FIELD OF THE INVENTION

The embodiments of the present invention relate to a method and arrangement in a telecommunication system, in particular to methods and arrangements relating to overlapping MBSFN- areas .

BACKGROUND

Figure 1 provides a schematic illustration of a part of a cellular communication system 10, wherein each cell 14 comprises a network node 12, typically a radio base station, providing communication services to and from user equipments 11. One particular communication service offered in a communication system is Multimedia Broadcast Multicast Services (MBMS) , which denote broadcast information services covering large geographic areas consisting of one or more cells. Since all these cells distribute the same services, the spectral efficiency of MBMS transmissions can be optimized by applying MBMS single frequency network (MBSFN) transmission. This means that identical data is transmitted on the same radio resources from more than one cell 14. The cells that offer the same set of MBMS services and the same scheduling of MBMS service sessions belong to on MBSFN area 13a, 13b. The MBMS control channel (MCCH) is needed for the User Equipment (UE) to obtain service specific information necessary for MBMS service reception, e.g. physical multicast channel (PMCH) configuration such as modulation and coding scheme, MBMS subframe allocation etc.

In the current releases of the 3GPP-specifications for the Long term evolution (LTE) of UTRAN, only non-overlapping MBSFN areas are supported, i.e. one cell 14 can only belong to one MBSFN area. This implies as a consequence that only one MCCH is needed. However, future releases of LTE will also provide for overlapping MBSFN areas 13a, 13b, i.e. one cell 14 can belong to several MBSFN areas 13a, 13b and there are several MCCHs per cell because there is one MCCH per MBSFN area 13a, 13b.

In order to reduce battery consumption, MBMS notification mechanisms have been introduced, which inform about a change of content for a certain MBMS service. This implies that a UE does not have to periodically read the MCCH but only when a content change has occurred. These notification methods are based on paging mechanisms, i.e. the UE has to monitor the Physical Downlink Control Channel (PDCCH) . There are mainly two options: According to one option, a new MBMS specific Radio Network Temporary Identifier (RNTI) , the M- RNTI, is introduced to address UEs having subscribed to MBMS services. As soon as the UE finds the M-RNTI, it reads the MCCH. According to another option, the UE starts reading a received paging message when having received a paging RNTI, P-RNTI. The paging message may include notification information for MBMS. In that case, UE having subscribed to MBMS services start reading the MCCH.

SUMMARY

It has been observed to be a problem that the prior art solutions for MBMS notifications only support non- overlapping MBSFN areas. Consequently, a UE having subscribed to MBMS-services must read all MBMS control channels (MCCH) that are defined on the broadcast channel (BCCH) as soon as it has received a MBMS notification. It is thus an object of the embodiments of the present invention to achieve an improved method and arrangement for notification of changes of the content of a MBMS service which is also applicable for overlapping MBSFN areas. The solution according to the embodiments of the present invention is to introduce notification mechanisms that allows a UE to distinguish notifications for different MBSFN areas and, thus, for different MCCHs. The UE then knows already upon reception of the notification whether it has to wake up and read a specific MCCH.

It is an advantage of the embodiments of the present invention to support multiple MBSFN areas per cell while still maintaining the benefits of reduced battery consumption in the UE due to said MBMS notification mechanism.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings and claims . BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a cellular communication system including by means of an example two MBFSN-areas.

Figure 2 illustrates an embodiment of the method according to the present invention performed in a network node. Figure 3 illustrates an embodiment of the method according to the present invention performed in a user equipment. Figure 4 illustrates an embodiment of an arrangement according to the present invention, in particular a network node.

Figure 5 illustrates an embodiment of an arrangement according to the present invention, in particular a user equipment .

DETAILED DESCRIPTION

There are several possibilities to signal to a UE which MCCH to read. The description below describes by means of examples embodiments that can be used to identify which MCCH a UE shall read on reception of a MBMS notification message. It is assumed for all embodiments that identifiers of at least some of the MBSFN areas, i.e. MBSFN area IDs, and their mapping to a respective MCCH are signaled on a broadcast channel, e.g. a BCCH.

A node 12 in a cellular communication system 10, intended to provide communication services to a plurality of user equipments 11 in a cell 14 of said cellular communication system and supporting broadcast information services in one or more MBSFN areas 13a, 13b which include said cell 14, performs the steps of broadcasting 21 information on identifiers of at least some of said MBSFN areas in order to identify the respective area-specific MBMS control channel and transmits 23 subsequently MBMS notification messages associated with one of said MBSFN areas based on said broadcasted information to the user equipments in said cell for notifying changes of the information 22yes in one of said MBSFN-areas.

Correspondingly, the user equipment 11 performs the steps of receiving 31 on a broadcast channel such information on identifiers of at least some of said MBSFN areas and can thereafter on reception 32 of a MBMS notification message derive 33 from the identifiers of the one or more MBSFN areas included in the received MBMS notification message, the MBMS control channel that is associated with the intended MBSFN areas . Example embodiments of the present invention to make accessible information on identifiers of at least some of said MBSFN areas to user equipments are described below:

According to a first embodiment of the present invention, one unique M-RNTI is used per MBSFN area. These values can be, e.g., RNTI values that are currently reserved for future use or values that are used to identify a UE within the cell (e.g. cell RNTI, C-RNTI) . The latter would reduce the number of RNTIs used for unicast. The mapping of the M-RNTIs identifying the MBSFN area to a MBSFN area specific MCCH is signaled on a broadcast channel, e.g. the BCCH. In this embodiment, the MBMS notification message of a content change in one of said MBSFN areas is associated with the unique identifier of said MBSFN area. According to another embodiment of the present invention, one common M-RNTI is used for all MBSFN areas. In this embodiment the broadcasted MBMS notification message generally informs about a content change in one of the MBSFN areas whereas a UE can distinguish the MCCH of the MBSFN area for which said content change applies from information provided on a physical downlink channel (PDCCH) including information about the MBSFN area identifier.

According to yet another embodiment of the present invention, one common M-RNTI is used for all MBSFN areas. The broadcasted mapping information comprises radio frame offset information for each of the various MBSFN areas such that MBMS notification messages are sent on different subframes and thus allow distinguishing the MBSFN area where a content change occurred and identifying the MCCH that should be read by UEs subscribing to the service in said MBSFN area. In this embodiment the broadcasted MBMS notification message generally informs about a content change in one of the MBSFN areas whereas a UE can distinguish the MCCHs of the various MBSFN areas from broadcasted radio frame offset information. Upon reception of a MBMS notification message a UE only needs to "wake up" if the MCCH for a service that the UE subscribes to has been modified. The UE can directly read the relevant MCCH instead of receiving information on each MCCH.