Abstract:
A scanning apparatus and method in a multi-hop relay Broadband Wireless Access (BWA) communication system are provided. In the scanning method, a Mobile Subscriber Station (MSS) sends a scan request message requesting scanning to a Base Station (BS) via a Relay Station (RS). The BS sends a scan response message containing information for the scanning of the MSS to the MSS via the RS. The BS then sends a scan notify message indicating the scanning of the MSS to the RS.

Description:
PRIORITY 
     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. 2005-85418, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a multi-hop relay Broadband Wireless Access (BWA) communication system and, in particular, to a scanning apparatus and method in a multi-hop relay BWA communication system. 
     2. Description of the Related Art 
     Provisioning of services with diverse Quality of Service (QoS) levels at about 100 Mbps to users is an active study area for a future-generation communication system called a 4 th  Generation (4G) communication system. Particularly, active research is conducted on provisioning of 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). Such major examples are Institute of Electrical and Electronics Engineers (IEEE) 802.16a and IEEE 802.16e. 
     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 a Subscriber Station (SS). In contrast, IEEE 802.16e supports SS mobility in the IEEE 802.16a communication system. A Mobile Subscriber Station is called an MSS. 
       FIG. 1  shows a typical IEEE 802.16e communication system configured in a multi-cell structure. 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 MSSs  111 ,  113 ,  130 ,  151  and  153 . Signals are sent and received between the BSs  110  and  140  and the MSSs  111 ,  113 ,  130 ,  151  and  153  in OFDM/OFDMA. The MSS  130  exists in a cell boundary area between the cells  100  and  150 , i.e. in a handover region. When the MSS  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 MSS  130  changes from the BS  110  to the BS  140 . 
       FIG. 2  shows signal flow between an MSS and a BS, for scanning in a conventional BWA communication system. An MSS  210  communicates with a serving BS  230  in step  211 . During the communication, the MSS  210  determines whether to scan pilot channel signals from the serving BS  230  and neighbor BSs. If scanning should be performed, the MSS  210  sends a Mobile Scanning Interval Allocation Request (MOB_SCN-REQ) message to the serving BS  230  in step  213 . The MOB_SCN-REQ message has the following configuration illustrated in Table 1 below. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Syntax 
                 Size (bits) 
                 Notes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 MOB_SCN-REQ_format( ) { 
                   
                   
               
               
                  Management Message Type=54 
                 8 
                 — 
               
               
                  Scan duration 
                 8 
                 Units are frames 
               
               
                  Interleaving interval 
                 8 
                 Units are frames 
               
               
                  Scan iteration 
                 8 
                 In frames 
               
               
                  N_Recommended_BS 
                 8 
                 Number of 
               
               
                   
                   
                 neighboring 
               
               
                   
                   
                 BSs to be scanned 
               
               
                  For (i=0; i&lt;N_Recommended_BS; 
               
               
                 i++) { 
               
               
                   Recommended BS_ID 
                 48 
                 BS Identifier 
               
               
                  } 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 1, the MOB_SCN-REQ message has a plurality of Information Elements (IEs). The IEs include “Management Message Type” identifying the type of the transmitted message, “Scan duration” indicating a desired scan duration during which pilot signals from the neighbor BSs are scanned, “Scan iteration” indicating the number of iterative scannings in the case of periodic scanning, “Interleaving interval” indicating the time interval between scannings in the case of iterative scanning, and “Recommended BS_ID” identifying a desired BS to be scanned. 
     Upon receipt of the MOB_SCN-REQ message, the serving BS  230  replies to the MSS  210  with a Mobile Scanning Interval Allocation Response (MOB_SCN-RSP) message containing scanning information for the MSS  210  and a scan duration set to non-zero. 
     The MOB_SCN-RSP message has the following structure. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Syntax 
                 (bits) 
                 Notes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 MOB_SCN-RSP_format( ) { 
                   
                   
               
               
                  Management Message Type=55 
                 8 
                 — 
               
               
                  Scan duration 
                 8 
                 Units are frames. When 
               
               
                   
                   
                 Scan duration is set to zero, 
               
               
                   
                   
                 no scanning parameters are 
               
               
                   
                   
                 specified in the message. 
               
               
                   
                   
                 When MOB_SCN-RSP is 
               
               
                   
                   
                 sent in response to 
               
               
                   
                   
                 MOB_SCN-REQ, setting 
               
               
                   
                   
                 Scan duration to zero 
               
               
                   
                   
                 denies MOB_SCN-REQ. 
               
               
                  Report mode 
                 2 
                 0b00: no report 
               
               
                   
                   
                 0b01: periodic report 
               
               
                   
                   
                 0b10: event triggered report 
               
               
                   
                   
                 0b11: reserved; shall be set 
               
               
                   
                   
                 to zero 
               
               
                  reserved 
                 6 
                 Shall be set to zero 
               
               
                  Report period 
                 8 
                 Available when the value of 
               
               
                   
                   
                 Report mode is set to 0b01. 
               
               
                   
                   
                 Report period in frames. 
               
               
                  Report metric 
                 8 
                 Bitmap indicating metrics 
               
               
                   
                   
                 on which the corresponding 
               
               
                   
                   
                 triggers are based: 
               
               
                   
                   
                 Bit 0: BS CINR mean 
               
               
                   
                   
                 Bit 1: BS RSSI mean 
               
               
                   
                   
                 Bit 2: Relative delay 
               
               
                   
                   
                 Bit 3: BS RTD 
               
               
                   
                   
                 Bit 4-7: reserved; shall be 
               
               
                   
                   
                 set to zero 
               
               
                  If (Scan duration!=0) { 
               
               
                  Start frame 
                 4 
                 — 
               
               
                  reserved 
                 4 
                 Shall be set to zero 
               
               
                  Interleaving interval 
                 8 
                 Duration in frames 
               
               
                  Scan iteration 
                 8 
                 — 
               
               
                  N_Recommended_BS 
                 8 
                 Number of neighboring BSs 
               
               
                   
                   
                 to be scanned 
               
               
                  for (i=0; i&lt;N_Recommended_BS; 
               
               
                 i++) { 
               
               
                   Recommended BS_ID 
                 48 
                 BS Identifier 
               
               
                  } 
               
               
                  } 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 2, the MOB_SCN-RSP message has a plurality of IEs. The IEs include “Management Message Type” identifying the type of the transmitted message, “Scan duration” indicating a scan duration during which the MSS is to scan, “Report mode”, “Report period” used when the report mode is a periodic report, “Report metric” indicating the type of information to be reported as a scanning result, “Start frame” indicating the start of the scanning, “Scan iteration” indicating the number of iterative scannings in the case of periodic scanning, “Interleaving interval” indicating the time interval between scannings, and “Recommended BS_ID” identifying a desired BS to be scanned. If Scan duration is 0, it implies that the scanning request from the MSS is rejected. Information indicating the scanning result may be Carrier-to-Interference and Noise Ratio (CINR), Received Signal Strength Indicator (RSSI), relative delay, or Round Trip Delay (RTD). 
     Upon receipt of the MOB_SCN-RSP message containing the scanning information, the MSS  210  scans pilot channel signals from the serving BS  230  and the neighbor BSs in correspondence with the parameters included in the MOB_SCN-RSP message in step  217 . 
     Meanwhile, the serving BS  230  discontinues data transmission to the MSS  210 , buffering data for the MSS  210  during the scanning in the MSS  210  in step  219 . 
     After the pilot scanning, the MSS  210  sends a Mobile Scanning Result Report (MOB_SCN-REP) message to the serving BS  230  to report the scanning result in step  221 . 
     The MOB_SCN-REP message is configured in the following structure. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Syntax 
                 (bits) 
                 Notes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 MOB_SCN-REP_format( ) { 
                   
                   
               
               
                  Management Message Type=60 
                 8 
                 — 
               
               
                  Report mode 
                 1 
                 0: Event triggered report 
               
               
                   
                   
                 1: Periodic report 
               
               
                  reserved 
                 7 
                 Shall be set to zero 
               
               
                  Report metric 
                 8 
                 Bitmap indicating presence 
               
               
                   
                   
                 of certain metrics: 
               
               
                   
                   
                 Bit 0: BS CINR mean 
               
               
                   
                   
                 Bit 1: BS RSSI mean 
               
               
                   
                   
                 Bit 2: Relative delay 
               
               
                   
                   
                 Bit 3: BS RTD 
               
               
                   
                   
                 Bit 4-7: reserved; shall be set 
               
               
                   
                   
                 to zero 
               
               
                  N_BS 
                 8 
                 Number of BSs to be 
               
               
                   
                   
                 scanned 
               
               
                  for (i=0; i&lt;N_BS; i++) { 
               
               
                   BS_ID 
                 48 
                 BS Identifier 
               
               
                   Scanning result 
                 8 
                 This field contains the 
               
               
                   
                   
                 scanning result 
               
               
                   
                   
                 corresponding to Report 
               
               
                   
                   
                 metric (CINR/RSSI/Relative 
               
               
                   
                   
                 delay/RTD/etc. 
               
               
                  } 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 3, the MOB_SCN-REP message has a plurality of IEs. The IEs include “Management Message Type” identifying the type of the transmitted message, “Report mode” indicating a mode in which the MSS reports the scanning result, “Report metric” indicating the type of information reported as a scanning result, “BS_ID” identifying a scanned BS, and “Scanning result” indicating the scanning result for the BS. “Scanning result” is included in the MOB_SCN-REP message according to the presence or absence of information to be reported. The scanning result may be CINR, RSSI, relative delay, or RTD. 
     In the typical IEEE 802.16e communication system, since signaling transmission/reception is carried out between a fixed BS and an MSS via a direct link, as shown in  FIG. 2 , 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 configured with flexibility. As a result, it is difficult to provide an efficient communication service in a radio environment with a fluctuating traffic distribution or a significant change in the number of calls. 
     To overcome the above shortcoming, a multi-hop relay data transmission scheme can be implemented through fixed Relay Stations (RSs), 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 may adaptively reconfigure a network quickly according to a communication environment change and efficiently operate the entire wireless network. Such a multi-hop relay wireless communication system also extends a cell service area and increases system capacity. In the case of a bad 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 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 bad channel state, a high-speed data channel can be provided and the cell service area can be expanded. 
       FIG. 3  shows a multi-hop relay wireless communication system which includes a BS  310 , a plurality of MSSs  311 ,  313 ,  331  and  333 , and an RS  320  for providing a multi-hop relay path between the BS  310  and an MSS. Signals are transmitted and received among the BS  310 , the RS  320 , and the MSSs  311 ,  313 ,  331  and  333  in OFDM/OFDMA. The BS  310  manages a cell  300 , and the MSSs  311  and  333  within the coverage area of the cell  300  and the RS  320  can communicate directly with the BS  310 . Yet, the MSSs  331  and  333  in an area outside the cell  300  cannot communicate directly with the BS  310 . Thus, the RS  320  covers the area  330  and relays signals between the BS  310  and the MSSs  331  and  333 . In this way, the MSSs  331  and  333  can send/receive a signal to/from the BS  310  via the relay  320 . 
     As described above, in the multi-hop relay wireless communication system using an RS, an MSS can communicate with a BS via the RS or by a direct link. Therefore, services and functions available in legacy wireless communication systems must also be provided in the multi-hop relay wireless communication system. 
     Since the communication of the MSS is expanded to the BS and the RS in a multi-hop relay BWA communication system, the MSS must scan neighbor RSs as well as neighbor BSs, for active communications. Legacy systems give no considerations to the multi-hop relay scheme and thus there is no specified scanning method involving an RS. Accordingly, there exists a need for defining a signal procedure for scanning in an MSS in the multi-hop relay BWA communication system. 
     SUMMARY OF THE INVENTION 
     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 for transmitting and receiving signals for scanning via an RS in an MSS in a multi-hop relay BWA communication system. 
     Another object of the present invention is to provide an apparatus and method for transmitting and receiving necessary signals between an RS and a BS to support scanning in an MSS in a multi-hop relay BWA communication system. 
     The above objects are achieved by providing a scanning apparatus and method in a multi-hop relay BWA communication system. 
     According to one aspect of the present invention, in a communication method in an RS in a multi-hop relay cellular communication system, the RS transmits a scan request message received from an MSS to a BS. The RS then transmits a scan response message received from the BS to the MSS. The scan response message contains information for scanning the MSS. 
     According to another aspect of the present invention, in a communication method in an RS in a multi-hop relay cellular communication system, the RS determines, upon receipt of a scan request message from an MSS, a scanning schedule for the MSS based on information included in the scan request message and transmits a scan response message containing the determined scanning schedule information to the MSS. 
     According to a further aspect of the present invention, in a scanning method in a multi-hop relay cellular communication system, an MSS transmits a scan request message requesting scanning to a BS via an RS. The BS transmits a scan response message containing information for scanning of the MSS to the MSS via the RS. The BS transmits a scan notify message indicating the scanning of the MSS to the RS. 
     According to still another aspect of the present invention, in a scanning method in a multi-hop relay cellular communication system, an MSS transmits a scan request message requesting scanning to an RS. The RS transmits a scan response message containing information for scanning of the MSS to the MSS. The RS transmits a scan notify message indicating the scanning of the MSS to the BS. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  illustrates the configuration of a typical IEEE 802.16e communication system; 
         FIG. 2  is a diagram illustrating a signal flow between an MSS and a BS, for scanning in a conventional BWA communication system; 
         FIG. 3  illustrates the configuration of a multi-hop relay wireless communication system according to the present invention; 
         FIG. 4  is a diagram illustrating a signal flow among an MSS, an RS and a BS, for scanning in the multi-hop relay BWA communication system according to the present invention; 
         FIG. 5  is a flowchart illustrating an RS operation in the multi-hop relay BWA communication system according the present invention; 
         FIG. 6  is a flowchart illustrating a BS operation in the multi-hop relay BWA communication system according to the present invention; 
         FIG. 7  is a diagram illustrating a signal flow among the MSS, the RS and the BS, for scanning in the multi-hop relay BWA communication system according to the present invention; 
         FIG. 8  is a flowchart illustrating an RS operation in the multi-hop relay BWA communication system according to the present invention; 
         FIG. 9  is a flowchart illustrating a BS operation in the multi-hop relay BWA communication system according to the present invention; 
         FIG. 10  is a diagram illustrating a signal flow among the MSS, the RS and the BS, for scanning in the multi-hop relay BWA communication system according to the present invention; 
         FIG. 11  is a diagram illustrating a signal flow among the MSS, the RS and the BS, for scanning in the multi-hop relay BWA communication system according to the present invention; 
         FIG. 12  is a flowchart illustrating an RS operation in the multi-hop relay BWA communication system according to the present invention; 
         FIG. 13  is a flowchart illustrating a BS operation in the multi-hop relay BWA communication system according to the present invention; 
         FIG. 14  is a flowchart illustrating a scanning operation in the MSS in the multi-hop relay BWA communication system according to the present invention; and 
         FIG. 15  is a block diagram of the MSS (the RS or the BS) according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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 since they would obscure the invention in unnecessary detail. 
     The present invention provides a signaling procedure for scanning neighbor BSs including a serving BS and neighbor RSs including a serving RS in an MSS in a multi-hop relay BWA communication system. 
     The multi-hop relay BWA communication system operates in OFDM or OFDMA. Hence, a physical channel signal is sent on a plurality of subcarriers, thereby enabling high-speed data transmission. Also, the multi-hop relay BWA communication system supports the mobility of MSSs by adopting a multi-cell structure. 
     An RS is a fixed or mobile node, or a particular system installed by the BS or a general SS. Any node having the above feature can be chosen as an RS according to a pre-defined rule for expansion of the cell area of a BS through a relay capabilities negotiation procedure with the BS. 
     While the following description is made in the context of a BWA communication system, it is to be clearly understood that the present invention is applicable to any cellular communication system as far as it uses a multi-hop relay scheme. 
       FIG. 4  shows a signal flow among an MSS, an RS and a BS, for scanning in the multi-hop relay BWA communication system according to the present invention. 
     Referring to  FIG. 4 , an MSS  410  communicates with an RS  440  in step  411  and the RS  440  communicates with a BS  450  in step  413 . In this way, the MSS  410  communicates with the BS  450  not directly but by signals relayed by the RS  440 . 
     When determining whether scanning should be performed during the communication with the RS  440 , the MSS  410  sends a MOB_SCN-REQ message to the RS  440 , requesting scanning of pilot channel signals from neighbor BSs including the serving BS  450  and neighbor RSs including the serving RS  440  in step  415 . The MOB_SCN-REQ message has the following configuration illustrated in Table 4 below. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Syntax 
                 Size (bits) 
                 Notes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 MOB_SCN-REQ_format( ) { 
                   
                   
               
               
                  Management Message Type=54 
                 8 
                 — 
               
               
                  Scan duration 
                 8 
                 Units are frames 
               
               
                  Interleaving interval 
                 8 
                 Units are frames 
               
               
                  Scan iteration 
                 8 
                 In frames 
               
               
                  N_Recommended 
                 8 
                 Number of neighboring 
               
               
                   
                   
                 RSs BSs to be scanned 
               
               
                  For (i=0; i&lt;N_Recommended; 
               
               
                 i++) { 
               
               
                   Recommended Node_ID 
                 48 
                 BS Identifier or RS 
               
               
                   
                   
                 Identifier 
               
               
                  } 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 4, the MOB_SCN-REQ message has a plurality of IEs. The IEs include “Management Message Type” identifying the type of the transmitted message, “Scan duration” indicating a desired scan duration during which pilot signals from the neighbor BSs and the neighbor RSs are scanned, “Scan iteration” indicating the number of iterative scannings in the case of periodic scanning, “Interleaving interval” indicating the time interval between scannings in the case of iterative scanning, and “Recommended Node_ID” identifying a desired BS or an RS to be scanned. The time when the MSS  410  requests scanning is beyond the scope of the present invention and thus its detailed description is not provided herein. 
     Upon receipt of the MOB_SCN-REQ message, the RS  440  relays it to the BS  450  in step  417 . In step  419 , the BS  450  replies to the RS  440  with a MOB_SCN-RSP message containing scanning information for the MSS  410  and a scan duration set to non-zero. 
     The MOB_SCN-RSP message has the following structure. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Syntax 
                 (bits) 
                 Notes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 MOB_SCN-RSP_format( ) { 
                   
                   
               
               
                  Management Message Type=55 
                 8 
                 — 
               
               
                  Scan duration 
                 8 
                 Units are frames. When 
               
               
                   
                   
                 Scan duration is set to zero, 
               
               
                   
                   
                 no scanning parameters are 
               
               
                   
                   
                 specified in the message. 
               
               
                   
                   
                 When MOB_SCN-RSP is 
               
               
                   
                   
                 sent in response to 
               
               
                   
                   
                 MOB_SCN-REQ, setting 
               
               
                   
                   
                 Scan duration to zero denies 
               
               
                   
                   
                 MOB_SCN-REQ. 
               
               
                  Report mode 
                 2 
                 0b00: no report 
               
               
                   
                   
                 0b01: periodic report 
               
               
                   
                   
                 0b10: event triggered report 
               
               
                   
                   
                 0b11: reserved; shall be set 
               
               
                   
                   
                 to zero 
               
               
                  reserved 
                 6 
                 Shall be set to zero 
               
               
                  Report period 
                 8 
                 Available when the value of 
               
               
                   
                   
                 Report mode is set to 0b01. 
               
               
                   
                   
                 Report period in frames. 
               
               
                  Report metric 
                 8 
                 Bitmap indicating metrics on 
               
               
                   
                   
                 which the corresponding 
               
               
                   
                   
                 triggers are based: 
               
               
                   
                   
                 Bit 0: BS CINR mean 
               
               
                   
                   
                 Bit 1: BS RSSI mean 
               
               
                   
                   
                 Bit 2: Relative delay 
               
               
                   
                   
                 Bit 3: BS RTD 
               
               
                   
                   
                 Bit 4-7: reserved; shall be set 
               
               
                   
                   
                 to zero 
               
               
                  If (Scan duration!=0) { 
               
               
                   Start frame 
                 4 
                 — 
               
               
                   reserved 
                 4 
                 Shall be set to zero 
               
               
                   Interleaving interval 
                 8 
                 Duration in frames 
               
               
                   Scan iteration 
                 8 
                 — 
               
               
                   N_Recommended 
                 8 
                 Number of neighboring BSs 
               
               
                   
                   
                 or RSs to be scanned 
               
               
                   for (i=0; i&lt;N_Recommended; 
               
               
                   i++) { 
               
               
                   Recommended Node_ID 
                 48 
                 BS Identifier or RS Identifier 
               
               
                   } 
               
               
                  } 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 5, the MOB_SCN-RSP message has a plurality of IEs. The IEs include “Management Message Type” identifying the type of the transmitted message, “Scan duration” indicating a scan duration during which the MSS is to scan, “Report mode”, “Report period” used when the report mode is a periodic report, “Report metric” indicating the type of information to be reported as a scanning result, “Start frame” indicating the start of the scanning, “Scan iteration” indicating the number of iterative scannings in the case of periodic scanning, “Interleaving interval” indicating the time interval between scannings in the case of iterative scanning, and “Recommended Node_ID” identifying a BS or an RS to be scanned. If “Scan duration” is 0, it implies that the scanning request from the MSS is rejected. Information reported as a scanning result may be CINR, RSSI, relative delay, or RTD. 
     Upon receipt of the MOB_SCN-RSP message containing the scanning information, the RS  440  relays it to the MSS  410  in step  421 . The MSS  410  then scans pilot channel signals from the neighbor BSs and the neighbor RSs in correspondence with the parameters included in the MOB_SCN-RSP message in step  423 . 
     Meanwhile, the BS  450  discontinues data transmission to the MSS  410  during the scanning in step  425 . At the same time, the BS  450  may buffer data destined for the MSS  410 . 
     After the pilot scanning, the MSS  410  sends a MOB_SCN-REP message containing the scanning result to the RS  440  in step  427 . 
     The MOB_SCN-REP message is configured in the following structure. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Syntax 
                 (bits) 
                 Notes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 MOB_SCN-REP_format( ) { 
                   
                   
               
               
                  Management Message Type=60 
                 8 
                 — 
               
               
                  Report mode 
                 1 
                 0: Event triggered report 
               
               
                   
                   
                 1: Periodic report 
               
               
                  Reserved 
                 7 
                 Shall be set to zero 
               
               
                  Report metric 
                 8 
                 Bitmap indicating presence 
               
               
                   
                   
                 of certain metrics: 
               
               
                   
                   
                 Bit 0: BS CINR mean 
               
               
                   
                   
                 Bit 1: BS RSSI mean 
               
               
                   
                   
                 Bit 2: Relative delay 
               
               
                   
                   
                 Bit 3: BS RTD 
               
               
                   
                   
                 Bit 4-7: reserved; shall be set 
               
               
                   
                   
                 to zero 
               
               
                  N_Node 
                 8 
                 Number of BSs or RSs to be 
               
               
                   
                   
                 scanned 
               
               
                  for (i=0; i&lt;N_Node; i++) { 
               
               
                   Node_ID 
                 48 
                 BS Identifier or RS Identifier 
               
               
                   Scanning result 
                 8 
                 This field contains the 
               
               
                   
                   
                 scanning result 
               
               
                   
                   
                 corresponding to Report 
               
               
                   
                   
                 metric (CINR/RSSI/Relative 
               
               
                   
                   
                 delay/RTD/etc. 
               
               
                  } 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 6, the MOB_SCN-REP message has a plurality of IEs. The IEs include “Management Message Type” identifying the type of the transmitted message, “Report mode” indicating a mode in which the MSS reports the scanning result, “Report metric” indicating the type of information reported as a scanning result, “Node_ID” identifying a scanned node, and “Scanning result” indicating the scanning result for the node. The scanning result may be CINR, RSSI, relative delay, or RTD according to the value of “Report metric”. 
     Meanwhile, the RS  440  relays the MOB_SCN-REP message to the BS  450  in step  429 . In step  431 , the BS  450  recognizes the scanning completion of the MSS  410  and sends the buffered data to the MSS  410 . 
     If the MSS  410  completes the scanning earlier than scheduled in step  415  through step  421  and sends uplink data, the RS  440  and the BS  450  recognize the scanning completion by receiving the uplink data. 
     In  FIG. 4 , it is assumed that the RS  440  can acquire knowledge of the scanning operation of the MSS  410  and the scanning result from the scanning control messages illustrated in Table 4, Table 5 and Table 6 exchanged between the MSS  410  and the BS  450 . 
     The operations of the RS and the BS in the procedure illustrated in  FIG. 4  are further described below. 
       FIG. 5  shows the RS operation in the multi-hop relay BWA communication system according to the present invention. 
     The RS  440  receives the MOB_SCN-REQ message requesting scanning from the MSS  410  in step  511  and relays the MOB_SCN-REQ message to the BS  450  in step  513 . The RS  440  receives the MOB_SCN-RSP message for the MOB_SCN-REQ message from the BS  450  in step  515  and relays it to the MSS  410  in step  517 . Since the RS  440  can read the MOB_SCN-REQ message and the MOB_SCN-RSP message exchanged between the MSS  410  and the BS  450 , it acquires information indicating whether the scanning will be performed and scanning schedule information. 
     Unless the MOB_SCN-RSP message contains information indicating the scanning is rejected, that is, the MSS  410  will perform scanning, the RS  440  is placed in an idle state in step  519 . The RS  440  then receives the MOB_SCN-REP message reporting the scanning result or uplink data from the MSS  410  in step  521 , thus recognizing completion of the MSS scanning. In step  523 , the RS  440  relays the MOB_SCN-REP message or the uplink data to the BS  450 . 
     If the MOB_SCN-RSP message contains information indicating the scanning is rejected, the RS  440  continues communications between the MSS  410  and the BS  450 , determining that the scanning has been denied. 
       FIG. 6  shows the BS operation in the multi-hop relay BWA communication system according to the present invention. 
     The BS  450  acquires scanning request information of the MSS  410  by receiving the MOB_SCN-REQ message from the RS  440  in step  611  and schedules a scanning for the MSS  410  based on the scanning request information in step  613 . 
     In step  615 , the BS  450  sends the MOB_SCN-RSP message containing scanning schedule information. When the scanning request from the MSS  410  is accepted as in this case, the BS  450  is placed in an idle state in step  617 . If the BS  450  rejects the scanning request, it continues to communicate with the MSS  410  via the RS  440 . 
     In step  619 , the BS  450  monitors reception of the MOB_SCN-REP message or uplink data of the MSS  410  from the RS  440  in the idle state. Upon receipt of the MOB_SCN-REP message or uplink data, the BS  450  resumes communications with the MSS  410 , determining that the scanning is completed and acquiring the scan result. 
     As shown in  FIGS. 4 ,  5  and  6 , the RS can interpret the scanning control messages exchanged between the MSS and the BS. 
     As described below, the RS may also not be able to interpret control messages between the MSS and the BS. Hence, the BS may notify the RS of information about a scanning operation and a scanning result of the MSS by separate signaling. 
       FIG. 7  shows a signal flow among the MSS, the RS and the BS, for scanning in the multi-hop relay BWA communication system according to the present invention. 
     An MSS  710  communicates with an RS  740  in step  711  and the RS  740  communicates with a BS  750  in step  713 . In this way, the MSS  710  communicates with the BS  750  not directly but by signals relayed by the RS  740 . 
     When determining whether scanning should be performed during the communication with the RS  740 , the MSS  710  sends a MOB_SCN-REQ message having the configuration illustrated in Table 4 to the RS  740 , requesting scanning of pilot channel signals from neighbor BSs including the serving BS  750  and neighbor RSs including the serving RS  740  in step  715 . Upon receipt of the MOB_SCN-REQ message, the RS  740  relays it to the BS  750  in step  717 . In step  719 , the BS  450  replies to the RS  740  with a MOB_SCN-RSP message illustrated in Table 5 containing scanning information for the MSS  710  and a scan duration set to non-zero. Upon receipt of the MOB_SCN-RSP message containing the scanning information, the RS  740  relays it to the MSS  710  in step  721 . 
     After sending the MOB_SCN-RSP message accepting the scanning request of the MSS  710 , the BS  750  sends a SCAN-NOTIFY message to the RS  740 , indicating that the MS  710  will scan. 
     The SCAN-NOTIFY message has the following configuration. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 Syntax 
                 Notes 
               
               
                   
                   
               
             
             
               
                   
                 SCAN-NOTIFY_format( ) { 
                   
               
               
                   
                  MS ID 
                 MS&#39;s identifier 
               
               
                   
                  Scan duration 
                 Units are frames. Time 
               
               
                   
                   
                 duration when MS performs 
               
               
                   
                   
                 scanning 
               
               
                   
                  Start frame 
                 First scanning interval start 
               
               
                   
                   
                 time 
               
               
                   
                  Interleaving interval 
                 Duration in frames 
               
               
                   
                   
                 The period interleaved 
               
               
                   
                   
                 between scanning intervals 
               
               
                   
                   
                 when MS shall perform 
               
               
                   
                   
                 normal operation 
               
               
                   
                  Scanning iteration 
                 The number of iterating 
               
               
                   
                   
                 scanning interval 
               
               
                   
                 } 
               
               
                   
                   
               
             
          
         
       
     
     Referring to Table 7, the SCAN-NOTIFY message has a plurality of IEs. The IEs include “MS ID” identifying the MSS that will scan, “Scan duration” indicating a time period for which the MSS will scan, “Start frame” indicating the start of the scanning, “Scan iteration” indicating the number of iterative scannings in the case of periodic scanning, and “Interleaving interval” indicating the time interval between scannings. 
     Meanwhile, upon receipt of the MOB_SCN-RSP message, the MSS  710  scans pilot channel signals from the neighbor BSs and the neighbor RSs in correspondence with the parameters included in the MOB_SCN-RSP message in step  725 . The BS  750  discontinues data transmission to the MSS  710  during the scanning in step  727 . At the same time, the BS  750  may buffer data destined for the MSS  710 . 
     After the pilot scanning, the MSS  710  sends a MOB_SCN-REP message containing the scanning result to the RS  740  in step  729 . The RS  740  relays the MOB_SCN-REP message to the BS  750  in step  731 . The BS  750  recognizes the scanning completion of the MSS  710  by the MOB_SCN-REP message and sends a SCAN-RESULT message result to the RS  740  to notify the scanning completion and the scanning result in step  733 . 
     The SCAN-RESULT message is configured as illustrated in Table 8 below. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                 Syntax 
                 Notes 
               
               
                   
                   
               
             
             
               
                   
                 SCAN-RESULT_format( ) { 
                   
               
               
                   
                  MS ID 
                 MS&#39;s identifier 
               
               
                   
                  Report metric 
                 Bitmap indicating presence 
               
               
                   
                   
                 of certain metrics: 
               
               
                   
                   
                 Bit 0: no scan result 
               
               
                   
                   
                 Bit 1: CINR mean 
               
               
                   
                   
                 Bit 2: RSSI mean 
               
               
                   
                   
                 Bit 3: Relative delay 
               
               
                   
                   
                 Bit 4-: RTD 
               
               
                   
                   
                 Bit 5-: reserved, shall be set 
               
               
                   
                   
                 to zero 
               
               
                   
                   
                 Note) Bit 0 = 1 indicates that 
               
               
                   
                   
                 this message does not 
               
               
                   
                   
                 contain MS&#39;s scanning 
               
               
                   
                   
                 result. When Bit 0 is set to 
               
               
                   
                   
                 1, the remaining bits in this 
               
               
                   
                   
                 field shall be set to 0. Also, 
               
               
                   
                   
                 the remaining field in this 
               
               
                   
                   
                 message shall be discarded. 
               
               
                   
                  N_Node 
                 Number of RSs or BSs to be 
               
               
                   
                   
                 scanned 
               
               
                   
                  for (i=0; i&lt;N_Node; i++) { 
               
               
                   
                   Node_ID 
                 BS Identifier or RS identifier 
               
               
                   
                   Scanning result 
                 This field contains the 
               
               
                   
                   
                 scanning result 
               
               
                   
                   
                 corresponding to Report 
               
               
                   
                   
                 metric (CINR/RSSI/Relative 
               
               
                   
                   
                 delay/RTD/etc.) 
               
               
                   
                  } 
               
               
                   
                   
               
             
          
         
       
     
     Referring to Table 8, the SCAN-RESULT message has a plurality of IEs. The IEs include “MS ID” identifying the MSS that has completed the scanning, “Report metric” indicating whether the scanning result of the MSS is included and indicating the type of information reported as the scanning result, “Node_ID” identifying a node that the MSS has scanned, and “Scanning result” indicating the scanning result for the node. The scanning result may be CINR, RSSI, relative delay or RTD depending on Report metric. 
     In step  735 , the BS  750  sends data which was buffered for the MSS  710  during the scanning. 
     If the MSS  710  completes the scanning earlier than scheduled in step  715  through step  721  and sends uplink data, the BS  750  recognizes the scanning completion by receiving the uplink data. Then the BS  750  notifies the RS  740  of the completed scanning by sending the SCAN-RESULT message. 
     The operations of the RS and the BS shown in  FIG. 7  are further described below. 
       FIG. 8  shows another RS operation in the multi-hop relay BWA communication system according to the present invention. 
     Referring to  FIG. 8 , the RS  740  receives the MOB_SCN-REQ message requesting scanning from the MSS  710  in step  811  and relays the MOB_SCN-REQ message to the BS  750  in step  813 . The RS  740  receives the MOB_SCN-RSP message for the MOB_SCN-REQ message from the BS  750  in step  815  and relays it to the MSS  710  in step  817 . Since the RS  440  cannot interpret the MOB_SCN-REQ message and the MOB_SCN-RSP message exchanged between the MSS  710  and the BS  750 , it cannot determine whether the scanning will be performed. 
     In step  819 , therefore, the RS  740  monitors reception of the SCAN-NOTIFY message indicating that the MSS  710  will scan from the BS  750 . If the SCAN-NOTIFY message is not received, the RS  740  continues to relay data between the MSS  710  and the BS  750  in step  821 . Upon receipt of the SCAN-NOTIFY message, the RS  740  recognizes that the MSS  710  will scan as scheduled and is placed into an idle state in step  823 . 
     The RS  740  then receives the MOB_SCN-REP message reporting the scanning result or uplink data from the MSS  710  in step  825  and relays the MOB_SCN-REP message or the uplink data to the BS  750  in step  827 . Since the RS  740  cannot interpret messages exchanged between the MSS  710  and the BS  750 , it cannot recognize the scanning completion. 
     Hence, the RS  740  receives the SCAN-RESULT message containing information indicating the completed scanning and the scanning result from the BS  750 , thus recognizing the scanning has been completed in step  829 . 
       FIG. 9  shows the BS operation in the multi-hop relay BWA communication system according to the present invention. 
     The BS  750  acquires scanning request information of the MSS  710  by receiving the MOB_SCN-REQ message from the RS  740  in step  911  and schedules a scanning for the MSS  710  based on the scanning request information in step  913 . 
     In step  915 , the BS  750  determines whether to accept the scanning request from the MSS  710 . If the scanning result is rejected, the BS  750  sends the MOB_SCN-RSP message containing information indicating that the scanning request has been denied to the RS  740  in step  917 . 
     When the scanning request from the MSS  710  is accepted, the BS  750  sends the MOB_SCN-RSP message containing scanning schedule information for the MSS  710  to the RS  740  in step  919 . Since the RS  740  cannot interpret the MOB_SCN-RSP message, a message indicating that the MSS  710  will scan needs to be sent to the RS  740 . 
     Thus, the BS  750  sends the SCAN-NOTIFY message indicating that the MSS  710  will scan to the RS  740  in step  921  and is placed in an idle state in step  923 . At the same time, the BS  750  may discontinue data transmission to the MSS  710 , while buffering data for the MSS  710 . 
     In step  925 , the BS  750  monitors reception of the MOB_SCN-REP message or uplink data of the MSS  710  from the RS  740  in the idle state. Upon receipt of the MOB_SCN-REP message or uplink data, the BS  750  resumes communications with the MSS  710 , determining that the scanning is completed and acquiring the scanning result. 
     The BS  750  then sends the SCAN-RESULT message indicating the scanning completion and the scanning result of the MSS  710  to the RS  740 . 
     While MSS-initiated scanning by sending the MOB_SCN-REQ message from the MSSs  410  and  710  has been described above, BS-initiated scanning can also be achieved in a similar manner by sending the MOB_SCN-RSP message without receiving the MOB_SCN-REQ message by the BSs  450  and  750 . 
     In the case where the RS directly communicating with the MSS is able to control and schedule scanning at the MSS by processing the MOB_SCN-REQ message and the MOB_SCN-RSP message, there is no need for sending information for negotiating a scanning operation with the MSS to the BS which does not communicate directly with the MSS. This will be described in more detail. 
       FIG. 10  shows another signal flow among the MSS, the RS and the BS, for scanning in the multi-hop relay BWA communication system according to the present invention. 
     An MSS  1010  communicates with an RS  1040  in step  1011  and the RS  1040  communicates with a BS  1050  in step  1013 . In this way, the MSS  1010  communicates with the BS  1050  not directly but by signals relayed by the RS  1040 . 
     When determining whether scanning should be performed during the communication with the RS  1040 , the MSS  1010  sends a MOB_SCN-REQ message having the configuration illustrated in Table 4 to the RS  1040 , requesting scanning of pilot channel signals from neighbor BSs including the serving BS  1050  and neighbor RSs including the serving RS  1040  in step  1015 . 
     Upon receipt of the MOB_SCN-REQ message, the RS  1040  schedules scanning for the MSS  1010  and sends a MOB_SCN-RSP message containing scanning schedule information to the MSS  1010  in step  1017 . Specifically, the MOB_SCN-RSP message is formatted as illustrated in Table 5 and includes information for scanning at the MSS  1010  and a scan duration set to non-zero. It is assumed herein that the RS  1140  acquires knowledge of neighbor BSs and neighbor RSs from a neighbor BS list broadcast by the BS  1150 . Upon receipt of the MOB_SCN-RSP message, the MSS  1010  scans pilot channel signals from the neighbor BSs and the neighbor RSs in correspondence with the parameters included in the MOB_SCN-RSP message in step  1019 . 
     Meanwhile, the RS  1040  discontinues data transmission to the MSS  1010  during the scanning in step  1021 . At the same time, the RS  10410  may buffer data destined for the MSS  1010 . To block data transmission from the BS  1050  to the MSS  1010 , the RS  1040  sends a Mobile Scanning Inform (MOB_SCN-INF) message to the BS  1050 , thus notifying that the MSS  1010  will scan in step  1023 . 
     The MOB_SCN-INF message has the following configuration. 
     
       
         
               
               
             
           
               
                 TABLE 9 
               
               
                   
               
               
                 Syntax 
                 Notes 
               
               
                   
               
             
             
               
                 MOB_SCN-INF_format ( ) { 
                   
               
               
                  Management Message Type=TBD 
                 To be determined 
               
               
                  N_MS 
                 Number of MSSs to perform 
               
               
                   
                 scanning 
               
               
                  for (i=0; i&lt;N_MS&lt; i++) { 
               
               
                   MSS ID 
                 Identifier of MSS 
               
               
                   Scan duration 
                 Duration (in units of frames) where 
               
               
                   
                 the MSS may perform scanning for 
               
               
                   
                 available BS/RS 
               
               
                   Start frame 
                 Measured from the frame in which 
               
               
                   
                 this message was received 
               
               
                   Interleaving interval 
               
               
                   Scan iteration 
               
               
                   reserved 
                 Shall be set to zero 
               
               
                  } 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 9, the MOB_SCN-INF message includes a plurality of IEs. The IEs contain “Management Message Type” identifying the type of the transmitted message, information about an MSS to perform scanning, and time-related parameters applied for the MSS to scan neighbor BSs and neighbor RSs. Since one or more MSSs can scan at the same time, information about these MSSs may be included in one MOB_SCN-INF message. The time-related parameters are “Scan duration” indicating a duration for which the MSS will scan, “Start frame” indicating the start of the scanning, “Scan iteration” indicating the number of iterative scannings in the case of periodic scanning, “Interleaving interval” indicating a time interval between scannings in the case of iterative scanning. In another case, the MOB_SCN-INF message may not contain the time-related parameters, or it may contain additional information besides the time-related parameters or part of the time-related parameters. The operation of the system according to the time-related parameters set in the MOB_SCN-INF message is beyond the cope of the present invention and will not be described. 
     Meanwhile, upon receipt of the MOB_SCN-INF message, the BS  1050  replies to the RS  1040  with a Mobile Scanning Inform Acknowledgement (MOB_SCN-INFACK) message indicating the reception of the MOB_SCN-INF message in step  1025 . 
     The MOB_SCN-INFACK message is configured as illustrated in Table 10 below. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 10 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Syntax 
                 (bits) 
                 Notes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 MOB_SCN-INFACK_format ( ) 
                   
                   
               
               
                 { 
               
               
                  Management Message 
                 8 
                 To be determined 
               
               
                 Type=TBD 
               
               
                  N_MS 
                 8 
                 Number of MSSs to perform 
               
               
                   
                   
                 scanning 
               
               
                  for (i=0; i&lt;N_MS&lt; i++) { 
               
               
                   MSS ID 
                 48 
                 Identifier of MSS 
               
               
                  } 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 10, the MOB_SCN-INFACK message includes a plurality of IEs. The IEs contain “Management Message Type” identifying the type of the transmitted message and the MSS information set in the MOB_SCN-INF message. 
     Meanwhile, the BS  1050  which has recognizes the MSS  1010  will scan discontinues data transmission to the MSS  1010 , buffering data for the MSS  1010 . The MSS  1010  scans pilot channel signals from the neighbor BSs and the neighbor RSs and sends a MOB_SCN-REP message containing the result of the scanning to the RS  1040  in step  1029 . 
     The RS  1040  relays the MOB_SCN-REP message to the BS  1050  in step  1031 . The message reporting the scanning result of the MSS  1010  sent from the RS  1040  to the BS  1050  is configured in a message format for transmission between the RS  1040  and the BS  1050 . For example, the message may contain the contents of the MOB_SCN-REP message illustrated in Table 6, or it can be the SCAN-RESULT message illustrated in Table 8. 
     The RS  1040  sends the data buffered during the scanning to the MSS  1010  in step  1033 . Meanwhile, upon receipt of the MOB_SCN-REP message, the BS  1050  recognizes the scanning completion of the MSS  1010  by the MOB_SCN-REP message and sends the data buffered for the MSS  1010  during the scanning in step  1035 . 
     If the MSS  1010  completes the scanning earlier than scheduled in step  715  through step  721 , it can resume communications by sending uplink data. In this case, the RS  1040  can recognize the scanning completion by receiving the uplink data from the MSS  1010 . The RS  1040  relays the uplink data to the BS  1050  which thus recognizes that the scanning has been completed. 
     While MSS-initiated scanning by sending the MOB_SCN-REQ message from the MSS  1010  has been described above, the third embodiment is also applicable in the same manner for BS-initiated scanning by sending the MOB_SCN-RSP message to the MSS  1010  without receiving the MOB_SCN-REQ message by the BS  1050  or for RS-initiated scanning by sending the MOB_SCN-RSP message to the MSS  1010  without receiving the MOB_SCN-REQ message by the RS  1040 . 
     In the case where the MSS does not report the scanning result after completing the scanning, the BS does not know the completed scanning. Therefore, the RS needs to notify the BS of the scanning completion. This will be described in more detail. 
       FIG. 11  shows another signal flow among the MSS, the RS and the BS, for scanning in the multi-hop relay BWA communication system according to the present invention. 
     An MSS  1110  communicates with an RS  1140  in step  1111  and the RS  1140  communicates with a BS  1150  in step  1113 . In this way, the MSS  1110  communicates with the BS  1150  not directly but by signals relayed by the RS  1140 . 
     When determining whether scanning should be performed during the communication with the RS  1140 , the MSS  1110  sends a MOB_SCN-REQ message having the configuration illustrated in Table 4 to the RS  1140 , requesting scanning of pilot channel signals from neighbor BSs including the serving BS  1150  and neighbor RSs including the serving RS  1140  in step  1115 . 
     Upon receipt of the MOB_SCN-REQ message, the RS  1140  replies to the MSS  1110  with a MOB_SCN-RSP message illustrated in Table 5 containing scanning information for the MSS  1110  and a scan duration set to non-zero. Upon receipt of the MOB_SCN-RSP message containing the scanning information, the MSS  1110  scans pilot channel signals from the neighbor BSs and the neighbor RSs in correspondence with the parameters included in the MOB_SCN-RSP message in step  1119 . 
     The RS  1140  discontinues data transmission to the MSS  1110  during the scanning in step  1121 . At the same time, the RS  1150  may buffer data destined for the MS  1110 . 
     To block data transmission from the BS  1150  to the MSS  1110 , the RS  1140  sends a MOB_SCN-INF message illustrated in Table 9 to the BS  1150  in step  1123 . Upon receipt of the MOB_SCN-INF message, the BS  1150  recognizes that the MSS  1010  will scan and replies to the RS  1140  with a MOB_SCN-INFACK message indicating the reception of the MOB_SCN-INF message in step  1125 . In step  1127 , the BS  1150  discontinues data transmission to the MSS  1110  during the scanning and buffers data for the MSS  1110 . 
     The MSS  1110  scans pilot channel signals from the neighbor BSs and the neighbor RSs and determines whether to report the scanning result. If determining that it will not report the scanning result, the MSS  1110  immediately resumes communications with the RS  1140  in step  1129 . The communication resumption may involve a periodic ranging procedure or an uplink bandwidth request procedure. These procedures have no direct relation to the subject matter of the present invention and thus they will not be described herein. 
     If the MSS  1110  resumes communications with the RS  1140  without sending a MOB_SCN-REP message, the RS  1140  recognizes that the scanning has been completed and sends a Mobile Scanning Finish (MOB_SCN-FIN) message to the BS  1150  to notify the completed scanning in step  1131 . In step  1133 , the RS  1140  sends the buffered data to the MSS  1110 . 
     The MOB_SCN-FIN message has the following configuration. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 11 
               
               
                   
                   
               
               
                   
                 Syntax 
                 Notes 
               
               
                   
                   
               
             
             
               
                   
                 MOB_SCN-FIN_format ( ) { 
                   
               
               
                   
                  Management Message Type=TBD 
                 To be determined 
               
               
                   
                  N_MS 
                 Number of MSSs to finish 
               
               
                   
                   
                 scanning operation 
               
               
                   
                  for (i=0; i&lt;N_MS&lt; i++) { 
               
               
                   
                   MSS ID 
                 Identifier of MSS 
               
               
                   
                  } 
               
               
                   
                 } 
               
               
                   
                   
               
             
          
         
       
     
     Referring to Table 11, the MOB_SCN-FIN message includes a plurality of IEs. The IEs contain “Management Message Type” identifying the type of the transmitted message and information about an MSS which has finished scanning. The MOB_SCN-FIN message may contain information about a plurality of MSSs that have finished scanning. 
     Upon receipt of the MOB_SCN-FIN message, the BS  1150  recognizes that the MSS  110  has completed the scanning and sends the buffered data to the MSS  1110  in step  1135 . 
     It is clear that the SCAN-RESULT message having the configuration illustrated in Table 8 can be sent instead of the MOB_SCN-FIN message illustrated in Table 11 as a message transmitted/received between the RS and the BS to notify the completed scanning of the MSS. 
     While MSS-initiated scanning by sending the MOB_SCN-REQ message from the MSSs  1010  and  1110  has been described above, RS-initiated scanning can also be achieved by sending the MOB_SCN-RSP message to the MSS  1010  without receiving the MOB_SCN-REQ message by the RSs  1040  and  1140 , in the same manner except for step  1115  illustrated in  FIG. 11 . 
     The operations of the RS and the BS in the procedures illustrated in  FIGS. 10 and 11  are further described below. 
       FIG. 12  shows another RS operation in the multi-hop relay BWA communication system according to the present invention. 
     The RS receives the MOB_SCN-REQ message requesting scanning from the MSS in step  1211  and replies to the MSS with the MOB_SCN-RSP message containing scanning information in step  1213 . 
     During scanning in the MSS, the RS discontinues data transmission to the MSS, buffering data for the MSS. In step  1215 , the RS sends the MOB_SCN-INF message to the serving BS, notifying that the MSS will scan. 
     The RS monitors reception of the MOB_SCN-INFACK message from the BS within a predetermined time period in step  1217 . If the MOB_SCN-INFACK message is not received within the predetermined time period, the RS retransmits the MOB_SCN-INF message in step  1215 . The number of retransmissions allowed for the MOB_SCN-INF message and the predetermined time period can be set and changed by a system designer. 
     Upon receipt of the MOB_SCN-INFACK message within the predetermined time period, the RS performs a relay operation other than traffic transmission/reception to/from the MSS in step  1219 . After the MSS completes the scanning, the RS resumes communications with the MSS in step  1221 . 
     In step  1223 , the RS monitors reception of the MOB_SCN-REP message containing the result of the scanning from the MSS. Upon receipt of the MOB_SCN-REP message, the RS relays it to the BS in step  1225 . If the MOB_SCN-REP message is not received within a predetermined time period, the RS sends the MOB_SCN-FIN message to the BS, notifying that the scanning has been completed in step  1227 . 
     Meanwhile, the RS may send the SCAN-RESULT message illustrated in Table 8 to the BS in order to notify the BS of the scanning result in step  1225  or the completed scanning in step  1227 . If the RS receives uplink data instead of the MOB_SCN-REP message from the MSS in step  1223 , it can relay the uplink data to the BS without sending a control message indicating the scanning completion. 
       FIG. 13  shows another BS operation in the multi-hop relay BWA communication system according to the present invention. 
     The BS receives the MOB_SCN-INF message indicating that scanning will be performed in at least one MSS from the RS in step  1311  and replies to the RS with the MOB_SCN-INFACK message in step  1313 . In step  1315 , the BS discontinues data transmission to the MSS, buffering data for the MSS. 
     During the buffering, the BS monitors reception of the MOB_SCN-REP message containing the result of the scanning from the RS. Upon receipt of the MOB_SCN-REP message, the BS recognizes that the scanning has been completed and sends the buffered data to the MSS in step  1321 . The MOB_SCN-REP message received in step  1317  can be replaced by the SCAN-RESULT message illustrated in Table 3 containing the scanning result. 
     If the MOB_SCN-REP message is not received, the BS monitors reception of the MOB_SCN-FIN message indicating completion of the scanning in step  1319 . If the MOB_SCN-FIN message is not received, the BS returns to step  1315 . Upon receipt of the MOB_SCN-FIN message, the BS sends the buffered data to the MSS in step  1321 . Obviously, the MOB_SCN-FIN message can be replaced by the SCAN-RESULT message illustrated in Table 3 indicating the scanning completion. Alternatively, the BS can recognize the completion of the scanning by receiving uplink data rather than receiving a control message indicating the completed scanning. 
       FIG. 14  shows a scanning operation in the MSS in the multi-hop relay BWA communication system according to the present invention. 
     When determining whether scanning should be performed, the MSS sends the MOB_SCN-REQ message requesting scanning to the serving RS in step  1411 . Upon receipt of the MOB_SCN-RSP message with a scan duration set to non-zero from the RS in step  1413 , the MSS scans neighbor BSs including the serving BS and neighbor RSs including the serving RS in correspondence with parameters included in the MOB_SCN-RSP message in step  1415 . 
     In step  1417 , the MS determines whether the scanning has been completed. If the scanning has been completed, the MSS resumes communications with the serving RS in step  1419 . For resuming communications, the MSS may send the MOB_SCN-REP message containing the scanning result to the RS or perform a predetermined communication procedure with the RS without transmitting the MOB_SCN-REP message. 
     Now a description will be made of the structures of the MSS, the RS and the BS. Since the MSS, the RS and the BS have identical interface modules (i.e. communication modules) and thus are configured in the same block structure, their operations will be described below with a single device. 
       FIG. 15  shows the MSS (the RS or the BS) according to the present invention. The following description is made mainly in the context of processing control messages. 
     An interface module  1521  is configured to communicate with the RS or the BS. It includes a Radio Frequency (RF) processor and a baseband processor. The RF processor downconverts a signal received through an antenna to a baseband signal and provides it to the baseband processor. It also upconverts a baseband signal received from the baseband processor to an RF signal for transmission in the air. For example, in the BWA system, the baseband processor acquires the original information data by Fast Fourier Transform (FFT)-processing and channel-decoding the signal received from the RF processor and provides the original information data to a controller  1519 . The baseband processor also channel-encodes and Inverse Fast Fourier Transform (IFFT)-processes data received from the controller  1519  and provides the IFFT signal to the RF processor. 
     The controller  1519  provides overall control to the MSS. For example, the controller  1519  processes and controls voice communication and data communication. In addition to the typical functionalities, the controller  1519  processes the scanning of the MSS. The controller  1519  provides a control message received from the RS to a message processor  1511 , and provides a transmission message for the RS received from the message generator  1513  to the interface module  1521 . 
     A storage  1517  stores programs for controlling the overall operations of the MSS and temporary data generated during execution of the programs. That is, the storage  1517  can store data and control information that the MSS will send to the RS. 
     The message processor  1511  disassembles a control message received from the RS and notifies the controller  1519  of the disassembly result. According to the present invention, upon receipt of the MOB_SCN-RSP message having the configuration illustrated in Table 5, the message processor  1511  extracts control information from the MOB_SCN-RSP message and provides the control information to the controller  1519 . The controller  1519  then controls a scanning processor  1515  based on the control information. 
     The scanning processor  1515  scans neighbor BSs and neighbor RSs in correspondence with parameters set in the MOB_SCN-RSP message under the control of the controller  1519  and collects scanning results. The controller  1519  provides the scanning results to a message generator  1513 . 
     The message generator  1513  generates the MOB_SCN-REQ message illustrated in Table 4 or the MOB_SCN-REP message illustrated in table  6  containing the scanning results for transmission to the RS under the control of the controller  1519 . The generated message is sent to the interface module  1521  via the controller  1519 . 
     In the above MSS&#39;s configuration, the controller  1519  controls the message processor  1511 , the message generator  1513 , and the scanning processor  1515 . In other words, the controller  1519  can perform the functions of the message processor  1511 , the message generator  1513 , and the scanning processor  1515 . While the message processor  1511 , the message generator  1513 , and the scanning processor  1515  are shown separately in  FIG. 15  for illustrative purposes, all or part of their functions may be incorporated into the controller  1519  in real implementation. 
     With reference to  FIG. 15 , the structure of the RS will be described. 
     The interface module  1521  is configured to communicate with the MSS or the BS. It includes the RF processor and the baseband processor. The RF processor downconverts a signal received through an antenna to a baseband signal and provides it to the baseband processor. It also upconverts a baseband signal received from the baseband processor to an RF signal for transmission in the air. For example, in the BWA system, the baseband processor acquires the original information data by FFT-processing and channel-decoding the signal received from the RF processor and provides the original information data to the controller  1519 . The baseband processor also channel-encodes and IFFT-processes data received from the controller  1519  and provides the IFFT signal to the RF processor. 
     The controller  1519  provides overall control to the RS. For example, the controller  1519  processes and controls voice communication and data communication. In addition to the typical functionalities, the controller  1519  processes the scanning of the MSS according to the present invention. The controller  1519  provides a control message received from the MSS or the BS to the message processor  1511 , and provides a transmission message for the MSS or the BS received from the message generator  1513  to the interface module  1521 . 
     The storage  1517  stores programs for controlling the overall operations of the RS and temporary data generated during execution of the programs. That is, the storage  1517  can store data and control information that the RS will send to the MSS or the BS. 
     The message processor  1511  disassembles a control message received from the MSS or the BS and notifies the controller  1519  of the disassembly result. According to the present invention, upon receipt of the MOB_SCN-REQ message having the configuration illustrated in Table 4 and the MOB_SCN-REP message having the configuration illustrated in Table 6 from the MSS, or upon receipt of the MOB_SCN-RSP message having the configuration illustrated in Table 5 and the MOB_SCN-INFACK message having the configuration illustrated in Table 10, or the SCAN_NOTIFY message having the configuration illustrated in Table 7 and the SCAN_RESULT message having the configuration illustrated in Table 8 from the BS, the message processor  1511  extracts control information from the messages and provides the control information to the controller  1519 . The controller  1519  operates correspondingly based on the control information. 
     The scanning processor  1515  manages MSSs that scan under the control of the controller  1519 . It recognizes the MSS that scans, and processes discontinuation of data transmission to the MSS. The scanning processor  1515  also recognizes scanning completion in the MSS and processes resumed transmission of data buffered in the storage  1517  to the MSS. 
     The message generator  1513  generates the MOB_SCN-RSP message illustrated in Table 5 for transmission to the MSS under the control of the controller  1519  and provides it to the controller  1519 . The message generator  1513  also generates the MOB_SCN-REP message illustrated in Table 4, the MOB_SCN-REP message illustrated in Table 6, the MOB_SCN-INF message illustrated in Table 9, and the MOB_SCN-FIN message illustrated in Table 11 for transmission to the BS and provides them to the controller  1519 . The messages generated from the message generator  1513  are provided to the interface module  1521  via the controller  1519 . 
     In the above RS&#39;s configuration, the controller  1519  controls the message processor  1511 , the message generator  1513 , and the scanning processor  1515 . In other words, the controller  1519  can perform the functions of the message processor  1511 , the message generator  1513 , and the scanning processor  1515 . While the message processor  1511 , the message generator  1513 , and the scanning processor  1515  are shown separately in  FIG. 15  for illustrative purposes, all or part of their functions may be incorporated into the controller  1519  in real implementation. 
     With reference to  FIG. 15 , the structure of the BS will be described. 
     The interface module  1521  is configured to communicate with the MSS or the RS. It includes the RF processor and the baseband processor. The RF processor downconverts a signal received through an antenna to a baseband signal and provides it to the baseband processor. It also upconverts a baseband signal received from the baseband processor to an RF signal for transmission in the air. For example, in the BWA system, the baseband processor acquires the original information data by FFT-processing and channel-decoding the signal received from the RF processor and provides the original information data to the controller  1519 . The baseband processor also channel-encodes and IFFT-processes data received from the controller  1519  and provides the IFFT signal to the RF processor. 
     The controller  1519  provides overall control to the BS. For example, the controller  1519  processes and controls voice communication and data communication. In addition to the typical functionalities, the controller  1519  processes the scanning of the MSS according to the present invention. The controller  1519  provides a control message received from the MSS or the RS to the message processor  1511 , and provides a transmission message for the MSS or the RS received from the message generator  1513  to the interface module  1521 . 
     The storage  1517  stores programs for controlling the overall operations of the BS and temporary data generated during execution of the programs. That is, the storage  1517  can store data and control information that the BS will send to the MSS or the RS. 
     The message processor  1511  disassembles a control message received from the MSS or the RS and notifies the controller  1519  of the disassembly result. According to the present invention, upon receipt of the MOB_SCN-REQ message having the configuration illustrated in Table 4, the MOB_SCN-REP message having the configuration illustrated in Table 6, the MOB_SCN-INF message having the configuration illustrated in Table 9, and the MOB_SCN-FIN message having the configuration illustrated in Table 11 from the RS, the message processor  1511  extracts control information from the messages and provides the control information to the controller  1519 . The controller  1519  operates correspondingly based on the control information. 
     The scanning processor  1515  manages MSSs that scan under the control of the controller  1519 . It recognizes the MSS that scans, and processes discontinuation of data transmission to the MSS. The scanning processor  1515  also recognizes scanning completion in the MSS and processes resumed transmission of data buffered in the storage  1517  to the MSS. 
     The message generator  1513  generates a message for transmission to the MSS or the RS under the control of the controller  1519  and provides it to the controller  1519 . According to the present invention, the message generator  1513  generates the MOB_SCN-RSP message illustrated in Table 5, the MOB_SCN-INFACK message illustrated in Table 10, the SCAN-NOTIFY message illustrated in Table 7, or the SCAN-RESULT message illustrated in Table 8 for transmission to the RS and provides the generated message to the controller  1519 . The message generated from the message generator  1513  is provided to the interface module  1521  via the controller  1519 . 
     In the above BS&#39;s configuration, the controller  1519  controls the message processor  1511 , the message generator  1513 , and the scanning processor  1515 . In other words, the controller  1519  can perform the functions of the message processor  1511 , the message generator  1513 , and the scanning processor  1515 . While the message processor  1511 , the message generator  1513 , and the scanning processor  1515  are shown separately in  FIG. 15  for illustrative purposes, all or part of their functions may be incorporated into the controller  1519  in real implementation. 
     In the multi-hop relay BWA communication system, scanning can MS-initiated by sending the MOB_SCN-REQ message by the MSS, RS-initiated by sending the MOB_SCN-RSP message to the MSS by the RS without receiving the MOB_SCN-REQ message from the MSS, or BS-initiated by sending the MOB_SCN-RSP message to the MSS by the BS. The RS-initiated scanning can be performed in the same manner as the MSS-initiated scanning except for transmission of the MOB_SCN-REQ message from the MSS to the RS and relay of the MOB_SCN-REQ message from the RS to the BS. The BS-initiated scanning can be performed in the same manner as the MSS-initiated scanning except for transmission of the MOB_SCN-REQ message from the MSS via the RS. 
     As described above, the present invention uses an RS that can provide a multi-hop relay path between an MSS and a BS in the case where a direct link between the MSS and the BS is in a bad channel state in an OFDM/OFDMA BWA communication system, such that the same services and functions can be provided to the MSS via the RS as if the MSS were communicating with the BS on the direct link. Also, the RS relays only necessary signals between the MSS and the BS by selective signaling in providing the services and performing the functions between the MSS and the BS, thereby preventing a waste of radio link channel resources. The present invention advantageously narrows the difference between systems which might be caused by separate signaling between the RS and the MSS and between the RS and the BS, and synchronizes the timings of system operations. 
     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.