Abstract:
A method of scheduling uplink resources in a wireless communication system supporting VoIP service is provided. A BS allocates an identical amount of the resource continuously until an uplink data rate is changed by an SS&#39;s request for a data rate change. When the data rate is changed, the SS reports this event to the BS so that the BS allocates an amount of resource corresponding to the requested data rate.

Description:
PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. § 119 to an application entitled “Uplink Scheduling Method In VoIP” filed in the Korean Intellectual Property Office on Aug. 17, 2004 and assigned Serial No. 2004-64854, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to an uplink scheduling method in a wireless system, and in particular, to a method of scheduling uplink resources for VoIP (Voice over Internet Protocol).  
         [0004]     2. Description of the Related Art  
         [0005]     A pressing need exists for a scheduling scheme to efficiently use resources in a wireless system that provides a variety of services with limited resources. It is ideal that unnecessarily allocated resources are quickly returned and re-allocated by scheduling. In addition, a technique for utilizing residual resource saved by reducing the data amount, for other purposes, can be considered.  
         [0006]     There are many conventional uplink scheduling types for VoIP service.  
         [0007]     Major examples are UGS (Unsolicited Grant Service) and rtPS (realtime Polling Service).  
         [0008]     The UGS allocates uplink resources of a fixed size upon user request. The user then sends transmission data to a base station (BS) using the uplink resources. The rtPS allocates required resources in response to a periodic uplink resource allocation request from the user. Thus, the user sends transmission data using resources allocated corresponding to the amount of the transmission data.  
         [0009]      FIG. 1  is a graph illustrating a conventional UGS-based uplink scheduling procedure.  
         [0010]     Referring to  FIG. 1 , mobile status is divided largely into a talk-spurt period (ON) and a silence period (OFF) on a time axis. Transmission data packets exist in the talk-spurt period, whereas no transmission data packets exist in the silence period. In the illustrated case of  FIG. 1 , resources supporting a maximum rate (Rate 1) are fixedly allocated.  
         [0011]     However, a subscriber station (SS) does not send data using all the allocated resources. Only minimum required resources (e.g. Rate ⅛) are used to maintain the service in silence periods  110  and  118 .  
         [0012]     Even in a talk-spurt period, only part of the allocated resources may be used. That is, the SS sends data packets using the allocated resources fully or partially in the talk-spurt period. For example, data packets are sent at Rate 1 using all the allocated resources in a talk-spurt period  112 . On the other hand, data packets are sent at Rate ½ in a talk-spurt period  114  due to a decrease in the amount of transmission data. In a talk-spurt period  116 , data packets are sent using no more than a quarter of the allocated resources. Then the SS uses the minimum resources in the silence period  118 . The minimum resources are those supporting the minimum rate, Rate ⅛.  
         [0013]     As described above, part of the fixedly allocated resources become residual resource in the periods  114 ,  116  and  118  using rates other than the maximum rate. This implies inefficient uplink scheduling. As a result, uplink resources are dissipated in the talk-spurt periods as well as in the silence periods.  
         [0014]      FIG. 2  is a graph illustrating a conventional rtPS-based uplink scheduling procedure.  
         [0015]     Referring to  FIG. 2 , the SS sends a resource allocation request to the BS in the rtPS, as indicated by reference numerals  212  to  236 . The BS allocates requested uplink resources to the SS. The SS then sends data packets using the allocated resources, as indicated by reference numerals  210 ,  220  and  230 .  
         [0016]     There are three talk-spurt periods  210 ,  220  and  230  according to the data rates used. Data packets are sent at Rate 1 in the first talk-spurt period  210 , at Rate ½ in the second talk-spurt period  220 , and at Rate ¼ in the third talk-spurt period  230 . Accordingly, the SS requests different amounts of resources in the talk-spurt periods  210 ,  220  and  230 . Transitions from the talk-spurt period  210  to the talk-spurt period  220  and from the talk-spurt period  220  to the talk-spurt period  230  occur due to the decrease of data rate in the MS.  
         [0017]     To be more specific, upon generation of data packets in a silence period, the SS requests resource allocation in step  212 . The BS allocates maximum resources to support a maximum data rate (e.g. Rate 1). The SS sends data packets at Rate 1 using the allocated resources. The data transmission at Rate 1 is repeated in the talk-spurt period  210 .  
         [0018]     As the data rate changes due to the decrease in the amount of transmission data in the talk-spurt period  210 , the SS requests resource allocation supporting a decreased data rate, Rate ½ in step  222 . Then, the SS sends data packets using resources allocated by the BS. The data transmission at Rate ½ is repeated in the talk-spurt period  220 .  
         [0019]     If the data rate is to be further reduced in the talk-spurt period  220 , the SS requests resource allocation supporting a decreased data rate, Rate ¼ in step  232 . Then, the SS sends data packets at Rate ¼. The data transmission at Rate ¼ is repeated in the talk-spurt period  230 .  
         [0020]     After the data transmission is completed, the SS operates using minimum resources (e.g. Rate ⅛) in a silence period  240 .  
         [0021]     As noted from the above description, a periodic polling from the SS (i.e. uplink resource requests  212  to  218 ,  222  to  226 , and  232  to  236 ) is required in the rtPS. Thus, even in the case where data packets are to be sent using the same resources as indicated by reference numerals  210 ,  220  and  230 , the periodic polling  214  to  218 ,  224  to  226 , and  234  to  236  is performed. The unnecessary polling leads to dissipation of uplink resources.  
         [0022]     As described above, the UGS and rtPS allocate uplink resources periodically according to their scheduling types irrespective of real-time mobile status. That is, the time-variant mobile status is not reflected in real time in the uplink scheduling. Accordingly, a need exists for developing an efficient uplink scheduling scheme for reflecting mobile status in real time.  
       SUMMARY OF THE INVENTION  
       [0023]     An object of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide an efficient uplink scheduling method for VoIP service.  
         [0024]     Another object of the present invention is to provide an uplink scheduling method for minimizing unnecessary resource consumption in allocating uplink resources.  
         [0025]     A further object of the present invention is to provide an uplink scheduling method for preventing an SS from unnecessarily requesting resource allocation to a BS.  
         [0026]     Still another object of the present invention is to provide an uplink scheduling method for allocating optimum resource to support a data rate requested by an SS.  
         [0027]     Yet another object of the present invention is to provide a method of performing uplink scheduling according to a rate-change notification from an SS.  
         [0028]     The above objects are achieved by providing a method of scheduling uplink resources in a wireless communication system supporting VoIP service.  
         [0029]     According to one aspect of the present invention, in a method of scheduling uplink resources in an SS in a wireless communication system supporting VoIP, the SS requests allocation of resources by which to send VoIP data to a BS and is allocated the resources supporting a maximum data rate periodically from the BS. The SS sends the VoIP data at the maximum data rate.  
         [0030]     When requesting the resource allocation, the SS also sends to the BS bandwidth request information requesting continuous allocation of the same resources until the maximum data rate is changed. In response to the resource allocation request, the first resources are allocated before the first resource allocation period comes after reception of the resource allocation request, irrespective of the period.  
         [0031]     According to another aspect of the present invention, in a method of scheduling uplink resources in a BS in a wireless communication system supporting VoIP, the BS receives a resource allocation request for transmission of VoIP data from an SS. In response to the resource allocation request, the BS periodically allocates resources required for data transmission at a maximum data rate from the SS. Along with the resource allocation request, the BS also receives from the SS bandwidth request information requesting continuous allocation of the same resources until the maximum data rate is changed. The first resources in response to the resource allocation request are allocated before the first resource allocation period comes after reception of the resource allocation request, irrespective of the period.  
         [0032]     According to a further aspect of the present invention, in a method of scheduling uplink resources in an SS in a wireless communication system supporting VoIP, the SS requests allocation of resources by which to send VoIP data to a BS. The SS sends the VoIP data at a maximum data rate using resources allocated by the BS. When the data rate is changed, the SS sends to the BS data at the changed data rate, and sends to the BS notification information indicating the rate change using remaining resources. When requesting resource allocation, the SS also sends bandwidth request information requesting continuous allocation of the same resources until the data rate is changed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0034]      FIG. 1  is a graph illustrating a conventional UGS-based uplink scheduling procedure;  
         [0035]      FIG. 2  is a graph illustrating a conventional rtPS-based uplink scheduling procedure;  
         [0036]      FIG. 3  is a graph illustrating an uplink scheduling procedure according to an embodiment of the present invention;  
         [0037]      FIG. 4  is a diagram illustrating signaling between an SS and a BS for the uplink scheduling according to the embodiment of the present invention;  
         [0038]      FIG. 5  is a flowchart illustrating an operation of the SS for the uplink scheduling according to the embodiment of the present invention; and  
         [0039]      FIG. 6  is a flowchart illustrating an operation of the BS for the uplink scheduling according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0040]     A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.  
         [0041]     In accordance with the present invention as described below, resources are allocated upon receipt of a resource allocation request from an SS. The SS sends data packets using the allocated resources without polling until it changes the resources. Meanwhile, the SS requests continuous allocation of the same resources from a BS without polling. For this purpose, a predetermined pattern is set in the Bandwidth Request field of a Bandwidth Request Header, prior to transmission. In the predetermined pattern, all bits of the Bandwidth Request field are set to 1 s.  
         [0042]     If a data rate-down is required, the SS sends data packets at a decreased data rate and notifies the BS that the resources used are changed due to the rate-down. Thus, the BS can use residual resource saved from the SS for another purpose.  
         [0043]     The SS can notify the BS of a rate change in two ways in the present invention.  
         [0044]     One of them is to add an STI (StaTus Indicator) field to an existing Grant Management subheader format. To apply this method, a bit value indicating a rate change must be defined for the STI field. For example, the bit is set to 1 if the data rate is changed and to 0 if the data rate is kept the same. The STI field is formed by borrowing one bit from a 16-bit PBR (Piggy Back Request) field in the conventional Grant Management subheader. The addition of the STI field results in a 15-bit PBR field. Thus, the following Grant Management subheader format can be proposed as shown in Table 1 below.  
                       TABLE 1                       Syntax   Size   Notes                   Grant Management subheader ( ) {               if (scheduling service type=UGS) {       SI    1 bit       PM    1 bit       Reserved   14 bit   Shall be set to               zero       }       Else if (Extended rtPS support &amp;&amp; scheduling       service type=rtPS) {       StaTus Indicator    1 bit       PiggyBack Request   15 bit       }       Else{       PiggyBack Request   16 bit       }       }                  
 
         [0045]     Table 2 below defines fields used for the embodiment of the present invention among the fields listed in Table 1.  
                       TABLE 2                           PBR   15 or   PiggyBack Request           16   The number of bytes of uplink bandwidth requested by the               SS. The bandwidth request is for the CID. The request shall               not include any PHY overhead. The request shall               incremental.               15 = Used by the Extended rtPS enabled SS               16 = default       PM   1   Poll-Me               0 = No action               1 = Used by the SS to request a bandwidth poll.       SI   1   Slip Indicator               0 = No action               1 = Used by the SS to indicate a slip of uplink grants               relative to the uplink queue depth       STI   1   StaTus Indicator               0 = No action               1 = Used by the SS to indicate a status of data rate               decrement.                  
 
         [0046]     In Table 2, the number of the bits in the PBR field is determined according to whether the 1-bit STI field is used or not. When the STI bit is used, the PBR field has 15 bits. In the absence of the STI bit, the PBR field has 16 bits. The STI bit indicates that the data rate is changed. If the STI bit is 0, no action is indicated in relation to a rate change. If the STI bit is 1, a rate change is indicated.  
         [0047]     The other way for the SS to notify the BS of a rate change is to use the PBR field of the existing Grant Management subheader format. For this method, a specific bit pattern must be defined for the PBR field, which indicates a rate change. This bit pattern is different from existing bit patterns used for other purposes. For example, the 16-bit PBR field is set to all Os to indicate a rate change. Table 3 below defines each field in the Grant Management subheader format to implement this PBR-based rate-change notification method.  
                                     TABLE 3                           Length           Name   (bits)   Description                                PBR   16   PiggyBack Request               The number of bytes of uplink bandwidth requested by               the SS. The bandwidth request is for the CID. The               request shall not include any PHY overhead.               The request shall incremental.               0000000000000000 = In case of the Extended rtPS used               by SS to indicate a status of data rate decrement       PM   1   Poll-Me               0 = No action               1 = Used by the SS to request a bandwidth poll.       SI   1   Slip Indicator               0 = No action               1 = Used by the SS to indicate a slip of uplink grants               relative to the uplink queue depth                  
 
         [0048]     A. Scheduling Procedure  
         [0049]     An uplink scheduling procedure proposed by the present invention will be described in detail below.  
         [0050]      FIG. 3  is a graph illustrating an uplink scheduling procedure according to an embodiment of the present invention. Referring to  FIG. 3 , mobile status is divided largely into a talk-spurt period (ON) and a silence period (OFF) on a time axis. Transmission data packets exist in the talk-spurt period, whereas no transmission data packets exist in the silence period.  
         [0051]     An SS requests resource allocation from a BS when it transitions from the silence period to the talk-spurt period, as indicated by reference numeral  310 . The resource allocation request is sent using pre-allocated minimum resources. For instance, the SS uses a Bandwidth Request Header to request resource allocation. The Bandwidth Request Header carries bandwidth request information requesting continuous allocation of the same resources even though the SS does not perform polling.  
         [0052]     Table 4 below lists fields in the Bandwidth Request Header and the lengths and characteristics of the fields.  
                                     TABLE 4                           Length           Name   (bits)   Description                                BR   19   Bandwidth Request               The number of bytes of uplink bandwidth requested by               the SS. The bandwidth request is for the COD. The               request shall not include any PHY overhead.               1111111111111111111 = In case of the Extended rtPS               used by SS to indicate a status of data rate increment       CID   16   Connection Identifier       EX   1   Always set to zero       HCS   8   Header Check Sequence               Same usage as HCS entry in Table 5       HT   1   Header Type = 1       Type   3   Indicates the type of bandwidth request header                  
 
         [0053]     The bandwidth request information is delivered in the Bandwidth Request (BR) field. In Table 4, the bandwidth request information is defined as a bit stream of 19 bits being set to all 1 s.  
         [0054]     Upon receipt of the Bandwidth Request Header, the BS periodically allocates resources required for data transmission at a maximum data rate to the SS. The SS sends data using the allocated resources, as indicated by reference numeral  312 . The data transmission is carried out at the maximum data rate, Rate  1 .  
         [0055]     However, the data transmission using the initially allocated resources for the resource allocation request is not periodical. That is, the data transmission using the initially allocated resources occurs between the resource allocation requested time and the first one of periodic data transmissions.  
         [0056]     If a rate change is required while periodically sending data at the maximum rate, the SS sends data at a changed rate in the next transmission interval. The changed rate is lower than the previous rate. In the illustrated case of  FIG. 3 , the SS changes its rate from Rate 1 to Rate ½. Meanwhile, the SS sends to the BS notification information indicating the rate change using residual resource saved from the rate-down. The specific methods of sending the notification message using the Grant Management subheader to the BS have been described before. The SS then periodically sends data at the changed rate, as indicated by reference numeral  314 .  
         [0057]     Upon receipt of the notification information in the Grant Management subheader, the BS allocates minimum required resources to support Rate ½ to the SS. The resource allocation accompanying the rate change is performed when needed. That is, if current available resources are sufficient, the BS does not need return allocated resources from the SS in real time.  
         [0058]     If a rate change is required while periodically sending data at Rate ½, the SS sends data at a changed rate, Rate ¼, in the next transmission interval and notifies the BS of the rate change. The SS then periodically sends data at Rate ¼, as indicated by reference numeral  316 . Upon receipt of the notification information in the Grant Management subheader, the BS allocates minimum required resources to support Rate ¼ to the MS.  
         [0059]     If a rate change is required or transmission data does not exist while periodically sending data at Rate ¼, the SS changes the rate to Rate ⅛ for the next transmission interval. Rate ⅛ is assumed to be the lowest rate available to the SS and notifies the BS of the rate change. Then the SS operates normally in a silence period  318 .  
         [0060]     B. Signaling  
         [0061]     Signaling between the SS and the BS in the uplink scheduling of the present invention will be described in detail with reference to the diagram of  FIG. 4 . Referring to  FIG. 4 , the BS allocates minimum required resources for transmission of a resource allocation request from the SS in step  410 . Typically, resources supporting transmission of 16-byte information suffice for transmission of the resource allocation request from the SS. Because it is assumed herein that the resource allocation request is sent at Rate ⅛, the minimum required resources for the resource allocation request support Rate ⅛.  
         [0062]     In the presence of transmission data, the SS sends to the BS a Bandwidth Request Header requesting resource allocation using the allocated minimum resources in step  412 . A talk-spurt period starts with sending the Bandwidth Request Header. Application of the uplink scheduling according to the present invention needs to be notified by the Bandwidth Request Header. That is, the Bandwidth Request Header carries information indicating that an additional resource allocation request will not be sent until the data rate is changed. For example, the BR field of the Bandwidth Request Header is set to all 1 s.  
         [0063]     Upon receipt of the Bandwidth Request Header, the BS allocates resources by which the SS can send data packets at the maximum data rate, Rate 1 in step  414 . The SS sends data packets at Rate 1 using the allocated resources in step  416 . The resource allocation step  414  and the data transmission step  416  are repeated until the data rate is changed.  
         [0064]     In step  418 , the SS is allocated resources supporting the current rate, Rate 1 by the BS. If the data rate is changed to Rate ½, the SS sends data packets at Rate ½ in step  420 . The SS also sends a Grant Management subheader indicating the rate change from Rate 1 to Rate ½ to the BS. The changed rate is not always indicated by the Grant Management subheader. In other words, the SS notifies the BS of only the rate change by the Grant Management subheader and the BS finds out from the Grant Management subheader that the uplink rate has been changed to a one level-lower rate. The rate change can be indicated by the Grant Management subheader in various ways. The present invention has proposed two main techniques: adding the STI field to the Grant Management subheader, and using the PBR field of the Grant Management subheader. These techniques have been described earlier and their description will not be repeated at this time.  
         [0065]     The BS determines from the Grant Management subheader that the uplink rate has been changed. In step  422 , the BS allocates resources supporting the changed rate, Rate ½. The resulting residual resource supporting up to Rate ½ can be used for other purposes. On the other hand, the resource allocation in step  422  may not be performed immediately after reception of the Grant Management subheader. If the BS has sufficient available resources, it allows the SS to maintain the previous allocated resources. When the residual resource are needed, the BS then re-allocates resources to the SS. Therefore, between steps  420  and  422 , the SS continues sending data packets to the BS using the existing allocated resources. Notably, some resources are saved as residual resource in the SS&#39;s data transmission in steps  420  and  422 . However, after the BS allocates resources supporting Rate ½, there are no residual resource produced from data transmission in step  424 .  
         [0066]     If the uplink rate is changed to Rate ¼ with the resources supporting Rate ½ in step  426 , the SS sends data packets at the changed rate, Rate ¼ in step  428 . The SS also sends the Grant Management subheader to the BS, indicating the rate change from Rate ½ to Rate ¼.  
         [0067]     The BS determines from the Grant Management subheader that the uplink rate has been changed. In step  430 , the BS allocates required resources supporting Rate ¼. The resulting residual resource supporting up to Rate ¼ can be used for other purposes. However, the resource allocation in step  430  may not be performed immediately after the Grant Management subheader is received. If the BS has sufficient available resources, it allows the SS to maintain the previous allocated resources. When the residual resource are needed, the BS then re-allocates resources to the SS. Therefore, the SS continues sending data packets to the BS using the existing resources until just before step  430 . In this case, residual resources are produced. However, as the SS sends data packets using resources re-allocated by the BS in step  432 , there are no residual resources produced from the data transmission.  
         [0068]     The BS allocates resources supporting Rate ¼ in step  434 . At the time, the uplink rate is changed to Rate ⅛. Rate ⅛ is the minimum rate that the SS can support. In the present invention, Rate ⅛ is used in a silence period. Therefore, the silence period starts with the rate change to Rate ⅛. The SS can send data using allocated resources or request resource allocation in the silence period. In the illustrated case of  FIG. 4 , the SS sends data at Rate ⅛ until just before the SS requests resource allocation in step  444 .  
         [0069]     In step  436 , the SS sends data packets at Rate ⅛ and a Grant Management subheader indicating the rate change from Rate ¼ to Rate ⅛. In the absence of data packets in step  436 , no data transmission is carried out.  
         [0070]     The BS determines from the Grant Management subheader that the uplink rate has been changed. In step  438 , the BS allocates required resources supporting Rate ⅛. The SS sends data packets at Rate ⅛ in steps  440  and  442 .  
         [0071]     The BS allocates required resources supporting Rate ⅛ in step  434 . It is assumed at this moment that transmission data to be sent at an increased rate has been generated in the SS. Therefore, this time becomes the start of a talk-spurt period.  
         [0072]     In step  444 , the SS sends a Bandwidth Request Header to the BS using the allocated minimum resources required to support Rate ⅛. The Bandwidth Request Header carries information indicating that an additional resource allocation request will not be sent until the data rate is changed.  
         [0073]     Upon receipt of the Bandwidth Request Header, the BS allocates resources by which the SS can send data packets at the maximum data rate, Rate 1 in step  446 . The SS then sends data packets at Rate 1 using the allocated resources in step  448 .  
         [0074]     C. Operation in the SS  
         [0075]      FIG. 5  is a flowchart illustrating an operation of the SS for the uplink scheduling according to the embodiment of the present invention. Referring to  FIG. 5 , the SS determines the presence or absence of data to be transmitted by VoIP in step  510 . In the presence of transmission data, the SS requests resource allocation to the BS by a Bandwidth Request Header in step  512 . The Bandwidth Request Header carries information indicating that an additional resource allocation request will not be sent until the data rate is changed. For this purpose, the SS can set the 19-bit BR field of the Bandwidth Request Header to all 1 s, for example. Meanwhile, the SS can be allocated resources required for transmission of the Bandwidth Request Header beforehand from the BS.  
         [0076]     After the BS allocates resources, the SS sends data using the allocated resources in step  514 . The allocated resources usually support the maximum data rate available for the SS (e.g. Rate 1).  
         [0077]     The SS continuously monitors the presence of data packets to be sent in step  516 . In the presence of data packets, the SS determines whether the currently allocated resource amount exceeds the amount for transmitting the data, that is, whether the current rate is likely to be decreased in step  518 . If a rate decrement is required, the SS sends the data with in the decreased resource amount, that is, at a changed rate (Rate ½) in step  522 . At the same time, the SS notifies the BS of the resource decrement, that is, the rate change. As stated before, the decrement of resources is indicated by the PBR field or the new STI bit of the Grant Management subheader. The SS then sends data packets at the changed rate in step  514 .  
         [0078]     If the current rate is not determined to be decreased at step  518 , then in step  520 , the SS determines whether are source increase is required. If resource increase is required, the SS requests resource allocation in step  512 . The SS then sends data packets at the maximum rate, Rate 1.  
         [0079]     While not shown in  FIG. 5 , even though the SS does not request resource allocation for each data frame transmission, the BS allocates resources to the SS in the previous amount.  
         [0080]     D. Operation in the BS  
         [0081]      FIG. 6  is a flowchart illustrating an operation of the BS for the uplink scheduling according to the embodiment of the present invention. Referring to  FIG. 6 , the BS monitors reception of a resource allocation request from the SS in step  610 . For example, the resource allocation request is received by a Bandwidth Request Header. Upon receipt of the Bandwidth Request Header, the BS checks the BR field value of the Bandwidth Request Header. If the BR field value indicates the request of the uplink scheduling proposed by the present invention, for example if the BR field value is set to all 1 s, the BS allocates uplink resources according to the uplink scheduling scheme of the present invention. Otherwise, a typical uplink scheduling method applies, which will not be described herein.  
         [0082]     After allocating resources required to support the maximum allowed rate for the SS in step  612 , the BS receives data transmitted using the allocated resources from the SS in step  614 . In step  616 , the BS monitors reception of a resource decrement request from the SS. If the BS receives the resource decrement request, the BS allocates the resource in an amount indicated by the resource decrement request at step  620 . If the BS does not receive the resource decrement request, the BS determines whether the resource allocation request is received at step  618 . If the resource allocation request is received, the BS allocates the maximum amount of resource available for the SS.  
         [0083]     Upon receipt of the resource decrement request in step  616 , the BS allocates a reduced amount of resources, that is, resources required to support a lower data rate to the SS in step  620  and returns to step  614  where the BS receives data by the SS in the changed amount of resources by the SS.  
         [0084]     On the other hand, if the BS receives the resource allocation request, the BS allocates the resources capable of supporting the maximum data rate in step  612 . While not shown in  FIG. 6 , the BS allocates required resources for every data frame.  
         [0085]     In accordance with the present invention as described above, uplink resources are allocated taking into account the uplink rate varying in real time. Therefore, optimum uplink scheduling is carried out. As a result, the following effects are achieved.  
         [0086]     Data transmission efficiency is maximized and the overhead of an SS is reduced. Thus, resource dissipation is prevented.  
         [0087]     Since resources are allocated taking into account the change of the uplink rate of the SS in real time, the resulting saved resources can be utilized for other purposes.  
         [0088]     The SS notifies a BS of a rate change using residual resources saved by reducing the uplink rate. Hence, additional overhead is not produced.  
         [0089]     The number of periodic resource allocation requests transmitted by the SS can be decreased. Therefore, unnecessary consumption of uplink resources for VoIP service can be reduced.  
         [0090]     While the invention has been shown and described with reference to a certain preferred embodiment 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.