Abstract:
A method of managing multimedia broadcast multicast service (MBMS) transmission for a network in a wireless communication system is disclosed. The method comprises the steps of reserving a plurality of MBMS subframes of a first radio frame for a MBMS service; configuring a first subframe set of the reserved MBMS subframes of the first radio frame for transmissions of MBMS data; and configuring a second subframe set of the reserved MBMS subframes of the first radio frame for transmissions of non-MBMS data.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/186,895, filed on Jun. 15, 2009 and entitled “Methods for transmitting and receiving multicast and broadcast messages in wireless communications system” the contents of which are incorporated herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     A method used in a wireless communication system and related communication device are provided, and more particularly to, a method of managing multimedia broadcast multicast service (MBMS) transmission in a wireless communication system and related communication device. 
     2. Description of the Prior Art 
     A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs). 
     A multimedia broadcast multicast service (MBMS) service has been introduced in LTE specification to give the opportunity to broadcast or multicast TV, film, information such as free overnight transmission of newspaper in digital form and other media in these networks. The broadcast or multicast capability enables to reach unlimited number of users with constant network load. Further, the MBMS also enables the possibility to broadcast or multicast information simultaneously to many cellular subscribers. 
     Two important scenarios have identified for the MBMS service. One is single-cell broadcast, and the second is MBMS Single frequency network (MBSFN). MBSFN is envisaged for delivering services such as Mobile TV, using the LTE infrastructure. In MBSFN the transmission happens from a tightly time-synchronized set of eNBs, using the same resource block. A UE receiver will therefore observe multiple version of the signal with different delays due to the multi-cell transmission. Since the transmissions from the multiple cells are sufficiently tightly synchronized for each to arrive at the UE, this makes the MBSFN transmission appear to the UE as a transmission from a single large cell, and the UE receiver may treat the multi-cell transmission in the same way as multi-path components of a single cell transmission without incurring any additional complexity. 
     The MBSFN transmission takes place on dedicated subframes referred to as MBSFN subframes, which would be used for other purpose than MBMS service. For example, the MBSFN subframes can be used for data transmission between relays and the eNB or data transmission for position measurement for the UE. Namely, the MBSFN subframes may be used for non-MBMS data transmission when the MBSFN subframes are not allocated for MBMS data. 
     The deployment of the MBMS in the LTE system has been defined based on various configurations of geographical cell distribution, carrier frequency allocation (known as “frequency layers”) and transmission mode. A geographical area where all eNBs can be synchronized and can perform MBSFN transmission is called an MBSFN synchronization area. Within the MBSFN synchronization area, a group of cells that are coordinated for an MBSFN transmission is called an MBSFN area. Strictly speaking, one cell belongs to only one MBSFN area. Based on such “one-to-one” mapping, the UE served by that cell only read MBSFN subframe configuration associated with that MBSFN area. However, when the multiple MBSFN areas overlap, one cell may serve multiple MBSFN areas simultaneously. The UE in the overlapping area only reads one MBSFN subframe configuration (e.g. the first MBSFN subframe configuration received) in a configuration list. This causes the other MBMS service ignored. 
     Moreover, mappings between the MBSFN subframe configurations and multicast channel (MCH), multicast control channel (MCCH) and multicast traffic channel (MTCH) have not been described explicitly in the current LTE specification. The MCTH is a point-to-multipoint downlink channel for transmitting data traffic from the network to the UE. The MCCH is a point-to-multipoint downlink channel used for transmitting MBMS control information form the network to the UE. Both the MCCH and the MTCH are mapped to the MCH transport channel in the MBSFN operation. The MCH is used to transport user data or control message for the MBSFN operation. 
     In short, allocation/configuration of the MBSFN subframe and corresponding channels, e.g. MCH/MCCH/MTCH, need appropriate handling to improve MBMS resource utilization. 
     SUMMARY OF THE INVENTION 
     A method of managing multimedia broadcast multicast service (MBMS) transmission in a wireless communication system is disclosed to teach how to use reserved MBMS subframes for MBMS data transmission and non-MBMS data transmission. 
     A method of managing multimedia broadcast multicast service (MBMS) transmission for a network in a wireless communication system is disclosed. The method comprises the steps of reserving a plurality of MBMS subframes of a first radio frame for a MBMS service; configuring a first subframe set of the reserved MBMS subframes of the first radio frame for transmissions of MBMS data; and configuring a second subframe set of the reserved MBMS subframes of the first radio frame for transmissions of non-MBMS data. 
     A communication device for managing multimedia broadcast multicast service (MBMS) transmission in a wireless communication system is disclosed. The communication device comprises a means for reserving a plurality of MBMS subframes of a first radio frame for a MBMS service, a means for configuring a first subframe set of the reserved MBMS subframes of the first radio frame for transmissions of MBMS data and a means for configuring a second subframe set of the reserved MBMS subframes of the first radio frame for transmissions of non-MBMS data. 
     A method of managing multimedia broadcast multicast services (MBMS) reception for a mobile device in a service overlapping area is disclosed. The service overlapping area comprises a plurality MBMS services. The method comprises the steps of receiving a first configuration associated with the first MBMS service and a second configuration associated with a second MBMS service; and reading the first configuration associated with the first MBMS service and the second configuration associated with a second MBMS service. 
     A communication device for managing multimedia broadcast multicast services (MBMS) reception in a service overlapping area is disclosed. The service overlapping area comprises a plurality of MBMS services. The communication device comprises a means for receiving a first configuration associated with a first MBMS service and a second configuration associated with a second MBMS service; and a means for reading the first configuration associated with the first MBMS service and the second configuration associated with the second MBMS service. 
     These and other objectives of the present disclosure will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the example that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic diagram of a wireless communication system according to an example. 
         FIG. 2  illustrates a schematic diagram of a communication device according to an example. 
         FIG. 3  is a flow chat of a process for a network according to an example. 
         FIGS. 4-6  illustrate mapping between the configuration(s) and the MCH(s)/MTCH(s)/MCCH(s) according to an example. 
         FIG. 7  is a flowchart of a process for a mobile device according to an example. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 , which illustrates a schematic diagram of a wireless communication system  10  according to an example. Briefly, the wireless communication system  10  supports multimedia broadcast multicast service (MBMS) services and is composed of a network and a plurality of mobile devices. In  FIG. 1 , the network and the mobile devices are simply utilized for illustrating the structure of the wireless communication system  10 . The wireless communication system  10  can be a UMTS (Universal Mobile Telecommunications System) or an LTE (long-term evolution) system. In the LTE system, the network is referred as a EUTRAN (evolved-UTRAN) comprising a plurality of eNBs, whereas the mobile devices are referred as user equipments (UEs). Each eNB may provide communication coverage for a particular area (called “a cell”). The UEs can be devices such as mobile phones, computer systems, etc. A geographical area where all eNBs can be synchronized and can perform MBMS Single frequency network (MBSFN) transmission is called an MBSFN synchronization area. Within the MBSFN synchronization area, a group of cells that are coordinated for an MBSFN transmission is called an MBSFN area. As shown in  FIG. 1 , within the (MBSFN) synchronization area, several MBSFN areas overlap geographically and form the overlapping MBSF area. The several MBMS services may be broadcasted in the overlapping MBSFN area. The overlapping MBSFN area would require the allocation of separate resources and signaling to support the different MBMS services transmitted simultaneously in that area. The UE served by a set of cells within the overlapping MBSF area may need to receive different MBMS content from the different MBMS service. 
     Please refer to  FIG. 2 , which illustrates a schematic diagram of a communication device  20  according to an example. The communication device  20  may be the mobile devices or the network shown in  FIG. 1  and may include a processing means  200  such as a microprocessor or ASIC, a memory unit  210  and a communication interfacing unit  220 . The memory unit  210  may be any data storage device that can store program code  214  for access by the processing means  200 . Examples of the memory unit  210  include but are not limited to a subscriber identity module (SIM), read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, hard disks, and optical data storage devices. The communication interfacing unit  220  may be preferably a radio transceiver and accordingly exchanges wireless signals according to processing results of the processing means  200 . 
     Please refer to  FIG. 3 , which is a flow chat of a process  30  according to an example. The process  30  is used for managing MBMS transmission for a network in a wireless communication system. The process  30  can be compiled into the program code  214  and include the following steps: 
     Step  300 : Start. 
     Step  302 : Reserve multiple MBMS subframes of a radio frame Frm 1  for a MBMS service. 
     Step  304 : Configure a subframe set S 1  of the reserved MBMS subframes of the radio frame Frm 1  for MBMS data transmission. 
     Step  306 : Configure a subframe set S 2  of the reserved MBMS subframes of the radio frame Frm 1  for non-MBMS data transmission. 
     Step  308 : Transmit a configuration Config 1  associated with subframe allocation of the subframe set  51  and a configuration Config 2  associated with subframe allocation of the subframe set S 2  to a UE. 
     Step  308 : End. 
     According to the process  30 , the network may reserve several MBMS subframes of the radio frame Frm 1 . Then, the network may configure the subframe set S 1  of the reserved MBMS subframes for the MBMS data transmission and the subframe set S 2  of the reserved MBMS subframes for the non-MBMS data transmission. In the next step, the network may transmit the configuration Config 1  and the configuration Config 2  to the UE. The Config 1  may define the subframe allocation of the subframe set S 1  and the Config 2  may define the subframe allocation of the subframe set S 2 . In other words, in one radio frame, the network may use the different configurations including the different subframe sets to transmit the MBMS data and the non-MBMS data. In some examples, after the UE receives the configurations (e.g. Config 1  and Config 2 ) sent by the network, based on the received configurations, the UE may exactly know which of the reserved MBMS subframes are used for the MBMS data transmission and which of the reserved MBMS subframes are used for non-MBMS data transmission. 
     In some example, the MBMS subframes may be referred as to a MBMS Single frequency network (MBSFN) subframes, which is used for sending broadcast and multicast information. In some examples, the wireless communication system may include a relay. The relay is a station that receives a transmission of data and/or other information from an upstream station (e.g. an eNB or a UE) and sends a transmission of the data and/or other information to a downstream station (e.g. a UE or an eNB). Thus, the non-MBMS data may be referred as to data transmitted between the eNB and the relay. In another example, the non-MBMS data may refer to the data used for assisting the UE with position measurement. 
     As known above, the subframe set S 1  and the subframe set S 2  may be defined in the Config 1  and Config 2 , respectively (or sometimes called MBSFN subframe configuration). The Config 1  explicitly indicates which of the reserved subframes are allocated to the subframe set S 1 . The Config 2  explicitly indicates which of the reserved subframes are allocated to the subframe set S 2 . For example, the radio frame Frm 1  includes ten MBSFN subframes subfrm 1 , subfrm 2  . . . subfrm 10 . And, a total of five subframes (subfrm 1 , subfrm 4 , subfrm 5 , subfrm 7 , subfrm  10 ) are reserved for the MBMS service. The subframe set S 1  is defined in the Config 1  by enumerating S 1 ={sunform 1 , subfrm 4 , subfrm 5 } and used for the MBMS data transmission. The subframe set S 2  is defined in the Config 2  by enumerating S 2 ={subfrm 7 , subfrm 10 } and used for non-MBMS data transmission. 
     It is more likely for the network to have more than two configurations. The different configurations may define the different allocation ways for the reserved MBMS subframes. In addition, the different configurations may be used for the different data transmission or the same data transmission. Those configurations may be sent in system information and read by the UE. The system information is structured by means of system information blocks (SIBs), each of which contains a set of functionality-related parameters. Besides the Config 1  and Config 2 , the network may transmit two other configurations (Config 3  and Config 4 ) to the UE, which may be included in the system information. The Config 1  and the Config 3  may be used for the MBMS data transmission, and individually define MBMS subframe allocations. The Config 2  is used for the data transmitted between the aforementioned relay and the eNB. The Config 4  is used for the data for UE position measurement. When the UE receives the system information, the UE only needs to read the configurations of interest. For example, the UE may only read the Config 1  and Config 3  for the MBMS data transmission and ignore the others. In some examples, the system information may not inform the UE of the purposes of the configurations. That is, the UE may not know which configurations are used for the MBMS data transmission and which configurations are used for the non-MBMS data transmission. In this situation, the UE may read and decode all possible configurations. 
     In some examples, MBMS subframe overlapping may be allowed among the different configurations to make the usage of the reserved MBMS subframes more flexible. Namely, one or more reserved MBMS subframes may be shared in one or more configurations. Take the aforementioned Config 4  for an example, likewise, the MBMS subframes (subfrm 1 , subfrm 4 , subfrm 5 , subfrm 7 , subfrm  10 ) are reserved for the MBMS service, the Config 4  may define a subframe set S 4  containing three subframes (subfrm 1 , subfrm 7 , subfrm 10 ) for the non-MBMS data transmission. As defined above, the Config 1  have three subframes (sunform 1 , subfrm 4 , subfrm 5 ) used for the MBMS data transmission. Apparently, the subframe subfrm 1  may be used both for the MBMS data transmission in the Config 1  and for the non-MBMS data transmission in the Config 4 . In this situation, the network may use the subframe subfrm 1  of the radio frame Frm 1  to transmit the MBMS data and then, in a radio frame Frm 2  following the radio frame Frm 1 , use corresponding subframe subfrm 1  to transmit the non-MBMS data, and so on. Thus, the MBMS resources have flexibility and can be fully utilized. This, undoubtedly, enhances capacity and efficiency of data transmission. 
     In some example, the aforementioned system information not only includes configurations, but also includes mapping between the configurations and UE channels, such as multicast channels (MCHs), multicast traffic channels (MTCHs) and multicast control channels (MCCHs). The mapping between the configuration(s) and the MCH(s)/MTCH(s)/MCCH(s) may include a “one-to-one” mapping, “many-to-one” mapping and “one-to-many” mapping. For “one-to-one” mapping, one configuration may be mapped to one MCH/MCCH/MTCH. For “many-to-one” mapping, several configurations may be mapped to one MCH/MCCH/MTCH. For “one-to-many” mapping, one configuration may be mapped to several MCHs/MCCHs/MTCHs. Please refer to  FIGS. 4-6 , which illustrate mappings between the configuration(s) and the MCH(s)/MTCH(s)/MCCH(s) according to an example. In  FIG. 4 , a Config (A) and Config(B) are mapped to a MCH(A)/MTCH(A)/MCCH(A) and MCH(B)/MTCH(B)/MCCH(B), respectively. Namely, the different MCHs/MTCHs/MCCHs may use the different configurations for the MBMS data multiplexing/demultiplexing. In  FIG. 5 , the Config(A) is mapped to MCH (A)/MTCH (A)/MCCH (A) and MCH (B)/MTCH (B)/MCCH (B), both. Namely, the different MCHs/MTCHs/MCCHs may share the same configuration for the MBMS data multiplexing/demultiplexing. In  FIG. 6 , the Config(A) and Config(B) are mapped to MCH(A)/MTCH(A)/MCCH(A). Namely, one MCH/MCCH/MTCH use the different configurations for the MBMS data multiplexing/demultiplexing. In another example, the system information broadcast by the network may further include a modulation and coding scheme (MCS) associated with the MCH and MBMS subframe allocation for the MCH. The UE may read the system information and learn which MBMS subframes are used for the MCH. 
     Please refer to  FIG. 7 , which is a flowchart of a process  70  according to an example. The process  70  is used for managing MBMS reception for a UE in a service overlapping area of a wireless communication system (e.g. the mobile device  14  in  FIG. 1 ). The service overlapping area may be referred as to an overlapping MBSFN area. The UE may be implemented by the communication device  20 . The process  70  can be compiled into the program code  214  and include the following steps: 
     Step  700 : Start. 
     Step  702 : Receive a configuration Config( 1 ) associated with a MBMS service MS( 1 ) and a configuration Config( 2 ) associated with a MBMS service MS( 2 ). 
     Step  704 : Read the configuration Config ( 1 ) associated with the MBMS service MS( 1 ) and the configuration Config( 2 ) associated with the MBMS service MS( 2 ). 
     Step  706 : End. 
     According to the process  70 , when the MBMS service MS( 1 ) and the MBMS service MS( 2 ) are broadcasted to the UE, the UE may receive and read the Config( 1 ) and the Config( 2 ), both. The Config( 1 ) may include a MBSFN subframe configuration related to the MBMS service MS( 1 ) and is used for transmitting the MBMS data of the MBMS service MS( 1 ). The Config( 2 ) may include a MBSFN subframe configuration related to the MBMS service MS( 2 ) and is used for transmitting the MBMS data of the MBMS service MS( 2 ). 
     In accordance with the process  70 , the UE may receive and read the different configurations associated to support the different MBMS services. For the different MBMS services, each of configurations may have its own subframe allocation and use the different MBMS subframes. An example is demonstrated below. The Config( 1 ) may define MBMS subframes {subfrm 4 , subfrm 5 } for the MBMS data transmission for the MBMS service MS( 1 ). The Config( 2 ) may define MBMS subframes {subfrm 7 , subfrm 10 } for the MBMS data transmission for the MBMS service MS( 2 ). Thus, the UE may be able to read both Config( 1 ) and Config( 2 ), supporting two MBMS services. The UE in the overlapping MBSFN area may read one or more configurations associated with the different MBMS services and support the MBMS data transmission for the different MBMS services. In some examples, the aforementioned MBMS subframe overlapping may be allowed among the configurations associated with the different MBMS services. 
     Note that the process  70  is not limited to two sets of configuration and two types of MBMS services and aims to provide the concept of utilization of multiple sets of configuration associated with overlapped MBMS services. 
     Please note that the abovementioned steps including suggested steps can be realized by means that could be hardware, firmware known as a combination of a hardware device and computer instructions and data that reside as read-only software on the hardware device, or an electronic system. Examples of hardware can include analog, digital and mixed circuits known as microcircuit, microchip, or silicon chip. Examples of the electronic system can include system on chip (SOC), system in package (Sip), computer on module (COM), and the communication device  20  in which the processor  200  processes the program code  214  related to the abovementioned processes and the processed results can handle MBMS service transmission and reception. 
     To sum up, the network reserves the MBMS subframes for the MBMS service and uses the different MBMS subframe configurations to transmit the MBSM data transmission and the non-MBMS data transmission. The MBMS configurations explicitly defining which MBMS subframes should be used for the MBMS data transmission or which MBMS subframes should be used for the non-MBMS data transmission is provided. Then, the network sends the MBMS subframe configurations to the UE. The UE may read any MBMS configuration of interest and decode data on the MBMS subframes defined in the MBMS configuration. In addition, according to the examples, the MBSM subframe overlapping is allowed. Thus, the network can use the same MBMS subframes in the different configurations. The network also explicitly defines mapping between the configurations and MCHs/MTCHs/MCCHs. Furthermore, when the several MBSFN areas overlap and several MBMS services are broadcasted in the overlapping MBSFN area, the UE in the overlapping MBSFN area can read one or more configurations associated with the different MBMS services. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the disclosure. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.