Abstract:
An apparatus and a method for processing media data so that an MBS is supported in a BWA communication system. A traffic processing method supports an MBS in a broadband wireless access communication system having a number of base stations and at least one contents server for transmitting various media traffics to the base stations. The method includes reserving a resource for MBS burst assignment with regard to the base stations; requesting the contents server to provide a traffic to be transmitted to the base stations when the resource has been successfully reserved; shaping a media traffic transmitted by the contents server; and transmitting the media traffic to the base stations.

Description:
PRIORITY  
       [0001]     This application claims priority to an application filed with the Korean Intellectual Property Office on Oct. 19, 2005 and assigned Serial No. 2005-98873 and an application entitled the same filed with the Korean Intellectual Property Office on Dec. 16, 2005 and assigned Serial No. 2005-124823, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a BWA (Broadband Wireless Access) system, and more particularly to an apparatus and a method for providing an MS (Mobile Station) with an MBS (Multicast/Broadcast Service) in a BWA system.  
         [0004]     2. Description of the Related Art  
         [0005]     As generally known in the art, communication systems have been primarily developed for voice communication services, but they are also evolving to provide data services and various multimedia services. However, conventional communication systems, which are mainly directed to providing voice communication services, still have a narrow data transmission bandwidth and require high subscription fee. For these reasons, they cannot satisfy diversified user demands. Furthermore, in line with rapid development in the communication industry and ever-increasing demands on Internet services, it is important to provide communication systems capable of providing Internet services efficiently. As a result of these trends, BWA systems having a bandwidth large enough to both satisfy the increasing user demands and provide efficient Internet services have been proposed.  
         [0006]     In addition to providing voice communication services, BWA systems also aim at supporting various data services both at low and high speeds and multimedia application services (e.g. high-quality moving pictures) in combination. BWA systems are based on wireless media using a broadband of 2 GHz, 5 GHz, 26 GHz, or 60 GHz and are able to access a PSTN (Public Switched Telephone Network), PSDN (Public Switched Data Network), Internet network, IMT-2000 (International Mobile Telecommunications-2000) network, and ATM (Asynchronous Transfer Mode) network in a mobile or stationary environment. In other words, BWA systems are wireless communication systems capable of supporting a channel transmission rate of at least 2 Mbps. BWA systems may be classified into broadband wireless local loops, broadband mobile access networks, and high-speed wireless LANs (Local Area Networks) according to the terminal&#39;s mobility (stationary or mobile), communication environment (indoor or outdoor), and channel transmission rate.  
         [0007]     The standardization of wireless access schemes of BWA systems is being conducted by IEEE (Institute of Electrical and Electronics Engineers), which is one of the international standardization organizations, particularly by IEEE 802.16 standardization group. Currently, IEEE 802.16d and IEEE 802.16e standards are being established as so to provide stationary or mobile stations with wireless broadband Internet services. Particularly, extensive studies are being made to enable BWA systems, including wireless LAN communication systems and wireless MAN (Metropolitan Area Network) communication systems, to provide high-speed services while guaranteeing mobility and various QoS (Quality of Service). Representative examples thereof include IEEE 802.16d communication systems and IEEE 802.16e communication systems (hereinafter, referred to as IEEE 802.16d/e communication systems).  
         [0008]     The IEEE 802.16d/e communication systems are obtained by applying an OFDM (Orthogonal Frequency Division Multiplexing) scheme and an OFDMA (Orthogonal Frequency Division Multiple Access) scheme to the wireless MAN communication systems so that their physical channels support broadband transmission networks. The IEEE 802.16d communication systems do not consider the mobility of SSs (Subscriber Stations), i.e. they assume that the SSs are currently stationary, but consider a single cell structure. In contrast, the IEEE 802.16e communication systems consider the mobility of the SSs. In this regard, SSs having mobility will hereinafter be referred to as MSs (Mobile Stations).  
         [0009]     Compared with conventional communication systems for voice communication services, the IEEE 802.16d/e communication systems have a larger data transmission bandwidth. Therefore, they can transmit more data for a limited period of time and share all user channels for efficient channel utilization. Since the QoS is guaranteed, users are provided with various services of different qualities based on the characteristics of services. The IEEE 802.16e communication systems enable all users connected to a BS (Base Station) to share and use common channels, and the base station assigns usable channel sections to respective users for every upward and downward frame. Therefore, the base station must provide respective users with upward and downward access information so that they can divide and use channels for each frame.  
         [0010]     To this end, the IEEE 802.16e communication systems divide channels into upward and downward channels and define information regarding each channel in terms of TLV (Type, Length, Value). The TLV is periodically transmitted to all users while being included in a DCD (Downlink Channel Descriptor) message and a UCD (Upward Channel Descriptor) message, so that corresponding MSs are informed of characteristics of the channels.  
         [0011]     Meanwhile, the 802.16 communication systems can provide an MBS (Multicast/Broadcast Service) in one of two modes, i.e. a single-BS access mode and a multi-BS access mode, according to how MSs access the service.  
         [0012]     In the single-BS access mode, each MS is provided with an MBS from a BS (e.g. serving BS), to which the MS has subscribed. In the multi-BS access mode, each MS is simultaneously provided with an MBS from at least two BSs, for example, both the serving BS and an adjacent BS, in a region where cells of the BSs overlap each other. The network construction of a system for providing an MBS will now be described briefly with reference to  FIGS. 1 and 2 .  
         [0013]      FIGS. 1 and 2  show the construction of a system for providing an MBS in an conventional BWA system. Particularly,  FIG. 1  shows the network construction based on a single-BS access mode, and  FIG. 2  shows that based on a multi-BS access mode. [PLEASE LABEL “PRIOR ART”] 
         [0014]     Referring to  FIGS. 1 and 2 , the network construction for providing an MBS in a conventional BWA system is based on one of two modes, i.e. a single-BS access mode ( FIG. 1 ) and a multi-BS access mode ( FIG. 2 ), according to how MSs access the service, as mentioned above.  
         [0015]     Particularly, according to the network construction shown in  FIG. 1 , MSs, e.g. first and second MSs  101  and  103 , are provided with an MBS from a single BS, e.g. BS  110 , to which they belong, in a single-BS mode. According to the network construction shown in  FIG. 2 , an MS, e.g. a second MS  203 , is simultaneously provided with an MBS from two BSs, e.g. a first BS  210 , to which it belongs, and an adjacent BS  230 , i.e. a second BS  230 , respectively, in a multi-BS access mode.  FIG. 2  also shows a first MB  201  receiving an MBS from a single BS, i.e. the first BS  210 , to which it belongs, and a third MB  205  receiving an MBS from a single BS, i.e. the second BS  230 , to which it belongs, in a single-BS access mode.  
         [0016]     As such, in the multi-BS access mode, the MBs do not need to subscribe to all BSs, e.g. the first and second BSs  210  and  230 , which provide an MBS, in contrast to the single-BS access mode.  
         [0017]     In particular, when an MS actually needs a service, it creates a connection for MBS between a corresponding BS and the MS through a service assignment procedure, such as DSA (Dynamic Service Assignment). In this case, the MS receives MBS contents identifier TLV encoding information so as to obtain MBS connection information.  
         [0018]     Based on the MBS contents identifier TLV encoding information, the MS can identify the same multicast/broadcast service zone (hereinafter, referred to as MBS_ZONE) with reference to different CIDs (Connection IDs) or different SAs (Security Associations).  
         [0019]     Particularly, the MBS_ZONE confirmed by CIDs and SAs refers to a zone having an effective MBS flow. Therefore, the BS broadcasts MBS_ZONE information to the MS via a DCD message, for example. In this regard, it can be said that the MBS_ZONE refers to a group of BSs using the same CID and SA so as to transmit contents.  
         [0020]     Meanwhile, in order to provide an MS with an MBS in the multi-BS access mode, it is necessary to equalize the synchronization of information regarding media transmitted by a contents server in the MBS_ZONE, as well as the position of bursts assigned to frames transmitted by BSs. Generally, the fact that the characteristics of media transmitted by the contents server, e.g. characteristics of traffic, are very diversified makes it difficult to properly assign bursts to a number of BSs with regard to each traffic.  
         [0021]     However, neither an apparatus nor a method for solving the above-mentioned problems occurring in the prior art has been proposed in the art. Therefore, it is an opportune time to provide a scheme for equalizing the synchronization of media information and the position of bursts so that BSs can efficiently provide MBs with an MBS in a BWA system, as well as a scheme for assigning bursts in accordance with various traffic characteristics.  
       SUMMARY OF THE INVENTION  
       [0022]     Accordingly, the present invention solves the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide an apparatus and a method for processing media traffic so that MSs are efficiently provided with an MBS in a BWA system.  
         [0023]     Another object of the present invention is to provide an apparatus and a method for providing MBs with an MBS based on a multi-BS access mode in a BWA system.  
         [0024]     Another object of the present invention is to provide an apparatus and a method for transmitting pieces of media information to a number of BSs within an MBS_ZONE in a BWA system after equalizing the synchronization of the information.  
         [0025]     Another object of the present invention is to provide an apparatus and a method for assigning bursts in accordance with the characteristics of a number of media in a BWA system.  
         [0026]     In order to accomplish this object, there is provided a traffic processing method for supporting an MBS (Multicast/Broadcast Service) in a broadband wireless access communication system having a number of base stations and at least one contents server for transmitting various media traffics to the base stations, the method including reserving a resource for MBS burst assignment with regard to the base stations; requesting the contents server to provide a traffic to be transmitted to the base stations when the resource has been successfully reserved; shaping a media traffic transmitted by the contents server; and transmitting the media traffic to the base stations.  
         [0027]     In accordance with another aspect of the present invention, there is provided a method for supporting an MBS in a broadband wireless access communication system having a mobile station, a contents server for providing various types of media information, a number of base stations, and a controller for transmitting the media information to the base stations, the method including reserving a resource for MBS burst assignment with regard to all base stations positioned in an identical MBS zone by the controller; transmitting information regarding possibility of assignment to the controller in response to a request for MBS burst assignment by the base stations positioned in the identical MBS zone, the information having been designated by a flag; requesting the contents server to provide media to be transmitted to the base stations by the controller when MBS burst assignment is possible; receiving a media stream from the contents server in response to a request of the media, shaping the media stream, and transmitting the media stream to the base stations in the identical MBS zone; transmitting the media stream to the mobile station by the base stations, the media stream having been shaped; and receiving the media stream transmitted to the base stations in the identical MBS zone, combining each received media stream, and providing a user with the media stream.  
         [0028]     In accordance with another aspect of the present invention, there is provided a traffic processing apparatus for supporting an MBS in a broadband wireless access communication system having at least one contents server for transmitting various media traffics, the apparatus including an MBS controller for reserving a resource for MBS burst assignment, requesting the contents server to provide a traffic to be transmitted, shaping the traffic provided by the contents server, and providing the traffic.  
         [0029]     In accordance with another aspect of the present invention, there is provided a system for supporting an MBS in a broadband wireless access communication system having a number of base stations and at least one contents server for transmitting various media streams to the base stations, the system including an MBS controller for reserving a resource for MBS burst assignment with regard to the base stations, requesting the contents server to provide media to be transmitted to the base stations, receiving a corresponding media stream, converting the media stream into an MBS media stream through shaping processing, and transmitting the MBS media stream to the base stations; a number of base stations for providing burst information requested by the MBS controller, notifying possibility of resource assignment for MBS burst assignment in response to a request of the MBS controller by means of a flag setup, and transmitting the MBS media stream to a mobile station; and a mobile station for receiving MBS media data from the base stations, combining the MBS media data, and providing a user with the MBS media data.  
         [0030]     In accordance with another aspect of the present invention, there is provided a traffic processing apparatus for supporting an MBS in a broadband wireless access communication system having at least one contents server for transmitting various media traffics, the apparatus including an MBS controller for reserving a resource for MBS burst assignment, requesting the contents server to provide a traffic to be transmitted, shaping and multiplexing the traffic provided by the contents server, providing the traffic, and creating a medium access control packet data unit. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]     The above and other objects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0032]      FIG. 1  shows the network construction of a system for providing an MBS in a conventional BWA system to prior art;  
         [0033]      FIG. 2  shows the network construction of a system for providing an MBS in a conventional BWA system to prior art;  
         [0034]      FIG. 3  shows the network construction of a system for providing an MBS in a BWA system according to the present invention;  
         [0035]      FIG. 4  shows steps for controlling a BS which provides an MBS in a BWA system according to the present invention;  
         [0036]      FIG. 5  shows steps for processing traffic in a BWA system according to the present invention; and  
         [0037]      FIG. 6  is a flowchart showing a traffic processing method by an MBS controller according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0038]     Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, detailed description of known functions and configurations incorporated herein is omitted to avoid making the subject matter of the present invention unclear.  
         [0039]     The present invention is directed to an apparatus and a method for providing MSs with an MBS by BSs in a BWA system. Particularly, the present invention provides an apparatus and a method for transmitting media information from a number of contents servers to a number of BSs within an MBS_ZONE in a BWA system after equalizing the synchronization of the information. To this end, the present invention provides an MBS controller for equalizing the synchronization and a method for processing the traffic of the MBS controller.  
         [0040]     In this regard, the present invention defines the function of an MBS controller for providing an MBS in a BWA system so that, in order to provide an efficient service, the traffic of a number of contents servers is processed through the functions of traffic shaping and multiplexing.  
         [0041]     According to the present invention, an MBS controller for controlling BSs in an MBS_ZONE controls a traffic pattern, which is to be transmitted, in a uniform manner through traffic multiplexing and shaping. In addition, the MBS controller transmits a reservation message for burst assignment to a number of BSs so as to equalize the synchronization of media information.  
         [0042]     Although it will be assumed in the following description that the present invention is applied to a BWA system, particularly an IEEE 802.16 system, the present invention is not limited to that and is applicable to any type of communication system for providing an MBS. Preferred embodiments of the present invention for providing an MBS will now be described with reference to the accompanying drawings.  
         [0043]      FIG. 3  briefly shows the network construction of a system for providing an MBS in a BWA system according to the present invention.  
         [0044]     As shown in  FIG. 3 , a system for providing an MBS according to the present invention includes an MS  310 , a number of BSs, e.g. first and second BSs  320  and  330 , a backhaul  340 , an MBS controller  350 , and a number of contents servers  360 .  
         [0045]     Referring to  FIG. 3 , first and second BSs  320  and  330  belong to the same MBS_ZONE. MBS controller  350  controls first and second BSs  320  and  330  via backhaul  340 . As used herein, backhaul  340  generally refers to a network through which data can be transmitted to a distributed location, or simply a backbone network.  
         [0046]     Contents servers  360  provide various types of media information, which is transmitted to a BS, e.g. the first or second BS  320  or  330 , via the MBS controller  350 .  
         [0047]     MS  310  is simultaneously provided with an MBS from the BSs, particularly the first and second BSs  320  and  330 , in a multi-BS access mode.  
         [0048]     A method for providing an MBS according to the present invention, which is based on the above-mentioned construction, will now be described.  
         [0049]     MS  310  simultaneously receives a frame from the first and second BSs  320  and  330 . According to the present invention, MS  310  can acquire a gain resulting from RF (Radio Frequency) combining. To this end, the first and second BSs  320  and  330  must perform synchronization for the MBS in advance.  
         [0050]     Parameters used for the synchronization are given in Table 1 below.  
                   TABLE 1                       Static Parameters   Dynamic Parameters                   Frequency assignment information   Burst assignment information       (Frequency band)   Frame information       Time information   Symbol       Sub-channelizing information   Sub-channel information       Permutation information                  
 
         [0051]     As given in Table 1, parameters used for synchronization may be classified into static and dynamic parameters. The static parameters include frequency assignment information, time information, sub-channelizing information, and permutation information. The dynamic parameters include burst assignment information, frame information, symbol, and sub-channel information.  
         [0052]     In order to equalize the synchronization between BSs, e.g. the first and second BSs  320  and  330  shown in  FIG. 3 , the present invention implements the information as given in Table 1. Alternatively, the system includes an MBS controller  350  for controlling respective BSs  320  and  330 .  
         [0053]     According to the present invention, the MBS controller  350  performs a number of functions so as to transmit various types of media information from contents servers  360  to respective BSs within the MBS_ZONE, e.g. first and second BSs  320  and  330 . Particularly, MBS controller  350  collects information regarding media transmitted by contents servers  360 , collects information regarding bursts of the BSs, processes the traffic, and reserves the assignment of MBS bursts of the BSs. Particularly, MBS controller  350  controls schedulers of the BSs so that the burst assignment information is synchronized. To this end, MBS controller  350  uses an MBS burst reservation method.  
         [0054]     Detailed operations for providing an MBS according to the present invention will now be described. A procedure for providing MSs with a media stream via multicast by BSs will now be described with reference to  FIG. 4 .  
         [0055]      FIG. 4  shows the steps for controlling BSs, which provide an MBS according to the present invention. Particularly,  FIG. 4  shows the flow of signals needed by an MBS controller to control schedulers of respective BSs within an MBS_ZONE according to the present invention.  
         [0056]     Referring to  FIG. 4 , an MBS controller  430  transmits a media information request message to a contents server  450  (step  401 ) and receives a media information response message from the contents server  450  in response to the request (step  403 ). After receiving the media information response message from contents server  450 , MBS controller  430  transmits an admission request message for requesting burst information to BSs  410  within the MBS_ZONE when it needs to transmit media, which are provided by contents server  450 , to the BSs  410  (step  405 ). MBS controller  430  receives an admission response message from BSs  410  in response to the burst information request (step  409 ).  
         [0057]     After receiving the admission response message from BSs  410 , MBS controller  430  determines regions for actual MBS burst assignment by using the information received from BSs  410  within the MBS_ZONE. MBS controller  430  then transmits an MBS burst reservation request message to BSs  410 . In response to the MBS burst reservation request message, BSs  410  transmit an MBS burst reservation response message to MBS controller  430  when reservation of MBS bursts is possible (step  411 ).  
         [0058]     After successfully making reservations regarding all BSs ( 410 ) within the MBS_ZONE, MBS controller  430  transmits a media request message to contents server  450  in order to transmit media to BSs  410  (step  413 ). Contents server  450  transmits a media response message in response to the media request of MBS controller  430  (step  415 ). Contents server  450  transmits requested media to MBS controller  430  (step  417 ).  
         [0059]     After receiving media from contents server  450 , MBS controller  430  subjects the received media to traffic multiplexing and shaping and transmits MBS media to the BSs (step  419 ). The step for traffic multiplexing and shaping will be described later in more detail.  
         [0060]     The procedure for transmitting signals among the BSs, the MBS controller, and the contents server so that the BSs can transmit media to the MS will now be described in more detail.  
         [0061]     Referring to  FIG. 4 , MBS controller  430  according to the present invention manages the list of contents, which contents server  450  can provide, and information regarding the traffic characteristics of the contents by using a media information request message and a media information response message (steps  401  and  403 ). When MBS controller  430  needs to transmit streaming media to all BSs within the MBS_ZONE, e.g. BSs  410 , it must check in advance if BSs  410  have regions for MBS burst assignment.  
         [0062]     To this end, MBS controller  430  transmits an admission request message to BSs  410  so as to request information regarding bursts available to BSs  410  (step  405 ). In response to the admission request message, BSs  410  transmits MBS burst information to MBS controller  430  via an admission response message (step  407 ).  
         [0063]     MBS controller  430  determines regions for actual MBS burst assignment by using information received from the BSs within the MBS_ZONE, e.g. BSs  410 , and transmits information regarding the determination to BSs  410  via an MBS burst reservation request message (step  409 ). The information regarding the determination of assignment regions, which is included in the MBS burst reservation request message and transmitted to BSs  410  so as to reserve MBS bursts, includes a start frame, a frame period, a frame duration, a start symbol, an end symbol, a start sub-channel, and an end sub-channel.  
         [0064]     In response to the received MBS burst reservation request message, BSs  410  transmit an MBS burst reservation response message to MBS controller  430  (step  411 ). BSs  410  add two flags: (1) a “success” flag to the MBS burst reservation response message if reservation regarding MBS bursts requested by MBS controller  430  is possible, and (2) a “failure” flag if the reservation has failed. Then, the MBS burst reservation response message is transmitted to MBS controller  430 .  
         [0065]     Particularly, when the reservation regarding MBS bursts has failed, MBS controller  430  newly determines MBS burst assignment regions and transmits another MBS burst reservation request message to all BSs  410  within the MBS_ZONE.  
         [0066]     In contrast, when reservation regarding all BSs ( 410 ) within the MBS_ZONE is successful, MBS controller  430  transmits a media request message to contents server  450  in order to transmit a media stream to BSs  410  (step  413 ). In response to the media request message, contents server  450  transmits a media response message to MBS controller  430  (step  415 ). Then, a media stream is transmitted to MBS controller  430  (step  417 ).  
         [0067]     MBS controller  430  subjects the media stream, which is transmitted by contents server  450 , to traffic multiplexing and shaping so as to create an MBS media stream, which is transmitted to BSs  410  (step  419 ).  
         [0068]     A traffic processing method by MBS controller  430 , particularly a procedure for traffic multiplexing and shaping of the media stream from contents server  450  will now described in more detail.  
         [0069]     It is clear from  FIG. 5  that, although the media information transmitted by contents server  510  has various traffic characteristics, the traffic characteristics of a streaming media tend to have a VBR (Variable Bit Rate) pattern in many cases. In other words, the transmitted data does not have uniform period and size, but the period and size vary as in the case of media streams  501 ,  503 , and  505  shown in  FIG. 5 .  
         [0070]     However, such a media having a VBR pattern makes it very difficult for BSs  550  to determine the position and size of MBS bursts to be reserved, because the period and size of burst assignment are not uniform.  
         [0071]     Therefore, according to the present invention, MBS controller  530  subjects the streaming media, which are transmitted by a number of contents servers  510 , to multiplexing  507 . The media are then subjected to shaping  509  so that they have a constant traffic pattern or a CBR (Constant Bit Rate). After undergoing the multiplexing and shaping, the streaming media are processed into mixed multicast streams, i.e. they have constant period and size as indicated by reference numeral  509  in  FIG. 5 .  
         [0072]     Therefore, the section and period regarding assignment of MBS bursts, which must be reserved for the media stream in respective BSs  550 , are clearly determined. A traffic processing method by the MBS controller will now be described with reference to  FIG. 6 .  
         [0073]     As shown in  FIG. 6 , the method includes requesting/responding to media information with regard to a media server; requesting/responding to a check of an assignable region of a BS; determining an MBS burst assignment region; requesting/responding to an MBS burst reservation; requesting/responding to media; traffic multiplexing and shaping; and transmitting to the BS a media stream, which has undergone traffic processing.  
         [0074]     Referring to  FIG. 6 , the MBS controller transmits a media information request message to a contents server in step  601 . Upon receiving a response from the contents server, the MBS controller checks if the BS has an MBS burst assignable region in step  603 . The MBS controller checks the MBS burst assignable region of the BS based on an admission request message and an admission request response message.  
         [0075]     In step  605 , the MBS controller collects information regarding bursts of the BS from the response message transmitted by the BS and determines an MBS burst assignment region based on the collected information. In step  607 , the MBS controller transmits information regarding the determination to the BS via an MBS burst reservation request message. After receiving a response from the BS, the MBS controller decides if reservation of the MBS burst has succeeded or not in step  609 .  
         [0076]     If it is determined in step  609  that the reservation of the MBS burst has failed, the MBS controller proceeds to step  605 , in which it newly determines an MBS burst assignment region and transmits another MBS burst reservation request message to the BS. If it is determined in step  609  that the reservation of the MBS burst is successful, the MBS controller proceeds to step  611  and transmits a media request message to the contents server.  
         [0077]     After receiving a response to the request and corresponding media from the contents server, the MBS controller subjects the received media to traffic multiplexing and shaping in step  613 . Finally, the MBS controller transmits traffic, which has undergone the multiplexing and shaping, to each BS in step  615 .  
         [0078]     According to the above-mentioned scheme for providing an MBS, after the MBS controller transmits IP packet-type data, which has undergone traffic processing, to all BSs within the MBS_ZONE, respective BSs create a MAC PDU (Packet Data Unit) based on the data and transmit it to the MS. However, the MAC PDU is affected by the condition of respective BSs or other traffic. In other words, the MAC PDU varies due to fragmentation or packing, which occurs when the MAC PDU is created.  
         [0079]     In order to avoid this problem, the present invention provides that the MAC PDU is created by the MBS controller.  
         [0080]     To this end, the MBS controller preferably incorporates the following functions, in addition to the above-mentioned functions. 
        Classification function and header compression function of CS (Convergence Sublayer) layer;     MAC PDU creation function of MAC layer;        
 
         [0083]     The CS layer acts as a sublayer for junction between layers. Particularly, the CS layer classifies data transmitted by a superior layer, maps it onto a suitable connection, and compresses the data. Since the aid of the CS layer is indispensable to the creation of the MAC PDU, the MBS controller incorporates both the function of the CS layer and the function of MAC PDU creation.  
         [0084]     As such, the MBS controller according to the present invention incorporates the above-mentioned functions so that, after processing traffic, the MBS controller creates a MAC PDU based on the traffic and transmits the MAC PDU to BSs within the MBS_ZONE. After receiving the MAC PDU, the BSs can transmit them to the MS through modulation and encoding without a separate process for creating the MAC PDU.  
         [0085]     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as further defined by the appended claims.