Abstract:
An apparatus and method for relaying neighbor BS in a multi-hop relay broadband wireless access (BWA) communication system are provided. In the BWA communication system, a BS transmits a neighbor BS advertisement message to a relay station (RS) within a cell area of the BS. The RS configures a relay neighbor BS advertisement message by eliminating unavailable neighbor BS information from the neighbor BS advertisement message, and broadcasts the relay neighbor BS advertisement message in a cell area of the RS.

Description:
PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. § 119 to an application filed in the Korean Intellectual Property Office on Sep. 13, 2005 and assigned Serial No. 2005-85447, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to relaying information in a communication system, and in particular to an apparatus and method for reconfiguring and broadcasting a neighbor Base Station (BS) advertisement message received from a serving BS by a relay station in a multi-hop relay Broadband Wireless Access (BWA) communication system.  
         [0004]     2. Description of the Related Art  
         [0005]     Currently, active research is being conducted to provide services with diverse Quality of Service (QoS) levels at about 100 Mbps to users in the 4 th  Generation (4G) communication system. Particularly, there is active research being conducted on providing high-speed service by ensuring mobility and QoS to a BWA communication system such as Wireless Local Area Network (WLAN) and Wireless Metropolitan Area Network (WMAN). Examples of such research are Institute of Electrical and Electronics Engineers (IEEE) 802.16d and IEEE 802.16e.  
         [0006]     The IEEE 802.16d and IEEE 802.16e communication systems are implemented by applying Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) to physical channels of the WMAN system. IEEE 802.16d considers only a single-cell structure with no regard to mobility of Subscriber Stations (SSs). In contrast, IEEE 802.16e supports the SS′ mobility to the IEEE 802.16d communication system. A mobile SS is called a Mobile Station (MS) or a Mobile Subscriber Station (MSS).  
         [0007]      FIG. 1  illustrates the configuration of the conventional IEEE 802.16e communication system, configured in a multi-cell structure. Specifically, the system includes cells  100  and  150 , base stations (BSs)  110  and  140  for managing the cells  100  and  150 , respectively, and a plurality of MSs  111 ,  113 ,  130 ,  151  and  153 . Signals are sent and received between the BSs  110  and  140  and the MSs  111 ,  113 ,  130 ,  151  and  153  in OFDM/OFDMA. The MS  130  exists in a cell boundary area between the cells  100  and  150 , i.e. in a handover region. When the MS  130  moves to the cell  150  managed by the BS  140  during signal transmission/reception to/from the BS  110 , the serving BS of the MS  130  changes from the BS  110  to the BS  140 .  
         [0008]      FIG. 2  illustrates an operation in a serving cell for broadcasting a Mobile_Neighbor-Advertisement (MOB_NBR-ADV) message in a cell in the conventional IEEE 802.16e communication system.  
         [0009]     Referring to  FIG. 2 , a serving BS  210  collects information about its neighbor BSs  220  to  290  by communicating with them over a wired or wireless backbone network, and periodically broadcasts the neighbor BS information in a cell by a MOB_NBR-ADV message  214 . Since the MOB_NBR-ADV message  214  is not intended for an MS at a particular location or in a particular direction within the cell, but is directed to all MSs within the cell, it delivers the neighbor BS information omni-directionally. An MS  212  recognizes the presence of the neighbor BSs  220  to  290  as well as the serving BS  210  by the MOB_NBR-ADV message  214 . If the MS  212  is at a cell boundary between the serving BS  210  and the neighbor BS  230  as illustrated in  FIG. 2 , it does not need information about neighbor BSs in the opposite direction to the cell coverage, such as the neighbor BS  270 . However, the serving BS  210  does not target the particular MS  212  in transmitting the neighbor BS information, and thus broadcasts the MOB_NBR-ADV message  214  across the cell. Although the MS  212  receives information about all of the neighbor BSs  220  to  290 , it does not need information about the neighbor BSs  260  to  290  because they are not around the MS  212 .  
         [0010]      FIG. 3  illustrates a conventional multi-hop relay broadband wireless communication system. Referring to  FIG. 3 , an MS  309  is located at a cell boundary of a BS  301 , though within the coverage area of the BS  301 . Therefore, the MS  309  can receive a service from the serving BS  301  but with poor quality due to the distance constraint. Compared to an MS close to the serving BS  301 , the MS  309  receives a service with a narrow bandwidth. Another MS  307  is outside the serving BS  301  and thus cannot communicate with the serving BS  301 .  
         [0011]     The application of a multi-hop relay scheme to both MSs  307  and  309  allows these MSs to receive a better-quality service in the manner of the MSs  311  and  313 . As with the MS  309 , the MS  311  is at the boundary of the service area of the BS  301 . Yet, since a relay station (RS)  303  is located near the MS  311 , the MS  311  can receive the service with higher quality than the MS  309  by communicating with the nearby RS  303  without the need for communication with the BS  301 , though it is at the boundary of the service area of the BS  301 . Like the MS  307 , the MS  313  is outside the coverage of the BS  301 , and cannot receive a signal or a service from the BS  301 . Nonetheless, due to the existence of an RS  305  near the MS  313 , the MS  313  can receive a service from the BS  301  via the RS  305 .  
         [0012]     In this manner, an MS which has difficulty in receiving a service or receives a poor quality service as illustrated in  FIG. 2  can communicate with its serving BS outside the coverage area of the serving BS or receive a good-quality service from the serving BS through relaying of an RS as illustrated in  FIG. 3 .  
         [0013]     Accordingly, there exists a need for reconfiguring the MOB_NBR-ADV message for effective communications among an MS, a BS and an RS in a multi-hop relay BWA communication system, when the pilot channel scanning procedure of  FIG. 2  is adopted.  
       SUMMARY OF THE INVENTION  
       [0014]     An object of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide an apparatus and method in an RS for retransmitting neighbor BS information received from a serving BS in a multi-hop relay BWA communication system.  
         [0015]     Another object of the present invention is to provide an apparatus and method in an RS for selecting information about available neighbor BSs from neighbor BS information received from a serving BS, reconfiguring a MOB_NBR-ADV message using the selected neighbor BS information, and transmitting the reconfigured MOB_NBR-ADV message to an MS in a multi-hop relay BWA communication system.  
         [0016]     A further object of the present invention is to provide an apparatus and method in an RS for reconfiguring a MOB_NBR-ADV message received from a serving BS by eliminating unnecessary information from the MOB_NBR-ADV message and transmitting the reconfigured MOB_NBR-ADV message so as to reduce the size of the message and thus save wireless network resources in a multi-hop relay BWA communication system.  
         [0017]     The above objects are achieved by providing an apparatus and method for relaying neighbor BS in a multi-hop relay BWA communication system.  
         [0018]     According to the present invention, in a BWA communication system for relaying neighbor BS information, a BS transmits a neighbor BS advertisement message to an RS within a cell area of the BS. The RS configures a relay neighbor BS advertisement message by eliminating unavailable neighbor BS information from the neighbor BS advertisement message, and broadcasts the relay neighbor BS advertisement message in a cell area of the RS.  
         [0019]     According to the present invention, in a method of relaying neighbor BS information in a BWA communication system, a neighbor BS advertisement message is received and it is determined whether the neighbor BS advertisement message includes unavailable neighbor BS information by checking neighbor BS information in the neighbor BS advertisement message. A relay neighbor BS advertisement message is configured by eliminating the unavailable neighbor BS information from the neighbor BS advertisement message, in the presence of the unavailable neighbor BS information. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0021]      FIG. 1  illustrates the configuration of a conventional IEEE 802.16e communication system;  
         [0022]      FIG. 2  illustrates an operation for broadcasting a MOB_NBR-ADV message across a cell in the conventional IEEE 802.16e communication system;  
         [0023]      FIG. 3  illustrates the configuration of a conventional multi-hop relay BWA communication system;  
         [0024]      FIG. 4  illustrates an operation for relaying neighbor BS information in an RS in the multi-hop relay BWA communication system according to the present invention;  
         [0025]      FIG. 5  illustrates an operation for reconfiguring and transmitting the MOB_NBR-ADV message in the RS in the multi-hop relay BWA communication system according to the present invention; and  
         [0026]      FIG. 6  is a flowchart illustrating an operation for relaying the neighbor BS information in the multi-hop relay BWA communication system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail for the sake of clarity and conciseness.  
         [0028]     Prior to describing the present invention, it is clarified that the multi-hop relay BWA communication system operates in OFDM and/or OFDMA. Hence, the multi-hop BWA communication system enables high-speed data transmission due to transmission of a physical channel signal on a plurality of subcarriers, and supports mobility of MSs by a multi-cell structure. Herein, “BS MOB_NBR-ADV” refers to a MOB_NBR-ADV message sent by a BS (or a serving BS) and “RS MOB_NBR-ADV” refers to a MOB_NBR-ADV message sent by an RS.  
         [0029]      FIG. 4  illustrates an operation for relaying neighbor BS information in an RS in the multi-hop relay BWA communication system according to the present invention.  
         [0030]     Referring to  FIG. 4 , the serving BS  210  collects information about neighbor BSs and broadcasts the BS MOB_NBR-ADV message  214  including the information about neighbor BSs within its cell. Upon receipt the BS MOB_NBR-ADV message  214 , an RS  400  separates a neighbor BS list included in the BS MOB_NBR-ADV message  214  into available neighbor BS information and unavailable neighbor BS information.  
         [0031]     The available neighbor BS information is information about the neighbor BSs  220 ,  230  and  240  near to the RS  400 , and the unavailable neighbor BS information is information about the neighbor BSs  250  to  290  remote from the RS  400  in the BS MOB_NBR-ADV message  214 .  
         [0032]     The RS  400  eliminates the unavailable neighbor BS information from BS MOB_NBR-ADV message  214  and configures a relay MOB_NBR-ADV message  404  with the available neighbor BS information. The RS  400  then sends the relay MOB_NBR-ADV message  404  in the cell coverage of the RS  400  so that an MS  402  can acquire the neighbor BS information by the relay MOB_NBR-ADV message  404 . If the BS MOB_NBR-ADV message  214  contains only the available neighbor BS information, the RS  400  forms the relay MOB_NBR-ADV message  404  with the available neighbor BS information and neighbor BS information managed by the RS  400  without any reconfiguration of the BS MOB_NBR-ADV message  214 , or broadcasts the BS MOB_NBR-ADV message  214  as the relay MOB_NBR-ADV message  404  to the MS  402 .  
         [0033]     The manner in which the RS  400  detects the available neighbor BS information from the BS MOB_NBR-ADV message  214  includes many ways, and its detailed description is not provided herein. It is also assumed that the RS  400  has neighbor BS information or neighbor RS information.  
         [0034]      FIG. 5  illustrates an operation for reconfiguring and transmitting the MOB_NBR-ADV message in the RS in the multi-hop relay BWA communication system according to the present invention.  
         [0035]     Referring to  FIG. 5 , the BS MOB_NBR-AVD message  214  broadcast from the serving BS  210  contains information about all neighbor BSs  220  to  290 . The RS  400  configures the relay MOB_NBR-ADV message  404  with information about the neighbor BSs  220 ,  230  and  240  near to the RS  400 , and sends the relay MOB_NBR-ADV message  404  to the MS  402 .  
         [0036]     Therefore, since the relay MOB_NBR-ADV message  404  delivers only the available neighbor BS information, the size of the message is much smaller than that of the BS MOB_NBR-ADV message  214 . As a consequence, radio resources are saved for transmission. The deletion of the information about the neighbor BSs  250  to  290 , i.e. the unavailable neighbor BS information does not affect the operation of the MS  402  because the unavailable neighbor BS information is not needed for the MS  402 .  
         [0037]      FIG. 6  is a flowchart illustrating an operation for relaying the neighbor BS information in the multi-hop relay BWA communication system according to the present invention.  
         [0038]     Referring to  FIG. 6 , the RS receives a BS MOB_NBR-ADV message periodically broadcast from the serving BS in step  600 . The RS checks a neighbor BS list in the BS MOB_NBR-ADV message in step  602  and determines whether the neighbor BS list includes information about neighbor BSs remote from the RS, i.e., unavailable neighbor BS information in step  604 . In the absence of the unavailable neighbor BS information, the RS broadcasts the BS MOB_NBR-ADV message within the cell area in step  610 .  
         [0039]     In the presence of the unavailable neighbor BS information, the RS deletes the unavailable neighbor BS information from the BS MOB_NBR-ADV message in step  606 , configures a relay MOB_NBR-ADV message with the remaining available neighbor BS information only in step  608 , and broadcasts the relay MOB_NBR-ADV message within the cell area in step  610 .  
         [0040]     The unavailable neighbor BS information is not necessary for the RS due to the difference in cell coverage between the serving BS and the RS. Thus, some neighbor BS close to the serving BS may be remote from the RS. The RS can detect the unavailable neighbor BS information in various ways in step  604 . Referring to  FIG. 3 , in a network including a BS, an RS and an MS, the BS cannot detect the location and direction of the roaming MS, but it can accurately locate the RS because the RS is installed at an installer-set location during network design and serves as a service providing node assisting the function of the BS, managed by the BS. In general, since the serving BS and its neighbor BSs exchange information necessary for a service by exchanging mutual information over a wired/wireless network, the information between the BSs is always currently updated. Hence, the serving BS provides the neighbor BS information to the RS. The RS can simply acquire the neighbor BS information in a typical procedure as done in the conventional mobile communication network, or in other manners. Thus, a description of the neighbor BS information acquisition in the RS is not provided herein.  
         [0041]     As described above, an RS separates a MOB_NBR-ADV message received from a serving BS into necessary and unnecessary neighbor BS information, reconfigures the MOB_NBR-ADV message with only the necessary neighbor BS information, and broadcasts the reconfigured MOB_NBR-ADV message. As a consequence, the size of the message is reduced and radio resources are saved.  
         [0042]     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 defined by the appended claims.