WO2017102288A1

WO2017102288A1 - Enhancement on reporting enb unavailability during write/stop pws message

Info

Publication number: WO2017102288A1
Application number: PCT/EP2016/078857
Authority: WO
Inventors: Yong Yang; Mikael Wass
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2015-12-15
Filing date: 2016-11-25
Publication date: 2017-06-22

Abstract

The solution herein is directed to a method of operation of a network node 22 of a cellular communications system 10 implementing a CBS for a PWS, comprising: receiving (304) from a CBC 24 a write-replace warning request message with respect to a PWS message; determining (310) that one or more base stations 16 are unavailable to the network node; and sending (312) to the CBC, a write-replace warning indication message including information indicative of the one or more base stations that are unavailable. *** Also, there is a method of operation of a network node 22 in a cellular communications system 10 implementing a CBS for a PWS comprising: receiving (202) from a CBC 24 a stop warning request message with respect to a PWS message; determining (408) that one or more base stations 16 are unavailable to the network node; and sending (410) to the CBC a stop warning indication message including information indicative of the one or more base stations that are unavailable.

Description

ENHANCEMENT ON REPORTING eNB UNAVAILABILITY DURING WRITE/STOP

PWS MESSAGE

Technical Field

The present disclosure relates to the Public Warning System (PWS) for Global System for Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS), and Enhanced or Evolved Universal Terrestrial Radio Access Network (E- UTRAN). Background

In recent years, there has been heightened focus on disaster preparedness measures and an increasing interest in a Public Warning System (PWS) using mobile technologies. In this regard, the Third Generation Partnership Project (3GPP) has standardized a Cell Broadcast Service (CBS) for providing a PWS in 3GPP Technical Specification (TS) 23.041 V13.1.0 (2015-06). In general, the 3GPP CBS includes a Cell Broadcast Centre (CBC), which is a node and/or a function typically located in a core network of the mobile network operator, and at least one Cell Broadcast Entity (CBE). The CBE is typically a node and/or a function controlled by a governmental entity or some trusted authority. In operation, a PWS message is generated at the CBE along with a target area for the PWS message. The CBE provides the PWS message to the CBC, which maps the target area to the appropriate areas (e.g., cells, tracking areas, etc.) within the cellular communications network. With respect to Long Term Evolution (LTE) and the Enhanced or Evolved Universal Terrestrial Radio Access Network (E-UTRAN), the CBC provides the PWS message to the appropriate Mobility Management Entity(ies) (MME(s)) in the core network, which in turn provides the PWS message to the appropriate enhanced or evolved Node Bs (eNBs) for broadcast.

One issue that arises in the current CBS, as discussed below, is that the CBC cannot quickly and easily determine whether there is a failed eNB that prevented broadcast of the PWS message in a corresponding geographic area. As such, there is a need for an improved CBS. Summary

The present disclosure relates to enhanced Write-Replace Warning Indication and Stop Warning Indication procedures for a Cell Broadcasting Service (CBS) providing a Public Warning System (PWS). In some embodiments, the enhanced Write-Replace Warning Indication and Stop Warning Indication procedures are for a Third Generation

Partnership Project (3GPP) network and, in particular, for a 3GPP network (e.g., a Long Term Evolution (LTE) network) utilizing an Evolved Packet Core (EPC) and an

Enhanced or Evolved Universal Terrestrial Radio Access Network (E-UTRAN). However, the present disclosure is not limited thereto.

In some embodiments, after receiving a Write-Replace Warning Request from a Cell Broadcast Centre (CBC), a Mobility Management Entity (MME) sends (e.g., immediately) a Write-Replace Warning Indication including information indicative of one or more enhanced or evolved Node Bs (eNBs) that are unavailable (e.g., a list of unavailable eNBs). In some embodiments, the eNBs that are unavailable are eNBs that the MME cannot contact, e.g. an S1 association towards those eNBs is down, so that the MME cannot forward the messages to the eNBs. In some embodiments, the Write-Replace Warning Indication includes a new Information Element (IE), preferably called

"unavailable eNB list," that comprises information indicating the unavailable eNBs.

In some embodiments, after receiving a Stop Warning Request from a CBC, a MME sends (e.g., immediately) a Stop Warning Indication including information indicative of one or more eNBs that are unavailable (e.g., a list of unavailable eNBs). In some embodiments, the eNBs that are unavailable are eNBs that the MME cannot contact, e.g. an S1 association towards those eNBs is down, so that the MME cannot forward the messages to the eNBs. In some embodiments, the Stop Warning Indication includes a new IE, preferably called "unavailable eNB list," that comprises information indicating the unavailable eNBs. Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the embodiments in association with the accompanying drawing figures. The accompanying drawing figures incorporated in and forming a part of this

specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

Figure 1 illustrates a system implementing a Cell Broadcast Service (CBS) for a Public Warning System (PWS) according to some

embodiments of the present disclosure;

Figure 2 illustrates a conventional Write-Replace Warning Indication

procedure for the CBS of Figure 1 ;

Figure 3 illustrates a conventional Stop Warning Indication procedure for the

CBS of Figure 1 ;

Figure 4 illustrates an enhanced Write-Replace Warning Indication procedure according to some embodiments of the present disclosure;

Figure 5 illustrates an enhanced Stop Warning Indication procedure

according to some embodiments of the present disclosure;

Figures 6 and 7 illustrate embodiments of the Mobility Management Entity (MME) of

Figure 1 according to some embodiments of the present disclosure. Detailed Description

The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure.

The present disclosure relates to a Cell Broadcasting Service (CBS) for a Public Warning System (PWS). In this regard, Figure 1 illustrates an exemplifying PWS implemented by a CBS provided by a cellular communications system 10 according to some embodiments of the present disclosure. Note that, in this example, the cellular communications system 10 is a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) network including an Enhanced or Evolved Universal Terrestrial Radio Access Network (E-UTRAN) 12 and an Evolved Packet Core (EPC) 14 at least comprising a Mobility Management Entity (MME) 22 and preferably also a Cell

Broadcast Centre (CBC) 24 as will be elaborated in some detail below; however, the present disclosure is not limited thereto. The concepts disclosed herein can be implemented in any suitable type of cellular communications system.

As illustrated, the E-UTRAN 12 includes an evolved Node Bs (eNB) 16 serving a corresponding cell(s) (not shown). The eNB 16 provide radio access to a User

Equipment device (UE) 20 in a respective cell. Note that while 3GPP LTE terminology (e.g., eNB and UE) is used herein, as stated above, the present disclosure is not limited to 3GPP LTE and, as such, more general terminology (e.g., radio access node or base station as opposed to eNB and wireless device as opposed to UE and coverage area as opposed to cell or beam) may be used. Further, while only one eNB 16 and one UE 20 is illustrated in Figure 1 , the cellular communications system 10 includes many eNBs 16 serving many UEs 20. The eNB 16 is connected to a MME 22 within the EPC 14 via a S1 -MME interface/connection. The MME 22 is connected to a CBC 24 within the EPC 14 via an SBc interface/connection. Note that while only one MME 22 and one CBC 24 are illustrated in Figure 1 , the EPC 14 may include many MMEs 22 and one or more CBCs 24. Further, while the CBC 24 is illustrated within the EPC 14, the CBC 24 may alternatively be located outside of the EPC 14.

In this example, one or more Cell Broadcasting Entities (CBEs) 26 are outside of the cellular communications system 10. The CBEs 26 are part of the PWS/CBS and operate to, among other things, originate PWS messages and to instruct the cellular

communications system 10 to stop broadcasting PWS messages, as desired or as appropriate. The CBEs 26 may be, e.g., governmental entities or other trusted authorities.

The general properties and functions of the MME 22 and the CBC 24 and the CBE 26 are well known to those skilled in the art and need no detailed description as such. However, specific properties and/or functions associated with embodiments of this disclosure will be elaborated in some detail below. Figure 2 illustrates a conventional Write-Replace Warning procedure by which the CBS broadcasts a PWS message. This procedure is currently specified in 3GPP Technical Specification (TS) 23.041 V13.1.0 (2015-06). As such, the details will not be repeated. In general, the eNB 16, the UE 20, and the MME 22 perform registration and security procedures (step 100). The CBE 26 sends an emergency broadcast request to the CBC 24 (step 102). The emergency broadcast request includes, e.g., a PWS warning message, an impacted (or target) area, and a time period. The CBC 24 uses the impacted area information to identify which MMEs 22 need to be contacted regarding the emergency broadcast request. The CBC 24 then sends a Write-Replace Warning Request message to the identified MMEs 22 (step 104). Note that, for clarity and ease of discussion, only one MME 22 is illustrated in this example. However, it should be understood that the CBC 24 may identify and send the Write-Replace Warning Request message to multiple MMEs 22. The Write-Replace Warning Request message includes, e.g., the warning message to be broadcast and one or more delivery attributes (e.g., message identifier (ID), serial number, Tracking Area Identifier (TAI) list, Warning Area, Send Write-Replace-Warning-lndication, etc.). The Warning Area may be a list of cell IDs or a list of TAIs or one or more Emergency Area IDs corresponding to the impact area, or target area, for the PWS warning message. The Warning Area is optional. If the Warning Area is not included, then this is interpreted as all cells.

The MME 22 sends a Write-Replace Warning Confirm message to the CBC 24 (step 106). This indicates that the MME 22 has started to distribute the PWS warning message to eNBs 16. Upon receiving the Write-Replace Warning Confirm message, the CBC 24 may confirm to the CBE 26 that the CBC 24 has started to distribute the PWS warning message (step 108).

The MME 22 may use the TAI(s) and/or the Warning Area(s) or similar in the Write- Replace Warning Request message received by the MME 22 in step 104 to determine which eNBs 16 serve cells within the impact area. Alternatively, if no Warning Area or similar is included, then the MME 22 may determine that all eNBs 16 are within the impact area. The MME 22 sends or forwards the Write-Replace Warning Request message to the eNBs 16 that the MME 22 has determined should receive the request (step 110). In this example, only one eNB 16 is illustrated for clarity and ease of discussion; however, it should be appreciated that the MME 22 would typically send the Write-Replace Warning Request message to many eNBs 16. The eNBs 16 then broadcast the PWS warning message to the UEs 20 in their respective cells (step 112). The eNBs 16 send a Write-Replace Warning Response to the MME 22 (step 114). The UE(s) 20 alerts the respective users of the warning message (step 116).

If the Send Warning-Message-Indication parameter was present in the Write-Replace Warning Request message, the MME 22 sends a Write-Replace Warning Indication message(s) to the CBC 24 (step 118). The Write-Replace Warning Indication message(s) include Broadcast Scheduled Area Lists containing Broadcast Completed Area Lists that the MME 22 has received from the eNBs 16. The MME 22 determines the success or failure of message delivery based on the Write-Replace Warning Response message(s) received from the eNB(s) 16 and records the success/failure (step 120). Figure 3 illustrates a conventional Stop Warning procedure by which the CBS stops, or cancels, broadcasts of a PWS message. This procedure is currently specified in 3GPP TS 23.041 V13.1.0 (2015-06). As such, the details will not be repeated. In general, the CBE 26 sends a Stop Emergency Broadcast Request to the CBC 24 (step 200). The Stop Emergency Broadcast Request includes, e.g., a message ID and a serial number of the PWS warning message to be cancelled. The CBC 24 identifies (e.g., based on the message ID and/or serial number of the PWS warning message to be cancelled) which MMEs 22 need to be contacted regarding the stop emergency broadcast request. The CBC 24 then sends a Stop Warning Request message to the identified MMEs 22

(step 202). Note that, for clarity and ease of discussion, only one MME 22 is illustrated in this example. However, it should be understood that the CBC 24 may identify and send the Stop Warning Request message to multiple MMEs 22. The Stop Warning Request message includes, e.g., the message ID, serial number, tracking area ID list, warning area, send stop warning indication, etc. The MME 22 sends a Stop Warning Confirm message to the CBC 24 (step 204). This indicates that the MME 22 has started to distribute a "kill request" to eNBs 16. Upon receiving the Stop Warning Confirm message, the CBC 24 may confirm to the CBE 26 that the CBC 24 has initiated the procedure for cancelling the warning message

(step 206).

The MME 22 sends a Kill Request message to the eNBs 16 that the MME 22 has determined should receive the request (step 208). The MME 22 may use, e.g., the TAI list to determine which eNBs 16 may be broadcasting the PWS warning message and thus should receive the Kill Request. In this example, only one eNB 16 is illustrated for clarity and ease of discussion; however, it should be appreciated that the MME 22 would typically send the Kill Request message to many eNBs 16. The eNBs 16 then stop broadcasting the PWS warning message to the UEs 20 in their respective cells

(step 210). The eNBs 16 send a Kill Response message to the MME 22 (step 212).

If the Send Warning-Message-Indication parameter was present in the Stop Warning Request message, the MME 22 sends a Stop Warning Indication message(s) to the CBC 24 (step 214). The Stop Warning Indication message(s) include Broadcast

Scheduled Area Lists containing Broadcast Cancelled Area Lists that the MME 22 has received from the eNBs 16. The MME 22 determines the success or failure of message delivery based on the Kill Response message(s) received from the eNB(s) 16 and records the success/failure (step 216).

A problem with the conventional Write-Replace Warning procedure and the conventional Stop Warning procedure of Figures 2 and 3, respectively, is as follows. When the CBC 24 sends a Write-Replace Warning Request message or a Stop Warning Request message to the MME 22 and the MME 22 cannot deliver the message to one or more eNBs 16, then the CBC 24 only becomes aware that message delivery failed by the fact that the cells under the eNBs 16 that did not get the message are not contained in the Write-Replace Warning Indication or the Stop Warning Indication. Note that, in the conventional procedures, if the MME 22 cannot contact an eNB 16, then steps 1 10-1 16 (for the Write-Replace Message procedure of Figure 2) and steps 208-212 (for the Stop Warning procedure of Figure 3) cannot be performed with respect to that eNB 16. In the case of message delivery failure, the CBC 24 may decide to repeat the Write-Replace Warning Request message or the Stop Warning Request message e.g. via a different MME 22 in the pool in that case. Waiting for all the Write-Replace Warning Indication or Stop Warning Indication messages to determine whether the message delivery succeeded or not is not a good approach as:

a) it causes latency to detect the failure and thus to repeat the message; i.e. the CBC 24 has to wait for a time-out to occur until the CBC 24 can conclude that message delivery must have failed;

b) it requires processing in the CBC 24 to aggregate all Write-Replace

Warning Indication or Stop Warning Indication messages and then check cells for which no response was received; and

c) the CBC 24 cannot differentiate the case where the Write-Replace

Warning Request was not received from the eNB 16 from the case where it was but the request was unsuccessful for all the requested cells of the eNB 16 for other reasons (e.g., cells off), if no Failure Indication was received (e.g., a pre-Release 13 eNB or Home eNB (HeNB) Gateway (GW) or the message was lost); in the latter case, it makes no sense to repeat the request.

On the other hand, the MME 22 knows the eNBs 16 for which the S1 AP interface is down.

There were a number of attempts in 3GPP to propose that MMEs 22 shall provide a list of failed eNB IDs in the Write-Replace Warning Response or the Stop Warning

Response message to allow the CBC 24 to timely get such eNB failure information, so that the CBC 24 can determine whether to retry with an alternative MME 22 to deliver the same message, e.g. at CT1#95 meeting, a change request was proposed

(one2many et al., "C1 -154162: Unavailable eNodeB List," 3GPP TSG-CT WG1 Meeting #95, November 16-20, 2015, Anaheim, California). There was a similar attempt in 2013 (one2many, "C1-133725: Unavailable eNodeB List," 3GPP TSG-CT WG1 Meeting #84bis, October 7-1 1 , 2013, Porto, Portugal).

Currently, the MME 22 will, as specified in 3GPP TS 23.041 V13.1.0, Section 9.1.3.4.2 Warning Message Delivery Procedure in E-UTRAN, step 8 (which corresponds to step If the Send Warning-Message-Indication parameter was present in the Write-Replace Warning Request and it is configured in the MME based on operator policy, the MME shall forward the Broadcast Scheduled Area Lists in a Write-Replace Warning Indication(s) to the CBC. The Broadcast Scheduled Area List shall contain the Broadcast Completed Area List the

MME has received from the eNodeB. The MME may aggregate Broadcast Completed Area Lists it receives from eNodeBs.

Section 9.1.3.4.3 Warning Message Cancel Procedure, step 7 (which corresponds to step 214 of Figure 3), states:

If the Send Stop Warning Indication parameter was present in the Stop Warning Request and it is configured in the MME based on operator policy, the MME forwards the Broadcast Cancelled Area List it has received from the eNodeB in a Stop Warning Indication(s) to the CBC. The MME may aggregate Broadcast Cancelled Area Lists it receives from eNodeBs.

If the CBC has requested the MME to send Stop Warning Indications, then the CBC releases the Serial Number of a message after it has stopped receiving the Stop Warning Indications for that message.

Such indication messages are further specified in Sections 9.2.20 and 9.2.21 of 3GPP TS 23.041 V13.1.0, as follows.

9.2.20 WRITE-REPLACE-WARNING-INDICATION Request/Indication

This Indication is sent by the MME to report to the CBC the Broadcast Scheduled Area List(s) the MME has received from the eNodeB(s) as Broadcast Completed Area List. Multiple responses from eNodeBs may be combined in a Broadcast Scheduled Area List.

If the MME interfaces with multiple CBCs (i.e., has active SCTP associations established with multiple CBCs), the MME shall forward the same WRITE-REPLACE-WARNING-INDICATION message to all CBCs.

The Broadcast Scheduled Area List IE is not included in the WRITE- REPLACE WARNING INDICATION when the broadcast is unsuccessful in all the cells within the eNodeBs. 9.2.21 STOP-WARNING-INDICATION Request/Indication

This message is sent by the MME to report to the CBC the Broadcast

Cancelled Area List the MME has received from the eNodeB in a KILL

RESPONSE. If the MME has received a KILL RESPONSE without a

Broadcast Cancelled Area List IE, then the eNodeB ID shall be included in the Broadcast Empty Area List instead. The MME may aggregate

Broadcast Cancelled Area Lists it receives from eNodeBs.

If the MME interfaces with multiple CBCs (i.e., has active SCTP associations established with multiple CBCs), the MME shall forward the same STOP-WARNING-INDICATION message to all CBCs.

The Broadcast Cancelled Area List IE is included in the STOP- WARNING-INDICATION when stopping the broadcast was successful in at least one of the cells within the eNodeBs.

The Broadcast Empty Area List IE shall be included in the STOP-

WARNING-INDICATION when the MME has received at least one KILL

RESPONSE without a Broadcast Cancelled Area List IE.

Note that the fact that the Broadcast Scheduled Area List IE is not included in the Write- Replace Warning Indication when the broadcast is unsuccessful in all the cells within the eNBs cannot be used as an indication of eNB failure as, in this case, the CBC 24 gets clear indication from the eNB 16 that none of the cells is successful (i.e., the eNB 16 is healthy but unable to perform PWS message broadcast). In such as case, there is no point in retrying with an alternative MME 22.

The previously proposed enhancement (adding a failed eNB list directly in the response message (Write-Replace Warning Response and Stop Warning Response messages)) has a large impact on the existing Write-Replace Warning and Stop Warning procedures. As of today, the MME 22 just checks if the included TAI or eNB ID is recognized. If so, it will respond to the CBC 24 that it will forward the request, i.e. the Write-Replace Warning Request or the Stop Warning Request, to all eNBs 16 addressed. The previously proposed enhancement will add extra processing load on the MME 22, thus leading to extra delay. More importantly, such eNB failure or S1 failure should be considered as an exceptional case, and hence impacting the normal procedure as previously proposed is less than ideal. The present disclosure proposes a new alternative by enhancing the existing Write- Replace Warning Indication and Stop Warning Indication procedures. The new alternative introduces a new requirement for the MME 22; that is, the MME 22 shall send (e.g., immediately) the Write-Replace Warning Indication or the Stop Warning Indication respectively for the Write-Replace Warning Request and the Stop Warning Request message for the eNBs 16 that the MME 22 cannot contact certain eNBs, e.g. S1 association towards those eNBs 16 are down, so that the MME 22 cannot forward the messages to the eNBs 16. In some embodiments, a new Information Element (IE), preferably called "unavailable eNB list," is added in the Write-Replace Warning

Indication and the Stop Warning Indication, as indicated below.

9.2.20 WRITE-REPLACE-WARNING-INDICATION Request/Indication

Note that the Broadcast Empty Area List, even though it denotes a list of eNB IDs, indicates that the eNB has responded to the Kill Request message, but no broadcast is to be stopped. The present disclosure proposes an idea without impact on the normal warning message write-replace or stop. The idea is naturally merged into the existing mechanism to report the outcome of a warning message write-replace or stop. In general, in some

embodiments, a network node (e.g., the MME 22) receives, from the CBC 24, a PWS signaling message (e.g., a Write-Replace Warning Request message or a Stop Warning Request message) addressed to multiple eNBs 16. The MME 22 determines or otherwise has knowledge that at least one of those eNBs 16 is unavailable and sends, to the CBC 24, an indication message (e.g., a Write-Replace Warning Indication message or a Stop Warning Indication message) including an indication of the at least one eNB 16 that is unavailable. The MME 22 may, e.g., determine that one or more eNBs 16 are unavailable in that the MME 22 knows for which eNB(s) the S1 AP interface is down, and/or in that the MME 22 has sent one or more messages or similar to one or more eNBs without receiving any acknowledging response or similar, and/or in that the MME 22 has received information from some other node or function in the network indicating that one or more eNBs 16 are unavailable.

In this regard, Figure 4 illustrates a Write-Replace Warning procedure according to some embodiments of the present disclosure. Steps 300-308 are the same as steps 100-108 of the procedure of Figure 2. In general, the eNB 16, the UE 20, and the MME 22 perform registration and security procedures (step 300). The CBE 26 sends an emergency broadcast request to the CBC 24 (step 302). The emergency broadcast request includes, e.g., a PWS warning message, an impacted (or target) area, and a time period. The CBC 24 uses the impacted area information to identify which MMEs 22 need to be contacted regarding the emergency broadcast request. The CBC 24 then sends a Write-Replace Warning Request message to the identified MMEs 22 (step 304). Note that, for clarity and ease of discussion, only one MME 22 is illustrated in this example. However, it should be understood that the CBC 24 may identify and send the Write-Replace Warning Request message to multiple MMEs 22. The Write-Replace Warning Request message includes, e.g., the warning message to be broadcast and one or more delivery attributes (e.g., message ID, serial number, TAI list, Warning Area, Send Write-Replace-Warning-lndication, etc.). The Warning Area may be a list of cell IDs or a list of TAIs or one or more Emergency Area IDs corresponding to the impact area, or target area, for the PWS warning message. The Warning Area is optional. If the Warning Area is not included, then this is interpreted as all cells.

The MME 22 sends a Write-Replace Warning Confirm message to the CBC 24 (step 306). This indicates that the MME 22 has started to distribute the PWS warning message to eNBs 16. Upon receiving the Write-Replace Warning Confirm message, the CBC 24 may confirm to the CBE 26 that the CBC 24 has started to distribute the PWS warning message (step 308). The MME 22 may use the TAI(s) and/or Warning Area(s) or similar in the Write-Replace Warning Request message received by the MME 22 in step 304 to determine which eNBs 16 serve cells within the impact area. Alternatively, if no Warning Area or similar is included, then the MME 22 may determine that all eNBs 16 are within the impact area. The MME 22 determines that one or more of the eNBs 16 in the impact area of the Write-Replace Warning Request message received by the MME 22 in step 304 are unavailable to the MME 22 (step 310). In this particular example, the illustrated eNB 16 is unavailable; however, it should be understood that there may be more than one unavailable eNB 16.

Since the eNB 16 is unavailable, the MME 22 sends, to the CBC 24, a Write-Replace Warning Indication message including information indicative of the unavailable eNB(s) 16, e.g., a list of IDs of the unavailable eNBs 16 (step 312). In some embodiments, the Write-Replace Warning Indication message includes a new IE, where the new IE includes information indicative of the unavailable eNBs 16, e.g., a list of IDs of the unavailable eNBs 16. Note that, with respect to the procedure for other available eNBs 16, the Write-Replace Warning Indication message of step 310 may be sent at any time between reception of the Write-Replace Warning Request message in step 304 and receipt of Write-Replace Warning Response message(s) from other eNBs 16 that are available (processing for the available eNBs 16 may be the same as that set forth in Figure 2). In some embodiments, the MME 22 sends the Write-Replace Warning Indication message including the indication of the unavailable eNB(s) 16 immediately after receiving the Write-Replace Warning Request message, immediately after sending the Write-Replace Warning Confirm message, or sometime before sending Write- Replace Warning Request messages to the available eNBs 16.

Figure 5 illustrates a Stop Warning procedure according to some embodiments of the present disclosure. Steps 400-406 are the same as steps 200-206 of Figure 3. The CBE 26 sends a Stop Emergency Broadcast Request to the CBC 24 (step 400). The Stop Emergency Broadcast Request includes, e.g., a message ID and a serial number of the PWS warning message to be cancelled. The CBC 24 identifies (e.g., based on the message ID and/or serial number of the PWS warning message to be cancelled) which MMEs 22 need to be contacted regarding the Stop Emergency Broadcast Request. The CBC 24 then sends a Stop Warning Request message to the identified MMEs 22 (step 402). Note that, for clarity and ease of discussion, only one MME 22 is illustrated in this example. However, it should be understood that the CBC 24 may identify and send the Stop Warning Request message to multiple MMEs 22. The Stop Warning Request message includes, e.g., the message ID, serial number, TAI list, warning area, send stop warning indication, etc.

The MME 22 sends a Stop Warning Confirm message to the CBC 24 (step 404). This indicates that the MME 22 has started to distribute a "kill request" to eNBs 16. Upon receiving the Stop Warning Confirm message, the CBC 24 may confirm to the CBE 26 that the CBC 24 has initiated the procedure for cancelling the warning message (step 406). The MME 22 determines which eNBs 16 should receive a Kill Request for the PWS warning message. The MME 22 may use, e.g., the TAI list to determine which eNBs 16 may be broadcasting the PWS warning message and thus should receive the Kill Request.

The MME 22 determines that one or more of the eNBs 16 in the impact area of the Stop Warning Request message received by the MME 22 in step 402 are unavailable to the MME 22 (step 408). In other words, the MME 22 determines that one or more of the eNBs 16 that should receive the Kill Request are unavailable. In this particular example, the illustrated eNB 16 is unavailable; however, it should be understood that there may be more than one unavailable eNB 16. Since the eNB 16 is unavailable, the MME 22 sends, to the CBC 24, a Stop Warning Indication message including information indicative of the unavailable eNB(s) 16 (step 410). In some embodiments, the Stop Warning Indication message includes a new IE, where the new IE includes information indicative of the unavailable eNBs 16, e.g., a list of IDs of the unavailable eNBs 16. Note that, with respect to the procedure for other available eNBs 16, the Stop Warning Indication message of step 410 may be sent at any time between reception of the Stop Warning Request message in step 402 and receipt of Stop Warning Response message(s) from other eNBs 16 that are available

(processing for the available eNBs 16 may be the same as that set forth in Figure 3). In some embodiments, the MME 22 sends the Stop Warning Indication message including the indication of the unavailable eNB(s) 16 immediately after receiving the Stop Warning Request message, immediately after sending the Stop Warning Confirm message, or sometime before sending Kill Request messages to the available eNBs 16. Figure 6 is a schematic diagram of the MME 22 in accordance with some embodiments of the present disclosure. Note that while the functionality of generating and sending the Write-Replace Warning Indication message and the Stop Warning Indication message including the list of unavailable eNBs 16 is implemented in the MME 22 in the example cellular communications system 10 described herein, the present disclosure is not limited thereto. This functionality may be implemented in any suitable network node.

The MME 22 includes one or more processors 28 (e.g., one or more Central Processing Units (CPUs), one or more Application Specific Integrated Circuits (ASICs), one or more Field Programmable Gate Arrays (FPGAs), and/or the like), memory 30, and a network interface 32. The processor(s) 28 can execute instructions stored in the memory 30 based on, e.g., signals or messages received from the CBC 24 and/or the eNBs 16. In particular, in some embodiments, the functionality of the MME 22 described herein is implemented in software that is stored in the memory 30 and executed by the processor(s) 28. The network interface 32 allows the MME 22 to interact with other network nodes such as, e.g., the CBC 24 and the eNBs 16.

In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the MME 22 according to any one of the embodiments described herein is provided. In some embodiments, a carrier containing the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as the memory 30).

Figure 7 illustrates the MME 22 (or more generally network node or core network node) according to some other embodiments of the present disclosure. The MME 22 includes a request process module 34 and an indication sending module 36, each of which is implemented in software. The request processing module 34 operates to process Write- Replace Warning Request messages and/or Stop Warning Request messages received from the CBC 24, as described above. The indication sending module 36 operates to send (e.g., via a network interface of the MME 22, not shown) the Write-Replace Warning Indication message including the indication of unavailable eNBs 16 and/or the Stop Warning Indication message including the indication of unavailable eNBs 16, as described above.

Those skilled in the art will recognize improvements and modifications to the

embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

The following acronyms are used throughout this disclosure.

3GPP Third Generation Partnership Project

ASIC Application Specific Integrated Circuit

CBC Cell Broadcast Centre

CBE Cell Broadcast Entity

CBS Cell Broadcast Service

CPU Central Processing Unit

eNB Enhanced or Evolved Node B

EPC Evolved Packet Core

E-UTRAN Enhanced or Evolved Universal Terrestrial Radio Access Network

FPGA Field Programmable Gate Array

GSM Global System for Mobile Communications

GW Gateway

HeNB Home Enhanced or Evolved Node B

ID Identifier

IE Information Element

LTE Long Term Evolution

MME Mobility Management Entity

PWS Public Warning System

TAI Tracking Area Identity

TS Technical Specification

UE User Equipment

UMTS Universal Mobile Telecommunications System

Claims

1. A method of operation of a network node (22) of a cellular communications system (10) implementing a Cell Broadcast Service, CBS, for a Public Warning System, PWS, comprising:

receiving (304), from a Cell Broadcast Centre, CBC, (24) a write-replace warning request message with respect to a PWS message;

determining (310) that one or more base stations (16) are unavailable to the network node; and

- sending (312), to the CBC, a write-replace warning indication message including information indicative of the one or more base stations that are unavailable.

2. The method according to claim 1 ; wherein sending the write-replace warning indication message comprises sending the write-replace warning indication message after receiving (304) the write-replace warning request message from the CBC and before receiving (1 14) write-replace warning response messages from one or more available base stations.

3. The method according to claim 1 ; wherein sending the write-replace warning indication message comprises sending the write-replace warning indication message after receiving (304) the write-replace warning request message from the CBC and before sending (1 10) write-replace warning request messages to one or more available base stations.

4. The method according to any one of claim 1 or 2; wherein the write-replace warning indication message comprises an Information Element, IE, including information indicative of the one or more base stations that are unavailable, e.g., a list of identifiers of the one or more base stations that are unavailable.

5. The method according to any one of claim 1-4; wherein the network node is a Mobility Management Entity, MME, (22) and the one or more unavailable base stations are enhanced or evolved Node Bs, eNBs, (16) that the MME is unable to contact.

6. The method according to any one of claim 1-4; wherein the network node is a Mobility Management Entity, MME, (22) and the one or more unavailable base stations are enhanced or evolved Node Bs, eNBs, (16) for which respective S1 associations are down.

7. A method of operation of a network node (22) in a cellular communications system (10) implementing a Cell Broadcast Service, CBS, for a Public Warning System, PWS, comprising:

receiving (202), from a Cell Broadcast Centre, CBC, (24) a stop warning request message with respect to a PWS message;

determining (408) that one or more base stations (16) are unavailable to the network node; and

sending (410), to the CBC, a stop warning indication message including information indicative of the one or more base stations that are unavailable.

8. The method according to claim 7; wherein sending the stop warning indication message comprises sending the stop warning indication message after receiving (202) the stop warning request message from the CBC and before receiving (212) kill response messages from one or more available base stations.

9. The method according to claim 7; wherein sending the stop warning indication message comprises sending the stop warning indication message after receiving (202) the stop warning request message from the CBC and before sending (208) kill request messages to one or more available base stations.

10. The method according to any one of claim 7 or 8; wherein the stop warning indication message comprises an Information Element, IE, including information indicative of the one or more base stations that are unavailable, e.g., a list of identifiers of the one or more base stations that are unavailable.

1 1 . The method according to any one of claim 7-10; wherein the network node is a Mobility Management Entity, MME, (22) and the one or more unavailable base stations are enhanced or evolved Node Bs, eNBs, (16) that the MME is unable to contact.

12. The method according to any one of claim 7-10; wherein the network node is a Mobility Management Entity, MME, (22) and the one or more unavailable base stations are enhanced or evolved Node Bs, eNBs, (16) for which respective S1 associations are down.

13. A network node (22) of a cellular communications system (10) implementing a Cell Broadcast Service, CBS, for a Public Warning System, PWS, the network node being adapted to operate according to any one of embodiment 1 -12.