Abstract:
Methods for operating a Base Station (BS) and a User Equipment (UE) in a wireless communication system using a primary frequency and one or more secondary frequencies, and apparatuses for the BS and UE for carry out the methods, are provided. The method for operating the BS includes determining whether to activate or deactivate at least one of the one or more secondary frequencies, and transmitting a message comprising a bitmap indicating the activation or deactivation of the at least one of the one or more secondary frequencies to the UE. The method for operating the US includes receiving a message comprising a bitmap indicating activation or deactivation of at least one of the one or more secondary frequencies from the BS, and activating or deactivating the at least one of the one or more secondary frequencies based on the received message.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of prior application Ser. No. 12/542,175, filed Aug. 17, 2009, which claims the benefit under 35 U.S.C. §119(a) of a Korean patent application filed in the Korean Intellectual Property Office on Aug. 18, 2008 and assigned Serial No. 10-2008-0080356 and a Korean patent application filed in the Korean Intellectual Property Office on May 27, 2009 and assigned Serial No. 10-2009-0046676, the entire disclosures of each of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a broadband wireless communication system using multiple bands. More particularly, the present invention relates to an apparatus and a method for reducing power consumption of a Mobile Station (MS) in the broadband wireless communication system using the multiple bands. 
         [0004]    2. Description of the Related Art 
         [0005]    In accordance with advances of wireless communication systems, various types and high quality of services provided by the wireless communication systems are demanded. To meet those demands, a broadband wireless communication system is drawing attention. As available frequency resources in the wireless communication system are limited, available frequency bands in the broadband wireless communication system are also limited. To offer a broadband service, the available frequency bands needs to increase. 
         [0006]      FIGS. 1A and 1B  are diagrams illustrating simplified structures for supporting a single frequency band and a simplified structure for supporting two frequency bands in a conventional wireless communication system. 
         [0007]    In the wireless communication system, more particularly, in the broadband wireless communication system represented by the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard, a Base Station (BS) operates one Frequency Assignment (FA) or two or more FAs. The BS offers a radio communication service to a Mobile Station (MS) through its FA. 
         [0008]    Referring to  FIG. 1A , an MS  100  may migrate from an FA 1  region  120  to an FA 2  region  140 . Herein, the FA 1  region  120  is a service coverage area where the MS  100  uses the radio communication service using an FA 1 , and the FA 2  region  140  is a service coverage area where the MS  100  uses the radio communication service using an FA 2 . When the MS  100  traveling in the FA 1  region  120  may operate only one FA or when the FA 1  and the FA 2  are managed by different BSs, the MS  100  hands over between the FAs and uses the radio communication service using the FA 2 . 
         [0009]    Referring to  FIG. 1B , when an MS  150  may operate two or more FAs or when two or more FAs are managed by the single BS, the MS  150  may use the radio communication service in both of the FA 1  region  160  and the FA 2  region  180 . As such, when transmitting and receiving signals over the multiple frequency bands, the MS and the BS may send mass data at a high data rate. 
         [0010]    As discussed above, by use of the multiple frequency bands at the same time, the system may offer the high-capacity services at a high data rate. However, currently, there is no band use control procedure for effective utilization of the multiple frequency bands. As a result, it is not possible to regulate the bands adaptively used based on a resource usage rate and a channel condition, and use of a secondary FA increases power consumption of the MS. 
       SUMMARY OF THE INVENTION 
       [0011]    An aspect of the present invention is to address at least the above mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide an apparatus and a method for efficiently using multiple frequency bands between a Mobile Station (MS) and a Base Station (BS) in a broadband wireless communication system. 
         [0012]    Another aspect of the present invention is to provide an apparatus and a method for regulating Frequency Assignments (FAs) optionally used according to a resource utilization rate and a channel condition in a broadband wireless communication system. 
         [0013]    Yet another aspect of the present invention is to provide an apparatus and a method for reducing power consumption in using secondary FAs in a broadband wireless communication system. 
         [0014]    Still another aspect of the present invention is to provide an apparatus and a method for suspending use of a secondary FA in a broadband wireless communication system. 
         [0015]    A further aspect of the present invention is to provide an apparatus and a method for resuming use of a suspended secondary FA in a broadband wireless communication system. 
         [0016]    According to an aspect of the present invention, a method for operating a BS in a wireless communication system using a primary frequency and one or more secondary frequencies is provided. The method includes determining whether to activate or deactivate at least one of the one or more secondary frequencies, and transmitting a message comprising a bitmap indicating the activation or deactivation of the at least one of the one or more secondary frequencies to a User Equipment (UE). 
         [0017]    According to another aspect of the present invention, a method for operating a UE in a wireless communication system using a primary frequency and one or more secondary frequencies is provided. The method includes receiving a message comprising a bitmap indicating activation or deactivation of at least one of the one or more secondary frequencies from a BS, and activating or deactivating the at least one of the one or more secondary frequencies based on the received message. 
         [0018]    According to yet another aspect of the present invention, an apparatus for a BS in a wireless communication system using a primary frequency and one or more secondary frequencies is provided. The apparatus includes a controller configured to determine whether to activate or deactivate at least one of the one or more secondary frequencies, and a transmitter configured to transmit a message comprising a bitmap indicating the activation or deactivation of the at least one of the one or more secondary frequencies to a UE. 
         [0019]    According to still another aspect of the present invention, an apparatus for a UE in a wireless communication system using a primary frequency and one or more secondary frequencies is provided. The apparatus includes a receiver configured to receive a message comprising a bitmap indicating activation or deactivation of at least one of the one or more secondary frequencies from a BS, and a controller configured to activate or deactivate the at least one of the one or more secondary frequencies based on the received message. 
         [0020]    Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
           [0022]      FIGS. 1A and 1B  are diagrams illustrating simplified structures according to a number of Frequency Assignments (FAs) supported in a wireless communication system; 
           [0023]      FIG. 2  is a diagram illustrating signal exchanges for Secondary (S)-FA on-off in a broadband wireless communication system according to an exemplary embodiment of the present invention; 
           [0024]      FIG. 3  is a diagram illustrating signal exchanges for S-FA on-off in a broadband wireless communication system according to an exemplary embodiment of the present invention; 
           [0025]      FIG. 4  is a diagram illustrating signal exchanges for S-FA on-off in a broadband wireless communication system according to an exemplary embodiment of the present invention; 
           [0026]      FIG. 5  is a diagram illustrating signal exchanges for S-FA on-off in a broadband wireless communication system according to an exemplary embodiment of the present invention; 
           [0027]      FIG. 6  is a diagram illustrating signal exchanges for S-FA on-off in a broadband wireless communication system according to an exemplary embodiment of the present invention; 
           [0028]      FIG. 7  is a diagram illustrating signal exchanges for S-FA on-off in a broadband wireless communication system according to an exemplary embodiment of the present invention; 
           [0029]      FIG. 8  is a flowchart illustrating operations of a Mobile Station (MS) in a broadband wireless communication system according to an exemplary embodiment of the present invention; 
           [0030]      FIG. 9  is a flowchart illustrating operations of a Base Station (BS) in a broadband wireless communication system according to an exemplary embodiment of the present invention; 
           [0031]      FIG. 10  is a flowchart illustrating operations of a BS in a broadband wireless communication system according to an exemplary embodiment of the present invention; 
           [0032]      FIG. 11  is a flowchart illustrating operations of an MS in a broadband wireless communication system according to an exemplary embodiment of the present invention; 
           [0033]      FIG. 12  is a block diagram illustrating an MS in a wireless communication system according to an exemplary embodiment of the present invention; and 
           [0034]      FIG. 13  is a block diagram illustrating a BS in a wireless communication system according to an exemplary embodiment of the present invention. 
       
    
    
       [0035]    Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0036]    The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein may be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. 
         [0037]    The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
         [0038]    It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
         [0039]    By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide. 
         [0040]    Exemplary embodiments of the present invention provide a technique for minimizing power consumption in using secondary Frequency Assignment (FA) in a broadband wireless communication system using multiple bands. Hereinafter, Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) wireless communication system is illustrated by way of example. Note that the present invention is applicable to other wireless communication systems. 
         [0041]    Hereinafter, a mode for transmitting and receiving signals between a Mobile Station (MS) and a Base Station (BS) through multiple FAs is referred to as an overlay mode. The term “MS” may also be referred to as “User Equipment (UE).” A wireless communication system operating in the overlay mode is referred to as an overlay wireless communication system. 
         [0042]      FIG. 2  is a diagram illustrating signal exchanges for secondary FA on-off in an overlay wireless communication system according to an exemplary embodiment of the present invention. In  FIG. 2 , an MS  200  and a BS  250  manage two frequency bands, that is, a Primary (P)-FA  251  and a Secondary (S)-FA  253 . Notably, the procedure of  FIG. 2  is applicable to a system which manages three or more FAs, that is, one P-FA and two or more S-FAs. 
         [0043]    Referring to  FIG. 2 , the MS  200  transmits and receives data with the BS  250  over its P-FA  201 , and transmits and receives data with the BS  250  over its S-FA  203  in step  211 . Herein, the P-FA  201  is determined at an initial connection of the MS  200 . Accordingly, when a plurality of MSs exists, the P-FAs of the MSs may be allocated to different FAs. That is, the P-FA of a certain MS may be the S-FA of another MS. 
         [0044]    In the process of the data communication, the MS  200  determines based on its battery status whether it needs to suspend use of the S-FA  203 . The suspension of the S-FA  203  is determined based on a signal strength measurement value of the S-FA  203  and power consumption. For example, when the signal strength measurement value of the corresponding S-FA is less than a threshold required for data delivery or when the remaining capacity of the battery is insufficient to keep using the S-FA  203 , the MS  200  determines to suspend the use of the S-FA  203 . 
         [0045]    Upon determining the suspension of the S-FA  203 , the MS  200  sends an S-FA off request message to the BS  250  to request the suspension of the usage of the S-FA  203  in step  213 . The S-FA off request message includes indication information of the S-FA  203  requested to suspend. For example, the indication information is one of frequency information of the S-FA  203 , an index of the S-FA  203 , and an S-FA bitmap representing the S-FA  203 . Herein, the index is a physical carrier index or a logical carrier index. The bitmap size is equal to a number of the S-FAs allocated to the MS  200 . When the S-FAs allocated to the MS  200  are different from the S-FAs actually used by the MS  200 , the bitmap size is determined by the number of the S-FAs actually used by the MS  200  and indicates a particular S-FA to suspend among the S-FAs actually used by the MS  200 . When the MS  200  is able to predict an off duration of the S-FA  203  by analyzing occurrence of uplink data, the MS  200  may add information indicative of the off duration of the S-FA  203  to the off request message. The information indicative of the off duration contained in the off request message may be used for the BS  250  to perform data scheduling of the MS  200 . 
         [0046]    The BS  250 , receiving the off request message from the MS  200 , sends an S-FA off response message in reply to the off request message in step  215 . Herein, the S-FA off response message includes an indicator indicative of the approval or disapproval of the use suspension request of the S-FA  203 . Accordingly, the MS  200  and the BS  250  recognize the suspension of the S-FA  203  and transmit and receive data only over the P-FA  250  in step  217 . When using two or more S-FAs in contrast to  FIG. 2 , the MS  200  transmits and receives data over at least one S-FA excluding the suspended S-FA  203  and the P-FA. 
         [0047]    Next, if it is determined that the data transmission and reception with the BS  250  is possible using the S-FA  203 , the MS  200  sends an S-FA readiness indicator to the BS  250  to inform the BS  250  of the availability of the S-FA  203  in step  219 . In so doing, the MS  200  may perform a ranging procedure for the S-FA  203  if necessary. 
         [0048]    Upon receiving the S-FA readiness indicator, the BS  250  determines whether to allow the use resumption of the suspended S-FA and sends an S-FA readiness indicator ACK to the MS  200  in step  221 . Whether to permit the use resumption of the suspended S-FA is determined based on the signal strength measurement value of the S-FA  203  reported by the MS  200 , the load of the S-FA  203 , and the existence and the number of MSs using the S-FA  203  as the P-FA. Hence, the S-FA readiness indicator ACK includes one of information informing of the permission to transmit and receive data over the S-FA  203  of the MS  200 , information informing of the disapproval on the data delivery over the S-FA  203  of the MS  200 , and information requesting to use other FA than the S-FA  203 . When the use of the S-FA  203  is not allowed, the BS  250  adds frequency information or FA identification information of the other FAs to the S-FA readiness indicator ACK. At this time, it is assumed that the data transfer over the S-FA  203  of the MS  200  is permitted. 
         [0049]    Upon confirming the permission of the data transfer with the BS  250  over the S-FA  203  from the S-FA readiness indicator ACK, the MS  200  transmits and receives data with the BS  250  over the P-FA  201  and data with the BS  250  over the S-FA  203  in step  223 . 
         [0050]    In  FIG. 2 , the MS sends a message for turning off the S-FA. Also, the MS may request the entrance into a sleep mode and the use suspension of the S-FA together, which shall be described below in detail by referring to  FIG. 3 . 
         [0051]      FIG. 3  is a diagram illustrating signal exchanges for S-FA on-off in an overlay wireless communication system according to an exemplary embodiment of the present invention. 
         [0052]    Referring now to  FIG. 3 , an MS  300  transmits and receives data with a BS  350  over the P-FA  301  and data with the BS  350  over the S-FA  303  in step  311 . Herein, the S-FA  301  is determined at the initial connection of the MS  300 . When a plurality of MSs exists, the P-FAs of the MSs may be set to different FAs. That is, the P-FA of a particular MS may be the S-FA of another MS. 
         [0053]    The MS  300  determines to enter into the sleep mode and concurrently determines to stop using the S-FA  303 . The suspension of the S-FA  303  is determined based on a signal strength measurement value of the S-FA  303  and power consumption. For example, when the signal strength measurement value of the corresponding S-FA is less than a threshold required for the data delivery or when the remaining capacity of the battery is insufficient to keep using the S-FA  303 , the MS  300  determines to stop using the S-FA  303 . 
         [0054]    The MS  300  sends a SLeeP (SLP)-REQuest (REQ) message including an S-FA off request which requests to suspend the use of the S-FA  303 , to the BS  350  in step  313 . The S-FA off request includes indication information of the S-FA  303  requested to stop. For example, the indication information is one of the frequency information of the S-FA  303 , the index of the S-FA  303 , and the S-FA bitmap representing the S-FA  303 . Herein, the index is the physical carrier index or the logical carrier index. The bitmap size is equal to the number of the S-FAs allocated to the MS  300 . When the S-FAs allocated to the MS  300  differ from the S-FAs actually used by the MS  300 , the bitmap size is determined according to the number of the S-FAs actually used by the MS  300  and is used to indicate a particular S-FA to suspend among the S-FAs actually used by the MS  300 . The S-FA off request may include off duration information of the S-FA  303 . 
         [0055]    Upon receiving the S-FA off request together with the SLP-REQ message, the BS  350  sends a SLP-ReSPonse (RSP) message including a response for the S-FA off request to the MS  300  in step  315 . The response for the S-FA off request includes an indicator indicative of the approval or the disapproval of the S-FA off request of the MS  300 . 
         [0056]    The MS  300 , receiving the SLP-RSP message, enters the sleep mode as indicated by the SLP-RSP message, concurrently stops using the S-FA  303 , and transmits and receives data with the BS  350  over the P-FA  301  in a listening interval of the sleep mode in step  317 . While the SLP-REQ/RSP procedures are conducted in steps  313  and  315 , the entrance into the sleep mode of the MS  300  may not be permitted. Even when the entrance into the sleep mode is not permitted, the S-FA off request and/or response for the S-FA  303  is still effective. In this situation, the MS  300  transmits and receives data with the BS  350  only through the P-FA  301  without entering into the sleep mode. In contrast to  FIG. 3 , when using two or more S-FAs, the MS  300  transmits and receives data over at least one S-FA excluding the suspended S-FA  303  and the P-FA. 
         [0057]    The MS  300  entering into the sleep mode determines that it is possible to transmit and receive data over the S-FA  303 . Thus, to inform the BS  350  of the communication resumption using the S-FA  303 , the MS  300  sends an S-FA readiness indicator over the P-FA  301  in step  319 . 
         [0058]    The BS  350  receiving the S-FA readiness indicator determines whether to allow the use resumption of the suspended S-FA and then sends an S-FA readiness indicator ACK to the MS  300  in step  321 . Whether to allow the use resumption of the suspended S-FA is determined based on the signal strength measurement value of the S-FA  303  reported from the MS  300 , the load of the S-FA  303 , and the existence and the number of MSs using the S-FA  303  as their P-FA. The S-FA readiness indicator ACK includes information informing of the permission of the data transfer over the S-FA  303  of the MS  300 , information informing of the prohibition on the data transfer over the S-FA  303  of the MS  300 , or information requesting to use other FA than the S-FA  303 . When the use of the S-FA  303  is not permitted, the BS  350  adds the frequency information or the FA identifier information of the other FA to the S-FA readiness indicator ACK. At this time, it is assumed that the data delivery over the S-FA  303  of the MS  300  is permitted. 
         [0059]    After confirming the permission on the data transfer with the BS  350  over the S-FA  303  from the S-FA readiness indicator ACK, the MS  300  transmits and receives data with the BS  350  over the P-FA  301  in the listening interval of the sleep mode and data with the BS  350  over the S-FA  303  in step  323 . The S-FA readiness indicator and the S-FA readiness indicator ACK used to resume the suspended S-FA in the sleep mode may be added to one of a control message of a Media Access Control (MAC) layer defined to control the sleep mode, and a MAC layer header. 
         [0060]    The MS requests the sleep mode entrance in  FIG. 3 , whereas the MS may add the S-FA off request to the SLP-RSP message even when the BS requests the sleep mode entrance. In this situation, the BS receiving the SLP-RSP message including the S-FA off request from the MS, recognizes the suspension of the S-FA of the MS. 
         [0061]      FIG. 4  is a diagram illustrating signal exchanges for S-FA on-off in an overlay wireless communication system according to an exemplary embodiment of the present invention. In  FIG. 4 , an MS  400  and a BS  450  employ (N+1)-ary FAs, that is, one P-FA  401  and N-ary S-FAs  403 - 1  through  403 -N. Note that the procedures in FIG.  4  are applicable to two FAs, that is, to one P-FA and one S-FA. 
         [0062]    Referring to  FIG. 4 , the MS  400  transmits and receives data to and from the BS  450  over the P-FA  401  and the N-ary S-FAs  403 - 1  through  403 -N in step  411 . Herein, the P-FA  401  is determined at the initial connection of the MS  400 . Accordingly, when a plurality of MSs exists, the P-FAs of the MSs may be set to different FAs. That is, the P-FA of a particular MS may be the S-FA of another MS. 
         [0063]    In the process of the data communication, the MS  400  determines to suspend at least one of the N-ary S-FAs  403 - 1  through  403 -N based on its battery status. The suspension of the at least one S-FA is determined based on the signal strength measurement value and the power consumption of each S-FA. For example, when the signal strength measurement value of the corresponding S-FA is less than a threshold required for the data delivery or when the remaining capacity of the battery is not enough to keep using the (N+1)-ary S-FAs, the MS  400  determines to suspend the usage of at least one of the N-ary S-FAs  403 - 1  through  403 -N. Hereafter, it is assumed that the S-FA 1   403 - 1  is suspended. 
         [0064]    Determining to suspend the S-FA 1   403 - 1 , the MS  400  sends an S-FA off request message, which requests to suspend the S-FA 1   403 - 1 , to the BS  450  in step  413 . The S-FA off request message includes indication information of the S-FA 1   403 - 1  requested to suspend. For example, the indication information may include an index of the S-FA 1   403 - 1  or the S-FA bitmap information representing the S-FA 1   403 - 1 . Herein, the index is a physical carrier index or a logical carrier index. The bitmap size is equal to the number of the S-FAs allocated to the MS  400 . When the S-FAs allocated to the MS  400  differ from the S-FAs actually used by the MS  400 , the bitmap size is determined by the number of the S-FAs actually used by the MS  400  and is used to represent a particular S-FA to suspend among the S-FAs actually used by the MS  400 . When the MS  400  is able to predict the off duration of the S-FA 1   403 - 1  by analyzing occurrence of uplink data, the MS  400  adds information indicative of the off duration to the S-FA off request message. The information indicative of the off duration contained in the S-FA off request message may be used for the BS  450  to perform data scheduling of the MS  400 . 
         [0065]    The BS  450 , receiving the off request message from the MS  400 , sends an S-FA off response message in reply to the off request message in step  415 . Accordingly, the MS  400  and the BS  450  recognize the suspension of the use of the S-FA 1   403 - 1  and transmit and receive data over the other FAs than the suspended S-FA in step  417 . 
         [0066]    Next, when determining the resumption of the S-FA 1   403 - 1 , the MS  400  sends an S-FA on request message, which requests the BS  450  to resume the S-FA 1   403 - 1 , to the BS  450  in step  419 . 
         [0067]    Upon receiving the S-FA on request message, the BS  450  determines whether to allow the resumption of the suspended S-FA and sends an S-FA on response message to the MS  400  in step  421 . Whether to allow the use resumption of the suspended S-FA 1   403 - 1  is determined based on the signal strength measurement value of the S-FA 1   403 - 1  reported from the MS  400 , the load of the S-FA 1   403 - 1 , and the existence and the number of MSs which use the S-FA 1   403 - 1  as their P-FA. The S-FA on response message includes one of the information informing of the permission on the resumption of the suspended S-FA, the information informing of the disapproval of the resumption of the suspended S-FA, and the information requesting to use other FA than the suspended S-FA. To direct to use the other FA, the BS  450  adds frequency information or FA identifier information of the other FA to the S-FA on response message. Hereafter, it is assumed that the communication over the suspended S-FA is permitted. 
         [0068]    Upon confirming the permission of the resumption of the suspended S-FA from the S-FA on response message, the MS  400  completes the preparation for the resumption of the suspended S-FA and then sends an S-FA readiness indicator in step  423 . For example, the preparation for the resumption includes synchronization procedure such as ranging, hardware status transition, and so on. Herein, unlike the readiness indicators of  FIGS. 2 and 3 , the S-FA readiness indicator is used to inform that the resumption of the suspended S-FA may be started. 
         [0069]    After sending the S-FA readiness indicator, the MS  400  transmits and receives data to and from the BS  450  over the P-FA  401  and the N-ary S-FAs  403 - 1  through  403 -N in step  425 . 
         [0070]    In  FIG. 4 , the MS sends the message for the off of the S-FA. In addition, the MS may request the suspension of the S-FA together with the request for the sleep mode entrance, which is now described in detail by referring to  FIG. 5 . 
         [0071]      FIG. 5  is a diagram illustrating signal exchanges for S-FA on-off in an overlay wireless communication system according to an exemplary embodiment of the present invention. 
         [0072]    In  FIG. 5 , an MS  500  transmits and receives data to and from a BS  550  over the P-FA  501  and the N-ary S-FAs  503 - 1  through  503 -N in step  511 . Herein, the P-FA  501  is determined at the initial connection of the MS  500 . Accordingly, when a plurality of MSs exists, the P-FAs of the MSs may be set to different FAs. That is, the P-FA of a particular MS may be the S-FA of another MS. 
         [0073]    The MS  500  concurrently determines to enter into the sleep mode and to suspend at least one of the N-ary S-FAs  503 - 1  through  503 -N. The suspension of the S-FA is determined based on the signal strength measurement value and the power consumption of each S-FA. For example, when a signal strength measurement value of the corresponding S-FA is less than a threshold required for the data delivery or when the remaining capacity of the battery is insufficient to keep using the (N+1)-ary S-FAs, the MS  500  determines to suspend the usage of at least one of the N-ary S-FAs  503 - 1  through  503 -N. Hereafter, it is assumed that the S-FA 1   503 - 1  is suspended. 
         [0074]    The MS  500  sends a SLP-REQ message including an S-FA off request which requests to suspend the use of the S-FA 1   503 - 1 , to the BS  550  in step  513 . The S-FA off request includes indication information of the S-FA 1   503 - 1  requested to stop. For example, the indication information is one of the frequency information of the S-FA 1   503 - 1 , the index of the S-FA 1   503 - 1 , and the S-FA bitmap representing the S-FA 1   503 - 1 . Herein, the index is the physical carrier index or the logical carrier index. The bitmap size is equal to the number of the S-FAs allocated to the MS  500 . When the S-FAs allocated to the MS  500  differ from the S-FAs actually used by the MS  500 , the bitmap size is determined by the number of the S-FAs actually used by the MS  500  and is used to indicate a particular S-FA to suspend among the S-FAs actually used by the MS  500 . 
         [0075]    The S-FA off request may include the off duration information of the suspended S-FA. 
         [0076]    Upon receiving the SLP-REQ message, the BS  550  determines whether to allow the sleep mode entrance and sends a SLP-RSP message informing of the approval or the disapproval to the MS  500  in step  515 . According to the S-FA off request in the SLP-REQ message, the BS  550  adds an S-FA off response to the SLP-RSP message. 
         [0077]    The MS  500 , receiving the SLP-RSP message, enters into the sleep mode as indicated by the SLP-RSP message, concurrently stops using the S-FA 1   503 - 1 , and transmits and receives data with the BS  550  over the other FAs than S-FA 1   503 - 1  in the listening interval of the sleep mode in step  517 . While the SLP-REQ/RSP procedures are conducted in steps  513  and  515 , the entrance into the sleep mode of the MS  500  may not be permitted. Even when the entrance into the sleep mode is not permitted, the S-FA off request and/or response for the S-FA 1   503 - 1  is still effective. In this situation, the MS  500  transmits and receives data with the BS  550  over at least one FA excluding the S-FA 1   503 - 1  without entering the sleep mode. 
         [0078]    Next, upon determining to resume the S-FA 1   503 - 1 , the MS  500  sends an S-FA on request message, which requests the BS  550  to resume using the S-FA 1   503 - 1 , to the BS  550  in step  519 . In so doing, the MS  500  may perform the ranging procedure for the S-FA 1   503 - 1 . 
         [0079]    Upon receiving the S-FA on request message, the BS  550  determines whether to allow the resumption of the suspended S-FA and sends an S-FA on response message to the MS  500  in step  521 . Whether to allow the usage resumption of the suspended S-FA is determined based on the load of the suspended S-FA, and the existence and the number of MSs which use the suspended S-FA as their P-FA. The S-FA on response message includes one of the information informing of the permission on the resumption of the suspended S-FA of the MS  500 , the information informing of the disapproval of the resumption of the suspended S-FA of the MS  500 , and the information requesting to use other FA than the suspended S-FA. To direct to use the other FA, the BS  550  adds frequency information or FA identifier information of the other FA to the S-FA on response message. Hereafter, it is assumed that the usage resumption of the S-FA 1   503 - 1  is permitted. An S-FA readiness indicator and an S-FA readiness indicator ACK used to resume the suspended S-FA in the sleep mode may be added to one of the control message of the MAC layer defined to control the sleep mode, and the MAC layer header. 
         [0080]    The MS  500 , confirming the permission of the resumption of the suspended S-FA from the S-FA on response message, completes the preparation for the resumption of the suspended S-FA and then sends the S-FA readiness indicator in step  523 . For example, the preparation for the resumption includes synchronization procedure such as ranging, hardware status transition, and so on. Herein, unlike the readiness indicators of  FIGS. 2 and 3 , the S-FA readiness indicator is used to inform that the resumption of the suspended S-FA may be started. 
         [0081]    After sending the S-FA readiness indicator, the MS  500  transmits and receives data to and from the BS  550  over the P-FA  501  and the N-ary S-FAs  503 - 1  through  503 -N in step  525 . 
         [0082]      FIG. 6  is a diagram illustrating signal exchanges for S-FA on-off in an overlay wireless communication system according to an exemplary embodiment of the present invention. In  FIG. 6 , the broadband wireless communication system includes an MS  600  and a BS  650 . The MS  600  and the BS  650  employ (N+1)-ary FAs, that is, one P-FA  601  and N-ary S-FAs  603 - 1  through  603 -N. Note that the procedures in  FIG. 6  are applicable to two FAs, that is, to one P-FA and one S-FA. 
         [0083]    Referring to  FIG. 6 , the MS  600  transmits and receives data to and from the BS  650  over the P-FA  601  and the N-ary S-FAs  603 - 1  through  603 -N in step  611 . Herein, the P-FA  601  is determined at the initial connection of the MS  600 . Accordingly, when a plurality of MSs exists, the P-FAs of the MSs may be set to different FAs. That is, the P-FA of a particular MS may be the S-FA of another MS. 
         [0084]    During the data communication, the BS  650  determines to suspend at least one of the N-ary S-FAs  603 - 1  through  603 -N in step  613 . The suspension of the S-FA is determined based on a signal strength measurement value of each S-FA reported from the MS  600 , and the load of each S-FA. For example, when the signal strength measurement value of the corresponding S-FA is less than a threshold required for the data delivery or when the load needs to be distributed because of the excessive load in the corresponding S-FA, the BS  650  determines to suspend the usage of at least one of the N-ary S-FAs  603 - 1  through  603 -N. Hereafter, it is assumed that the S-FA 1   603 - 1  is suspended. 
         [0085]    The BS  650  sends an S-FA off request message for the at least one of the N-ary S-FAs  603 - 1  through  603 -N to the MS  600  in step  615 . The S-FA off request message includes indication information of the S-FA 1   603 - 1  requested to suspend. For example, the indication information is one of the frequency information of the S-FA 1   603 - 1 , the index of the S-FA 1   603 - 1 , and the S-FA bitmap information representing the S-FA 1   603 - 1 . Herein, the index is the physical carrier index or the logical carrier index. The bitmap size is equal to the number of the S-FAs allocated to the MS  600 . When the S-FAs allocated to the MS  600  differ from the S-FAs actually used by the MS  600 , the bitmap size is determined by the number of the S-FAs actually used by the MS  600  and is used to represent a particular S-FA to suspend among the S-FAs actually used by the MS  600 . When able to predict the off duration of the suspended S-FA by analyzing the occurrence of downlink data, the BS  650  adds information indicative of the off duration of the suspended S-FA to the S-FA off request message. In addition, the S-FA off request message may include information requesting to use other FAs than the suspended S-FA. To direct to use the other FAs, the BS  650  adds the indication information of the other FA, for example, one of the frequency information, the index, and the bitmap to the S-FA off request message. Herein, the index is the physical carrier index or the logical carrier index. Hereafter, it is assumed that the information requesting to use the other FA is not included. 
         [0086]    The MS  600 , receiving the S-FA off request message from the BS  650 , sends an S-FA off response message in reply to the S-FA off request message in step  617 . Accordingly, the MS  600  and the BS  650  suspend at least one of the N-ary S-FAs  603 - 1  through  603 -N and transmit and receive data over the other FAs excluding the suspended S-FA in step  619 . 
         [0087]    If it is determined that the resumption of the usage of the S-FA 1   603 - 1  is necessary and that the usage resumption is feasible, the BS  650  sends an S-FA on request message requesting to resume the suspended S-FA to the MS  600  in step  621 . Whether to resume the S-FA is determined based on criteria similar to the aforementioned S-FA suspension. Whether to resume the S-FA is determined based on the signal strength measurement value of each S-FA reported from the MS  600 , and the load of each S-FA. For example, when a signal strength measurement value of the corresponding S-FA is greater than a threshold required for the data delivery or when the load in the corresponding S-FA is quite little and additional traffic may be accommodated, the BS  650  determines that it is possible to resume the S-FA 1   603 - 1 . 
         [0088]    Upon receiving the S-FA on request message, the MS  600  sends an S-FA on response message to the BS  650  in reply to the S-FA on request message in step  623 . Next, the MS  600  completes the preparation for the usage resumption of the suspended S-FA and then sends an S-FA readiness indicator in step  625 . For example, the preparation for the usage resumption includes the synchronization procedure such as ranging, and the hardware status transition. Herein, unlike the readiness indicators of  FIGS. 2 and 3 , the S-FA readiness indicator is used to inform that the usage resumption of the suspended S-FA may begin. 
         [0089]    After sending the S-FA readiness indicator, the MS  600  and the BS  650  transmit and receive data over the P-FA  601  and the N-ary S-FAs  603 - 1  through  603 -N in step  627 . 
         [0090]    In  FIG. 6 , the MS  600  transmits the S-FA on response message and S-FA readiness indicator upon receiving the S-FA on request message. However, according to another exemplary embodiment of the present invention, step  625  where the MS  600  transmits the S-FA readiness indicator may is excluded, and step  623  where the MS  600  transmits the S-FA on response message is performed after completing the preparation for the usage resumption of the suspended S-FA. That is, the S-FA on response message is used to reply to the S-FA on request message and to inform that the usage resumption of the suspended S-FA may begin. 
         [0091]    In  FIG. 6 , the BS sends the message for turning off the S-FA. Besides, the BS may request the suspension of the S-FA together with the request for the sleep mode entrance, which is now explained in detail by referring to  FIG. 7 . 
         [0092]      FIG. 7  is a diagram illustrating signal exchanges for S-FA on-off in an overlay wireless communication system according to an exemplary embodiment of the present invention. 
         [0093]    In  FIG. 7 , an MS  700  transmits and receives data to and from a BS  750  over the P-FA  701  and the N-ary S-FAs  703 - 1  through  703 -N in step  711 . Herein, the P-FA  701  is determined at the initial connection of the MS  700 . Accordingly, when a plurality of MSs exists, the P-FAs of the MSs may be set to different FAs. That is, the P-FA of a particular MS may be the S-FA of another MS. 
         [0094]    In the process of the data communication, the MS  700  determines to enter into the sleep mode and sends an SLP-REQ message to the BS  750  in step  713 . The BS  750  determines to suspend at least one of the N-ary S-FAs  703 - 1  through  703 -N in step  715 . The usage suspension of the S-FA is determined based on the load of each S-FA, the signal strength measurement value of each S-FA reported from the MS  700 , and so forth. For example, when a signal strength measurement value of the corresponding S-FA is less than a threshold required for the data delivery or when the load needs to be distributed because of the excessive load in the corresponding S-FA, the BS  750  determines to suspend the usage of at least one of the N-ary S-FAs  703 - 1  through  703 -N. Hereafter, it is assumed that the S-FA 1   703 - 1  is suspended. 
         [0095]    Upon receiving the SLP-REQ message, the BS  750  determines whether to allow the sleep mode entrance of the MS  700  and sends an SLP-RSP message informing of the approval or the disapproval in step  717 . The SLP-RSP message includes the S-FA off request which requests to suspend the S-FA 1   703 - 1  as determined in step  715 . The S-FA off request includes indication information of the S-FA 1   703 - 1  requested to be suspended. For example, the indication information is one of the frequency information of the S-FA 1   703 - 1 , an index of the S-FA 1   703 - 1 , and the S-FA bitmap representing the S-FA 1   703 - 1 . Herein, the index is the physical carrier index or the logical carrier index. The bitmap size is equal to the number of the S-FAs allocated to the MS  700 . When the S-FAs allocated to the MS  700  differ from the S-FAs actually used by the MS  700 , the bitmap size is determined by the number of the S-FAs actually used by the MS  700  and is used to indicate a particular S-FA to suspend among the S-FAs actually used by the MS  700 . The S-FA off request may include the off duration information of the S-FA 1   703 - 1 . 
         [0096]    Upon receiving the S-FA off request contained in the SLP-RSP message, the MS  700  recognizes that it is necessary to suspend the S-FA 1   703 - 1  and sends an S-FA off response message including a response for the S-FA off request to the BS  750  in step  719 . Next, the MS  700  receiving the SLP-RSP message enters into the sleep mode as indicated by the SLP-RSP message, simultaneously suspends the S-FA 1   703 - 1 , and transmits and receives data with the BS  750  over the FAs excluding the S-FA 1   703 - 1  in the listening interval of the sleep mode in step  721 . While the sleep request and/or response procedures are performed in steps  713  and  717 , the sleep mode entrance of the MS  700  may not be permitted. Even when the sleep mode entrance is not permitted, the S-FA off request and/or response for the S-FA 1   703 - 1  is still valid. In this situation, the MS  700  transmits and receives data to and from the BS  750  over the other FAs excluding the S-FA 1   703 - 1  without entering to the sleep mode. 
         [0097]    Next, when determining that the resumption of the usage of the S-FA 1   703 - 1  is necessary and that the usage resumption is feasible, the BS  750  sends an S-FA on request message requesting to resume the S-FA 1   703 - 1  to the MS  600  in step  723 . Whether to resume the S-FA is determined based on criteria similar to the aforementioned S-FA suspension. Whether to resume the S-FA is determined based on the signal strength measurement value of each S-FA reported from the MS  700 , and the load of each S-FA. For example, when the signal strength measurement value of the corresponding S-FA is greater than a threshold required for the data delivery or when the load in the corresponding S-FA is quite little and additional traffic may be accommodated, the BS  750  determines that it is possible to resume the S-FA 1   703 - 1 . 
         [0098]    Upon receiving the S-FA on request message, the MS  700  sends an S-FA on response message to the BS  750  in reply to the S-FA on request message in step  725 . Next, the MS  700  completes the preparation for the usage resumption of the suspended S-FA and then sends an S-FA readiness indicator in step  727 . For example, the preparation for the usage resumption includes the synchronization procedure such as ranging, and the hardware status transition. Herein, unlike the readiness indicators of  FIGS. 2 and 3 , the S-FA readiness indicator is used to inform that the usage resumption of the suspended S-FA may begin. The S-FA readiness indicator and an S-FA readiness indicator ACK used to resume the suspended S-FA in the sleep mode may be added to one of the control message of the MAC layer defined to control the sleep mode, and the MAC layer header. 
         [0099]    After sending the S-FA readiness indicator, the MS  700  and the BS  750  transmit and receive data over the P-FA  701  and the N-ary S-FAs  703 - 1  through  703 -N in step  729 . 
         [0100]    In  FIG. 7 , the MS  700  transmits the S-FA on response message and S-FA readiness indicator upon receiving the S-FA on request message. However, according to another exemplary embodiment of the present invention, step  727  where the MS  700  transmits the S-FA readiness indicator may is excluded, and step  725  where the MS  700  transmits the S-FA on response message is performed after completing the preparation for the usage resumption of the suspended S-FA. That is, the S-FA on response message is used to reply to the S-FA on request message and to inform that the usage resumption of the suspended S-FA may begin. 
         [0101]    In  FIGS. 2 through 7 , it is assumed that the off state of the S-FA does not affect Quality of Service (QoS) policy for the MS. In a case where the S-FA off operation of the MS affects the QoS policy, the MS and the BS need to additionally perform a dynamic service negotiation procedure, for example, a Dynamic Service Change (DSC) procedure. In other words, even when the off state of the S-FA decreases the available radio resources, the MS and the BS have to modify QoS parameters of the ongoing service flow so as to meet the required QoS according to the QoS policy. 
         [0102]    In this case, the procedures of transmitting and receiving the S-FA on request message and the S-FA on response message in  FIGS. 4 through 7  may be included to the dynamic service negotiation procedure. That is, by including the contents of the S-FA on request message and the S-FA on response message to the message transmitted and received for the dynamic service negotiation procedure, the MS and the BS may process the dynamic service negotiation procedure and the S-FA usage resumption procedure as a single procedure. 
         [0103]    Now, structures and operations of the MS and the BS for turning on/off the S-FA as stated above are elucidated by referring to the drawings. 
         [0104]      FIG. 8  is a flowchart illustrating operations of an MS in a broadband wireless communication system according to an exemplary embodiment of the present invention. 
         [0105]    In step  801 , the MS communicates over the P-FA and at least one S-FA. That is, the MS transmits and receives data to and from the BS using all of the multiple FAs. 
         [0106]    In step  803 , the MS determines whether it is necessary to reduce the power consumption by stopping using the S-FA. More specifically, the MS continuously monitors its battery status and determines based on the battery status whether to reduce the power consumption. For instance, if it is determined that the remaining capacity of the battery falls below the threshold, the MS determines to reduce the power consumption. To the contrary, when the signal strength measurement value for the S-FA is less than threshold required for the data delivery, the MS may determine that the suspension of the corresponding S-FA is required. When the suspension of the S-FA is unnecessary, the MS returns back to step  801 . 
         [0107]    When the suspension of the S-FA is required, the MS sends an S-FA off request message to the BS in step  805 . The S-FA off request message includes the indication information of the S-FA requested to suspend. For example, the indication information is one of the frequency information of the S-FA, the index of the S-FA, and the S-FA bitmap representing the S-FA. Herein, the index is the physical carrier index or the logical carrier index. When able to predict the off duration of the S-FA by analyzing the occurrence of the uplink data, the MS sends the S-FA off request message including the off duration information. 
         [0108]    In step  807 , the MS determines whether the S-FA off response message is received from the BS. Herein, the S-FA off response message includes the indicator indicative of the approval or the disapproval on the usage suspension request of the S-FA. 
         [0109]    In step  809 , the MS communicates only over the P-FA. When using two or more S-FAs, the MS communicates over the other S-FAs than the suspended S-FA and the P-FA. In more detail, the MS confirms the approval of its S-FA suspension request from the S-FA off response message, and recognizes that no data is received over the suspended S-FA. Thus, the MS does not operate to maintain the synchronization for the suspended S-FA and to receive the control message in the suspended S-FA. 
         [0110]    In step  811 , the MS determines whether the use of the suspended S-FA may be resumed. Namely, the MS determines whether the usage of the suspended S-FA is resumed, based on the battery status or the signal strength measurement value. The MS determines whether the remaining battery capacity is enough to accommodate the power consumption increased by the resumption of the suspended S-FA, or whether the signal strength measurement value of the suspended S-FA is greater than the threshold. When the suspended S-FA may not be resumed, the MS returns to step  809 . 
         [0111]    When the suspended S-FA is resumed, the MS sends an S-FA readiness indicator to the BS in step  813 . Although it is not illustrated in  FIG. 8 , before sending the S-FA readiness indicator, the MS may perform the ranging procedure on the S-FA if necessary. For instance, when the S-FA is physically close to the P-FA, frequency/time adjustment value of the P-FA may be applied to the S-FA. By contrast, when the S-FA is not physically close to the P-FA, it is not preferable to apply the frequency/time adjustment value of the P-FA to the S-FA. Hence, the MS conducts the ranging procedure on the S-FA. 
         [0112]    In step  815 , the MS determines whether an S-FA readiness indicator ACK is received from the BS. The S-FA readiness indicator ACK informs of the determination result of the BS with respect to the S-FA usage resumption request of the MS. Herein, the determination result of the BS is one of the usage approval of the S-FA, the usage disapproval of the S-FA, and the instruction to use other FA. 
         [0113]    When receiving the S-FA readiness indicator ACK, the MS confirms the determination result of the BS from the S-FA readiness indicator ACK in step  817 . More specifically, the MS determines whether the usage of the S-FA is approved, the usage of the S-FA is disapproved, or the usage of another FA is instructed. When the usage of the S-FA is allowed, the MS returns back to step  801 . When the usage of the S-FA is not allowed, the MS returns back to step  809 . 
         [0114]    When the usage of the other FA is instructed, the MS sets the other FA as its S-FA in step  819 . That is, the MS determines to use the other FA as its S-FA as instructed by the BS. To set the other FA as the S-FA, the MS may perform the ranging on the other FA. Next, the MS returns to step  801 . 
         [0115]    Another exemplary implementation of the MS is now illustrated. 
         [0116]    In step  805 , the MS requests to enter into the sleep mode and to suspend the S-FA at the same time. In other words, the MS sends the SLP-REQ message including the S-FA off request. In step  807 , the MS determines whether the SLP-RSP message including the S-FA off response is received. Next, the MS confirms whether the sleep mode entrance is approved, from the SLP-RSP message. Since the sleep mode entrance may not be permitted while the suspension request of the S-FA is accepted, the MS examines whether the sleep mode entrance is approved. When the sleep mode entrance is approved, the MS enters the sleep mode and communicates over at least one FA excluding the suspended S-FA in step  809 . When the sleep mode entrance is not permitted, the MS communicates in at least one FA excluding the suspended FA without entering the sleep mode in step  809 . 
         [0117]    Yet another exemplary implementation of the MS is now described. 
         [0118]    In step  813 , the MS sends an S-FA on request message to the BS. In step  815 , the MS determines whether an S-FA on response message is received. Herein, the S-FA on response message includes one of the information informing of the approval of the usage resumption of the suspended S-FA, the information informing of the disapproval of the usage resumption of the suspended S-FA, and the information requesting to use other FA than the suspended S-FA. When the information informing of the disapproval of the usage resumption of the suspended S-FA is included, the MS returns back to step  809 . When the information requesting to use other FA is included, the MS proceeds to step  819 . When the information informing of the approval of the usage resumption of the suspended S-FA is carried, the MS completes the preparation for the resumption of the suspended S-FA and sends the S-FA readiness indicator. For example, the preparation for the usage resumption includes the synchronization procedure such as ranging, and the hardware status transition. 
         [0119]    Still another exemplary implementation of the MS is now described. 
         [0120]    In step  805 , the MS requests to enter into the sleep mode and simultaneously requests to stop using the S-FA. That is, the MS sends the SLP-REQ message including the S-FA off request. In step  807 , the MS determines whether the SLP-RSP message including the S-FA off response is received. Next, based on the SLP-RSP message, the MS confirms the approval or the disapproval of the sleep mode entrance. Since the sleep mode entrance may not be approved while the S-FA suspension request is accepted, the MS confirms the approval or the disapproval of the sleep mode entrance. When the sleep mode entrance is allowed, the MS enters the sleep mode and communicates over at least one FA excluding the suspended S-FA in the listening interval in step  809 . By contrast, when the sleep mode entrance is not allowed, the MS communicates over at least one FA excluding the suspended S-FA in the listening interval without entering into the sleep mode in step  809 . 
         [0121]    In step  813 , the MS sends an S-FA on request message to the BS. In step  815 , the MS determines whether an S-FA on response message is received. Herein, the S-FA on response message includes one of the information informing of the approval of the usage resumption of the suspended S-FA, the information informing of the disapproval of the usage resumption of the suspended S-FA, and the information requesting to use other FA than the suspended S-FA. When the information informing of the disapproval of the usage resumption of the suspended S-FA is included, the MS returns back to step  809 . When the information requesting to use other FA is included, the MS proceeds to step  819 . When the information informing of the approval of the usage resumption of the suspended S-FA is carried, the MS completes the preparation for the resumption of the suspended S-FA and sends the S-FA readiness indicator. For example, the preparation for the usage resumption includes the synchronization procedure such as ranging, and the hardware status transition. 
         [0122]      FIG. 9  is a flowchart illustrating operations of a BS in a broadband wireless communication system according to an exemplary embodiment of the present invention. 
         [0123]    In step  901 , the BS determines whether an S-FA off request message is received from the MS. More specifically, the BS determines whether the usage suspension of the S-FA is requested from the MS which is communicating over the P-FA and the S-FA. The S-FA off request message is received over the P-FA of the MS. The S-FA off request message includes the indication information of the S-FA requested to suspend. For example, the indication information is one of the frequency information of the S-FA, the index of the S-FA, and the S-FA bitmap representing the S-FA. Herein, the index is the physical carrier index or the logical carrier index. 
         [0124]    Receiving the S-FA off request message, the BS updates FA use status information of the MS in step  903 . By receiving the S-FA off request message, the BS determines to suspend the usage of the S-FA at the MS. Correspondingly, to reflect the suspension of the S-FA in the resource allocation, the BS excludes the S-FA from a list of the used FAs of the MS. Consequently, the resource in the S-FA is not allocated to the MS. When the S-FA off request message includes the off duration information, the BS reflects the off duration information to its scheduling. 
         [0125]    In step  905 , the BS sends an S-FA off response message to the MS. Herein, the S-FA off response message includes the indicator indicative of the approval or the disapproval of the suspension request of the S-FA. 
         [0126]    In step  907 , the BS determines whether an S-FA readiness indicator is received from the MS. That is, the BS determines whether the MS requests the resumption of the S-FA. 
         [0127]    Upon receiving the S-FA readiness indicator, the BS determines whether the usage of the S-FA may be allowed in step  909 . Herein, whether to permit the use of the S-FA is determined based on the load of the S-FA, the existence and the number of the MSs which employ the S-FA as their P-FA. 
         [0128]    When the use of the S-FA may be allowed, the BS sends an S-FA readiness indicator ACK notifying of the approval of the S-FA usage to the MS in step  911 . Next, the BS updates the FA use status information of the MS. 
         [0129]    In contrast, when not allowing the use of the S-FA in step  909 , the BS determines whether to permit the usage of other FA in step  913 . The BS examines whether there exists the FA usable by the MS among the FAs except for the S-FA and the P-FA of the MS. Herein, whether to allow using the other FA is determined based on a resource usage rate of the other FA, and the existence and the number of the MSs which employ the other FA as the P-FA. 
         [0130]    When the usage of the other FA is allowable in step  913 , the BS sends the S-FA readiness indicator ACK instructing to use the other FA, to the MS in step  915 . Next, the BS updates the FA use status information of the MS. 
         [0131]    In contrast, when the usage of the other FA is not allowable in step  913 , the BS sends the S-FA readiness indicator ACK notifying of the disapproval of the S-FA use in step  917 . 
         [0132]    Another exemplary implementation of the BS is now described. 
         [0133]    The BS determines whether the SLP-REQ message is received from the MS. Upon receiving the SLP-REQ message, the BS determines whether the SLP-REQ message includes the S-FA off request in step  901 . When the SLP-REQ message includes the S-FA off request, the BS proceeds to step  903 . Next, the BS determines whether to allow the sleep mode entrance of the MS. In step  905 , the BS sends the SLP-RSP message notifying of the approval or the disapproval of the sleep mode entrance. The SLP-RSP message includes the S-FA off response. 
         [0134]    Yet another exemplary implementation of the BS is now described. 
         [0135]    In step  907 , the BS determines whether the S-FA on request message is received. Herein, the S-FA on request message informs of the request of the resumption of the suspended S-FA. Upon receiving the S-FA on request message, the BS proceeds to step  909 . In step  911 ,  915  or  917 , the BS sends an S-FA on response message including one of the information informing of the approval of the usage resumption of the suspended S-FA, the information informing of the disapproval of the usage resumption of the suspended S-FA, and the information requesting to use other FA than the suspended S-FA. Next, the BS determines whether the S-FA readiness indicator is received from the MS. Receiving the S-FA readiness indicator, the BS updates the FA use status information of the MS. 
         [0136]    Still another exemplary implementation of the BS is now described. 
         [0137]    The BS determines whether the SLP-REQ message is received from the MS. Upon receiving the SLP-REQ message, the BS determines whether the SLP-REQ message includes the S-FA off request in step  901 . When the SLP-REQ message includes the S-FA off request, the BS proceeds to step  903 . Next, the BS determines whether to allow the sleep mode entrance of the MS. In step  905 , the BS sends the SLP-RSP message informing of the approval or the disapproval of the sleep mode entrance. The SLP-RSP message includes the S-FA off response. 
         [0138]    In step  907 , the BS determines whether the S-FA on request message is received. Herein, the S-FA on request message informs of the request to resume the suspended S-FA. When receiving the S-FA on request message, the BS proceeds to step  909 . In step  911 ,  915  or  917 , the BS sends an S-FA on response message including one of the information informing of the approval of the usage resumption of the suspended S-FA, the information informing of the disapproval of the usage resumption of the suspended S-FA, and the information requesting to use other FA than the suspended S-FA. Next, the BS determines whether the S-FA readiness indicator is received from the MS. Receiving the S-FA readiness indicator, the BS updates the FA use status information of the MS. 
         [0139]      FIG. 10  is a flowchart illustrating operations of a BS in a broadband wireless communication system according to an exemplary embodiment of the present invention. 
         [0140]    In step  1001 , the BS communicates with the MS over the P-FA and at least one S-FA. That is, the BS transmits and receives data to and from the MS using all of the multiple FAs. 
         [0141]    In step  1003 , the BS determines whether to need to suspend the use of at least one S-FA. The suspension of the at least one S-FA is determined based on a signal strength measurement value of each S-FA reported from the MS, and the load of each S-FA. For example, when the signal strength measurement value of the corresponding S-FA is less than a threshold required for the data delivery or when the load needs to be distributed because of the excessive load in the corresponding S-FA, the BS determines to suspend the usage of at least one S-FA. In so doing, the subject of the suspension is all or part of the at least one S-FA. 
         [0142]    When determining to suspend the use of the at least one S-FA, the BS determines whether it is possible to allow using other FA in step  1005 . In other words, the BS determines whether a new FA may be allocated in place of the suspended S-FA. 
         [0143]    When the use of the other FA is not allowable, the BS sends the S-FA request message including the indication information of the suspended S-FA in step  1007 . By contrast, when the use of the other FA is allowable, the BS sends the S-FA request message including the indication information of the suspended S-FA and the newly allowed FA in step  1009 . For example, the indication information is one of the frequency information of the corresponding FA, the index, and the S-FA bitmap representing the corresponding FA. Herein, the index is the physical carrier index or the logical carrier index. When the BS is able to predict the off duration of the suspended S-FA by analyzing the occurrence of the downlink data, the BS adds the information indicative of the off duration to the S-FA off request message. 
         [0144]    In step  1011 , the BS determines whether an S-FA off response message is received from the MS. The BS determines whether the MS receives the use suspension instruction of the S-FA. 
         [0145]    Receiving the S-FA off response message, the BS communicates over one or more FAs including the P-FA in step  1013 . Namely, the BS communicates over the at least one FA except for the suspended S-FA. 
         [0146]    In step  1015 , the BS determines whether the usage resumption of the suspended S-FA is determined. The BS determines whether the usage resumption of the suspended S-FA is necessary and whether the usage resumption is feasible. Whether the usage resumption of the S-FA is feasible is determined based on the criteria similar to the aforementioned S-FA usage suspension. Whether it is possible to resume the S-FA is determined based on the signal strength measurement value of each S-FA reported from the MS, and the load of each S-FA. For example, when the signal strength measurement value of the corresponding S-FA is greater than the threshold required for the data delivery or when the load in the corresponding S-FA is quite little and additional traffic may be accommodated, the BS determines that it is possible to resume the S-FA. 
         [0147]    Upon determining to resume the suspended S-FA, the BS sends an S-FA on request message including the indication information of the resumed S-FA in step  1017 . For example, the indication information is one of the frequency information of the corresponding FA, the index, and the S-FA bitmap representing the corresponding FA. Herein, the index is the physical carrier index or the logical carrier index. 
         [0148]    In step  1019 , the BS determines whether the S-FA on response message and an S-FA readiness indicator are received from the MS in sequence. Herein, the S-FA on response message notifies of the reception of the S-FA on request and the S-FA readiness indicator notifies of the readiness for the resumption of the S-FA. Hence, the BS confirms from the S-FA on response message that the MS received the S-FA on request, confirms the readiness for the resumption of the S-FA based on the S-FA readiness indicator, and then returns back to step  1001 . 
         [0149]    Another exemplary implementation of the BS is now described. 
         [0150]    In the communication over the P-FA and the at least one S-FA in step  1001 , upon receiving the SLP-REQ message from the MS, the BS determines whether to permit the sleep mode entrance of the MS. In step  1003 , the BS determines whether it is necessary to suspend the usage of the at least one S-FA. Upon determining to suspend the at least one S-FA, the BS sends the SLP-RSP message informing of the approval or the disapproval of the sleep mode entrance in step  1007  or step  1009 . At this time, the SLP-RSP message includes the S-FA off request. The S-FA off request includes the indication information of at least one of the suspended S-FA and the permitted FA. For example, the indication information is one of the frequency information of the corresponding FA, the index, and the S-FA bitmap representing the corresponding FA. The index is the physical carrier index or the logical carrier index. When able to predict the off duration of the suspended S-FA by analyzing the occurrence of downlink data, the BS adds the information indicative of the off duration to the S-FA off request message. Next, the BS proceeds to step  1011 . 
         [0151]    Referring  FIG. 10 , the BS returns to step  1001  from step  1019  when the S-FA on response message and an S-FA readiness indicator are received from the MS. However, according to another exemplary embodiment of the present invention, the S-FA readiness indicator is not considered. In this case, in step  1019 , if the S-FA on response message is received from the MS, then the BS returns to step  1001 . That is, the S-FA on response message is used to reply to the S-FA on request message and to inform that the usage resumption of the suspended S-FA may begin. 
         [0152]      FIG. 11  is a flowchart illustrating operations of an MS in a broadband wireless communication system according to an exemplary embodiment of the present invention. 
         [0153]    In step  1101 , the MS communicates with the BS over the P-FA and at least one S-FA. Namely, the MS transmits and receives data to and from the BS using all of the multiple FAs. 
         [0154]    In step  1103 , the MS determines whether the S-FA off request message is received from the BS. The S-FA off request message directs to suspend the use of all or part of the at least one S-FA, and includes indication information of at least one of the suspended S-FA and the newly allowed FA. For example, the indication information is one of the frequency information of the corresponding FA, the index, and the S-FA bitmap representing the corresponding FA. Herein, the index is the physical carrier index or the logical carrier index. In addition, the S-FA off request may carry the information indicative of the off duration of the suspended S-FA. 
         [0155]    Upon receiving the S-FA off request message, the MS stops using the S-FA indicated by the S-FA off request message in step  1105 . That is, the MS does not maintain the synchronization for the suspended S-FA and receive the control message over the suspended S-FA. 
         [0156]    In step  1107 , the MS determines whether the S-FA off request message includes the use instruction of the other FA. The MS determines whether the S-FA off request message includes the indication information of the newly allowed FA. When the use instruction of the other FA is not contained, the MS proceeds to step  1111 . 
         [0157]    When the use instruction of the other FA is contained, the MS sets the other FA as its S-FA in step  1109 . That is, the MS determines to utilize the other FA as the S-FA as instructed by the BS. To set the other FA to the S-FA, the MS may perform the ranging on the other FA. 
         [0158]    In step  1111 , the MS sends an S-FA off response message to the BS. Accordingly, the BS may acquire that the MS received the S-FA off request. 
         [0159]    In step  1113 , the MS communicates over one or more FAs including the P-FA. The MS communicates over at least one FA excluding the suspended S-FA. 
         [0160]    In step  1115 , the MS determines whether the S-FA on request message is received from the BS. The S-FA on request message requests to resume the use of the suspended S-FA and includes the indication information of the suspended S-FA. For example, the indication information is the frequency information of the corresponding FA, the index, and the S-FA bitmap representing the corresponding FA. Herein, the index is the physical carrier index or the logical carrier index. 
         [0161]    Receiving the S-FA on request message, the MS sends an S-FA on response message to the BS in step  1117 . Thus, the BS acquires that the MS received the S-FA on request. 
         [0162]    In contrast, if it is determined that the S-FA on request message is not received from the BS in step  1115 , the MS returns to step  1113 . 
         [0163]    In step  1119 , the MS prepares for the usage resumption of the suspended S-FA. For example, the preparation for the usage resumption includes the synchronization procedure such as ranging, and the hardware status transition. 
         [0164]    In step  1121 , the MS sends the S-FA readiness indicator. Herein, an S-FA readiness indicator notifies that the use resumption of the suspended S-FA may be commenced. After sending the S-FA readiness indicator, the MS returns to step  1101 . 
         [0165]    Another exemplary implementation of the MS is now described. 
         [0166]    While communicating over the P-FA and one or more S-FAs in step  1101 , the MS determines to enter into the sleep mode and sends the SLP-REQ message to the BS. Next, upon receiving the SLP-RSP message from the BS, the MS determines whether the sleep mode entrance is permitted. In step  1103 , the MS determines whether the SLP-RSP message includes the S-FA off request. The S-FA off request directs to stop using all or part of the one or more S-FAs and includes the indication information of at least one of the suspended S-FA and the newly allowed FA. For example, the indication information is one of the frequency information of the corresponding FA, the index, and the S-FA bitmap representing the corresponding S-FA. Herein, the index is the physical carrier index or the logical carrier index. In addition, the S-FA off request may include the information indicative of the off duration of the suspended S-FA. 
         [0167]    Referring  FIG. 11 , the MS transmits the S-FA on response message in step  1117 , prepares to resume the suspended S-FA in step  1119  and transmits the S-FA readiness indicator. However, according to another exemplary embodiment of the present invention, the step  1121  where the MS transmits the S-FA readiness indicator may is excluded, and step  1117  where the MS  700  transmits the S-FA on response message is performed after step  1119  where completing the preparation for the usage resumption of the suspended S-FA. That is, the S-FA on response message is used to reply to the S-FA on request message and to inform that the usage resumption of the suspended S-FA may begin. 
         [0168]    Referring  FIG. 11 , the MS transmits the S-FA off response message in step  1111  after stopping the use of the S-FA or setting the other FA as its S-FA. However, according to another exemplary embodiment of the present invention, the step  1111  where the MS transmits the S-FA off response message is performed before step  1105  where the MS stops using the S-FA. That is, upon receiving the S-FA off request message, the MS transmit the S-FA off response message before stopping the use of the S-FA. 
         [0169]      FIG. 12  is a block diagram illustrating an MS in a wireless communication system according to an exemplary embodiment of the present invention. 
         [0170]    The MS of  FIG. 12  includes a plurality of encoders  1202 - 1  through  1202 -N, a plurality of symbol modulators  1204 - 1  through  1204 -N, a subcarrier mapper  1206 , an OFDM modulator  1208 , a Radio Frequency (RF) transmitter  1210 , an RF receiver  1212 , an OFDM demodulator  1214 , a subcarrier demapper  1216 , a plurality of symbol demodulators  1218 - 1  through  1218 -N, a plurality of decoders  1220 - 1  through  1220 -N, a data buffer  1222 , a message generator  1224 , a message analyzer  1226 , a power consumption regulator  1228 , and a communication controller  1230 . 
         [0171]    The encoders  1202 - 1  through  1202 -N each encode a data bit stream transmitted over the respective FAs. The symbol modulators  1204 - 1  through  1204 -N modulate the encoded bit stream to transmit over the respective FAs and convert to complex symbols. The subcarrier mapper  1206  maps the complex symbols output from the symbol modulators  1204 - 1  through  1204 -N into the frequency domain. Since the symbol modulators  1204 - 1  through  1204 -N correspond to the FAs respectively, the subcarrier mapper  1206  maps the complex symbols output from the symbol modulators  1204 - 1  through  1204 -N to the frequency region of the multiple FAs. The OFDM modulator  1208  converts the complex symbols mapped to the frequency domain to time-domain signals using an Inverse Fast Fourier Transform (IFFT) operation, and constitutes OFDM symbols by inserting a Cyclic Prefix (CP). The RF transmitter  1210  up-converts the OFDM symbols to an RF signal and transmits the RF signal via an antenna. 
         [0172]    The RF receiver  1212  down-converts an RF signal received via the antenna to a baseband signal. The OFDM demodulator  1214  divides the baseband signal output from the RF receiver  1212  on the OFDM symbol basis, eliminates the CP, and restores the frequency-domain complex symbols using a Fast Fourier Transform (FFT) operation. The subcarrier demapper  1216  extracts the complex symbols mapped to the allocated resource from the frequency-domain complex symbols. The subcarrier demapper  1216  divides the complex symbols on the FA basis and distributes the complex symbols to the symbol demodulators  1218 - 1  through  1218 -N. The symbol demodulators  1218 - 1  through  1218 -N each demodulate and convert the complex symbols to the encoded bit stream. The decoders  1220 - 1  through  1220 -N each decode the encoded bit stream. The data buffer  1222  temporarily stores the data exchanged with the BS and outputs the stored data under the control of the communication controller  1230 . 
         [0173]    The message generator  1224  generates a control message to send to the BS. For example, the message generator  1224  generates at least one of the S-FA off request message to request to stop using the S-FA, the SLP-REQ message including the S-FA off request, an S-FA readiness indicator to request to use the suspended S-FA, the S-FA on request message to request to use the suspended S-FA, the S-FA readiness indicator informing that the usage resumption of the suspended S-FA may start, the S-FA off response message notifying of the reception of the S-FA off request, and the S-FA on response message notifying of the reception of the S-FA on request. When generating one of the S-FA off request message, the SLP-REQ message including the S-FA off request, and the S-FA on request message, the message generator  1224  may add the indication information and the off duration information of the suspended S-FA. For example, the indication information is one of the frequency information of the corresponding FA, the index, and the S-FA bitmap representing the corresponding FA. Herein, the index is either the physical carrier index or the logical carrier index. 
         [0174]    The message analyzer  1226  analyzes the control message received from the BS and provides the information obtained from the control message to the communication controller  1230 . For instance, the message analyzer  1226  analyzes at least one of an S-FA off response message, an SLP-RSP message including the S-FA off response, an S-FA readiness indicator ACK, the S-FA on response message, an S-FA off request message, the S-FA on request message, and the SLP-RSP message including the S-FA off request message. More particularly, as analyzing one of the S-FA readiness indicator ACK and the S-FA on response message, the message analyzer  1226  attains the determination result of the BS including at least one of the approval of the usage resumption of the suspended S-FA, the disapproval of the usage resumption of the suspended S-FA, and the allowance of the new FA usage. As analyzing one of the S-FA off request message and the SLP-RSP message including the S-FA off request, the message analyzer  1226  acquires at least one of the use suspension request of the S-FA and the allowance of the other FA usage. 
         [0175]    The power consumption regulator  1228  monitors the battery status of the MS. The power consumption regulator  1228  determines whether to reduce the power consumption based on the battery status. For instance, when the remaining battery capacity falls below the threshold, the power consumption regulator  1228  determines to reduce the power consumption. Hence, the power consumption regulator  1228  determines to stop using the S-FA or to reduce the power consumption in other manners. According to the battery status, the power consumption regulator  1228  determines whether to resume the use of the suspended S-FA. Determining to reduce the power consumption by turning off the S-FA or determining to resume the use of the suspended S-FA, the power consumption regulator  1228  informs the communication controller  1230  of its determination. 
         [0176]    The communication controller  1230  controls the functions for the communication of the MS. More particularly, the communication controller  1230  controls the operations and the signalings for the suspension and the resumption of the S-FA usage. The detailed operations of the communication controller  1230  are now described in the various embodiments of the present invention. 
         [0177]    In an exemplary implementation, when the power consumption regulator  1228  notifies of the necessity of the power consumption reduction by suspending the use of the S-FA, the communication controller  1230  controls the message generator  1224  to generate the S-FA off request message. Meanwhile, when the signal strength measurement value of the corresponding S-FA is less than the threshold required for the data delivery, the communication controller  1230  itself determines the necessity of the usage suspension of the S-FA and controls the message generator  1224  to generate the S-FA off request message. The S-FA off request message is transmitted to the BS through the encoders  1202 - 1  through  1202 -N, the symbol modulators  1204 - 1  through  1204 -N, the subcarrier mapper  1206 , the OFDM modulator  1208 , and the RF transmitter  1210 . Next, when the message analyzer  1226  confirms the S-FA off response message, the communication controller  1230  controls to communicate over at least one S-FA excluding the suspended S-FA. Determining that the usage of the suspended S-FA may be resumed, the communication controller  1230  controls the message generator  1224  to generate the S-FA readiness indicator. Herein, the usage resumption of the suspended S-FA is determined by the battery status or the signal intensity measurement value notified from the power consumption regulator  1228 . Before controlling to generate the S-FA readiness indicator, the communication controller  1230  may perform the ranging procedure on the suspended S-FA. When the message analyzer  1226  receives the S-FA readiness indicator ACK and confirms the determination result of the BS, the communication controller  1230  controls the MS to operate according to the determination result. 
         [0178]    In an exemplary implementation, notably, when determining the necessity of the sleep mode entrance and the usage suspension of the S-FA, the communication controller  1230  controls the message generator  1224  to generate the SLP-REQ message including the S-FA off request. When the message analyzer  1226  confirms the SLP-RSP message including the S-FA off response, the communication controller  1230  controls to communicate in at least one S-FA excluding the suspended S-FA, and the P-FA. 
         [0179]    In an exemplary implementation, notably, when determining that the use of the suspended S-FA may be resumed, the communication controller  1230  controls the message generator  1224  to generate the S-FA on request message. Next, when the message analyzer  1226  receives the S-FA on response message and confirms the determination result of the BS, the communication controller  1230  controls the functions of the MS to operate according to the determination result. When the usage resumption of the suspended S-FA is allowed, the communication controller  1230  completes the preparation for the use resumption of the suspended S-FA, and controls the message generator  1224  to generate the S-FA readiness indicator. By way of example, the preparation for the use resumption includes the synchronization procedure such as ranging, and the hardware status transition. 
         [0180]    In an exemplary implementation, distinctively, when determining the necessity of the sleep mode entrance and the usage suspension of the S-FA, the communication controller  1230  controls the message generator  1224  to generate the SLP-REQ message including the S-FA off request. When the message analyzer  1226  confirms the SLP-RSP message including the S-FA off response, the communication controller  1230  controls to communicate in at least one S-FA excluding the suspended S-FA, and the P-FA. When determining that the use of the suspended S-FA may be resumed, the communication controller  1230  controls the message generator  1224  to generate the S-FA on request message. Next, when the message analyzer  1226  confirms the reception of the S-FA on response message and the determination result of the BS, the communication controller  1230  controls the functions of the MS to operate according to the determination result. In so doing, when the use resumption of the suspended S-FA is allowed, the communication controller  1230  completes the preparation for the use resumption of the suspended S-FA, and then controls the message generator  1224  to generate the S-FA readiness indicator. For example, the preparation for the use resumption includes the synchronization procedure such as ranging, and the hardware status transition. 
         [0181]    In an exemplary implementation, when the message analyzer  1226  confirms the S-FA off request message from the BS, the communication controller  1230  stops using the S-FA indicated by the S-FA off request message. When the S-FA off request message includes the use instruction of the other FA, the communication controller  1230  sets the other FA to its S-FA. To define the other FA as the S-FA, the communication controller  1230  may perform the ranging on the other FA. Next, the communication controller  1230  controls the message generator  1224  to generate the S-FA off response message. The S-FA off response message is transmitted to the BS through the encoders  1202 - 1  through  1202 -N, the symbol modulators  1204 - 1  through  1204 -N, the subcarrier mapper  1206 , the OFDM modulator  1208 , and the RF transmitter  1210 . Next, the communication controller  1230  controls to communicate over at least one FA except for the suspended S-FA. When the message analyzer  1226  confirms the S-FA on request message from the BS, the communication controller  1230  controls the message generator  1224  to generate the S-FA on response message, and prepares for the usage resumption of the suspended S-FA. For example, the preparation for the use resumption includes the synchronization procedure such as ranging, and the hardware status transition. After getting ready to resume the suspended S-FA, the communication controller  1230  controls the message generator  1224  to generate the S-FA readiness indicator. Herein, the S-FA readiness indicator notifies that the resumption of the suspended S-FA may begin. 
         [0182]    In an exemplary implementation, distinctively, when the entrance into the sleep mode is determined, the communication controller  1230  controls the message generator  1224  to generate the SLP-REQ message. When the message analyzer  1226  confirms the SLP-RSP message, the communication controller  1230  confirms the approval or the disapproval of the sleep mode entrance and determines whether the SLP-RSP message includes the S-FA off request. When the S-FA off request is contained, the communication controller  1230  operates the same as in the case where the S-FA off request message is received in the further exemplary embodiment of the present invention. 
         [0183]      FIG. 13  is a block diagram illustrating a BS in the wireless communication system according to an exemplary embodiment of the present invention. 
         [0184]    The BS of  FIG. 13  includes an RF receiver  1302 , an OFDM demodulator  1304 , a subcarrier demapper  1306 , a plurality of symbol demodulators  1308 - 1  through  1308 -N, a plurality of decoders  1310 - 1  through  1310 -N, a plurality of encoders  1312 - 1  through  1312 -N, a plurality of symbol modulators  1314 - 1  through  1314 -N, a subcarrier mapper  1316 , an OFDM modulator  1318 , an RF transmitter  1320 , a data buffer  1322 , a message analyzer  1324 , a message generator  1326 , a resource allocator  1328 , an FA manager  1330 , and a communication controller  1332 . 
         [0185]    The RF receiver  1302  down-converts an RF signal received via an antenna to a baseband signal. The OFDM demodulator  1304  divides the baseband signal output from the RF receiver  1302  on the OFDM symbol basis, eliminates the CP, and restores the frequency-domain complex symbols using the FFT operation. The subcarrier demapper  1306  divides the frequency-domain complex symbols on the FA basis and distributes the complex symbols to the symbol demodulators  1308 - 1  through  1308 -N. The symbol demodulators  1308 - 1  through  1308 -N each demodulate and convert the complex symbols to the encoded bit stream. The decoders  1310 - 1  through  1310 -N each decode the encoded bit stream. 
         [0186]    The encoders  1312 - 1  through  1312 -N each encode the data bit stream transmitted over the respective FAs. The symbol modulators  1314 - 1  through  1314 -N modulate the encoded bit stream transmitted over the respective FAs and convert to complex symbols. The subcarrier mapper  1316  maps the complex symbols output from the symbol modulators  1314 - 1  through  1314 -N into the frequency domain. Since the symbol modulators  1314 - 1  through  1314 -N correspond to the FAs respectively, the subcarrier mapper  1316  maps the complex symbols output from the symbol modulators  1314 - 1  through  1314 -N to the different FAs. The OFDM modulator  1318  converts the complex symbols mapped to the frequency domain to time-domain signals using the IFFT operation, and constitutes OFDM symbols by inserting the CP. The RF transmitter  1320  up-converts the OFDM symbols to an RF signal and transmits the RF signal via the antenna. The data buffer  1322  temporarily stores the data exchanged with the MS and outputs the stored data under the control of the communication controller  1332 . 
         [0187]    The message analyzer  1324  analyzes the control message received from the MS, and provides the information obtained from the control message to the communication controller  1332 . For instance, the message analyzer  1324  analyzes at least one of the S-FA off request message requesting to stop using the S-FA, the SLP-REQ message including the S-FA off request, an S-FA readiness indicator requesting to resume the suspended S-FA, the S-FA on request message requesting to resume the suspended S-FA, the S-FA readiness indicator informing of the start of the resumption of the suspended S-FA, the SLP-REQ message requesting the sleep mode entrance, the S-FA off response message informing of the reception of the S-FA off request, and the S-FA on response message informing of the reception of the S-FA on request. 
         [0188]    The message generator  1326  generates the control message transmitted to the MS. For example, the message generator  1326  generates at least one of the S-FA off response message informing of the reception of the S-FA use suspension request, the SLP-RSP message including the S-FA off response, an S-FA readiness indicator ACK informing of the reception of the S-FA readiness indicator, the S-FA on response message informing of the determination result in relation with the S-FA on request, the S-FA off request message to request to stop using the S-FA, the S-FA on request message to request the resumption of the S-FA, and the SLP-RSP message including the S-FA off request. Particularly, as generating either the S-FA readiness indicator ACK or the S-FA on response message, the message generator  1326  adds the determination result of the BS including at least one of the approval of the usage resumption of the suspended S-FA, the disapproval of the usage resumption of the suspended S-FA, and the usage allowance of the new FA. As generating either the S-FA off request message or the SLP-RSP message including the S-FA off request, the message analyzer  1326  adds at least one of the use suspension request of the S-FA and the use allowance of the other FA. 
         [0189]    The resource allocator  1328  allocates the radio resource to the MS. In the resource allocation, the resource allocator  1328  refers to the list of the used FAs of the MS provided from the FA manager  1330 . More specifically, to allocate the resource to the MS, the resource allocator  1328  allocates the resources in the FAs belonging to the list of the used FAs of the MS. The FA manager  1330  manages the list of the used FAs of the accessed MS, and provides the FA use list of the MS to the resource allocator  1328 . The FA manager  1330  updates the FA use list of the MS under the control of the communication controller  1332 . 
         [0190]    The communication controller  1332  controls the functions for the communication of the BS. The communication controller  1332  controls the operations and the signalings for the suspension and the resumption of the S-FA use. In the various embodiments of the present invention, the detailed operations of the communication controller  1332  are now described. 
         [0191]    In an exemplary implementation, the when the message analyzer  1324  confirms the S-FA off request message, the communication controller  1332  controls the FA manager  1330  to exclude the S-FA from the FA use list of the MS. The communication controller  1332  controls the message generator  1326  to generate the S-FA off response message. Hence, the S-FA off response message is transmitted to the BS through the encoders  1312 - 1  through  1312 -N, the symbol modulators  1314 - 1  through  1314 -N, the subcarrier mapper  1316 , the OFDM modulator  1318 , and the RF transmitter  1320 . The communication controller  1332  controls the FA manager  1330  to add the suspended S-FA into the FA use list of the MS. Next, when the message analyzer  1324  identifies the S-FA readiness indicator, the communication controller  1332  determines whether to permit the use request of the suspended S-FA. When not allowing the use request of the suspended S-FA, the communication controller  1332  determines whether the use of other FA may be allowed. The communication controller  1332  controls the message generator  1326  to generate the S-FA readiness indicator ACK notifying of its determination result. 
         [0192]    In an exemplary implementation, distinctively, when the message analyzer  1324  confirms the SLP-REQ message, the communication controller  1332  determines whether the SLP-REQ message includes the S-FA off request. When the SLP-REQ message contains the S-FA off request, the communication controller  1332  controls the message generator  1326  to generate the SLP-RSP message including the S-FA off response message. 
         [0193]    In an exemplary implementation, distinctively, when the message analyzer  1324  identifies the S-FA on request message, the communication controller  1332  determines whether to approve the use request of the suspended S-FA. When not allowing the use request of the suspended S-FA, the communication controller  1332  determines whether the use of the other FA may be permitted. Next, the communication controller  1332  controls the message generator  1326  to generate the S-FA on response message notifying of its determination result. The message analyzer  1324  identifies the S-FA readiness indicator, and the communication controller  1332  controls the FA manager  1330  to update the FA use status information of the MS. 
         [0194]    In an exemplary implementation, distinctively, when the message analyzer  1324  confirms the SLP-REQ message, the communication controller  1332  determines whether the SLP-REQ message includes the S-FA off request. When the SLP-REQ message contains the S-FA off request, the communication controller  1332  controls the message generator  1326  to generate the SLP-RSP message including the S-FA off response message. When the message analyzer  1324  confirms the S-FA on request message, the communication controller  1332  determines whether to allow the use request of the suspended S-FA. When not allowing the use request of the suspended S-FA, the communication controller  1332  determines whether to permit the use of the other FA. Next, the communication controller  1332  controls the message generator  1326  to generate the S-FA on response message informing of its determination result. When the message analyzer  1324  identifies the S-FA readiness indicator, the communication controller  1332  controls the FA manager  1330  to add the suspended S-FA into the FA use list of the MS. 
         [0195]    In an exemplary implementation, the communication controller  1332  determines whether to suspend the use of at least one S-FA. The suspension of the at least one S-FA is determined based on the signal strength measurement value of each S-FA reported from the MS, and the load of each S-FA. Determining to suspend the at least one S-FA, the communication controller  1332  determines whether to allow using other FA. When not allowing use of the other FA, the communication controller  1332  controls the message generator  1326  to generate the S-FA request message including the indication information of the suspended S-FA. Conversely, when allowing the use of the other FA, the communication controller  1332  controls the message generator  1326  to generate the S-FA request message including the indication information of the suspended S-FA and the newly allowed FA. When the message analyzer  1324  confirms the S-FA off response message, the communication controller  1332  controls the FA manager  1330  to erase the suspended S-FA from the FA use list of the MS. Next, when the use resumption of the suspended S-FA is determined, the communication controller  1332  controls the message generator  1326  to generate the S-FA on request message including the indication information of the resumed S-FA. When the message analyzer  1324  confirms the S-FA on response message and the S-FA readiness indicator, the communication controller  1332  controls the FA manager  1330  to add the suspended S-FA into the FA use list of the MS. 
         [0196]    In an exemplary implementation, distinctively, when the message analyzer  1324  confirms the SLP-REQ message, the communication controller  1332  determines whether to permit the sleep mode entrance of the MS and whether to suspend the use of the at least one S-FA. Upon determining to suspend the at least one S-FA, the communication controller  1332  controls the message generator  1326  to generate the SLP-RSP message including the approval or the disapproval of the sleep mode entrance and the S-FA off request. 
         [0197]    As set forth above, in the broadband wireless communication system employing the multiple FAs, the power consumption of the MS incurred in using the S-FA may be reduced by turning on and off the S-FA of the MS. 
         [0198]    While the invention has been shown and described with reference to certain exemplary 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 and their equivalents.