Abstract:
A Mobile Subscriber Station (MSS) and an active Base Station (BS) for measuring/reporting a channel quality in a broadband wireless access communication system. The MSS includes a receiver for receiving, from an active BS, channel quality measurement information for the MSS to measure channel qualities of the active BS and a plurality of neighbor BSs, and channel quality report information defining a report mode for the MSS to report measured channel qualities of the active BS and the plurality of neighbor BSs, a processor for measuring the channel qualities of the active BS and the plurality of neighbor BSs according to the channel quality measurement information, and a transmitter for reporting the measured channel qualities of the active BS and the plurality of neighbor BSs to the active BS according to the channel quality report information.

Description:
PRIORITY 
     This application is a Continuation Application of U.S. application Ser. No. 11/772,716, which was filed on Jul. 2, 2007 and issued as U.S. Pat. No. 7,920,525 on Apr. 5, 2011, as a Continuation Application of U.S. application Ser. No. 10/835,158, which was filed on Apr. 29, 2004 and issued as U.S. Pat. No. 7,260,405 on Aug. 21, 2007, which claims priority under 35 U.S.C. §119(a) to an application filed in the Korean Intellectual Property Office on Apr. 30, 2003 and assigned Serial No. 10-2003-27885, the content of all of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a broadband wireless access communication system, and more particularly to a method for measuring and reporting a channel quality in a broadband wireless access communication system for use with an OFDM (Orthogonal Frequency Division Multiplexing) scheme. 
     2. Description of the Related Art 
     A great deal of intensive research has been conducted on the 4 G (4th Generation) communication system as one of the next generation communication systems to provide a plurality of users with a specific service having a variety of QoSs (Quality of Services) at a transfer rate of about 100 Mbps. Presently, the 3 G (3rd Generation) communication system provides a transfer rate of about 384 kbps in an outdoor channel environment having a relatively poor channel environment, and provides a maximum transfer rate of about 2 Mbps in an indoor channel environment having a relatively good channel environment. A wireless Local Area Network (LAN) system and a wireless Metropolitan Area Network (MAN) system have been designed to provide a transfer rate of 20˜50 Mbps. Further, a new communication system based on the 4 G communication system has been developed to provide the wireless LAN and MAN systems for guaranteeing a relatively high transfer rate with mobility and QoS. As a result, many developers have conducted intensive research into a high-speed service to be provided from the 4 G communication system. 
     However, the wireless MAN system is suitable for a high-speed communication service in that it has a wide coverage and supports a high-speed transfer rate, but it does not consider the mobility of a subscriber station (SS). Consequently, there is no consideration of a handover operation caused by the high-speed movement of the SS. The communication system currently considered in the IEEE (Institute of Electrical and Electronics Engineers) 802.16a specification acts as a specific communication system for performing a ranging operation between the SS and a base station (BS). FIG. 
       FIG. 1  is a block diagram illustrating a broadband wireless access communication system using an OFDM/OFDMA (Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access) scheme. More specifically,  FIG. 1  depicts the IEEE 802.16a communication system. 
     The wireless MAN system acting as a BWA (Broadband Wireless Access) communication system has a much wider coverage and a much higher transfer rate than the wireless LAN system. When adapting the OFDM scheme and the OFDMA scheme to a physical channel of the wireless MAN system to provide the wireless MAN system with a broadband transmission network, this application system is called an IEEE 802.16a communication system. The IEEE 802.16a communication system applies the OFDM/OFDMA scheme to the wireless MAN system, such that it transmits a physical channel signal using a plurality of sub-carriers, resulting in high-speed data transmission. 
     The IEEE 802.16e communication system has been designed to consider the SS&#39;s mobility in the IEEE 802.16a communication system, and there is no detailed specification for the IEEE 802.16e communication system. The IEEE 802.16a communication system and the IEEE 802.16e communication system act as a broadband wireless access communication system for use with the OFDM/OFDMA schemes. For the convenience of description, the IEEE 802.16a communication system will be adapted as an example. 
     Referring to  FIG. 1 , the IEEE 802.16a communication system has a single cell structure, and comprises a BS  100  and a plurality of SSs  110 ,  120 , and  130 , which are managed by the BS  100 . Signal transmission/reception among the BS  100  and the SSs  110 ,  120 , and  130  can be established using the OFDM/OFDMA scheme. FIG. 
       FIG. 2  is a conceptual diagram illustrating the downlink frame structure for use in the BWA communication system using the OFDM/OFDMA scheme. More specifically,  FIG. 2  depicts a downlink frame structure for use in the IEEE 802.16a/IEEE 802.16e communication system. 
     Referring to  FIG. 2 , the downlink frame includes a preamble field  200 , a broadcast control field  210 , and a plurality of TDM (Time Division Multiplexing) fields  220  and  230 . A synchronous signal (i.e., a preamble sequence) for synchronizing the BS and the SSs is transmitted via the preamble field  200 . The broadcast control field  210  includes a DL(DownLink)_MAP field  211  and a UL(UpLink)_MAP field  213 . The DL_MAP field  211  transmits the DL_MAP message. A plurality of IEs (Information Elements) contained in the DL_MAP message are shown in Table 1 below. 
     
       
         
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
             
               
                 DL_MAP_Message_Format( ){ 
                   
                   
               
               
                 Management Message Type=2 
                 8 bits 
                   
               
               
                 PHY Synchronization Field 
                 Variable 
                 See Appropriate PHY 
               
               
                   
                   
                 specification 
               
               
                 DCD Count 
                 8 bits 
                   
               
               
                 Base Station ID 
                 48 bits  
                   
               
               
                 Number of DL_MAP Element n 
                 16 bits  
                   
               
               
                 Begin PHY Specific section { 
                   
                 See Applicable PHY 
               
               
                   
                   
                 section 
               
             
          
           
               
                   
                 For(i=1; i&lt;=n; i++) 
                   
                 For each DL_MAP 
               
             
          
           
               
                   
                   
                 element 1 to n 
               
               
                 DL_MAP Information Element( ) 
                 Variable 
                 See corresponding PHY 
               
               
                   
                   
                 specification 
               
             
          
           
               
                   
                 if! (byte boundary) { 
                 4 bits 
                 Padding to reach byte 
               
             
          
           
               
                   
                 Padding Nibble 
                   
                 boundary 
               
             
          
           
               
                   
                 } 
               
             
          
           
               
                   
                 } 
               
             
          
           
               
                   
                 } 
               
             
          
           
               
                   
                 } 
               
               
                   
                   
               
             
          
         
       
     
     Referring to Table 1, the DL_MAP message includes a Management Message Type field including a plurality of IEs (i.e., transmission message type information); a PHY (PHYsical) Synchronization field established in response to a modulation or demodulation scheme applied to a physical channel in order to perform synchronization acquisition; a DCD count field including count information in response to a DCD (Downlink Channel Descript) message configuration variation containing a downlink burst profile; a Base Station ID field including a Base Station Identifier; and a Number of DL_MAP Element n field including the number of elements found after the Base Station ID. Particularly, the DL_MAP message (not shown in Table 1) includes information associated with ranging codes allocated to individual ranging processes to be described later. 
     The UL_MAP field  213  transmits the UL_MAP message. A plurality of IEs contained in the UL_MAP message are shown in Table 2 below. 
     
       
         
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
             
               
               
             
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
             
               
                 UL_MAP_Message_Format( ){ 
                   
                   
               
               
                 Management Message Type=3 
                 8 bits 
                   
               
               
                 Uplink Channel ID 
                 8 bits 
                   
               
               
                 UCD Count 
                 8 bits 
                   
               
               
                 Number of UL_MAP Element n 
                 16 bits  
                   
               
               
                 Allocation Start Time 
                 32 bits  
                   
               
               
                 Begin PHY Specific section { 
                   
                 See Applicable PHY 
               
               
                   
                   
                 section 
               
             
          
           
               
                   
                 for(I=1; i&lt;=n; i++) 
                   
                 For each DL_MAP 
               
             
          
           
               
                   
                   
                 element 1 to n 
               
               
                 UL_MAP Information_Element( ) 
                 Variable 
                 See corresponding PHY 
               
               
                   
                   
                 specification 
               
             
          
           
               
                   
                 } 
               
             
          
           
               
                   
                 } 
               
             
          
           
               
                   
                 } 
               
               
                   
                   
               
             
          
         
       
     
     Referring to Table 2, the UL_MAP message includes a Management Message Type field including a plurality of IEs (i.e., transmission message type information); an Uplink Channel ID field including a used Uplink Channel ID; a UCD (Uplink Channel Descript) count field including count information in response to a UCD message configuration variation containing an uplink burst profile; and a Number of UL_MAP Element n field including the number of elements found after the UCD count field. In this case, the uplink channel ID can only be allocated to a Media Access Control (MAC) sub-layer. 
     The TDM fields  220  and  230  are timeslots using a TDM/TDMA (Time Division Multiple/Time Division Multiple Access) scheme. The BS transmits broadcast information to be broadcast to SSs managed by the BS over the DL_MAP field  211  using a predetermined center carrier. The SSs monitor all the frequency bands having been previously allocated to individual SSs upon receipt of a power-on signal, such that they detect a pilot channel signal having a highest signal intensity, i.e., the highest SINR (Signal to Interference and Noise Ratio). It is determined that the SS belongs to a specific BS, which has transmitted the pilot channel signal with the highest SINR. The SSs check the DL_MAP field  211  and the UL_MAP field  213  of the downlink frame transmitted from the BS, such that they recognize their own uplink and downlink control information and specific information for indicating a real data transmission/reception position. 
     The aforementioned UCD message configuration is shown in Table 3 below. 
     
       
         
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
             
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Syntax 
                 Size 
                 Notes 
               
               
                   
                   
               
             
             
               
                   
                 UCD-Message_Format( ){ 
                   
                   
               
               
                   
                 Management Message Type=0 
                 8 bits 
                   
               
               
                   
                 Unlink channel ID 
                 8 bits 
                   
               
               
                   
                 Configuration Change Count 
                 8 bits 
                   
               
               
                   
                 Mini-slot size 
                 8 bits 
                   
               
               
                   
                 Ranging Backoff Start 
                 8 bits 
                   
               
               
                   
                 Ranging Backoff End 
                 8 bits 
                   
               
               
                   
                 Request Backoff Start 
                 8 bits 
                   
               
               
                   
                 Request Backoff End 
                 8 bits 
                   
               
               
                   
                 TLV Encoded Information for the 
                 Variable 
                   
               
               
                   
                 overall channel 
               
               
                   
                 Begin PHY Specific Section { 
               
             
          
           
               
                   
                 for (I=1; i&lt;n; i+n) 
               
             
          
           
               
                   
                 Uplink_Burst_Descriptor 
                 Variable 
                   
               
               
                   
                 } 
               
             
          
           
               
                   
                 } 
               
             
          
           
               
                   
                 } 
               
               
                   
                   
               
             
          
         
       
     
     Referring to Table 3, the UCD message includes a Management Message Type field including a plurality of IEs (i.e., transmission message type information); an Uplink Channel ID field including a used Uplink Channel Identifier; a Configuration Change Count field counted by the BS; a mini-slot size field including the size of the mini-slot of the uplink physical channel; a Ranging Backoff Start field including a backoff start point for an initial ranging process, i.e., an initial backoff window size for the initial ranging process; a Ranging Backoff End field including a backoff end point for the initial ranging process, i.e., a final backoff window size; a Request Backoff Start field including a backoff start point for establishing contention data and requests, i.e., an initial backoff window size; and a Request Backoff End field including a backoff end point for establishing contention data and requests, i.e., a final backoff window size. In this case, the backoff value indicates a kind of standby time which is a duration time between the start of SS&#39;s access failure and the start of SS&#39;s re-access time. If the SS fails to execute an initial ranging process, the BS must transmit the backoff values indicative of standby time information for which the SS must wait for the next ranging process to the SS. For example, provided that a specific number of 10 is determined by the “Ranging Backoff Start” and “Ranging Backoff End” fields shown in the Table 3, the SS must pass over 2 10  access executable chances (i.e., 1024 access executable chances) and then execute the next ranging process according to the Truncated Binary Exponential BackoffAlgorithm. 
       FIG. 3  is a conceptual diagram illustrating an uplink frame structure for use in a BWA communication system using an OFDM/OFDMA scheme. More specifically,  FIG. 3  depicts an uplink frame structure for use in the IEEE 802.16a communication system. 
     Prior to describing the uplink frame structure illustrated in  FIG. 3 , three ranging processes for use in the IEEE 802.16a communication system, i.e., an initial ranging process, a maintenance ranging process (also called a period ranging process), and a bandwidth request ranging process will hereinafter be described in detail. 
     The initial ranging process for establishing synchronization acquisition between the BS and the SS establishes a correct time offset between the SS and the BS, and controls a transmission power (also called a transmit power). More specifically, the SS is powered on, and receives the DL_MAP message, the UL_MAP message, and the UCD message to establish synchronization with the BS in such a way that it performs the initial ranging process to control the transmission power between the BS and the time offset. In this case, the IEEE 802.16a communication system uses the OFDM/OFDMA scheme, such that the ranging procedure requires a plurality of ranging sub-channels and a plurality of ranging codes. The BS allocates available ranging codes to the SS according to objectives of the ranging processes (i.e., the ranging process type information). This operation will hereinafter be described in more detail. 
     The ranging codes are created by segmenting a PN (Pseudorandom Noise) sequence having a length of 2 15 -1 bits into predetermined units. Typically, one ranging channel is composed of two ranging sub-channels each having a length of 53 bits, PN code segmentation is executed over the ranging channel having the length of 106 bits, resulting in the creation of a ranging code. A maximum of 48 ranging codes RC#1˜RC#48 can be assigned to the SS. More than two ranging codes for every SS are applied as a default value to the three ranging processes having different objectives, i.e., an initial ranging process, a period ranging process, and a bandwidth request ranging process. In this way, a ranging code is differently assigned to the SS according to each objective of the three ranging processes. For example, N ranging codes are assigned to the SS for the initial ranging process as denoted by a prescribed term of “N RC (Ranging Codes) for Initial Ranging”, M ranging codes are assigned to the SS for the periodic ranging process as denoted by a prescribed term of “M RCs for maintenance ranging”, and L ranging codes are assigned to the SS for the bandwidth request ranging process as denoted by a prescribed term of “L RCs for BW-request ranging”. The assigned ranging codes are transmitted to the SSs using the DL_MAP message, and the SSs perform necessary ranging procedures using the ranging codes contained in the DL_MAP message. 
     The period ranging process is periodically executed such that an SS which has controlled a time offset between the SS and the BS and a transmission power in the initial ranging process can control a channel state associated with the BS. The SS performs the period ranging process using the ranging codes assigned for the period ranging process. 
     The bandwidth request ranging process enables the SS, which has controlled a time offset between the SS and the BS and a transmission power in the initial ranging process, to request a bandwidth allocation from the BS in such a way that the SS can communicate with the BS. 
     Referring to  FIG. 3 , the uplink frame includes an initial maintenance opportunity field  300  using the initial and period ranging processes, a request contention opportunity field  310  using the bandwidth request ranging process, and an SS scheduled data field  320  including uplink data of a plurality of SSs. The initial maintenance opportunity field  300  includes a plurality of access burst fields each having initial and period ranging processes, and a collision field in which there is a collision between the access burst fields. The request contention opportunity field  310  includes a plurality of bandwidth request fields each having a real bandwidth request ranging process, and a collision field in which there is a collision between the bandwidth request ranging fields. The SS scheduled data fields  320  each include a plurality of SS scheduled data fields (i.e., SS  1  scheduled data field ˜SS N scheduled data field). The SS transition gap is positioned between the SS scheduled data fields (i.e., SS  1  scheduled data field ˜SS N scheduled data field). 
     The UIUC (Uplink Interval Usage Code) area records information identifying the usage of offsets recorded in the offset area. For example, provided that 2 is recorded in the UIUC area, a starting offset for use in the initial ranging process is recorded in the offset area. When 3 is recorded in the UIUC area, a starting offset for use in either the bandwidth request ranging or the maintenance ranging process is recorded in the offset area. The offset area records a starting offset value for use in either the initial ranging process or the maintenance ranging process according to the information recorded in the UIUC area. Physical channel characteristic information to be transferred from the UIUC area is recorded in the UCD. 
     As described above, the IEEE 802.16a communication system has considered a fixed state of a current SS (i.e., there is no consideration given to the mobility of the SS) and a single cell structure. However, the IEEE 802.16e communication system has been defined as a system for considering the SS&#39;s mobility in the IEEE 802.16a communication system, such that the IEEE 802.16e communication system must consider the SS&#39;s mobility in a multi-cell environment. In order to provide the SS&#39;s mobility in the multi-cell environment, individual operations modes of the SS and the BS must be converted. More specifically, many developers have conducted intensive research into an SS handover system considering a multi-cell structure to provide the SS&#39;s mobility. 
     As such, in order to enable the IEEE 802.16e communication system to support a handover function, the SS must measure SINRs of pilot signals transferred from neighbor BSs and an active BS to which the SS currently belong. When the SINR of the pilot signal transferred from the active BS is lower than SINRs of pilot signals transferred from the neighbor BSs, the SS transmits a handover request to the active BS. A method for controlling a mobile SS to measure the SINRs of the pilot signals transferred from the active BS and the neighbor BSs in the IEEE 802.16e communication system will be described later in more detail with reference to  FIG. 4 . In this case, the expression “Pilot signal&#39;s SINR measurement” is called a “Pilot signal&#39;s SINR scan or scanning” for the convenience of description. It should be noted that the term “Scan” is substantially equal to the other term “Scanning”. 
       FIG. 4  is a flow chart illustrating a method for measuring SINRs of pilot signals transferred from the active BS and the neighbor BSs in a broadband wireless access communication system for use with a conventional OFDM/OFDMA scheme. More specifically, the method for measuring SINRs of pilot signals transferred from the active BS and the neighbor BSs in the IEEE 802.16e communication system is illustrated in  FIG. 4 . 
     However, prior to describing  FIG. 4 , as indicated above, the IEEE 802.16e communication system considers the mobility of SSs in the IEEE 802.16a communication system. The SS with the mobility in the IEEE 802.16e communication system is called an MSS (Mobile Subscriber Station). 
     Referring to  FIG. 4 , the BS  450  transmits an NBR_ADV (Neighbor BSs Advertisement) message to the MSS  400  at step  411 . The detailed configuration of the NBR_ADV message is shown in Table 4 below. 
     
       
         
               
               
               
             
               
             
               
               
               
               
             
               
               
               
               
             
               
               
             
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 NBR_ADV Message_Format( ){ 
               
             
          
           
               
                   
                 Management Message Type=? 
                 8 bits 
                   
               
               
                   
                 N_NEIGHBORS 
                 8 bits 
                   
               
               
                   
                 For(i=0;j&lt;N_NEIGHBORS;j++){ 
               
             
          
           
               
                   
                 Neighbor BS-ID 
                 48 bits  
                   
               
               
                   
                 Configuration Change Count 
                 8 bits 
                   
               
               
                   
                 Physical Frequency 
                 16 bits  
                   
               
               
                   
                 TLV Encoded Neighbor Information 
                 Variable 
                 TLV specific 
               
             
          
           
               
                   
                 } 
               
             
          
           
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 4, the NBR_ADV message includes a Management Message Type field including transmission message type information; an N_NEIGHBORS field including the number of neighbor BSs; a neighbor BS-ID field including ID information of the neighbor BSs; a Configuration Change Count field including the number of configuration changes; a physical frequency field including physical channel frequencies of the neighbor BSs; and a TLV (Type/Length/Value) Encoded Neighbor Information field including other information associated with neighbor BSs other than the above described information. It should be noted that the Management Message Type field to which the NBR_ADV message will be transmitted is currently in an undecided state, as denoted by “Management Message Type=? (undecided)”. 
     The MSS  400  that is receiving the NBR_ADV message transmits a SCAN_REQ (Scan Request) message to the BS  450  when it wishes to scan SINRs of pilot signals transferred from the neighbor BSs at step  413 . In this case, the time at which the MSS  400  generates a scan request is not directly associated with the pilot SINR scanning operation, such that its detailed description will herein be omitted. 
     The SCAN_REQ message configuration is shown in Table 5 below. 
     
       
         
               
               
               
             
               
             
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 SCN_REQ Message_Format( ){ 
               
             
          
           
               
                   
                 Management Message Type=? 
                  8 bits 
                   
               
               
                   
                 Scan Duration 
                 20 bits 
                 For SCa PHY, units 
               
             
          
           
               
                   
                   
                 are mini-slots. For 
               
               
                   
                   
                 OFDM/OFDMA PHY, 
               
               
                   
                   
                 units are OFDM 
               
               
                   
                   
                 symbols 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 5, the SCAN_REQ message includes a Management Message Type field including a plurality of IEs (i.e., transmission message type information), and a Scan Duration field including a scan-desired scan duration for SINRs of pilot signals transferred from the neighbor BSs. If the IEEE 802.16e communication system is a system for use with a Single Carrier (SC), i.e., if the scan duration field is applied to an SC physical channel, the scan duration field is configured in units of mini-slots. If the IEEE 802.16e system acts as the OFDM/OFDMA system, i.e., if the IEEE 802.16e system is applied to the OFDM/OFDMA physical channel, it is configured in the form of OFDM-symbol units. It should be noted that the Management Message Type field to which the SCAN_REQ message will be transmitted is currently in an undecided state, as denoted by “Management Message Type=? (undecided)”. 
     The BS  450  receiving the SCAN_REQ message transmits a DL_MAP message including information to be scanned by the MSS  400  to the MSS  400  at step  415 . In this case, the SCANNING_IE message including scan information contained in the DL_MAP message is shown in Tables 6, 7, and 8 below. 
     
       
         
               
             
               
               
               
             
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 For SCa PHY: 
               
             
          
           
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
          
           
               
                 Scanning_IE { 
               
             
          
           
               
                   
                 CID 
                 16 bits 
                 MSS basic CID 
               
               
                   
                 Scan Start 
                 22 bits 
                 Offset (in units of mini-slots) to the 
               
             
          
           
               
                   
                 start of the scanning interval from the 
               
               
                   
                 mini-slot boundary specified by the 
               
               
                   
                 downlink Allocation_Start_Time 
               
             
          
           
               
                   
                 Scan Duration 
                 22 bits 
                 Duration (in units of mini-slots) 
               
             
          
           
               
                   
                   
                 where the MSS may scan for 
               
               
                   
                   
                 neighbor BS 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 6, the SCANNING_IE message includes scan information for use in the SC physical channel. Parameters contained in the SCANNIG_IE message are a CID (Connection ID), a Scan Start value, and a scan duration value. The CID includes an MSS basic CID for use with the SCANNING_IE message. The Scan Start value is a predetermined time at which the MSS begins a pilot SINR scanning operation. The scan duration is a predetermined interval during which the MSS performs the pilot SINR scanning operation. The scan start and scan duration values for use in the SC physical channel are configured in the form of mini-slot units. 
     
       
         
               
             
               
               
               
             
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 For OFDM PHY: 
               
             
          
           
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
          
           
               
                 Scanning_IE { 
               
             
          
           
               
                   
                 CID 
                 16 bits 
                 MSS basic CID 
               
               
                   
                 Scan Start 
                 18 bits 
                 Indicate the scanning interval start 
               
             
          
           
               
                   
                 time, in units of OFDM symbol 
               
               
                   
                 duration, relative to the start of the 
               
               
                   
                 first symbol of the PHY PDU 
               
               
                   
                 (including preamble) where the 
               
               
                   
                 DL_MAP message is transmitted 
               
             
          
           
               
                   
                 Scan Duration 
                 18 bits 
                 Duration (in units of OFDM symbols) 
               
             
          
           
               
                   
                   
                 where the MSS may scan for 
               
               
                   
                   
                 neighbor BS 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 7, the SCANNING_IE message includes scan information for use in the OFDM physical channel. Parameters contained in the SCANNIG_IE message are a CID (Connection ID), a Scan Start value, and a scan duration value. The CID indicates an MSS basic CID for use with the SCANNING_IE message. The Scan Start value is a predetermined time at which the MSS begins a pilot SINR scanning operation. The scan duration is a predetermined interval during which the MSS performs the pilot SINR scanning operation. The scan start and scan duration values for use in the OFDM physical channel are configured in the form of OFDM-symbol units. 
     
       
         
               
             
               
               
               
             
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 For OFDM PHY: 
               
             
          
           
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
          
           
               
                 Scanning_IE { 
               
             
          
           
               
                   
                 CID 
                 16 bits 
                 MSS basic CID 
               
               
                   
                 Scan Start 
                 18 bits 
                 The offset of the OFDM symbol in 
               
             
          
           
               
                   
                 which the scanning interval starts. 
               
               
                   
                 Measured in OFDM symbols from the 
               
               
                   
                 time specified by the 
               
               
                   
                 Allocation_Start_time_Field in the 
               
               
                   
                 DL_MAP 
               
             
          
           
               
                   
                 Scan Duration 
                 18 bits 
                 Duration (in units of OFDM symbols) 
               
             
          
           
               
                   
                   
                 where the MSS may scan for 
               
               
                   
                   
                 neighbor BS 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 8, the SCANNING_IE message includes scan information for use in the OFDMA physical channel. Parameters contained in the SCANNIG_IE message are a CID (Connection ID), a Scan Start value, and a scan duration value. The CID includes an MSS basic CID for use with the SCANNING_IE message. The Scan Start value is a predetermined time at which the MSS begins a pilot SINR scanning operation. The scan duration is a predetermined interval during which the MSS performs the pilot SINR scanning operation. The scan start and scan duration values for use in the OFDM physical channel are configured in the form of OFDM-symbol units. 
     The MSS  400 , having received the DL_MAP message including the scanning_IE message, scans pilot SINRs associated with neighbor BSs recognized by the NBR_ADV message according to parameters contained in the SCANNING_IE message at step  417 . It should be noted that SINRs of pilot signals transferred from the neighbor BSs and the SINR of the pilot signal transferred from the BS  450  to which the MSS  400  currently belongs are continuously scanned, even though it is not illustrated in  FIG. 4 . 
       FIG. 5  is a flow chart illustrating a handover request process of an MSS in a broadband wireless access communication system for use with a conventional OFDM/OFDMA scheme. More specifically, an MSS handover request process for use in the IEEE 802.16e communication system is illustrated in  FIG. 5 . 
     Referring to  FIG. 5 , the BS  550  transmits an NBR_ADV message to the MSS  500  at step  511 . The MSS  500 , having received the NBR_ADV message, transmits a SCAN_REQ message to the BS  550  when it wishes to scan SINRs of pilot signals transferred from the neighbor BSs at step  513 . In this case, the time at which the MSS  500  generates a scan request is not directly associated with the pilot SINR scanning operation, such that its detailed description will herein be omitted. The BS  550 , having received the SCAN_REQ message, transmits a DL_MAP message including the SCANNING_IE message (i.e., information to be scanned by the MSS  500 ) to the MSS  500  at step  515 . In association with the neighbor BSs recognized by the NBR_ADV message, the MSS  500 , having received the DL_MAP message including the SCANNING_IE message, scans SINRs of pilot signals in response to parameters (i.e., a scan start value and a scan duration) contained in the SCANNING_IE message at step  517 . It should be noted that SINRs of pilot signals transferred from the neighbor BSs and the SINR of the pilot signal transferred from the BS  550  to which the MSS  500  currently belongs are continuously scanned, even though it is not illustrated in  FIG. 5 . 
     If it is determined that the MSS  500  must change its current active BS to another BS at step  519 , after the scanning operations of the SINRs of pilot signals received from the neighbor BSs have been completed, i.e., if it is determined that the MSS  500  must change its current active BS to a new BS, the MSS  500  transmits an MSSHO_REQ (Mobile Subscriber Station HandOver Request) message to the BS  550  at step  521 . The MSSHO_REQ message configuration is shown in Table 9 below. 
     
       
         
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
               
               
             
               
               
             
               
               
             
           
               
                   
                 TABLE 9 
               
               
                   
                   
               
               
                   
                 Syntax 
                 Size 
                 Notes 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 MSSHO_REQ Message_Format( ){ 
               
             
          
           
               
                   
                 Management Message Type=? 
                 8 bits 
                   
               
               
                   
                 Estimated HO time 
                 8 bits 
                   
               
               
                   
                 N_Recommended 
                 8 bits 
                   
               
               
                   
                 For(i=0;j&lt;N_NEIGHBORS;j++){ 
               
             
          
           
               
                   
                 Neighbor BS-ID 
                 48 bits  
                   
               
               
                   
                 BS S/(N+I) 
                 8 bits 
                   
               
             
          
           
               
                   
                 } 
               
             
          
           
               
                   
                 } 
               
               
                   
                   
               
             
          
         
       
     
     Referring to Table 9, the MSSHO_REQ message includes a Management Message Type field identifying a plurality of IEs (i.e., transmission message type information), an estimated HO time field including a handover start time, and an N_Recommended field including the scanning result of the MSS. In this case, the N_Recommended field includes ID information of neighbor BSs and SINR information of pilot signals of the neighbor BSs. It should be noted that the Management Message Type field to which the MSSHO_REQ message will be transmitted is currently in an undecided state, as denoted by “Management Message Type=? (undecided)”. 
     After transmitting the MSSHO_REQ message to the BS  550 , the MSS  500  re-scans SINRs of pilot signals in association with the neighbor BSs at step  523 . 
     First and second problems of the MSS scanning operation for use in the IEEE 802.16e communication system will now be described herein below. 
     In the first problem, although the MSS scans pilot SINRs of neighbor BSs in response to the scanning information received from the active BS, there is no procedure for additionally reporting the pilot SINR scanning result of the active BS and neighbor BSs. In the second problem, there is no procedure for enabling the MSS to scan pilot SINRs of neighbor BSs before the MSS transmits a scan request to the active BS. 
     In order to enable the IEEE 802.16e communication system to support a handover function of the MSS, a handover function of a mobile subscriber must be made available upon receipt of a request signal from the MSS and a request signal from the BS. In order to enhance system efficiency, it is desirable that the BS continues to manage the pilot SINR scanning state (i.e., the MSS state) after the MSS has been powered on. However, the IEEE 802.16e communication system cannot report an MSS handover procedure and an MSS pilot SINR scanning state upon receiving a request signal from the BS, such that there must be newly developed such procedures for reporting the MSS handover procedure and the MSS pilot SINR scanning state. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been designed in view of the above and other problems, and it is an object of the present invention to provide a method for measuring and reporting a channel quality in a broadband wireless access communication system. 
     It is another object of the present invention to provide a method for measuring a channel quality in a broadband wireless access communication system even though there is no additional request from a mobile subscriber. 
     It is yet another object of the present invention to provide a method for performing a handover function in response to a channel quality in a broadband wireless access communication system. 
     In accordance with an aspect of the present invention, a Mobile Subscriber Station (MSS) in a communication system is provided. The MSS includes a receiver for receiving, from an active Base Station (BS), channel quality measurement information for the MSS to measure channel qualities of the active BS and a plurality of neighbor BSs, and channel quality report information defining a report mode for the MSS to report measured channel qualities of the active BS and the plurality of neighbor BSs; a processor for measuring the channel qualities of the active BS and the plurality of neighbor BSs according to the channel quality measurement information; and a transmitter for reporting the measured channel qualities of the active BS and the plurality of neighbor BSs to the active BS according to the channel quality report information. The report mode includes one of a first report mode and a second report mode. The first report mode and the second report mode include information on a time at which the measured channel qualities of the active BS and the plurality of neighbor BSs are reported. The channel quality report time of the first report mode includes a period indicated in the channel quality report information. The channel quality report time of the second report mode identifies a specific time at which a magnitude order of Signal to Interference and Noise Ratios (SINRs) of individual reference channel signals measured is different from a magnitude order of SINRs of reference channel signals of the active BS and the plurality of neighbor BSs previously measured. The channel quality measurement information includes a measurement start time at which a channel quality measurement operation begins, and a measurement duration for executing the channel quality measurement operation. 
     In accordance with another aspect of the present invention, a Mobile Subscriber Station (MSS) in a communication system is provided. The MSS includes a receiver for receiving, from an active Base Station (BS), channel quality measurement information for the MSS to measure channel qualities of the active BS and a plurality of neighbor BSs, and channel quality report information defining a report mode for the MSS to report measured channel qualities of the active BS and the neighbor BSs; a processor for measuring the channel qualities of the active BS and the plurality of neighbor BSs according to the channel quality measurement information; and a transmitter for reporting the measured channel qualities of the active BS and the plurality of neighbor BSs to the active BS according to the channel quality report information. The receiver receives reference channel signals from the active BS and the plurality of neighbor BSs. The processor measures Signal to Interference and Noise Ratios (SINRs) of the reference channel signals from the active BS and the plurality of neighbor BSs. The report mode includes information on a time at which the measured channel qualities of the active BS and the plurality of neighbor BSs are reported, the channel quality report time being a specific time during which an SINR of a reference channel signal received from the active BS is determined to be less than one of the SINRs of the reference channel signals received from the plurality of neighbor BSs, such that a determined state is maintained during a predetermined time. The channel quality measurement information includes a measurement start time at which a channel quality measurement operation begins, and a measurement duration for executing the channel quality measurement operation. 
     In accordance with another aspect of the present invention, a Mobile Subscriber Station (MSS) in a communication system is provided. The MSS includes a receiver for receiving, from an active BS (Base Station), a message requesting the MSS to scan and measure at least one channel quality of the active BS and at least one neighbor BS, the message defining reporting parameters for the MSS to report the at least one channel quality to the active BS; a processor for measuring the at least one channel quality of the active BS and the at least one neighbor BS according to the message; and a transmitter for reporting the at least one channel quality of the active BS and the at least one neighbor BS to the active BS according to the reporting parameters. The reporting parameters include a report mode selected from among a first report mode, a second report mode, and a third report mode. The first report mode, the second report mode, and the third report mode include information on a time at which measured channel qualities of the active BS and the neighbor BSs are reported. The channel quality report time of the first report mode is a period indicated in the message. The channel quality report time of the second report mode identifies a specific time at which a magnitude order of Signal to Interference and Noise Ratios (SINRs) of individual reference channel signals measured is different from a magnitude order of SINRs of reference channel signals of the active BS and the neighbor BSs previously measured. The channel quality report time of the third report mode is a specific time during which an SINR of a reference channel signal received from the active BS is determined to be lower than one of the SINRs of the reference channel signals received from the neighbor BSs, such that a determined state is maintained during a predetermined time. The message includes a measurement start time at which measuring the at least one channel quality begins, and a measurement duration for measuring the at least one channel quality. 
     In accordance with another aspect of the present invention, an active Base Station (BS) in a communication system is provided. The active BS includes a transmitter for transmitting, to a Mobile Subscriber Station (MSS), channel quality measurement information for the MSS to measure channel qualities of the active BS and a plurality of neighbor BSs, and channel quality report information defining a report mode for the MSS to report measured channel qualities of the active BS and the plurality of neighbor BSs; and a receiver for receiving, from the MSS, the measured channel qualities of the active BS and the plurality of neighbor BSs. The measured channel qualities of the active BS and the plurality of neighbor BSs are generated by measuring, by the MSS, channel qualities of the active BS and the plurality of neighbor BSs using the channel quality measurement information. The report mode includes one of a first report mode and a second report mode. The first report mode and the second report mode include information on a time at which the measured channel qualities of the active BS and the plurality of neighbor BSs are reported. The channel quality report time of the first report mode is a period indicated in the channel quality report information. The channel quality report time of the second report mode identifies a specific time at which a magnitude order of Signal to Interference and Noise Ratios (SINRs) of individual reference channel signals measured is different from a magnitude order of SINRs of reference channel signals of the active BS and the plurality of neighbor BSs previously measured. The channel quality measurement information includes a measurement start time at which a channel quality measurement operation begins, and a measurement duration for executing the channel quality measurement operation. 
     In accordance with another aspect of the present invention, an active Base Station (BS) in a communication system is provided. The active BS includes a transmitter for transmitting, to a Mobile Subscriber Station (MSS), channel quality measurement information for the MSS to measure channel qualities of the active BS and a plurality of neighbor BSs, and channel quality report information defining a report mode for the MSS to report measured channel qualities of the active BS and the plurality of neighbor BSs; and a receiver for receiving, from the MSS, the measured channel qualities of the active BS and the plurality of neighbor BSs. The measured channel qualities of the active BS and the plurality of neighbor BSs are generated by receiving, by the MSS, reference channel signals received from the active BS and the plurality of neighbor BSs, and measuring, by the MSS, Signal to Interference and Noise Ratios (SINRs) of the reference channel signals from the active BS and the plurality of neighbor BSs. The report mode includes information on a time at which the measured channel qualities of the active BS and the plurality of neighbor BSs are reported, the channel quality report time being a specific time during which an SINR of a reference channel signal received from the active BS is determined to be less than one of the SINRs of the reference channel signals received from the plurality of neighbor BSs, such that a determined state is maintained during a predetermined time. The channel quality measurement information includes a measurement start time at which a channel quality measurement operation begins, and a measurement duration for executing the channel quality measurement operation. 
     In accordance with another aspect of the present invention, an active Base Station (BS) in a communication system is provided. The active BS includes a transmitter for transmitting, to a Mobile Subscriber Station (MSS), a message requesting the MSS to scan and measure at least one channel quality of the active BS and at least one neighbor BS, the message defining reporting parameters for the MSS to report the at least one channel quality to the active BS; and a receiver for receiving, from the MSS, the at least one channel quality of the active BS and of the at least one neighbor BS. The at least one channel quality of the active BS and the at least one neighbor BS is measured according to the message. The reporting parameters include a report mode selected from a first report mode, a second report mode, and a third report mode. The first report mode, the second report mode, and the third report mode each include information on a time at which measured channel qualities of the active BS and the at least one neighbor BS are reported. The time of the first report mode is a period indicated in the message. The time of the second report mode identifies a specific time at which a magnitude order of Signal to Interference and Noise Ratios (SINRs) of individual reference channel signals measured is different from a magnitude order of SINRs of reference channel signals of the active BS and the at least one neighbor BS previously measured. The time of the third report mode is a specific time during which an SINR of a reference channel signal received from the active BS is determined to be lower than either an SINR of a reference channel signal received from the at least one neighbor BS, such that a determined state is maintained during a predetermined time. The message includes a measurement start time at which measuring the at least one channel quality begins, and a measurement duration for measuring the at least one channel quality. 
     In accordance with another aspect of the present invention, a Mobile Subscriber Station (MSS) in a communication system is provided. The MSS includes a receiver for receiving, from an active Base Station (BS), channel quality measurement information for the MSS to measure channel qualities of the active BS and a plurality of neighbor BSs, and channel quality report information defining a report mode for the MSS to report the channel qualities of the active BS and the plurality of neighbor BSs; a processor for measuring channel qualities of the active BS and the plurality of neighbor BSs using the channel quality measurement information; and a transmitter for reporting measured channel qualities of the active BS and the plurality of neighbor BSs to the active BS using the channel quality report information. The report mode includes one of plurality of report modes, and the plurality of report modes include information on a channel quality report time at which the measured channel qualities of the active BS and the plurality of neighbor BSs are reported. The channel quality report time of a first report mode among the plurality of report modes is a period. The channel quality report time of a second report mode among the plurality of report modes identifies a specific time at which a trigger condition is met. The trigger condition is met when a value order of the measured channel qualities is different from a value order of channel qualities of the active BS and the plurality of neighbor BSs previously measured. The trigger condition includes at least one of a first condition and a second condition. The first condition is met when a channel quality of at least one neighbor BS from among the plurality of neighbor BSs is greater than a channel quality of the active BS. The second condition is met when a channel quality of at least one neighbor BS is less than a channel quality of the active BS. The channel quality measurement information includes a measurement start time at which a channel quality measurement operation begins, and a measurement duration for executing the channel quality measurement operation. 
     In accordance with another aspect of the present invention, an active Base Station (BS) in a communication system is provided. The active BS includes a transmitter for transmitting, to a Mobile Subscriber Station (MSS), channel quality measurement information for the MSS to measure channel qualities of the active BS and a plurality of neighbor BSs, and channel quality report information defining a report mode for the MSS to report the channel qualities of the active BS and the plurality of neighbor BSs; and a receiver for receiving, from the MSS, measured channel qualities of the active BS and the plurality of neighbor BSs using the channel quality report information. The measured channel qualities of the active BS and the plurality of neighbor BSs are generated by measuring, by the MSS, the channel qualities of the active BS and the plurality of neighbor BSs using the channel quality measurement information. The report mode includes one of a plurality of report modes. The plurality of report modes include information on a channel quality report time at which the measured channel qualities of the active BS and the plurality of neighbor BSs are reported. The channel quality report time of a first report mode from among the plurality of report modes is a period. The channel quality report time of a second report mode from among the plurality of report modes identifies a specific time at which a trigger condition is met. The trigger condition is met when a value order of the measured channel qualities is different from a value order of channel qualities of the active BS and the plurality of neighbor BSs previously measured. The trigger condition includes at least one of a first condition and a second condition. The first condition is met when a channel quality of at least one neighbor BS from among the plurality of neighbor BSs is greater than a channel quality of the active BS. The second condition is met when a channel quality of at least one neighbor BS from among the plurality of neighbor BSs is less than a channel quality of the active BS. The channel quality measurement information includes a measurement start time at which a channel quality measurement operation begins, and a measurement duration for executing the channel quality measurement operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating a broadband wireless access communication system using an OFDM/OFDMA scheme; 
         FIG. 2  is a conceptual diagram illustrating a downlink frame structure for use in a broadband wireless access communication system using an OFDM/OFDMA scheme; 
         FIG. 3  is a conceptual diagram illustrating an uplink frame structure for use in a broadband wireless access communication system using an OFDM/OFDMA scheme; 
         FIG. 4  is a flow chart illustrating a method for measuring SINRs of pilot signals transferred from active BS and neighbor BSs in a broadband wireless access communication system using an OFDM/OFDMA scheme; 
         FIG. 5  is a flow chart illustrating a handover request process of an MSS in a broadband wireless access communication system using an OFDM/OFDMA scheme; 
         FIG. 6  is a block diagram illustrating a broadband wireless access communication system using an OFDM/OFDMA scheme in accordance with the present invention; 
         FIG. 7  is a flow chart illustrating a pilot SINR scanning procedure in accordance with a first preferred embodiment of the present invention; 
         FIG. 8  is a flow chart illustrating a pilot SINR scanning procedure in accordance with a second preferred embodiment of the present invention; 
         FIG. 9  is a flow chart illustrating a pilot SINR scan report procedure in accordance with a third preferred embodiment of the present invention; 
         FIG. 10  is a flow chart illustrating a pilot SINR scan report procedure in accordance with a fourth preferred embodiment of the present invention; and 
         FIG. 11  is a flow chart illustrating a pilot SINR scan report procedure in accordance with a fifth preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described in detail herein below with reference to the annexed drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. 
     Prior to describing the present invention, the handover procedure proposed by the current IEEE 802.16e system includes only two procedures, i.e., a scanning procedure and an SINR scanning result report procedure. More specifically, the scanning procedure is used to measure an SINR of a pilot signal upon receipt of an MSS request, and the SINR scanning result report procedure is used to report the SINR scanning result of a pilot signal upon receiving a handover request from an MSS. In this case, the expression “Pilot signal&#39;s SINR measurement” is considered to be the same as the other expression “Pilot signal&#39;s SINR scan or scanning” for the convenience of description. It should be noted that the term “Scan” is substantially equal to the term “Scanning”. However, in order to provide the MSS with an effective handover operation, the MSS must conduct pilot SINR scanning operations of neighbor BSs before generating a handover request. Where an active BS for providing the MSS with a desired service is changed to another BS due to movement of the MSS, the MSS must continuously conduct pilot SINR scanning operations of the active BS and the neighbor BSs, and must inform the active BS of the scanning pilot SINR results, such that a handover function for the changed active BS is performed. In order to implement an effective handover operation of the MSS, the present invention provides a method for performing a pilot SINR scanning operation upon receiving a control signal from a BS without using a request signal of the MSS, and a method for controlling the MSS to report the scanned pilot SINR results. 
       FIG. 6  is a block diagram illustrating a broadband wireless access communication system using an OFDM/OFDMA scheme in accordance with the present invention. However, prior to describing the BWA communication system illustrated in  FIG. 6 , it should be noted that the IEEE 802.16e communication system acting as a communication system for considering the SS&#39;s mobility in the IEEE 802.16a communication system has not been developed yet. Provided that the SS&#39;s mobility is considered in the IEEE 802.16a communication system, it is possible to consider the multi-cell structure and an SS&#39;s handover operation between the multi-cells. Therefore, the present invention provides the IEEE 802.16e communication system as illustrated in  FIG. 6 . The present invention utilizes the IEEE 802.16e communication system as a BWA (Broadband Wireless Access) communication system using an OFDM/OFDMA scheme as a representative example. Accordingly, it should be noted that an SC (Single Carrier) scheme is applicable to the IEEE 802.16e communication system. In this case, the pilot signal&#39;s SINR indicates a channel quality of a specific channel established between the MSS and the BS. 
     Referring to  FIG. 6 , the IEEE 802.16e communication system includes a multi-cell structure, i.e., a plurality of cells  600  and  650 . More specifically, the IEEE 802.16e communication system includes a first BS  610  for managing the cell  600 , a second BS  640  for managing the cell  650 , and a plurality of MSSs  611 ,  613 ,  630 ,  651 , and  653 . Signal transmission and reception among the BSs  610  and  640  and the MSSs  611 ,  613 ,  630 ,  651 , and  653  is established using the OFDM/OFDMA scheme. The MSS  630  from among the MSSs  611 ,  613 ,  630 ,  651 , and  653  is positioned in a boundary (i.e., a handover area) between the first cell  600  and the second cell  650 . The IEEE 802.16e communication system can provide the MSS&#39;s mobility on the condition that the handover operation for the MSS  630  must be supported. 
       FIG. 7  is a flow chart illustrating a pilot SINR scanning procedure in accordance with a first preferred embodiment of the present invention. Referring to  FIG. 7 , the BS  750  transmits a DL(DownLink)_MAP message to the MSS  700  at step  711 . In this case, the DL_MAP message includes a SCANNING_IE (Information Element) message identifying scan information of the MSS  700  in a conventional DL_MAP message of the IEEE 802.16e system described in the prior art. More specifically, if the powered-on MSS  700  is initialized to control the MSS  700  to perform the SINR scanning operation, the BS  750  includes the SCANNING_IE message in the DL_MAP message, and transmits the SCANNING_IE message including the DL_MAP message to the MSS  700  without receiving a scan request signal from the MSS  700 . In this case, the SCANNING_IE message may be equal to the SCANNING_IE messages shown in Tables 6 to 8 of the prior art, or may also be equal to a new SCANNING_IE message of the present invention. The SCANNING_IE message acts as channel quality measurement information for measuring the pilot SINR (i.e., a channel quality). The new SCANNING_IE messages of the present invention are shown in Tables 10 to 12 below. 
     
       
         
               
             
               
               
               
             
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 10 
               
             
             
               
                   
               
               
                 For SCa PHY: 
               
             
          
           
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
          
           
               
                 Scanning_IE { 
               
             
          
           
               
                   
                 CID 
                 16 bits 
                 MSS basic CID 
               
               
                   
                 Scan Start 
                 22 bits 
                 Offset (in units of mini-slots) to the 
               
             
          
           
               
                   
                 start of the scanning interval from the 
               
               
                   
                 mini-slot boundary specified by the 
               
               
                   
                 downlink Allocation_Start_Time 
               
             
          
           
               
                   
                 Scan Duration 
                 22 bits 
                 Duration (in units of mini-slots) 
               
             
          
           
               
                   
                 where the MSS may scan for 
               
               
                   
                 neighbor BS 
               
             
          
           
               
                   
                 Scan Period 
                 22 bits 
                 Period (in units of mini-slots) when 
               
             
          
           
               
                   
                   
                 the MSS may scan for neighbor BS 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 10, the SCANNING_IE message includes scan information for use in the SC physical channel. Parameters contained in the SCANNIG_IE message are a CID (Connection ID), a Scan Start value, a Scan Duration value, and a Scan Period value. The CID identifies an MSS basic CID for use with the SCANNING_IE message. The Scan Start value is a predetermined time at which the MSS begins a pilot SINR scanning operation. The Scan Duration is a predetermined interval during which the MSS performs the pilot SINR scanning operation. The scan period is a predetermined period during which the MSS performs the pilot SINR scan operation. The scan start value, the scan duration value, and the scan period value for use in the SC physical channel are configured in the form of mini-slot units. 
     
       
         
               
             
               
               
               
             
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 11 
               
             
             
               
                   
               
               
                 For OFDM PHY: 
               
             
          
           
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
          
           
               
                 Scanning_IE { 
               
             
          
           
               
                   
                 CID 
                 16 bits 
                 MSS basic CID 
               
               
                   
                 Scan Start 
                 18 bits 
                 Indicate the scanning interval start 
               
             
          
           
               
                   
                 time, in units of OFDM symbol 
               
               
                   
                 duration, relative to the start of the 
               
               
                   
                 first symbol of the PHY PDU 
               
               
                   
                 (including preamble) where the 
               
               
                   
                 DL_MAP message is transmitted 
               
             
          
           
               
                   
                 Scan Duration 
                 18 bits 
                 Duration (in units of OFDM symbols) 
               
             
          
           
               
                   
                 where the MSS may scan for 
               
               
                   
                 neighbor BS 
               
             
          
           
               
                   
                 Scan Period 
                 18 bits 
                 Period (in units of OFDM symbols) 
               
             
          
           
               
                   
                   
                 when the MSS may scan for neighbor 
               
               
                   
                   
                 BS 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 11, the SCANNING_IE message includes scan information for use in the OFDM physical channel. Parameters contained in the SCANNIG_IE message are a CID (Connection ID), a Scan Start value, a Scan Duration value, and a Scan Period value. The CID identifies an MSS basic CID for use with the SCANNING_IE message. The Scan Start value is a predetermined time at which the MSS begins a pilot SINR scanning operation. The scan duration is a predetermined interval during which the MSS performs the pilot SINR scanning operation. The scan period is a predetermined period during which the MSS performs the pilot SINR scan operation. The scan start value, the scan duration value, and the scan period value for use in the OFDM physical channel are configured in the form of OFDM-symbol units. 
     
       
         
               
             
               
               
               
             
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 12 
               
             
             
               
                   
               
               
                 For OFDMA PHY: 
               
             
          
           
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
          
           
               
                 Scanning_IE { 
               
             
          
           
               
                   
                 CID 
                 16 bits 
                 MSS basic CID 
               
               
                   
                 Scan Start 
                 18 bits 
                 The offset of the OFDM symbol in 
               
             
          
           
               
                   
                 which the scanning interval starts. 
               
               
                   
                 Measured in OFDM symbols from the 
               
               
                   
                 time specified by the 
               
               
                   
                 Allocation_Start_time_Field in the 
               
               
                   
                 DL_MAP 
               
             
          
           
               
                   
                 Scan Duration 
                 18 bits 
                 Duration (in units of OFDM symbols) 
               
             
          
           
               
                   
                 where the MSS may scan for 
               
               
                   
                 neighbor BS 
               
             
          
           
               
                   
                 Scan Period 
                 18 bits 
                 Period (in units of OFDM symbols) 
               
             
          
           
               
                   
                   
                 when the MSS may scan for neighbor 
               
               
                   
                   
                 BS 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 12, the SCANNING_IE message includes scan information for use in the OFDMA physical channel. Parameters contained in the SCANNIG_IE message are a CID (Connection ID), a Scan Start value, and a scan duration value. The CID identifies an MSS basic CID for use with the SCANNING_IE message. The Scan Start value is a predetermined time at which the MSS begins a pilot SINR scanning operation. The scan duration is a predetermined interval during which the MSS performs the pilot SINR scanning operation. The scan period is a predetermined period during which the MSS performs the pilot SINR scan operation. The scan start value, the scan duration value, and the scan period value for use in the OFDM physical channel are configured in the form of OFDM-symbol units. 
     The BS  750  transmits an NBR_ADV (Neighbor BSs Advertisement) message to the MSS  700 . As previously stated in Table 4, the NBR_ADV message includes a Management Message Type field including transmission message type information; an N_Neighbors field including the number of neighbor BSs; a neighbor BS-ID field including ID information of the neighbor BSs; a Configuration Change Count field including the number of configuration changes; a physical frequency field including physical channel frequencies of the neighbor BSs; and a TLV Encoded Neighbor Information field including information associated with the neighbor BSs, other than the above neighbor-BSs-associated information. 
     The MSS  700 , having received the NBR_ADV message including the information associated with the neighbor BSs from the BS  750 , scans neighbor BSs recognized by the NBR_ADV message (i.e., SINRs of pilot signals transferred from the neighbor BSs) according to parameters contained in the SCANNING_IE message contained in the DL_MAP message at step  715 . It should be noted that SINRs of pilot signals transferred from the neighbor BSs and the SINR of the pilot signal transferred from the BS  750  to which the MSS  700  currently belongs are continuously scanned, even though it is not illustrated in  FIG. 7 . 
     As a result, in accordance with the MSS scanning procedure illustrated in  FIG. 7 , the BS transmits scan information associated with the scanning operation to the MSS even though the MSS does not transmit an additional request to the BS, such that the MSS can effectively perform a scan operation. 
       FIG. 8  is a flow chart illustrating a pilot SINR scanning procedure in accordance with a second preferred embodiment of the present invention. However, prior to describing  FIG. 8 , the SINR scanning process of the first preferred embodiment illustrated in  FIG. 7  is a pilot SINR scanning process of the MSS in response to the scan information of the BS. The SINR scanning process of the second preferred embodiment changes scan information such as scan duration and scan period information to other information upon receiving a request from the MSS while the MSS scans the pilot SINR in response to scan information transferred from the BS, such that the pilot SINR can be scanned. 
     Referring to  FIG. 8 , the BS  850  transmits a DL_MAP message to the MSS  800  at step  811 . The DL_MAP message includes the SCANNING_IE message including the MSS  800 &#39;s scan information in the conventional DL_MAP message of the IEEE 802.16e communication system previously stated in the prior art. In this case, the SCANNING_IE message may be the same as the SCANNING_IE messages shown in Tables 6 to 8 of the prior art, or may also be equal to a new SCANNING_IE message of the present invention, i.e., the same SCANNING_IE message described in Tables 10 to 12. 
     After transmitting the DL_MAP message, the BS  850  transmits the NBR_ADV message to the MSS  800  at step  813 . As previously stated in Table 4, the NBR_ADV message includes a Management Message Type field including transmission message type information (i.e., a plurality of IEs); an N_Neighbors field including the number of neighbor BSs; a neighbor BS-ID field including ID information of the neighbor BSs; a Configuration Change Count field including the number of configuration changes; a physical frequency field including physical channel frequencies of the neighbor BSs; and a TLV Encoded Neighbor Information field including information associated with the neighbor BSs other than the above neighbor-BSs-associated information. 
     The MSS  800 , having received the NBR_ADV message including the information associated with the neighbor BSs from the BS  850 , scans neighbor BSs recognized by the NBR_ADV message (i.e., SINRs of pilot signals transferred from the neighbor BSs) according to parameters contained in the SCANNING_IE message contained in the DL_MAP message at step  815 . It should be noted that SINRs of pilot signals transferred from the neighbor BSs and the SINR of the pilot signal transferred from the BS  850  to which the MSS  800  currently belongs are continuously scanned, even though it is not illustrated in  FIG. 8 . 
     As a result, the MSS decides to change scan-associated information (i.e., scan information such as scan duration and scan period information) while scanning SINRs of the pilot signals transferred from the neighbor BSs at step  817 . In this case, there may be a plurality of conditions for controlling the MSS  80  to change scan-associated information. For example, where the measurement period must be adjusted according to physical channel capacity, scanning information conversion may be requested. More specifically, if there is too much load in the physical channel, the MSS  800  may determine a measurement period to be a long measurement period. If there is relatively little load in the physical channel, the MSS  800  may determine a measurement period to be a relatively short measurement period. 
     The MSS  800 , having decided to change scanning information to other information, transmits a SCAN_REQ message to the BS  850  at step  819 . In this case, the SCAN_REQ message includes a Management Message Type field including transmission message type information (i.e., a plurality of IEs) and a Scan Duration field indicative of a desired scan duration during which the SINRs of the pilot signals transferred from the neighbor BSs will be scanned. If the IEEE 802.16e communication system is based on an SC scheme, i.e., if the scan duration field is adapted to an SC physical channel, the scan duration field is configured in the form of mini-slot units. If the IEEE 802.16e communication system is an OFDM/OFDMA system, i.e., if the IEEE 802.16e communication system is applied to an OFDM/OFDMA physical channel, the scan duration field is configured in the form of OFDM symbols. 
     The BS  850 , having received the SCAN_REQ message, transmits the DL_MAP message including information to be scanned by the MSS  800  to the MSS  800  at step  821 . The MSS  800  receives the DL_MAP message including the SCANNING_IE message and performs a pilot SINR scanning process associated with the neighbor BSs in response to parameters contained in the SCANNING_IE message at step  823 . 
       FIG. 9  is a flow chart illustrating a pilot SINR scan report procedure in accordance with the third preferred embodiment of the present invention. However, prior to describing  FIG. 9 , it should be noted that a current IEEE 802.16e communication system has not proposed additional procedures for controlling the MSS to report pilot SINR scan result information. Because there is no process for reporting such pilot SINR scan result information in the IEEE 802.16e communication system, the BS may command the MSS to be handed over to another BS even though it does not recognize SINR scan result data associated with neighbor BSs of the MSS, resulting in deterioration of communication efficiency. For example, it is assumed that the neighbor BSs of the MSS are composed of first to sixth BSs and an SINR value of a pilot signal received from the second BS is a maximum value. In this case, the MSS may have the best channel condition when it is handed over to the second BS from among six neighbor BSs, but an active BS to which the MSS currently belongs does not recognize the SINR scan result data of the neighbor BSs. The MSS may also be handed over to another BS (e.g., the sixth BS) different from the second BS. The BS can transmit a handover request signal to the MSS in the following two cases. 
     The first case indicates a specific case where the current BS&#39;s capacity reaches a threshold value. The second case indicates a specific case where an MSS having a priority higher than that of the current service MSS enters the BS. 
     Due to the aforementioned reasons, it is very important for the MSS to report pilot SINR scanning result data. The present invention proposes two pilot SINR scanning result report methods, i.e., a periodic scan report method and an event triggering scan report method. The periodic scan report method and the event trigger scan report method will hereinafter be described in more detail. 
     (1) Periodic Scan Report Method 
     In accordance with the periodic scan report method, the MSS reports SINRs of pilot signals of the scanned active BS and neighbor BSs to the active BS according to a predetermined period. 
     (2) Event Triggering Scan Report Method 
     In accordance with the event triggering scan report method, the MSS reports SINRs of pilot signals of the scanned active BS and neighbor BSs to the active BS only when prescribed setup events have been generated. The event triggering scan report method controls the MSS to report SINRs of pilot signals of the scanned active BS and neighbor BSs to the active BS only when either one of events “a” and “b” has been generated. The event “a” and the other event “b” are shown in Table 13 below. 
     
       
         
               
               
               
             
           
               
                 TABLE 13 
               
               
                   
               
               
                 Event 
                 Condition 
                 Operation 
               
               
                   
               
             
             
               
                 Event a 
                 When active BS is 
                 When event “a” occurs after 
               
               
                   
                 unchanged but the 
                 transmitting initial measurement, pilot 
               
               
                   
                 order of neighbor 
                 SINR measurement of neighbor BS is 
               
               
                   
                 BSs&#39; SINRs 
                 transmitted to serving BS via 
               
               
                   
                 is changed 
                 Scan_Report message 
               
               
                 Event b 
                 When neighbor BS&#39;s 
                 When event “b” occurs, MSS transmits 
               
               
                   
                 pilot SINR is higher 
                 MSSHO_REQ message with neighbor 
               
               
                   
                 than serving BS&#39;s 
                 BS&#39;s pilot SINR value to request 
               
               
                   
                 SINR 
                 handover function to serving BS 
               
               
                   
               
             
          
         
       
     
     Referring to Table 13, the event “a” indicates a specific case when a pilot SINR of an active BS is not less than pilot SINRs of neighbor BSs, but the magnitudes of the pilot SINRs of neighbor BSs are changed, such that the order of the magnitudes is changed to another order. More specifically, the event “a” indicates a specific case when the magnitudes of pilot SINRs of neighbor BSs are changed to others on the condition that the active BS of the MSS is unchanged. The scan report operations in case of generating the event “a” will hereinafter be described. Before generating the event “a”, the MSS reports initially-scanned pilot SINRs of the active BS and neighbor BSs to the active BS. When generating the event “a” while scanning the pilot SINRs, the scanned pilot SINRs of the active BS and neighbor BSs are reported to the active BS. The scan report operation for the event “a” enables the active BS to continuously recognize the pilot SINRs of the neighbor BSs in the same manner as in the periodic scan report method. Further, the scan report operation for the event “a” reduces the number of scan report operations of the MSS as compared to the periodic scan report operation when the MSS moves to another position at a relatively low speed, such that it minimizes the amount of resource use in response to the scan report operation, resulting in increased overall efficiency of system resources. In this case, the scan report operation is carried out using a SCAN_REPORT message, which will be described later in more detail, such that its detailed description will herein be omitted. 
     Referring to Table 13, the event “b” indicates a specific case where there arises a neighbor BS with a pilot SINR magnitude higher than a pilot SINR magnitude of an active BS to which the MSS currently belongs. More specifically, the event “b” indicates a specific case where the active BS of the MSS is changed to another BS. 
     Before generating the event “b”, the MSS reports initially-scanned pilot SINRs of the active BS and neighbor BSs to the active BS. Thereafter, in the case of generating the event “b”, the MSS transmits an MSSHO_REQ (Mobile Subscriber Station HandOver Request) message containing scanning result data of the active BS and neighbor BSs to the active BS, such that it can request such a handover function from the active BS. As previously shown in Table 9 of the prior art, the MSSHO_REQ message includes a Management Message Type field including transmission message type information (i.e., a plurality of IEs), an Estimated_Ho_Time field including a handover start time, and an N_Recommended field including MSS scanning result data. In this case, the N_Recommended field includes IDs of the neighbor BSs and SINRs of pilot signals of the neighbor BSs. Therefore, the scan report operation for the event “b” performs a scan report operation only when the MSS generates its request signal, such that it reduces the number of scan report operations of the MSS as compared to the periodic scan report operation, such that it minimizes the amount of resource use in response to the scan report operation, resulting in an increased overall efficiency of system resources. 
     It is assumed that the scan report method could be applied in  FIG. 9 . Referring to  FIG. 9 , the BS  950  transmits a DL_MAP message to the MSS  900  at step  911 . In this case, the DL_MAP message includes a SCAN_REPORT_IE message for implementing a scan report operation. In this case, the SCAN_REPORT_IE message acts as channel quality report information for reporting a channel quality. The SCAN_REPORT_IE message is shown in Table 14 below. 
     
       
         
               
               
               
             
               
             
               
               
               
               
               
             
               
               
             
               
               
             
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
             
               
             
           
               
                 TABLE 14 
               
               
                   
               
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Scan_Report_IE { 
               
             
          
           
               
                   
                 CID 
                 16 
                 bits 
                 MSS basic CID 
               
               
                   
                 PERIODIC_N_REPORTMODE 
                 8 
                 bits 
                 Periodic Report Mode 
               
             
          
           
               
                   
                 number 
               
             
          
           
               
                   
                 For(i=0;j&lt;PERIODIC_N_REPORTMODE; 
               
             
          
           
               
                 j++){ 
               
             
          
           
               
                   
                 Report Period 
                 8 
                 bits 
                 Only if report Mode 
               
             
          
           
               
                   
                 number 
               
             
          
           
               
                   
                 } 
                   
                   
                   
               
               
                   
                 Event A mode 
                 1 
                 bit 
                 0: Event A not used 
               
             
          
           
               
                   
                 1: Event A used 
               
             
          
           
               
                   
                 Event B mode 
                 1 
                 bit 
                 0: Event B not used 
               
             
          
           
               
                   
                 1: Event B used 
               
             
          
           
               
                   
                 If (Event B mode = = 1) 
               
             
          
           
               
                   
                 Timer 1 
                 8 
                 bits 
                 Only if report mode is 
               
             
          
           
               
                   
                 event b. Timer 1 is the 
               
               
                   
                 shortest time to maintain 
               
               
                   
                 the situation that pilot 
               
               
                   
                 SINR of certain neighbor 
               
               
                   
                 BS is higher than pilot 
               
               
                   
                 SINR of serving BS 
               
             
          
           
               
                   
                 } 
               
             
          
           
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 14, the SCAN_REPORT_IE message includes an N_REPORTMODE parameter. The N_REPORTMODE parameter indicates that there are N report modes for the scan report function. 
     The present invention will hereinafter disclose three modes, i.e., a periodic report mode in response to a periodic scan report operation, an Event “a” mode in response to a scan report operation for occurrence of the Event “a”, and an Event “b” mode in response to a scan report operation for occurrence of the Event “b”. The present invention may carry out a scan report operation using either the event “a” mode or the event “b” mode along with the periodic report mode, such that the MSS can periodically report pilot SINRs of the active BS and neighbor BSs and can also perform an optimum scan report operation according to the MSS moving situation. 
     The SCAN_REPORT_IE message shown in Table 14 includes a PERIODIC_N_REPORTMODE parameter. The PERIODIC_N_REPORTMODE parameter indicates the number of periodic scan report operations of the MSS. In this case, the scan report period may be variably determined, such that a Report Period value acting as the scan report period is marked on the PERIODIC_N_REPORTMODE parameter. An event is applied to the scan report operation on a one by one basis, the SCAN_REPORT_IE message includes Event A mode- and Event B mode-parameters indicating which one of the events is associated with a corresponding event triggering scan report operation. 
     The scan report operation for the Event “b” occurs in the case where pilot SINRs of neighbor BSs are higher than a pilot SINR of the active BS. In this case, it is desirable that the MSSHO_REQ message be transmitted to the active BS only when the pilot SINRs of the neighbor BSs are continuously higher than the pilot SINR of the active BS during a predetermined time, because there may arise a ping-pong phenomenon when the active BS&#39;s pilot SINR and the pilot SINRs of the neighbor BSs are continuously changed to others. In this case, a timer for waiting for a predetermined time to prevent the ping-pong phenomenon is called a first timer (i.e., timer  1 ). The timer  1  is associated with only a specific case in which the scan report operation occurs in response to the event “b”. The DL_MAP message includes the SCANNING_IE message for scanning the MSS  900 , and the SCANNING_IE message is shown above in Tables 10 to 12. 
     Referring to  FIG. 9 , after transmitting a DL_MAP message including the SCAN_REPORT_IE and SCANNING_IE messages at step  911 , the BS  950  transmits an NBR_ADV message to the MSS  900  at step  913 . As previously shown in Table 4, the NBR_ADV message includes a Management Message Type field including transmission message type information (i.e., a plurality of IEs); an N_Neighbors field including the number of neighbor BSs; a neighbor BS-ID field including ID information of the neighbor BSs; a Configuration Change Count field including the number of configuration changes; a physical frequency field including physical channel frequencies of the neighbor BSs; and a TLV Encoded Neighbor Information field including information associated with the neighbor BSs, other than the above neighbor-BSs-associated information. 
     The MSS  900  receives the NBR_ADV message including the information associated with the neighbor BSs from the BS  950  and scans neighbor BSs recognized by the NBR_ADV message (i.e., SINRs of pilot signals transferred from the neighbor BSs) according to parameters contained in the SCANNING_IE message contained in the DL_MAP message at step  915 . It should be noted that SINRs of pilot signals transferred from the neighbor BSs and the SINR of the pilot signal transferred from the BS  950  to which the MSS  900  currently belongs are continuously scanned, even though it is not illustrated in  FIG. 9 . 
     Accordingly, if a current time reaches a time period corresponding to the Report Period message of the SCAN_REPORT_IE message contained in the DL_MAP message at step  917 , the MSS transmits the SCAN_REPORT message having pilot SINRs of the scanned neighbor BSs to the BS  950  at step  919 . The SCAN_REPORT message is shown in Table 15 below. 
     
       
         
               
               
               
             
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
               
               
             
               
               
             
               
             
           
               
                 TABLE 15 
               
               
                   
               
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 SCAN_REPORT_Message_Format ( ) { 
               
             
          
           
               
                   
                 Management Message Type = ? 
                 8 bits 
                   
               
               
                   
                 Report Mode 
                 2 bits 
                 00: Periodic 
               
             
          
           
               
                   
                 01: event a 
               
               
                   
                 10: event b 
               
             
          
           
               
                   
                 N_NEIGHBORS 
                 8 bits 
                   
               
               
                   
                 For(i=0;j&lt;N_NEIGHBORS;j++){ 
               
             
          
           
               
                   
                 Neighbor BS-ID 
                 48 bits  
                   
               
               
                   
                 S(I+N) 
                 16 bits  
                   
               
             
          
           
               
                   
                 } 
               
             
          
           
               
                 } 
               
               
                   
               
             
          
         
       
     
     Referring to Table 15, the SCAN_REPORT message includes a Management Message Type field indicating transmission message type information (i.e., a plurality of IEs), a Report Mode field including a report mode, an N_Neighbors field including the MSS scanning result. Neighbor BS-IDs of neighbor BSs and pilot SINRs of individual neighbor BSs are marked in the N_Neighbors field. In this case, the Report Mode indicates which mode is adapted to transmit the SCAN_REPORT message. 
     As described above, where the MSS performs the scan report operation simultaneously with transmitting a handover request, IEs contained in the SCAN_REPORT message are contained in the MSSHO_REQ message without any change. The associated operations of the MSS will be described later in more detail. 
     The MSS  900  transmits the SCAN_REPORT message to the BS  950 , and scans pilot SINRs of neighbor BSs in response to parameters contained in the SCANNING_IE message at step  921 . If a current time reaches a time period corresponding to the Report Period message of the SCAN_REPORT_IE message during the scanning times of the SINRs of the pilot signals transmitted from the neighbor BSs at step  923 , the MSS transmits the SCAN_REPORT message including pilot SINRs of the scanned neighbor BSs to the BS  950  at step  925 . The MSS  900  transmits the SCAN_REPORT message to the BS  950 , and re-scans pilot SINRs of neighbor BSs in response to parameters contained in the SCANNING_IE message at step  927 . Therefore, the MSS  900  can periodically report pilot SINRs of the active BS and neighbor BSs to the BS  950 . 
       FIG. 10  is a flow chart illustrating a pilot SINR scan report procedure in accordance with a fourth preferred embodiment of the present invention. It is assumed that the scan report method utilizes the scan report method based on the event “a” occurrence in  FIG. 10 . 
     Referring to  FIG. 10 , the BS  1050  transmits a DL_MAP message including the SCAN_REPORT_IE message to the MSS  1000  at step  1011 . The SCAN_REPORT_IE message includes the same parameters as in Table 14. The scan report method is based on the occurrence of the event “a”, such that the Event “a” mode value is determined to be a value of 1. The DL_MAP message also includes the SCANNING_IE message for the MSS  1000 &#39;s scanning operation, and the SCANNING_IE message is shown in Tables 10 to 12. 
     The BS  1050  transmits the DL_MAP message including the SCAN_REPORT_IE and SCANNING_IE messages to the MSS  1000 , and transmits the NBR_ADV message to the MSS  1000  at step  1013 . The NBR_ADV message is the same as in Table 4 of the prior art, such that its detailed description will herein be omitted. 
     The MSS  1000 , having received the NBR_ADV message including the information associated with the neighbor BSs from the BS  1050 , scans neighbor BSs recognized by the NBR_ADV message (i.e., SINRs of pilot signals transferred from the neighbor BSs) according to parameters contained in the SCANNING_IE message contained in the DL_MAP message at step  1015 . It should be noted that SINRs of pilot signals transferred from the neighbor BSs and the SINR of the pilot signal transferred from the BS  1050  to which the MSS  1000  currently belongs are continuously scanned, even though it is not illustrated in  FIG. 10 . 
     After scanning SINRs of pilot signals transferred from the active BS (i.e., the BS  1050 ) and neighbor BSs, the MSS transmits the SCAN_REPORT message including the SINRs of the scanned BS  1050  and neighbor BSs to the BS  1050  at step  1017 . The scan report operation for the event “a” allows the MSS  1000  to firstly report pilot SINRs of the BS  1050  and neighbor BSs to the BS  1050 , and then re-performs the scan report operation only when the order of magnitudes of the pilot SINRs of the initially-reported BS  1050  and neighbor BSs is changed to another order, such that the MSS  1000  initially performs the scan report operation only once. 
     Accordingly, the MSS  1000  transmits the SCAN_REPORT message to the BS  1050 , and scans pilot SINRs of the BS  1050  and neighbor BSs according to parameters contained in the SCANNING_IE message at step  1019 . If the event “a” occurs during the scanning time of the SINRs of the pilot signals transferred from the BS  1050  and neighbor BSs, i.e., if there arises a variation in the magnitude order of pilot SINRs of the neighbor BSs even though the magnitudes of the pilot SINRs of the BS  1050  are higher than the pilot SINRs of the neighbor BSs at step  1021 , the MSS  1000  transmits the SCAN_REPORT message including the SINRs of the scanned neighbor BSs to the BS  1050  at step  1023 . The MSS  1000  transmits the SCAN_REPORT message to the BS  1050 , and scans pilot SINRs of the BS  1050  and neighbor BSs according to parameters contained in the SCANNING_IE message at step  1025 . The MSS  1000  reports pilot SINRs of the BS  1050  and neighbor BSs to the BS  1050  only in the case of generating the event “a”, such that it uses minimum resources for the scan report operation, resulting in increased overall efficiency of system resources. 
       FIG. 11  is a flow chart illustrating a pilot SINR scan report procedure in accordance with a fifth preferred embodiment of the present invention. It is assumed that the scan report method is adapted to the scan report method based on the event “b” occurrence in  FIG. 11 . 
     Referring to  FIG. 11 , the BS  1150  transmits a DL_MAP message including the SCAN_REPORT_IE message to the MSS  1100  at step  1111 . The SCAN_REPORT_IE message includes the same parameters as in Table 14. The scan report method is based on the occurrence of the event “b”, such that the Event “b” mode value is determined to be a value of 1. The DL_MAP message also includes the SCANNING_IE message for the MSS  1100 &#39;s scanning operation, and the SCANNING_IE message is shown above in Tables 10 to 12. 
     The BS  1150  transmits the DL_MAP message including the SCAN_REPORT_IE and SCANNING_IE messages to the MSS  1100 , and transmits the NBR_ADV message to the MSS  1100  at step  1113 . In this case, the NBR_ADV message is the same as in Table 4 of the prior art, such that its detailed description will herein be omitted. 
     The MSS  1100 , having received the NBR_ADV message including the information associated with the neighbor BSs from the BS  1150 , scans neighbor BSs recognized by the NBR_ADV message (i.e., SINRs of pilot signals transferred from the neighbor BSs) according to parameters contained in the SCANNING_IE message contained in the DL_MAP message at step  1115 . It should be noted that SINRs of pilot signals transferred from the neighbor BSs and the SINR of the pilot signal transferred from the BS  1150  to which the MSS  1100  currently belongs are continuously scanned, even though it is not illustrated in  FIG. 11 . 
     If the MSS  1100  decides to change its current active BS to another BS while scanning SINRs of pilot signals of the neighbor BSs at step  1117 , i.e., if the MSS  1100  decides to change its current active BS to a new BS different from the BS  1150  at step  1117 , the MSS  1100  transmits the MSSHO_REQ message to the BS  1150  at step  1119 . In this case, the MSSHO_REQ message must include IEs of the SCAN_REPORT message as described above. 
     After transmitting the MSSHO_REQ message to the BS  1150 , the MSS  1100  re-scans pilot SINRs of neighbor BSs according to parameters contained in the SCANNING_IE message at step  1121 . The MSS  1100  reports pilot SINRs of the BS  1150  (i.e., an active BS) and neighbor BSs to the BS  1150  only in the case of generating the event “b”, such that it minimizes the amount of resources needed for the scan report operation, resulting in increased overall efficiency of system resources. 
     As is apparent from the above description, the present invention provides a method for measuring and reporting a channel quality (i.e., a pilot SINR) in the IEEE 802.16e communication system used in a broadband wireless access (BWA) communication system for use with an OFDM/OFDMA scheme. The present invention enables an MSS to scan pilot SINRs of neighbor BSs even though there is no request from the MSS. Therefore, if the active BS for transmitting a desired service to the MSS is changed to another BS due to the MSS&#39;s mobility, the present invention performs a handover function associated with the changed active BS according to pilot SINR scanning result data of the MSS. 
     Although preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.