Patent Publication Number: US-2007105585-A1

Title: Apparatus and method for constructing neighbor node list in cellular communication system

Description:
PRIORITY  
      This application claims priority under 35 U.S.C. § 119 to an application filed in the Korean Intellectual Property Office on Nov. 9, 2005 and allocated Serial No. 2005-106798, the contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to a cellular communication system, and, in particular, to an apparatus and method for constructing a neighbor node list in a Broadband Wireless Access (BWA) communication system using a multi-hop relay scheme.  
      2. Description of the Related Art  
      Recently, extensive research is being conducted to provide various Quality of Service (QoS) features with a data rate of about 100 Mbps in the advanced fourth-generation (4G) communication system. The 4G communication system is evolving to provide mobility, high data rate transmission, and high QoS in a Broadband Wireless Access (BWA) system such as a Local Area Network (LAN) system and a Metropolitan Area Network (MAN) system. Examples of the above system are identified in the Institute of Electrical and Electronics Engineers (IEEE) 802.16d system and the IEEE 802.16e system standards.  
      The IEEE 802.16d system and the BWA system use an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme. The IEEE 802.16d system considers only a fixed Subscriber Station (SS) and a single cell structure (i.e., the mobility of an SS is not considered). The IEEE 802.16e system considers the mobility of an SS. When the mobility of an SS is considered, the SS will be referred to as a Mobile Station (MS).  
       FIG. 1  is a block diagram of a conventional BWA system. Referring to  FIG. 1 , the BWA system has a multi-cell structure. The IEEE  802 . 16 e system includes a cell  100 , a cell  150 , a base station (BS)  110  managing the cell  100 , a BS  140  managing the cell  150 , and a plurality of MSs  111 ,  113 ,  130 ,  151  and  153 . The signal exchange between the BSs  110  and  140  and the MSs  111 ,  113 ,  130 ,  151  and  153  is performed using an OFDM/OFDMA scheme. The MS  130  is located in a boundary region (i.e., a handover region) between the cells  100  and  150 . When the MS  130  moves from the cell  100  of the BS  110  into the cell  150  of the BS  140  while communicating with the BS  110 , the serving BS of the MS  130  changes from the BS  110  to the BS  140 .  
      In such a BWA system (e.g., an IEEE 802.16 system), a ranging channel is used as an uplink (UL) random access channel. An initial ranging operation, a periodic ranging operation, and a bandwidth request ranging operation are performed using the ranging channel. When an MS enters a network (i.e., a network entry procedure) or loses its system information, it performs an initial ranging operation to achieve UL synchronization. During the initial ranging operation of the MS, a BS measures the precise time of arrival of a ranging signal received from the MS, calculates a Round Trip Delay (RTD) between the BS and the MS, and informs the MS of a timing offset corresponding to the calculated RTD.  
       FIG. 2  is a flow diagram illustrating an initial ranging procedure in the conventional BWA system. Referring to  FIG. 2 , when powered on, an MS  201  receives a downlink (DL) preamble from a serving BS  203  to achieve synchronization with the BS  203 . In step  204 , the MS  201  receives a DL-MAP message and a Downlink Channel Descriptor (DCD) message from the BS  203  and acquires DL channel information from the received messages. In addition, the MS  201  receives a UL-MAP message and an Uplink Channel Descriptor (UCD) message from the BS  203  and acquires UL channel information and initial ranging parameters from the received messages.  
      Using the acquired UL/DL channel information, the MS  201  performs a basic access procedure, which is called an initial ranging procedure. In the initial ranging procedure, the MS  201  transmits a ranging request (RNG-REQ) message to the BS  203  (step  205 ) and the BS  203  transmits a ranging response (RNG-RSP) message to the MS  201  in response to the RNG-REQ message (step  207 ). The messages used for the initial ranging procedure are described in detail below.  
      Table 1 below illustrates the format of the RNG-REQ message transmitted from the MS to the BS.  
                       TABLE 1                       Syntax   Size   Note                  RNG-REQ_Message_Format( ) {                Management Message Type = 4   8bits        Downlink Channel ID        TLV encoded Information {   variable   TLV specific         SS MAC Address         Requested Downlink Burst Profile         MAC Version         Ranging Anomalies         AAS broadcast capability         }        }                  
 
      As illustrated in Table 1, the RNG-REQ message includes a plurality of information fields. A “Management Message Type” field has a value of ‘4’ to indicate the RNG-REQ message. “SS MAC Address” is a MAC layer address of the MS and is used as an identifier of the MS. “Downlink Channel ID” indicates a DL channel through which an UCD message including UL channel information is received. “Requested Downlink Burst Profile” includes a 0-3 bit section and a 4-7 bit section. In the 0-3 bit section, a Downlink Interval Usage Code (DIUC) is recorded for requesting formats (e.g., a modulation scheme and an error correction scheme) that are required to receive and transmit physical channel signals. The 4-7 bit section is a section for recording the four Least Significant Bits (LSBs) of a Configuration Change Count field of the UCD message used for ranging request. The BS transmits a predetermined physical channel signal to the MS in accordance with the information stored in the 0-3 bit section.  
      As also illustrated in Table 1, “MAC Version” indicates the version of a MAC layer used by the MS. “Ranging Anomalies” includes information about whether the MS tries to access the BS at a maximum transmission (TX) power or a minimum TX power. When the BS commands the MS to increase or decrease TX power to correct the TX power, time information, etc., the MS can use the Ranging Anomalies in response to the command of the BS. “AAS broadcast capability” indicates whether the MS is capable of receiving a broadcast message.  
      Table 2 below illustrates the format of the RNG-RSP message transmitted from the BS to the MS.  
                       TABLE 2                       Syntax   Size   Note                  RNG-RSP_Message_Format( ) {                Management Message Type = 5   8bits        Uplink Channel ID        TLV encoded Information {   variable   TLV specific         SS MAC Address   6         Downlink Operational Burst Profile   2         Primary Management CID   2         Basic CID   2         Ranging Status   4   1 = continue               2 = abort               3 = success               4 = rerange         Timing adjust   4         Power level adjust   1         Downlink frequency override   4   Center Frequency               (kHz) allowing an               SS to perform an               initial Ranging         }       Request again        }                  
 
      As illustrated in Table 2, the RNG-RSP message includes a plurality of information fields. A “Management Message Type” field has a value of ‘5’ to indicate that the present message is the RNG-RSP message. A “SS MAC Address” field contains a MAC layer address of the MS that will receive the RNG-RSP message. “Downlink Operational Burst Profile” is used as a response to the “Requested Downlink Burst Profile” of the RNG-REQ message from the MS and indicates a DIUC number that will be used by the BS. “Uplink Channel ID” indicates a UL channel for the MS. “Primary Management CID” and “Basic CID” are CIDs that are assigned to the MS by the BS in order to manage the connection between the BS and the MS while the MS receives a service from the BS after a ranging procedure.  
      As also illustrated in Table 2, “Ranging Status” indicates a response of the BS to a ranging request of the MS. When the Ranging Status field has a value of ‘1’, it indicates the need to continue the ranging process. When the Ranging Status field has a value of ‘2’, it indicates the need to abort (stop) the ranging process. When the Ranging Status field has a value of ‘3’, it indicates the success of the ranging process. When the Ranging Status field has a value of ‘4’, it indicates the need to perform the ranging request again.  
      As further illustrated in Table 2, “Timing Adjust” contains information that enables the MS to correct incorrect time information. “Power Level Adjust” contains information that enables the MS to adjust its TX/RX power. “Downlink Frequency Override” is used to inform the MS of a frequency value of another channel, so that the MS can again perform an initial ranging request with another frequency when the Ranging Status field is set to ‘2’ indicating the need to abort the ranging process.  
      After the ranging procedure is completed to achieve synchronization with the BS and to establish basic environments for communication with the BS (e.g., adjustment of power), the remaining initial network entry procedure (e.g., a basic capability negotiation process, an authorization process and a registration process) are performed to complete connection to the BS.  
      Because a signaling communication between a stationary BS and an MS is performed through a direct link as illustrated in  FIG. 1 , the IEEE 802.16e system can easily provide a highly reliable wireless link between the BS and the MS. However, because the BS is stationary, the IEEE 802.16e system has a low flexibility in constructing a wireless network. Accordingly, use of the IEEE 802.16e system makes it difficult to provide an efficient communication service in a radio environment where traffic distribution or call requirements change frequently.  
      In order to overcome this problem, a stationary or fixed Relay Station (RS), a mobile RS or general MSs can be used to apply a multi-hop relay data transmission scheme to a general cellular communication system such as the IEEE 802.16e system. The use of the multi-hop relay wireless communication system makes it possible to reconfigure a network in rapid response to a change in the communication environment and to operate the entire wireless network more efficiently. For example, the multi-hop relay wireless communication system can expand a cell coverage area and increase system capacity. When channel conditions between a BS and an MS are poor, an RS is installed between the BS and the MS to establish a multi-hop relay link therebetween, thereby making it possible to provide the MS with a radio channel having better channel conditions. In addition, the multi-hop relay scheme is used in a cell boundary region with poor channel conditions, thereby making it possible to provide a high-rate data channel and to expand the cell coverage area.  
       FIG. 3  is a block diagram illustrating a BWA system that uses a multi-hop relay scheme to expand a BS coverage area. Referring to  FIG. 3 , the multi-hop relay BWA system has a multi-cell structure. The multi-hop relay BWA system includes a cell  300 , a cell  340 , a BS  310  managing the cell  300 , a BS  350  managing the cell  340 , a plurality of MSs  311  and  313  located within the cell  300 , a plurality of MSs  321  and  323  located in a region  330  outside the cell  300  of the BS  310  yet communicating with the BS  310 , an RS  320  providing a multi-hop relay path between the BS  310  and the MSs  321  and  323  located in the region  330 , a plurality of MSs  351 ,  353  and  355  located in the cell  340 , a plurality of MSs  361  and  363  located in a region  370  outside the cell  340  of the BS  350  yet communicating with the BS  350 , and an RS  360  providing a multi-hop relay path between the BS  350  and the MSs  361  and  363  located in the region  370 . An OFDM/OFDMA scheme is used for communication among the BS  310  and  350 , the RS  320  and  360 , and the MSs  311 ,  313 ,  321 ,  323 ,  351 ,  353 ,  355 ,  361 , and  363 .  
      Although the MSs  311  and  313  located in the cell  300  and the RS  320  can directly communicate with the BS  310 , the MSs  321  and  323  located in the region  330  cannot directly communicate with the BS  310 . Therefore, the RS  320  covers the region  330  to relay signals between the BS  310  and the MSs  321  and  323 . That is, the MSs  321  and  323  can communicate with the BS  310  through the RS  320 .  
      Further, the RS  360  and the MSs  351 ,  353 , and  355  located in the cell  340  can directly communicate with the BS  350 . However, the MSs  361  and  363  located in the region  370  cannot directly communicate with the BS  350 . Therefore, the RS  360  covers the region  370  to relay signals between the BS  350  and the MSs  361  and  363 . That is, the MSs  361  and  363  can communicate with the BS  350  through the RS  360 .  
      As described above, in the multi-hop relay BWA system, the MS can communicate with the BS via a direct link and also can communicate with the BS via the RS when it cannot communicate with the BS via the direct link. Therefore, operations must be defined so that the multi-hop relay BWA system can also support services and functions that are provided by a conventional wireless communication system.  
      For example, because a target of communication with the MS is expanded to include the RS as well as the BS, the MS must be able to scan neighbor RSs as well as neighbor BSs. To this end, the MS must receive information about neighbor BSs and neighbor RSs from a serving station (RS or BS). However, a method of providing the MS with information about neighbor BSs and all neighbor RSs connected to the neighbor BSs is impossible to implement, due to a limited transport capacity.  
       FIG. 4  is a diagram illustrating the distribution of BSs and RSs in the multi-hop relay BWA system.  FIG. 4  illustrates a case where each BS (or cell) includes ten RSs by way of example. However, it will be apparent to those skilled in the art that each BS may include a larger (smaller) number of RSs.  
      Referring to  FIG. 4 , an MS  411  communicates with a BS 1   401  through a serving relay station RS 8  As shown in  FIG. 4 , BS 2   403  and BS 3   405  neighbor BS 1   401 . At this point, so that the MS  411  can scan all the neighbor nodes, the serving relay station RS 8  must transmit to the MS  411  information about not only the BS 2   403  and the BS 3   405  but also about RSs connected to the two BSs  403  and  405  (i.e., information about 2 neighbor BSs and also about the 20 neighbor RSs shown in  FIG. 4  associated with BS 2   403  and BS 3   405 ).  
      In general, a mobile communication network manages information about several tens of neighbor BSs and broadcasts the information to MSs. Therefore, if 20 neighbor BSs, each having 10 RSs, exist in the multi-hop relay BWA system, an MS must be provided with information about a total of 220 nodes. Accordingly, too many resources are wasted in transmitting control information, rather than transmitting actual traffic data.  
      As described above, it is inefficient for the conventional multi-hop relay BWA system to provide an MS with information about all neighbor RSs as well as neighbor BSs.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide an apparatus and method for a multi-hop relay BWA system for constructing a neighbor node list on the basis of the scanning results received from an MS.  
      Another object of the present invention is to provide an apparatus and method for a multi-hop relay BWA system for scanning neighbor nodes at an MS in an initial network entry mode and reporting the scanning results to a serving station.  
      A further object of the present invention is to provide an apparatus and method for a multi-hop relay BWA system for optimizing a broadcast neighbor node list using information about nodes that can be acquired by an MS.  
      According to one aspect of the present invention, there is provided a communication method of an MS in a cellular communication system, including acquiring neighbor nodes through a scanning operation in an initial network entry mode; and transmitting information about the acquired neighbor nodes to a serving station.  
      According to another aspect of the present invention, there is provided a communication method of a serving station in a cellular communication system, determining if a predetermined message is received from an MS performing an initial network entry procedure; if the predetermined message is received, determining if the received message includes information about neighbor nodes; and if the received message includes the information about the neighbor nodes, updating a periodically-broadcast neighbor node list using the information about the neighbor nodes.  
      According to a further aspect of the present invention, there is provided an MS apparatus for a cellular communication system, including a scanning unit for acquiring neighbor nodes in an initial network entry mode; a controller for selecting the neighbor node with the highest RX signal strength as a serving node and providing information about information of neighbor nodes satisfying a predetermined criterion; a message generator for generating a message including the information about the neighbor nodes satisfying the predetermined criterion; and a transmitter for processing the generated message in accordance with a predetermined wireless standard and transmitting the processed message to the serving station through an antenna.  
      According to still another aspect of the present invention, there is provided a serving station apparatus for a cellular communication system, including a database for managing a neighbor node list that is broadcast periodically; a message processor for processing a message that is received from an MS performing an initial network entry procedure; and a controller for updating the neighbor node list using information of neighbor nodes that is included in a predetermined message received from the MS.  
      According to yet another aspect of the present invention, there is provided a method for constructing a neighbor node list in a cellular communication system, including acquiring neighbor nodes at an MS through a scanning operation in an initial network entry procedure, inserting information about the acquired neighbor nodes into a predetermined message, and transmitting the predetermined message to a serving station; and updating a periodically-broadcast neighbor list at the serving station on the basis of the information about the neighbor nodes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
       FIG. 1  is a block diagram of a conventional BWA system;  
       FIG. 2  is a flow diagram illustrating an initial ranging procedure in the conventional BWA system;  
       FIG. 3  is a block diagram illustrating a BWA system that uses a multi-hop relay scheme to expand a BS coverage area;  
       FIG. 4  is a diagram illustrating the distribution of BSs and RSs in the multi-hop relay BWA system;  
       FIG. 5  is a flow diagram illustrating an overall signaling procedure for constructing a neighbor node list in a multi-hop relay BWA system according to the present invention;  
       FIG. 6  is a flowchart illustrating an operation of an MS for initial network entry in a multi-hop relay BWA system according to the present invention;  
       FIG. 7  is a flowchart illustrating an operation of a serving station for constructing a neighbor node list in a multi-hop relay BWA system according to the present invention; and  
       FIG. 8  is a block diagram of an MS (or a serving station) in a multi-hop relay BWA system according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the invention with unnecessary detail. Also, the terms used herein are defined according to the functions of the present invention. Thus, the terms may vary depending on user&#39;s or operator&#39;s intension and usage. That is, the terms used herein must be understood based on the descriptions made herein.  
      The present invention provides an apparatus and method for updating a neighbor node list in a multi-hop relay BWA system by providing a serving station with information about neighbor nodes that are scanned by an MS in an initial network entry mode. Hereinafter, the term “node” is used to refer to both of a BS and an RS.  
      The multi-hop relay BWA system uses an OFDM scheme or an OFDMA scheme, for example. Accordingly, the multi-hop relay BWA system can transmit physical channel signals using a plurality of subcarriers, thereby enabling high-rate data transmission. In addition, the multi-hop relay BWA system supports a multi-cell structure, thereby supporting the mobility of an MS. Although a multi-hop relay BWA system is used as an example in the following description, the present invention can be applied to any cellular communication system that uses a multi-hop relay scheme.  
       FIG. 5  is a flow diagram illustrating an overall signaling procedure for constructing a neighbor node list in a multi-hop relay BWA system according to the present invention. As illustrated in  FIG. 5 , it is assumed that a BS 1   51 , an RS 1   52 , a BS 2   53 , an RS 2   54  and an RS 3   55  neighbor an MS  50 .  
      Referring to  FIG. 5 , when powered on, the MS  50  scans neighbor nodes using given information (e.g., frequencies and preamble indexes), in step  501 . At this point, it is assumed that the MS  50  has acquired DL preamble signals of the BS 1   51 , the RS 1   52 , the BS 2   53 , the RS 2   54  and the RS 3   55 .  
      In step  503 , the MS  50  selects the BS 1   51  with the highest RX signal strength as a serving station, arranges the remaining neighbor nodes in the order of RX signal strength, and stores information about the arranged neighbor nodes in a neighbor node management table. Examples of the stored information are node identifiers (IDs), preamble indexes, and RX signal strengths.  
      In step  505 , the MS  50  acquires system synchronization with the BS 1   51  and receives broadcasting information from the BS 1   51 . At this point, for example, the MS  50  receives a MAP message, a Downlink Channel Descriptor (DCD) message, and an Uplink Channel Descriptor (UCD) message from the BS 1   51  and acquires physical channel information and initial ranging parameters from the received messages.  
      In step  507 , the MS  50  searches the stored neighbor node information to select neighbor nodes to be reported to the BS 1   51 . At this point, the MS  50  may select neighbor nodes whose RX signal strength is greater than a predetermined threshold. Alternatively, the MS  50  may select a predetermined number of neighbor nodes in the descending order of RX signal strength.  
      In step  509 , the MS  50  transmits to the BS  151  a ranging request (RNG-REQ) message including information about the selected neighbor nodes. At this point, the information about the selected neighbor nodes may include node IDs (e.g., MAC addresses and preamble indexes) and RX signal strengths (or signal arrival delays) and may be inserted into the ranging request message in Type/Length/Value (TLV) format.  
      In step  510 , the BS 1   51  receives the ranging request message from the MS  50 , extracts the information of the selected neighbor nodes from the received ranging request message, and adds the extracted information to a neighbor node list that is broadcast periodically. In step  511 , the BS 1   51  transmits a ranging response (RNG-RSP) message to the MS  50  in response to the ranging request message, thereby completing an initial ranging procedure.  
      In step  513 , the MS  50  and the BS 1   51  perform the remaining initial network entry procedure. Examples of the remaining initial network entry procedure include a basic capability negotiation process, an authorization process, and a registration process.  
       FIG. 6  is a flowchart illustrating an operation of an MS for initial network entry in a multi-hop relay BWA system according to the present invention. Referring to  FIG. 6 , when powered on in step  601 , the MS scans neighbor nodes (BSs and RSs) using given information (e.g., frequencies and preamble indexes), in step  603 . In step  605 , the MS analyzes the scanning results. In step  607 , the MS determines if two or more valid neighbor nodes are acquired (detected). If so, the operation proceeds to step  609 ; and if not (i.e., if only one valid neighbor node is acquired), the operation proceeds to step  619 . In step  619 , the MS performs a general initial network entry procedure.  
      In step  609 , the MS arranges the acquired neighbor nodes in accordance with a predetermined criterion (e.g., RX signal strength) and determines the priorities of the acquired neighbor nodes. At this point, the first-priority neighbor node (BS or RS) is selected as a serving station that will communicate with the MS.  
      In step  611 , the MS starts to perform an initial network entry procedure on the serving station (i.e., the first-priority neighbor node). At this point, the MS acquires system synchronization with the serving station and receives broadcasting information from the serving station. For example, the MS receives a MAP message, a DCD message, and a UCD message from the serving station and acquires physical channel information and initial ranging parameters from the received messages. In this way, the MS acquires information for an initial ranging procedure.  
      In step  613 , the MS selects a predetermined number of neighbor nodes among the acquired neighbor nodes except the first-priority neighbor node, and transmits to the serving station a ranging request (RNG-REQ) message including information about the selected neighbor nodes. At this point, the information about the selected neighbor nodes may include node IDs (e.g., MAC addresses and preamble indexes) and RX signal strengths (or signal arrival delays) and may be inserted into the ranging request message in Type/Length/Value (TLV) format.  
      In step  615 , the MS receives a ranging response (RNG-RS) message from the serving station, thereby completing an initial ranging procedure.  
      In step  617 , in association with the serving station, the MS performs the remaining initial network entry procedure. Examples of the remaining initial network entry procedure include a basic capability negotiation process, an authorization process, and a registration process.  
       FIG. 7  is a flowchart illustrating an operation of a serving station for constructing a neighbor node list in a multi-hop relay BWA system according to the present invention. The serving station may be a BS or an RS. Referring to  FIG. 7 , the serving station constructs a neighbor node management table on the basis of given information, in step  701 . If the serving station is a BS, the neighbor node management table may be constructed using information about neighbor BSs that can be provided through a backbone network. If the serving station is an RS, the neighbor node management table may be constructed using information about infrastructure nodes that is provided from a serving BS.  
      In step  703 , the serving station determines if a neighbor node list is to be transmitted at the present time. If so, the operation proceeds to step  705 ; and if not, step  703  is repeated.  
      In step  705 , the serving station broadcasts a neighbor node list (or a neighbor node advertisement message), which is managed using the neighbor node management table, to MSs that are located within a service coverage area. At this point, the neighbor node list may be broadcast periodically.  
      In step  707 , the serving station determines if a ranging request (RNG-REQ) message is received from an MS. If so, the operation proceeds to step  709 ; and, if not, the operation returns to step  703 . In step  709 , the serving station analyzes the received ranging request message.  
      In step  711 , the serving station determines if information about neighbor nodes is contained in the received ranging request message. If so, the operation proceeds to step  713 ; and, if not, the operation returns to step  703 . In step  713 , the serving station adds the information about the neighbor nodes to the neighbor node management table. Thereafter, the operation returns to step  703 .  
      Configurations of the MS and the serving station (RS or BS) are described in detail below. The MS and the serving station using the same interface module (communication module) are similarly configured and, accordingly, the configurations of the MS and the serving station will be described with reference to one block diagram.  
       FIG. 8  is a block diagram of an MS (or a serving station) in a multi-hop relay BWA system according to the present invention. Although not so limited, the following description assumes that the MS (or the serving station) uses a Time Division Duplex (TDD)/OFDMA scheme, focusing on control message processing.  
      Referring to  FIG. 8 , the MS (or the serving station) includes an antenna, an RX Radio Frequency (RF) processor  801 , an Analog-to-Digital Converter (ADC)  803 , an OFDM demodulator  805 , a decoder  807 , a message processor  809 , a controller  811 , a neighbor node management table  813 , a message generator  815 , an encoder  817 , an OFDM modulator  819 , a Digital-to-Analog Converter (DAC)  821 , a TX RF processor  823 , a switch  825 , and a time controller  827 .  
      The time controller  827  controls a switching operation of the switch  825  based on frame synchronization. For example, when in an RX section of a frame, the time controller  827  controls the switch  825  so that the antenna is connected to the RX RF processor  801 . When in a TX section of the frame, the time controller  827  controls the switch  825  so that the antenna is connected to the TX RF processor  823 .  
      In the RX section of the frame, the RX RF processor  801  converts an RF signal received through the antenna into a baseband analog signal. The ADC  803  converts the analog signal into sample data (digital data). The OFDM demodulator  805  Fast Fourier Transform (FFT) processes the sample data to output frequency-domain data.  
      The decoder  807  selects data of desired subcarriers from the frequency-domain data, and decodes the selected data in accordance with a predetermined Modulation &amp; Coding Scheme (MCS) level.  
      The message processor  809  processes a control message from the decoder  807  and provides the resulting information to the controller  811 . The controller  811  processes the information received from the message processor  809  and, if necessary, provides the results of the processing to the message generator  815 .  
      The neighbor node management table  813  is a database for managing information about neighbor nodes. The information about the neighbor node may include a node ID, a preamble index, RX signal strength, and a signal arrival delay (e.g., an RTD). The RX signal strength information may be a Carrier-to-Interference plus Noise Ratio (CINR) or a Received Signal Strength Indicator (RSSI). If the device illustrated in  FIG. 8  is the MS, the neighbor node management table  813  manages information about neighbor nodes that are acquired through a scanning operation of the MS. If the device illustrated in  FIG. 8  is the serving station, the neighbor node management table  813  manages a neighbor node list to be broadcast periodically.  
      The message generator  815  generates a message using a variety of information received from the controller  811  and provides the message to the encoder  817 .  
      The encoder  817  encodes data received from the message generator  815  in accordance with a predetermined MCS level. The OFDM modulator  819  Inverse Fast Fourier Transform (IFFT) processes data received from the encoder  817 , thereby generating sample data (OFDM symbols). The DAC  821  converts the sample data into an analog signal. The TX RF processor  823  converts the analog signal received from the DAC  821  into an RF signal and transmits the RF signal through the antenna.  
      In the above-described configuration, the controller  811  is a protocol controller that controls the message processor  809 , the message generator  815 , and the neighbor node management table  813 . The controller  811  can perform the functions of the message processor  809 , the message generator  815 , and the neighbor node management table  813 . Although separate units are provided for respective functions of the controller  811 , the controller  811  can perform all or some of the functions instead of such separate units.  
      Operations of the MS, the RS, and the BS will now be described with reference to the configuration shown in  FIG. 8 , focusing on a control message processing in a MAC layer.  
      The operation of the MS will be first described. In an initial network entry mode, a scanning unit (not illustrated) of a physical layer scans neighbor nodes (BSs and RSs) using given information (frequencies and preamble indexes), and provides information about acquired neighbor nodes to the controller  811  of a MAC layer.  
      The controller  811  arranges the information about the neighbor nodes and stores the arranged information in the neighbor node management table  813 . In addition, the controller  811  selects a neighbor node with the highest RX signal strength as a serving station and performs an initial network entry procedure.  
      In an initial ranging procedure, the controller  811  reads from the neighbor node management table  813  information about neighbor nodes that satisfy a predetermined criterion, and provides the read information to the message generator  815 . At this point, the MS may select neighbor nodes whose RX signal strength is higher than a predetermined threshold. Alternatively, the MS may select a predetermined number of neighbor nodes in the descending order of RX signal strength.  
      Under the control of the controller  811 , the message generator  815  generates a ranging request message (as in Table 1) containing information about the neighbor nodes in TLV format, and provides the generated ranging request message to the encoder  817  of the physical layer. The generated ranging request message is processed in a format suitable for the physical layer and is transmitted through the antenna to the serving station.  
      The operation of the serving station will now be described. The message processor  809  of the serving station analyzes a message received from the MS and provides the results to the controller  811 . According to the present invention, if a ranging request message is received from the MS, the message processor  809  extracts a variety of control information from the received ranging request message and provides the extracted control information to the controller  811 .  
      The controller  811  performs operations corresponding to the control information received from the message processor  809 . According to the present invention, the controller  811  determines if the received ranging request message contains information about neighbor nodes. If so, the controller  811  adds the information about the neighbor nodes to the neighbor node management table  813  to update a neighbor node list.  
      If a neighbor node list is to be transmitted at the present time, the controller  811  reads the neighbor node list from the neighbor node management table  813  and provides the a neighbor node list to the message generator  815 .  
      Under the control of the controller  811 , the message generator  815  generates a neighbor node advertisement message containing the neighbor node list and provides the same to the physical layer. The neighbor node advertisement message is used to broadcast information about nodes (BSs and RSs) neighboring on the serving station to MSs that are located within a service coverage area. The generated neighbor node advertisement message is processed suitable for the physical layer and is broadcast through the antenna.  
      As described above, the ranging request message of the ranging procedure in the initial network entry procedure is used to provide the information about the neighbor nodes (BSs and RSs) to the serving station. In another embodiment, the information about the neighbor nodes may be contained in any message transmitted from the MS to the BS in the initial network entry procedure. In a further embodiment, a separate message (of a signaling procedure) may be defined to provide the information about the neighbor nodes to the serving station.  
      As described above, the MS acquires neighbor nodes through a scanning operation in an initial network entry mode. The MS does not discard but provides information about the acquired neighbor nodes to the serving station (BS or RS), thereby making it easy for the serving station to acquire information about the neighbor BS and RS. In addition, the serving station can provide a neighbor node list for neighbor nodes that are actually detected by the MS. Therefore, it is possible to enhance the accuracy of the neighbor node advertisement message broadcast from the serving station and to optimize the neighbor node list. Accordingly, it is possible to prevent a waste of resources that may occur due to transmission of information of all the neighbor nodes.  
      While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention, as defined by the appended claims.