WO2018171892A1

WO2018171892A1 - Mbms bearer handling in a group communications system

Info

Publication number: WO2018171892A1
Application number: PCT/EP2017/057049
Authority: WO
Inventors: Magnus TRÄNK; Joakim ÅKESSON
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2017-03-24
Filing date: 2017-03-24
Publication date: 2018-09-27
Anticipated expiration: 2019-09-24

Abstract

There is provided mechanisms for MBMS bearer handling in a group communications system. A method is performed by a control node. The method comprises activating a second MBMS bearer using SC-PTM transmission in the group communications system upon need. The method comprises announcing the second MBMS bearer on an already activated and announced first MBMS bearer to client nodes of the group communications system.

Description

MBMS BEARER HANDLING

IN A GROUP COMMUNICATIONS SYSTEM

TECHNICAL FIELD

Embodiments presented herein relate to methods, a control node, a client node, computer programs, and a computer program product for MBMS bearer handling in a group communications system.

BACKGROUND

An example of applications available in some communications system is group communications services. In general terms, group communication means that the same information or media is delivered to multiple client nodes. In group communication systems (e.g., Push-To-Talk (PTT) systems) the client nodes receiving the same media constitute a group of client nodes. These client nodes may be located at different locations. If many client nodes are located within the same area, multicast or broadcast based transmission using e.g., Multicast-Broadcast Multimedia Services (MBMS) is efficient for communications to the group of client nodes, because communications resources such as time and frequency resources are shared among client nodes. If client nodes are spread out over a large geographical area it can be more efficient to use unicast transmission for communications to the group of client nodes.

Before using MBMS there are two different activities that currently must be performed.

Firstly, an MBMS bearer must be activated. This will enable media to be sent over the network and be broadcasted to wireless devices hosting the client nodes. In a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) network this is initiated in a Broadcast Multicast Service Center (BMSC) as defined in 3GPP TS 23.246 νΐ ΐ.ο.

Secondly, the client nodes must be informed of the service being broadcasted over the MBMS bearer. This is required so that the client nodes know how to receive the media over the MBMS bearer. This procedure is commonly known as a service announcement procedure and is defined in 3GPP TS 26.346

V14.2.0.

The information sent in the service announcement message includes several aspects of the service that shall be broadcasted. For example, it includes a reference to the MBMS bearer, it includes Internet protocol (IP) address, ports, protocols and codecs used to receive the media that shall broadcasted. This type of information is currently essential in order for the client node to, via its hosting wireless device, receive anything on the MBMS bearer, and is therefore currently mandatory. Furthermore, the service announcement may contain several other type of information, such as service area, scheduling information, reception reporting procedures, error correction information, etc.

When using MBMS for group communication both of the above mandatory activities must be performed before a group call over MBMS may start. The reason for this is that, at least currently, both bearer activation and service announcement is too time consuming to be performed at the start of the group call.

Due to the group communications dynamic need for MBMS capacity, and the time consuming provisioning process (which includes both the activation of the MBMS bearer as well as the service announcement process), it can be difficult to efficiently use the MBMS capacity for a group communication system such as a PTT system.

Hence, there is a need for mechanisms that enable efficient use of MBMS capacity in a group communications system.

SUMMARY

An object of embodiments herein is to provide efficient use of MBMS capacity in a group communications system. According to a first aspect there is presented a method for MBMS bearer handling in a group communications system. The method is performed by a control node. The method comprises activating a second MBMS bearer using Single Cell Point to Multipoint (SC-PTM) transmission in the group communications system upon need. The method comprises announcing the second MBMS bearer on an already activated and announced first MBMS bearer to client nodes of the group communications system.

According to a second aspect there is presented a control node for MBMS bearer handling in a group communications system. The control node comprises processing circuitry. The processing circuitry is configured to cause the control node to activate a second MBMS bearer using SC-PTM transmission in the group communications system upon need. The

processing circuitry is configured to cause the control node to announce the second MBMS bearer on an already activated and announced first MBMS bearer to client nodes of the group communications system.

According to a third aspect there is presented a control node for MBMS bearer handling in a group communications system. The control node comprises processing circuitry and a storage medium. The storage medium stores instructions that, when executed by the processing circuitry, cause the control node to perform operations, or steps. The operations, or steps, cause the control node to activate a second MBMS bearer using SC-PTM

transmission in the group communications system upon need. The

operations, or steps, cause the control node to announce the second MBMS bearer on an already activated and announced first MBMS bearer to client nodes of the group communications system.

According to a fourth aspect there is presented a control node for MBMS bearer handling in a group communications system. The control node comprises an activate module configured to activate a second MBMS bearer using SC-PTM transmission in the group communications system upon need. The control node comprises an announce module configured to announce the second MBMS bearer on an already activated and announced first MBMS bearer to client nodes of the group communications system.

According to a fifth aspect there is presented a computer program for MBMS bearer handling in a group communications system. The computer program comprises computer program code which, when run on processing circuitry of a control node, causes the control node to perform a method according to the first aspect.

According to a sixth aspect there is presented a method for MBMS bearer handling in a group communications system. The method is performed by a client node. The method comprises obtaining announcement of a second MBMS bearer on an already announced first MBMS bearer from a control node of the group communications system, wherein the second MBMS bearer uses SC-PTM transmission.

According to a seventh aspect there is presented a client node for MBMS bearer handling in a group communications system. The client node comprises processing circuitry. The processing circuitry is configured to cause the client node to obtain announcement of a second MBMS bearer on an already announced first MBMS bearer from a control node of the group communications system, wherein the second MBMS bearer uses SC-PTM transmission.

According to an eighth aspect there is presented a client node for MBMS bearer handling in a group communications system. The client node comprises processing circuitry and a storage medium. The storage medium stores instructions that, when executed by the processing circuitry, cause the client node to obtain announcement of a second MBMS bearer on an already announced first MBMS bearer from a control node of the group

communications system, wherein the second MBMS bearer uses SC-PTM transmission.

According to a ninth aspect there is presented a client node for MBMS bearer handling in a group communications system. The client node comprises an obtain module configured to obtain announcement of a second MBMS bearer on an already announced first MBMS bearer from a control node of the group communications system, wherein the second MBMS bearer uses SC-PTM transmission. According to a tenth aspect there is presented a computer program for MBMS bearer handling in a group communications system, the computer program comprising computer program code which, when run on processing circuitry of a client node, causes the client node to perform a method according to the sixth aspect. According to an eleventh aspect there is presented a computer program product comprising a computer program according to at least one of the fifth aspect and the tenth aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium. Advantageously these methods, these control nodes, these client nodes, and these computer programs provide efficient use of MBMS capacity in a group communications system.

Advantageously these methods, these control nodes, these client nodes, and these computer programs could be used to combine the benefits of using Multicast-Broadcast Single Frequency Network (MBSFN) transmission, which gives improved Signal-to-Interference Ratio (SIR), and SC-PTM, that provides a quick setup time for a MBMS bearers.

Advantageously these methods, these control nodes, these client nodes, and these computer programs could be used to increase call setup performance for client nodes using unicast transmission.

Advantageously these methods, these control nodes, these client nodes, and these computer programs could be used to improve resource efficiency since the second MBMS bearer could be activated only in cells in which activation is justified. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, module, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram illustrating a communications system wherein according to embodiments can be applied;

Fig. 2 is a signalling diagram;

Figs. 3, 4, 5, and 6 are flowcharts of methods according to embodiments;

Fig. 7 is a signalling diagram according to an embodiment; Fig. 8 is a schematic diagram showing functional units of a control node according to an embodiment;

Fig. 9 is a schematic diagram showing functional modules of a control node according to an embodiment;

Fig. 10 is a schematic diagram showing functional units of a client node according to an embodiment;

Fig. 11 is a schematic diagram showing functional modules of a client node according to an embodiment; and Fig. 12 shows one example of a computer program product comprising computer readable means according to an embodiment.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

Fig. l is a schematic diagram illustrating a communications system 100 where embodiments presented herein can be applied. The communications system 100 is assumed to provide services for group communications and may hence be regarded as a group communications system. The group communications system 100 is, according to some aspects, a push to talk (PTT) system. The group communications system provides group

communication services to client nodes 300a, 300b, 300c, 30od. Each client node 300a, 300b, 300c, 30od could implement the functionality of a mission critical (MC) service client. Each client node 300a, 300b, 300c, 30od may be provided in, or installed on, a respective wireless device 160a, 160b, 160c, i6od. Thus, any operation, step, action, or similar as performed by a client node 300a, 300b, 300c, 30od can be seen as performed by the corresponding wireless device 160a, 160b, 160c, i6od.

The communications system 100 comprises a radio access network 120, a core network 130, and a service network 140. The communications system 100 further comprises at least one control node 200. The at least one control node 200 may be provided in, or installed on, a radio access network node 110a, 110b, 110c providing network access in cells 150a, 150c, lsod or in another entity or device in the radio access network 120, in an entity or device of the core network 130, or in an entity or device of the service network 140. The at least one control node 200 could implement the functionality of a group communication service application server (GCS AS) or an MC service server or a Broadcast Multicast Service Center (BMSC). The nodes indicated herein may be seen as functions, where each function may be implemented in one or more physical entities.

The radio access network 120 is operatively connected to the core network 130 which in turn is operatively connected to the service network 140. The radio access network node 110 thereby enables the wireless devices 160a, 160b, 160c, i6od, and hence the client nodes 300a, 300b, 300c, 30od, to access services and exchange data as provided by the service network 140. Particularly, the client nodes 300a, 300b, 300c, 30od are thereby enabled to communicate with the control node 200.

Examples of wireless devices 160a, 160b, 160c, i6od include, but are not limited to, mobile stations, mobile phones, handsets, wireless local loop phones, user equipment (UE), smartphones, laptop computers, and tablet computers. Examples of radio access network nodes 110a, 110b, 100c, lood include, but are not limited to, radio base stations, base transceiver stations, Node Bs, evolved Node Bs, gigabit Node Bs and access points. As the skilled person understands, the communications system 100 may comprise a plurality of radio access network nodes 110a, 110b, 110c, each providing network access in cells 150a, 150b, 150c to a plurality of wireless devices 160a, 160b, 160c, i6od. The herein disclosed embodiments are not limited to any particular number of radio access network nodes 110a, 110b, 110c, client nodes 300a, 300b, 300c, 30od or wireless devices 160a, 160b, 160c, i6od.

In MBMS two transmission modes can be applied. The first transmission mode, MBSFN, is a transmission mode where a group of adjacent radio access network nodes 110a, 110b, 110c sends the same signal simultaneously on the same frequency. In effect, this makes the MBSFN transmission appears to a wireless device 160a, 160b, 160c, i6od as a transmission from a single large cell 150a, 150b, 150c, which dramatically increase the SIR due to the absence of inter-cell interference.

A second transmission mode, SC-PTM, was introduced for E-UTRAN

Evolved Universal Terrestrial Radio Access Network) in 3GPP Release 13 (Rel-13). For this transmission mode only one radio access network node 110a, 110b, 110c and cell 150a, 150b, 150c transmit the data. This mode does not provide the benefit of improved SIR due to contributions from

neighboring radio access network nodes as for MBSFN transmission.

However SC-PTM transmission can be used with finer geographically granularity since SC-PTM transmission could be used only in cells 150a, 150b, 150c where the wireless devices 160a, 160b, 160c, i6od are located.

Another difference between MBSFN transmission and SC-PTM transmission is the activation procedure in the radio network. When using MBSFN transmission an MBMS Control Channel (MCCH) is used to inform the wireless devices 160a, 160b, 160c, i6od in which subframe data will be transmitted. The MCCH can be transmitted every 320 ms and modified only every 5120 ms. In SC-PTM transmission there is a corresponding channel (SC-MCCH) that can be transmitted every 20 ms and modified every 20 ms.

In the illustrative example of Fig. 1 it is assumed that MBSFN transmission is used in all cells 150a, 150b, 150c whereas SC-PTM transmission only is used in cells 150a, 150b.

One example of MBMS bearer handling in a group communications system 100 will now be disclosed in detail with reference to the signalling diagram of Fig. 2. When using MBMS there are two preparation steps that must be performed. First an MBMS bearer must be activated. This will enable media to be sent over the network and broadcasted in the radio access network 120 to the wireless devices 160a, 160b, 160c. In a third generation partnership project (3GPP) Long Term Evolution (LTE) network this is initiated in a Broadcast Multicast Service Center (BMSC) as defined in 3GPP TS 23.246 V14.1.0. The second part of the preparation is to inform the client nodes 300a, 300b, 300c, 30od of the service being broadcasted over the MBMS bearer. This is required so that the client nodes 300a, 300b, 300c, 30od knows how to, via the wireless devices 160a, 160b, 160c, i6od, receive the media over the MBMS bearer. This procedure is commonly known as an MBMS bearer announcement and is defined in 3GPP TS 23.280 V14.1.0. These two preparation steps are included in step S301:

S301: The control node 200 activates and announces an MBMS bearer for group communications to the client nodes 300a, 300b, 300c, 30od in the group communications system 100.

Group calls are typically short with long periods of silence between the calls. The announcement as well as group calls may thus be followed by periods of silence. During the period of silence the client nodes 300a, 300b, 300c, 30od, via its wireless devices 160a, 160b, 160c, i6od, monitors the MBMS bearer and waits for group call setup messages.

S302: One of the client nodes 300b sends a group call setup message to the control node 200 and the control node sets up the group call for the client nodes 300a, 300b, 300c, 30od.

Step S302 illustrates a new group call setup message initiated by client node 300b. The group call setup message is first sent to the control node 200 which forwards the setup message of the group call on the MBMS bearer to the remaining client nodes 300a, 300c, 30od.

S303: The client node 300b sends group call media to the control node 200 and the control node 200 forwards the media on the MBMS bearer to the remaining client nodes 300b, 300c, 30od.

The group call media is thus sent in step S303 from client node 300b to the the control node 200 which broadcast the media on the MBMS bearer

In a group communication system 100 the performance requirements for a call setup is typically <300 ms. When using MBSFN transmission this implies that the MBSFN transmission must be pre-activated in the network and announced to the client nodes 300a, 300b, 300c, 30od prior the call setup, in accordance with the signalling diagram of Fig. 2. As illustrated above, the announcement of the MBMS bearer is followed by a period of silence and the client nodes 300a, 300b, 300c, 30od need to monitor the MBMS bearer on the MBSFN transmission to listen for any call setup message. The constant monitoring of the MBMS bearer is power consuming.

On the other hand, when using SC-PTM transmission the MBMS bearer can be started by the call setup requests, and it is still possible to reach the call setup performance requirements. Thus, simply using SC-PTM transmission instead of MBSFN transmission in the signalling diagram of Fig. 2 would mitigate latency issues but would increase the risk of inter-cell interference, especially for wireless devices located at cell borders. Furthermore, the MBMS bearer using SC-PTM transmission could be activated only in the cells in which it is needed.

The embodiments disclosed herein therefore relate to mechanisms for MBMS bearer handling in a group communications system 100. In order to obtain such mechanisms there is provided a control node 200, a method performed by the control node 200, a computer program product comprising code, for example in the form of a computer program, that when run on processing circuitry of the control node 200, causes the control node 200 to perform the method. In order to obtain such mechanisms there is further provided a client node 300a, 300b, 300c, 30od, a method performed by the client node 300a, 300b, 300c, 30od, and a computer program product comprising code, for example in the form of a computer program, that when run on processing circuitry of the client node 300a, 300b, 300c, 30od, causes the client node 300a, 300b, 300c, 30od to perform the method.

Figs. 3 and 4 are flowcharts illustrating embodiments of methods for MBMS bearer handling in a group communications system 100 as performed by the control node 200. Figs. 5 and 6 are flowcharts illustrating embodiments of methods for MBMS bearer handling in a group communications system 100 as performed by the client node 300a, 300b, 300c, 30od. The methods are advantageously provided as computer programs 1220a, 1220b.

Reference is now made to Fig. 3 illustrating a method for MBMS bearer handling in a group communications system 100 as performed by the control node 200 according to an embodiment.

The control node 200 is configured to activate a second MBMS only when needed. Hence the control node 200 is configured to perform step S106:

S106: The control node 200 activates the second MBMS bearer using SC- PTM transmission in the group communications system 100 upon need. Different examples of needs upon which the second MBMS bearer is activated (and thus reasons for the control node 200 to activate the MBMS bearer) will be disclosed below.

The second MBMS bearer is announced on an already existing MBMS bearer. Hence, the control node 200 is configured to perform step S108: S108: The control node 200 announces the second MBMS bearer on an already activated and announced first MBMS bearer to client nodes 300a, 300b, 300c, 30od of the group communications system 100.

This provides an efficient announcement of the second MBMS bearer, without wasting unnecessary radio resources. Embodiments relating to further details of MBMS bearer handling in a group communications system 100 as performed by the control node 200 will now be disclosed.

Reference is now made to Fig. 4 illustrating methods for MBMS bearer handling in a group communications system 100 as performed by the control node 200 according to further embodiments. It is assumed that steps S106, S108 are performed as described above with reference to Fig. 3 and a thus repeated description thereof is therefore omitted. As disclosed above, the first MBMS bearer is already activated and announced when the second MBMS bearer is announced. Hence, according to an embodiment the control node 200 is configured to perform step S102:

S102: The control node 200 activates and announces the first MBMS bearer for announcing the second MBMS bearer. For example, the first MBMS bearer may be activated and announced as in step S301 above.

As specified in step S106 the second MBMS bearer is activated upon need. There may be different examples of such needs. Embodiments relating thereto will now be disclosed in turn. In some aspects the second MBMS bearer is activated in response to a new group call being started by one of the client nodes 300a, 300b, 300c, 30od.

Particularly, according to an embodiment the control node 200 is configured to perform step Si04a:

Si04a: The control node 200 obtains an indication of a group call in the group communications system 100 being started by one of the client nodes 300a, 300b, 300c, 30od. According to this embodiment the obtained indication defines the need in step S106. The second MBMS bearer is thus activated and announced in response thereto (i.e., in response to the indication being obtained in step Si04a). Hence, the control node 200 could thus activate the second MBMS bearer upon detecting that a new group call is started.

In some aspects the second MBMS bearer is activated in response to a capacity need during an ongoing call. Particularly, according to an embodiment the control node 200 is configured to perform step Si04b: Si04b: The control node 200 obtains an indication of modified payload capacity need during an ongoing group call in the group communications system 100. According to this embodiment the obtained indication defines the need in step S106. The second MBMS bearer is thus activated and announced in response thereto (i.e., in response to the indication being obtained in step Si04b).

Typically, the modified payload capacity need represents an increase in payload capacity need. An example is that transmission of a video stream is added to an ongoing group call only using audio. Hence, the control node 200 could thus activate the second MBMS bearer upon detecting that a video stream is added to an ongoing group call.

In some aspects the second MBMS bearer is activated in response to an increased number of client nodes 300a, 300b, 300c, 30od taking part in an ongoing group call. Particularly, according to an embodiment the control node 200 is configured to perform step S104C:

S104C: The control node 200 obtains an indication of increasing number of client nodes 300a, 300b, 300c, 30od taking part in an ongoing group call in the group communications system 100. According to this embodiment the obtained indication defines the need in step S106. The second MBMS bearer is thus activated and announced in response thereto (i.e., in response to the indication being obtained in step S104C).

Hence, the control node 200 could thus activate the second MBMS bearer upon detecting that the number of client nodes 300a, 300b, 300c, 30od participating in the ongoing group call has increased.

In some aspects the second MBMS bearer is not activated in all cells 150a, 150b, 150c of the group communication system 100. Therefore, the control node 200 could evaluate in which cells to activate the second MBMS bearer.

According to an embodiment where the group communications system 100 comprises cells 150a, 150b, 150c served by radio access network nodes 110a, 110b, 110c, the control node 200 is configured to perform step Sio6a as part of step S106:

Sio6a: The control node 200 determines to activate the second MBMS bearer in a subset 150a, 150b of all cells 150a, 150b, 150c of the group communication system 100. The second MBMS bearer is activated only in this subset of cells 150a, 150b.

There could be different ways for the control node 200 to determine in which cells 150a, 150b to activate the second MBMS bearer. One example is for the control node 200 to activate the second MBMS only in those cells in which comparatively many client nodes are located. Thus, the determination could be based on subjecting the number of client nodes in each cell to a threshold. More particularly, the second MBMS bearer could be activated only in the cells 150a, 150b where client nodes 300a, 300b, 300c interested in the group call are located. There might be other client nodes in the same area which are monitoring the first MBMS bearer but are not interested in the specific group call.

In some aspects the announcement of the second MBMS bearer comprises a list of those cells 150a, 150b in which the second MBMS bearer is activated. That is, according to an embodiment the announcement of the second MBMS bearer comprises information of the subset of cells 150a, 150b in which the second MBMS bearer is activated.

If there are very few client nodes 30od in a cell 150c, and the second MBMS bearer cannot be justified from a resource usage perspective, an improved call setup performance is provided, since the call setup message on the first MBMS bearer will notify the client node 30od about an incoming group call more quickly than a normal paging procedure could do.

In some aspects the control node 200 is notified about any client nodes 30od located outside those cells in which the second MBMS bearer is activated and for which unicast is needed, see also step S204 below. Hence, according to an embodiment the control node 200 is configured to perform step S110:

S110: The control node 200 obtains, from a client node 30od located outside the subset of cells 150a, 150b in which the second MBMS bearer is activated, a request for unicast transmission of media of a group call of the group communications system 100. The control node 200 could use unicast transmission for transmitting media of the group call for those client nodes located outside the cells in which the second MBMS bearer is activated. Hence, according to an embodiment the control node 200 is configured to perform step Sii2b: Sii2b: The control node 200 transmits the media using unicast transmission to the client node 30od located outside the subset of cells 150a, 150b in which the second MBMS bearer is activated.

This would make it possible for also client node 30od to receive the media of the group call. However, it could be assumed that most of the client nodes 300a, 300b, 300c of the group call are located within those cells in which the second MBMS bearer is activated. Hence, the control node 200 could broadcast media of the group call using the second MBMS bearer. That is, according to an

embodiment the control node 200 is configured to perform step Sii2a: Sii2a: The control node 200 transmits media of a group call of the group communications system 100 using the second MBMS bearer.

Steps Sii2a and Sii2b could be performed in parallel.

Reference is now made to Fig. 5 illustrating a method for MBMS bearer handling in a group communications system 100 as performed by the client node 300a, 300b, 300c, 30od according to an embodiment.

As disclosed above, the control node 200 in step 108 announces the second MBMS bearer. The client node 300a, 300b, 300c, 30od is therefore configured to perform step S202:

S202: The client node 300a, 300b, 300c, 30od obtains announcement of the second MBMS bearer on an already announced first MBMS bearer from the control node 200 of the group communications system 100. As disclosed above, the second MBMS bearer uses SC-PTM transmission. Embodiments relating to further details of MBMS bearer handling in a group communications system 100 as performed by the client node 300a, 300b, 300c, 30od will now be disclosed.

Reference is now made to Fig. 6 illustrating methods for MBMS bearer handling in a group communications system 100 as performed by the client node 300a, 300b, 300c, 30od according to further embodiments. It is assumed that step S202 is performed as described above with reference to Fig. 5 and a thus repeated description thereof is therefore omitted.

As disclosed above, according to some aspects the announcement of the second MBMS bearer comprises a list of cells in which the second MBMS bearer is activated. Hence, according to an embodiment the group

communications system 100 comprises cells 150a, 150b, 150c served by radio access network nodes 110a, 110b, 110c, and the second MBMS bearer is activated only in a subset of cells 150a, 150b, and the announcement of the second MBMS bearer comprises information of the subset of cells 150a, 150b in which the second MBMS bearer is activated.

In some aspects the control node 200 is notified about client nodes 30od located outside the cells 150a, 150b in which the second MBMS bearer is activated and thus for which unicast transmission is needed. Hence, according to an embodiment where the client node 30od is located outside the subset of cells 150a, 150b in which the second MBMS bearer is activated, the client node 30od is configured to perform step S204:

S204: The client node 30od provides, to the control node 200, a request for unicast transmission of media of a group call of the group communications system 100.

As disclosed above, unicast transmission of the media of the group call could be used for those client nodes 30od being outside the cells 150a, 150b in which the second MBMS bearer is activated. Hence, according to an embodiment the client node 30od is configured to perform step S2o6b: l8

S2o6b: The client node 30od receives the media (of the group call) on a unicast bearer from the control node 200.

As further disclosed above, the media is broadcasted using the second MBMS bearer inside the subset of cells 150a, 150b in which the second MBMS bearer is activated. Hence, according to an embodiment the client node 300a, 300b, 300c is configured to perform step S2o6a:

S2o6a: The client node 300a, 300b, 300c receives media of a group call of the group communications system (100) on the second MBMS bearer.

Aspects and embodiments equally applicable to the control node 200 and the client nodes 300a, 300b, 300c, 30od and the methods performed by the control node 200 and the client nodes 300a, 300b, 300c, 30od will now be disclosed.

There could be different kinds of first MBMS bearers. According to an embodiment the first MBMS bearer is using MBSFN transmission. As disclosed above, MBSFN transmission is efficient when the same media is to be transmitted in many cells 150a, 150b.

There could be different information provided about the second MBMS bearer when it is announced in step S108. According to an embodiment the announcement of the second MBMS bearer comprises identity information of the second MBMS bearer. One example of identity information is a

Temporary Mobile Group Identity (TMGI). This enables the client nodes 300a, 300b, 300c, 30od to identify the second MBMS bearer.

There could be different ways for announcing the second MBMS bearer in step S108. In some aspects a group call setup message is broadcasted on the first MBMS bearer. Therefore, according to an embodiment the

announcement of the second MBMS bearer is sent in a call setup message broadcasted on the first MBMS bearer. This is an efficient way to announce the second MBMS bearer. There could be different purposes for the control node 200 to activate and use the first MBMS bearer. In some aspects the first MBMS bearer is mostly used for application level control signalling. That is, according to an embodiment the already activated and announced MBMS bearer is used for application level control signalling in the group communications system 100. This enables efficient transmission of application level control signalling in the group communications system 100.

There could be different purposes for the control node 200 to activate and use the second MBMS bearer. In some aspects the second MBMS bearer is mostly used for media transmission (i.e., for transmission of the group communication data). That is, according to an embodiment the second MBMS bearer is activated for supporting media transmission in a group call of the group communications system 100. This enables efficient transmission of media in the group communications system 100. One particular embodiment for MBMS bearer handling in a group

communications system 100 as performed by the control node 200 and the client node 300a, 300b, 300c, 30od based on at least some of the above disclosed embodiments will now be disclosed in detail with reference to the signalling diagram of Fig. 7. S401: The control node 200 activates and announces a first MBMS bearer for group communications to the client nodes 300a, 300b, 300c, 30od in the group communications system 100. The MBMS bearer is activated with a quality of service and bandwidth that is suitable and dimensioned for group communication signaling messages (also known as application level control signaling in 3GPP TS 23.280 νΐ ΐ.ο). One way to implement step S401 is to perform step S102. The capacity of the first MBMS bearer could be low (such as lower than the capacity of the second MBMS bearer) and one main purpose of the first MBMS bearer is for application level control signalling messages, e.g. call setup messages, floor control messages. Typically, the first MBMS bearer is not intended for media. S402: The client nodes 300a, 300b, 300c, 30od start to monitor the MBMS bearer and acknowledge reception of the MBMS bearer to the control node 200.

S403: Client node 300b starts a new group call by sending a group call setup message to the control node 200. One way to implement step S403 is to perform step Si 04 a.

S404: The control node 200 evaluates in which of the cells 150a, 150b, 150c it is efficient to use MBMS transmission. The control node 200 could decide to start a new, second, MBMS bearer with SC-PTM transmission in all cells 150a, 150b, 150c that the first MBMS bearer is started in or a subset of these cells. One way to implement step S404 is to perform step Sio6a.

Step S405 and S406 could then be performed in parallel.

S405: The control node 200 activates the second MBMS bearer for SC-PTM transmission. This second MBMS bearer may be started with a different quality of service and bandwidth compared to the first MBMS bearer, with the objective to carry the media of the group call. One way to implement step S405 is to perform step S106. Preferably, the second MBMS bearer is only activated in the cells where client nodes 300a, 300b, 300c, 30od interested to take part in the group call are located. There may be other client nodes 300a, 300b, 300c, 30od in other cells that are monitoring the first MBMS bearer but are not interested in the specific group call. Activation of the second MBMS bearer in less than all cells gives improved utilization of network resources . Also, activating the second MBMS bearer for SC-PTM

transmission is quicker than activating an MBMS bearer for MBSFN transmissions.

S406: The control node 200 broadcasts the group call setup message on the first MBMS bearer. The group call setup message includes an announcement message for the second MBMS bearer. The control node 200 thus announces the second MBMS bearer on the first MBMS bearer. This announcement message comprises at least the TMGI of the second MBMS bearer. The TMGI is acting as the identity of the second MBMS bearer. The message may further comprise a list of the cells 150a, 150b in which the second MBMS bearer is activated. One way to implement step S406 is to perform step S108 and step S202. S407: Client node 30od located in a cell 150c, in which the second MBMS bearer is not activated in, requests the control node 200 to transmit the group call using unicast transmission to this client node 30od. This will improve call setup time since paging for this client node 30od is not required. One way to implement step S407 is to perform step S110 and step S204. S408: The control node 200 broadcasts the media of the group call over the second MBMS bearer to client nodes 300a, 300b, 300c and/or over unicast transmission to client node 300b not in cells 150a, 150b in which the second MBMS bearer has been activated. One way to implement step S408 is to perform any of step Sii2a and/or step Sii2b, and step S2o6a and/or step S2o6b.

Fig. 8 schematically illustrates, in terms of a number of functional units, the components of a control node 200 according to an embodiment. Processing circuitry 210 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 1210a (as in Fig. 12), e.g. in the form of a storage medium 230. The processing circuitry 210 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA). Particularly, the processing circuitry 210 is configured to cause the control node 200 to perform a set of operations, or steps, Si02-Sii2b, as disclosed above. For example, the storage medium 230 may store the set of operations, and the processing circuitry 210 may be configured to retrieve the set of operations from the storage medium 230 to cause the control node 200 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry 210 is thereby arranged to execute methods as herein disclosed.

The storage medium 230 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory.

The control node 200 may further comprise a communications interface 220 for communications with other entities, nodes, and devices of the group communications system 100 and particularly the client nodes 300a, 300b, 300c, 30od. As such the communications interface 220 may comprise one or more transmitters and receivers, comprising analogue and digital

components.

The processing circuitry 210 controls the general operation of the control node 200 e.g. by sending data and control signals to the communications interface 220 and the storage medium 230, by receiving data and reports from the communications interface 220, and by retrieving data and instructions from the storage medium 230. Other components, as well as the related functionality, of the control node 200 are omitted in order not to obscure the concepts presented herein.

Fig. 9 schematically illustrates, in terms of a number of functional modules, the components of a control node 200 according to an embodiment. The control node 200 of Fig. 9 comprises a number of functional modules; an activate module 2ioe configured to perform step S106, and an announce module 2iog configured to perform step S108. The control node 200 of Fig. 9 may further comprise a number of optional functional modules, such as any of an activate and announce module 210a configured to perform step S102, a first obtain module 210b configured to perform step Si04a, a second obtain module 210c configured to perform step Si04b, a third obtain module 2iod configured to perform step S104C, a determine module 2iof configured to perform step Sio6a, a fourth obtain module 2ioh configured to perform step S110, a first transmit module 2101 configured to perform step Sii2a, and a second transmit module 2ioj configured to perform step Sii2b.

In general terms, each functional module 2ioa-2ioj may be implemented in hardware or in software. Preferably, one or more or all functional modules 2ioa-2ioj may be implemented by the processing circuitry 210, possibly in cooperation with the communications interface 220 and/or the storage medium 230. The processing circuitry 210 may thus be arranged to from the storage medium 230 fetch instructions as provided by a functional module 2ioa-2ioj and to execute these instructions, thereby performing any steps of the control node 200 as disclosed herein.

The control node 200 may be provided as a standalone device or as a part of at least one further device. For example, the control node 200 may be provided in a node of the radio access network 120 or in a node of the core network 130 or in a node of the service network 140. Alternatively, functionality of the control node 200 may be distributed between at least two devices, or nodes. These at least two nodes, or devices, may either be part of the same network part (such as the radio access network or the core network or the service network) or may be spread between at least two such network parts. Some examples of where in the communications system 100 the control node 200 may be provided are illustrated in Fig. 1.

Functionality of the control node 200 may be implemented at the service layer of the protocol stack. In general terms, instructions that are required to be performed in real time may be performed in a device, or node, operatively closer to the radio access network 120 than instructions that are not required to be performed in real time. In this respect, at least part of the control node 200 may reside in the radio access network 120, such as in the radio access network node 110a, 110b, 100c, lood, for cases when embodiments as disclosed herein are performed in real time.

Thus, a first portion of the instructions performed by the control node 200 may be executed in a first device, and a second portion of the of the instructions performed by the control node 200 may be executed in a second device; the herein disclosed embodiments are not limited to any particular number of devices on which the instructions performed by the control node 200 may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a control node 200 residing in a cloud computational environment. Therefore, although a single processing circuitry 210 is illustrated in Fig. 8 the processing circuitry 210 may be distributed among a plurality of devices, or nodes. The same applies to the functional modules 2ioa-2ioj of Fig. 9 and the computer program 1210a of Fig. 12 (see below).

Fig. 10 schematically illustrates, in terms of a number of functional units, the components of a client node 300a, 300b, 300c, 30od according to an embodiment. Processing circuitry 310 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 1210b (as in Fig. 12), e.g. in the form of a storage medium 330. The processing circuitry 310 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA). Particularly, the processing circuitry 310 is configured to cause the client node 300a, 300b, 300c, 30od to perform a set of operations, or steps, S202- S2o6b, as disclosed above. For example, the storage medium 330 may store the set of operations, and the processing circuitry 310 may be configured to retrieve the set of operations from the storage medium 330 to cause the client node 300a, 300b, 300c, 30od to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry 310 is thereby arranged to execute methods as herein disclosed.

The storage medium 330 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The client node 300a, 300b, 300c, 30od may further comprise a

communications interface 320 for communications with other entities, nodes, and devices of the group communications system 100 and particularly the control node 200. As such the communications interface 320 may comprise one or more transmitters and receivers, comprising analogue and digital components.

The processing circuitry 310 controls the general operation of the client node 300a, 300b, 300c, 30od e.g. by sending data and control signals to the communications interface 320 and the storage medium 330, by receiving data and reports from the communications interface 320, and by retrieving data and instructions from the storage medium 330. Other components, as well as the related functionality, of the client node 300a, 300b, 300c, 30od are omitted in order not to obscure the concepts presented herein.

Fig. 11 schematically illustrates, in terms of a number of functional modules, the components of a client node 300a, 300b, 300c, 30od according to an embodiment. The client node 300a, 300b, 300c, 30od of Fig. 11 comprises an obtain module 310a configured to perform step S202. The client node 300a, 300b, 300c, 30od of Fig. 11 may further comprise a number of optional functional modules, such as any of a provide module 310b configured to perform step S204, a first receive module 310c configured to perform step S2o6a, and a second receive module 3iod configured to perform step S2o6b.

In general terms, each functional module 3ioa-3iod may be implemented in hardware or in software. Preferably, one or more or all functional modules 3ioa-3iod may be implemented by the processing circuitry 310, possibly in cooperation with the communications interface 320 and/or the storage medium 330. The processing circuitry 310 may thus be arranged to from the storage medium 330 fetch instructions as provided by a functional module 3ioa-3iod and to execute these instructions, thereby performing any steps of the client node 300a, 300b, 300c, 30od as disclosed herein. The client node 300a, 300b, 300c, 30od may be provided as a standalone device or as a part of at least one further device. For example, the client node 300a, 300b, 300c, 30od may be provided in a wireless device 160a, 160b, 160c, i6od. Fig. 12 shows one example of a computer program product 1210a, 1210b comprising computer readable means 1230. On this computer readable means 1230, a computer program 1220a can be stored, which computer program 1220a can cause the processing circuitry 210 and thereto operatively coupled entities and devices, such as the communications interface 220 and the storage medium 230, to execute methods according to embodiments described herein. The computer program 1220a and/or computer program product 1210a may thus provide means for performing any steps of the control node 200 as herein disclosed. On this computer readable means 1230, a computer program 1220b can be stored, which computer program 1220b can cause the processing circuitry 310 and thereto operatively coupled entities and devices, such as the communications interface 320 and the storage medium 330, to execute methods according to embodiments described herein. The computer program 1220b and/or computer program product 1210b may thus provide means for performing any steps of the client node 300a, 300b, 300c, 30od as herein disclosed.

In the example of Fig. 12, the computer program product 1210a, 1210b is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 1210a, 1210b could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 1220a, 1220b is here schematically shown as a track on the depicted optical disk, the computer program 1220a, 1220b can be stored in any way which is suitable for the computer program product 1210a, 1210b.

The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

Claims

1. A method for multimedia broadcast multicast service, MBMS, bearer handling in a group communications system (100), the method being performed by a control node (200), the method comprising:

activating (S106, S405) a second MBMS bearer using single-cell point- to-multipoint, SC-PTM, transmission in the group communications system (100) upon need; and

announcing (S108, S406) the second MBMS bearer on an already activated and announced first MBMS bearer to client nodes (300a, 300b, 300c, 30od) of the group communications system (100).

2. The method according to claim 1, further comprising:

activating and announcing (S102, S401) the first MBMS bearer for announcing the second MBMS bearer.

3. The method according to any of the preceding claims, further

comprising:

obtaining (Si04a, S403) an indication of a group call in the group communications system (100) being started by one of the client nodes (300a, 300b, 300c, 30od), said indication defining said need; and wherein the second MBMS bearer is activated and announced in response thereto.

4. The method according to any of claims 1 or 2, further comprising:

obtaining (Si04b) an indication of modified payload capacity need during an ongoing group call in the group communications system (100), said indication defining said need; and wherein the second MBMS bearer is activated and announced in response thereto.

5. The method according to any of claims 1 or 2, further comprising:

obtaining (S104C) an indication of increasing number of client nodes (300a, 300b, 300c, 30od) taking part in an ongoing group call in the group communications system (100), said indication defining said need; and wherein the second MBMS bearer is activated and announced in response thereto.

6. The method according to any of the preceding claims, wherein the group communications system (100) comprises cells (150a, 150b, 150c) served by radio access network nodes (110a, 110b, 110c), the method further comprising:

determining (Sio6a, S404) to activate the second MBMS bearer in a subset (150a, 150b) of all cells (150a, 150b, 150c) of the group communication system (100), and wherein the second MBMS bearer only is activated in said subset (150a, 150b).

7. The method according to claim 6, wherein announcement of the second MBMS bearer comprises information of the subset of cells (150a, 150b) in which the second MBMS bearer is activated.

8. The method according to claim 7, further comprising:

obtaining (S110, S407), from a client node (30od) located outside the subset of cells (150a, 150b) in which the second MBMS bearer is activated, a request for unicast transmission of media of a group call of the group communications system (100).

9. The method according to any of the preceding claims, further comprising:

transmitting (Sii2a, S408) media of a group call of the group

communications system (100) using the second MBMS bearer.

10. The method according to claim 8, further comprising:

transmitting (Sii2b, S408) the media using unicast transmission to said client node (30od) located outside those cells (150a, 150b) in which the second MBMS bearer is activated.

11. A method for multimedia broadcast multicast service, MBMS, bearer handling in a group communications system (100), the method being performed by a client node (300a, 300b, 300c, 30od), the method

comprising:

obtaining (S202, S406) announcement of a second MBMS bearer on an already announced first MBMS bearer from a control node (200) of the group communications system (100), wherein the second MBMS bearer uses single- cell point-to-multipoint, SC-PTM, transmission.

12. The method according to claim 11, wherein the group communications system (100) comprises cells (150a, 150b, 150c) served by radio access network nodes (110a, 110b, 110c), wherein the second MBMS bearer is activated only in a subset of cells (150a, 150b), and wherein the

announcement of the second MBMS bearer comprises information of the subset of cells (150a, 150b) in which the second MBMS bearer is activated.

13. The method according to claim 12, wherein when the client node (30od) is located outside the subset of cells (150a, 150b) in which the second MBMS bearer is activated, the method further comprising:

providing (S204, S407), to the control node (200), a request for unicast transmission of media of a group call of the group communications system (100).

14. The method according to any of claims 11 to 13, further comprising: receiving (S2o6a, S408) media of a group call of the group

communications system (100) on the second MBMS bearer.

15. The method according to claim 13, further comprising:

receiving (S2o6b, S408) the media on a unicast bearer from the control node (200).

16. The method according to any of the preceding claims, wherein the first MBMS bearer is using multicast-broadcast single-frequency network, MBSFN, transmission.

17. The method according to any of the preceding claims, wherein announcement of the second MBMS bearer comprises identity information of the second MBMS bearer.

18. The method according to any of the preceding claims, wherein announcement of the second MBMS bearer is sent in a call setup message broadcasted on the first MBMS bearer.

19. The method according to any of the preceding claims, wherein the already activated and announced MBMS bearer is used for application level control signalling in the group communications system (100).

20. The method according to any of the preceding claims, wherein the second MBMS bearer is activated for supporting media transmission in a group call of the group communications system (100).

21. A control node (200) for multimedia broadcast multicast service, MBMS, bearer handling in a group communications system (100), the control node (200) comprising processing circuitry (210), the processing circuitry being configured to cause the control node (200) to:

activate a second MBMS bearer using single-cell point-to-multipoint, SC-PTM, transmission in the group communications system (100) upon need; and

announce the second MBMS bearer on an already activated and announced first MBMS bearer to client nodes (300a, 300b, 300c, 30od) of the group communications system (100).

22. A control node (200) for multimedia broadcast multicast service, MBMS, bearer handling in a group communications system (100), the control node (200) comprising:

processing circuitry (210); and

a storage medium (230) storing instructions that, when executed by the processing circuitry (210), cause the control node (200) to:

activate a second MBMS bearer using single-cell point-to- multipoint, SC-PTM, transmission in the group communications system (100) upon need; and

23. A control node (200) for multimedia broadcast multicast service, MBMS, bearer handling in a group communications system (100), the control node (200) comprising:

an activate module (2ioe) configured to activate a second MBMS bearer using single-cell point-to-multipoint, SC-PTM, transmission in the group communications system (100) upon need; and

an announce module (2iog) configured to announce the second MBMS bearer on an already activated and announced first MBMS bearer to client nodes (300a, 300b, 300c, 30od) of the group communications system (100).

24. A client node (300a, 300b, 300c, 30od) for multimedia broadcast multicast service, MBMS, bearer handling in a group communications system (100), the client node (300a, 300b, 300c, 30od) comprising processing circuitry (310), the processing circuitry being configured to cause the client node (300a, 300b, 300c, 30od) to:

obtain announcement of a second MBMS bearer on an already announced first MBMS bearer from a control node (200) of the group communications system (100), wherein the second MBMS bearer uses single- cell point-to-multipoint, SC-PTM, transmission.

25. A client node (300a, 300b, 300c, 30od) for multimedia broadcast multicast service, MBMS, bearer handling in a group communications system (100), the client node (300a, 300b, 300c, 30od) comprising:

processing circuitry (310); and

a storage medium (330) storing instructions that, when executed by the processing circuitry (310), cause the client node (300a, 300b, 300c, 30od) to:

26. A client node (300a, 300b, 300c, 30od) for multimedia broadcast multicast service, MBMS, bearer handling in a group communications system (100), the client node (300a, 300b, 300c, 30od) comprising:

an obtain module (310a) configured to obtain announcement of a second MBMS bearer on an already announced first MBMS bearer from a control node (200) of the group communications system (100), wherein the second MBMS bearer uses single-cell point-to-multipoint, SC-PTM, transmission.

27. A computer program (1220a) for multimedia broadcast multicast service, MBMS, bearer handling in a group communications system (100), the computer program comprising computer code which, when run on processing circuitry (210) of a control node (200), causes the control node (200) to:

activate (S106, S405) a second MBMS bearer using single-cell point-to- multipoint, SC-PTM, transmission in the group communications system (100) upon need; and

announce (S108, S406) the second MBMS bearer on an already activated and announced first MBMS bearer to client nodes (300a, 300b, 300c, 30od) of the group communications system (100).

28. A computer program (1220b) for multimedia broadcast multicast service, MBMS, bearer handling in a group communications system (100), the computer program comprising computer code which, when run on processing circuitry (310) of a client node (300a, 300b, 300c, 30od), causes the client node (300a, 300b, 300c, 30od) to:

obtain (S202, S406) announcement of a second MBMS bearer on an already announced first MBMS bearer from a control node (200) of the group communications system (100), wherein the second MBMS bearer uses single- cell point-to-multipoint, SC-PTM, transmission.

29. A computer program product (1210a, 1210b) comprising a computer program (1220a, 1220b) according to at least one of claims 27 and 28, and a computer readable storage medium (1230) on which the computer program is stored.