(19)
(11)EP 3 437 348 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
17.06.2020 Bulletin 2020/25

(21)Application number: 17712164.7

(22)Date of filing:  23.03.2017
(51)Int. Cl.: 
H04W 4/06  (2009.01)
(86)International application number:
PCT/EP2017/057026
(87)International publication number:
WO 2017/167648 (05.10.2017 Gazette  2017/40)

(54)

MOBILE COMMUNICATIONS NETWORK

MOBILKOMMUNIKATIONSNETZWERK

RÉSEAU DE COMMUNICATIONS MOBILES


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 31.03.2016 EP 16163451

(43)Date of publication of application:
06.02.2019 Bulletin 2019/06

(73)Proprietor: British Telecommunications public limited company
London EC1A 7AJ (GB)

(72)Inventors:
  • AL-DAHER, Zaid
    London EC4V 5BT (GB)
  • MACKENZIE, Richard
    London EC4V 5BT (GB)
  • FITCH, Michael
    London EC4V 5BT (GB)

(74)Representative: British Telecommunications public limited company Intellectual Property Department 
Ground Floor, Faraday Building 1 Knightrider Street
London EC4V 5BT
London EC4V 5BT (GB)


(56)References cited: : 
EP-A1- 1 650 989
WO-A1-2015/061983
WO-A1-2015/000912
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    Field of the Invention



    [0001] The present invention relates to mobile communication networks and to a base station for a mobile communications network.

    Background of the Invention



    [0002] Multimedia content, such as video playback, live streaming, online interactive gaming, file delivery and mobile TV, is seen as the key driver for data traffic demand on wireless cellular networks. Multimedia content to a large number of users can be distributed by unicast, broadcast and multicast. In the following, the term "multicast" is used to include "broadcast" and vice versa. Unicast is a dedicated bidirectional point-to-point link for transmission between the base station and one user mobile device. Evolved Multimedia Broadcast Multicast Service (eMBMS) is an LTE technique offering a specific broadcast bearer to deliver data content to multiple users over shared downlink resources, which is more efficient than dedicating a unicast bearer for each user. Multicast-broadcast single-frequency network (MBSFN) further improves spectral efficiency by dynamically forming single-frequency networks whereby a mobile terminal (in LTE, the UE) can seamlessly receive the same content over eMBMS from multiple base stations (in LTE, the eNodeB) within a MBSFN area. A single-frequency network comprises groups of adjacent eMBMS base stations at which the same signal is synchronised and broadcast simultaneously on the same MBSFN sub-carrier frequencies and time-slots. The combination of eMBMS transmission from multiple base stations in a MBSFN service area provides a degree of transmission robustness in the form of spatial transmit diversity and effectively eliminates internal cell edges. However, a problem exists in handling the transfer of a mobile terminal between different MBSFN areas and between MBSFN and reserved unicast cells. A similar a problem exists in handling the transfer of a mobile terminal between eMBMS cells. Seamless mobility of the mobile terminals across an LTE network with different MBSFNs is not supported in 3GPP, so that service interruption may result, i.e. due to delays at the cell-edges while the mobile terminal acquires information about the targeted area or cell. Service interruption may also result when a the mobile terminal moves from a MBSFN providing an eMBMS broadcast service to a MBSFN where the service in question may only be available by unicast.

    [0003] eMBMS and MBSFN basics are described in 3GPP TS 23.246 Multimedia Broadcast/Multicast Service (MBMS); Architecture and functional description (Release 9), V9.5.0 (2010-06); the 3rd Generation Partnership Project (http://www.3gpp.org).

    [0004] In WO2015/000912, a method for providing multicast/broadcast service continuity for mobile terminals in a radio access network is described, wherein a decision on actions to be performed by said mobile terminal for preserving reliable transmission/reception is based on radio measurements. In WO2015/061983, a method of maintaining continuity of eMBMS broadcast service at UEs is disclosed, in which the UE detects insufficient eMBMS coverage at the UE.

    Summary of the Invention



    [0005] Various aspects and features of the present invention are defined in the claims. One embodiment provides a method of operating a base station for a mobile communications network, in which the base station is in communication with a plurality of mobile terminals; in which the method comprises the base station: interrogating each of the plurality of the mobile terminals for an indication of signal quality of a signal received by the mobile terminal; dividing the plurality of the mobile terminals between a first group and a second group based on the received indications of signal quality, in which the indications received from the mobile terminals in the first group indicate relatively low signal quality and in which the indications received from the mobile terminals in the second group indicate relatively high signal quality; and communicating with at least some of the mobile terminals in the first group over unicast and communicating with the mobile terminals in the second group over multicast.

    [0006] In this way mobile devices located nearer to the edge of a cell may be switched to unicast in a timely manner before transferring to be served by a different base station, i.e before the handover process. In particular, the invention can enhance mobile terminal mobility for eMBMS services operating in MBSFN architectures so as to reduce service interruption when a mobile terminal moves between MBSFN areas or between eMBMS base stations.

    [0007] According to an embodiment, the present invention provides: the base station communicating over unicast with mobile terminals in the first group that were previously in the second group and subsequently moved into the first group; and communicating over multicast with all other mobile terminals in the first group.

    [0008] According to an embodiment, the first group is served by a first set of resources and the second group is served by a second set of resources. According to an embodiment, the first set of resources is a subset of the second set of resources. Here, a resource is a sub-division of the total radio resources available for communication between mobile terminals and the base station and may be defined as a sub-division of the frequency domain (e.g. a particular frequency range) or as a combination of frequency and time domain a sub-divisions (e.g. a time slot at a particular frequency range).

    [0009] Another embodiment provides a base station for a mobile communications network, in which the base station comprises: a plurality of transmitters, in which each transmitter is configured to provide transmit radio signals to a plurality of mobile terminals; a plurality of receivers, in which each receiver is configured to detect receive radio signals from the plurality of mobile terminals; and a processor configured to:
    interrogate each of the plurality of the mobile terminals for an indication of signal quality of a signal received by the mobile terminal; and assign each of the plurality of the mobile terminals to one of two groups based on the received indications of signal quality, in which the indications received from the mobile terminals assigned to the first group indicate relatively low signal quality and in which the indications received from the mobile terminals assigned to the second group indicate relatively high signal quality; in which the plurality of transmitters are configured to communicate with at least some of the mobile terminals in the first group over unicast and to communicate with the mobile terminals in the second group over multicast.

    [0010] According to an embodiment, the plurality of transmitters are configured to communicate over unicast with mobile terminals in the first group that were previously in the second group and subsequently moved into the first group; and in which the plurality of transmitters are configured to communicate over multicast with all other mobile terminals in the first group.

    [0011] According to an embodiment, a decision to assign each of the plurality of the mobile terminals to one of two groups is based on a signal quality threshold value, in which an indication of signal quality that falls below the threshold value is deemed to indicate a relatively low signal quality while an indication of signal quality that falls above the threshold value is deemed to indicate relatively high signal quality; in which the threshold value is variable, dependent on at least one of the radio resource usage load at the base station and traffic levels on communications channels between the base station and the plurality of the mobile terminals.

    [0012] According to an embodiment, a decision to assign each of the plurality of the mobile terminals to one of two groups is based on a signal quality threshold value, in which an indication of signal quality that falls below the threshold value is deemed to indicate a relatively high signal quality while an indication of signal quality that falls above the threshold value is deemed to indicate relatively low signal quality; in which the threshold value is variable, dependent on at least one of the radio resource usage load at the base station and traffic levels on communications channels between the base station and the plurality of the mobile terminals.

    [0013] According to an embodiment, the plurality of transmitters are configured to communicate with the first group over a different frequency when compared to the second group.

    [0014] According to an embodiment, the indication of signal quality is based on at least one of: serving cell reference signal, channel quality, signal-to-noise ratio, signal-to-interference-plus-noise ratio, block-error-rate and neighbour cell reference signal level.

    [0015] According to an embodiment, the plurality of transmitters are configured to communicate with the first group using a first set of resources and in which the plurality of transmitters are configured to communicate with the second group using a second set of resources.

    [0016] The present invention accordingly provides, in a third aspect, a computer program element comprising computer program code to, when loaded into a computer system and executed thereon, cause the computer to perform the steps of the method set out above.

    Brief Description of the Drawings



    [0017] In order that the present invention may be better understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings in which:

    Figures 1 and 2 show a conventional 3GPP mobile communications network;

    Figure 3 shows a sequence of events according to an embodiment of the invention;

    Figures 4a and 4b shows a mobile communications network according to an embodiment of the invention;

    Figure 5 is a block diagram of a computer system suitable for the operation of embodiments of the present invention.


    Detailed Description of the Preferred Embodiments



    [0018] This invention enhances mobile terminal mobility for eMBMS services operating in MBSFN architectures so as to reduce service interruption when a mobile terminal moves between MBSFN areas or between eMBMS cells. The invention relates to techniques that can enable service switching from broadcast to unicast when a mobile terminal is moving from being served by a base station within a first MBSFN area towards being served by a base station within another MBSFN area. In particular, the invention can avoid service interruption by defining triggers for initiating switching eMBMS service for the mobile terminal from broadcast to unicast before the mobile terminal is transitioned to being served by a base station in another MBSFN area. According to an embodiment, the trigger is independent of the decision to transition the mobile terminal to being served by the target base station.

    [0019] According to an embodiment, the invention exploits interference management techniques, such as Inter-Cell Interference Coordination (ICIC), to trigger the switching to unicast communication of some mobile terminals being served by a base station close to the boundary between two MBSFN areas. According to another embodiment, the invention exploits such interference management techniques to trigger the switching to unicast communication of some mobile terminals close to a boundary between two eMBMS base stations. Use of partial or fractional reuse techniques by a base station form the basics of ICIC in LTE, whereby the available spectral bandwidth in a cell is managed in a way to reduce interference throughout the cell. According to ICIC techniques such as fractional frequency reuse (FFR), hard frequency reuse (HFR) and soft frequency reuse (SFR), each cell supports a set of resources that are subject to lower interference from neighbouring cells. The base station can use this a set of resources to improve the service provided to mobile terminals served by the base station that are located towards the cell edge (i.e. close to a region where the mobile terminals can experience signals from a neighbouring base station that are of similar strength to signals received from the serving base station, so that the signals from the neighbouring base station may cause interference with the signals from the serving base station).

    [0020] Interference management is designed to reduce interference throughout a cell and, in particular, in the areas towards the edges of a cell. To achieve this, the plurality of mobile terminals served by a base station are divided between a number of groups, for example first group and a second group depending on the received signal quality reported to the serving base station by the mobile terminal, where mobile terminals of the first group report a lower signal quality and mobile terminals of the second group report a higher signal quality. The inventors have determined that mobile terminals reporting a lower signal quality are more likely than the mobile terminals reporting a higher signal quality to be located near the edge of the cell and are more likely to transition to a target, neighbouring base station. According to the invention, where a cell lies at a boundary between two different MBSFN areas or between two eMBMS base stations, all mobile terminals in the first group or, alternatively, only mobile terminals transferring from the second group to the first group are restricted to unicast transmission, while the mobile terminals in the second group or, alternatively, the mobile terminals in the second group combined with the mobile terminals in the first group that have not transferred from the second group, will use multicast. In this way, the mobile terminals that are likely to transition to a target eMBMS cell or to a cell in another MBSFN area are switched to unicast in a timely manner.

    [0021] When a mobile terminal using multicast moves out of an MBSFN area into another MBSFN area or to a cell that does not provide the required MBMS service, then service interruption may be expected. For mobility between MBSFN areas, there is anticipated to be a service interruption of around 1.5 seconds. This is a combination of mobility time plus the time to read and decode system information block (SIB) messages of the new serving cell (see Figure 3). For mobility to a non-MBSFN cell the interruption is anticipated to be around 0.5 seconds. This includes time to read the SIBs of the new serving cell and then to setup a unicast bearer. Switching a mobile terminal from a multicast service to a unicast service reduces service interruption when moving out of an MBSFN area (whether moving into another MBSFN area or to a non-MBSFN cell). Where the switch to unicast occurs while the mobile terminal is still receiving good coverage of its serving base station, then the switch to unicast should further reduce service interruption. For example minimal interruptions may result from an increased likelihood of achieving make-before-break service continuity from multicast to unicast and a reduced likelihood of random access channel failure (which can adversely affect initial call setup step and registration). Where a base station takes responsibility for managing the transition of a mobile terminal that is moving out of an MBSFN area to a different MBSFN area, it can appropriately manage the timing of a transition from multicast to unicast. This removes risk of service interruptions for mobile terminals entering a different MBSFN area (as service interruption for switching from unicast to multicast can be zero).

    [0022] In Evolved Universal Terrestrial Radio Access Network (E-UTRAN), eMBMS services may be provisioned by defining MBSFN areas within a geographical area designated for broadcast (or multicast) services. A broadcast service area could be a single cell or multiple cells. A multi-cell MBSFN area defines a set of base stations participating in MBSFN service modes. Figure 1 illustrates a MBSFN network structure. Within MBSFN network 10, an operator operates a MBSFN service area 12 for deploying a broadcast (or multicast) service. Within that service area there may be a plurality of MBSFN areas 14. Each MBSFN area 14 consists of a number of base stations 16, each serving a different cell (not shown). The base stations 16 in a particular MBSFN area 14 are capable of synchronising together to provide the MBSFN service across multiple cells in the MBSFN area. Some of the base stations 16 within the MBSFN areas 14, serve reserved cells 18. A MBSFN area reserved cell is a cell within a MBSFN area that does not contribute to the MBSFN transmission and may be used for other services, e.g. unicast. Within a MBSFN area, eMBMS can be provided over a single frequency layer dedicated to MBSFN transmission or over a single frequency layer that is shared between MBSFN transmission and unicast services. Where Radio Resource Control (RRC) is used, reception of eMBMS services is available for the mobile terminals in RRC_Connected or RRC_Idle states.

    [0023] LTE supports overlap between MBSFN service areas, for example, smaller MBSFN areas can overlap larger ones for regional and national coverage. In 3GPP LTE or 4G, one base station can belong to up to eight MBSFN areas. All base stations transmitting MBSFN in a single area are required to be synchronised, so that the same multimedia content is transmitted from all the base station stations with a mutual offset of no more than a few micro-seconds.

    [0024] One of the key features of the LTE network is mobility provision. Supporting seamless user mobility across the network requires service continuity for eMBMS users and plays an important role in maintaining service quality and customer satisfaction. There are a number of scenarios where it would be desirable for a LTE mobile terminal to be able to move from one base station to another whilst receiving MBSFN service, for example when a the mobile terminal is moving into a MBSFN area reserved cell whilst receiving an eMBMS service and when moving from one MBSFN cell to another cell not within the same MBSFN area. Figure 2 shows MBSFN service area 20 comprising exemplary MBSFN areas 22, 24 and 26 - each MBSFN area comprising a plurality of cells, each cell defined by a different base station (not shown). MBSFN area 22 comprises a plurality of multicast cells 220 and one MBSFN area reserve (unicast) cell 226. MBSFN area 24 comprises a plurality of multicast cells 222 but no MBSFN area reserve (unicast) cell. MBSFN area 26 comprises a plurality of multicast cells 224 and one MBSFN area reserve (unicast) cell 228. Exemplary transitions between the cells of MBSFN service area 20 are shown, as follows. Transitions 230 and 234 represent a mobile terminal passing from one multicast cell to another multicast cell in a different MBSFN area. Transition 232 represents a mobile terminal passing from a multicast cell to an MBSFN area reserved cell in the same MBSFN area. 3GPP standards do not describe any mechanism for switching a mobile terminal that is receiving a multicast service from multicast to unicast.

    [0025] According to an embodiment, the invention leverages interference management techniques practised by base stations to trigger switching mobile terminals to unicast. According to this embodiment, mobile terminals are classified in a dynamic manner by the base station as reporting either lower or higher signal quality. In this example, the two groups of mobile terminals (i.e. lower signal quality and higher signal quality) are assigned different sets of resources (e.g. different sub-channels or time slots). The base station decides what set of resources to assign to each group. The base station may change resource assignments (e.g. assign more resources to the cell edge group and fewer resources to the cell centre group). The resources assigned to a mobile terminal will normally be from the resources assigned to the group of which it is a member. However schedulers may occasionally assign resources to a mobile terminal from the other group's resources when the mobile terminal's own group is short of resources and the other group has resources to spare (e.g. when there is little traffic for mobile terminals in the lower signal quality group, the assigned resources could be scheduled for mobile terminals in the higher signal quality group).

    [0026] Figure 4a shows a mobile communications network, by way of example, a LTE network 70 comprising a first MBSFN area 72 comprising cells 720 and a second MBSFN area 74 comprising cells 740. First MBSFN area 72 and a second MBSFN area 74 overlap at cells 760 and 762, which form part of both first and second MBSFN areas. Shared cells 760, 762 are frequency reuse cells that are divided between two sets of resources. As indicated above, in a frequency reuse cell, the mobile terminals are divided between a first group and a second group depending on the received signal quality reported by the mobile terminal. The first group is served by a first set of resources and the second group by a second set of resources. The first set of resources may also be referred to as an "outer set", because the mobile terminals allocated to this set are those reporting a lower signal quality and this is more likely to mean that the mobile terminals in this set are farther away from the base station. Similarly, the second set of resources may also be referred to as an "inner set", because the mobile terminals allocated to this set are those reporting a higher signal quality and this is more likely to mean that the mobile terminals in this set are closer to the base station. According to an embodiment, the first set of resources may be a sub-set of the second set of resources. The other cells 720, 740 in first MBSFN area 72 and second MBSFN area 74 are multicast. First MBSFN area 72 therefore comprises multicast cells 720 and frequency reuse cells 760, 762 and serves a first eMBMS service. Second MBSFN area 74 therefore comprises multicast cells 740 and frequency reuse cells 760, 762 and serves a second eMBMS service.

    [0027] Figure 4b shows shared frequency reuse cell 762 in more detail. Each cell comprises a base station, although only base station 770 in cell 762 is shown. The base station 770 allocates the mobile terminals operating in cell 762 to one of two sets of resource: an inner resource set and an outer resource set. This allocation can be thought of as creating two zones within the cell. Figure 4b shows, for example, zone 764 located towards the centre of the cell 762 serving terminals in the higher signal quality group and zone 766 located towards the periphery of the cell serving terminals in the higher signal quality group. In reality these zones may not have the clearly-defined boundary indicated in Figure 4b and could overlap. Mobile terminals operating in MBSFN cells at the boundary between MBSFN areas can accordingly be divided between the higher signal-quality zone 764 and the lower signal-quality zone 766, whereby resources in the lower signal-quality zone are reserved to unicast transmission only. According to an alternative embodiment, only mobile terminals transferring from the higher signal-quality group to the lower signal-quality group are restricted to unicast transmission, so that the resources in the lower signal-quality zone 766 may support unicast and multicast transmission for different mobile terminals. Typically a mobile terminal will be allocated to one of the groups based on comparing a signal quality parameter threshold value with a signal quality parameter (such as the signal-to-noise ratio (SNR) or signal-to-interference-plus-noise ratio (SINR)) reported by the mobile terminal, that the mobile terminal is experiencing. Other parameters that can be used to determine the group for a mobile terminal include: serving-cell reference signal-level, channel quality information, block-error-rates and neighbour-cell reference signal-level. A low value of any of: serving cell reference signal, channel quality, SNR and SINR or a high value of any of: block-error-rates and neighbour cell reference signal would increase the likelihood that the mobile terminal would be allocated to the outer resource set. The mobile terminals indicating a low value of serving cell reference signal, channel quality, SNR or SINR or a high value of block-error-rates or neighbour cell reference signal are more likely to transfer to a different base station as the respective parameter value probably indicates that the mobile terminal is approaching the point where a signal from the different base station in an adjacent MBSFN cell would provide a better quality of service. In this way, the mobile terminals that are likely to transition to a cell in another MBSFN area are switched to unicast in a timely manner before handover. According to an embodiment, the rate of transfer of the mobile terminals from inner resource set to outer resource set, i.e. from multicast to unicast, may be regulated so as to control the load (since unicast places a higher load). The load may be defined as at least one of: the radio resource usage load at the base station and traffic levels on communications channels between the base station and the plurality of the mobile terminals. In particular, the number of unicast mobile terminals in the cell can be controlled by adjusting a parameter threshold used to discriminate between higher and lower signal quality.

    [0028] The mobile terminal eMBMS procedures are now described in more detail. LTE eMBMS protocol architecture consists of physical, transport and logical layers, with the physical layer supporting a radio interface between the mobile terminal and base station. The radio interface comprises two point-to-multipoint logical channels for eMBMS: Multicast Control Channel (MCCH) and Multicast Traffic Channel (MTCH). The MCCH is a logical channel that exists in the control plane of the radio interface between the mobile terminal and the base station and is used to broadcast eMBMS related Radio Resource Control (RRC) protocol messages. Information carried by MCCH includes sub-frame allocation and modulation and coding scheme (MCS) configuration. MTCH on the other hand exists in the user plane of the radio interface between the mobile terminal and the base station. MTCH is a logical channel and carries the eMBMS application data. One or more MTCH are mapped to the multicast channel (MCH) in order to obtain multiplexing gains while only one MCCH is multiplexed onto MCH. Each MCCH corresponds to an MBSFN area. Different MCCHs are assigned for different MBSFN areas. In the case where multiple MBSFN areas overlap, one base station could provide multiple MCCHs broadcasted in different MBSFN sub-frames. Both MCCH and MTCH are mapped to the MCH by the media access control (MAC) sublayer. MCH is mapped to a physical multicast channel (PMCH) The PMCH is very similar to the physical downlink shared channel (PDSCH) in unicast mode. MCH is transmitted over MBSFN in specific subframes.

    [0029] With reference to Figure 3, at 30, the mobile terminal acquires from the serving base station a system information block type 2 (SIB2) containing radio resource configuration information that is common for all the mobile terminals. At 31, the mobile terminal reads SIB2 to discover which sub-frames are allocated for MBSFN on PMCH and unicast on PDCH. At 32, the mobile terminal, being interested in eMBMS, acquires SIB13, which contains information required to acquire the MBMS control information associated with one or more MBSFN areas. For example, SIB13 lists: MBSFN areas, cells, MCCH and MCS. At 34, the mobile terminal receives from the base station RRC signalling and MBSFN area configuration information and, at 35, the mobile terminal receives PMCH instances and MCCH. At 36, the mobile terminal monitors MCCH for any changes.

    [0030] 3GPP Release 12 has introduced a Group Communication Server Application Server (GCS AS). The GCS AS function is to signal to the mobile terminal the required configuration information that the mobile terminal needs in order to receive application data via eMBMS bearer services. As the mobile terminal detects it is moving away from the MBSFN area, for example by detecting a poor MBSFN signal quality or by monitoring one of the other parameters, listed above, it elects to receive data over unicast whilst it is still able to communicate effectively with the serving MBMS cell. The mobile terminal sets up a unicast flow to receive eMBMS data via unicast and, accordingly, ceases receiving eMBMS data via MBSFN. The mobile terminal is able to receive the eMBMS data from unicast and MBMS simultaneously thereby avoiding service interruption during this switching process. At a later time, the mobile terminal notifies the GCS AS that it is approaching the limit of communicating effectively with the serving MBSFN cell and will soon be too far from the serving MBMS cell to guarantee reliable operation and so initiates transition to a cell that is able to provide the mobile terminal with a stronger signal.

    [0031] Switching from unicast delivery to eMBMS is also possible if the mobile terminal happens to enter an adjacent MBSFN area. The mobile terminal has ongoing communications with GCS AS, which will inform the mobile terminal when eMBMS delivery is available over MBSFN - along with the corresponding bearer service configurations. Whilst the mobile terminal is still receiving downlink unicast delivery, when eMBMS delivery becomes available over MBSFN, the mobile terminal can start receiving MBMS scheduling information over MCH and eMBMS bearer over MTCH. During this switching period, the mobile terminal will receive the eMBMS data from both unicast and MBMS. The mobile terminal will then notify the GCS AS that it is within the adjacent MBSFN area and that it is receiving eMBMS bearer service. The GCS AS will then stop the unicast delivery to the mobile terminal, which now will only receive services over MBSFN.

    [0032] Figure 5 is a block diagram of a computer system 50 suitable for the operation of embodiments of the present invention. A central processor unit (CPU) 510 is communicatively connected to communications interface 508, a memory 512, a storage 514 and an input/output (I/O) interface 516 via a data bus 520. The memory 512 can be any read/write storage device such as a random access memory (RAM) or a non-volatile storage device suitable for storing data for use by processor 512. The storage 514 can be any read-only or read/write storage device such as a random access memory (RAM) or a non-volatile storage device suitable for storing program code for controlling the operation of processor 510. Memory 512 and storage 514 may comprise the same device or devices. An example of a non-volatile storage device includes a disk or tape storage device. The user interface 516 is an interface to devices for the input or output of data provided to or received from a user or operator of computer system 50. Examples of I/O devices connectable to user interface 516 include a keyboard, a mouse, a display (such as a monitor) and a network connection. Communications interface 508 is an interface to other devices and may comprise one or more radio transmit interfaces and one or more wired or wireless core network interfaces.

    [0033] The present invention has application to audio and video broadcasting but also file broadcasting in mobile networks. In addition to mobile networks, the present invention may also have application to femtocell and small cell deployments, for example, in pre-loading certain content on devices to enhance QoE and optimise use of resources. Similar scenarios may arise for simultaneous software updates on multiple devices. The present invention has been described in an LTE context that could be deployed with existing multicast mobile networks, but the invention can be applied in any multicast mobile network where the network elements have similar roles regarding unicast and multicast service provision. The present invention has been described, by way of example and for reasons of economy, in relation to a specific set of parameters however, it will be appreciated that the invention is not limited to any particular measure of signal quality but can be implemented based on any reliable technique for characterising signal quality.

    [0034] As set out in the Abstract hereto, the invention relates to a base station for a mobile communications network, in which the base station comprises: a plurality of transmitters, in which each transmitter is configured to provide transmit radio signals to a plurality of mobile terminals; and a plurality of receivers, in which each receiver is configured to detect receive radio signals from the plurality of mobile terminals. The base station also comprises a processor configured to interrogate each of the plurality of the mobile terminals for an indication of signal quality of a signal received by the mobile terminal; and to assign each of the plurality of the mobile terminals to one of two groups based on the received indications of signal quality. The mobile terminals assigned to the first group are those that indicate relatively low signal quality and the mobile terminals assigned to the second group are those that indicate relatively high signal quality. The plurality of transmitters are configured to communicate with at least some of the mobile terminals in the first group over unicast and to communicate with the mobile terminals in the second group over multicast. The invention also relates to a corresponding method for operating a base station for a mobile communications network.

    [0035] According to an embodiment, from time to time, during operation of the invention, it is possible that one or other group may have no members. During such occurrences, the operation for the invention may comprise either: waiting for one or more mobile terminals to report signal quality that indicated that the one or more mobile terminals belonged in the empty group or, alternatively, waiting for the threshold to adjust so that teach group had members.

    [0036] Insofar as embodiments of the invention described are implementable, at least in part, using a software-controlled programmable processing device, such as a microprocessor, digital signal processor or other processing device, data processing apparatus or system, it will be appreciated that a computer program for configuring a programmable device, apparatus or system to implement the foregoing described methods is envisaged as an aspect of the present invention. The computer program may be embodied as source code or undergo compilation for implementation on a processing device, apparatus or system or may be embodied as object code, for example.

    [0037] Suitably, the computer program is stored on a carrier medium in machine or device readable form, for example in solid-state memory, magnetic memory such as disk or tape, optically or magneto-optically readable memory such as compact disk or digital versatile disk etc., and the processing device utilises the program or a part thereof to configure it for operation. The computer program may be supplied from a remote source embodied in a communications medium such as an electronic signal, radio frequency carrier wave or optical carrier wave. Such carrier media are also envisaged as aspects of the present invention.

    [0038] It will be understood by those skilled in the art that, although the present invention has been described in relation to the above described example embodiments, the invention is not limited thereto and that there are many possible variations and modifications which fall within the scope of the invention.

    [0039] The scope of the present invention includes any novel features or combination of features disclosed herein. The applicant hereby gives notice that new claims may be formulated to such features or combination of features during prosecution of this application or of any such further applications derived therefrom. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the claims.


    Claims

    1. A method for operating a base station (16) for a mobile communications network, in which the base station (16) is in communication with a plurality of mobile terminals; in which the method comprises the base station (16):

    interrogating each of the plurality of the mobile terminals for an indication of signal quality of a signal received by the mobile terminal;

    assigning each mobile terminal of the plurality of mobile terminals to one of two groups based on the indications of received signal quality, in which the indications received from the mobile terminals assigned to the first group indicate relatively low signal quality and in which the indications received from the mobile terminals assigned to the second group indicate relatively high signal quality, in which the first group is served by a first set of resources and the second group is served by a second set of resources whereby the first set is a subset of the second set;

    communicating with at least some of the mobile terminals assigned to the first group over unicast and communicating with the mobile terminals assigned to the second group over multicast;

    in which a decision to assign each mobile terminal of the plurality of mobile terminals to one of the first group and the second group is based on comparing the indication of signal quality for that mobile terminal with a signal quality threshold value; and

    in which the threshold value is variable, dependent on at least one of the radio resource usage load at the base station (16) and traffic levels on communications channels between the base station (16) and the plurality of the mobile terminals.


     
    2. The method of claim 1, comprising: communicating over unicast with mobile terminals assigned to the first group that were previously in the second group and were subsequently assigned to the first group; and communicating over multicast with at least some other mobile terminals assigned to the first group.
     
    3. The method of any of claims 1 to 2, in which the first group is served over a different frequency when compared to the second group.
     
    4. The method of any of claims 1 to 3, in which the indication of signal quality is based on at least one of: serving cell reference signal, channel quality, signal-to-noise ratio, signal-to-interference-plus-noise ratio, block-error-rate and neighbour cell reference signal level.
     
    5. A computer program element comprising computer program code to, when loaded into a computer system and executed thereon, cause the computer to perform the steps of a method as claimed in any of claims 1 to 4.
     
    6. A base station (16) for a mobile communications network, in which the base station (16) comprises:

    a plurality of transmitters, in which each transmitter is configured to transmit radio signals to a plurality of mobile terminals;

    a plurality of receivers, in which each receiver is configured to receive radio signals from the plurality of mobile terminals; and

    a processor (510) configured to:

    interrogate each of the plurality of the mobile terminals for an indication of signal quality of a signal received by the mobile terminal;

    assign each mobile terminal of the plurality of the mobile terminals to one of two groups based on the indications of received signal quality, in which the first group is served by a first set of resources and the second group is served by a second set of resources whereby the first set is a subset of the second set;

    in which the base station (16) is configured such that:
    a decision to assign each mobile terminal of the plurality of mobile terminals to one of the first group and the second group is based on comparing the indication of signal quality for that mobile terminal with a signal quality threshold value;

    in which the threshold value is variable, dependent on at least one of the radio resource usage load at the base station and traffic levels on communications channels between the base station and the plurality of the mobile terminals; and

    in which the plurality of transmitters are configured to communicate with at least some of the mobile terminals in the first group over unicast and to communicate with the mobile terminals in the second group over multicast.


     
    7. The base station (16) of claim 6, in which the plurality of transmitters are configured to communicate over unicast with mobile terminals assigned to the first group that were previously in the second group and subsequently assigned to the first group; and in which the plurality of transmitters are configured to communicate over multicast with all other mobile terminals assigned to the first group.
     
    8. The base station (16) of any of claims 6 to 7, in which the plurality of transmitters are configured to communicate with the first group over a different frequency when compared to the second group.
     
    9. The base station (16) of any of claims 6 to 8, in which the indication of signal quality is based on at least one of: serving cell reference signal, channel quality, signal-to-noise ratio, signal-to-interference-plus-noise ratio, block-error-rate and neighbour cell reference signal level.
     


    Ansprüche

    1. Verfahren zum Betreiben einer Basisstation (16) für ein Mobilfunknetzwerk, wobei die Basisstation (16) in einer Kommunikation mit einer Vielzahl von Mobilfunkendgeräten steht; wobei das Verfahren die folgenden Schritte umfasst, die von der Basisstation (16) ausgeführt werden:

    Abfragen von jedem aus der Vielzahl von Mobilfunkendgeräten hinsichtlich einer Anzeige einer Signalqualität eines in dem Mobilfunkendgerät empfangenen Signals;

    Zuteilen von jedem Mobilfunkendgerät aus der Vielzahl von Mobilfunkendgeräten zu einer von zwei Gruppen aufgrund der Anzeigen der empfangenen Signalqualität, wobei die Anzeigen, die von den Mobilfunkendgeräten empfangen wurden, die der ersten Gruppe zugeteilt wurden, eine relativ niedrige Signalqualität anzeigen, und wobei die Anzeigen, die von den Mobilfunkendgeräten empfangen wurden, die der zweiten Gruppe zugeteilt wurden, eine relativ hohe Signalqualität anzeigen, wobei die erste Gruppe von einer ersten Gruppe von Ressourcen bedient wird und wobei die zweite Gruppe von einer zweiten Gruppe von Ressourcen bedient wird, wobei die erste Gruppe eine Teilgruppe der zweiten Gruppe ist;

    Kommunizieren mit mindestens einigen der Mobilfunkendgeräte, die der ersten Gruppe zugeteilt wurden, über eine Unicast-Verbindung und Kommunizieren mit den Mobilfunkendgeräten, die der zweiten Gruppe zugeteilt wurden, über eine Multicast-Verbindung;

    wobei eine Entscheidung zum Zuteilen von jedem Mobilfunkendgerät aus der Vielzahl von Mobilfunkendgeräten zu einer der ersten und der zweiten Gruppe auf einem Vergleichen der Anzeige der Signalqualität für dieses Mobilfunkendgerät mit einem Signalqualitätsschwellenwert beruht; und

    wobei der Schwellenwert abhängig von mindestens einer der Funkressourcennutzungslast in der Basisstation (16) und den Datenverkehrspegeln auf den Kommunikationskanälen zwischen der Basisstation (16) und der Vielzahl von Mobilfunkendgeräten variabel ist.


     
    2. Verfahren nach Anspruch 1, umfassend: Kommunizieren über eine Unicast-Verbindung mit den Mobilfunkendgeräten, die der ersten Gruppe zugeteilt wurden, die sich zuvor in der zweiten Gruppe befunden haben und die nachfolgend der ersten Gruppe zugeteilt wurden; und Kommunizieren über eine Multicast-Verbindung mit mindestens einigen anderen Mobilfunkendgeräten, die der ersten Gruppe zugeteilt wurden.
     
    3. Verfahren nach einem der Ansprüche 1 bis 2, wobei die erste Gruppe im Vergleich zur zweiten Gruppe über eine andere Frequenz bedient wird.
     
    4. Verfahren nach einem der Ansprüche 1 bis 3, wobei die Anzeige der Signalqualität mindestens auf Einem beruht von: einem Dienstzellenreferenzsignal, einer Kanalqualität, einem Signal-Rausch-Verhältnis, einem Signal-Interferenz-plus-Rausch-Verhältnis, einer Blockfehlerrate und einem Nachbarzellenreferenzsignalpegel.
     
    5. Computerprogrammelement, das einen Computerprogrammcode umfasst, der, wenn er in ein Computersystem geladen und darin ausgeführt wird, den Computer veranlasst, die Schritte eines Verfahrens nach einem der Ansprüche 1 bis 4 auszuführen.
     
    6. Basisstation (16) für ein Mobilkommunikationsnetzwerk, wobei die Basisstation (16) umfasst:

    eine Vielzahl von Sendern, wobei jeder Sender konfiguriert ist zum Senden von Funksignalen an eine Vielzahl von Mobilfunkendgeräten;

    eine Vielzahl von Empfängern, wobei jeder Empfänger konfiguriert ist zum Empfangen von Funksignalen von der Vielzahl von Mobilfunkendgeräten; und

    einen Prozessor (510), der konfiguriert ist zum:

    Abfragen von jedem aus der Vielzahl von Mobilfunkendgeräten hinsichtlich einer Anzeige einer Signalqualität eines Signals, das in dem Mobilfunkendgerät empfangen wird;

    Zuteilen von jedem Mobilfunkendgerät aus der Vielzahl von Mobilfunkendgeräten zu einer von zwei Gruppen aufgrund der Anzeigen der empfangenen Signalqualität, wobei die erste Gruppe von einer ersten Gruppe von Ressourcen bedient wird und wobei die zweite Gruppe von einer zweiten Gruppe von Ressourcen bedient wird, wobei die erste Gruppe eine Teilgruppe der zweiten Gruppe ist;

    wobei die Basisstation (16) so konfiguriert ist, dass:
    eine Entscheidung zum Zuteilen von jedem Mobilfunkendgerät aus der Vielzahl von Mobilfunkendgeräten zu einer der ersten und der zweiten Gruppe auf einem Vergleichen der Anzeige der Signalqualität für dieses Mobilfunkendgerät mit einem Signalqualitätsschwellenwert beruht;

    wobei der Schwellenwert abhängig von mindestens einer der Funkressourcennutzungslast in der Basisstation und den Datenverkehrspegeln auf den Kommunikationskanälen zwischen der Basisstation und der Vielzahl von Mobilfunkendgeräten variabel ist; und

    wobei die Vielzahl von Sendern konfiguriert ist zum Kommunizieren mit mindestens einigen der Mobilfunkendgeräte in der ersten Gruppe über eine Unicast-Verbindung und zum Kommunizieren mit den Mobilfunkendgeräten in der zweiten Gruppe über eine Multicast-Verbindung.


     
    7. Basisstation (16) nach Anspruch 6, wobei die Vielzahl von Sendern konfiguriert ist zum Kommunizieren über eine Unicast-Verbindung mit den Mobilfunkendgeräten, die der ersten Gruppe zugeteilt wurden, die sich zuvor in der zweiten Gruppe befunden haben und die nachfolgend der ersten Gruppe zugeteilt wurden; und wobei die Vielzahl von Sendern konfiguriert ist zum Kommunizieren über eine Multicast-Verbindung mit allen anderen Mobilfunkendgeräten in der ersten Gruppe.
     
    8. Basisstation (16) nach einem der Ansprüche 6 bis 7, wobei die Vielzahl von Sendern konfiguriert ist zum Kommunizieren mit der ersten Gruppe über eine andere Frequenz im Vergleich zur zweiten Gruppe.
     
    9. Basisstation (16) nach einem der Ansprüche 6 bis 8, wobei die Anzeige der Signalqualität mindestens auf Einem beruht von: einem Dienstzellenreferenzsignal, einer Kanalqualität, einem Signal-Rausch-Verhältnis, einem Signal-Interferenz-plus-Rausch-Verhältnis, einer Blockfehlerrate und einem Nachbarzellenreferenzsignalpegel.
     


    Revendications

    1. Procédé d'expédition d'une station de base (16) d'un réseau de communications mobiles, dans lequel la station de base (16) est en communication avec une pluralité de terminaux mobiles ; le procédé comprenant par la station de base (16) :

    l'interrogation de chacun de la pluralité des terminaux mobiles pour obtenir une indication de qualité de signal d'un signal reçu par le terminal mobile ;

    l'assignation de chaque terminal mobile de la pluralité de terminaux mobiles à un de deux groupes sur la base des indications de qualité de signal reçu, dans lequel les indications reçues depuis les terminaux mobiles assignés au premier groupe indiquent une qualité de signal relativement basse et dans lequel les indications reçues depuis les terminaux mobiles assignés au second groupe indiquent une qualité de signal relativement élevée, dans lequel le premier groupe est desservi par un premier ensemble de ressources et le second groupe est desservi par un second ensemble de ressources moyennant quoi le premier ensemble est un sous-ensemble du second ensemble ;

    la communication avec au moins certain des terminaux mobiles assignés au premier groupe par unidiffusion et la communication avec les terminaux mobiles assignés au second groupe par multidiffusion ;

    dans lequel une décision d'assigner chaque terminal mobile de la pluralité de terminaux mobiles à un du premier groupe et du second groupe est basée sur une comparaison de l'indication de qualité de signal pour ce terminal mobile à une valeur seuil de qualité de signal ; et

    dans lequel la valeur seuil est variable en fonction d'au moins la charge d'utilisation des ressources radio au niveau de la station de base (16) ou des niveaux de trafic sur les canaux de communication entre la station de base (16) et la pluralité des terminaux mobiles.


     
    2. Procédé selon la revendication 1, comprenant : la communication par unidiffusion avec des terminaux mobiles assignés au premier groupe qui se trouvaient précédemment dans le second groupe et ont été ultérieurement assignés au premier groupe ; et la communication par multidiffusion avec au moins certains autres terminaux mobiles assignés au premier groupe.
     
    3. Procédé selon l'une quelconque des revendications 1 à 2, dans lequel le premier groupe est desservi sur une fréquence différente de celle utilisée avec le second groupe.
     
    4. Procédé selon l'une quelconque des revendications 1 à 3, dans lequel l'indication de qualité de signal est basée sur au moins : un signal de référence de cellule de desserte, une qualité de canal, un rapport signal/bruit, un rapport signal/interférence et bruit, un taux d'erreurs sur les blocs, ou un niveau de signal de référence de cellule voisine.
     
    5. Elément de programme informatique comprenant un code de programme informatique pour, à son chargement dans un système informatique et son exécution sur celui-ci, amener l'ordinateur à réaliser les étapes d'un procédé selon l'une quelconque des revendications 1 à 4.
     
    6. Station de base (16) d'un réseau de communications mobiles, dans lequel la station de base (16) comprend :

    une pluralité d'émetteurs, chaque émetteur étant configuré pour émettre des signaux radio vers une pluralité de terminaux mobiles ;

    une pluralité de récepteurs, chaque récepteur étant configuré pour recevoir des signaux radio en provenance de la pluralité de terminaux mobiles ; et

    un processeur (510) configuré pour :

    interroger chacun de la pluralité des terminaux mobiles pour obtenir une indication de qualité de signal d'un signal reçu par le terminal mobile ;

    assigner chaque terminal mobile de la pluralité de terminaux mobiles à un de deux groupes sur la base des indications de qualité de signal reçu, dans lequel le premier groupe est desservi par un premier ensemble de ressources et le second groupe est desservi par un second ensemble de ressources moyennant quoi le premier ensemble est un sous-ensemble du second ensemble ;

    la station de base (16) étant configurée de telle sorte que :
    une décision d'assigner chaque terminal mobile de la pluralité de terminaux mobiles à un du premier groupe et du second groupe soit basée sur une comparaison de l'indication de qualité de signal pour ce terminal mobile à une valeur seuil de qualité de signal ;

    dans lequel la valeur seuil est variable en fonction d'au moins la charge d'utilisation des ressources radio au niveau de la station de base ou des niveaux de trafic sur les canaux de communication entre la station de base et la pluralité des terminaux mobiles ; et

    dans lequel la pluralité d'émetteurs est configurée pour communiquer avec au moins certains des terminaux mobiles dans le premier groupe par unidiffusion et communiquer avec les terminaux mobiles dans le second groupe par multidiffusion.


     
    7. Station de base (16) selon la revendication 6, dans laquelle la pluralité d'émetteurs est configurée pour communiquer par unidiffusion avec des terminaux mobiles assignés au premier groupe qui se trouvaient précédemment dans le second groupe et ont été ultérieurement assignés au premier groupe ; et dans laquelle la pluralité d'émetteurs est configurée pour communiquer par multidiffusion avec tous les autres terminaux mobiles assignés au premier groupe.
     
    8. Station de base (16) selon l'une quelconque des revendications 6 à 7, dans laquelle la pluralité d'émetteurs est configurée pour communiquer avec le premier groupe sur une fréquence différente de celle utilisée avec le second groupe.
     
    9. Station de base (16) selon l'une quelconque des revendications 6 à 8, dans laquelle l'indication de qualité de signal est basée sur au moins : un signal de référence de cellule de desserte, une qualité de canal, un rapport signal/bruit, un rapport signal/interférence et bruit, un taux d'erreurs sur les blocs, ou un niveau de signal de référence de cellule voisine.
     




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    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description




    Non-patent literature cited in the description