Method for device to device communication and control node using the same

The present disclosure proposes a method for device to device (D2D) communication. The method includes the step of receiving from the first device a first callee identification (ID) as the first device is handed over to the control node, searching for the second device having a second callee ID in response to receiving from the first device the first callee ID, determining that the second device has been found includes when the first callee ID is identical to the second callee ID, and arranging for the D2D communication between the first device and the second device in response to the second device is found when a first condition is fulfilled, wherein the first condition is fulfilled at least includes the second device has been found when the first callee ID is identical to the second callee ID.

TECHNICAL FIELD

The present disclosure generally relates to a method for device to device communication and a control node using the same.

BACKGROUND

Wireless technologies have brought about conveniences and benefits to many people's daily lives as devices such as cell phones, notebooks, and tablet PCs, have enabled users to communicate with each other from just about any location and to make resources on the internet more easily accessible. Among various wireless technologies, Device-to-Device (D2D) communication has drawn more and more attention since D2D communication, unlike the traditional cellular communication system, does not require information exchanges to always pass through a base station and a core network upon transmission as users communicating in a D2D mode could make direct link establishment and transmission between devices.

While a conventional cellular communication requires resources allocated for both uplink (UL) and downlink (DL), D2D communication could only require resources allocated for a direct link. Also for a convention cellular system, resources are dedicated to a device within the coverage of a cell for a particular point in time; whereas for D2D communication, resources could be allocated to different pairs of devices at a particular point in time as long as each pair of devices would cause no interferences between other pairs of devices engaging in D2D communication.

Since a conventional cellular communication system requires a base station to deliver UL and DL data from one device to another while D2D communication has one direct link, D2D communication would result in less data transmission overall. In a conventional cellular communication system, there would be uplink and downlink radio links transmission delay as well as the transmission delay in the core network and even other networks. However, in D2D communication, only one radio link transmission delay would exist normally.

Because of the improved resource utilization and the reduced transmission delay in D2D communication as previous mentioned, both network providers and consumers would benefit from D2D communication. Efficient resource utilization in D2D communication could translate to more users served by the network providers, and the benefit of having less round trip delay could include uninterrupted conversations and more pleasant feelings during a conversation.

Methods of D2D connection establishment could be roughly divided into two categories. One category would be to establish D2D connections by devices themselves, and the other category is to establish D2D connections with the assistance of a network. For the former category, one device may send a signal to detect neighboring devices, and then a nearby device may receive the detection signal. After device synchronizations and coordination are finished, devices may communicate with each other directly, and thus D2D communication is established by devices themselves. As for the latter category, devices would synchronize with each other with the help of the network, or otherwise the devices could also synchronize with each other by using default parameters or by negotiating parameters agreeable to both devices through the network. Once the network assisted synchronization and coordination is finished, a direct communication between devices could be performed under the guidance of the network.

Unlike a conventional cellular communication system in which devices could communicate regardless of the distances between them, D2D communication would less likely allow communications over long distances. For this reason, the aforementioned D2D connection establishment method may require a device to possess a foreknowledge of the presence of other devices nearby as well as explicit indications as to whether these devices have activated their D2D communication capabilities. Otherwise, a blind initiation to attempt D2D communications would not only consume the battery power of the device itself but also waste radio resources of the network. Therefore, when one wants to communicate with another user without knowing the proximity of such user, the person usually would make a normal call through the conventional cellular communication means. However, in many situations, people could practically be right by each other but at the same time not being aware of such fact and thus may dial another user in proximity through the conventional cellular communication means without taking D2D communication.

A method has to be proposed for a device to automatically perform D2D communication if such capability exists and is activated in the device without making mandatory the foreknowledge of the proximities of other devices or the explicit indications for whether other devices and would be capable and willing to participate in D2D communications.

SUMMARY OF THE DISCLOSURE

Accordingly, the present disclosure is directed to a method for device to device (D2D) communication a base station using the same and a user equipment (UE) using the same.

The present disclosure directs to a method of device to device (D2D) communication, adapted for a control node to arrange D2D communication between a first device and a second device, wherein the first device undergoes a handover procedure to the first control node, and the method includes the step of receiving from the first device a first callee identification (ID) as the first device is handed over to the control node, searching for the second device having a second callee ID in response to receiving from the first device the first callee ID, determining that the second device has been found includes when the first callee ID is identical to the second callee ID, and arranging for the D2D communication between the first device and the second device in response to the second device is found when a first condition is fulfilled, wherein the first condition is fulfilled at least includes the second device has been found when the first callee ID is identical to the second callee ID.

The present disclosure directs to a control node comprising a transmitter and a receiver for respectively transmitting and receiving wireless data, a storage medium for storing information of at least a first device and a second device, and a processing circuit coupled to the transmitter, the receiver, and the storage medium and is configured for executing the functions of receiving from the first device a first callee identification (ID) as the first device is handed over to the control node, searching for the second device having a second callee ID in response to receiving from the first device the first callee ID, determining that the second device has been found includes when the first callee ID is identical to the second callee ID, and arranging for the D2D communication between the first device and the second device in response to the second device is found when a first condition is fulfilled, wherein the first condition is fulfilled at least includes the second device has been found when the first callee ID is identical to the second callee ID.

In order to make the aforementioned features of the present disclosure comprehensible, preferred embodiments accompanied with figures are described in detail below. It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

In this disclosure, 3GPP-like keywords or phrases are used merely as examples to present inventive concepts in accordance with the present disclosure; however, the same concept presented in the disclosure can be applied to any other systems such as IEEE 802.11, IEEE 802.16, WiMAX, and so like by persons of ordinarily skilled in the art.

A control node in this disclosure would be referred to as a base station (BS) or an eNB. It should be noted that the references of such are merely exemplary and therefore do not serve as limitations to the type of control nodes as it would be apparent to those skilled in the art that other types of control node could be selected to achieve network control purposes such as an advanced base station (ABS), a base transceiver system (BTS), an access point, a home base station, a relay station, a repeater, an intermediate node, an intermediary, and/or satellite-based communication base stations.

The control node may also be referred to entities such as a Mobility Management Entity (MME), a Serving Gateway (S-GW), a Packet Data Network Gateway (PDN-GW), a Serving GPRS Support Node (SGSN), a Gateway GPRS Support Node (GGSN), a Mobile Switching Center (MSC), and a Home Subscriber Server (HSS) or a node maintaining a database related to subscriber information.

From the hardware perspective, a control node may also be referred to as an apparatus including at least but not limited to a transmitter circuit, a receiver circuit, an analog-to-digital (A/D) converter, a digital-to-analog (D/A) converter, a processing circuit, one or more antenna units, and optionally a storage medium. The transmitter and the receiver transmit downlink signals and receive uplink signals wirelessly. The receiver may include functional elements to perform operations such as low noise amplifying, impedance matching, frequency mixing, down frequency conversion, filtering, amplifying, and so forth. The transmitter may include function elements to perform operations such as amplifying, impedance matching, frequency mixing, up frequency conversion, filtering, power amplifying, and so forth. The analog-to-digital (A/D) or the digital-to-analog (D/A) converter is configured to convert from an analog signal format to a digital signal format during uplink signal processing and from a digital signal format to an analog signal format during downlink signal processing.

The processing circuit is configured to process digital signal and to perform procedures related to the proposed method in accordance with exemplary embodiments of the present disclosure. Also, the processing circuit may optionally be coupled to a memory circuit to store programming codes, device configurations, a codebook, buffered or permanent data, and etc. The functions of the processing circuit may be implemented using programmable units such as a micro-processor, a micro-controller, a DSP chips, FPGA, etc. The functions of the processing circuit may also be implemented with separate electronic devices or ICs, and the processing circuit may also be implemented with either hardware or software.

The term “user equipment” (UE) in this disclosure could represent various embodiments which for example could include but not limited to a mobile station, an advanced mobile station (AMS), a server, a client, a desktop computer, a laptop computer, a network computer, a workstation, a personal digital assistant (PDA), a tablet personal computer (PC), a scanner, a telephone device, a pager, a camera, a television, a hand-held video game device, a musical device, a wireless sensor, and so like. In some applications, a UE may be a fixed computer device operating in a mobile environment, such as a bus, train, an airplane, a boat, a car, and so forth.

From the hardware perspective, a UE may also be referred to as an apparatus which includes at least but not limited to a transmitter circuit, a receiver circuit, an analog-to-digital (A/D) converter, a digital-to-analog (D/A) converter, a processing circuit, one ore more antenna units, and optionally a memory circuit. The memory circuit may store programming codes, device configurations, buffered or permanent data, codebooks, and etc. The processing circuit may also be implemented with either hardware or software. The function of each element of a UE is similar to a control node and therefore detailed descriptions for each element will not be repeated.

FIG. 1Aillustrates a concept of path switching in a non mobile scenario in accordance with one of the exemplary embodiments of the present disclosure. After UE1102and UE2103establish network authorizations from a communication system through the eNB101, the communication. The communication system would be capable of selecting the data traffic session of the UE1102and UE2103between a conventional infrastructure path106and a D2D Communication path105. In the conventional infrastructure path106, UE1102and UE103exchange data through a network as and the eNB101delivers the data exchanges in between. In the D2D communication path105, UE1102and UE2103exchange data directly with minimal interaction with the eNB101.

One of the purposes of the present disclosure is for the users (e.g. UE1102UE2103) to not perceive the switching of data traffic sessions between the D2D communication path and infrastructure path as the establishment of the data traffic sessions as well as the transition between the paths are performed automatically and under the control of the network. However, it also should be noted that users in general may have options of activating and deactivating D2D communication at will. In the case that should a user chooses to deactivate D2D communication, the data traffic session would be conducted through the conventional infrastructure path106.

FIG. 1Billustrates in accordance with the present disclosure an exemplary communication network100in which the network provides wireless services to a plurality of UEs110a˜110fthrough control nodes120a120bin a scenario without device mobility. It should be noted that the numbers of devices and their exact arrangements forFIG. 1Band for the remaining figures, if applicable, are merely exemplary and are not construed as limitations as a person skilled in the art could alter the quantities and the exactly arrangement in accordance with the spirit of the present disclosure. Control nodes120aand120bin the wireless network100may each serve a number of devices (i.e. control node120aserves UE110a˜110d, and control node120bserves UE110e˜f). UE110aand UE110bcould establish an intra-eNB D2D communication under the eNB120a, and UE110cand110ecould communicate across two eNBs120a102b. In both cases, the UEs110a-110band110c-110fwhich engage in D2D communication would not actually perceive that the communication is actually D2D as the switching of data traffic sessions is controlled automatically by the network100. One of the proposes of the present disclosure is to propose a method to automatically perform D2D communication when users make calls or other service requests in close proximity or in radio range with other users.

FIG. 2Ais a flow chart illustrating the process for automatic D2D communication trigger in accordance with one of the exemplary embodiments of the present disclosure. For an exemplary purpose,FIG. 2Ashows an interaction among a caller UE102, a callee UE103, a control node101, and a network104. It is assumed inFIG. 2Athat the UE102and the UE103are served by the same control node101. In general, when a UE wants to communicate with at least one other UE, these UEs would be attached to a network through a base station. The network could then decide whether to arrange the subsequent communication according to a conventional cellular communication procedure or to implement the proposed D2D method including variants of the proposed D2D method. Assuming that the caller UE102calls the callee UE103, the D2D communication could be implemented according to an exemplary embodiment as follows.

In step S201, the caller UE102performs a connection setup procedure by transmitting data which may include a connection establishment cause (i.e. mobile originating call (MO)) and a D2D identification (ID) of the callee UE103. The data with the establishment cause and the D2D ID could be an independent message or could be embedded in a message intended for other purposes. In step S202, in response to the connection setup procedure of S201being performed, the control node101would then store the connection establishment causes indicating MO and the D2D ID of the callee UE103and link these information with the caller UE102. After the connection between the caller UE102and the control node101have been established, the caller UE102would use the connection to send a service request of the UE102to the network104. The service request could be routed through other network nodes before arriving at the control node101. In step S203, the service request routing is made as the authorization for network and spectrum usage is performed, and upon granting of the service request, the network104would transmit to the control node101data including information related to authorization and resource allocation. In response to step S203, assuming that the service request routing has been successful, in step S204the control node101would inform (e.g. paging) the callee UE103that the call UE103has a call coming.

The callee UE103would connect to the network104through the control node101in order to respond, and hence in step S205, the callee UE103establishes a connection with the control node101in order to respond to the request. During the connection establishment of the callee UE103in step S205, the callee UE103would send the D2D ID of the callee UE103and an establishment cause (e.g. mobile terminating access (MT)) to the control node101either through an independent message or by embedding the D2D ID of the callee UE103and the establishment cause in a message intended for another purpose. In step S206, in response to connection setup procedure with the UE103being performed, the control node101stores the information include the establishment cause (e.g. MT) and the D2D ID of the callee UE103and links the information with the callee UE103. In step S207, the control node101searches among stored information of the control node101to locate a device with an establishment cause indicating a caller (e.g. mobile originating) and a corresponding D2D ID which is the ID of the callee103. After the caller UE102is found by the control node101, the control node101would then automatically arrange for a D2D communication between the caller UE102and the callee UE103.

FIG. 2Billustrates the automatic D2D triggering procedure from the view point of the control node101. In step S251, the control node101receives a callee D2D ID during a connection establishment setup. In step S252, the control node101stores the callee D2D ID and links the stored callee D2D ID with the caller UE102. In step S253, in response to a service request routing to the network104being complete, the control node101pages the callee UE103which establishes a connection setup with the control node101. In step S254, the control node101receives the callee D2D ID from the callee103, finds the caller with the callee D2D ID from the stored information of the control node101, and then determine whether D2D could be triggered between the caller102and the callee103and triggers the D2D communication in step S255if the control node101could do so.

In general, a control node could search its database to trigger D2D communications in different ways. The control node may search its database when it receives a callee ID from a device and the device is a callee. Also, a control node may search its database every time it receives a callee ID from a device.

It should be noted that in general the establishment cause sent from a device to a control node would inform the control node that whether the device is a caller or callee in order for the control node to have the necessary information to couple between a caller and a callee. Therefore, a person of ordinary skills in the art may apply any format or value for the establishment cause as long as the establishment indicates whether a device is a caller or a callee.

Also the caller/callee mentioned herein may be a phone call requester/responder or a Packet-Switch (PS) service requester/responder or a Circuit-Switch (CS) service requester/responder or other service requester/responder.

FIG. 2Cillustrates automatic D2D communication trigger for specific connections in accordance with one of the exemplary embodiments of the present disclosure. The procedure ofFIG. 2Cis similar to the procedure ofFIG. 2Aexcept for the connection ID which is not present inFIG. 2A.

In step S251, the caller UE102performs a connection setup procedure by transmitting data which may include a MO and a D2D ID of the callee UE103. The data with the establishment cause and the D2D ID could be an independent message or could be embedded in a message intended for other purposes. In step S252, in response to the connection setup procedure of S251being performed, the control node101stores the MO connection establishment cause and the D2D ID of the callee UE103, and the control node101links these information with a connection ID of caller UE102. After the connection between the caller UE102and the control node101have been established, the caller UE102in step S253uses the connection to send the service request of the UE102to the network104. In response to step S253, assuming that the service request routing has been successful; in step S254the control node101would page the callee UE103for an incoming call. The callee UE103would connect to the network104through the control node101in order to respond, and hence in step S255, the callee UE103establishes a connection with the control node101in order to respond to the request. During the connection establishment of the callee UE103in step S256, the callee UE103would send the D2D ID of the callee UE103and an establishment cause (e.g. mobile terminating access (MT)) to the control node101either through an independent message or through embedded a message intended for another purpose. In step S256, in response to a connection setup procedure between the eNB101and the UE103being performed, the control node101stores the information including the MT and the D2D ID of the callee UE103and links these information with the connection ID of the callee UE103.

Next, in step S257, the control node101searches among stored information of the control node101to locate a device with an establishment cause indicating a caller (e.g. mobile originating) and a corresponding D2D ID which is the ID of the callee103. As the caller UE102being found by the control node101, the control node101would then automatically arrange for a D2D communication between the caller UE102and the callee UE103as the arrangement is only for a specific connection. In this way, it is not necessary for UE102and UE103to communicate in D2D mode for all of their connections. While the eNB101may arrange D2D communication for some connection establishment types, other connection establishment types may be arranged through non D2D related means such as the cellular system.

The connection establishment herein may be a control signalling connection establishment or a data connection establishment or a logical connection establishment or an other network layer connection establishment. Moreover, the control signalling connection establishment may be LTE signalling radio bearer (SRB) setup. The data connection setup may be LTE dedicated radio bearer (DRB) setup or LTE EPS bearer setup. The connection establishment may also be application connection setup, such as Session Initiation Protocol (SIP) connection setup.

In one exemplary embodiment, a caller device would send a callee ID only when caller device supports D2D communication, and therefore the sending of the callee ID may implicitly indicates that whether a caller device at that point in time supports D2D communication or not.

Although inFIG. 2A, the caller UE102and the callee UE103are served by the same control node101, it may also be served by different control nodes. In general when a caller UE and a callee UE are served by different control nodes, the control nodes may share stored information with each other through direct or indirect communications and thus could search not only the stored information but also the shared information among each other to find the caller and the callee devices. Thus, automatic D2D communication could still be performed even if two devices are served by different control nodes.

One application ofFIG. 2Cmay be applied to the current LTE or the current LTE-A system as illustrated byFIG. 3A-FIG. 3C.FIG. 3Ais a communication establishment procedure of a conventional LTE/LTEA system. Assuming that UE A calls UE B in a LTE/LTE-A network, a conventional communication procedure typically includes a radio link establishment procedure and a EPS bearer establishment procedure to establish UE A as an EPS bearer, and a service request routing procedure associated with UE A. A conventional communication procedure also typically include and a radio link establishment procedure and an EPS bearer establishment procedure to establish UE B as an EPS bearer, and a service request routing procedure associated with UE B.

FIG. 3Billustrates an intra-eNB D2D communication setup between a caller UE302, a callee UE303, and a control node301in accordance with one of the exemplary embodiments of the present disclosure. It is assumed that both the caller UE302and the callee UE303are serviced by the same network through the same eNB301. Similar to embodiment ofFIGS. 2A and 2B, the UE A initiates a communicate request by calling the eNB301, and the eNB301would then page the callee UE303to inform the callee UE303that it has been called. The eNB301may then facilitate the D2D communication between the caller UE302and the callee UE303.

FIG. 3Cillustrates implementing D2D communication in an existing LTE/LTE A system in accordance with one of the exemplary embodiments of the present disclosure. The exemplary embodiment ofFIG. 3Cis built upon a typical existing communication procedure such as the one inFIG. 3Aso that a complete overhaul of a communication system is not required to order to accommodate D2D communication in the existing LTE/LTE A system. The radio link establishment of UE A302could be implemented as followings. In step S311, the eNB301may broadcast or unicast system information to the caller UE A302which indicates that the communicate system supports D2D communication. In step S302, the eNB301transmits system information which indicates that the communication system supports D2D communication to the callee UE B303. Assuming that both UE A302and UE B303are in the RRC IDLE mode, UE A302would establish a RRC connection with the eNB301first by transmitting RRCConnectionRequest which includes a MO establishment cause. In step S313, the eNB301stores the MO and links the MO with the UE A302. After eNB301transmits the RRCConnectionSetup to UE A302, in step S314the UE A302may in response transmit the RRCConnectionSetupComplete which includes the D2D ID of the UE B303. After receiving the D2D ID of the UE B303, in step S315the eNB301stores the D2D ID of the UE B303and links the D2D ID of the UE B303with UE A302and the MO.

In another exemplary embodiment, the D2D ID of the UE B303does not necessarily need to be in RRCConnectionSetupComplete but could be embedded in another message. In another exemplary embodiment, the D2D ID of the UE A302could be sent along with the D2D ID of the UE B303. Also, it should be noted that the D2D ID of the UEs in general could be implemented based on a number of different options. For example the D2D ID could be cell radio network temporary identifier (C-RNTI). The D2D ID could also be an ID assigned by an application server external to the network. The D2D ID may also be the mobile station integrated services digital network number (MSISDN), IP address, international mobile subscriber identity (IMSI), or the composition SAE-temporary mobile subscriber identity (S-TMSI). A list of options are listed in Table 1 below:

After the RRC connection establishment of UE A302is complete, the EPS bearer establishment and the service request routing for UE A302proceed as the procedures inFIG. 3A. The request may be routed through other network nodes, such as S-GW, P-GW, etc., and then arrives at the eNB301which then informs UE B303that the UE B303is being called. The UE B303then establishes a RRC connection with eNB301in order to respond to the request. After serving the RRC connection request, the eNB301would in step S316store the RRC establishment cause (e.g. MT). Afterwards, the eNB301would respond by transmitting RRCConnection setup to the UE B303. The UE B303may in step S317transmit RRCConnectionSetupComplete which includes a D2D ID of the UE B303. In response to receiving the RRCConnectionSetupComplete, the eNB301in step S318may store the D2D ID of eNB301and link the D2D ID with the UE B303and MT. In another exemplary embodiment, the establishment cause (e.g. MT) or the D2D ID may also be embedded in a different message other than RRCConnectionSetupComplete or be sent as an independent message. In step S319, the eNB301then searches the stored information of the eNB301to find whether there is a device whose establishment cause indicates that it is a caller (e.g. mobile originating) and the corresponding ID (the callee ID) is the ID of the UE B303. The control node or eNB301will find that UE B303is just the device being sought and then would try to arrange for the D2D communication to automatically occur between UE A302and UE B303. And then, the EPS bearer setup for UE B303and the rest of the SIP procedure asFIG. 3Awould proceed.

The aforementioned embodiment ofFIG. 3Capplies to the circumstance when the caller UE A302and the callee UE B303are in the idle mode and thus are not RRC connected with the eNB301. Therefore, during the RRC connection process, the callee D2D ID is carried over to eNB301in order for the D2D communication to be automatically triggered. However, in the case that the caller UE A302is already in RRC connected mode and would like to initiate a phone call, a different embodiment could be required. For the case in which the UE A302is already in the RRC connected mode, the information necessary to trigger an automatic D2D communication could be carried in the radio bearer setup procedure.

FIG. 4Aillustrates a conventional communication procedure known by persons skilled in the art in a scenario in which UE A and UE B are already in RRC connected mode for LTE/LTE A. The conventional procedure would include a procedure to setup EPS bearer establishment for UE A and a procedure to setup EPS bearer establishment for UE B.

FIG. 4Billustrates D2D connection trigger by an eNB in a RRC connected scenario in accordance with one of the exemplary embodiments of the present disclosure. The exemplary embodiment ofFIG. 4Bcould be implemented in different ways and is built uponFIG. 4Aso that a complete overhaul of a communication system is not required to order to accommodate D2D communication in the existing LTE/LTE A system. Assuming that UE A402and UE B403are served by the same eNB401, the concept ofFIG. 3Bhere would also apply.

In step S401and S402, the eNB401respectively transmits to both UE A402and UE B403system information which would indicate that the communication system would support D2D mode of communication. When UE A402wants to communicate with UE B403and both of them are in the RRC connected mode, the UE A402would request to establish a radio/EPS bearer, which is an instance of a specific connection as previously described forFIG. 2C. During the radio/EPS bearer establishment of UE A402, the UE A402in step S403may send the ID of UE B403, the callee, and an establishment cause such as MO to the eNB401via either an independent RRC message or embedded in another RRC message such as the RRC UL Information Transfer as illustrated inFIG. 4B. When the eNB401receives the ID of UE B403and MO, the eNB401in step S404stores the MO establishment cause and ID of UE B403. The eNB401then sends RRCConnectionsReconfiguration which contains a dedicated radio bearer (DRB) ID for UE A402, and UE A402responds by transmitting RRCConnectionReconfigurationComplete. In step S405, the eNB401links these stored information to the dedicated radio bearer ID of UE A402.

During the radio/EPS bearer establishment of UE B403, UE B in step S406may send the D2D ID and the MT establishment cause to the eNB either through an independent RRC message or by embedding D2D ID and MT in another message such as UL Information Transfer. When the eNB401receives the D2D ID of the UE B403and the establishment cause, the MT, the eNB401in step S407stores the D2D ID of the UE B403and the establishment cause with UE B403. In step S408, eNB401links the stored information to the DRB ID of UE B403. Then, in step S409, the eNB401searches the stored information of the eNB401to find whether there is a UE with a radio bearer, and the establishment cause of the UE indicates that the UE is a caller (e.g. mobile originating) having transmitted a corresponding callee D2D ID which is the ID of the UE B403. When the eNB401have found the established radio bearer of UE A401, the eNB401would automatically try to perform D2D communication for the corresponding established radio bearers of UE A402and UE B403.

Although inFIG. 4B, the D2D ID of the UE B403is carried in a RRC message, RRC UL Information Transfer, the ID may also be carried in another message, e.g. RRCConnectionReconfigurationComplete, or another RRC message. Also in general, in addition to the callee D2D ID being transmitted, the caller D2D may also be transmitted by the caller UE so that eNB may have more information to perform a UE search and to check whether D2D could be performed.

WhileFIG. 3Cmay be applied to UEs in RRC idle mode,FIG. 4Bmay be applied to UEs in RRC connected mode. However, if one or both of the two UEs are originally in RRC idle mode, one or both UEs could enter RRC connected mode first and then apply the procedure inFIG. 4B.FIG. 4Cshows an example in which two UEs originally in the RRC idle mode would follow the radio link establishment procedure as illustrated inFIG. 4Cand enter RRC connected mode to perform the procedure ofFIG. 4B. In this way, the procedure ofFIG. 4Bmay also be applied to UEs in the RRC idle mode. Regardless whether candidate D2D UEs are in connected mode or in an idle mode, the callee D2D ID would be carried to an eNB the during radio bearer establishment for in order for the automatic D2D trigger to be arranged by the eNB.

For the circumstance in which the caller and the callee UEs are situated within each other's radio range but are served by two different eNBs, the existing LTE/LTE A system could be further modified to accommodate D2D communications for UEs served by different control nodes. One solution could be to adopt a MME for the role of a control node.FIG. 5Aillustrates intra-MME D2D communication in accordance with one of the exemplary embodiments of the present disclosure. In the exemplary scenario a UE502is served by the eNB504, and another UE503is served by the eNB505. Assuming that the UE502calls the UE503, a modification could be made to an existing LTE/LTE system such that the MME506could automatically arrange D2D communication based on information carried during specific connection establishments.FIG. 5Billustrates a conventional communication procedure for a normal call setup in connected cases when UEs are served by different eNBs. A proposed modification ofFIG. 5Bis illustrated byFIG. 5C, and an exemplary embodiment is proposed as follows.

Assuming that UE A502and UE B503are already in a RRC connected state. In step S501, the eNB A503which services UE A502transmits system information which would indicate that D2D communication is supported through a connection with eNB A504. Also in step S505, eNB B505would similarly transmit system information including an indication for D2D capability to UE B503. When the UE A502calls UE B503, the caller UE502may request to establish an EPS bearer, i.e. a specific connection. During the EPS bearer establishment of UE A502, in step S502, UE A502may send the D2D ID of UE B503and an establishment cause such as mobile originating to the MME506either through an individual NAS message or by embedding the D2D ID and the establishment cause in another NAS message such as NAS Bearer Resource Allocation Request. When the MME506receives the MO and D2D ID of UE B503, in step S503the MME506stores D2D ID of UE B503and the establishment cause. In step S504, the MME506links the stored D2D ID of UE B503and the establishment cause with UE A502and the established EPS bearer ID of UE A502.

Similarly, the callee UE503would request to establish an EPS bearer by following a similar procedure. During the EPS bearer establishment of the callee UE503, the callee UE503in step S506may send its D2D ID and an establishment cause such as MT to the MME506either through an individual NAS message or by embedding the D2D ID of UE B503and the establishment cause in another NAS message such as NAS Bearer Resource Allocation Request. When the MME506receives D2D ID of UE B503and the establishment cause, in step S507the MME506stores D2D ID of UE B503and the establishment cause. In step S508, the MME506and links the stored D2D ID of UE B503and the establishment cause (e.g. MT) with the callee UE503and the established EPS bearer ID of the callee UE506. Then, in step S509the MME506searches the stored information to find whether there is a UE with an EPS bearer which contains an establishment cause indicating that the UE is a caller (e.g. mobile originating) and the corresponding callee ID being the ID of the UE503. If such a UE and its EPS bearer are found and/or the two UEs502503are close to each other based on eNB and/or tracking area (TA) and/or other location information, the MME506would try to arrange D2D communication for the corresponding EPS bearers of UE502and UE503.

Although inFIG. 5C, the ID of UE B503is carried in a NAS message, NAS Bearer Resource Allocation Request, the ID of UE B503may also be carried in other modified messages by persons skilled in the art. Also, in addition to the callee ID being carried, the caller ID may also be carried in NAS messages or other messages to a MME so that the MME may have more information to perform UE searches and to check whether D2D could be performed at a later time.

Also similar toFIG. 4B,FIG. 5Cmay be applied when UEs in the RRC idle mode. If one or both of the two UEs are originally in RRC idle mode, the same concept asFIG. 4Ccould be applied so that they could enter RRC connected mode first and then apply procedures ofFIG. 5C. In this way, the procedure ofFIG. 5Cmay also be applied to UEs in the RRC idle mode. Also, it should be noted that the embodiment ofFIG. 5Ccould be applied regardless whether the UEs are served by the same eNB or by different eNBs.

BesidesFIG. 5C, in the case that UEs are served by different eNBs, there is another method to perform automatic D2D communication without directly involving a MME.FIG. 6Aillustrates Inter-eNB D2D communication in accordance with one of the exemplary embodiments of the present disclosure. InFIG. 6A, UE602is served by eNB604and UE603is served by eNB605. Assuming that UE602calls UE603, UE602would first establish a connection with eNB604and then use the connection to request services from the serving network. After service request is accomplished, the eNB605would page the UE603to inform that the UE603is being called by the UE602. One of the differences from previous embodiments is that two eNBs would coordinate between each other through an interface such as X2 interface to obtain necessary information to decide whether proper conditions exist to automatically trigger D2D connections.

A specific embodiment is shown inFIG. 6Bby illustrates D2D connection trigger by eNB coordination in accordance with one of the exemplary embodiments of the present disclosure. The procedures ofFIG. 6Bis similar toFIG. 4Bexcept that an eNB may query or/and share stored information, such as callee IDs, radio bearer IDs, and establishment causes with other eNBs either directly or indirectly through other nodes so that the eNB may search not only its own stored information but also the information stored by other eNBs through sharing.

In steps S601and S602, the eNB A604and eNB B605transmits system information which indicates that D2D mode of communication is supported by the serving network respectively to UE A602and UE B603. In step S603, UE A establishes a radio bearer by transmitting data such as UL Information Transfer which includes a MO and D2D ID of UE B603to eNB A604. In response to receiving UL Information Transfer, in step S604eNB A604stores the MO and D2D ID of UE B603and links such information with UE A603. Next, the eNB A exchanges RRC Connection Reconfiguration messages with UE A602and in step S605links the DRB ID of UE A602with the stored MO and the corresponding D2D ID of the UE B603.

In step S606UE B603also establishes a radio bearer by transmitting UL Information Transfer which includes a MT establishment cause and the D2D ID of the UE B603to eNB B605. In response to receiving the UL Information Transfer, in step S607the eNB B605stores the MT establishment cause and the D2D ID of the UE B603and links them with UE B603. After exchanges of RRC Connection Reconfiguration between eNB B605and UE B603, in step S608the eNB B605links the DRB ID of UE B603with the MT and the D2D ID of UE B603.

Next in step S609, the eNB B605searches for the calling UE from the stored information of eNB B605by looking for a UE having a MO establishment cause and a corresponding D2D ID being the D2D ID of the UE B603. However, such information would not be found by the eNB B605since they would not be stored in eNB B605but somewhere else in another eNB. In step S610, the eNB B transmits a query to other eNBs including eNB A604for a UE having a MO establishment cause and a corresponding D2D ID of the UE B603. In step S611, the eNB A604searches from its own stored information and locates the caller UE A602. In step S612, eNB A604transmits to eNB B605a query response through the X2 interface. In response to receiving the query response, in step S613the eNB A604and the eNB B605would attempt to arrange for D2D communication between UE A602and UE B603.

According to another embodiment, one variation for the embodiment ofFIG. 6Bis that the MO establishment cause and the D2D ID of the UE B603could be delivered through RRCConnectionReconfigurationComplete or another message. Also D2D ID of the UE A602could also be delivered along with the D2D ID of the UB B603. Also the D2D ID could be implemented based on other IDs as listed in Table 1.

The procedure ofFIG. 6Bwould allow some DRBs using D2D communication while other DRBs using non-D2D based cellular communications. Also a procedure similar toFIG. 4Ccould be applied so that the procedure ofFIG. 6Bcould be applied regardless whether the UEs are originally idle or connected.

FIG. 7Ais a flow chart illustrating proposed D2D communication method from the perspective of a caller. In step S701the caller transmits a callee ID and an establishment cause during connection setup. S702the caller receives a notification and/or related information to perform D2D communication. In step S703the caller perform D2D communication based on received information.

FIG. 7Bis a flow chart illustrating proposed D2D communication method from the perspective of a callee. In step S751, the callee transmits a callee ID and an establishment cause during a connection setup. In step S752, the callee receives a notification and/or related information to perform D2D communication. In step S753the callee perform D2D communication based on received information.

FIG. 7Cis a flow chart illustrating proposed D2D communication method from the perspective of a control node after the control has been informed by the network of an incoming call, and the control node pages a device accordingly. In step S761the control node receives a callee ID and an establishment cause of the device during a connection establishment. In step S762the control node stores the callee ID and the establishment cause of the device. In step S763if the establishment cause implies a callee, search for a candidate caller device linked with the received callee ID and has an establishment cause implying a caller. In step S764if such device is found, equating the found device as the caller and try to perform D2D communication between the found device and the device from which the callee ID and the establishment cause have been received from step S761.

FIG. 8Ais a flow chart illustrating proposed D2D communication method consistent withFIG. 2Cfor a specific connection type from the perspective of a control node after the control has been informed by the network of an incoming call, and the control node pages a device accordingly. In step S801, the control node receives a callee ID and an establishment cause of a device during a specific connection establishment. In step S802, the control node stores the callee ID and the establishment cause of the device and links them with the specific connection establishment. In step S803, if the establishment cause implies a callee, search for a device linked with a callee ID being the received callee ID from step S801and an establishment cause implying a caller. In step S804if such device is found, equating the found device as the caller and try to perform D2D communication between the found device for the specific connection and the device from which the callee ID and the establishment cause have been received back in step S801. The process ofFIG. 8Bis also consistent withFIGS. 4B, 5C and 6B.

FIG. 8Bis a flow chart illustrating proposed D2D communication method involving control nodes coordination from the perspective of a querying control node and is consistent with the embodiment ofFIG. 6B. In step S851the control node receives a callee ID and an establishment cause of a device during a specific connection establishment. In step S852the control node stores the callee ID and the establishment cause of the device and links them with the specific connection establishment. In step S853, if the establishment cause implies a callee, search for a device linked with a callee ID being the received callee ID from step S851and an establishment cause implying a caller. In step S854if the caller is not found, query other control nodes. In step S855, if such device is found from another control node, equating the found device as the caller and try to perform D2D communication between the found device for the specific connection and the device from which the callee ID and the establishment cause have been received back in step S851by coordinating with the another control node.

FIG. 8Cis a flow chart illustrating proposed D2D communication method involving control nodes coordination from the perspective of a queried control node and is consistent with the embodiment ofFIG. 6B. In step S861the control node receives a callee ID queried by another querying control node. In step S862the queried control node search from its own stored information for a device having an establishment cause implying a caller and a corresponding callee ID linked with the received callee ID. In step S863, if the caller is found, the control node notifies the querying control node of the found device and share related information of the found device. In step S864, the queried control node coordinates with the querying control node to perform D2D communication between the found caller and the callee under the querying control node.

As for circumstances involving device mobility, please refer to the scenario ofFIG. 9which illustrates a general concept in a case when automatic D2D communication could be triggered after one device approaches the other device because of device mobility. For the scenario ofFIG. 9, assuming that UE911is served under eNB901, UE912is served under UE902, and eNB901and eNB902could be in communication of each other across an established interface. In response to UE911approaching UE912, based on the method of the present disclosure, the network could automatically arrange UE911to engage in D2D mode of communication with UE912after a certain condition(s) has been met, or the network could stay with the conventional cellular communication procedure if the certain condition (s) is lacking or because of other reasons. The present disclosure may apply to cases when UE911and UE912are served under the same eNB. The present disclosure may also apply to cases when eNB901and eNB902are each served by different NAS control nodes such as different MMEs.

In should be noted that for the present disclosure, a pair of UEs such as a caller and a callee, namely, UE911and UE912, could already be in cellular conversation, but after the migration of either the caller UE or the callee UE, the network could automatically arrange for D2D communication between UE911and UE912when these UE pair are within the radio range of each other and thus could communicate directly with each other or when other conditions are also fulfilled such as the channel quality between the UE pair is adequate. One of the features of the present disclosure is that upon the migration of devices the network could automatically arrange for the D2D communication to occur without the awareness or the explicit willingness of the UE devices such that the user could benefit from the convenience of the automatic D2D arrangement from the network without experiencing interruptions or inconsistencies of the network service even though the user may migrate from one control node to another. Also, signalling overhead could be reduced due to ordinary procedures being used for both D2D communication and conventional cellular communication and the simplification of the communication paths of the D2D communication.

Also it should be noted that even though the present disclosure proposes embodiments to switch from the conventional cellular communication to D2D mode of communication upon device mobility, it should be apparent to one skilled in the art that the network could also switch from D2D communication to the conventional cellular communication due to reasons such as device mobility, the change of channel conditions, and etc.

FIG. 10Aillustrates the D2D communication method with device mobility in a wireless communication network in accordance with the present disclosure. In the wireless network, UE A1011is served under control node A1001and UE B1012is served under control node B1002, and control node A1001is assumed to be in communication with control node B1002but could also be idle. Control node A and control node B could also communicate with the network through another control node(s) such as a MME, a gateway, an IP multimedia subsystem (IMS), or another network entity in the non access stratum (NAS) layer. Assuming in this exemplary scenario that UE A1011awhich is served under control node A1001migrates to another location in order to be served under control node B1002, the network would then automatically arrange UE A1011bto engage in D2D communication with UE B1012. During the migration of UE A1011, the handover procedure from the domain of control node A1001to the domain of control node B1002could be classified under three phases—a during measurement phase1021, a during handover phase1022, and an after handover phase1023.

FIG. 10Billustrates automatic D2D communication establishment procedure upon a caller device handover in accordance with one of the exemplary embodiments of the present disclosure. Referring toFIG. 10AandFIG. 10B, first, a connection setup between control node A1001and UE A1011is established in an optional step S1025during which UE A1011transmits a MO establishment cause and D2D ID of UE B1012to control node A1001. The control node A1001then links the MO and the D2D ID of UE B1012to UE A1011. Similarly, a connection setup between control node B1002and UE B1012is established in an optional step S1026during which UE B1012transmits a MT establishment cause and D2D ID of UE B1012to control node B1012. The control B1002then links the MT and the D2D ID of UE B1012to UE B1012. It should be noted that steps S1025and S1026are optional since UE A1011and UE B1012could already be in conversation with each other and hence connection setups are not required.

Next, the measurement phase1021commences as in step S1027control node A1001transmits to UE A1011a measurement configuration containing measurement instructions and parameters. In step S1028, UE A1011responds by transmitting a measurement report back to control node A1011. Steps S1027and S1028could be triggered upon potential handover situations such as when UE A1011is close to the edge of the radio range of the control node A1001.

Next, control node A1001has decided to handover UE A1011to control node B as necessitated by reasons such as movements of UE A, and the during handover phase1022would start in step S1031during which control node A1001would transmit a handover request to control node B1002. The handover request would contain UE A1011information including the MO establishment cause, D2D ID of UE B1012, and optionally the connection ID of UE A1011which have been previously linked with UE A1011. In step S1032, these information including the MO establishment cause, D2D ID of UE B1012, and optionally the connection ID of UE A1011are stored by control node B1002. In step1033, control node B searches for the corresponding device with the MT establishment cause, the D2D ID of UE B1012and/or the connection ID of the UE B1012. If such device has been found, the network would arrange the D2D communication between UE A1011and UE B1012after the during handover phase1022is complete. In step S1034, control node B1002would respond to the handover request from control node A1001by transmitting a handover request response to control A1001. In step S1035, control node A would transmit a handover command to UE A1011in order to handover the UE A1011to control node B1002. In step S1035, after the rest of the HO procedure has been completed, the after the handover phase1023would commence, and the network would automatically arrange D2D communication between UE A1011and UE B1012(for a specific connection) assuming that UE B1012has been found back in step S1033.

FIG. 10Cis flow chart illustrating the automatic D2D communication triggering process in general in accordance with one of the exemplary embodiments of the present disclosure. In step S1050, a callee D2D ID is transmitted from a first control node to a second control node during a measurement phase or a handover phase of an overall communication procedure. In step S1051, the second control node would store the callee D2D ID and links the information with the caller. In step S1052, a control node which could be an access stratum control node or a non access stratum control node searches for the callee and see if D2D communication could be triggered. In step S1053, the control node arranges the D2D communication between the caller and the callee (if appropriate condition(s) is met).

FIG. 11Aillustrates automatic D2D communication establishment after MT device handover in accordance with one of the exemplary embodiment of the present disclosure. The scenario ofFIG. 11Ais similar toFIG. 10Aexcept that UE B1012aor the callee device is the migrating device, and the control node B1002hands UE B1012ato the control A1001which would become the serving control node for the migrating UE B1012b.

FIG. 11Billustrates automatic D2D communication establishment procedure upon a callee device handover in accordance with one of the exemplary embodiments of the present disclosure.FIG. 11Bis similar to10B in the same wayFIG. 11Ais similar toFIG. 10A. After optional specific connection setups are complete, control node B in step S11011002would send a measurement configuration information to the migrating UE B1012, and the UE B1012in step S1102would respond by transmitting back a measurement report. In step S1103, the control node B1002would then send a handover request containing UE B1012information which includes the MT establishment cause, the D2D ID of UE B1012and optionally a connection ID of UE B1012to control node A1001. Upon receiving these information, control node A1001would in step S1104store the MT establishment cause, the D2D ID of UE B1012and optionally a connection ID of UE B1012and links these information with UE B1012. In step S1105, the control node A1101would search for a corresponding caller device linked to the establishment cause indicating MO, the D2D ID of the UE B1012, and the connection ID of the UEB1012. If such device is found, step S1107would proceed. Afterwards, in step S1106control node A would transmit back a handover command to control node B1002. After the rest of the handover procedures are complete, the network would in step S1107automatically arrange D2D communication between UE A1011and UE B1012(for a specific connection).

Even though in both scenarios ofFIG. 10AandFIG. 11Athat the caller and the callee devices during the after handover phase1023are served by the same control nodes, the automatic D2D communication could still be implemented if the caller and the callee devices during the after handover phase are served by different control nodes. In that case, the control nodes may share stored information with each other through direct or indirect communication so that the control nodes would not only search their own stored information but also would search shared information stored in other control nodes.

Suppose that steps S1035ofFIG. 10Band S1107ofFIG. 11Bare to be executed, a serving control node would executeFIG. 11Cto automatically arrange D2D communication between UE A1011and UEB1012as follows. In step S1121and S1123, the serving control node1001or1002would respectively transmit a channel measurement configuration to UE B1012and UE A1011. The measurement configuration may include parameters and instructions to estimate a channel between UE A1011and UE B1012. In steps S1122and S1124, the serving control node1001or1002would receive measurement reports may include channel measurement between UE A1011and UE B1012. In step S1125, the serving control node1001or1002would determine whether channel(s) between UE A1011and UE B1012is favorable or is better than their cellular channel(s), which is the channel(s) between UE A1011and the serving control node1001or1002and the channel(s) between UE B1012and the serving control node1001or1002. If the channel condition is favorable, then steps S1126-S1129would be executed. Otherwise, D2D communication may not be arranged. In steps S1126and S1127, the network would allocate D2D radio resources through the serving control node1001or1002to UE B1102and UE A1101respectively. In step S1128, UE A1011and UE B1012perform device synchronization with each other. In step S1129, UE A1011and UE B1012engage in D2D communication.

According to another variation similar toFIG. 10BandFIG. 11B, instead of arranging for automatic D2D communication establishment during the after handover phase1023, automatic D2D communication could also be arrange during the handover phase1022or during the measurement phase1021.FIG. 12Aillustrates automatic D2D communication establishment during a handover phase in accordance with one of the exemplary embodiments of the present disclosure. Assuming that UE A1011is the caller and is to be handed over from control node A1001to control node B1002. After the optional connection setup procedure for a specific connection in step S1201and after the measurement phase1021during which the measurements have been configured and performed in step S1202, in step S1203, control node A1001transmits a handover request including a MO establishment cause, the D2D ID of the callee device, and an optional connection ID of the callee device. In step S1204, these information are stored and linked with UE A1011. In step S1025, control node B searches from its database for the corresponding callee device having the MT establishment cause, the D2D ID of the UE B1012, and optionally the connection ID of UE B1012. If such device could be found, then control node A1001and control node B1002could first optionally coordinate to measure channels between UE A1011and UE B1012and/or between UE A1011and control node B1002, and then automatically arrange for D2D communication between UE A1011and UE B1012. After step S1205is completed, the rest of the HO procedure would proceed.

FIG. 12Billustrates automatic D2D communication establishment during a measurement phase in accordance with one of the exemplary embodiments of the present disclosure. It is assumed that control node A1001and control node B could share information with each other. After the optional connection setup between control node A1001and UE A1011is complete and/or the optional connection setup between control node B1002and UE B1012is complete, if UE A1011and UE B1012have been determined to be in communication and close to each other by the network, in step S1211control node A1001would configure UE A1011for a subsequent channel measurement, and in step S1212control node B would configure UE B for a subsequent channel measurement. Please note that steps1211and s1212may occur simultaneous or any one of the two steps could occur before the other.

In steps S1213and1215, control node A1001and control node B1002would respectively transmit a measurement configuration to UE A1011including the configuration to measure channel(s) between UE A1011and UE B1012and a measurement configuration to UE B1012including the configuration to measure channel(s) between UE A1011and UE B1012. In steps S1214and S1216, UE A1011and UE B1012would respectively transmit the channel(s) measurement report to control node A1001and control node B1002. It should be noted that the steps S1215˜S1216could precede steps S1213˜S1214. In step S1217, control node A1001and control node B1002could share measurement result received from steps S1214and S1216. In step S1218, if UE A1011and UE B1012could be found to be in communication with each other and the channel(s) between them are good enough or are better than their cellular channels, then control node A1001and control node B1002would coordinate D2D communication between UE A1011and UE B1012(for a specific connection type) separately or cooperatively without waiting for the during handover phase1022to begin. If control node A1001or control node B arranges the D2D communication separately, the procedure ofFIG. 11Cwould be used to arrange for the automatic D2D communication.

If however, control node A1001and Control Node B1002arranges the D2D communication cooperatively, the procedure ofFIG. 12Ccould be used to realize automatic D2D communication. In step S1251, control node A1001and control node B1002coordinate with each other to determine resource allocation, parameters negotiation, etc. In step S1252, control node A1001would transmit resource allocation to UE A1011, and similarly in step S1253, control node B1002would also transmit resource allocation to UE B1012. In step S1254, UE A1011and UE B1012would perform device synchronization. In step S1255, UE A1011and UE B1012would engage in D2D communication. It should be noted that device synchronization between UE A1011and UE B1012could be performed before steps S1251˜S1253.

Besides triggering automatic D2D communication during different occasions, device information search and mapping for automatic D2D communication establishment may be triggered by a message from different nodes.FIGS. 13A˜13F propose device information search for automatic D2D communication establishment triggered by messages from a device, a control node, or a NAS control node.

FIG. 13A&FIG. 13Billustrate triggering automatic D2D communication by a device message. In the network scenario ofFIG. 13A, UE A1011ais to be handed over from control node A1001to control node B1002. When UE A1011bis handed over to control node B1002, control node B arranges for automatic D2D communication between UE A1011band UE B1012. Please note that1011aand1011brefers to two different states of the same UE1011, and UE A1011abecomes1011bafter being handed over. The same notation would also apply for all the embodiments. The triangle ofFIG. 13Abetween the path of UE A1011band control node B1002signifies that UE A1011bwould transmit specific information during one of the stages of the handover process which would result in the potential D2D communication trigger. The star ofFIG. 13Asignifies that control node B1002would initiate the arrangement for D2D communication to occur after certain information has been received from UE A1011b.

FIG. 13Bfurther illustrates the device triggering event by UE A1011for the network scenario ofFIG. 13A. In step S1301, UE A1011sends a handover command response which includes the MO establishment cause, the D2D ID of UE B1012, and optionally the connection ID to control node B1002. Control node B1002then in step S1302stores these information and links them with UE A1011. In step S1303, by receiving the information related to the MO establishment cause, the D2D ID of UE B1012, and optionally the connection ID, the event of step S1301triggers a search for the corresponding device with the MT establishment cause, the D2D ID of the UE B1012, and optionally a connection with UE B1012. When such device is found, automatic D2D communication would be arranged between UE A1011and UE B1012(for a specific connection type). For this exemplary embodiment, the specific information which would result in the potential D2D communication trigger is the information transmitted during step S1301including the MO establishment cause, the D2D ID of UE B1012, and optionally the RB ID. Upon receiving these specific information, control node B1002would initiate the process to perform D2D communication.

FIG. 13C&FIG. 13Dillustrate triggering automatic D2D communication by a control node message. The network scenario ofFIG. 13Cis similar toFIG. 13Aexcept that control node A1001and control B1002are connected to a NAS control node1350which could be a MME for example. In response to UE A1011btransmitting specific information to control node B1002, the control node B would store these information and initiates D2D communication to be arranged based on a certain condition(s).

FIG. 13Dillustrates the D2D triggering event by a control node message for the network scenario ofFIG. 13A. In step S1311, UE A1011and UE B1012establish connection setup with control node A1001, control node B1002, and the NAS control node1350. In step S1312, UE A1011ais handed over from control node A1001to control node B1002. In step S1313, when control node A1001hands over UE A1011to control node B1002, control node A sends UE A1011linked information, such as the MO establishment cause, D2D ID of UE B1012(and connection ID) to NAS control node1350and therefore trigger device search and mapping in NAS control node1350for automatic D2D communication establishment. If such device could be found, the NAS control node1350may check further whether UE A1011and the found device which is UE B1012, would be close enough to each other. Assuming so, D2D communication would be automatically arranged between UE A1011band UE B1012(for the specific connections). Therefore, the transmitting of specific information in step S1301would cause the control node B to store these information and performing searches for the corresponding MT device. When such device is found, the finding of such device could be one of the conditions to trigger the control node B to initiate for the D2D communication to be arranged.

FIG. 13E&FIG. 13Fillustrate triggering automatic D2D communication by a NAS control node message. The network scenario ofFIG. 13Eis similar toFIG. 13Cexcept that control node A1001is connected to NAS control node A1351, and control B1002is connected to a NAS control node B1352. When NAS control node A1351such as MME A (not shown) transmits specific information, it would potentially trigger an automatic D2D communication to be initiated by NAS Control Node B1352.

FIG. 13Fillustrates the D2D triggering event by a NAS control node message for the network scenario ofFIG. 13E. In step S1321, UE A1011establishes connection setup with control node A1001and NAS control node A1351, and UE B establishes connection setup with control node B1002and NAS control node B1352. In step S1322, during the during handover phase1022when control nodes perform handover for UE A1011, NAS control node A1351would send information linked with UE A1011a, such as the MO establishment cause and the D2D ID of UE B1012(and optionally connection ID) to NAS control node B1352and therefore trigger device search and mapping in NAS control node B1352required for the subsequent automatic D2D communication establishment in step S1324. In step S1323, the information linked with UE A1011awould be stored by NAS control node B1352. In step S1324, if the corresponding device which would have been in communication with UE A1011bis found, then the NAS control center node B1352would further determine whether UE A1011band the found device UE B1012would be close enough to each other. If UE A1011band UE B1012would be close enough to each other, automatic D2D communication between UE A1011band UE B1012would be arranged (for the specific connections).

The aforementioned disclosure involving device mobility could be embodied in the current LTE/LTE A system in various ways. One such embodiment could be to implement automatic D2D communication establishment by eNB upon X2-based handover of a MO UE.FIG. 14Aillustrates a X2 handover protocol involving a source eNB handing over a UE to a target eNB across the X2 interface, and the protocol is currently known in the art. Please note that the current disclosure is built upon the existing X2-based handover protocol such as a complete overhaul is not needed in order to accommodate D2D communication in the current system.

FIG. 14Billustrates an eNB controlled automatic D2D trigger after a handover across the X2 interface. In the scenario ofFIG. 14B, it is assumed that UE A1011is served by eNB1012, UE B1012is served by eNB B1002and UE A1011, and UEA1011is to be handed over from eNB A1001to eNB B1002because of device mobility. In step S1401, as UE A1011intends to communicate with UE B1012, UE A1011may first complete a radio bearer setup procedure during which UE A1011transmits a MO establishment cause and the D2D ID of UE B1012to eNB A1001either through an independent message or embedded in a message for another purpose. Upon receiving the message, the eNB A1001stores the MO establishment cause, the D2D ID of UE B1012, and/or the established radio bearer ID of UE A1011and links these information with UE A1011. Similarly, also in step S1401, the UE B1012may also complete a radio bearer setup procedure during which UE B1012transmits a MT establishment cause and the D2D ID of UE B1012to eNB B1002either through an independent message or embedded in a message for another purpose. Upon receiving the message, the eNB A1001stores the MT establishment cause, the D2D ID of UE B1012, and/or the established radio bearer ID of UE B1012and links these information with UE B1012. In step S1402, eNB A1001transmits the channel measure parameters to UE A1011, and UE A1011responds with the channel measurement report for the channel between UE A1011and eNB B1002.

Assuming that the channel measurement report is favorable or that a handover has been decided for another reason, the eNB A1001then hands over UE A1011to eNB B1002across the X2-based interface which includes procedures similar toFIG. 14A. In step S1403, the eNB A1001sends the stored UE A information to eNB B1002either through an independent message or by embedded the stored information in a message intended for another purpose, such as the handover request message. The stored information sent from eNB A1001to eNB B1002may include the MO establishment cause, the D2D ID of UE B1012, and the radio bearer ID of UE A1011. Upon receiving the stored information of UE A1011, eNB B1002searches from its own stored information or under its own domain to find whether there exists another device (with a radio bearer) whose establishment cause indicates that it is a callee (e.g. MT) and the corresponding ID (the callee ID) is the D2D ID of UE B1012. Assuming that eNB B1002is able to find such a device which in this case is UE B1012, the eNB1002would subsequently then try to arrange D2D communication for the corresponding established radio bearers of UE A and UE B in step S1409after the handover procedures have been complete. But before the handover procedures could be completed, in step S1407, eNB A1001transmits a RRC connection reconfiguration message, and in step S1408, UE A1011responds with the RRC connection reconfiguration complete message. Afterwards, the rest of the HO procedures similar toFIG. 14Awould be executed, and then the D2D communications between UE A1011and UE B1012would be arranged by the network in step S1409.

Even though the embodiment ofFIG. 14Bis an implementation of automatic D2D communication establishment by an eNB upon a X2-based handover of a caller or MO UE, a similar procedure could also be applied for a scenario similar toFIG. 11Awhich involves a callee or MT UE handover. Since the exact procedure could be readily apparent based on the combination ofFIGS. 11A and 14Bfor a person skilled in the art, the details would not be described further. Furthermore, according to one exemplary embodiment, the D2D ID of UE A1011may also be carried during connection establishment of step S1401so that eNB B1002may have more information to perform a UE search and to determine whether D2D could be arranged after the handover procedures are complete.

FIG. 15illustrates another exemplary embodiment of an eNB controlled automatic D2D trigger after a handover across the X2 interface. In this case, the information sent from one control node to another control node could be delivered over another message such as RRCConnectionReconfigurationComplete. Assuming that the circumstance ofFIG. 15is similarFIG. 14B, in step S1501, UE A1011transmits the caller indicator (e.g. MO establishment cause), the D2D ID of UE B1012, and the radio bearer ID of UE A1011to eNB B1002over the RRCConnectionReconfigurationComplete message. In step S1502, eNB B1002upon receiving these information stores them and link them with UE A1011. In step S1503, the eNB B1002searches from its own database or under its own domain for a responding callee device which would possess a MT establishment cause, a D2D ID of the UE B1012, and optionally the radio bearer ID of UE B1012. After the rest of the handover procedure is completed, in step S1504, assuming that such device has been found, the network would automatically arrange D2D communication between UE A1011and UE B1012(for specific radio bearers).

As for the circumstance involving handling over in the level of NAS, a handover procedure across the S1 interface could be implemented. The S1 interface is a backhaul link between an eNB and a NAS control node as defined in the LTE/LTE A system.FIG. 16Aillustrates a current handover scheme across the S1 interface. Similar to the X2 interface which could be used to handover one device from one access stratum (AS) level control node to another AS level control node such as a base station, S1 interface could be used to handover the network attachment of a device from one NAS control node to another NAS control node (e.g. MME). By modifying the current S1 based handover scheme, the existing infrastructures could be utilized to accommodate D2D communication such that a complete overhaul would not be required.

FIG. 16Billustrates an exemplary scenario of a S1 interface handover involving a mobile caller UE. It is assumed that UE A1605(1605a,1605b) is a caller UE and is initially served by eNB A1063. After UE A1605ais handed over to eNB B1604, UE A1605bwould be served by eNB B1604. However, assuming that the eNB A1063and eNB B1604are served under different domains in the NAS level as eNB A1603is served by MME A1601and eNB B1604is served by MME B1602, the mobile caller UE which is UE A1605would be handed over across S1 interface from MME A1601to MME B1602.

Assuming the same exemplary scenario ofFIG. 16B,FIG. 16Cillustrates a modified procedure for triggering automatic D2D communication establishment by an eNB upon S1-based handover of a MO UE in accordance with one of the exemplary embodiments of the present disclosure. In step S1611, UE A1605optionally attempts to communicate with UE B1606by performing a radio bearer connection setup. During the radio bearer establishment of UE A1605, UE A1605may send D2D ID of UE B1606, and a MO establishment cause, to eNB A1603either through an independent message or through another message intended for another purpose. When eNB A1603receives such information, eNB A1604stores the MO establishment cause, the D2D ID of UE B1606and optionally the established radio bearer ID of UE A1605and links them with UE A. Also, UE B1606may request a similar implementation to establish a radio bearer, and eNB B1604would store the information received from UE B1606including MT establishment cause, D2D ID of UE B1606and optionally the established radio bearer ID of UE B1606and link these information with UE B1606.

As UE A1605migrates from eNB A to eNB B based on X2-based handover, eNB A1603would send the previously stored information linked with UE A1605to eNB B1604directly or indirectly through either an independent messages or by embedded the stored information in a message intended for another purpose. In step S1612, these stored information would be forwarded to MME A1601through the message Handover Required. In step S1613, the MME A1601would send these stored UE A information to MME B1602via the Forward Relocation Request message. After other necessary steps of the handover procedure are completed as required by the conventional S1 handover scheme, in step S1614, MME B1602would deliver the stored UE A1605information to eNB B1606via the Handover Request message. Upon receiving the stored UE A1605information, in step S1615, eNB B1604would store these information which has been linked with UE A1605including the MO establishment cause, the D2D ID of UE B1606and optionally the established radio bearer ID. In step S1616, eNB B1604would search among eNB B1604's own stored information or under its own domain to locate whether there is another device (with the corresponding established radio bearer) whose establishment cause indicates that it is a callee (e.g. MT) and the corresponding (callee) ID is the D2D ID of UE B1606. Assuming that eNB B1604would be able to locate such device, and in step S1617, the eNB B1604would try to initiate the D2D communication between UE A1605and UE B1606after the S1 handover have been completed.

It should be noted that although inFIG. 16C, the required information of UE A1605for D2D communication such as the establishment cause, the callee ID, and optionally the established radio bearer ID has been sent from eNB A1603to eNB B1604through the message Handover Required, Forward Relocation Request, and Handover Request, it would be apparent for one skilled in the art that these information could also be sent through another message such as the RRCConnectionReconfigurationComplete message.

Also, even though the embodiment ofFIG. 16Crelates to the migrating caller device, it would also be apparent to one skilled in the art that the same concept and procedure could also be modified and applied to the case related to a migrating callee device. Furthermore, the D2D ID of UE A1605could also be included during the connection establishment In step S1611such that eNB A1603and eNB B1604may have more information to perform searches for devices and to discern whether D2D could be performed after the handover procedure is finished.

Similar to the embodiment ofFIG. 14BandFIG. 15, another embodiment of D2D communication trigger upon X2 based handover could be implemented except that the D2D communication would be triggered by a NAS control node such as MME instead of a AS control node such as an eNB. In other words, the MME is the entity which initiates and arranges for the D2D communication to occur instead of an eNB even though the handover is performed across the X2 interface between eNBs.FIG. 17Aillustrates an exemplary scenario of a MME triggered D2D communication after a X2-based handover which is also a modification of an existing X2 based handover procedure such as a complete overhaul of the existing infrastructure is not required.FIG. 17Billustrates a MME triggered D2D communication procedure after a X2-based handover based on the scenario ofFIG. 17Ain accordance with one of the exemplary embodiments of the present disclosure.

Referring toFIG. 17A, assuming that UE A1704(1704a,1704b) communicates with UE B1705, and UE A1704ais initially served by eNB A1702but would eventually be handed over because of device mobility and be served by eNB B1703, and UE B1705is served by eNB B1703. Also assuming that both eNB A1702and eNB B1703are under the domain of the same MME1701and could communicate with each other through the X2 communication interface between them. After UE A1704bis handed over to eNB B1703, the MME1702would automatically arrange for D2D communication between UE A1704band UE B1705.

FIG. 17Billustrates the scenario ofFIG. 17Ain greater details. In step S1751, UE A1704may initiate a call to communicate with UE B1705by establishing an EPS bearer, i.e. a specific connection type, first with the MME1701. During the EPS bearer establishment of UE A in step S1751, UE A1704may send the MO establishment cause, the D2D ID of UE B1705to the MME either through an independent message or through a message intended for another purpose. When the MME1701receives the information, it stores them and links them with UE A1704(and the established EPS bearer ID of UE A1704). Similarly, UE B1705may also request to establish a EPS bearer. During the EPS bearer establishment of UE B1705, UE B1705may send the MT establishment cause and D2D ID of UE B1705to the MME either through an independent message or through a message intended for another purpose. When the MME1701receives the information, it stores them and links them with UE B1705(and the established EPS bearer ID of UE B).

After related handover preparation and handover execution steps are completed as required by the current X2-based handover procedure and shown inFIG. 17B, in step S1752after eNB A1702has handed UE A1704over eNB B1705based on X2-based handover, eNB B1703may transmit messages to the MME1701. When the MME1701receive a message from eNB B1703related to the handover of UE A1704such as the Path Switch Request message, MME1701would know that UE A1704has moved and would then search from its own stored information or stored information from a control node under its own domain such as eNB B to find whether there is a device (with a radio bearer) matching the description of a device with an establishment cause indicates a callee (e.g. MT) and the corresponding (callee) ID being the D2D ID of UE B1705. If such device has been found by MME1701, MME1701may further check whether UE A1704and UE B1705may communicate in D2D mode possibly based on tracking areas or/and location information or/and speed. When MME1701finds that it is feasible for UE A1704and UE B1705to communicate in D2D mode, MME1701would initiate for the D2D communication to be arranged for (the corresponding established radio bearers of) UE A1704and UE B1705.

FIG. 18Aillustrates an exemplary scenario of a MME triggered D2D communication after a S1-based handover of a caller UE. For this exemplary scenario, assuming that MME A1801and MME B1802could communicate through the S1 interface. MME A1801is a NAS control node which provides service to eNB A1803, and MME B1802is a NAS control node which provides service to eNB B1804. eNB A1803provides service to UE A1805, and eNB B1804provides service to UE B1806. Assuming that UE A would move from1805aunder the domain of eNB A to1805bafter being handed over to the domain of eNB B1804. MME B1802in this exemplary scenario would eventually initiate D2D communication to be arranged after information related to the caller device handover is transmitted over the S1 interface.

FIG. 18Billustrates a MME triggered D2D communication procedure after a S1-based handover based on the scenario ofFIG. 18Ain accordance with one of the exemplary embodiments of the present disclosure. In step S1811, UE A1805intends to communicate with UE B1806by establishing an EPS bearer with MME A1801. During the EPS bearer establishment of UE A1805, UE A1805may send the MO establishment cause and the D2D ID of UE B1806to MME A1801either through an independent message or through a message intended for another purpose. When the MME A1801receives the data, MME A1801stores them and links them with UE A1805(and the established EPS bearer ID of UE A). Similarly in step S1811, UE B1806may establish an EPS bearer during which the MT establishment cause and the D2D ID of UE B1806may be transmitted to MME B1802. When MME B1802receives the data, MME B1802stores them and links them with UE B1806(and the established EPS bearer ID of UE B).

As UE A1805migrates from eNB A1803which is under the domain of MME A1801to eNB B1804which is under the domain of MME B1802, MME A1801would send the previously stored information linked with UE A1805to MME B1802across the S1 interface either directly or indirectly through either an independent message or by embedding the information linked with UE A1805in a message intended for another purpose. More specifically, in step S1812, MME A1801could send the stored UE A information to MME B1802through the Forward Relocation Request message. In step S1813, upon the reception of these information linked with UE A1805, MME B1802would store these information in its storage medium. In step S1814, MME B would search for the corresponding device (with the corresponding established EPS bearer) which matches the description of a callee (e.g. MT establishment cause) and the corresponding (callee) ID being the D2D ID of UE1806. When such device has been found, MME B would initiate the D2D communication to be automatically arranged for (the corresponding established EPS bearers of) UE A1805and UE B1806.

Although inFIG. 18B, during the device handover the information linked with UE A1805was sent by MME A to MME B via the message Forward Relocation Request, the message may also be sent through such as the Forward Relocation Complete Acknowledge message. The information linked with UE A1805may also be initially delivered from UE A1805to eNB1804B through the RRC message RRCConnectionReconfigurationComplete and then be delivered by eNB B1804to MME B1802through the Handover Notify message.

Even though the exemplary scenario ofFIGS. 18A & 18Bteaches an example of automatic D2D communication establishment by MME upon S1-based handover of a migrating caller UE. It would be apparent for one skilled in the art that aforementioned disclosure could be modified and applied to a migrating callee UE. Also, the ID of UE A1805or the caller ID may also be carried during EPS bearer establishment so that MME B1802may have more information to perform a UE search and to discern whether D2D could be feasible upon a device handover. Also it is worth noting that although the embodiments betweenFIG. 14A˜FIG. 18Bteaches automatically arranging D2D communication establish after the completion of the handover procedure, it would be apparent for those skilled in the art that the aforementioned procedure could be modified so that D2D communication establishment could be triggered during device handover rather than after the completion of the device handover and therefore the disclosure would not be repeated.

FIG. 19Aillustrates the process of automatic D2D communication after device handover from the view point of a caller device or a callee device. In step S1901the caller/callee receives a notification and/or related information for D2D communication. In step S1902, the caller or callee then performs D2D communication based on the received information.

FIG. 19Billustrates the process of automatic D2D communication after device handover from the view point of a control node. Please note that inFIG. 19Bor any other figures of the specification, texts within parentheses or dotted blocks mean that optional these elements are optional elements which may not be needed under some circumstances. In step S1911, the control node receives from a first device a D2D ID of a callee and optionally an establishment cause which may indicate a caller or a callee, and optionally a corresponding connection ID of the first device during the handover of the first device. In step S1912, these information are stored in a storage medium of the control node in the form of a database of the control node. In step S1913, the control node searches whether there is a second stored device linked with a callee ID matching the previously received callee ID of the first device (and optionally the connection ID matching the connection ID of the first device). If the second device has been found based on the condition of the step S1913, then in step S1914, the control node would automatically arrange D2D communication between the first device and the second device by sending notifications and/or other related information to these devices.

Between steps S1913and S1914, one of the two or both additional checks could be performed. In step S1915, if the first device has indicated that it is a caller such as by having an establishment cause equals MO, the control node would check whether the second device or the found device has the establishment cause which equals MT (i.e. the second device is a callee device). In step S1916, if the first device has indicated that it is a callee device such as by having an establishment cause equals MT, the control node would then check whether the second device or the found device has the establishment cause equals to MO which means that the second device would indicate that it is a caller device. If the condition of step S1913together with the conditions of steps S1915and S1916are fulfilled, then the control node may execute step S1914.

Please note that for some embodiments, steps S1915and S1916could be skipped and the control node would arrange for D2D communications to take place as long as the same callee IDs would match between two devices such that not only two devices could communicate in D2D mode but also more than two devices may perform D2D communication together as long as they have the same callee ID or the same group ID which serves the purpose of identifying them as a D2D communication group.

FIG. 20Aillustrates the process of automatic D2D communication during device handover from the view point of a caller device or a callee device in accordance with one of the exemplary embodiments of the present disclosure. In the optional step S2001, the caller or callee receives from a control node a measurement configuration or measurement instruction to measure channel between itself and a first device or a first control node. In the optional step S2002, the caller or callee performs channel measurement based on the configuration or instruction from step S2001. In the optional step S2003, the caller or callee transmits the report containing the measurement result to the network. In step S2004, the caller or callee receives a notification and/or related information needed to perform the subsequent D2D communication. In step S2005, the caller or callee performs D2D communication based on the received information from step S2004.

FIG. 20Billustrates the process of automatic D2D communication during device handover from the view point of a control node in accordance with one of the exemplary embodiments of the present disclosure. In step S2011, the control receives from a first device a callee ID during the handover of the first device. The control may also optionally receive the establishment cause and the connection ID from the first device. In step S2012, the received information from the first device are stored in the storage medium of the control node itself, and these information would be linked with the first device. In step S2013, the control node searches whether there is a second stored device whose callee ID matches the callee ID from the received first device. If the second device has been found, the control node may directly execute step S2017in which the control mode may coordinate with another control node in order to perform D2D communication with the first device and the second device by sending notification and related information to these devices.

In addition to step S2013, the control node may perform additional checks so as to determine whether the step S2017could be performed. Optionally, in step S2014, if the second device has been found back in step S2013and if the first device has the MO establishment cause indicating a caller, then in step S2014the control node would determine whether the found device or the second device has the MT establishment cause indicating a callee. Similarly, in step S2015, if the first device has the MT establishment cause indicating that it is a callee, then in step S2015the control node would determine whether the second device or the found device is the MO establishment cause indicating a caller. If the checks between steps S2013˜S2015has been successful, then optionally, the control node may execute step S2016by coordinating with another control node to further measure channels between the first device and the second device or between the first device and a control node.

FIG. 21Aillustrates the process of automatic D2D communication during channel measurement from the view point of a caller device or a callee device in accordance with one of the exemplary embodiments of the present disclosure. The process ofFIG. 21Ais very similar to the process ofFIG. 20A. In step S2101, the caller/callee receives measurement configuration or instruction to measure channel between itself and another device or another control node. In step S2102, the caller/callee performs the channel measurement based on the information received from step S2101. In step S2103, the caller/callee reports the measurement result to its serving control node. In step S2014, the caller/callee receives a notification and/or related information from the network to perform D2D communication. In step S2015, the caller/callee performs D2D communication based on the received information.

FIG. 21Billustrates the process of automatic D2D communication during channel measurement from the view point of a control node in accordance with one of the exemplary embodiments of the present disclosure.FIG. 22Bis very similar toFIG. 21B. In step S2111, the control node obtains access of stored device information from another control node(s) or shares stored device information among one or more control nodes. The stored device information may include information such as establishment cause, callee ID, and connection ID. In step S2112, the control nodes examines whether one device is in fact communicating with another device. The is accomplished by examining the establishment cause of these devices. If one device indicates a caller or has a MO establishment cause, the other device would indicate a callee or has a MT establishment, and vice versa. In step S2113, the control node receives a measurement report containing a channel measurement between a caller and a callee or between a user device and a control node. After receiving the measurement report, the control would share the report with another control node whose stored information was found to contain one of the two devices. In step S2114, if the channel between the caller device and the callee device is sufficient, or is better than their cellular channels with their serving base stations, and if the caller device and the callee device are still in communication with each other, then the control node would coordinate with the another control node whose stored information was found to contain one of the two devices to automatically arrange for D2D communication between the caller device and the callee device (for the specific connection) by sending notifications and/or related information to these devices.

FIG. 22Aillustrates the process of NAS control node arranged automatic D2D communication triggered by a control node message from the view point of a caller device or a callee device in accordance with one of the exemplary embodiments of the present disclosure. This particular process is similar to the process ofFIG. 19A. In step S2201, the caller or callee device receives a notification and/or related information to perform D2D communication. In step S2202, the caller/callee device performs D2D communication based on the received information from step S2201.

FIG. 22Billustrates the process of NAS control node arranged automatic D2D communication triggered by a control node message from the view point of a NAS control node in accordance with one of the exemplary embodiments of the present disclosure. In step S2211, the NAS control node such as the MME receives a message indicating or implying a device handover. In step S2212, the NAS control node searches if the device handed over is communicating with another device based on the stored information such as their callee IDs being equivalent and/or one of their establishment causes is MO and the other being MT and vice versa and/or the connection ID of these two devices are equivalent. If the pair of devices has been found such that they are indeed in communication with each other, then the NAS control node may determine whether these two devices are close enough to each other, and if so, the NAS control node would initiate the D2D communication to be arranged between these two devices (for their specific connections) by sending notifications and/or related information to these devices either directly or indirectly.

In the disclosure and all of the embodiments, when the D2D communication is established between the caller and the callee, the original cellular communication and/or connection(s) may be released or may still remain.

In the disclosure and all of the embodiments, a connection may be identified/stored by a connection ID. Connection ID may be SRB (signaling radio bearer) ID, DRB (dedicated radio bearer) ID, EPS bearer ID, TCP/IP connection ID, an application connection ID, e.g. SIP session ID, or any other identity for connection identification.

In the disclosure of all the embodiments, whenever an ID is mentioned, it could be implemented as MSISDN or IMSI or IMEI or C-RNTI or S-TMSI or an application identity or an IP address or an identity used for device-to-device communication or an identity used in other layer as Table 1 could be apply. Also, when a control node checks whether two IDs are equivalent, the control node may adopt means such as an identity mapping table to check the ID equivalence based on ID mapping.

In the disclosure and all of the embodiments, a control node may broadcast or send dedicated information indicating whether the control node supports automatic D2D communication so that UEs devices may use the system information to decide whether to carry D2D related information, such as the callee ID, during the connection establishment. In another embodiment, the UEs themselves may send information to a control node to indicate whether the UEs would supports D2D and/or the locations of the UEs so that the control node has more information to decide whether to perform automatic D2D communication. In addition, the device may send an explicit indication to the control node to indicate whether an ID search should be performed by the control node in order to arrange D2D communication. In this way, the control node may not need to search for a caller ID every time a callee ID is received as the indication would decide whether an ID search should be performed. If a UE chooses not to use D2D communication, the UE may signal the refusal with the explicit indication.

In the disclosure and all of the embodiments, when the control node receives and/or stores the D2D related information, such as the callee ID and/or the establishment cause and/or the connection ID corresponding to some device, the control node may retain the D2D related information during the time when the established connection is maintained, or the control node may only retain the D2D related information over a fixed time interval or over a variable time interval based on the connection properties and/or the device conditions, such as mobility and/or locations.

In the disclosure and all of the embodiments, when the control node finds that automatic D2D communication may be performed, the control node may perform D2D communication for devices directly or/and the control node may send information to the devices, including the caller and/or the callee, to indicate the possible D2D availability, and/or the probability that D2D communication could be established successfully, and/or the location of the devices including the caller and/or the callee. When the devices receive the information, it may display the information in its user interfaces so that users may know the information and may decide whether to perform D2D communication.

In the disclosure and all of the embodiments, no element, act, or instruction used in the description of the present application should be construed as absolutely critical or essential to the present disclosure unless explicitly described as such. Also, as used herein, each of the indefinite articles “a” and “an” is intended to exclude more than one item. If only one item is intended, the terms “a single” or similar languages could be used. Furthermore, the terms “any of” followed by a listing of a plurality of items and/or a plurality of categories of items, as used herein, are intended to include “any of”, “any combination of”, “any multiple of”, and/or “any combination of multiples of the items and/or the categories of items, individually or in conjunction with other items and/or other categories of items. Further, as used herein, the term “set” is intended to include any number of items, including zero. Further, as used herein, the term “number” is intended to include any number, including zero.

In view of the aforementioned descriptions, the present disclosure is able to implement a D2D communication method in which a network could automatically trigger a D2D communication without requiring a user's awareness and without an explicit indication from the user to use D2D communication such that a user could make a call without even being aware that the connection is switched to the D2D mode, which could in turn enhance signaling efficiencies and reduce radio links transmission delays.