mobile that supports two SIM cards. In an embodiment, to avail the RRC connection sharing, both SIM cards may have to be listening to same PLMN. The UTRAN 102 may be configured to communicate with the UE 101 and the core network 103 and facilitates communication between them to provide at least one service being offered by the core network 103, to the UE 101.
[0027] The UTRAN 102 may be configured to receive paging message from the CN 103 and identify the SIM to which the paging message is directed to. In an embodiment, the UTRAN 102 can be configured to identify the SIM card the paging message is directed to, based on IMSI of the SIM to be paged, and that of the neighbor SIM; which are included in the paging message as ‘Permanent NAS UE Identity’ and a ‘Neighbor SIM Permanent NAS UE identity’, respectively. In an embodiment of the invention, the SIMs can be configured to communicate with UTRAN 102 using a single RRC Connection and the UTRAN 102 can be configured to communicate with the CN 103 with separate signalling connections for corresponding SIMs. In an embodiment, both the SIM cards may have to be camped on the same PLMN to be able to share a common RRC channel. Both the SIM cards of the Dual SIM mobile can be allowed to communicate with the UTRAN 102 through the same RRC connection. The UTRAN 102 can be configured to communicate to the CN 103 with two signalling connections, i.e. dedicated signalling connection for each SIM.
[0028] In Semi-Connected Dual SIM mobile communication system, assume that one SIM has already established RRC connection with the UTRAN 102. The UE 101 receives paging message for SIM which is in idle mode, through the RRC Connection which is owned and being used by the other SIM. At the UE side, the SIM which is in idle mode can make use of available RRC Connection of the connected mode SIM to trigger Initial Message (Initial Direct Transfer) to UTRAN 102 to initiate a signalling connection to CN 103.
[0029] In Fully Connected Dual SIM mobile communication system, at the UE 101 side the SIMs can send and receive the corresponding signalling messages and corresponding user data through the same RRC connection. The UTRAN 102 can send and receive signalling messages and user data of both the SIMs through the same RRC Connection. In an embodiment, in the fully connected as well as semi connected modes, the RRC channel sharing based dual SIM communication system 100 can be configured to provide at least one option to help the network components UE 101, UTRAN 102, and the core network 103 differentiate between messages being directed to SIM 1 and SIM 2. In a an embodiment, the RRC connection sharing based dual SIM communication system 100 uses an identifier, preferably in the form of a flag, to help the network components differentiate between SIM1 messages and SIM2 messages. In an embodiment, the differentiation between SIM 1 and SIM 2 messages with the help of the flag value is done for initial direct transfer, UDT, and DDT messages. However, in paging process, the messages intended for SIM 1 and SIM 2 can be differentiated based on the IMSI values mentioned in the paging message.
[0030] FIG. 2 is a block diagram illustrating a User Equipment (UE) 101, according to embodiments as disclosed herein. In the embodiment of the invention, UE 101 is Dual SIM mobile. The UE 101 comprises of SIM slots 201, a messenger 202, a differentiator 203, and RAB (Radio Access Bearer) & RB (Radio Bearer) Identifier 204. SIM slots 201 can be used for supporting the SIM cards and help the user receive at least one service the user has subscribed for, by allowing connection between the SIM cards and their corresponding network.
[0031] The messenger 202 in the UE 101 can be configured to send Initial Direct transfer (IDT) message which comprises of the unique identifier that represents the SIM from which the IDT message is being originated/initiated. Consider that a flag ‘Neighbor SIM message’ is used to differentiate between messages that correspond to either of the two SIM cards. The flag ‘Neighbor SIM message’ can have two values i.e. ‘True’ and ‘False. In an embodiment, the flag value set to ‘False’ may indicate message that corresponds to the SIM that has already established the RRC channel communication with the UTRAN 102, whereas a message with the flag value set to ‘True’ may indicate that the message corresponds to the SIM that is currently in Idle mode. In another embodiment, the value ‘True’ of the flag may indicate that the message corresponds to the SIM that has established the RRC channel connection with the UTRAN 102, whereas the value ‘False’ may indicate that the message corresponds to the SIM that is currently in Idle state.
[0032] Messenger 202 can also be configured to send and receive, Uplink Direct Transfer message (UDT) and Downlink Direct Transfer (DDT) message respectively, corresponding to each SIM, through the shared RRC Connection. Further, the messenger 202 can be configured to send Security Mode complete message once Security Mode Control procedures are complete. Further, once Setup or Reconfiguration or Release of Radio bearers in UE 101 are completed, then the messenger 202 can be configured to trigger corresponding complete message to the UTRAN 102.
[0033] The differentiator 203 can be configured to differentiate between paging message that corresponds to SIM 1 and SIM 2. In the Dual SIM mobile communication system, RAB (Radio Access Bearer) & RB (Radio Bearer) Identifier 204 can be configured for differentiating RABs and RBs corresponding to both the SIM cards based on the unique information element i.e. value of the flag, associated with the message.
[0034] FIG. 3 is a block diagram illustrating a Universal Terrestrial Radio Access Network (UTRAN), according to embodiments as disclosed herein. UTRAN comprises at least one Radio Network Controller (RNC) 302, NodeBs 301, an encoder 303, a decoder 304, an identifier 305, a Radio Bearer (RB) assignor 306, and a memory module 307.
[0035] The Node B 301 refers to a base station which is configured to communicate directly with the UE 101. Node Bs 301 comprises of radio frequency transmitters and the receivers used to communicate directly with the UE 101.
[0036] The RNC 302 may be configured to act as a governing element in UTRAN 102, and may be responsible for controlling the Node B 301 that is connected to the RNC 302. The RNC 302 carries out radio resource management, mobility management functions and is the point where encryption is done before user data is sent to and from the mobile. The RNC 302 connects to Circuit-Switched Core Network through Media Gateway (MGW), and to SGSN (Serving GPRS Support Node) in the Packet-Switched Core Network. RNC 302 also controls power of a NodeB.
[0037] The encoder 303 can be configured to add the flag ‘Neighbor SIM Message’ to an outgoing message, with a value that represents the SIM the message corresponds to. The decoder 304 can be configured to decode incoming messages to check the value of the flag Neighbor SIM Message, which in turn may help the UTRAN 102 identify the SIM the message corresponds to.
[0038] In the RRC connection sharing based dual SIM communication system 100, the UTRAN 102 may be configured to identify that there can be a maximum of 4 signalling connections corresponding to one RRC Connection, such that out of the 4 signalling connections, a maximum of 2 signalling connections correspond to each SIM. The UTRAN 102 may be further configured to map the lu-signalling connections with the corresponding RRC connection, such that any message received via any of the 4 signalling connection can be routed to the corresponding RRC connection. The UTRAN 102, using the identifier 305, identifies the mapping between each lu-signalling connection and corresponding RRC channel.
[0039] The Radio Bearer (RB) Assignor 306 can be configured to assign RB identities (RB Id) to SIMs of the UE 101. In an embodiment, the RB Assignor 306 can be further configured to assign same/different RB identities to both the SIMs of UE 101 of the Dual SIM mobile communication system.
[0040] The memory module 307 may be configured to maintain all data related to the RRC channel sharing mechanism as well as normal communication procedures supported by the system. For example, one database may possess information on IMSI’s (International Mobile Subscriber Identity) of each SIM being served, and corresponding RRC channel and lu-signalling channels information. This information can be used for triggering either Paging type 1 or paging type 2 messages to UEs 101.
[0041] FIG. 4 is a block diagram illustrating a Core Network (CN), according to one embodiment as disclosed herein. The Core Network 103 comprises Packet Switched Core Network 401, Circuit Switched Core Network 402, Signalling & Security Mode Commands Assignor 403, Connection Identifier Module 404, RAB (Radio Access Bearer) Assignor 405 and Dual SIM registered IMSI Database 406.
[0042] The Circuit Switched Core Network 402 can connect to RNC 302 through lu-CS and/or through lu-PS signalling connections. The RAB assignor 405 can be configured to assign RAB identity. The Signalling & Security Mode Commands Assignor 403 can be configured to send a Iu-release command to UTRAN 102, and the UTRAN 102 can be configured to trigger a signalling connection release message to the UE 101, upon receiving the Iu Release Command from Core network 103.
[0043] The Signalling & Security Mode Commands Assignor 403 can be configured to send security mode command message to UTRAN 102. The CN 103 can be configured to maintain a database of IMSI International Mobile Subscriber Identity (IMSI) Pairs (IMSI of both the SIMs in the UE 101). The dual SIM registered IMSI Database 406 possesses information on IMSI pairs i.e. IMSI numbers which correspond to the SIM cards in the same UE 101, and which share the same RRC connection. The data stored in the Dual SIM registered IMSI database 406 can be used to avail paging coordination. In one embodiment of the invention, the CN 103 adds IMSI pair information in Dual SIM registered IMSI Database 406 when both the SIMs of the UE 101 gets registered on the network. In another embodiment of the invention, the CN 103 can be configured to derive IMSIs of SIMs from temporary identities received from the UE 101. The CN 103 can be configured to store the IMSIs in the Dual SIM Registered IMSI Database 406.
[0044] FIG. 5 is a flow diagram depicting a method of handling paging in a Dual SIM mobile communication system, according to one embodiment as disclosed herein. In the embodiment of the invention, a method of differentiating the paging message of a particular SIM is disclosed. The purpose of paging message is to make the UE 101 to intimate that there is an incoming request for a particular SIM.
[0045] The core network 101 maintains a “Dual SIM registered IMSI database (hereinafter referred to as database)”. The database comprises of information such as but not limited to IMSI of each SIM, IMSI of each neighbor SIM, temporary UE identity, and at least one other information element.
[0046] Initially, the core network 101 initiates (502) a paging procedure. While initiating the paging procedure, the core network 101 checks if the UE 101 for which the paging is being initiated is a single SIM type or a dual SIM type. If the paging process is for a single SIM UE, then the core network sets a ‘neighbor SIM’ field in the paging message to ‘NULL’; wherein the NULL value of the neighbor SIM field indicates that the paging message is directed to a single SIM type UE 101. If the paging message is for a dual SIM UE 101, the core network 101 identifies, from the database, the IMSI of the neighboring SIM, and adds the identified value to the neighbor SIM field of the paging message. The core network then sends (504) the paging message to the UTRAN 102. In an embodiment, the paging message comprises of:
? Permanent NAS UE Identity (IMSI of the SIM being paged)
? Neighbor SIM Permanent NAS UE Identity (IMSI of Neighbor SIM)
? Temporary UE Identity (TMSI of the SIM being paged) and
? Other necessary details for paging

[0047] The UTRAN 102 receives the paging message from the core network 101. Further, by processing the paging message, the UTRAN 102 identifies the primary SIM and/or neighboring SIM IMSI information. The UTRAN 102 further checks (508) whether an RRC connection already exists with the primary SIM, and if yes, then a paging type 2 message is triggered (510) with a cause as sent by the core network 101. Examples of paging messages with cause received from the core network are mentioned below:
Paging Cause to be sent to UE in Paging type 2 Message from UTRAN to UE
Terminating Conversational Call
Terminating Streaming Call
Terminating Interactive Call
Terminating Background Call
Terminating High Priority Signalling
Terminating Low Priority Signalling
Terminating – cause unknown

[0048] If the RRC connection with the primary SIM doesn’t exist, the UTRAN 102 checks (512) if an RRC connection exists with the neighbor SIM. If the RRC connection exists with the neighbor SIM, the UTRAN 102 triggers (514) a paging type 2 message, with a new cause; wherein the new cause indicates that the paging message is intended for the idle mode SIM (i.e. the neighbor SIM), in a UE 101 that is in semi connected mode. Examples of paging messages with cause mapped to cause received from the core network are mentioned below:
Mapped Paging Cause to be sent to UE (101) in Paging type 2 Message from UTRAN to UE
Neighbor SIM Terminating Conversational Call
Neighbor SIM Terminating Streaming Call
Neighbor SIM Terminating Interactive Call
Neighbor SIM Terminating Background Call
Neighbor SIM Terminating High Priority Signalling
Neighbor SIM Terminating Low Priority Signalling
Neighbor SIM Terminating – cause unknown

[0049] If there is no RRC connection with the primary SIM and the neighbor SIM, then the UTRAN 102 triggers (516) a paging type 1 message through a paging channel.
[0050] The UE 101, upon receiving the paging message from the UTRAN 102, identifies whether the paging message is for the primary SIM or the neighbor SIM, and accordingly forwards the message. In an embodiment, the UE 101 identifies the SIM to which the paging message is related to, based on at least one of the cause associated with the paging message, and the SIM with which the RRC connection through which the paging message has been received.
[0051] In an embodiment, the RRC channel sharing can be done for a fully connected dual SIM UE. If the UE 101 is in fully connected mode, SIM1 is termed as parent SIM and SIM2 is termed as child SIM. In this system, upon receiving the UTRAN 102, based on information pertaining to IMSI’s and corresponding RRC channel connections, identifies the SIM the received message corresponds to.
[0052] The various actions in 500 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 5 may be omitted.
[0053] FIG. 6 is a flow diagram depicting a method of requesting signalling connection in a Semi-Connected Dual SIM mobile communication system, according to one embodiment as disclosed herein. The UE 101 sends (602) signalling connection request to the UTRAN 102, wherein the signalling connection request is an Initial Direct Transfer (IDT) message. The UTRAN 102 receives (604) the signalling connection request from the UE 101, and in response, sends (606) an Initial UE Message to Core Network. The Initial UE Message indicates that the UE 101 intends to initiate (608) a signalling connection. Upon receiving the Initial UE Message, the CN 103 initiates a signalling connection. The various actions in 600 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 6 may be omitted.
[0054] FIG. 7 is a flow diagram depicting a method of triggering signalling connection request in a Semi-Connected Dual SIM mobile communication system, according to one embodiment as disclosed herein. Initially, the idle mode SIM in the UE 101 triggers a Non Access Spectrum (NAS) message (IDT message) to the UTRAN 102 through the existing RRC Connection of the connected mode SIM. The IDT message comprises of an information element i.e. the Neighbor SIM Message, value of which represents message to either the idle mode Neighbor SIM or for the connected mode SIM.
[0055] If IDT message is triggered from idle mode SIM through the connected mode SIM’s RRC Connection then the information element Neighbor SIM Message can be set to True, else the information element Neighbor SIM Message can be set to False.
[0056] The UE 101 can trigger (702) the request for signalling connection for a particular domain through the IDT message to UTRAN 102, and in turn the UTRAN 102 triggers Initial UE Message to Core Network, which in turn triggers a signalling connection. The UE 101 checks (704) if the IDT message is for connected mode SIM. If IDT message is triggered from the connected mode SIM, through the connected mode SIM’s RRC connection, then the value of the information element Neighbor SIM Message can be set to False, and the message is then sent (706) to the UTRAN 102. If the IDT message corresponds to the Idle mode SIM, then the value of the information element Neighbor SIM Message can be set to True, and the message is then sent (708) to the UTRAN 102.
[0057] The various actions in 700 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 7 may be omitted.
[0058] FIG. 8 is a flow diagram depicting a method of handling signalling connection request in an UTRAN in a Semi-Connected Dual SIM mobile communication system, according to one embodiment as disclosed herein. The UTRAN 102 receives (802) the IDT message from the UE 101. The UTRAN 102 further decodes (804) the IDT message received from the UE 101 and sends the UE’s NAS Message to CN 103 as an Initial UE Message. The UTRAN 102 checks (806) if the IDT message is for idle mode SIM. If the value of information element Neighbor SIM Message is set as True then the UTRAN 102 triggers (808) an Initial UE Message to CN 103, even though there is a signalling connection existing for the connected mode SIM for the same domain. A Iu signalling connection identifier which is included in the Initial UE message is linked with the RRC Connection from where IDT message is received. If the value of information element Neighbor SIM Message is set as False then IDT message is for connected mode SIM (810).
[0059] The various actions in 800 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 8 may be omitted.
[0060] FIG. 9 is a flow diagram depicting a method of handling Non-Access Stratum (NAS) signalling messages in a Fully Connected Dual SIM mobile communication system, according to one embodiment as disclosed herein.
In a fully connected mode scenario:
? ‘Parent SIM’:- Refers to the SIM that has initiated RRC connection with the core network 101
? ‘Child SIM’:- Refers to the SIM that makes use of the parent SIM’s RRC connection to establish communication with the core network 101
? ‘Parent SIM’s signaling connection’: Signaling Connection established for Parent SIM i.e. the Signaling Connection which had got initiated by the Initial Direct transfer message from a Dual SIM mobile with the value of information element “Neighbor SIM Message” set as FALSE.
? ‘Child SIM’s signaling connection’: Signaling Connection established for Child SIM i.e. the Signaling Connection which had got initiated by the Initial Direct transfer message from a Dual SIM mobile with the value of information element “Neighbor SIM Message” set as TRUE.
[0061] Initially, NAS Signalling message is sent from the UE 101 and received at UTRAN 102 as Uplink Direct Transfer (UDT) Message. The NAS Signalling message can also refer to a Downlink Direct Transfer (DDT) message sent from the UTRAN 102 to the UE 101. In order to handle the NAS Signalling messages, the UDT message and the DDT message contain an information element Neighbor SIM Message, which can help the UE 101, and the UTRAN 102 to differentiate the messages from the two different SIM cards being supported by the UE 101.
[0062] In order to communicate with the CN 103, to avail any of the services being offered by the CN 103, the UE 101 initiates (902) a NAS signalling message (UDT message). The UTRAN 102 receives (904) the NAS signalling message (UDT message). UTRAN checks the value of information element Neighbor SIM Message to differentiate the messages from Parent SIM and Child SIM of the fully connected mode UE 101. Depending on the value of the information element, UTRAN sends (906) Direct Transfer message to the CN 103 through parent SIM’s signalling connection or child SIM’s signalling connection. Further, in response, the UTRAN 102 receives (908) Direct Transfer message from the CN 103. The UTRAN 102 checks if the Direct Transfer message is received through parent SIM’s Signalling Connection or the child SIM’s Signalling Connection and accordingly sends (910) the NAS signalling message (DDT message) to the parent SIM or the child SIM of the Fully connected mode UE 101.
[0063] The various actions in 900 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 9 may be omitted
[0064] FIG. 10 is a flow diagram depicting a method of handling of Radio bearer management procedures in UTRAN in a Fully Connected Dual SIM mobile communication system, according to one embodiment as disclosed herein. For the UE 101 to share a single RRC connection for data transfer pertaining to both the SIM cards, the radio bearer setup procedures is to be managed accordingly. The core network 103 initiates the Radio Access Bearer (RAB) Assignment procedure, which in turn initiates the procedure for Radio bearer establishment from the UTRAN 102. In various embodiments, two methods are disclosed for the Radio Access bearer management for the fully connected Dual SIM Mobiles.
First Method:-
[0065] In the first method, while assigning RB identity and RAB identity, the UTRAN 102 and the Core network 103 consider both the SIM cards of the UE 101 as separate SIM cards of different UEs 101 i.e. there can be repetition of the same RB id or same RAB id for both the SIMs and the UTRAN 102 manage the same internally. For example, SIM 1 can be assigned with RAB 5 under which RB 5, RB 6, RB 7 are available. At the same time, SIM 2 can also be assigned with the RAB 5 under which RB 5, RB 6, RB 7 are available or RB 8, RB 6, RB 7 are available. While contacting the UE 101 for setup, reconfigure or release of Radio bearers/Radio Access bearers, the UTRAN 102 adds an information element Neighbor SIM Message in both RAB level and RB level in any of the possible 3GPP defined messages which contains setup, reconfigure or release of Radio Bearers in order to help the UE 101 differentiate the RABs and RBs for both the SIMs. In this method of Radio Bearer management procedures, the information element Neighbor SIM Message is added in both RAB level as well as RB level in any of the possible 3GPP defined messages which contains triggers setup procedure and also, the information element Neighbor SIM Message is added in both RAB level and also RB level in any of the possible 3GPP defined messages which contains triggers reconfigure or release.
[0066] In the first method, the UTRAN 102 checks; at periodic intervals or instantly, whether an RAB assignment request has been received from the core network 101 or not. If yes, then the UTRAN 102 checks if the RAB assignment request has been received from the parent SIM’s signalling connection or from the child SIM’s signalling connection.
[0067] If the RAB assignment request has been received through signalling connection that belongs to the parent SIM, then the UTRAN triggers set up procedures for Radio Bearers/Radio Access Bearers to the dual SIM UE 101, through the linked connection, with value of an associated information element ‘neighbor SIM message’ set to ‘FALSE’. The information element ‘neighbor SIM message’ may be added at RB level, as well as at RAB level for all messages which trigger the set up procedure. The procedures to trigger reconfiguration or release of the RBs and/or RABs may also have the information element ‘neighbor SIM message’ set to ‘FALSE’. The information element ‘neighbor SIM message’ may be added at RB level, as well as at RAB level for all messages which trigger re-configuration or release.
[0068] If the RAB assignment request has been received through signalling connection that belongs to the child SIM, then the UTRAN triggers set up procedures for Radio Bearers/Radio Access Bearers to the dual SIM UE 101, through the linked connection, with value of an associated information element ‘neighbor SIM message’ set to ‘TRUE’. The information element ‘neighbor SIM message’ may be added at RB level, as well as at RAB level for all messages which trigger the set up procedure. The procedures to trigger reconfiguration or release of the RBs and/or RABs may also have the information element ‘neighbor SIM message’ set to ‘TRUE’. The information element ‘neighbor SIM message’ may be added at RB level, as well as at RAB level for all messages which trigger re-configuration or release.
[0069] At the UE 101, the RBs and RABs from the parent SIM and the child SIM are differentiated based on the value of the information element ‘Neighbor SIM message’. Upon receiving a setup/reconfiguration/release message, the UE 101 checks if the neighbor SIM message is available at RAB level or RB level.
[0070] If the neighbor SIM message is available at the RAB level, then the UE 101 checks value of the ‘neighbor SIM message’. If the value is ‘False’, then the UE 101 identifies the RAB information, and the RB information (if available) under the RAB information, as that of the parent SIM. If the value if ‘True’, then the UE 101 identifies the RAB information, and the RB information (if available) under the RAB information, as that of the child SIM.
[0071] If the neighbor SIM message is available at the RB level, then the UE 101 checks value of the ‘neighbor SIM message’. If the value is ‘False’, then the UE 101 identifies the RB information as that of the parent SIM. If the value if ‘True’, then the UE 101 identifies the RB information, as that of the child SIM.
Second Method
[0072] In the second method, the RAB ids assigned for both the SIM cards of the UE 101 may be same, whereas the RB ids are different. For example, SIM 1 can be assigned with RAB 5 under which RB 5, RB 6 and RB 7 are available. At the same time, SIM 2 can also be assigned with the RAB 5 under which RB ids may be RB 8, RB 9 and RB 10. In this method, the RB ids for SIM1 and SIM2 are different. In this method, the information element Neighbor SIM Message is added in RAB level only in any of the possible 3GPP defined messages which contains triggers Setup procedure and also, the information element Neighbor SIM Message is added in only RAB level in any of the possible 3GPP defined messages which contains reconfigure or release of Radio bearers or Radio access bearers. In both methods, it is possible for UTRAN to send setup/reconfiguration/release of the RBs for both the SIMs in one single message. Further, in both the methods, after handling the Setup or Reconfiguration or Release of the Radio bearers in the Dual SIM Mobile the Parent SIM triggers the corresponding complete message to the UTRAN.
[0073] In the second method, the UTRAN 102 checks whether the RAB assignment request from the core network 101 is received through the parent SIM’s signalling connection or through the child SIM’s signalling connection.
[0074] If the Rab assignment request has been received through signalling connection that belongs to the parent SIM, then the UTRAN triggers set up procedures for Radio Bearers/Radio Access Bearers to the dual SIM UE 101, through the linked connection, with value of an associated information element ‘neighbor SIM message’ set to ‘FALSE’. The information element ‘neighbor SIM message’ may be added at RAB level alone, for all messages which trigger the set up procedure. The procedures to trigger reconfiguration or release of the RBs and/or RABs may also have the information element ‘neighbor SIM message’ set to ‘FALSE’. The information element ‘neighbor SIM message’ may be added at RAB level alone, for all messages which trigger re-configuration or release.
[0075] If the Rab assignment request has been received through signalling connection that belongs to the child SIM, then the UTRAN triggers set up procedures for Radio Bearers/Radio Access Bearers to the dual SIM UE 101, through the linked connection, with value of an associated information element ‘neighbor SIM message’ set to ‘TRUE’. The information element ‘neighbor SIM message’ may be added at RAB level alone, for all messages which trigger the set up procedure. The procedures to trigger reconfiguration or release of the RBs and/or RABs may also have the information element ‘neighbor SIM message’ set to ‘TRUE’. The information element ‘neighbor SIM message’ may be added at RAB level alone, for all messages which trigger re-configuration or release.
[0076] Upon receiving a setup/reconfigure/release of RB, the UE 101 checks if RAB information is available. If yes, then the UE 101 checks value of ‘neighbor SIM message’. If the value of ‘neighbor SIM message’ is FALSE, then the UE 101 identifies the RAB information, and RB information (if available) under the RAB information, as from the parent SIM, and then maps the RB Ids to present SIM. If the value of ‘neighbor SIM message’ is TRUE, then the UE 101 identifies the RAB information, and RB information (if available) under the RAB information, as from the child SIM, and then maps the RB Ids to present SIM.
[0077] If the RAB information is not available in the received setup/reconfigure/release data, the UE 101 checks if RB information is available. If yes, the UE 101 checks if the received RB is mapped to parent SIM or child SIM. If the RB information is mapped to the parent SIM, then the UE 101 identifies the RB information received, as that of the parent SIM. If the RB information is mapped to the child SIM, then the UE 101 identifies the RB information received, as that of the child SIM.
[0078] Upon receiving (1002) a RAB assignment request from the CN 103, the UTRAN 102 checks (1004) if RAB Assignment request is received through parent SIM’s signalling connection. If the RAB assignment request is received through Parent SIM’s signalling connection, then the UTRAN 102 triggers (1006) setup procedures for Radio Bearers/Radio Access Bearers to UE 101 through the linked RRC connection with the value of information element Neighbor SIM message set to False. Further, the UTRAN 102 triggers (1008) reconfiguration or release for the Radio Bearers/Radio Access Bearers, with the value of the information element Neighbor SIM message set to False.
[0079] If the RAB assignment request is received through Child SIM’s signalling connection, then the UTRAN 102 triggers (1010) setup procedures for Radio Bearers/Radio Access Bearers to UE 101 through the linked RRC connection, with the value of information element Neighbor SIM message set to True. The UTRAN 102 further triggers (1012) reconfiguration or release for the Radio Bearers/Radio Access Bearers, with value of the information element Neighbor SIM message set to True.
[0080] The various actions in 1000 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 10 may be omitted.
[0081] FIG. 11 is a flow diagram depicting a method of handling of security mode control procedures at UTRAN and at UE in a Fully Connected Dual SIM mobile communication system, according to one embodiment as disclosed herein. Security Mode procedures are defined in order to maintain a secured air interface such that the UE’s data and signalling messages are maintained confidentially. In order to make both the SIMs of a UE 101 differentiate the security mode command message for the corresponding SIMs, an information element Neighbor SIM Message is added on to the Security Mode Command message which is then sent to UE 101 from the UTRAN 102.
[0082] The UTRAN 102 receives the security mode command message from a particular Core network 103, wherein the security mode command message comprises information on configuration of the Ciphering and Integrity protection, to be communicated to the UE 101. In response for security mode command, the UTRAN 102 receives either Security mode Complete or Security Mode failure message from the UE 101. The Security Mode complete or Security Mode Failure message does not contain information element Neighbor SIM Message. The UTRAN 102 can consider Security Mode complete or Security Mode Failure message as a response for the last sent security mode command message for the Parent SIM or the Child SIM. The UTRAN 102 sends the security mode command message to the UE 101 with the value of information element Neighbor SIM Message set as either TRUE or FALSE.
[0083] Upon receiving (1102) the security mode command message from the CN 103, the UTRAN 102 checks (1104) whether the security mode command message is received from Parent SIM's signalling connection. If the Security Mode Command message is received from Parent SIM's signalling connection, then the UTRAN 102 sends (1106) the security mode command message to UE 101 with the value of information element Neighbor SIM message set as False. If the security mode command message is received from Child SIM's signalling connection, then the UTRAN 102 sends (1108) the security mode command message to UE 101, with the value of information element Neighbor SIM message set as True.
[0084] Upon receiving (1110) the security mode command message from the UTRAN 102, the UE 101 checks (1112) the value of information element Neighbor SIM message in the security mode command message. If the value of information element Neighbor SIM message is set as True then, Security Mode Command message is received and processed (1114) for the Child SIM. If the value of information element Neighbor SIM message is set as False, then the security mode command message is received (1116) and processed for parent SIM. In response for Security Mode Command, the parent SIM performs security mode procedures, and sends (1118) either a security mode complete or security Mode failure message to UTRAN.
[0085] In an embodiment, the signalling radio bearers are common for both the SIMs of the UE 101, and hence, the Signalling Radio bearers are ciphered and integrity protected by last updated ciphering and integrity keys out of CS Domain Ciphering and Integrity Keys of SIM 1, PS Domain Ciphering and Integrity keys of SIM 1, CS Domain Ciphering and Integrity keys of SIM 2 and PS Domain Ciphering and Integrity keys of SIM 2. In case of Data Radio bearers, there are at least three methods of ciphering. In the first method, the CS Data Radio bearers of SIM 1 are ciphered with SIM 1 CS ciphering keys, PS Data Radio bearers of SIM 1 are ciphered with the SIM 1 PS ciphering keys, the CS Data Radio bearers of SIM 2 are ciphered with the SIM 2 CS ciphering keys, and the PS Data Radio bearers of SIM 2 are ciphered with the SIM 2 PS ciphering keys. In the second method, the CS Data Radio bearers of SIM 1 and SIM 2 are ciphered with the last updated CS Ciphering key out of SIM 1 CS ciphering key and SIM 2 CS Ciphering Key. Also, the PS Data Radio bearers of SIM 1 and SIM 2 are ciphered with the last updated PS Ciphering key out of SIM 1 PS ciphering key and SIM 2 PS Ciphering Key. In the third method, the CS and PS Data Radio bearers of SIM 1 and SIM 2 are ciphered with last updated Ciphering key out of SIM 1 CS Ciphering key, SIM 2 CS Ciphering Key, SIM 1 PS Ciphering Key and SIM 2 PS Ciphering key.
[0086] The various actions in 1100 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 11 may be omitted.
[0087] FIG. 12 is a flow diagram depicting a method of triggering of Signalling Connection Release message from UTRAN and reception of Signalling Connection Release message at UE in a Fully Connected Dual SIM mobile communication system, according to one embodiment as disclosed herein. Messages that are transferred between the UE 101 and the UTRAN 102 for release of signalling connection are Signalling Connection release (from UTRAN 102 to UE 101) and signalling connection release indication (from UE 101 to UTRAN 102). In an embodiment, signalling connection release message from UTRAN 102 and signalling connection release indication from UE 101 comprises an information element Neighbor SIM Message, value of which helps differentiate between messages that correspond to SIM1 and SIM2.
[0088] Upon receiving (1202) the Iu release command from Core network 103, the UTRAN 102 checks (1204) whether Iu Release Command is received from Parent SIM's signalling connection. If the Iu release command is received from parent SIM's signalling connection, then the UTRAN 102 sends (1206) signalling connection release message to UE 101 with the value of information element Neighbor SIM Message set as False. If the Iu Release Command is received from Child SIM's signalling connection then the UTRAN 102 sends (1208) signalling connection release message to UE 101 with the value of information element Neighbor SIM Message set as True.
[0089] The UE receives (1210) the signalling connection release message from UTRAN 102, and checks (1212) whether the value of information element Neighbor SIM Message in the signalling connection release message. If the value of information element Neighbor SIM Message is set to True, then the UE 101 forwards (1214) the signalling connection release message is to the child SIM. If the value of information element Neighbor SIM Message is set to False, then the UE 101 forwards (1216) the signalling connection release message is to the parent SIM.
[0090] The various actions in 1200 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in Fig. 12 may be omitted.
[0091] FIG. 13 is a flow diagram depicting a method of triggering of signaling connection release Indication message from UE and reception of signaling connection release Indication message at UTRAN in a Fully Connected Dual SIM mobile communication system, according to one embodiment as disclosed herein.
[0092] While triggering (1302) a signalling connection release Indication, the UE checks (1304) if the Signalling connection release Indication is from Parent SIM or the child SIM. If the Signalling connection release Indication is from Parent SIM then the UE 101 triggers (1306) the signalling connection release Indication with the value of information element Neighbor SIM Message set as False. If the signalling connection release Indication is from the child SIM, then the UE 101 triggers (1308) Signalling connection release Indication with the value of information element Neighbor SIM Message set as True.
[0093] Upon receiving the Signalling connection release Indication from UE 101, the UTRAN 102 checks (1312) the value of information element Neighbor SIM Message in Signalling connection release Indication. If the value of information element Neighbor SIM Message is set as True, then the UTRAN 102 triggers (1314) a Iu Release Request to the Core Network 103 through Child SIM's signalling connection. If the value of information element Neighbor SIM Message is set as False, then the UTRAN 102 triggers (1316) the Iu Release Request to Core Network 103, through Parent SIM's signalling connection.
[0094] Other connected mode procedures supported by the RRC channel sharing based dual SIM communication system 100 are:
1) RRC connection Release Procedure:
[0095] In this procedure, the UTRAN 102 checks activity of all RBs that are mapped to both the SIMs in the UE 101, for triggering the RRC connection release with the cause as ‘Unser inactivity’ i.e., when the parent SIM and the child SIM are connected mode, and if at least one of them is active, then the UTRAN 102 cannot trigger the RRC connection release with the cause as ‘Unser inactivity’.
2) Procedures triggered by UTRAN to Core network
[0096] If the UTRAN 102 intends to trigger any procedure to the core network, and if the procedure is specific to the link between UTRAN 102 and the UE 101, then the UTRAN 102 triggers the messages corresponding to the procedure, to both the parent SIM, as well as the child SIM; when both the parent SIM and the child SIM are in connected mode.
[0097] The various actions in method 1300 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 13 may be omitted.
[0098] The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the elements. The elements shown in FIG 1 through FIG 13 can be at least one of a hardware device, or a combination of hardware device and software module.
[0099] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

STATEMENT OF CLAIMS
We claim:

1. A method for sharing a Radio Resource Control (RRC) connection in a communication network, said method comprising:
establishing an RRC connection with a Universal Terrestrial radio Access Network (UTRAN) of said communication network, by one of a plurality of SIM cards in a User Equipment (UE) of said communication network;
sharing said RRC connection for establishing communication with said UTRAN, by said plurality of SIM cards, wherein sharing said RRC connection involves mapping signalling connection of said plurality of SIM cards to said RRC connection;
receiving at least one message for at least one of said plurality of SIM cards, through said RRC connection, from said UTRAN, by said UE; and
identifying said at least one message as a message that correspond to a specific SIM card of said plurality of SIM cards, based on value of a unique identifier associated with said message, by said UE.

2. The method as claimed in claim 1, wherein said RRC connection is shared for paging said UE, wherein said sharing of the RRC connection for paging further comprises:

setting value of a ‘neighbor SIM’ field in said paging message as ‘NULL’, if said paging message is for a single SIM UE, by said CN;
identifying a SIM card said paging message corresponds to, in a dual SIM UE, if said paging message belongs to said dual SIM UE, by said CN;
setting an International Mobile Subscriber Identity (IMSI) value of a neighboring SIM of said identified SIM card as value of said ‘neighbor SIM’ field in said paging message, by said CN, wherein said IMSI value of said neighboring SIM is identified from a reference database, by said CN;
identifying a SIM card said paging message belongs to, based on value of said ‘neighbor SIM’ field in said paging message, by said UTRAN; and
triggering at least one of a paging type 1 message and a paging type 2 message to said identified SIM card, by said UTRAN.

3. The method as claimed in claim 1, wherein said RRC channel is shared for signalling said UTRAN from said UE, wherein said sharing of the RRC channel for said signalling of the UTRAN from the UE further comprises of:
receiving a signalling connection request from said UE through a common RRC channel, by said UTRAN, wherein said signaling connection request is an Initial Direct Transfer (IDT) message;
identifying a SIM card that triggered said signalling connection request, by said UTRAN; and
sending an initial UE message to said CN, in response to said signalling connection request, through a signalling channel of said identified SIM card that triggered said signalling connection request, by said UTRAN.

4. The method as claimed in claim 3, wherein identifying said SIM card that triggered said signalling request further comprises of:
checking value of a unique identifier associated with said signalling connection request, wherein value of said unique identifier is pre-configured by said UE;
identifying a SIM1 as said SIM card that triggered said signalling request if said value of said unique identifier is ‘False’; and
identifying a SIM2 as said SIM card that triggered said signalling request if said value of said unique identifier is ‘True’.

5. The method as claimed in claim 1, wherein said RRC channel is shared for signalling said UE from said UTRAN, wherein said sharing of the RRC channel for signalling said UE from said UTRAN further comprises:
receiving a signalling request from said CN by said UTRAN, wherein said signalling request is a Direct Transfer Message;
identifying a SIM card to said received signalling request corresponds, by said UTRAN; and
sending a Non Access stratum (NAS) signalling message to said identified SIM card, through said shared RRC channel, wherein a unique identifier value corresponds to identified SIM card is associated with said NAS signalling message.

6. The method as claimed in claim 5, wherein identifying said SIM card that triggered said signalling request further comprises:
identifying a SIM1 as said SIM card said signalling request corresponds to, if said signalling request has been received from a signalling connection that belongs to said SIM1; and
identifying a SIM2 as said SIM card said signalling request corresponds to, if said signalling request has been received from a signalling connection that belongs to said SIM2.

7. The method as claimed in claim 1, wherein said RRC channel is shared for a Radio Access Bearer (RAB) signalling, wherein said sharing of RRC channel for the RAB signalling further comprises:
receiving a RAB assignment request from said CN, by said UTRAN;
identifying a SIM card said RAB assignment request corresponds to, by said UTRAN; and
triggering a setup procedure corresponding to said identified SIM card, by said UTRAN, wherein a unique identifier value corresponding to said identified SIM card is associated with message corresponding to said triggering setup procedure.

8. The method as claimed in claim 7, wherein identifying said SIM card to said RAB assignment request corresponds, further comprises:

checking a signalling connection from which said RAB assignment request is received by said UTRAN;
identifying a SIM1 as said SIM card to said RAB assignment request corresponds, if said RAB assignment request is received from a signalling connection that corresponds to said SIM1; and
identifying a SIM2 as said SIM card to said RAB assignment request corresponds, if said RAB assignment request is received from a signalling connection that corresponds to said SIM2.

9. The method as claimed in claim 8, wherein differentiating said RAB and corresponding Radio Bearer (RB) that belong to different SIM cards of said dual SIM mobile further comprises of:
collecting an RAB assignment request from said dual SIM UE, by said UTRAN;
differentiating between RAB that belongs to said SIM1 and said SIM2, wherein said differentiation is done at at least one of an RAB level and an RB level;
setting value of an information element ‘neighbor SIM message’ to ‘FALSE’ if said is received from said SIM1 of said dual SIM UE; and
setting value of said information element ‘neighbor SIM message’ to ‘TRUE’ if said is received from said SIM2 of said dual SIM UE.

10. The method as claimed in claim 1, wherein said RRC is shared for handling security mode procedures, said method comprises:
receiving a security mode command from said CN by said UTRAN;
identifying a SIM card in said dual SIM UE, said received security mode command corresponds to, based on a signalling connection from which the security mode command is received, by said UTRAN;
sending said security mode command to said UE, wherein a unique identifier corresponding to said identified SIM card is associated with said security mode command; and
processing said security mode command for said identified SIM card, by said UE, wherein said processing of the security mode command further comprises of:
performing at least one security mode procedure for said SIM card, based on said security mode command; and
sending at least one of a 'security mode complete' and 'security mode failure' as a response to said UTRAN using said UE, wherein said response indicates status of said performed security mode procedure.

11. A system for sharing a Radio Resource Control (RRC) connection in a communication network, said system comprising:
at least a User Equipment (UE) of said Communication Network (CN) establishing an RRC connection with a Universal Terrestrial radio Access Network (UTRAN) of said CN, wherein said RRC connection with said UTRAN is established by one of a plurality of SIM cards in said UE;
a plurality of SIM cards in said UE sharing said RRC connection for establishing communication with said UTRAN, wherein sharing said RRC connection involves mapping signalling connection of said plurality of SIM cards to said RRC connection;
said UE receiving at least one message for at least one of said plurality of SIM cards, through said RRC connection, from said UTRAN; and
said UE identifying said at least one message as a message that correspond to a specific SIM card of said plurality of SIM cards, based on value of a unique identifier associated with said message.

12. The system as claimed in claim 11, wherein said system is configured to share said RRC connection for paging said UE, wherein said system shares said RRC connection for paging by:

setting value of a ‘neighbor SIM’ field in said paging message as ‘NULL’, if said paging message is for a single SIM UE, by said CN;
identifying a SIM card said paging message corresponds to, in a dual SIM UE, if said paging message belongs to said dual SIM UE, by said CN;
setting an International Mobile Subscriber Identity (IMSI) value of a neighboring SIM of said identified SIM card as value of said ‘neighbor SIM’ field in said paging message, by said CN, wherein said IMSI value of said neighboring SIM is identified from a reference database, by said CN;
identifying a SIM card said paging message belongs to, based on value of said ‘neighbor SIM’ field in said paging message, by said UTRAN; and
triggering at least one of a paging type 1 message and a paging type 2 message to said identified SIM card, by said UTRAN.

13. The system as claimed in claim 11, wherein said system is configured to share said RRC channel for signalling said UTRAN from said UE, by:

receiving a signalling connection request from said UE through a common RRC channel, by said UTRAN, wherein said signaling connection request is an Initial Direct Transfer (IDT) message;
identifying a SIM card that triggered said signalling connection request, by said UTRAN; and
sending an initial UE message to said CN, in response to said signalling connection request, through a signalling channel of said identified SIM card that triggered said signalling connection request, by said UTRAN.

14. The system as claimed in claim 13, wherein said UTRAN is configured to identify said SIM card that triggered said signalling request by:
checking value of a unique identifier associated with said signalling connection request, wherein value of said unique identifier is pre-configured by said UE;
identifying a SIM1 as said SIM card that triggered said signalling request if said value of said unique identifier is ‘False’; and
identifying a SIM2 as said SIM card that triggered said signalling request if said value of said unique identifier is ‘True’.

15. The system as claimed in claim 11, wherein said system is configured to share said RRC channel for signalling said UE from said UTRAN, by:
receiving a signalling request from said CN, by said UTRAN, wherein said signalling request is a Direct Transfer Message;
identifying a SIM card to said received signalling request corresponds, by said UTRAN; and
sending a Non Access stratum (NAS) signalling message to said identified SIM card, through said shared RRC channel, wherein a unique identifier value corresponds to identified SIM card is associated with said NAS signalling message.

16. The system as claimed in claim 15, wherein said UTRAN is configured to identify said SIM card that triggered said signalling request by:
identifying a SIM1 as said SIM card said signalling request corresponds to, if said signalling request has been received from a signalling connection that belongs to said SIM1; and
identifying a SIM2 as said SIM card said signalling request corresponds to, if said signalling request has been received from a signalling connection that belongs to said SIM2.

17. The system as claimed in claim 11, wherein said system is configured to share said RRC channel for a Radio Access Bearer (RAB) signalling, by:
receiving a RAB assignment request from said CN, by said UTRAN;
identifying a SIM card said RAB assignment request corresponds to, by said UTRAN; and
triggering a setup procedure corresponding to said identified SIM card, by said UTRAN, wherein a unique identifier value corresponding to said identified SIM card is associated with message corresponding to said triggering setup procedure.

18. The system as claimed in claim 17, wherein said UTRAN is configured to identify said SIM card said RAB assignment request corresponds to, by:

checking a signalling connection from which said RAB assignment request is received;
identifying a SIM1 as said SIM card to said RAB assignment request corresponds, if said RAB assignment request is received from a signalling connection that corresponds to said SIM1; and
identifying a SIM2 as said SIM card to said RAB assignment request corresponds, if said RAB assignment request is received from a signalling connection that corresponds to said SIM2.

19. The system as claimed in claim 18, wherein said system is configured to differentiate said RAB and corresponding Radio Bearer (RB) that belong to different SIM cards of said dual SIM mobile by:
collecting an RAB assignment request from said dual SIM UE, by said UTRAN;
differentiating between RAB that belongs to said SIM1 and said SIM2, by said UTRAN, wherein said differentiation is done at at least one of an RAB level and an RB level;
setting value of an information element ‘neighbor SIM message’ to ‘FALSE’ if said is received from said SIM1 of said dual SIM UE, by said UTRAN; and
setting value of said information element ‘neighbor SIM message’ to ‘TRUE’ if said is received from said SIM2 of said dual SIM UE, by said UTRAN.

20. The system as claimed in claim 11, wherein said system is configured to share said RRC for handling security mode procedures, by:
receiving a security mode command from said CN, by said UTRAN;
identifying a SIM card in said dual SIM UE, said received security mode command corresponds to, based on a signalling connection from which the security mode command is received, by said UTRAN;
sending said security mode command to said UE, wherein a unique identifier corresponding to said identified SIM card is associated with said security mode command; and
processing said security mode command for said identified SIM card, by said UE, wherein said UE is configured to process said security mode command by:
performing at least one security mode procedure for said SIM card, based on said security mode command; and
sending at least one of a 'security mode complete' and 'security mode failure' as a response to said UTRAN using said UE, wherein said response indicates status of said performed security mode procedure.

Dated this 25th November 2015

Signature:

Name of the Signatory: Dr. Kalyan Chakravarthy

ABSTRACT
Method and system for utilizing a single RRC Connection for SIM cards of a Multi SIM mobile communication system is disclosed. A User Equipment (UE), a UTRAN, and a Core network (CN) which are part of the communication system are configured for identifying, based on value of a unique identifier associated with each message being transmitted between the UE and the CN, the SIM card in the UE to which the message corresponds. Further, the system is configured for sharing a Radio Resource Control (RRC) channel for the SIM cards in the UE to communicate with the UTRAN, and the Core network.

FIG. 1