DESC:CROSS REFERENCE TO RELATED PATENT APPLICATIONS
[001] This patent application is related to and claims the benefit of priority from the Indian Provisional Patent Application with Serial No. 1328/CHE/2015 titled “A SYSTEM AND METHOD FOR ESTABLISHING DEVICE-TO-DEVICE COMMUNICATION”, filed on March 18, 2105, the contents of which are incorporated in entirety by the way of reference.

TECHNICAL FIELD
[002] The present disclosure relates to wireless communication networks. Particularly, the present disclosure relates to device-to-device (D2D) communication.

BACKGROUND
[003] Device-to-device (D2D) communication enables multiple devices (typically user equipments) to communicate with one another when they are in proximity to one another. LTE (Long Term Evolution) D2D communication operates based on a peer-to-peer link that does not mandate availability of cellular network infrastructure. LTE D2D communication is preferred in comparison with conventional communication methods keeping in view the fact that LTE D2D communication methodology offers comparatively higher data transfer rates, reliable and instant communication between devices proximate to one another, comparatively improved power saving abilities and comparatively lesser interference levels.
[004] Typically, user equipments, though in proximity to one another, might be remotely located with reference to availability of cellular infrastructure, and might not be able to offer higher data rates. Therefore, LTE D2D communication can overcome this drawback and offer improved data transfer rates since the LTE D2D communication does not depend upon availability of conventional cellular network infrastructure. Further it is preferable that localized communication between user equipments in proximity to one another is rendered reliable and safe. Further, since LTE D2D communication does not rely upon availability of conventional cellular infrastructure, the user equipments could be used for instant communications in a manner similar to the use of walkie-talkies.
[005] In contrast to conventional device-to-device communication methods such as Wi-Fi and Bluetooth, LTE D2D communication method makes use of licensed communication spectrum which provides communication frequencies with comparatively lesser levels of noise and interference. In case of LTE D2D communication method, since no direct communication with a base station is necessitated, the amount of data transferred towards the base station on the allocated frequency is drastically reduced, thereby bringing about a reduction in the overall interference levels. Further, since LTE D2D communication is implemented typically amongst user equipments proximate to one another, the communication process typically necessitates comparatively lower levels of transmission power, which in turn brings about an enhancement in terms of energy efficiency.
[006] LTE based D2D communication methodology would establish a direct communication link between the user equipments in proximity (within a predetermined range) to one another, thereby allowing large volumes of data to be exchanged there between. LTE D2D based communication provides an alternative to the conventional cellular network based communication and envisages setting up a direct communication link between user equipments (devices) proximate to one another, via a mobile radio network. Since devices are in a direct communication with one another, the phenomenon of network overloading is typically obviated.
[007] However, despite the advantages specified hitherto, LTE D2D communication cannot be established between two devices (user equipments) operated by different network service providers (operators), which translates to the fact LTE does not support Inter-Operator D2D (IOD2D) communication. Referring to FIG.1, there is shown a prior art network architecture 100 incorporating two mobile stations, namely first mobile station 10 and second mobile station 16. As shown in FIG.1, the first mobile station 10 is communicably coupled to a first eNodeB 12 and the second mobile station 16 is communicably coupled to a second eNodeB 18. Subsequently, the first eNodeB 12 cooperates with the first mobile management entity 14, and the second eNodeB 16 cooperates with the second mobile management entity 20. The first mobile station is assigned ‘frequency 1’ and ‘frequency 2’ (uplink and downlink frequencies, denoted by ‘solid lines’ in FIG.1) by a first network operator (not shown in figures) for communication with the first eNodeB 12. Similarly, the second mobile station 16 is assigned ‘frequency 3’ and ‘frequency 4’ (uplink and downlink frequencies, denoted by ‘solid lines’ in FIG.1) by a second network operator (not shown in figures) for communication with the second eNodeB 18. The exchange of control information between the first mobile station 10 and first eNodeB 12, and the second mobile station 16 and second eNodeB 18 is denoted by ‘dashed lines’ in FIG.1. In a (conventional) scenario where the first network operator and second network operator are different, the first mobile station would not be allowed to use the ‘frequency 3’ and ‘frequency 4’ (offered by the second network operator), and similarly the second mobile station would not be able to use the ‘frequency 1’ and ‘frequency 2’ (offered by the first network operator), despite the first mobile station being proximate to the second mobile station. In view of the aforementioned scenario, there has been felt a need for a system and method that facilitates inter-operator D2D communication.

OBJECTS
[008] An object of the present disclosure is to facilitate D2D communication link between multiple user equipments.
[009] Another object of the present disclosure is to provide for availability of improved data transfer rates by facilitating D2D communication link between multiple user equipments.
[0010] Yet another object of the present disclosure is to facilitate reliable communication between multiple LTE compliant devices.
[0011] Still a further object of the present disclosure is to provide a communication model which works independent of the conventional cellular network infrastructure.
[0012] One more object of the present disclosure is to provide a communication model that is comparatively less prone to interference.
[0013] Yet another object of the present disclosure is to facilitate power savings in LTE complaint devices interconnected via a D2D communication link.
[0014] Still a further object of the present disclosure is to facilitate larger volumes of data to be shared between LTE complaint devices using a direct communication link.
[0015] One more object of the present disclosure is to facilitate a communication network supported by mobile radio network.
[0016] Still a further object of the present disclosure is to provide an efficient network architecture that obviates the problem of network overloading.

SUMMARY
[0017] The present disclosure envisages a method for implementing a device-to-device (D2D) communication between a first mobile station and a second mobile station. The first mobile station is typically controlled by a first network operator and the second mobile station controlled by a second network operator, and preferably the first network operator is different from the second network operator.
[0018] A database of registration information that associates the first mobile station with the first network operator and the second mobile station with the second network operator is compiled. Further, the registration information also includes coordinate information corresponding to the first mobile station and the second mobile station. When an inquiry for establishing a direct communication link between the first mobile station and second mobile station is received, preferably from the first mobile station, the coordinate information corresponding to the first mobile station and second mobile station are analyzed to determine whether a direct communication link can be established there between. The coordinate information typically includes latitude and longitude of the first mobile station and second mobile station.
[0019] Subsequent to the analysis of the coordinate information corresponding to the first mobile station and the second mobile station, and post successful assertion of the possibility of a direct communication link between the first mobile station and second mobile station, an operating frequency of the first mobile station is determined, and control information is transmitted from the first mobile station onto the second mobile station over the (determined) operating frequency.
[0020] The second mobile station is triggered to identify and compare operating frequencies of the first network operator and second network operator, and subsequently establish a direct connection between the first mobile station and second mobile station using at least one of the operating frequencies of the first network operator and second network operator.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0021] The other objects, features and advantages envisaged by the present disclosure will be apparent to those skilled in the art from the following description and the accompanying drawings in which:
[0022] FIG.1 is a prior art diagram illustrating a conventional device-to-device communication;
[0023] FIG.2 is a diagram describing a telecommunication network facilitating inter-operator device-to-device (D2D) communication, in accordance with the present disclosure; and
[0024] FIG.3 is a flow chart illustrating the steps involved in the method for implementing a device-to-device (D2D) communication between a first mobile station and a second mobile station, in accordance with the present disclosure.

DETAILED DESCRIPTION
[0025] In order to overcome the drawbacks associated with conventional D2D communication mechanisms, the present disclosure envisages an inter-operator D2D communication mechanism. The inter-operator D2D mechanism envisaged by the present disclosure makes it possible for two LTE compliant devices managed by different network operators, to be interconnected via a direct communication link. Even though the inter-operator D2D mechanism envisaged by the present disclosure is explained with reference to FDD (Frequency Division Duplex) scheme, the inter-operator D2D mechanism envisaged by the present disclosure could be seamlessly incorporated in a TDD (Time Division Duplex) scheme.
[0026] Referring to FIG.2, there is shown a block diagram illustrating a system 200 for facilitating a D2D communication link. The system 200 comprises at least two user equipments, namely a first mobile station 20 which is communicably coupled to a first mobile management entity 24 via a first eNodeB 22, and a second mobile station 26 which is communicably coupled to a second mobile management entity 30 via a second eNodeB 28. Preferably, the first eNodeB 22 uses OFDMA (Orthogonal Frequency Division Multiple Access) modulation scheme for the downlink transmission and the first mobile station 20 uses SC-FDMA (Single Carrier Frequency Division Multiple Access) modulation scheme for the uplink transmission. The same modulation schemes are used by the second mobile station 26 and the second eNodeB 28 for uplink and downlink transmissions.
[0027] In accordance with the present disclosure, the first mobile station 20 and the second mobile station 26 are preferably spaced apart by a predetermined distance. The location of the first mobile station 20 and the second mobile station 26 are preferably unchanging. Under certain predetermined circumstances, the location of the first mobile station 20 and the second mobile station 26 is varied, but it is ensured that the distance between the two mobile stations remains never exceeds a predetermined distance, which otherwise would have resulted in comparatively higher bit error rates and poorer communication bandwidth.
[0028] In accordance with the present disclosure, a database of registration information (not shown in figures) is generated prior to establishing a D2D communication link between the first mobile station 20 and the second mobile station 26. The database (of registration information) is preferably compiled and maintained by the network operators responsible for the management of the first mobile station 20 and the second mobile station 26.
[0029] In accordance with the present disclosure, the first mobile station 20 is managed by a first network operator (not shown in figures), and the second mobile station 26 is managed by a second network operator (not shown in figures), and the first network operator is different from the second network operator. Therefore, in this case, since the first mobile station 20 and the second mobile station 26 are managed by two different network operators, two synchronized versions of the database of registration information (for example a first database 32 and a second database 34) are maintained by the first mobile management entity 24 and the second mobile management entity 30 respectively. The first mobile station 20 accesses and updates a first database 32 and the second mobile station 26 accesses and updates a second database 34. The first database 32 is managed by the first mobile management entity 24 and the second database 34 is managed by the second mobile management entity 30.
[0030] In accordance with the present disclosure, whenever there is a requirement/necessity for a direct communication to be set up between the first mobile station 20 and the second mobile station 26, the coordinate information (i.e., the latitude and longitude) corresponding to the first mobile station 20 and the second mobile station 26 are added onto the respective database(s) of registration information. Typically, the first mobile station 20 adds the second mobile station 26 onto the first database 32, and the second mobile station 26 adds the first mobile station 20 onto the second database 34 to pre-provision D2D call option or preference whenever in proximity.
[0031] In accordance with the present disclosure, post the addition of coordinate information (of the first mobile station 20 and the second mobile station 26) onto the respective replica databases 32 and 34, the first mobile station 20 transmits the corresponding coordinate information (including latitude and longitude) in combination with a ‘connection establishment request’ to the first mobile management entity 24. Subsequently, the first mobile management entity 24 transmits the ‘connection establishment request’ and the coordinate information corresponding to the first mobile station 20, to the second mobile management entity 30. Prior to transmitting the ‘connection establishment request’ and the coordinate information, the first mobile management entity 24 determines whether a reference (entry) incorporating the coordinate information of the second mobile station 26 with which the direct communication link is to be established, is available in the first database 30. The first mobile management entity 24 transmits the ‘connection establishment request’ and the coordinate information corresponding to the first mobile station 20, to the second mobile management entity 30 only in the event that the first database 30 incorporates a reference/entry corresponding to the coordinate information related to the second mobile station 26.
[0032] Subsequently, the second mobile management entity 30 analyzes the coordinate information corresponding to the first mobile station 20, and compares the coordinate information corresponding to the first mobile station 20 with the coordinate information corresponding to the second mobile station 26. The second mobile management entity 30, based on the coordinate information corresponding to the first mobile station 20 and second mobile station 26, determines whether a direct communication link (D2D communication link) is feasible between the first mobile station 20 and second mobile station 26. The feasibility of a direct communication link (D2D communication link) is determined, at least in part based on the presence of a reference/entry corresponding to the coordinate information of the first mobile station 20 in the second database 34, and further based upon the comparison of the latitude and longitude of the first mobile station 20, and the latitude and longitude of the second mobile station 26.
[0033] In accordance with the present disclosure, in the event that the second mobile management entity 30 determines a direct communication link between the first mobile station 20 and the second mobile station 26 to be feasible, the second mobile management entity 30 requests from the mobile management entity 24, the frequencies utilized by the first mobile station 20. In this case, the first mobile station preferably uses ‘frequency 1’ as an uplink frequency and ‘frequency 2’ as a downlink frequency to communicate with first eNodeB 22. Subsequently, the first mobile management entity 24 designates the first mobile station 20 as a ‘master’ and identifies the uplink frequency (frequency 1) and the downlink frequency (frequency 2) utilized by the first mobile station 20. The frequencies at which the first mobile station 20 communicates with the first eNodeB, i.e., ‘frequency 1’ and ‘frequency 2’ are identified by the first mobile management entity 24 (by the way of probing the first eNodeB 22). Subsequently the first mobile management entity 24 transmits the information corresponding to the identified frequencies (‘frequency 1’ and ‘frequency 2’) to the second mobile management entity 30.
[0034] In accordance with the present disclosure, after receiving the information corresponding to the (operating) frequencies of the first mobile station 20, the second mobile management entity 30 designates the second mobile station 26 as a ‘slave’ and transmits to second mobile station 26 the information corresponding to the (operating) frequencies of the first mobile station 20. Subsequently, the second mobile station 26 scans for at least one of ‘frequency 1’ and ‘frequency 2’, and preferably the uplink frequency (‘frequency 1’) since the second mobile station 26 is required to establish a direct communication link with the first mobile station 20 in a master-slave configuration, with the first mobile station 20 as the ‘master’, and the second mobile station 26 as the ‘slave’.
[0035] During the master-slave configuration process, the first mobile station 20 as well as the second mobile station 26 might typically incorporate more than one Phased Lock Loops (PLL), since the operating spectrum of the first network operator and second network operator are widely spaced from one another. Further, during the master-slave configuration process, the first mobile station 20 would be communicably coupled to the first eNodeB 22 and the second mobile station 26 would be communicably coupled to the second eNodeB 28 as well as the first mobile station 20 (as a ‘slave’). While the second mobile station 26 is implemented as a ‘slave’, preferably only control information necessary to establish a direct communication link between the first mobile station 20 and second mobile station 26 is exchanged there between.
[0036] Subsequently, the second mobile station 26 iteratively scans the (operating) frequencies offered by the first network operator (controlling the first mobile station 20), and the second network operator (controlling the second mobile station 26), and selects at least one frequency having lowest interference levels. Subsequently, the second mobile station 26 informs the second mobile management entity 30 about the selected frequency. Further, the frequency selected by the second mobile station 26 is communicated to the first mobile station 20 via the first mobile management entity 24 and first eNodeB 22. Preferably, the second mobile station 26 scans the frequencies on offer until a frequency with lowest interference levels is identified and selected.
[0037] In accordance with the present disclosure, after a direct communication link is established between the first mobile station 20 and the second mobile station 26, the Radio Resource Controller (RRC) connections between the first mobile station 20 and first eNodeB 22, and the second mobile station 26 and second eNodeB 28 are preferably terminated in order to optimize network resource utilization at the first and second mobile stations 20 and 26 as well as the first and second eNodeBs 22 and 24. Preferably, the first and second mobile stations 20 and 26 communicate with one another using Single Carrier Frequency Division Multiple Access (SC-FDMA).
[0038] Referring to FIG.3, there is shown a flowchart illustrating the steps involved in the method for implementing a device-to-device (D2D) communication between a first mobile station and a second mobile station. At step 300, a database comprising registration information corresponding to the first mobile station and the second mobile station is compiled. The registration information associates the first mobile station with the first network operator and the second mobile station with the second network operator. Further, the registration information also comprises preference related to D2D call or connection and also coordinate information corresponding to the first mobile station and the second mobile station.
[0039] At step 302, an enquiry is received from the first mobile station to establish a direct communication link with the second mobile station. Such an enquiry incorporates coordinate information corresponding to the first mobile station. At step 304, the coordinate information corresponding to the first mobile station is compared with the coordinate information corresponding to the second mobile station.
[0040] At step 306, based at least on the coordinate information corresponding to the first mobile station and the second mobile station, it is determined whether the direct connection can be established between the first mobile station and second mobile station. At step 308, an operating frequency of the first mobile station is determined. Subsequently ‘control information’ necessary for establishing a direct communication link is shared with the second mobile station using the determined operating frequency.
[0041] At step 310, the second mobile station is triggered to identify and compare operating frequencies offered by the first network operator and second network operator. Subsequently, a direct communication link is established between the first mobile station and second mobile station using at least one of the operating frequencies of the first network operator and second network operator.
[0042] In accordance with the present disclosure, the first network operator is different from the second network operator. Preferably, the coordinate information comprises information corresponding to latitude and longitude of the first mobile station and second mobile station.
[0043] In accordance with the present disclosure, the step of determining an operating frequency of the first mobile station further includes the step of configuring the first mobile station as a master and configuring the second mobile station to be a slave, in order to transmit control information from the first mobile station to the second mobile station. Further, the step of establishing the direct connection further includes the step of selecting an operating frequency having lowest interference among the operating frequencies of the first network operator and second network operator.
[0044] Before establishing a direct communication link between the first mobile station and the second mobile station, it is determined whether the registration information corresponding to the first mobile station and second mobile station is available in the database of registration information. Typically, the direct connection between the first mobile station and second mobile station is established using a frequency selected from a group of frequencies predesignated for the device-to-device (D2D) call based on at least the location of and proximity between the first mobile station and second mobile station. The first mobile station and second mobile station are equipped with at least two phase locked loops (PLL), based on the operating frequencies corresponding to the first network operator and second network operator.

TECHNICAL ADVANTAGES
[0045] The technical advantages of the present disclosure include the realization of a system and method that facilitates a D2D communication link between multiple user equipments. The system and method also envisages data transfer rates by facilitating D2D communication link between multiple user equipments. The present disclosure envisages a system and method that facilitates reliable communication between multiple LTE compliant devices. The present disclosure also envisages a communication model which works independent of the conventional cellular network infrastructure. Further, the communication model envisaged by the present disclosure is comparatively less prone to interference. The present disclosure also aims to facilitate power savings in LTE complaint devices interconnected via a D2D communication link. Further, the present disclosure provides for larger volumes of data to be shared between LTE complaint devices using a direct communication link. Further, the present disclosure envisages a communication network supported by mobile radio network. The present disclosure also envisages an efficient network architecture that obviates the problem of network overloading.
[0046] The foregoing description of the specific embodiments would 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 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, those skilled in the art will recognize that the embodiments herein can be practiced with modifications. ,CLAIMS:1. A method for implementing a device-to-device (D2D) communication between a first mobile station and a second mobile station, said first mobile station controlled by a first network operator and said second mobile station controlled by a second network operator, said method comprising the following steps:
compiling a database of registration information for the first mobile station and the second mobile station, said registration information associating the first mobile station with the first network operator and the second mobile station with the second network operator, said registration information comprising preference of D2D communication over a normal communication and coordinate information corresponding to the first mobile station and the second mobile station;
receiving an enquiry from the first mobile station to establish a direct communication link with the second mobile station, wherein said enquiry comprises coordinate information corresponding to the first mobile station;
analyzing the coordinate information corresponding to the first mobile station and the coordinate information corresponding to the second mobile station;
determining, based at least on the coordinate information corresponding to the first mobile station and the second mobile station, whether the direct connection can be established between the first mobile station and second mobile station;
determining an operating frequency of the first mobile station, only in the event that the direct communication link is determined to be established between the first mobile station and second mobile station, and transmitting control information from the first mobile station onto the second mobile station over determined operating frequency; and
triggering the second mobile station to identify and compare operating frequencies offered by the first network operator and second network operator, and establishing the direct communication link between the first mobile station and second mobile station using at least one of the operating frequencies of the first network operator and second network operator.
2. The method as claimed in claim 1, wherein the first network operator is different from the second network operator.
3. The method as claimed in claim 1, wherein the coordinate information comprises information corresponding to latitude and longitude of the first mobile station and second mobile station.
4. The method as claimed in claim 1, wherein the step of determining an operating frequency of the first mobile station further includes the step of configuring the first mobile station as a master and configuring the second mobile station to be a slave, in order to transmit control information from the first mobile station to the second mobile station.
5. The method as claimed in claim 1, wherein the step of establishing the direct connection between the first mobile station and second mobile station using at least one of the operating frequencies of the first network operator and second network operator, further includes the step of selecting an operating frequency having lowest interference among the operating frequencies of the first network operator and second network operator.
6. The method as claimed in claim 1, wherein the method further includes the step of enabling the first mobile station and second mobile station to initiate a device-to-device call subsequent to establishing the direct connection between the first mobile station and second mobile station.
7. The method as claimed in claim 1, wherein the step of determining whether the direct connection can be established between the first mobile station and second mobile station, further includes the step of checking whether the registration information comprises D2D communication preference over a normal connection between the first mobile station and second mobile station.
8. The method as claimed in claim 1, wherein the step of establishing the direct connection between the first mobile station and second mobile station, further includes the step of establishing the direct connection using a frequency selected from a group of frequencies predetermined for the device-to-device (D2D) call based on at least the location of and proximity between the first mobile station and second mobile station.
9. The method as claimed in claim 1, wherein the method further includes the step of equipping the first mobile station and second mobile station with at least two phase locked loops (PLL), based on the operating frequencies corresponding to the first network operator and second network operator.
10. A system for implementing a device-to-device (D2D) communication between a first mobile station and a second mobile station, said first mobile station controlled by a first network operator and said second mobile station controlled by a second network operator, said system configured to :
compile a database of registration information for the first mobile station and the second mobile station, said registration information associating the first mobile station with the first network operator and the second mobile station with the second network operator, said registration information comprising preference of D2D communication over a normal communication and coordinate information corresponding to the first mobile station and the second mobile station;
receive an enquiry from the first mobile station to establish a direct communication link with the second mobile station, wherein said enquiry comprises coordinate information corresponding to the first mobile station;
analyze the coordinate information corresponding to the first mobile station and the coordinate information corresponding to the second mobile station;
determine, based at least on the coordinate information corresponding to the first mobile station and the second mobile station, whether the direct connection can be established between the first mobile station and second mobile station;
determine an operating frequency of the first mobile station, only in the event that the direct communication link is determined to be established between the first mobile station and second mobile station, and transmit control information from the first mobile station onto the second mobile station over determined operating frequency; and
trigger the second mobile station to identify and compare operating frequencies offered by the first network operator and second network operator, and establish the direct communication link between the first mobile station and second mobile station using at least one of the operating frequencies of the first network operator and second network operator.