WO2015051843A1

WO2015051843A1 - Using a base station with a failed interface to core network to configure and advertise cluster head for device-to-device (d2d) wireless communications

Info

Publication number: WO2015051843A1
Application number: PCT/EP2013/071122
Authority: WO
Inventors: Vinh Van Phan; Ling Yu
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2013-10-10
Filing date: 2013-10-10
Publication date: 2015-04-16

Abstract

A technique is provided for detecting, by a base station (BS), a failure of an interface between the BS and a core network, sending a failure notification message to one or more mobile stations (MSs) indicating the failure of the BS-core network interface, selecting one or more of the MSs to be a cluster head, and broadcasting a cluster notification message to one or more MSs of the cluster, the cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals for synchronization by other MSs within the cluster.

Description

DESCRIPTION

TITLE

USING A BASE STATION WITH A FAILED INTERFACE TO CORE NETWORK TO CONFIGURE AND ADVERTISE CLUSTER HEAD FOR DEVICE-TO- DEVICE (D2D)

WIRELESS COMMUNICATIONS

TECHNICAL FIELD

[0001 ] This description relates to wireless networks.

BACKGROUND

[0002] A communication system may be a facility that enables communication between two or more nodes or devices, such as fixed or mobile communication devices. Signals can be carried on wired or wireless carriers.

[0003] An example of a cellular communication system is an architecture that is being standardized by the 3^rd Generation Partnership Project (3GPP). A recent development in this field is often referred to as the long-term evolution (LTE) of the

Universal Mobile Telecommunications System (UMTS) radio-access technology. E-UTRA (evolved UMTS Terrestrial Radio Access) is the air interface of 3GPP's Long Term Evolution (LTE) upgrade path for mobile networks. In LTE, base stations, which are referred to as enhanced Node Bs (eNBs), provide wireless access within a coverage area or cell. In LTE, mobile devices, or mobile stations are referred to as user equipments (UE). LTE has included a number of improvements or developments.

SUMMARY

[0004] According to an example implementation, a method may includedetecting, by a base station (BS), a failure of an interface between the BS and a core network (BS- core network interface), sending, by the BS, a failure notification message to one or more mobile stations (MSs) of a cell indicating the failure of the BS-core network interface, selecting, by the BS, one or more of the MSs to be a cluster head, and broadcasting a cluster notification message to one or more MSs of the cluster, the cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals to be used for synchronization by other MSs within the cluster.

[0005] According to another example implementation, an apparatus may include at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: detect, by a base station (BS), a failure of an interface between the BS and a core network (BS-core network interface), send, by the BS, a failure notification message to one or more mobile stations (MSs) of a cell indicating the failure of the BS-core network interface, select, by the BS, one or more of the MSs to be a cluster head, and broadcast a cluster notification message to one or more MSs of the cluster, the cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals to be used for synchronization by other MSs within the cluster.

[0006] According to another example implementation, a computer program product is provided that includes a non-transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: detecting, by a base station (BS), a failure of an interface between the BS and a core network (BS-core network interface), sending, by the BS, a failure notification message to one or more mobile stations (MSs) of a cell indicating the failure of the BS- core network interface, selecting, by the BS, one or more of the MSs to be a cluster head, and broadcasting a cluster notification message to one or more MSs of the cluster, the cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals to be used for synchronization by other MSs within the cluster.

[0007] According to another example implementation, a method is provided that includes receiving, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface, sending, from the MS to the BS, a cluster head capability indication indicating the MS is capable of being a cluster head, the cluster head capability indication also identifying resources to be used by the

MS to send reference signals for synchronization if selected by the BS to be a cluster head for a cluster, and receiving, by the MS from the BS, a cluster head configuration message indicating that the MS has been selected to be a cluster head.

[0008] According to another example implementation, an apparatus includes at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: receive, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface, send, from the MS to the BS, a cluster head capability indication indicating the MS is capable of being a cluster head, the cluster head capability indication also identifying resources to be used by the MS to send reference signals for synchronization if selected by the BS to be a cluster head for a cluster, and receive, by the MS from the BS, a cluster head configuration message indicating that the MS has been selected to be a cluster head.

[0009] According to yet another example implementation, a computer program product includes a non-transitory computer-readable storage medium and stores executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: receiving, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface, sending, from the MS to the BS, a cluster head capability indication indicating the MS is capable of being a cluster head, the cluster head capability indication also identifying resources to be used by the MS to send reference signals for synchronization if selected by the BS to be a cluster head for a cluster, and receiving, by the MS from the BS, a cluster head configuration message indicating that the MS has been selected to be a cluster head.

[0010] According to another example implementation, a method is provided that includes receiving, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface, reconfiguring, by the MS, the MS from a cellular or infrastructure mode to operate as a cluster head for a device-to- device (D2D) wireless cluster in response to the failure notification based on

preconfigured information stored in the MS, sending, from the MS to the BS, a cluster head notification message indicating that the MS has been configured to operate as a D2D cluster head.

[0011 ] According to another example implementation, an apparatus includes at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: receive, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface, reconfigure, by the MS, the MS from a cellular or

infrastructure mode to operate as a cluster head for a device-to-device (D2D) wireless cluster in response to the failure notification based on preconfigured information stored in the MS, and send, from the MS to the BS, a cluster head notification message indicating that the MS has been configured to operate as a D2D cluster head.

[0012] According to yet another example implementation, a computer program product includes a non-transitory computer-readable storage medium and stores executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: receiving, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface, reconfiguring, by the MS, the MS from a cellular or infrastructure mode to operate as a cluster head for a device-to-device (D2D) wireless cluster in response to the failure notification based on preconfigured information stored in the MS, sending, from the MS to the BS, a cluster head notification message indicating that the MS has been configured to operate as a D2D cluster head.

[0013] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a block diagram of a wireless network 130 according to an example implementation.

[0015] FIG. 2 is a diagram illustrating operation of a wireless network according to an example implementation.

[0016] FIG. 3 is a diagram illustrating operation of a wireless network according to another example implementation in which a MS reconfigures itself to operate as a cluster head.

[0017] FIG. 4 is a flow chart illustrating operation of a base station (BS) according to an example implementation.

[0018] FIG. 5 is a flow chart illustrating operation of a base station according to another example implementation.

[0019] FIG. 6 is a flow chart illustrating operation of a base station according to another example implementation.

[0020] FIG. 7 is a block diagram of a wireless station (e.g., BS or MS) 700 according to an example implementation. DETAILED DESCRIPTION

[0021 ] In some cases, a S1 interface between a base station and core network may fail, such as during a natural disaster, equipment failure, or other condition. In such a situation, according to an example implementation, the mobile stations (MSs) within the cell may switch from a normal or infrastructure mode where signals and data are relayed via the base station (BS) to a device-to-device (D2D) mode in which MSs may directly communicate with each other within the cell. A cluster may be established, including a cluster head (or master) to perform various control and/or coordination functions for the cluster, and one or more slave MSs. [0022] According to an example implementation, a technique is provided for detecting, by a base station (BS), a failure of an interface between the BS and a core network, sending a (e.g., S1 interface) failure notification message to one or more mobile stations (MSs) indicating the failure of the BS-core network interface (e.g., S1 interface or link), and determining one or more device-to-device (D2D) mode-capable MSs within the cell that are capable of being a cluster head for a cluster of MSs. The technique may also include selecting one or more of the MSs to be a cluster head, sending a cluster head configuration message to each of the selected MSs indicating that the selected MS has been selected to be a cluster head, and broadcasting a cluster notification message to one or more MSs of the cluster. The cluster notification message may identify at least cell resources to be used by the cluster head to transmit reference signals for synchronization by other MSs within the cluster.

[0023] FIG. 1 is a block diagram of a wireless network 130 according to an example implementation. In the wireless network 130 of FIG. 1 , mobile stations (MSs) 131 , 132 and 133, which may also be referred to as user equipments (UEs), may be connected (and in communication) with a base station (BS) 134, which may also be referred to as an enhanced Node B (eNB). BS 134 provides wireless coverage within a cell 136. Although only two MSs are shown within cell 136 (connected or attached to BS 134), any number of MSs may be provided. BS 134 is also connected to a core network 150 via a S1 interface 151 (an example of a BS-core network interface). This is merely one simple example of a wireless network, and others may be used.

[0024] In LTE, core network 150 may be referred to as Evolved Packet Core (EPC), which may include a mobility management entity (MME) which may handle or assist with mobility/handover of MSs between BSs, one or more gateways that may forward data and control signals between the BSs and packet data networks or the

Internet, and other control functions or blocks. Only a few of the blocks or functions of the example core network are described, and the core network 150 may include different and/or additional blocks/functions, for example.

[0025] In some situations, the S1 interface 151 or link (or BS-core network interface or link) may fail or break, which interrupts or prevents transmission of data between the BS and the core network 150. A failed or broken S1 interface may occur due to a variety of circumstances, such as natural disasters (e.g., earthquakes, hurricane or storm), war, failure of power company infrastructure, or other crisis or emergency. These are merely some example situations where a failed S1 interface is likely to occur, but there may be other situations as well. When the S1 interface fails, packets or data from the core network 150 will no longer be received by the BS 134, and BS 134 is unable to send or forward data or other signals to the core network 150.

[0026] According to an example implementation, after failure of an S1 interface, it may be desirable to allow MSs of at least one or more select classes of MSs to continue communicating or operating in a device-to-device (D2D) mode in which MSs may directly communicate with each other. According to one example implementation, access to the cell may be limited to public safety MSs (e.g., policemen, firemen, doctors, and other emergency or rescue personnel) that are capable of D2D communications may be permitted to continue communicating via a D2D mode of operation. This may allow mission critical communications to continue for PS D2D MSs, even though the S1 (or BS- core network) interface is broken or failed.

[0027] Furthermore, even though the S1 interface is failed or broken, the BS may still be capable of operating within the cell by transmitting downlink signals, receiving and processing uplink signals from one or more MSs, etc. Therefore, although not required, in some cases, the BS may continue operating in a D2D assistance mode in which the BS may assist the D2D communications within the cell.

[0028] According to an example implementation, in the event of a failure of an S1 interface for a cell, one or more MSs within the cell may transition from a normal (cellular or infrastructure mode) of operation that relies on the BS 134 to relay or forward data to and from a connected MS(s), to a D2D (or device-to-device) mode of operation in which direct MS-to-MS communication is performed.

[0029] Also, according to an example implementation, some of the MSs within cell 136 may be organized into a cluster for D2D communications, in which at least one of the MSs within the cluster is assigned or assumes the position of cluster head or master, with the other MSs being slave MSs. For example, the MSs within a cluster may be a subset of the MSs within the cell 136, and there may be one or more clusters set up within a cell.

Clusters may share resources and may be used to coordinate operation of MSs within the cluster and allocate resources between MSs for D2D communication. Allocated resources may include any type of radio or wireless resources, such as time, frequency and/or code resources, such as, symbols (e.g., orthogonal frequency division multiplex access or OFDMA symbols), or other resources.

[0030] A cluster head (or master MS within a cluster) may perform a variety of control and coordination functions for the cluster, depending on the implementation.

According to one example implementation, a cluster head may transmit reference (or synchronization) signals that may allow other MSs within the cell to become synchronized with each other with respect to the reference signals. The cluster head may also perform authorization and authentication of MSs for the cluster. Authorization may include, for example, the cluster head admitting MSs to the cluster, e.g., based on certain criteria such as being a member of a specific access class, a preconfigured user group (e.g., policemen or firemen, or rescue personnel for a specific town), or having a specific capability (e.g., PS MS, D2D MS), or having a certain signal strength or other signal quality, or other admission criteria. For authentication, the cluster head may authenticate each MS that is admitted to the cluster, e.g., based one or more encryption keys that have been preconfigured or pre-stored by the MSs and the cluster head. A cluster head may also receive resource requests from one or more MSs for D2D communications, may coordinate or allocate resources to one or more D2D MSs within the cluster, and may send a message to one or more MSs within the cluster allocating or assigning resources, such as by broadcasting a resource allocation table. The slave MSs (members of the cluster) within the cluster may then perform D2D communications via their

allocated/assigned resources. In this manner, the cluster head may coordinate operation and/or allocate resources so as to reduce the probability of interference or collisions between MSs within the cluster. These are merely some example functions, and a cluster head may perform other functions.

[0031 ] Also, rather than a cluster head performing all of the control functions for a cluster, some of these functions may be performed by other special MS(s) within the cluster. For example, a security agent MS within the cluster may perform the authorization and authentication functions for the cluster. In a similar fashion, some of the control functions for a cluster may be performed by different MSs.

[0032] In addition, in the event of a failed S1 interface, the BS may limit or restrict access to resources within the cell to only specific MSs, or specific users, such as D2D MSs (MSs capable of D2D communications), emergency services users/MSs, and/or public safety users/MSs. For example, public safety (PS) users/MSs may include any MS that is assigned to a user that is related to or involved with public safety, such as firemen, policemen, doctors and nurses, rescue teams, and other emergency or crisis personnel, for example. Each MS may store access class membership information, e.g., within a SIM (Subscriber Identity Module) card or a USIM (Universal Subscriber Identity Module) that is stored within the MS, that indicates that the MS is a member of one or more access classes. For example, access class 14 may be for emergency services MSs. Similarly, separate access classes may be provided for: D2D MSs (MSs that are capable of D2D operation), public safety MSs, and/or PS D2D MSs (public safety MSs that are capable of D2D operation). A BS may transmit barring information or access class barring information, e.g., within a system information block (SIB), such as SIB1 or SIB2, which may be broadcast to MSs within the cell, or by sending other message. The barring information may include, for example, an access barring list that identifies one or more access classes in order to bar or prevent certain access classes from accessing a cell or network (e.g., by preventing the MSs from access resources of such cell or network), and/or to permit or admit other classes to access or use such cell or network resources. Thus, for example, the access barring information may be used to limit access to the cell to only the specified class(es) of MSs, e.g.,: D2D MSs (MSs that are capable of D2D operation), public safety (PS) MSs and/or PS D2D MSs, as examples.

[0033] FIG. 2 is a diagram illustrating operation of a wireless network according to an example implementation. Mobile station (MS) 212 may be, for example, connected to a base station (BS) 210. Although not shown, other MSs may be connected or attached to BS 210. Also, although not shown in FIG. 2, there may be one or more MSs within a cell provided by BS 210 that are not connected to BS 210. For example, these non- connected MSs in the cell may be in an idle (e.g., RRC-ldle) state, and not in a connected or attached (e.g., RRC-connected) state with respect to the BS or cell. In addition, there are other MSs that may be connected to the BS 210. In an example implementation, MS 212 and other MSs may be members of a cluster, as described in greater detail below.

[0034] At 214, BS 210 detects a failure of a S1 interface to the core network, which may be more generally referred to as the BS-core network interface. This breakage or failure of the S1 interface (or link or connection) may be detected, for example, by the BS 210 detecting an expiration of a re-transmission timer, or failure of the core network 150 to provide an expected signal or acknowledgement to BS 210 within a certain time period, or other condition indicating the failure of the S1 interface or link between the BS 210 and the core network. Also, MS 212, and other MSs 213 within the cell, may also be in communication with the core network 150, e.g., to receive handover instructions or other communications. Therefore, a MS, such as MS 212 may similarly detect a non- responsive BS 210, and may report this information to BS 210 as a failed S1 interface. These are merely some examples, and other techniques may be used to detect a failed S1 interface.

[0035] As shown in FIG. 2, BS 210 may transmit or send a S1 failure notification message 216 to one or more (or all) of the MSs within the cell, including to MS 212.

According to an example implementation, the S1 failure notification message 216 may include one or more fields or parameters, such as: a S1 status field that may indicate a status of the S1 interface as "failed" in this example, a transition period length, a barring information, and a cell ID for the cell.

[0036] The transition period length identifies a length of a transition period 222 after the detection of the failed S1 interface (or sending of the S1 failure notification message) during which the BS 210 may continue operating in a normal (cellular or infrastructure) mode. As noted by box 224, during the transition period 222, BS 210 may be operated in a normal (cellular or infrastructure) mode, at least (for example) for transmission of common control information to MSs including the BS 210 transmitting the cell's physical cell ID (PCI), system information blocks (SIBs), reference signals, etc. The BS 210 may also communicate with connected MSs to exchange control plane messages during the transition period 222. Also, during the transition period 222, the BS 210 may select and configure one or more MSs to be a cluster head (or master MS) for the cluster, as described in greater detail herein. The BS 210 may enter a new mode of operation (e.g., a D2D assistance mode to provide some assistance to the cluster, or a non- operational mode) after expiration of the transition period 222.

[0037] A BS may limit access to a cell by sending or broadcasting access class barring information. For example, the BS may transmit the access class barring information via broadcasted system information block (e.g., SIB2), or within a S1 failure notification message 216, or within other message(s). Some MSs may be members of one or more high-priority access classes, such as emergency MSs, or other high-priority MSs. Some example high-priority access classes may include: Access class 1 1 - PLMN (public land mobile network); Access class 12 - security services; Access class 13 - public utilities; Access class 14 - emergency services; Access class 15 - PLMN (public land mobile network) staff. According to an example implementation, one or more additional high-priority access classes may be provided or assigned to various public safety (PS) MSs and/or D2D MSs, such as: Access class 16 - D2D MSs; Access class 17 - public safety MSs; Access class 18 for public safety (PS) D2D MSs, etc.

[0038] As noted, the BS may broadcast access class barring information to restrict access to the network or cell. According to an example implementation, the access class barring information may include, for example, a barring time which may indicate a time period for which the barring information is valid, and a bit string for high priority access classes (e.g., ac-BarringForSpecialAC). The bit string for high-priority access classes may include a bit for each high-priority access class, e.g., to indicate whether one or more of the high-priority access class (e.g., access classes 1 1 , 12, 13, ...18) is barred or not barred from the cell. For example, the bit string for high-priority access classes will indicate a status of "not barred" for an access class to indicate that the associated access class is permitted to access the cell. If at least one bit for an access class of which a MS is a member indicates "not barred", then the MS is not barred, for example. Therefore, in this manner, access class barring information may be used to admit or permit certain access classes of MSs to access a cell, while barring or preventing other access classes from accessing the cell. In an example implementation, in the event of an S1 failure, for example, this access class barring information may be used by a BS to admit or permit only D2D MSs (MSs that are capable of D2D operation), public safety (PS) MSs, or PS D2D MSs (public safety MSs that are D2D capable) to access or use the cell.

[0039] Referring to FIG. 2, one or more of the fields/parameters may be omitted from the notification message 216, e.g., if such field or parameter is preconfigured or specified for the BS and/or MSs in advance based on a standard or predetermined configuration. Alternatively, one or more of the fields or parameters of the S1 failure notification message 216 may be omitted from the notification message 216, and instead, sent (or updated) via other message(s) sent by the BS 210, such as, for example, in broadcasted system information block (or SIB), e.g., SIB1 , SIB2, etc.

[0040] At 218, in response to the S1 failure notification message 216, each of the MS 212 and other MSs 213 may determine whether they are D2D capable (e.g. capable of directly communicating with other MSs in a D2D mode), e.g., based on D2D capability information stored within the MS. If the MS 212 is not D2D capable, then MS may release its RRC (radio resource connection) connection with the cell. This is because, for example, the MS knows that the cell will move from an infrastructure (or cellular) mode to a D2D mode at the end of the transition period length, and only D2D capable MSs may then be able to communicate within the cell in the D2D mode. Thus, in this example, there is no need for the MS 212 to continue its connection to BS 210 after the S1 failure unless the MS 212 is D2D capable, for example. This is merely one illustrative operation for the MS 212, and other operations may be performed instead.

[0041 ] In addition, at 218, in response to the S1 failure notification 216, each of the MS 212 and MSs 213 may determine if they are cluster head capable (capable of operating as a cluster head or master MS within a cluster), e.g., based on cluster head capability information stored within each one or more of the MSs 212, 213. In addition to device capability, the MS may determine if it has an actual pre-configured service profile, e.g., which may identify services that the MS can provide or expects to provide, what kinds of targeted user groups for each service, etc.

[0042] According to one example implementation, in response to receiving the S1 failure indication 216, one or more of the MSs 212, 213 in the cell that are D2D capable and cluster head capable may send a cluster head capability indication 220, e.g., within the transition period 222, indicating that the sending MS is capable of being (or operating as) a cluster head. Therefore, BS 212 may receive a cluster head capability indication 220 from each of one or more MSs within the cell, according to an example implementation. According to an example implementation, the cluster head capability indication 220 may also identify resources to be used by the MS to transmit reference (or synchronization) signals, e.g., in the event that the MS is selected to be a cluster head. Alternatively, the BS 210 may specify, e.g., in a reply message, or in cluster head configuration message 226, the resources that should be used by the cluster head to transmit reference signals.

[0043] At 224, based on the one or more received cluster head capability indications 220, BS 210 may select one or more of the cluster head capable MSs to be a cluster head for the cluster. The cluster may have just one cluster head, or may have multiple cluster heads. In the event of multiple cluster heads, cluster head responsibilities may be divided among the multiple cluster heads, or cluster head responsibility may be rotated among the multiple cluster heads so as to reduce power consumption at any one cluster head. Multiple clusters may be provided to cover a larger geographical area, as compared to a single cluster. One cluster head may be provided for each cluster. For example, cluster heads may be selected that are spatially distributed so as to allow multiple clusters to cover a larger geographical area (e.g., higher percentage of cell area), as compared to just one cluster. A variety of factors may be used to select one or more of the cluster head capable MSs to be a cluster head, such as signal strength, or other criteria.

[0044] According to one example implementation, at 224, the BS 210 may select cluster heads based on various information or criteria, such capability information known by BS, e.g., obtained by BS during connection establishment by each MS where capability information may be provided to the BS 210 by one or more (or each) MS during such connection establishment process. Therefore, according to this example implementation, cluster head capability indications 220 may be omitted, and the BS 210 may select a cluster head among active or connected BSs that previously indicated a D2D and cluster head capability, e.g., via the capability exchange that may be performed as part of the connection establishment process. In another example implementation at 224, BS 210 may select one or more MSs to be a cluster head based on the cluster head capability indication(s) 220 sent to BS 210, e.g., select one or more of the MSs that indicated they are cluster head capable based on message(s) 220.

[0045] In addition to capability information, cluster heads may be selected based on other criteria or information, such as, for example: 1 ) MS battery condition, 2) MS location within the cell, and 3) MS user group information. For example, a MS battery with a higher charge may be more desirable as a cluster head than a MS with lower battery charge, since operating as a cluster head may drain a MS battery more quickly than normal MS operation. Also, a MS location for a MS that is more stable within the cell may be selected to be cluster head, e.g., since such a MS may be expected to remain at a same or similar location for a longer period of time. Also, a MS located at a central location within the cell that is selected as cluster head may be more desirable to cover a larger portion of the cell. Or if multiple clusters are provided, then location of MS may be a factor in cluster head selection since it may be desirable to provide spatially-diverse or geographically-diverse MSs to provide multiple clusters that cover a larger area. Location of a MS may be determined or estimated based on, e.g., received signal strength of signals from MS (or received signal strength of signals received by MS from BS, and reported to BS), uplink timing advance information, user location information (e.g., GPS location or other reported location of MS). Each MS may be a member of one or more user groups. User group information/membership may be a criteria in cluster head selection. For example, a MS may be selected for cluster head that is a member of the highest number of user groups, or a member of a specific user group that may be important or may be mission critical, e.g., public safety, police, firemen, or rescue user groups, etc. Thus, a MS may be selected as cluster head if the MS is a member of a specific user group(s). For example, a MS that is a member of a user group that is critical or important to a service area of interest may be selected as the cluster head.

[0046] BS 210 may then transmit or send a cluster head configuration message 226 to each of the one or more selected cluster head MSs to indicate that the MS has been selected to be a cluster head. The cluster head configuration message 226 may optionally provide additional configuration information in order to configure the MS as cluster head, such as confirming or identifying resources that are to be used to transmit reference signals, identify a set of resources that may be available to the cluster for (D2D) communications, e.g., in the event that there are adjacent clusters, in order to avoid interference between clusters. According to an example implementation, the cluster head configuration message 226 may include the cluster head identity (e.g., MS ID) as configured or confirmed, a cluster head transmit power, as configured or confirmed, and a cluster head service profile, e.g., that may specify one or more services that the MS is capable of providing or assistance to be provided and/or what the MS expects to receive from other MSs or BS. MS discovery may rely upon, e.g., the reference signals, and some additional beaconing information (or beacon information) that may be broadcast from the BS or cluster head.

[0047] The BS 210 may also send or broadcast a cluster notification message 228 to one or more (or all) of the MSs within the cell. The cluster notification message 228 may identify at least the cell resources to be used for transmission of reference signals for the cluster. The cluster notification message 228 may include additional information, such as an MS identifier for the cluster head, such as a MSID, and a cluster ID. According to an example implementation, one purpose of the broadcasted cluster notification message 228 is to identify the resources for cluster reference signals to allow slave MSs to synchronize to the cluster head, and thereby decrease interference or collisions between MSs in the cluster. Other information may be broadcasted or advertised by the BS 210, including any information that may assist MSs (e.g., public safety D2D MSs) to discover the cluster head and each other quicker, and to allow the MSs to perform D2D communications in a more secure and efficient way, such as identities of MSs, reference sequences, service profiles of MSs, any limitation/restriction of cluster heads, the number of existing members of cluster heads.

[0048] A variety of different messages may be used to send or broadcast the cluster notification message 228. In a first example implementation, the cluster notification message 228 may be broadcast via a system information block (SIB) broadcasted by the BS 210. In a second example implementation, the MSs may be notified of a broadcast group address. A transmission is then scheduled on the broadcast group address, and the cluster notification message may be broadcasted via the scheduled transmission. In yet another example implementation, the cluster notification message may be sent as a radio resource control (RRC) connection release message, e.g., with cause indicated as D2D, or cluster, or S1 interface failure, etc. This connection release message may cause the MS to release its connection and then transition to a D2D mode of operation for D2D communication within the cluster.

[0049] According to an alternative example implementation, cluster head configuration message 226 may be omitted, and each selected cluster head may be notified that it was selected as cluster head within the cluster notification message 228.

Thus, in such an example embodiment, the cluster notification message 228 may include at least the MSID of each MS selected for cluster head and identify the resources to be used for transmission of reference signals for the cluster. Thus, in such a case, both cluster head configuration message 226 and cluster notification message 228 may be included together as a single broadcasted message, for example.

[0050] At 230, the one or more MSs selected to be cluster head, such as MS 212, begin operating as cluster head for the cluster. As noted above, MS 212, operating as cluster head, may perform a variety of control functions for the cluster, such as by transmitting reference signals, performing authorization and authentication of MSs for the cluster, and allocating resources to slave MSs within the cluster.

[0051 ] For example, cluster head (MS 212) may broadcast reference signals 242. Cluster head (MS 212) may also receive resource requests 244 from slave (other) MSs 213 in the cluster for resources to be used for D2D communications. Cluster head (MS 212) may then allocate resources (246) to one or more MSs within the cluster. According to an example implementation, these allocated resources may be, e.g., within a range of resources allocated to the cluster head by the BS 210 via cluster head configuration message 216. Cluster head (e.g., MS 212) may then notify one or more MS of allocated resources, e.g., by broadcasting a resource allocation table 248 to the MSs within the cluster. MSs within the cluster may then perform D2D communications via their allocated resources.

[0052] Also, at 234, BS determines a new operation mode such as transitioning to a non-operational mode 238 where the BS 210 ceases operation, or a D2D assistance mode, e.g., a DL (downlink) only D2D assistance mode 240 in which the BS 210 may transmit downlink signals in order to provide some assistance to the cluster. Prior to entering the new mode (either non-operational mode or DL only D2D assistance mode), the BS 210 may send or broadcast the cluster notification message to provide or identify at least the identity of the cluster and resources for transmission of the reference signals for the cluster. If the BS enters the D2D assistance mode 240, the BS 210 may perform a repeat broadcast (250) of the cluster notification message 228 (or at least retransmit the identification of resources of reference signals for cluster at 250). This retransmission or repeat broadcast of cluster notification message at 250 may be performed repeatedly over time, e.g., periodically, such as every 5 ms, every 7 ms, etc., to allow any new MSs entering the cluster to identify and receive such reference signals for the cluster.

According to one example implementation, the retransmission of the broadcast (250) of cluster notification message 228 may have a period that is a multiple of a frame length. For example, for a frame length of 10ms, the retransmission of broadcast information may be repeated every 60ms, 70ms, or 80ms, as examples.

[0053] Alternatively, the BS 210, operating in the D2D assistance mode, may periodically or repeatedly transmit the reference signals for the cluster (instead of the cluster head transmitting these reference signals). In such a case, the cluster head would perform the other/remaining cluster head functions or operations, such as MS

authorization and authentication, resource allocation, etc.

[0054] FIG. 3 is a diagram illustrating operation of a wireless network according to another example implementation in which a MS reconfigures itself to operate as a cluster head. The same reference numerals in FIGs. 2 and 3 refer to the same elements.

Elements 318, 318, 320 and 326 have been added to FIG. 3, and some elements have been removed, as compared to FIG. 2. After receiving the S1 failure notification message 216 (see FIG. 2), the MS 212 determines if it is preconfigured to operate as a D2D cluster head. If the MS 212 is configured to operate as a cluster head, then at 319, the MS 212 reconfigures MS 212 from a cellular or infrastructure mode of operation to operation as a cluster head for a device-to-device (D2D) wireless cluster in response to the failure notification message 216. The MS 212 reconfiguring itself to operate as a D2D cluster head may be done based on preconfigured (or stored) information within the MS 212, e.g., regardless of any permission or authorization received from BS 210, and regardless of any further communication with BS 210.

[0055] Referring to FIG. 3 again, the MS 212 may then send a cluster head notification message 320 to the BS 210 indicating that the MS 212 has been configured to operate as a D2D cluster head. The cluster head notification message 320 may identify the identify, e.g., the MSID, of the MS 212, and resources to be used by the MS to send reference signals for synchronization. The cluster head notification message may also identify a service profile that identifies one or more services to be provided by the MS 212 as cluster head.

[0056] FIG. 4 is a flow chart illustrating operation of a base station (BS) according to an example implementation. At 410, a base station (BS) detects a failure of an interface between the BS and a core network (BS-core network interface). At 420, the BS sends a failure notification message to one or more mobile stations (MSs) of a cell indicating the failure of the BS-core network interface. At 430, the BS selects one or more of the MSs to be a cluster head. And, at 440, the BS broadcasts a cluster notification message to one or more MSs of the cluster, the cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals to be used for synchronization by other MSs within the cluster.

[0057] According to another example implementation, the method of FIG. 4 may further include determining, by the BS, one or more device-to-device (D2D) mode-capable MSs within the cell that are capable of being a cluster head for a cluster of MSs within the cell, selecting, by the BS, one of the MSs to be a cluster head for the cluster, and sending a cluster head configuration message to the selected MS indicating that the selected MS has been selected to be a cluster head for the cluster.

[0058] According to another example implementation, the method of FIG. 4 may further include the BS switching to a non-operational mode after broadcasting the cluster notification message.

[0059] According to another example implementation, the method of FIG. 4 may further include the BS switching to a downlink (DL) only D2D assistance mode in which the BS periodically broadcasts a message identifying at least cell resources used by the cluster head to transmit reference signals.

[0060] According to another example implementation, in the method of FIG. 4, the failure notification message includes an interface status field that indicates the status of the BS-core network interface as failed or broken, the notification message also including a barring information that indicates that an access class of public safety D2D MSs are permitted to access resources of the cell.

[0061 ] According to another example implementation, in the method of FIG. 4, the failure notification message includes: a transition period length field to indicate a period length for the BS to perform a transition from a cellular or infrastructure mode of operation to a new mode of operation, an interface status field that indicates the status of the BS- core network interface as failed or broken, and a cell ID to identify the cell.

[0062] According to another example implementation, in the method of FIG. 4, the selecting includes determining by the BS, based on capability information known by the BS for one or more MSs in the cell, one or more device-to-device (D2D) mode-capable MSs within the cell that are capable of being a cluster head for a cluster of MSs within the cell.

[0063] According to another example implementation, in the method of FIG. 4, the selecting includes receiving, in response to the failure notification message, a cluster head capability indication from one or more D2D capable MSs within the cell, each cluster head capability indication indicating that the MS is capable of being a cluster head, and selecting one of the cluster head-capable MSs to be the cluster head for the cluster.

[0064] According to another example implementation, in the method of FIG. 4, the selecting includes receiving a cluster head capability indication from one or more D2D capable MSs within the cell, each cluster head capability indication indicating that the MS is capable of being a cluster head and identifying resources to be used by the MS to transmit reference signals for synchronization, and selecting one of the cluster head- capable MSs to be the cluster head for the cluster.

[0065] According to another example implementation, in the method of FIG. 4, the cluster notification message includes at least a MS ID for the cluster head and identifies cell resources to be used by the cluster head to transmit reference signals to be used for synchronization by other MSs within the cluster.

[0066] According to another example implementation, in the method of FIG. 4, the broadcasting the cluster notification message includes broadcasting the cluster notification message via a system information block (SIB). [0067] According to another example implementation, in the method of FIG. 4, the broadcasting the cluster notification message includes: notifying one or more of the MSs within the cell of a broadcast group address, scheduling a transmission via the broadcast group address, and broadcasting the cluster notification message via the scheduled transmission.

[0068] According to another example implementation, in the method of FIG. 4, the broadcasting the cluster notification message includes transmitting, to each of one or more MSs, a radio resource control (RRC) connection release, with cause set to D2D or cluster.

[0069] According to another example implementation, in the method of FIG. 4, the broadcasting the cluster notification message includes transmitting a radio resource control (RRC) connection release, with cause set to S1 interface failure.

[0070] According to an example implementation, an apparatus is provided that includes at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: detect, by a base station (BS), a failure of an interface between the BS and a core network (BS-core network interface), send, by the BS, a failure notification message to one or more mobile stations (MSs) of a cell indicating the failure of the BS-core network interface, select, by the BS, one or more of the MSs to be a cluster head, and broadcast a cluster notification message to one or more MSs of the cluster, the cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals to be used for synchronization by other MSs within the cluster.

[0071 ] According to another example implementation, a computer program product is provided that includes a non-transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method that includes: detecting, by a base station (BS), a failure of an interface between the BS and a core network (BS-core network interface), sending, by the BS, a failure notification message to one or more mobile stations (MSs) of a cell indicating the failure of the BS- core network interface, selecting, by the BS, one or more of the MSs to be a cluster head, and broadcasting a cluster notification message to one or more MSs of the cluster, the cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals to be used for synchronization by other MSs within the cluster.

[0072] FIG. 5 is a flow chart illustrating operation of a mobile station according to another example implementation. The flow chart of FIG. 5 includes several operations. At 510, a mobile station (MS) receives from a base station (BS), a failure notification message indicating a failure of a BS-core network interface. At 520, the MS sends to the BS, a cluster head capability indication indicating the MS is capable of being a cluster head, the cluster head capability indication also identifying resources to be used by the MS to send reference signals for synchronization if selected by the BS to be a cluster head for a cluster. And, at 530, the MS receives from

the BS a cluster head configuration message indicating that the MS has been selected to be a cluster head.

[0073] According to an example implementation, the flow chart of FIG. 5 further includes broadcasting the reference signals via the identified resources in a device-to- device (D2D) mode of operation from the MS to one or more other MSs within the cluster in response to being selected as a cluster head.

[0074] According to an example implementation, the flow chart of FIG. 5 further includes receiving, by the MS from the BS, a broadcasted cluster notification message that identifies at least the identified resources for transmission of the reference signals or synchronization signals.

[0075] According to an example implementation, the flow chart of FIG. 5 further includes receiving, by the MS from the BS, a broadcasted cluster notification message that identifies at least the identified resources and a MS ID for the cluster head.

[0076] According to an example implementation, in the flow chart of FIG. 5 the failure notification message includes: an interface status field that indicates the BS-core network interface as failed or broken, and access class barring information indicating that an access class of public safety D2D mode devices may access the cell and become members of the cluster.

[0077] According to an example implementation, in the flow chart of FIG. 5 the failure notification message includes a transition period length field, wherein the broadcasting the reference signals includes the MS, operating as cluster head, broadcasting the reference signals via the identified resources in the D2D mode of operation after expiration of the transition period length.

[0078] According to an example implementation, the flow chart of FIG. 5 further includes the MS, operating as a cluster head in a D2D mode of operation, sending a resource allocation to one or more other MSs within the cluster to allocate resources within the cluster for D2D communication.

[0079] According to an example implementation, in the flow chart of FIG. 5, the cluster head includes a first MS, the method further including: receiving, by the cluster head as a D2D communication, a resource request from a second MS within the cluster for a D2D communication between the second MS and a third MS within the cluster, allocating, by the cluster head, resources for the D2D communication between the second MS and the third MS, and sending, by the cluster head, a resource allocation message identifying the allocated resources to at least the second MS.

[0080] According to an example implementation, an apparatus includes at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: receive, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface, send, from the MS to the BS, a cluster head capability indication indicating the MS is capable of being a cluster head, the cluster head capability indication also identifying resources to be used by the MS to send reference signals for

synchronization if selected by the BS to be a cluster head for a cluster, and receive, by the MS from the BS, a cluster head configuration message indicating that the MS has been selected to be a cluster head.

[0081 ] According to an example implementation, a computer program product is provided that includes a non-transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: receiving, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface, sending, from the MS to the BS, a cluster head capability indication indicating the MS is capable of being a cluster head, the cluster head capability indication also identifying resources to be used by the MS to send reference signals for synchronization if selected by the BS to be a cluster head for a cluster, and receiving, by the MS from the BS, a cluster head configuration message indicating that the MS has been selected to be a cluster head.

[0082] FIG. 6 is a flow chart illustrating operation of a mobile station according to an example implementation. At 610, a MS mobile station (MS) receives from a base station (BS) a failure notification message indicating a failure of a BS-core network interface. At 620, the MS reconfigures the MS from a cellular or infrastructure mode to operate as a cluster head for a device-to-device (D2D) wireless cluster in response to the failure notification based on preconfigured information stored in the MS. And, at 630, the MS sends to the BS a cluster head notification message indicating that the MS has been configured to operate as a D2D cluster head.

[0083] According to an example implementation, the method of FIG. 6 may further include receiving, by the MS from the BS, a cluster head confirmation message confirming the MS operating as cluster head.

[0084] According to an example implementation, the method of FIG. 6 may further include receiving, by the MS from the BS, a cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals.

[0085] According to an example implementation, in the method of FIG. 6, the cluster head notification message identifies a MS ID of the MS, resources to be used by the MS to send reference signals for synchronization.

[0086] According to an example implementation, in the method of FIG. 6, the cluster head notification message identifies a MS ID of the MS, resources to be used by the MS to send reference signals for synchronization and a service profile to identify one or more services to be provided by the cluster head.

[0087] According to an example implementation, an apparatus may include at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: receive, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface, reconfigure, by the MS, the MS from a cellular or

[0088] According to another example implementation, a computer program product includes a non-transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: receiving, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface, reconfiguring, by the MS, the MS from a cellular or infrastructure mode to operate as a cluster head for a device-to-device (D2D) wireless cluster in response to the failure notification based on preconfigured information stored in the MS, and sending, from the MS to the BS, a cluster head notification message indicating that the MS has been configured to operate as a D2D cluster head.

[0089] FIG. 7 is a block diagram of a wireless station (e.g., BS or MS) 700 according to an example implementation. The wireless station 700 may include, for example, two RF (radio frequency) or wireless transceivers 702A, 702B, where each wireless transceiver includes a transmitter to transmit signals and a receiver to receive signals. The wireless station also includes a processor 504 to execute instructions or software and control transmission and receptions of signals, and a memory 706 to store data and/or instructions.

[0090] Processor 704 may also make decisions or determinations, generate frames, packets or messages for transmission, decode received frames or messages for further processing, and other tasks or functions described herein. Processor 704, which may be a baseband processor, for example, may generate messages, packets, frames or other signals for transmission via wireless transceiver 702. Processor 704 may control transmission of signals or messages over a wireless network, and may receive signals or messages, etc., via a wireless network (e.g., after being down-converted by wireless transceiver 702, for example). Processor 704 may be programmable and capable of executing software or other instructions stored in memory or on other computer media to perform the various tasks and functions described above, such as one or more of the tasks or methods described above. Processor 704 may be (or may include), for example, hardware, programmable logic, a programmable processor that executes software or firmware, and/or any combination of these. Using other terminology, processor 704 and transceiver 702 together may be considered as a wireless transmitter/receiver system, for example.

[0091 ] In addition, referring to FIG. 7, a controller (or processor) 708 may execute software and instructions, and may provide overall control for the station 700, and may provide control for other systems not shown in FIG. 7, such as controlling input/output devices (e.g., display, keypad), and/or may execute software for one or more applications that may be provided on wireless station 700, such as, for example, an email program, audio/video applications, a word processor, a Voice over IP application, or other application or software.

[0092] In addition, a storage medium may be provided that includes stored instructions, which when executed by a controller or processor may result in the processor 704, or other controller or processor, performing one or more of the functions or tasks described above.

[0093] Implementations of the various techniques described herein may be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Implementations may implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine-readable storage device or in a propagated signal, for execution by, or to control the operation of, a data processing apparatus, e.g., a programmable processor, a computer, or multiple computers. A computer program, such as the computer program(s) described above, can be written in any form of programming language, including compiled or interpreted languages, and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

[0094] Method steps may be performed by one or more programmable processors executing a computer program to perform functions by operating on input data and generating output. Method steps also may be performed by, and an apparatus may be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

[0095] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. Elements of a computer may include at least one processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer also may include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory may be supplemented by, or incorporated in, special purpose logic circuitry.

[0096] To provide for interaction with a user, implementations may be

implemented on a computer having a display device, e.g., a cathode ray tube (CRT) or liquid crystal display (LCD) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0097] Implementations may be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation, or any combination of such back-end, middleware, or front-end components. Components may be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (LAN) and a wide area network (WAN), e.g., the Internet.

[0098] While certain features of the described implementations have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the various embodiments.

Claims

WHAT IS CLAIMED IS:

1 . A method comprising:

detecting, by a base station (BS), a failure of an interface between the BS and a core network (BS-core network interface);

sending, by the BS, a failure notification message to one or more mobile stations (MSs) of a cell indicating the failure of the BS-core network interface;

selecting, by the BS, one or more of the MSs to be a cluster head; and

broadcasting a cluster notification message to one or more MSs of the cluster, the cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals to be used for synchronization by other MSs within the cluster.

2. The method of claim 1 and further wherein the selecting comprises:

determining, by the BS, one or more device-to-device (D2D) mode-capable MSs within the cell that are capable of being a cluster head for a cluster of MSs within the cell;

selecting, by the BS, one of the MSs to be a cluster head for the cluster; and

sending a cluster head configuration message to the selected MS indicating that the selected MS has been selected to be a cluster head for the cluster.

3. The method of claim 1 and further comprising the BS switching to a non- operational mode after broadcasting the cluster notification message.

4. The method of claim 1 and further comprising the BS switching to a downlink (DL) only D2D assistance mode in which the BS periodically broadcasts a message identifying at least cell resources used by the cluster head to transmit reference signals.

5. The method of claim 1 wherein the failure notification message comprises an interface status field that indicates the status of the BS-core network interface as failed or broken, the notification message also including a barring information that indicates that an access class of public safety D2D MSs are permitted to access resources of the cell.

6. The method of claim 1 wherein the failure notification message comprises: a transition period length field to indicate a period length for the BS to perform a transition from a cellular or infrastructure mode of operation to a new mode of operation; an interface status field that indicates the status of the BS-core network interface as failed or broken; and

a cell ID to identify the cell.

7. The method of claim 1 wherein the selecting, by the BS, comprises determining by the BS, based on capability information known by the BS for one or more MSs in the cell, one or more device-to-device (D2D) mode-capable MSs within the cell that are capable of being a cluster head for a cluster of MSs within the cell.

8. The method of claim 1 wherein the selecting, by the BS, comprises:

receiving, in response to the failure notification message, a cluster head capability indication from one or more D2D capable MSs within the cell, each cluster head capability indication indicating that the MS is capable of being a cluster head; and

selecting one of the cluster head-capable MSs to be the cluster head for the cluster.

9. The method of claim 1 wherein the selecting, by the BS, comprises:

receiving a cluster head capability indication from one or more D2D capable MSs within the cell, each cluster head capability indication indicating that the MS is capable of being a cluster head and identifying resources to be used by the MS to transmit reference signals for synchronization; and

10. The method of claim 1 wherein the cluster notification message includes at least a MS ID for the cluster head and identifies cell resources to be used by the cluster head to transmit reference signals to be used for synchronization by other MSs within the cluster.

1 1 . The method of claim 1 wherein the broadcasting the cluster notification message comprises broadcasting the cluster notification message via a system information block (SIB).

12. The method of claim 1 wherein the broadcasting the cluster notification message comprises:

notifying one or more of the MSs within the cell of a broadcast group address; scheduling a transmission via the broadcast group address; and

broadcasting the cluster notification message via the scheduled transmission.

13. The method of claim 1 wherein the broadcasting the cluster notification message comprises transmitting, to each of one or more MSs, a radio resource control (RRC) connection release, with cause set to D2D or cluster.

14. The method of claim 1 wherein the broadcasting the cluster notification message comprises transmitting a radio resource control (RRC) connection release, with cause set to S1 interface failure.

15. An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to:

detect, by a base station (BS), a failure of an interface between the BS and a core network (BS-core network interface);

send, by the BS, a failure notification message to one or more mobile stations (MSs) of a cell indicating the failure of the BS-core network interface;

select, by the BS, one or more of the MSs to be a cluster head; and

broadcast a cluster notification message to one or more MSs of the cluster, the cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals to be used for synchronization by other MSs within the cluster.

16. A computer program product, the computer program product comprising a non-transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method comprising:

selecting, by the BS, one or more of the MSs to be a cluster head; and broadcasting a cluster notification message to one or more MSs of the cluster, the cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals to be used for synchronization by other MSs within the cluster.

17. A method comprising:

receiving, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface;

sending, from the MS to the BS, a cluster head capability indication indicating the MS is capable of being a cluster head, the cluster head capability indication also identifying resources to be used by the MS to send reference signals for synchronization if selected by the BS to be a cluster head for a cluster; and

receiving, by the MS from the BS, a cluster head configuration message indicating that the MS has been selected to be a cluster head.

18. The method of claim 17 and further comprising broadcasting the reference signals via the identified resources in a device-to-device (D2D) mode of operation from the MS to one or more other MSs within the cluster in response to being selected as a cluster head.

19. The method of claim 17 and further comprising receiving, by the MS from the

BS, a broadcasted cluster notification message that identifies at least the identified resources for transmission of the reference signals or synchronization signals.

20. The method of claim 17 and further comprising receiving, by the MS from the BS, a broadcasted cluster notification message that identifies at least the identified resources and a MS ID for the cluster head.

21 . The method of claim 17 wherein the failure notification message comprises: an interface status field that indicates the BS-core network interface as failed or broken; and

access class barring information indicating that an access class of public safety D2D mode devices may access the cell and become members of the cluster.

22. The method of claim 17 wherein the failure notification message comprises a transition period length field; wherein the broadcasting the reference signals includes the MS, operating as cluster head, broadcasting the reference signals via the identified resources in the D2D mode of operation after expiration of the transition period length.

23. The method of claim 17 and further comprising the MS, operating as a cluster head in a D2D mode of operation, sending a resource allocation to one or more other MSs within the cluster to allocate resources within the cluster for D2D communication.

24. The method of claim 17 wherein the cluster head comprises a first MS, the method further comprising:

receiving, by the cluster head as a D2D communication, a resource request from a second MS within the cluster for a D2D communication between the second MS and a third MS within the cluster;

allocating, by the cluster head, resources for the D2D communication between the second MS and the third MS;

sending, by the cluster head, a resource allocation message identifying the allocated resources to at least the second MS.

25. An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to:

receive, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface;

send, from the MS to the BS, a cluster head capability indication indicating the MS is capable of being a cluster head, the cluster head capability indication also identifying resources to be used by the MS to send reference signals for synchronization if selected by the BS to be a cluster head for a cluster; and

receive, by the MS from the BS, a cluster head configuration message indicating that the MS has been selected to be a cluster head.

26. A computer program product, the computer program product comprising a non-transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method comprising: receiving, by a mobile station (MS) from a base station (BS), a failure notification message indicating a failure of a BS-core network interface;

27. A method comprising:

reconfiguring, by the MS, the MS from a cellular or infrastructure mode to operate as a cluster head for a device-to-device (D2D) wireless cluster in response to the failure notification based on preconfigured information stored in the MS; and

sending, from the MS to the BS, a cluster head notification message indicating that the MS has been configured to operate as a D2D cluster head.

28. The method of claim 27 and further comprising receiving, by the MS from the BS, a cluster head confirmation message confirming the MS operating as cluster head.

29. The method of claim 27 and further comprising receiving, by the MS from the BS, a cluster notification message identifying at least cell resources to be used by the cluster head to transmit reference signals.

30. The method of claim 27 wherein the cluster head notification message identifies a MS ID of the MS, resources to be used by the MS to send reference signals for synchronization.

31 . The method of claim 27 wherein the cluster head notification message identifies a MS ID of the MS, resources to be used by the MS to send reference signals for synchronization and a service profile to identify one or more services to be provided by the cluster head.

32. An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to:

reconfigure, by the MS, the MS from a cellular or infrastructure mode to operate as a cluster head for a device-to-device (D2D) wireless cluster in response to the failure notification based on preconfigured information stored in the MS; and

send, from the MS to the BS, a cluster head notification message indicating that the MS has been configured to operate as a D2D cluster head.

33. A computer program product, the computer program product comprising a non- transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method comprising: