WO2009023477A1

WO2009023477A1 - Method and apparatus for providing improved single frequency network mbms

Info

Publication number: WO2009023477A1
Application number: PCT/US2008/072232
Authority: WO
Inventors: Vinod Kumar Ramachandran; Richa Dham; Vihang Gangaram Kamble; Suresh Kalyanasundaram; Ivan Vukovic; Igor Filipovich
Original assignee: Motorola, Inc.
Priority date: 2007-08-14
Filing date: 2008-08-05
Publication date: 2009-02-19

Abstract

Various embodiments are described that are able to reduce MBMS service interruption times in a relatively efficient manner. A network node (121) that is included within a single frequency network (SFN) area associated with an MBMS service, transmits MBMS content associated with this MBMS service. A remote unit (101) receiving this MBMS content also receives from the network node, via a multicast control channel (MCCH), an indication of whether the network node is a boundary node of the SFN area. Based on this indication, the remote unit can assume, when the network node is not a boundary node, that neighboring network nodes (122-124) are also transmitting the MBMS service. Only when the network node is indicated to be a boundary node, does the remote unit need to either determine further whether a neighboring network node is transmitting content for the MBMS service or perhaps simply report that it is presently receiving content for the MBMS service.

Description

METHOD AND APPARATUS FOR PROVIDING IMPROVED SINGLE FREQUENCY NETWORK MBMS

Field of the Invention

The present invention relates generally to communication systems and, in particular, to providing improved multicast and broadcast multimedia service (MBMS) to remote units in a single frequency network (SFN) area.

Background of the Invention

In 4G cellular systems (e.g., 3GPP Long Term Evolution (LTE)), single frequency network (SFN) operation is likely to be used for delivering multicast and broadcast multimedia services (MBMS) over a contiguous set of cells. In SFN operation, identical MBMS content will be transmitted in all the cells of the SFN area at identical time-frequency slots to provide content synchronization over the air. To accomplish this, the cells of the SFN area are time-synchronized. There may be an SFN area per service and the different SFN areas may be overlapping. User equipment (UEs) listening to just the MBMS services alone are considered to be in idle mode and do not have an active radio resource control (RRC) connection with an eNodeB. In this setting, there will be scenarios where the UEs may move from within the SFN area to a cell outside the SFN area. The objective is to minimize the service interruption time during this mobility without impacting the battery consumption of the UE at other time instants.

The UE can perform cell reselection to a cell outside the SFN area and then read the multicast control channel (MCCH) of the new cell to determine if the same service is being transmitted. In case the same service is not transmitted, the UE can move to active mode and request the service. Depending on the cell's configuration, the eNodeB can join the multicast tree and transmit the service in point-to-point, single cell, or SFN mode. However, this will incur additional, and perhaps substantial, service interruption times during such handovers. To reduce this service interruption time, a UE may monitor the MCCH of one or more of its neighboring cells on an ongoing basis in order to take action, before cell reselection, should a neighboring cell not be transmitting the service. Since techniques and/or mechanisms for reducing service interruption times serve to improve MBMS for users, additional techniques / mechanisms that may also reduce service interruption times, perhaps more advantageously than what is presently known, are desirable for advancing the art.

Brief Description of the Drawings

FIG. 1 is a block diagram depiction of a wireless communication system in accordance with multiple embodiments of the present invention.

FIG. 2 is a block diagram depiction of overlapping single frequency network (SFN) areas in an MBMS-capable communication system, in accordance with multiple embodiments of the present invention.

FIG. 3 is a logic flow diagram that depicts detailed functionality performed by user equipment (UE) receiving an MBMS service from a current cell while monitoring a neighbor cell, in accordance with certain embodiments of the present invention.

FIG. 4 is a logic flow diagram that depicts detailed functionality performed by user equipment (UE) and a cell from which the UE is receiving an MBMS service that is not being transmitted by a neighbor cell, in accordance with a first set of embodiments of the present invention. FIG. 5 is a logic flow diagram that depicts detailed functionality performed by user equipment (UE) and a cell from which the UE is receiving an MBMS service that is not being transmitted by a neighbor cell, in accordance with a second set of embodiments of the present invention.

FIG. 6 is a logic flow diagram that depicts detailed functionality performed by user equipment (UE) and a cell from which the UE is receiving an MBMS service that is not being transmitted by a neighbor cell, in accordance with a third set of embodiments of the present invention.

Specific embodiments of the present invention are disclosed below with reference to FIGs. 1-6. Both the description and the illustrations have been drafted with the intent to enhance understanding. For example, the dimensions of some of the figure elements may be exaggerated relative to other elements, and well-known elements that are beneficial or even necessary to a commercially successful implementation may not be depicted so that a less obstructed and a more clear presentation of embodiments may be achieved. In addition, although the signaling flow diagrams and/or the logic flow diagrams above are described and shown with reference to specific signaling exchanged and/or specific functionality performed in a specific order, some of the signaling / functionality may be omitted or some of the signaling / functionality may be combined, sub-divided, or reordered without departing from the scope of the claims. Thus, unless specifically indicated, the order and grouping of the signaling / functionality depicted is not a limitation of other embodiments that may lie within the scope of the claims.

Simplicity and clarity in both illustration and description are sought to effectively enable a person of skill in the art to make, use, and best practice the present invention in view of what is already known in the art. One of skill in the art will appreciate that various modifications and changes may be made to the specific embodiments described below without departing from the spirit and scope of the present invention. Thus, the specification and drawings are to be regarded as illustrative and exemplary rather than restrictive or all- encompassing, and all such modifications to the specific embodiments described below are intended to be included within the scope of the present invention.

Detailed Description of Embodiments

Various embodiments are described that are able to reduce MBMS service interruption times in a relatively efficient manner. A network node that is included within a single frequency network (SFN) area associated with an MBMS service, transmits MBMS content associated with this MBMS service. A remote unit receiving this MBMS content also receives from the network node, via a multicast control channel (MCCH), an indication of whether the network node is a boundary node of the SFN area. Based on this indication, the remote unit can assume, when the network node is not a boundary node, that neighboring network nodes are also transmitting the MBMS service. Only when the network node is indicated to be a boundary node, does the remote unit need to either determine further whether a neighboring network node is transmitting content for the MBMS service or perhaps simply report that it is presently receiving content for the MBMS service.

The disclosed embodiments can be more fully understood with reference to FIGs. 1 -6. FIG. 1 is a block diagram depiction of a wireless communication system 100 in accordance with multiple embodiments of the present invention. At present, standards bodies such as OMA (Open Mobile Alliance), 3GPP (3rd Generation Partnership Project), 3GPP2 (3rd Generation Partnership Project 2), IEEE (Institute of Electrical and Electronics Engineers) 802, and WiMAX Forum are developing standards specifications for wireless telecommunications systems. (These groups may be contacted via http://www.openmobilealliance.com, http://www.3gpp.org/, http://www.3gpp2.com/, http ://www. ieee802.org/, and http://www.wimaxforum.org/ respectively.) Communication system 100 represents a system having an architecture in accordance with one or more of the 3GPP technologies (such as LTE), suitably modified to implement the present invention. Alternative embodiments of the present invention may be implemented in communication systems that employ other or additional technologies such as, but not limited to, those described in the OMA, WiMAX Forum, IEEE 802, and / or 3GPP2 specifications.

Communication system 100 is depicted in a very generalized manner. For example, system 100 is shown to simply include remote unit 101 , network nodes 121-124 and signaling network 131. Network nodes 121-124 are shown having interconnectivity via signaling network 131. Network node 121 is shown providing network service to remote unit 101 using wireless interface 111. The wireless interface used is in accordance with the particular access technology supported by network node 121 , such as one based on LTE. Network nodes 121 -124 may all utilize the same wireless access technology, or they may utilize different access technologies. Those skilled in the art will recognize that FIG. 1 does not depict all of the physical fixed network components that may be necessary for system 100 to operate but only those system components and logical entities particularly relevant to the description of embodiments herein.

For example, FIG. 1 does not depict that network nodes 122-124 each comprise processing units, network interfaces and transceivers. In general, components such as processing units, transceivers and network interfaces are well-known. For example, processing units are known to comprise basic components such as, but neither limited to nor necessarily requiring, microprocessors, microcontrollers, memory devices, application-specific integrated circuits (ASICs), and/or logic circuitry. Such components are typically adapted to implement algorithms and/or protocols that have been expressed using high-level design languages or descriptions, expressed using computer instructions, expressed using signaling flow diagrams, and/or expressed using logic flow diagrams. Thus, given a high-level description, an algorithm, a logic flow, a messaging / signaling flow, and/or a protocol specification, those skilled in the art are aware of the many design and development techniques available to implement a processing unit that performs the given logic. Therefore, devices 121-124 represent known devices that have been adapted, in accordance with the description herein, to implement multiple embodiments of the present invention. Furthermore, those skilled in the art will recognize that aspects of the present invention may be implemented in or across various physical components and none are necessarily limited to single platform implementations. For example, a network node may be implemented in or across one or more RAN components, such as a base transceiver station (BTS) and/or a base station controller (BSC), a Node-B and/or a radio network controller (RNC), or an HRPD AN and/or PCF, or implemented in or across one or more access network (AN) components, such as an access service network (ASN) gateway and/or ASN base station (BS), an access point (AP), a wideband base station (WBS), and/or a WLAN (wireless local area network) station. Remote unit 101 and network node 121 are shown communicating via technology-dependent, wireless interface 111. Remote units, subscriber stations (SSs) and/or user equipment (UEs), may be thought of as mobile stations (MSs), mobile subscriber stations (MSSs), mobile devices or mobile nodes (MNs). In addition, remote unit platforms are known to refer to a wide variety of consumer electronic platforms such as, but not limited to, mobile stations (MSs), access terminals (ATs), terminal equipment, mobile devices, gaming devices, personal computers, and personal digital assistants (PDAs). In particular, remote unit 101 comprises a processing unit (103) and transceiver (105). Depending on the embodiment, remote unit 101 may additionally comprise a keypad (not shown), a speaker (not shown), a microphone (not shown), and a display (not shown). Processing units, transceivers, keypads, speakers, microphones, and displays as used in remote units are all well-known in the art.

Operation of embodiments in accordance with the present invention occurs substantially as follows, first with reference to FIG. 1. As depicted in FIG. 1 , network node 121 is the current serving node for remote unit 101 , while network nodes 122-124 represent neighboring nodes to which remote unit 101 may hand off. For the sake of illustration, network node 121 is assumed to be included within a single frequency network (SFN) area associated with an MBMS service that network node 121 is transmitting. Processing unit 126 of network node 121 also transmits via transceiver 125 an indication of whether network node 121 is a boundary node of the SFN area. This indication is transmitted via a multicast control channel of wireless interface 111.

Processing unit 103 of remote unit 101 receives via transceiver 105 the MBMS content associated with the MBMS service that network node 121 is transmitting. Processing unit 103 also receives the indication of whether network node 121 is a boundary node of the SFN area and uses this indication to determine what additional information it may need to obtain. Whether network node 121 is considered a boundary node or not may depend on the embodiment of the present invention. For example, in some embodiments network node 121 would only be considered a boundary node if it is adjacent to an edge of the SFN area. In other embodiments, network node 121 would be considered a boundary node if it is within a region (e.g., some predefined region) that is adjacent to an edge of the SFN area, such as a region defined as a certain number of cells (e.g., two cells) from any edge of the SFN area.

Whatever the case, when network node 121 is indicated to be a boundary node, processing unit 103 may proceed to determine whether a neighboring network node is transmitting content for the MBMS service. In other embodiments, however, processing unit 103 may not try to determine what MBMS service a neighboring network node is transmitting but rather simply transmit an indication that remote unit 101 is receiving content associated with the MBMS service. In other words, remote unit 101 may simply report that it is listening to the MBMS service. Depending on the embodiment, remote unit 101 may transmit this indication to network node 121 and/or one or more neighboring network nodes. Such a notification by remote unit 101 could then trigger the activation of the MBMS service at one or more neighboring network nodes, if the MBMS service is not already active there. However, if network node 121 is indicated to not be a boundary node, then remote unit 101 can continue providing MBMS service content to its user and proceed with any handoff or cell reselection activity while assuming that its neighboring network nodes are also transmitting the MBMS service. Reference has been made to 3GPP LTE embodiments above.

Therefore, a summary that focuses on certain LTE embodiments appears below to provide some additional and more particular examples. They are intended to further the reader's understanding of the variety of possible embodiments rather than to limit the scope of the invention. At present, a UE in a cell belonging to an SFN area, monitors one or more neighboring cell Multicast Control Channels (MCCHs) to determine if the same MBMS service is being transmitted in the neighboring cell(s). It does this to reduce the MBMS service interruption time that may result should the neighbor cell to which it hands off not already be transmitting the MBMS service. (This service interruption time can be substantially reduced if the new cell starts transmitting the MBMS service that the UE is currently listening to before the UE moves to the new cell.)

In certain LTE embodiments of the present invention a bit ("boundary bit") is introduced in the MCCH of every cell indicating whether that cell is in a boundary region of the associated SFN area. If a cell belongs to multiple SFN areas, then the cell may broadcast one bit for every SFN area to which it belongs in the MCCH. Diagram 200 in FIG. 2 depicts an example of overlapping SFN areas and a "boundary bit" indication for each.

FIG. 3 is a logic flow diagram (300) that depicts detailed functionality performed by a UE receiving (301 ) an MBMS service from a current cell while monitoring (302) a neighbor cell, in accordance with various LTE embodiments of the present invention. During mobility, the UE may observe (302) an increased signal-to-noise ratio (SNR) from a neighboring cell. In this case, the UE will first determine (304) whether the current cell is actually part of a boundary region of the SFN area by reading the "boundary bit" of the current cell. The SFN boundary region may be defined as K cells deep; in which case, the boundary bit would be transmitted in cells K cells away from the physical SFN area boundary.

If the current cell is part of the SFN area boundary region, then the UE will have to determine whether the neighboring cell towards which it is observing an increased SNR is actually a cell outside the current SFN area. If the current cell is not part of the boundary region, the UE simply performs reselection (305) as it otherwise would. Since in this case the UE is in the interior of the SFN area, there is no need for the UE to monitor the neighboring cell's MCCH. UE battery life can thus be extended by eliminating this unnecessary monitoring.

To illustrate the potential savings, consider an SFN area of 217 cells (i.e., a hexagonal cell structure with 9 rings) with the UE initially in the center cell. The UE will perform an average of 66 cell transitions before exiting the SFN area if the UE has a transition probability of 1/6 towards each of the current cell's neighbors. If the UE reads an average of 3 neighbors' MCCHs during every cell residence time and if the average cell residence time is 30 seconds, then the UE will consume battery life by reading neighboring cell MCCHs unnecessarily at the rate of 5.8 MCCHs per minute. Furthermore, reading neighbor control channel information can be difficult due to low SNR in single frequency networks. The boundary bit avoids this issue by allowing a UE to read neighbor cell MCCH only when necessary.

If the current cell is indicated to be in the SFN area boundary region, the UE may then determine whether the neighboring cell is transmitting that service. Depending on the embodiment, the UE may acquire the neighbor cell MCCH and get this information from the neighbor cell directly (306). In an alternative embodiment, the UE may determine whether the neighboring cell is transmitting the MBMS service by obtaining the information from the current cell. For example, the UE's current cell may duplicate the neighbor cell MCCH, transmit portions of the neighbor cell MCCH, and/or transmit relevant differences between the current cell MCCH information and that of the neighbor cell. In the case (307) where the neighboring cell is transmitting the same MBMS service (either because the neighboring cell is part of another SFN area transmitting the same service or the service being transmitted in the neighboring cell as a single-cell MBMS service, e.g.), the UE may obtain the resources being allocated for that service and perform cell reselection to that neighboring cell when desired (308). By reading the neighboring cell's MCCH a priori, the interruption time can be reduced, since otherwise some amount of time would have been spent reading the MCCH after the UE performed the cell reselection. For the case (307) where the neighboring cell is not transmitting the same MBMS service, a number of varied embodiments are considered. FIGs. 4-6 are logic flow diagrams (400, 500, 600) that each depict detailed functionality to provide an example of each of the groups of embodiments that will be discussed. As depicted in diagrams 400 and 500, in the case where the neighboring cell is not transmitting the same MBMS service, the UE may perform an idle mode to active mode transition in the current cell (401 , 501 ) and inform (402, 502) the current cell about MBMS services that it is listening to but which are not available in the neighbor cell.

Subsequently, the UE may in some embodiments stay in the active mode and wait (404) for a Handover Command before it starts receiving MBMS services from the neighboring cell (405). In other embodiments, the UE may return to idle mode (504) and perform cell reselection (505) when the cell reselection criteria are met. In both cases, the neighbor cell would be informed by the UE's current cell to start transmitting the MBMS service(s) requested by the UE (403, 503). In response, the neighbor cell may then start transmitting the MBMS service(s) subject to resource availability.

As depicted in diagram 600, in the case where the neighboring cell is not transmitting the same MBMS service, the UE may not perform an idle mode to active mode transition. Instead, the UE can request that the MBMS service be activated in the neighboring without transitioning to active mode (601 , 602). Such a request may be transmitted by the UE on a reserved resource (e.g., a dedicated random access signature) which is associated with the MBMS service. (Associations between reserved resources and MBMS services may be broadcast on the MCCH channel.) The serving cell can then, based on, a number of requests from UEs, for example, decide to notify the neighboring cell (603) to turn on the MBMS service. The UE may then move to the neighboring cell (604) and continue receiving the MBMS service, assuming it is able to be activated.

In yet another embodiment, when the current cell is indicated to be in the SFN area boundary region, the UE may not then determine whether the neighboring cell is transmitting the particular MBMS service(s) that the UE is listening to. Rather, the UE may simply report which MBMS services it is listening to as a means to request the network to activate the particular MBMS service(s) that the UE may need at the neighboring cell. To do this, the UE may or may not transition to active mode and may or may not wait for a Handover Command from the current cell. The introduction of boundary bit enables the UE to prepare the target cell a priori before making a cell reselection thereby reducing the potential service interruption time. The boundary bit also allows the UE to avoid unnecessarily reading neighboring cell MCCHs and may thereby extend UE battery life. One of skill in the art will appreciate that various modifications and changes may be made to the specific embodiments described above with respect to FIGs. 1-6 without departing from the spirit and scope of the present invention. Thus, the discussion of certain embodiments in greater detail above is to be regarded as illustrative and exemplary rather than restrictive or all- encompassing, and all such modifications to the specific embodiments described above are intended to be included within the scope of the present invention.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments of the present invention. However, the benefits, advantages, solutions to problems, and any element(s) that may cause or result in such benefits, advantages, or solutions, or cause such benefits, advantages, or solutions to become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims.

As used herein and in the appended claims, the term "comprises," "comprising," or any other variation thereof is intended to refer to a non- exclusive inclusion, such that a process, method, article of manufacture, or apparatus that comprises a list of elements does not include only those elements in the list, but may include other elements not expressly listed or inherent to such process, method, article of manufacture, or apparatus. The terms a or an, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. Unless otherwise indicated herein, the use of relational terms, if any, such as first and second, and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.

The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. Terminology derived from the word "indicating" (e.g., "indicates" and "indication") is intended to encompass all the various techniques available for communicating or referencing the information or object being indicated. Some, but not all examples of techniques available for communicating or referencing the information or object being indicated include the conveyance of the information or object being indicated, the conveyance of an identifier of the information or object being indicated, the conveyance of information used to generate the information or object being indicated, the conveyance of some part or portion of the information or object being indicated, the conveyance of some derivation of the information or object being indicated, and the conveyance of some symbol representing the information or object being indicated. The terms program, computer program, and computer instructions, as used herein, are defined as a sequence of instructions designed for execution on a computer system. This sequence of instructions may include, but is not limited to, a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a shared library/dynamic load library, a source code, an object code and/or an assembly code.

What is claimed is:

Claims

1. A method for providing improved multicast and broadcast multimedia service (MBMS) to remote units in a single frequency network (SFN) area, the method comprising: transmitting, by a network node, MBMS content associated with an MBMS service, wherein the network node is included within an SFN area associated with the MBMS service; transmitting, by the network node via a multicast control channel (MCCH), an indication of whether the network node is a boundary node of the SFN area.

2. The method of claim 1 , wherein transmitting the indication of whether the network node is a boundary node of the SFN area comprises transmitting an indication that the network node is a boundary node when at least one of the network node is adjacent to an edge of the SFN area, the network node within a region that is adjacent to an edge of the SFN area, and the network node is a predefined number of cells from an edge of the SFN area is true for the network node.

3. The method of claim 1 , further comprising transmitting, by the network node to a neighboring network node, a request to begin transmitting the MBMS service.

4. The method of claim 3, further comprising receiving, by the network node from the remote unit, an indication that the MBMS service is not available from the neighboring network node, wherein transmitting to the neighboring network node the request to begin transmitting the MBMS service is performed in response to receiving the indication that the MBMS service is not available from the neighboring network node.

5. A method for providing improved multicast and broadcast multimedia service (MBMS) to remote units in a single frequency network (SFN) area, the method comprising: receiving, by a remote unit from a network node, MBMS content associated with an MBMS service, wherein the network node is included within an SFN area associated with the MBMS service; receiving, by the remote unit from the network node via a multicast control channel (MCCH), an indication of whether the network node is a boundary node of the SFN area; when the network node is indicated to be a boundary node, performing at least one of determining, by the remote unit in response to the received indication, whether a neighboring network node is transmitting content for the MBMS service and transmitting, by the remote unit in response to the received indication, an indication that the remote unit is receiving content associated with the MBMS service.

6. The method of claim 5, wherein determining in response to the received indication whether the neighboring network node is transmitting content for the MBMS service comprises at least one of monitoring an MCCH of the neighboring network node for an indication of what services are being transmitted and receiving from the network node an indication of what services are being transmitted by the neighboring network node.

7. The method of claim 5, further comprising transitioning, by the remote unit, from an idle mode to an active mode.

8. The method of claim 7, further comprising transmitting, by the remote unit, an indication to the network node that the MBMS service is not available from the neighboring network node.

9. The method of claim 7, further comprising after transitioning to the active mode, waiting to receive a handover command from the network node before handing over to the neighboring network node and receiving the MBMS service from the neighboring network node.

10. The method of claim 5, further comprising transmitting, by the remote unit without transitioning to an active mode, an indication to the network node that the MBMS service is not available from the neighboring network node.

11. The method of claim 10, transmitting the indication that the MBMS service is not available from the neighboring network node comprises transmitting the indication via a dedicated random access signature associated with the MBMS service.

12. A network node comprising: a transceiver; a network interface; a processing unit, communicatively coupled to the transceiver and the network interface, adapted to transmit, via the transceiver, multicast and broadcast multimedia service (MBMS) content associated with an

MBMS service, wherein the network node is included within a single frequency network (SFN) area associated with the MBMS service, and adapted to transmit, via the transceiver and via a multicast control channel (MCCH), an indication of whether the network node is a boundary node of the SFN area.

13. A remote unit comprising: a transceiver; a processing unit, communicatively coupled to the transceiver, adapted to receive, from a network node via the transceiver, multicast and broadcast multimedia service (MBMS) content associated with an MBMS service, wherein the network node is included within a single frequency network (SFN) area associated with the MBMS service, adapted to receive, from a network node via the transceiver and via a multicast control channel (MCCH), an indication of whether the network node is a boundary node of the SFN area, and adapted to performing at least one of determining, when the network node is indicated to be a boundary node, in response to the received indication whether a neighboring network node is transmitting content for the MBMS service and transmitting, via the transceiver in response to the received indication, an indication that the remote unit is receiving content associated with the MBMS service.