Abstract:
A method and system for acquiring information about neighbor base stations (BSs) and neighbor relay stations (RSs) in a multi-hop relay broadband wireless access communication system are provided. In the method, a serving BS collects information about the neighbor BSs and the neighbor RSs, generates a message including the collected information, and transmits the message to a serving RS and an MSS directly communicating with the serving BS. The serving RS transmits the message to an MSS communicating with the serving BS via the serving RS.

Description:
PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. § 119 to an application entitled “Method and System for Acquiring Information about Neighbor Base Stations and Neighbor Relay Stations in a Multi-Hop Relay Broadband Wireless Access Communication System” filed in the Korean Intellectual Property Office on Sep. 13, 2005 and assigned Serial No. 2005-85421, 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 a multi-hop relay Broadband Wireless Access (BWA) communication system and, in particular, to a method and system for acquiring information about neighbor Base Stations (BSs) and neighbor Relay Stations (RSs) in a Mobile Subscriber Station (MSS).  
         [0004]     2. Description of the Related Art  
         [0005]     In the future-generation 4 th  Generation (4G) communication system, extensive research is being provided into services with diverse Quality of Service (QoS) levels at about 100 Mbps. Particularly, active research being is conducted into 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) 802.16a and IEEE 802.16e.  
         [0006]     The IEEE 802.16a 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 802.16a considers only a single-cell structure with no regard to mobility of SSs. In contrast, IEEE 802.16e supports the SS&#39; mobility to the IEEE 802.16a communication system. A mobile SS is called an 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 , BSs  110  and  140  for managing the cells  100  and  150 , respectively, and a plurality of MSSs  111 ,  113 ,  130 ,  151  and  153 . Signals are sent and received between BSs  110  and  140  and MSSs  111 ,  113 ,  130 ,  151  and  153  in OFDM/OFDMA. The MSS  130  exists in a cell boundary area between cells  100  and  150 , i.e. in a handover region. When MSS  130  moves to cell  150  managed by BS  140  during signal transmission/reception to/from BS  110 , the serving BS of MSS  130  changes from BS  110  to BS  140 .  
         [0008]     In the conventional IEEE 802.16e communication system as illustrated in  FIG. 1 , signaling transmission/reception is performed between a fixed BS and an MSS via a direct link, such that a highly reliable radio communication link can be easily established between them. Yet, due to the fixed position of the BS, a radio network cannot be flexibly configured. As a result, it is difficult to provide an efficient communication service in a radio environment with a fluctuating traffic distribution or a substantial change in the number of calls required.  
         [0009]     To overcome the above shortcoming, a multi-hop relay data transmission scheme can be implemented through fixed or mobile RSs or general MSSs in a typical cellular wireless communication system such as the IEEE 802.16e communication system. The multi-hop relay wireless communication system adaptively reconfigures a network according to a communication environment change and efficiently operates the entire wireless network. It also extends a cell service area and increases system capacity. When there is poor channel status between a BS and an MSS, an RS is installed between them\, thus establishing a multi-hop relay path through the RS, so that a good radio channel can be provided to the MSS. Also, with the use of the multi-hop relay in a cell boundary area with a poor channel state, a high-speed data channel can be provided and the cell service area can be expanded.  
         [0010]      FIG. 2  illustrates the configuration of a multi-hop relay BWA communication system.  
         [0011]     Referring to  FIG. 2 , the multi-hop relay BWA communication system, which is configured in a multi-cell structure, includes cells  200  and  240 , BSs  210  and  250  for managing the cells  200  and  240 , respectively, a plurality of MSSs  211  and  213  within the coverage area of the cell  200 , a plurality of MSSs  221  and  223  managed by the BS  210  but located outside the coverage area  230  of the cell  200 , an RS  220  for providing a multi-hop relay path between the BS  210  and the MSSs  221  and  223  within the coverage area  230 , a plurality of MSSs  251 ,  253  and  255  within the coverage area of the cell  240 , a plurality of MSSs  261  and  263  managed by the BS  250  but outside the coverage area  270  of the cell  240 , and an RS  260  for providing a multi-hop relay path between the BS  250  and the MSSs  261  and  263  within the coverage area  270 . Signals are transmitted and received among the BSs  210  and  250 , the RSs  220  and  260 , and the MSSs  211 ,  213 ,  221 ,  223 ,  251 ,  253 ,  255 ,  261  and  263  in OFDM/OFDMA. Although the MSSs  211  and  213  within the coverage area of the cell  200 , and the RS  220  can communicate directly with the BS  210 , the MSSs  221  and  223  within the coverage area  230  cannot communicate with the BS  210 , directly. Therefore, the RS  220  controlling the coverage area  230  relays signals between the BS  210  and the MSSs  221  and  223 . Meanwhile, although the MSSs  251 ,  253  and  255  within the coverage area of the cell  240 , and the RS  260  can communicate directly with the BS  250 , the MSSs  261  and  263  within the coverage area  270  cannot directly communicate with the BS  250 . Therefore, the RS  260  controlling the coverage area  270  relays signals between the BS  250  and the MSSs  261  and  263 .  
         [0012]     As the RSs  220  and  260  and the MSSs  211 ,  213 ,  221 ,  223 ,  251 ,  253 ,  255 ,  261  and  263  may have mobility, inter-cell handover or handover from inside to outside a cell can occur. Accordingly, a handover MSS and a handover RS need neighbor RS information, and the handover MSS needs neighbor BS information in the IEEE 802.16e communication system illustrated in  FIG. 1 .  
       SUMMARY OF THE INVENTION  
       [0013]     An object of the present invention is to substantially solve at least the above shortcomings and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide a method and system for providing information about neighbor BSs and neighbor RSs to an MSS and an RS that communicate directly with a BS in a multi-hop relay BWA communication system.  
         [0014]     Another object of the present invention is to provide a method and system for providing information about neighbor BSs and neighbor RSs to a relay-mode MSS which cannot communicate directly with a BS by an RS in a multi-hop relay BWA communication system.  
         [0015]     The above objects are achieved by providing a method and system for acquiring information about neighbor BSs and neighbor RSs in a multi-hop relay BWA communication system.  
         [0016]     According to the present invention, in a first embodiment of a method of acquiring information about neighbor BSs and neighbor RSs in a multi-hop relay BWA communication system, a serving BS generates a message including the collected information, and transmits the message to a serving RS and an MSS directly communicating with the serving BS. The serving RS transmits the message to an MSS communicating with the serving BS via the serving RS.  
         [0017]     According to the present invention, in a second embodiment of a method of acquiring information about neighbor BSs and neighbor RSs in a multi-hop relay BWA communication system, a serving BS collects information about the neighbor BSs and the neighbor RSs, generates a first message including information about the neighbor BSs and neighbor RSs managed by the neighbor BSs, and generates a second message including information about neighbor RSs managed by the serving BS. The serving BS checks transmission periods of the first and second messages and transmits the first and second messages to a serving RS and an MSS directly communicating with the serving BS in the transmission periods.  
         [0018]     According to the present invention, in a third embodiment of a method of acquiring information about neighbor BSs and neighbor RSs in a multi-hop relay BWA communication system, a serving BS collects information about the neighbor BSs and the neighbor RSs, generates a first message including information about the neighbor BSs, and generates a second message including information about the neighbor RSs. The serving BS checks transmission periods of the first and second messages and transmits the first and second messages to a serving RS and an MSS directly communicating with the serving BS in the transmission periods. The serving RS transmits the first and second messages to an MSS communicating with the serving BS via the serving RS.  
         [0019]     According to the present invention, in a fourth embodiment of a method of acquiring information about neighbor BSs and neighbor RSs in a multi-hop relay BWA communication system, a serving BS collects information about the neighbor BSs and the neighbor RSs, generates a first message including the collected information, and transmits the first message to a serving RS and an MSS directly communicating with the serving BS. The serving RS creates a list of neighbor BSs and neighbor RSs required for the MSS communicating with the serving BS via the serving RS, generates a second message including the list, and transmits the second message to an MSS communicating with the serving BS via the serving RS.  
         [0020]     According to the present invention, in a first embodiment of a system for acquiring information about neighbor BSs and neighbor RSs in a multi-hop relay BWA communication system, a serving BS collects information about the neighbor BSs and the neighbor RSs, generating a first message including the collected information, and transmits the first message to a serving RS and an MSS directly communicating with a serving BS. The serving RS acquires the information about the neighbor BSs and the neighbor RSs, creates a list of neighbor BSs and neighbor RSs required for an MSS communicating with the serving BS via the serving RS, generates a second message including the list, and transmits the second message to the MSS communicating with the serving BS via the serving RS.  
         [0021]     According to the present invention, in a second embodiment of a system for providing information about neighbor BSs and neighbor RSs in a multi-hop relay BWA communication system, a serving BS collects information about the neighbor BSs and the neighbor RSs, generates a first message including information about neighbor BSs and neighbor RSs managed by the neighbor BSs and a second message including information about neighbor RSs managed by the serving BS, checks transmission periods of the first and second messages, and transmits the first and second messages to a serving RS and an MSS directly communicating with the serving BS in the transmission periods. Upon receipt of the first message, the serving RS transmits the first message to an MSS communicating with the serving BS via the serving RS, and upon receipt of the second message, it generates a third message including information about the serving BS and the neighbor RSs managed by the serving BS, and transmits the third message to the MSS communicating with the serving BS via the serving RS.  
         [0022]     According to the present invention, in a third embodiment of a system for providing information about neighbor BSs and neighbor RSs in a multi-hop relay BWA communication system, a serving BS collects information about the neighbor BSs and the neighbor RSs, generates a first message including information about the neighbor BSs and a second message including information about the neighbor RSs, checks transmission periods of the first and second messages, and transmits the first and second messages to a serving RS and an MSS directly communicating with the serving BS in the transmission periods. Upon receipt of the first and second messages, the serving RS transmits the first and second messages to an MSS communicating with the serving BS via the serving RS.  
         [0023]     According to the present invention, a serving BS collects information about the neighbor BSs and the neighbor RSs, generates a message containing the collected information, checks a transmission period of the message, and transmits the message to a serving RS and an MSS directly communicating with the serving BS in the transmission period. Upon receipt of the message, the serving RS transmits the message to an MSS communicating with the serving BS via the serving RS. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     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:  
         [0025]      FIG. 1  illustrates the configuration of a conventional IEEE 802.16e communication system;  
         [0026]      FIG. 2  illustrates the configuration of a conventional multi-hop relay BWA communication system;  
         [0027]      FIG. 3  is a diagram illustrating a signal flow for sending information about neighbor BSs and neighbor RSs configured by a serving BS in the multi-hop relay BWA communication system according to a first embodiment of the present invention;  
         [0028]      FIG. 4  is a diagram illustrating a signal flow for sending information about neighbor BSs and neighbor RSs configured by the serving BS in the multi-hop relay BWA communication system according to a second embodiment of the present invention;  
         [0029]      FIG. 5  is a diagram illustrating a signal flow for sending information about neighbor BSs and neighbor RSs configured by the serving BS in the multi-hop relay BWA communication system according to a third embodiment of the present invention;  
         [0030]      FIG. 6  is a diagram illustrating a signal flow for sending information about neighbor BSs and neighbor RSs configured by the serving BS in the multi-hop relay BWA communication system according to a fourth embodiment of the present invention;  
         [0031]      FIG. 7  is a block diagram of an MSS in the multi-hop relay BWA communication system according to the present invention; and  
         [0032]      FIG. 8  is a block diagram of an RS or a BS in the multi-hop relay BWA communication system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     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.  
         [0034]     The present invention is intended to provide a method and system for acquiring information about neighbor BSs and neighbor RSs by an MSS in a multi-hop relay BWA communication system. The multi-hop relay BWA communication system operates in OFDM/OFDMA. Because of transmission of physical channel signals on multiple subcarriers, the multi-hop relay BWA communication system enables high-speed data transmission. The multi-hop relay BWA communication system also supports a multi-cell structure, thus supporting the mobility of the MSS. The RS is a fixed or mobile node, or it may include a particular system installed by the BS or a conventional subscriber station (SS 0 . Any node having the above feature can be chosen as an RS according to a pre-defined rule for expansion of cell area or cell capacity in the BS through a relay capabilities negotiation procedure with the BS.  
         [0035]      FIG. 3  is a diagram illustrating a signal flow for sending information about neighbor BSs and neighbor RSs configured by a serving BS in the multi-hop relay BWA communication system according to a first embodiment of the present invention.  
         [0036]     Referring to  FIG. 3 , in relay mode, an MSS  310  communicates with a serving RS  340  in step  311  and the serving RS  340  communicates with a serving BS  350  in step  313 . An MSS  360  communicates directly with the serving BS  350  in direct mode in step  315 .  
         [0037]     In step  317 , the serving BS  350  collects information about neighbor BSs and neighbor RSs, and checks the transmission period of a neighbor BS/RS advertisement (NBR-ADV) message including the neighbor BS and RS information. The serving BS  350  then broadcasts the NBR-ADV message to the serving RS  340  and the direct-mode MSS  360  in step  319 .  
         [0038]     The NBR-ADV message has the following configuration illustrated in Table 1.  
                       TABLE 1                       Syntax   Size (bits)   Notes                   NBR-ADV_format( ){                Management Message Type   8   To be determined       =TBD        N_BS   8   Number of BSs; the serving BS may be               included        for(i=0;i&lt;N_BS;i++){         BS ID   48    BS Identifier         BS preamble index   8   —         BS  synchronization   variable   The BS information that is necessary for MSS       information       or RS to acquire synchronization with this BS        N_RS   8   Number of relay stations        for(j=0;j&lt;N_RS;j++){         RS ID   48    RS Identifier         RS preamble index   8   —         RS  synchronization   variable   The RS information that is necessary for MSS       information       or other RS to acquire synchronization with               this RS         }        }        TLV information   Variable       }                  
 
         [0039]     Referring to Table 1, the NBR-ADV message includes the message type of the transmitted message, the number of neighbor BSs included, the identifier (ID) of each neighbor BS, the preamble index of the neighbor BS, information necessary for synchronization with the neighbor BS, the number of neighbor RSs managed by the neighbor BS, the ID of each neighbor RS, the preamble index of the neighbor RS, information necessary for synchronization with the neighbor RS, and type/length/value (TLV) information that can be temporarily included for the neighbor BS and the neighbor RS. The neighbor RS information included in the NBR-ADV message is about RSs managed by both the neighbor BSs and the serving BS. The neighbor BSs may include the serving BS.  
         [0040]     The serving RS  340  and the direct-mode MSS  360  receive the NBR-ADV message from the serving BS  350  in steps  321  and  323 , respectively, thereby acquiring the neighbor BS and RS information. The serving RS  340  or the direct-mode MSS  360  may hand over to one of the neighbor BSs or the neighbor RSs based on the neighbor BS and RS information.  
         [0041]     In step  325 , the serving RS  340  broadcasts the NBR-ADV message to the relay-mode MSS  310  managed by the serving RS  340 . The NBR-ADV message may be sent using a particular connection ID (CID) so that it reaches only within the coverage area of the serving RS  340 .  
         [0042]     The relay-mode MSS  310  thus acquires the neighbor BS and RS information from the NBR-ADV message received from the serving RS  340  in step  327 . The relay-mode MSS  310  can handover to a neighbor BS or a neighbor RS based on the neighbor BS and RS information.  
         [0043]      FIG. 4  is a diagram illustrating a signal flow for sending information about neighbor BSs and neighbor RSs configured by the serving BS in the multi-hop relay BWA communication system according to a second embodiment of the present invention.  
         [0044]     Referring to  FIG. 4 , a relay-mode MSS  410  communicates with a serving RS  440  in step  411  and the serving RS  440  communicates with a serving BS  450  in step  413 . A direct-mode MSS  460  communicates directly with the serving BS  450  in step  415 .  
         [0045]     In step  417 , the serving BS  450  collects information about neighbor BSs and neighbor RSs, and checks the transmission period of an NBR-ADV message containing the neighbor BS except the serving BS itself and RS information, formatted as illustrated in Table  1 . The serving BS  450  then broadcasts the NBR-ADV message to the serving RS  440  and the direct-mode MSS  460  in step  419 .  
         [0046]     The serving RS  440  and the direct-mode MSS  460  receive the NBR-ADV message from the serving BS  450  in steps  421  and  423 , respectively, thereby acquiring the neighbor BS and RS information. The serving RS  440  or the direct-mode MSS  460  may hand over to a neighbor BS or a neighbor RS based on the neighbor BS and RS information.  
         [0047]     In step  425 , the serving RS  440  creates a list of neighbor BSs and neighbor RSs for which information is required for the relay-mode MSS  410  managed by the serving RS  440 . The serving RS  440  broadcasts a neighbor BS/RS information (RS_NBR-INFO) message including the neighbor BS and RS list in step  427 . The RS_NBR-INFO message has the configuration illustrated below in Table 2. The RS_NBR-INFO message may be sent using a particular CID so that it reaches only within the coverage area of the serving RS  440 .  
                       TABLE 2                       Syntax   Size (bits)   Notes                   RS_NBR-INFO_format( ){                Management Message Type   8   To be determined       =TBD        N_BS   8   Number of BSs; the serving BS may be               included        for(i=0;i&lt;N_BS;i++){         BS ID   48    BS Identifier         BS preamble index   8   —         BS  synchronization   variable   The BS information that is necessary for MSS       information       or RS to acquire synchronization with this BS        N_RS   8   Number of relay stations        for(j=0;j&lt;N_RS;j++){         RS ID   48    RS Identifier         RS preamble index   8   —         RS  synchronization   variable   The RS information that is necessary for MSS       information       or other RS to acquire synchronization with               this RS         }        }        TLV information   Variable       }                  
 
         [0048]     Referring to Table 2, the RS_NBR-INFO message includes the message type of the transmitted message, the number of neighbor BSs included, the ID of each neighbor BS, the preamble index of the neighbor BS, information necessary for synchronization with the neighbor BS, the number of neighbor RSs managed by the neighbor BS, the ID of each neighbor RS, the preamble index of the neighbor RS, information necessary for synchronization with the neighbor RS, and TLV information that can be temporarily included for the neighbor BS and the neighbor RS. The neighbor RS information included in the RS_NBR-INFO message is about RSs managed by the neighbor BSs and the serving BS. The neighbor BSs may include the serving BS.  
         [0049]     As the relay-mode MSS  410  receives the RS_NBR-INFO message in step  429 , it acquires the neighbor BS and RS information. The relay-mode MSS  410  can handover to a neighbor BS or a neighbor RS based on the neighbor BS and RS information.  
         [0050]      FIG. 5  is a diagram illustrating a signal flow for sending information about neighbor BSs and neighbor RSs configured by the serving BS in the multi-hop relay BWA communication system according to a third embodiment of the present invention. The serving BS provides information about neighbor RSs within a serving cell and information about neighbor RSs within neighbor cells by separate messages.  
         [0051]     Referring to  FIG. 5 , a relay-mode MSS  510  communicates with a serving RS  540  in step  511  and the serving RS  540  communicates with a serving BS  550  in step  513 . A direct-mode MSS  560  communicates directly with the serving BS  550  in step  515 .  
         [0052]     In step  517 , the serving BS  550  collects information about neighbor BSs and neighbor RSs managed by the neighbor BSs, and checks the transmission period of a modified NBR-ADV message including the neighbor BS and RS information.  
         [0053]     The serving BS  550  then broadcasts the modified NBR-ADV message to the serving RS  540  and the direct-mode MSS  560  in step  519 .  
         [0054]     The modified NBR-ADV message is configured as illustrated below in Table 3.  
                       TABLE 3                       Syntax   Size (bits)   Notes                   NBR-ADV_format( ){                Management Message Type   8   To be determined       =TBD        N_BS   8   Number of neighbor BSs        for(i=0;i&lt;N_BS;i++){         BS ID   48    BS Identifier         BS preamble index   8   —         BS  synchronization   variable   The BS information that is necessary for MSS       information       or RS to acquire synchronization with this BS        N_RS   8   Number of relay stations        for(j=0;j&lt;N_RS;j++){         RS ID   48    RS Identifier         RS preamble index   8   —         RS  synchronization   variable   The RS information that is necessary for MSS       information       or other RS to acquire synchronization with               this RS         }        }        TLV information   Variable       }                  
 
         [0055]     Referring to Table 3, the modified NBR-ADV message includes the message type of the transmitted message, the number of neighbor BSs included, the ID of each neighbor BS, the preamble index of the neighbor BS, information necessary for synchronization with the neighbor BS, the number of neighbor RSs managed by the neighbor BS, the ID of each neighbor RS, the preamble index of the neighbor RS, information necessary for synchronization with the neighbor RS, and TLV information that can be temporarily included for the neighbor BS and the neighbor RS. The neighbor RS information included in the NBR-ADV message is about RSs managed by the neighbor BSs.  
         [0056]     The serving RS  540  and the direct-mode MSS  560  receive the modified NBR-ADV message from the serving BS  550  in steps  521  and  523 , respectively, thereby acquiring the information about the neighbor BSs and the neighbor RSs managed by the neighbor BSs. The serving RS  540  or the direct-mode MSS  560  may hand over to one of the neighbor BSs or the neighbor RSs based on the neighbor BS and RS information.  
         [0057]     In step  525 , the serving RS  540  broadcasts the modified NBR-ADV message to the relay-mode MSS  510  managed by the serving RS  540 . The NBR-ADV message may be sent using a particular CID so that it reaches only within the coverage area of the serving RS  540 .  
         [0058]     As the relay-mode MSS  510  receives the modified NBR-ADV message in step  527 , it acquires the information about the neighbor BSs and the neighbor RSs managed by the neighbor BSs. The relay-mode MSS  510  can handover to one of the neighbor BSs or the neighbor RSs based on the neighbor BS and RS information.  
         [0059]     In step  529 , the serving BS  550  configures a serving cell relay station advertisement (BS_RS-ADV) including information about its managed RSs on a periodic basis and checks the transmission period of the BS_RS-ADV message. The serving BS  550  then broadcasts the BS_RS-ADV message to the serving BS  540  and the direct-mode MSS  560  in step  531 .  
         [0060]     The BS_RS-ADV message has the configuration illustrated below in Table 4.  
                       TABLE 4                       Syntax   Size (bits)   Notes                   BS_RS-ADV_format( ){                Management Message Type   8   To be determined       =TBD        N_RS   8   Number of relay               stations in serving cell        for(j=0;j&lt;N_RS;j++){         RS ID   48    RS Identifier         RS preamble index   8   —         RS  synchronization   variable   The RS information that is       information       necessary for MSS or other               RS to acquire synchronization               with this RS        }        TLV information   Variable       }                  
 
         [0061]     Referring to Table 4, the BS_RS-ADV message includes the message type of the transmitted message, the number of neighbor RSs included, the ID of each neighbor RS, the preamble index of the neighbor RS, information necessary for synchronization with the neighbor RS, and TLV information that can be temporarily included for the neighbor RS. The neighbor RSs listed in the BS_RS-ADV message are those managed by the serving BS.  
         [0062]     The serving RS  540  and the direct-mode MSS  560  receive the BS_RS-ADV message from the serving BS  550  in steps  533  and  535 , respectively, thereby acquiring the information about the neighbor RSs managed by the serving BS  550 . The serving RS  540  or the direct-mode MSS  560  may hand over to one of the neighbor RSs based on the neighbor RS information.  
         [0063]     In step  537 , the serving RS  540  configures an RS_Serving-ADV message including information about the serving BS  550  and the neighbor RSs within the serving cell.  
         [0064]     The RS_Serving-ADV message has the configuration illustrated below in Table 5.  
                       TABLE 5                       Syntax   Size (bits)   Notes                   RS_Serving-ADV_format( ){                Management Message Type   8   To be determined       =TBD         BS ID   48    Serving BS Identifier         BS preamble index   8   —         BS  synchronization   variable   The BS information that is necessary for MSS       information       or RS to acquire synchronization with this BS        N_RS   8   Number of relay stations in serving cell        for(j=0;j&lt;N_RS;j++){         RS ID   48    RS Identifier         RS preamble index   8   —         RS  synchronization   variable   The RS information that is necessary for MSS       information       or other RS to acquire synchronization with               this RS        }        TLV information   Variable       }                  
 
         [0065]     Referring to Table 5, the RS_Serving-ADV message includes the message type of the transmitted message, the ID of the serving BS, the preamble index of the serving BS, information necessary for synchronization with the serving BS, the number of neighbor RSs managed by the serving BS, the ID of each neighbor RS, the preamble index of the neighbor RS, information necessary for synchronization with the neighbor RS, and TLV information that can be temporarily included for the serving BS and the neighbor RS.  
         [0066]     The serving RS  540  broadcasts the RS_Serving-ADV message to the relay-mode MSS  510  in step  539 . The RS_Serving-ADV message may be sent using a particular CID so that it reaches only within the coverage area of the serving RS  540 .  
         [0067]     As the relay-mode MSS  510  receives the RS_Serving-ADV message in step  541 , it acquires the information about the serving BS  550  and the neighbor RSs managed by the serving BS  550 . The relay-mode MSS  510  can handover to the serving BS  550  or a neighbor RS managed by the serving BS  550  based on the neighbor RS information.  
         [0068]      FIG. 6  is a diagram illustrating a signal flow for sending information about neighbor BSs and neighbor RSs configured by the serving BS in the multi-hop relay BWA communication system according to a fourth embodiment of the present invention. The serving BS provides information about neighbor BSs and neighbor RSs by separate messages.  
         [0069]     Referring to  FIG. 6 , a relay-mode MSS  610  communicates with a serving RS  640  in step  611  and the serving RS  640  communicates with a serving BS  650  in step  613 . A direct-mode MSS  660  communicates directly with the serving BS  650  in step  615 .  
         [0070]     In step  617 , the serving BS  650  collects information about neighbor BSs and checks the transmission period of a modified NBR-ADV message including the neighbor BS information. The serving BS  650  then broadcasts the modified NBR-ADV message to the serving RS  640  and the direct-mode MSS  660  in step  619 .  
         [0071]     The modified NBR-ADV message is configured as illustrated below in Table 6.  
                       TABLE 6                       Syntax   Size (bits)   Notes                   NBR-ADV_format( ){                Management Message Type   8   To be determined       =TBD        N_BS   8   Number of neighbor BSs        for(i=0;i&lt;N_BS;i++){         BS ID   48    BS Identifier         BS preamble index   8   —         BS  synchronization   variable   The BS information that is       information       necessary for MSS or RS to               acquire synchronization with               this BS        }        TLV information   Variable       }                  
 
         [0072]     Referring to Table 6, the modified NBR-ADV message includes the message type of the transmitted message, the number of neighbor BSs included, the ID of each neighbor BS, the preamble index of the neighbor BS, information necessary for synchronization with the neighbor BS, and TLV information that can be temporarily included for the neighbor BS.  
         [0073]     The serving RS  640  and the direct-mode MSS  660  receive the modified NBR-ADV message from the serving BS  650  in steps  621  and  623 , respectively, thereby acquiring the neighbor BS information. The serving RS  640  or the direct-mode MSS  660  may hand over to a neighbor BS based on the neighbor BS information.  
         [0074]     In step  625 , the serving RS  640  broadcasts the modified NBR-ADV message to the relay-mode MSS  610  managed by the serving RS  640 . The NBR-ADV message includes the information of the serving BS  650 . The NBR-ADV message may be sent using a particular CID so that it reaches only within the coverage area of the serving RS  640 .  
         [0075]     As the relay-mode MSS  610  receives the modified NBR-ADV message in step  627 , it acquires the neighbor BS information. The relay-mode MSS  610  can hand over to one of the neighbor BSs based on the neighbor BS information.  
         [0076]     In step  629 , the serving BS  650  configures a relay station advertisement (RS-ADV) message including information about RSs managed by the serving BS  650  and the neighbor BSs on a periodic basis and checks the transmission period of the RS-ADV message. The serving BS  650  then broadcasts the RS-ADV message to the serving RS  640  and the direct-mode MSS  660  in step  631 .  
         [0077]     The RS-ADV message has the configuration illustrated below in Table 7.  
                       TABLE 7                       Syntax   Size (bits)   Notes                   RS-ADV_format( ){                Management Message Type   8   To be determined       =TBD        N_BS   8   Number of neighbor BSs;               including serving BS        for(i=0;i&lt;N_BS;i++){         BS ID   48    BS Identifier         N_RS   8   Number of relay stations         for(j=0;j&lt;N_RS;j++){          RS ID   48    RS Identifier          RS preamble index   8   —          RS  synchronization   variable   The RS information that is       information       necessary for MSS or other               RS to acquire               synchronization with this               RS         }        }        TLV information   Variable       }                  
 
         [0078]     Referring to Table 7, the RS-ADV message includes the message type of the transmitted message, the number of neighbor BSs included, the ID of each neighbor BS, the number of neighbor RSs managed by the neighbor BS, the ID of each neighbor RS, the preamble index of the neighbor RS, information necessary for synchronization with the neighbor RS, and TLV information that can be temporarily included for the neighbor RS. The serving BS and the neighbor RS list managed by the serving BS are included.  
         [0079]     The serving RS  640  and the direct-mode MSS  660  receive the RS-ADV message from the serving BS  650  in steps  633  and  635 , respectively, thereby acquiring the information about the neighbor RSs managed by the serving BS  650  and the neighbor BSs. The serving RS  640  or the direct-mode MSS  660  may hand over to a neighbor RS based on the neighbor RS information.  
         [0080]     In step  637 , the serving RS  640  broadcasts the RS-ADV message to the relay-mode MSS  610 . The RS-ADV message may be sent using a particular CID so that it reaches only within the coverage area of the serving RS  640 .  
         [0081]     As the relay-mode MSS  610  receives the RS-ADV message in step  639 , it acquires the information about the neighbor RSs managed by the serving BS  550  and the neighbor BSs. The relay-mode MSS  610  can handover to a neighbor RS based on the neighbor RS information.  
         [0082]     Methods of providing information about neighbor BSs and neighbor RSs to a direct-mode MSS and an RS which communicate directly with a BS and to a relay-mode MSS which cannot communicate directly with the BS in a multi-hop relay BWA communication system have been described above. The following description applies to a system for providing the neighbor BS and RS information in conjunction with the block diagrams of the BS, the RS, and the MSS in the multi-hop relay BWA communication system.  
         [0083]      FIG. 7  is a block diagram of the MSS in the multi-hop relay BWA communication system according to the present invention.  
         [0084]     Referring to  FIG. 7 , the MSS includes a Micro-Processor Unit (MPU)  701 , a memory  703 , a neighbor BS/RS information processor  705 , a message processor  707  and an interface module  709 .  
         [0085]     In operation, the MPU  701  controls the operation of the MSS. For example, the MPU  701  processes and controls voice and data communication. In addition to the typical functionality, the MPU  701  processes neighbor BS or neighbor RS information received from the BS or the RS by controlling the message processor  707  and the neighbor BS/RS information processor  705 . A description of the conventional processing and control operation of the MPU  701  is not provided herein for the sake of conciseness.  
         [0086]     The memory  703  stores the micro-codes of programs for processing and controlling in the MPU  701 , reference data, temporary data generated during execution of the programs and updatable data. In addition, the memory  703  includes a data buffer for storing data and control information to be sent to the BS or the RS. Additionally, the memory  703  stores the neighbor BS or neighbor RS information received from the BS or the RS.  
         [0087]     The neighbor BS/RS information processor  705  recognizes the information about neighbor BSs and neighbor RSs received from the BS or the RS and operates according to the information.  
         [0088]     The message processor  707  processes messages received from an antenna through the interface module  709  and the MPU  701 , such as the NBR-ADV message illustrated in Table 1, the RS_NBR-INFO message illustrated in Table 2, the NBR-ADV message illustrated in Table 3, the BS_RS-ADV message llustrated in Table 4, the RS_Serving-ADV message illustrated in Table 5, the NBR-ADV message illustrated in Table 6, and the RS-ADV message illustrated in Table 7.  
         [0089]     The interface module  709  processes messages and data transmitted and received between the MSS and the BS or between the MSS and the RS, and radio processes the data. Specifically, the interface module  709  upconverts a message or data to be transmitted to a frequency band, processes the upconverted message or data in a transmission scheme, and transmits the processed message or data. The interface module  709  also processes a received message or data in the reverse order of the transmission operation and downconverts the received message or data.  
         [0090]      FIG. 8  is a block diagram of the RS for processing neighbor BS and neighbor RS information in the multi-hop relay BWA communication system according to the present invention.  
         [0091]     Referring to  FIG. 8 , the RS includes an MPU  801 , a memory  803 , a neighbor BS/RS information processor  805 , a message generator  807 , a message processor  809  and an interface module  811 .  
         [0092]     In operation, the MPU  801  provides overall control to the operation of the RS. The MPU  801  controls the message processor  809 , the message generator  807 , and the neighbor BS/RS information processor  805 , configures neighbor BS and RS information to be sent to the relay-mode MSS based on neighbor BS and RS information received from the BS, and transmits the configured neighbor BS and RS information to the relay-mode MSS.  
         [0093]     The memory  803  includes a data buffer for storing data and control information to be transmitted to the relay-mode MSS and the BS. The memory  803  stores the neighbor BS and RS information received from the BS.  
         [0094]     The neighbor BS/RS information processor  805  recognizes the information about neighbor BSs and neighbor RSs received from the BS and operates according to the information. The neighbor BS/RS information processor  805  also configures neighbor BS and RS information to be transmitted to the relay-mode MSS and performs an operation required for sending the configured neighbor BS and RS information to the relay-mode MSS.  
         [0095]     The message generator  807  generates a message to be transmitted to the MSS, such as the NBR-ADV message illustrated in Table 1, the RS_NBR-INFO message illustrated in Table 2, the NBR-ADV message illustrated in Table 3, the RS_Serving-ADV message illustrated in Table 5, the NBR-ADV message illustrated in Table 6, and the RS-ADV message illustrated in Table 7. The message is broadcast to the MSS through the MPU  801  and the interface module  811 . The broadcast transmission may be limited to MSSs managed by the RS.  
         [0096]     The message processor  809  processes a message received through the interface module  811  and the MPU  801 , such as the NBR-ADV message illustrated in Table 1, the NBR-ADV message illustrated in Table 3, the BS_RS-ADV message illustrated in Table 4, the NBR-ADV message illustrated in Table 6, and the RS-ADV message illustrated in Table 7.  
         [0097]     The interface module  811  processes messages and data transmitted and received between the RS and the BS or between the RS and the relay-mode MSS, and radio processes the data. Specifically, the interface module  811  upconverts a message or data to be transmitted to a frequency band, processes the upconverted message or data in a transmission scheme, and transmits the processed message or data. The interface module  811  also processes a received message or data in the reverse order of the transmission operation and downconverts the received message or data.  
         [0098]     In the present invention, in an OFDM/OFDMA BWA communication system, particularly a multi-hop relay BWA communication system including an RS which can provide a multi-hop relay path between a BS and an MSS when a direct link channel between the BS and the MSS is in a poor channel state, the BS sends a message including information about neighbor RSs and neighbor BSs to the RS, relay-mode MSSs and direct-mode MSSs so that the RS, the relay-mode MSSs, and the direct-mode MSSs can hand over to the neighbor BSs or the neighbor RSs based on the neighbor BS and RS information.  
         [0099]     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.