Abstract:
A method for variably controlling a bit rate of video data through end-to-end channel status sensing in a Wireless Broadband (WiBro) network is provided. The method includes classifying wireless channel statuses of a transmission side and a reception side into normal and abnormal statuses during video data transmission; variably controlling and determining an encoding bit rate of a transmission side&#39;s encoder according to the classification result; and comparing the determined encoding bit rate with a Down Link Modulation &amp; Coding Selection Level (DL MCS Level) which is a parameter of the reception side, so as to vary a final encoding bit rate of the transmission side.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a Continuation of PCT/KR2008/007052 filed on Nov. 28, 2008 which in turn clams a priority to an earlier Korean Patent application 10-2007-0123443 filed on Nov. 30, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to a method for varying a video transfer rate in a Wireless Broadband (WiBro) network, and in particular, to a method for sensing end-to-end channel status, and a method for varying an encoding bit rate of a transmission side&#39;s encoder by integrating channel statuses of transmission/reception sides under a category of the sensed statuses, thereby improving the quality of video data during transmission of the video data. 
         [0004]    2. Description of the Related Art 
         [0005]    A video streaming service in the wireless network was hard to be commercialized for its high bandwidth and strict restriction on the transmission delay time. Recently, however, due to an increase in wireless access rate and the development of video compression technology, the video streaming service in the wireless network is increasingly available. 
         [0006]    WiBro (defined in IEEE 802.16e), which is Korean-style Mobile Worldwide interoperability for Microwave Access (Mobile WiMAX), has attracted attention of mobile carriers as the next generation mobile communication network, providing a bandwidth of several tens of Mbps and a mobility of several tens of Km/H, and started its commercialization on 2007, starting with Best-Effort (BE) service. 
         [0007]    Generally, the term ‘WiBro’ refers to a super high-speed Internet service in which the user can access the Internet at a high transfer rate of about 1 Mbps using a portable terminal anytime anyplace while at a standstill and on the move, and can enjoy various information and contents. WiBro, which uses a 2.3-GHz frequency band, guarantees a seamless wireless Internet service within a 1-Km cell radius even while the user moves at a speed of 60 Km/H or higher, and it is a new service by which the user can enjoy the wireless Internet at a lower fee. The currently available WiBro technology can support a mobility of 70 Km/H and a transfer rate of up to 1 Mbps per subscriber, and when commercialized, it is expected to support a mobility of 100 Km/H and a transfer rate of up to 3 Mbps. Therefore, with use of the WiBro Internet, the user can enjoy movies on the street or in the running vehicle, and can enjoy on-line games and web surfing as if he/she enjoys the Internet in the room using the wire network. 
         [0008]    The WiBro system, a technology evolved one step further from the 2.3-GHz Wireless Local Loop (WLL) technology, covers a 4 th  generation mobile communication area, and has a field broader than International Mobile Telecommunication (IMT)-2000 which is 3 rd  generation mobile communication. Accordingly, WiBro is called a 3.5 th  generation mobile communication technology. 
         [0009]    WiBro has both a characteristic of the existing mobile terminal and a characteristic of a Broadband convergence Network (BcN) that converges communication, broadcasting and Internet. Therefore, it has a type in which on/off-line wire/wireless communication is combined with a broadcast service, and the multimedia service requiring a real-time property, such as Voice over IP (VoIP), Video Telephony (VT), Personal Broadcasting, etc. especially over the WiBro network, is the factor directly linked to the success of WiBro. 
         [0010]    During operation of a video transfer application over the WiBro network, such as VT and Personal Broadcasting, WiBro controls a level of Modulation &amp; Coding Selection (MCS) and power of a terminal depending on characteristic parameters of a WiBro wireless channel, such as Carrier to Interference and Noise Ratio (CINR), transmission (Tx) power, etc, and increases efficiency of the entire data throughput by an algorithm of a scheduler based thereon. 
         [0011]    However, the available bandwidth continuously varies due to occurrence of traffic congestion and a characteristic of wireless channels that suddenly change because of a property of the WiBro system using the wireless network, and also due to a change in the number of users in the cell. In other words, in WiBro, unlike in the wire network, physical medium characteristics such as data transfer rate can abruptly change according to characteristic and environment of the wireless medium. The change in the characteristics can hardly be estimated. This does not raise any significant problem when the user simply enjoys a service such as Internet search, but may cause significant service degradation in terms of delay and jitter for the multimedia service such as moving picture, causing interrupted reproduction of moving images and degradation of the image quality. In addition, a service requiring guarantee of its bandwidth may suffer significant service degradation in terms of Quality of Service (QoS). Since the users&#39; demand for multimedia also increases along with the development of the network, it is recognized that the QoS guarantee issue should necessarily be considered during development of the communication system. 
         [0012]    In order to solve this problem, the existing WiBro terminal, when it attempts to transmit video data to the other party, estimates a bandwidth to be allocated thereto by sensing an end-to-end channel status, and varies its video transfer rate according thereto. That is, for a good channel status, the WiBro terminal increases the video transfer rate by increasing an encoding bit rate of a video encoder, and for a poor wireless channel status, the WiBro terminal decreases the encoding bit rate of the video encoder, solving the problem. The channel status estimation method is generally performed depending on a calculated delay exchanged between terminals through RTP/RTCP (Real Time Transport Protocol). 
         [0013]    However, even though the same-size data is transmitted and received in the same WiBro network situation, a significant deviation of the delay may occur due to application of Adaptive Modulation and Coding (AMC) and Repetition. Therefore, there is a demand for an absolute reference by which the delay having a relative value can be compensated for. 
       SUMMARY OF THE INVENTION 
       [0014]    An aspect of the present invention is to address at least the problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a method for properly controlling a bit rate of a video CODEC according to status of fast-varying WiBro wireless channels of a transmission side and a reception side during video data transmission in a WiBro system. 
         [0015]    According to one aspect of the present invention, there is provided a method for variably controlling a bit rate of video data through end-to-end channel status sensing in a Wireless Broadband (WiBro) network. The method includes classifying wireless channel statuses of a transmission side and a reception side into normal and abnormal statuses during video data transmission; variably controlling and determining an encoding bit rate of a transmission side&#39;s encoder according to the classification result; and comparing the determined encoding bit rate with a Down Link Modulation &amp; Coding Selection Level (DL MCS Level) which is a parameter of the reception side, so as to vary a final encoding bit rate of the transmission side. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The above and other aspects, 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: 
           [0017]      FIG. 1  is a diagram illustrating the entire configuration of a general WiBro system to which the present invention is applied; 
           [0018]      FIG. 2  is a flowchart illustrating a bit rate control method of a video CODEC during video data transmission according to an embodiment of the present invention; 
           [0019]      FIGS. 3A to 3D  are detailed flowcharts illustrating bit rate decision based on channel status in the bit rate control method of a video CODEC during video data transmission according to an embodiment of the present invention; and 
           [0020]      FIG. 4  is a diagram schematically illustrating a simulator environment for a test of video data transmission quality according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0021]    Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of exemplary embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiment described herein can be made without departing from the scope and spirit of the invention. 
         [0022]      FIG. 1  is a diagram illustrating the entire configuration of a general WiBro system to which the present invention is applied. With reference to  FIG. 1 , a description will now be made of a configuration of the general WiBro system. 
         [0023]    As illustrated in  FIG. 1 , the WiBro system includes Access Control Routers (ACRS)  120 , each of which includes a plurality of Radio Access Stations (RASs, or Base Stations)  130  and accesses the IP network  100  to control the RASs  130 . In addition, the WiBro system includes a plurality of Portable Subscriber Stations (PSSs, or terminals)  140  that exchange data with the RASs  130 . 
         [0024]    The RASs  130  each exchange data with the PSSs  140  through air interfaces at an end of the wire network. In addition, the RASs  130  each have an allocated service area, i.e., cell, and provide a service to the PSSs  140  existing in the cell. The PSSs  140  can include portable communication equipments such as Personal Digital Assistant (PDA), mobile phone, notebook computer, etc. In addition, the WiBro system can include a Home Agent (HA, not shown) for supporting Internet Protocol (IP) mobility of the terminals (or PSSs) in the home network, and an Authentication, Authorization, Accounting (AAA, not shown) for performing authentication, authorization and accounting on the users and terminals to provide network access and service only to the authorized users. 
         [0025]    Allocating a bandwidth to a WiBro terminal so that it can transmit video data is determined by a Media Access Control (MAC) scheduler algorithm of a base station (ACR or RAS). The MAC scheduler algorithm is determined depending on a service class provided by WiBro, i.e., a combination of a Carrier to interference and Noise Ratio (CINR) and transmission (Tx) power, periodically reported to the base station by the terminal, and the number of users in the cell that the base station presently perceives. Allocated the bandwidth, the terminal transmits data, the amount of which corresponds to the allocated bandwidth, and the bandwidth allocated to the terminal continuously varies due to the characteristic of wireless channels. 
         [0026]    A bit rate control method of a video coder/decoder (CODEC) according to an embodiment of the present invention is a Cross Layer Optimization algorithm for acknowledging wireless channel characteristics of the WiBro network, estimating the wireless channel status, and controlling a bit rate of the video CODEC according to the wireless channel status of the transmission side and the reception side. 
         [0027]      FIG. 2  is a flowchart illustrating a bit rate control method of a video CODEC during video data transmission according to an embodiment of the present invention. 
         [0028]    Referring to  FIG. 2 , in step  200 , the bit rate control method classifies end-to-end wireless channel status of the WiBro system into normal and abnormal statuses based on a Frame Per Second (FPS) value. The FPS value is the number of video frames per second that a transmission side&#39;s terminal has sent to a reception side&#39;s terminal, and the transmission side can perceive it through a feedback from the reception side. The abnormal wireless channel status means traffic congestion-happening status, increase in the number of users, interference or other unstable channel status, etc. 
         [0029]    A process of classifying the wireless channel status into normal and abnormal statuses based on the FPS value can be mathematically expressed as Equation (1). 
         [0000]    
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             
                               Abnormal 
                                
                               
                                 : 
                               
                                
                               
                                   
                               
                                
                               FPS 
                             
                             - 
                             1 
                           
                           &gt; 
                           
                             
                               
                                 FPS 
                                 
                                   N 
                                   - 
                                   1 
                                 
                               
                                
                               
                                   
                               
                                
                               or 
                                
                               
                                   
                               
                                
                               FPS 
                             
                             + 
                             1 
                           
                           &lt; 
                           
                             FPS 
                             
                               N 
                               - 
                               1 
                             
                           
                         
                       
                     
                     
                       
                         
                           Normal 
                            
                           
                             : 
                           
                            
                           
                               
                           
                            
                           Otherwise 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0030]    When an FPS value FPS N−1  that the reception terminal has received one second before the current time maintains the FPS N−1  value within a predetermined scope (Step  210 ), the control method determines the channel status as normal status. The control method compares the current FPS N  measured in the normal status with FPS−1 (Step  212 ). If the current FPS N  is less than FPS−1, the control method sets the bit rate one step below a previous target bit rate (Step  214 ), and if the current FPS N  is greater than or equal to FPS−1, the control method determines the final bit rate based on a target bit rate preset according to each uplink (UL) MCS level, i.e., 64 kbps, 128 kbps, 192 kbps and 256 kbps (Step  216 ). 
         [0031]    If it is determined in step  210  that the wireless channel status is not a normal status, the control method compares an FPS value FPS N−1  that it has received one second before the current time with FPS−1 (Step  218 ). If FPS N−1 &lt;FPS−1, the control method determines if a preset FPS Avg , or Avg(FPS N−1 +FPS N ), is True or False (Step  220 ). If FPS Avg  is True, the control method increases the bit rate by one step against the previous target bit rate (Step  224 ). 
         [0032]    However, if FPS Avg  is False, the control method decreases the bit rate by one step against the previous target bit rate (Step  226 ). 
         [0033]    Further, if it is determined in step  210  that the wireless channel status is not a normal status, the control method compares the FPS value FPS N−1  that it has received one second before the current time with FPS−1 (Step  218 ). If FPS N−1 &gt;FPS+1 (Step  222 ) and the preset FPS Avg  is True (Step  228 ), the control method maintains the bit rate at the previous target bit rate. However, when the previous target bit rate is the minimum bit rate, for example, 64 kbps, the control method increases the bit rate by one step (Step  230 ). If FPS Avg  is False, the control method decreases the bit rate by one step against the previous target bit rate (Step  232 ). 
         [0034]    The process of determining an encoding bit rate of the video encoder by classifying the wireless channel status into normal and abnormal statuses based on the FPS value (Steps 212˜232) can be mathematically expressed as Equation (2). 
         [0000]    
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             
                               
                                 
                                   Normal 
                                   , 
                                   
                                     { 
                                     
                                       
                                         
                                           
                                             If 
                                              
                                             
                                                 
                                             
                                              
                                             
                                               ( 
                                               
                                                 
                                                   FPS 
                                                   N 
                                                 
                                                 &lt; 
                                                 
                                                   FPS 
                                                   - 
                                                   1 
                                                 
                                               
                                               ) 
                                             
                                           
                                         
                                       
                                       
                                         
                                           
                                             = 
                                             
                                               { 
                                               
                                                 
                                                   
                                                     
                                                       True 
                                                       , 
                                                       
                                                         
                                                           T 
                                                           BitRate 
                                                         
                                                         = 
                                                         
                                                           Decrease 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Bit 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Rate 
                                                         
                                                       
                                                     
                                                   
                                                 
                                                 
                                                   
                                                     
                                                       False 
                                                       , 
                                                       
                                                         
                                                           T 
                                                           BitRate 
                                                         
                                                         = 
                                                         
                                                           Refer 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Uplink 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           MCS 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Level 
                                                         
                                                       
                                                     
                                                   
                                                 
                                               
                                             
                                           
                                         
                                       
                                     
                                   
                                 
                               
                             
                             
                               
                                 
                                   Abnormal 
                                   , 
                                   
                                     { 
                                     
                                       
                                         
                                           
                                             If 
                                              
                                             
                                                 
                                             
                                              
                                             
                                               ( 
                                               
                                                 
                                                   FPS 
                                                   
                                                     N 
                                                     - 
                                                     1 
                                                   
                                                 
                                                 &lt; 
                                                 
                                                   FPS 
                                                   - 
                                                   1 
                                                 
                                               
                                               ) 
                                             
                                           
                                         
                                       
                                       
                                         
                                           
                                             
                                               FPS 
                                               Avg 
                                             
                                             = 
                                             
                                               { 
                                               
                                                 
                                                   
                                                     
                                                       True 
                                                       , 
                                                       
                                                         
                                                           T 
                                                           BitRate 
                                                         
                                                         = 
                                                         
                                                           Increase 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Bit 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Rate 
                                                         
                                                       
                                                     
                                                   
                                                 
                                                 
                                                   
                                                     
                                                       False 
                                                       , 
                                                       
                                                         
                                                           T 
                                                           BitRate 
                                                         
                                                         = 
                                                         
                                                           Decrease 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Bit 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Rate 
                                                         
                                                       
                                                     
                                                   
                                                 
                                               
                                             
                                           
                                         
                                       
                                       
                                         
                                           
                                             If 
                                              
                                             
                                                 
                                             
                                              
                                             
                                               ( 
                                               
                                                 
                                                   FPS 
                                                   
                                                     N 
                                                     - 
                                                     1 
                                                   
                                                 
                                                 &gt; 
                                                 
                                                   FPS 
                                                   + 
                                                   1 
                                                 
                                               
                                               ) 
                                             
                                           
                                         
                                       
                                       
                                         
                                           
                                             
                                               FPS 
                                               Avg 
                                             
                                              
                                             
                                               { 
                                               
                                                 
                                                   
                                                     
                                                       True 
                                                       , 
                                                       
                                                         
                                                           T 
                                                           BitRate 
                                                         
                                                         = 
                                                         
                                                           Compensate 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Bit 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Rate 
                                                         
                                                       
                                                     
                                                   
                                                 
                                                 
                                                   
                                                     
                                                       False 
                                                       , 
                                                       
                                                         
                                                           T 
                                                           BitRate 
                                                         
                                                         = 
                                                         
                                                           Decrease 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Bit 
                                                            
                                                           
                                                               
                                                           
                                                            
                                                           Rate 
                                                         
                                                       
                                                     
                                                   
                                                 
                                               
                                             
                                           
                                         
                                       
                                     
                                   
                                 
                               
                             
                           
                            
                           
                             
 
                           
                           * 
                           FPS 
                         
                         - 
                         1 
                       
                       &lt; 
                       
                         PFS 
                         Avg 
                       
                       &lt; 
                       
                         FPS 
                         + 
                         
                           1 
                            
                           
                             
 
                           
                            
                           where 
                         
                       
                     
                     , 
                     
                       
                         FPS 
                         Avg 
                       
                       = 
                       
                         Avg 
                         · 
                         
                           ( 
                           
                             ∑ 
                             
                               ( 
                               
                                 
                                   PFS 
                                   
                                     N 
                                     - 
                                     1 
                                   
                                 
                                 + 
                                 
                                   PFS 
                                   N 
                                 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0035]    The control method compares the bit rate determined from each step with a target bit rate designated by a downlink (DL) MCS level of a remote (Step  234 ), and determines the final target bit rate (Step  236 ). This can be mathematically expressed as Equation (3). 
         [0000]    
       
         
           
             
               
                 
                   
                     If 
                      
                     
                         
                     
                      
                     
                       ( 
                       
                         
                           T 
                           BitRate 
                         
                         ≤ 
                         
                           BitRate 
                            
                           
                               
                           
                            
                           RemoteDMCLevel 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             True 
                             , 
                             
                               
                                 T 
                                 FinalBitRate 
                               
                               = 
                               
                                 T 
                                 BitRate 
                               
                             
                           
                         
                       
                       
                         
                           
                             False 
                             , 
                             
                               
                                 T 
                                 FinalBitRate 
                               
                               = 
                               
                                 BitRate 
                                  
                                 
                                     
                                 
                                  
                                 RemoteDMCSLevel 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0036]    As described above, the present invention senses the channel status in the 
         [0037]    WiBro system, and if the channel status of the reception side is unstable even though the channel status of the transmission side is good, the invention can determine the final encoding bit rate of the video encoder taking into account the channel status of the reception side, making it possible to efficiently receive video data. 
         [0038]    In the WiBro system according to an embodiment of the present invention, the video quality can be guaranteed as the bit rate given during video data encoding is higher. However, in the network congestion situation, as the bit rate is higher, a Packet Loss Ratio (PLR) is higher, resulting in a decrease in the video quality. Therefore, for high video quality, it is necessary to properly adjust the bit rate according to the network situation. 
         [0039]      FIGS. 3A to 3D  are detailed flowcharts illustrating bit rate decision based on channel status in the bit rate control method of a video CODEC during video data transmission according to an embodiment of the present invention. This is bit rate decision based on each set range of the bit rate previously set in the UL MCS Level according to an embodiment of the present invention, and the bit rate&#39;s set range is divided into 4 levels of 64 kbps, 128 kbps, 192 kbps and 256 kbps. It should be noted that the bit rate&#39;s set range can be properly set taking into account the target video size and access rate of the service network. 
         [0040]    In  FIG. 3A , the control method determines if the set range of a previous bit rate is 64 kbps (Step  310 ). If the set range is 64 kbps, the control method determines the target bit rate as 128 kbps (Step  312 ), and if the previous bit rate is not 64 kbps, the control method determines the current bit rate as the previous bit rate (Step  314 ). 
         [0041]    In  FIG. 3B , the control method determines if the target bit rate of the current bit rate is 192 kbps (Step  316 ). If the target bit rate is 192 kbps, the control method determines if DL MCS Level of the remote is QPSK 1/2 (Step  318 ). If DL MCS Level of the remote is QPSK 1/2, the control method sets the target bit rate as 128 kbps (Step  320 ), and otherwise, sets the target bit rate as 192 kbps (Step  322 ). 
         [0042]    The control method determines if the target bit rate of the current bit rate is 256 kbps (Step  324 ) and checks if DL MCS Level of the remote is QPSK 3/4 (Step  326 ). If DL MCS Level of the remote is QPSK 3/4, the control method sets the target bit rate as 128 kbps (Step  328 ). Otherwise, the control method determines if DL MCS Level of the remote is QPSK 3/4 or 16QAM 1/2 (Step  330 ). If DL MCS Level of the remote is QPSK 3/4 or 16QAM 1/2, the control method sets target bit rate as 192 kbps (Step  332 ), and otherwise, sets the target bit rate as 256 kbps (Step  334 ). 
         [0043]    In  FIG. 3C , the control method determines if the set range of the previous bit rate is 64 kbps (Step  310 ). If the set range is 64 kbps, the control method determines the target bit rate as 128 kbps (Step  338 ), and if the previous bit rate is not 64 kbps, the control method determines if the previous bit rate is 128 kbps (Step  340 ). If the previous bit rate is 128 kbps, the control method sets the target bit rate as 192 kbps (Step  342 ), and otherwise, checks if the previous bit rate is 192 kbps (Step  344 ). If the previous bit rate is 192 kbps, the control method sets the target bit rate as 256 kbps (Step  348 ). 
         [0044]    In  FIG. 3D , the control method determines if the previous bit rate is 64 kbps (Step  350 ). If the previous bit rate is 64 kbps, the control method sets the target bit rate as 64 kbps (Step  352 ), and otherwise, checks if the previous bit rate is 128 kbps (Step  354 ). If it is checked that the previous bit rate is 128 kbps, the control method sets the target bit rate as 64 kbps (Step  352 ), and otherwise, checks if the previous bit rate is 192 kbps (Step  356 ). If it is checked that the previous bit rate is 192 kbps, the control method sets the target bit rate as 128 kbps (Step  382 ), and otherwise, checks if the previous bit rate is 256 kbps (Step  360 ). If the previous bit rate is 256 kbps, the control method sets the target bit rate as 192 kbps. 
         [0045]    For performance verification of the present invention, the above-stated embodiment of the present invention will be simulated using a network simulator. 
         [0046]    For this purpose,  FIG. 4  schematically illustrates a simulator environment for a test of video data transmission quality according to the present invention. The simulator environment for a scenario used herein is as shown in  FIG. 4 . 
         [0047]    Referring to  FIG. 4 , the system bandwidth is 8.75 MHz, a Time Division Duplex (TDD) frame length is 5 ms, the number of Fast Fourier Transform (FFT) points is 1024, a Tx/Rx Transition Gap (TTG) is 87.2 us, an Rx/Tx Transition Gap (RTG) is 74.4 us, a ratio of cyclic prefix is 1/8, and a DL:UL Ratio is 27:15. The total number of terminals is 32, a network simulator ‘QualNet version 3.9.5’ is used to simulate the real-time video transmission quality of the present invention depending on the presence/absence of network congestion, and a virtual WiBro network suitable for the presence/absence of network congestion is made. The simulation conditions used for simulation of the present invention are as shown in Table 1, and the simulation results based thereon are as shown in Table 2. 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Simulation conditions 
                 Set values 
               
               
                   
               
             
             
               
                 Simulation time 
                 200 sec 
               
               
                 MS1a -&gt; MS1b, . . . , 
                 CBR 130 kbps for 10~200 sec 
               
               
                 MS13a -&gt; MS13b 
               
               
                 MS1a -&gt; MS1b, . . . , 
                 CBR 130 kbps for 10~200 sec 
               
               
                 MS13a -&gt; MS13b 
               
               
                 MS14a-MS14b 
                 Bidirectional CBR 500 kbps for 20~70 sec and 
               
               
                   
                 130~170 sec 
               
               
                 MS15a-MS15b 
                 Real-time video stream @ fixed 256 kbps for 
               
               
                   
                 10~200 sec 
               
               
                 MS16a-MS16b 
                 Real-time video stream to which proposed 
               
               
                   
                 algorithm and four fixed video bit rates are 
               
               
                   
                 applied for 10~200 sec 
               
               
                 MS15a, MS16a 
                 60-Km/H movement, handover occurred 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Simulation result 
                 Comparison in 
               
               
                   
                 values 
                 Improvement between 
               
             
          
           
               
                   
                 PSNR 
                 PLR 
                 prior application 
               
               
                   
                 (dB) 
                 (%) 
                 and this application 
               
             
          
           
               
                   
                 average 
                 average 
                 PSNR (dB) 
                 PLR(%) 
               
               
                 MS16a-MS16b 
                 value 
                 value 
                 improvement 
                 Improvement 
               
               
                   
               
             
          
           
               
                 Invention 
                 27.165 
                 0.0092 
                 — 
                 — 
               
               
                 KR Patent 
                 27.768 
                 0.0645 
                 −0.6 
                 5.5% 
               
               
                 Application No. 
               
               
                 2007-102000 
               
               
                 KR Patent 
                 24.671 
                 0.0095 
                 2.5 
                 0.0% 
               
               
                 Application No. 
               
               
                 2007-39530 
               
             
          
           
               
                 Fixed video 
                  64 kbps 
                 24.542 
                 0.0140 
                 2.6 
                 0.5% 
               
               
                 bit rate 
                 128 kbps 
                 27.119 
                 0.0327 
                 0.0 
                 2.4% 
               
               
                   
                 192 kbps 
                 25.656 
                 0.1660 
                 1.5 
                 15.7% 
               
               
                   
                 256 kbps 
                 22.400 
                 0.2828 
                 4.8 
                 27.4% 
               
               
                   
               
             
          
         
       
     
         [0048]    The simulation results show that though the invention is almost similar to the prior art in a Peak Signal to Noise Ratio (PSNR), PLR improves up to 0%˜27%. It can be appreciated that a high PLR, since it prevents restoration of frames, causes degradation of the video quality, and this is proved by the PSNR value. 
         [0049]    In conclusion, the algorithm according to an embodiment of the present invention shows the improved results compared with the fixed video bit rate, in all cases. This algorithm can adaptively decrease the video bit rate in the poor network situation and increase the video bit rate in the better network situation, thereby obtaining the best video quality. 
         [0050]    As is apparent from the foregoing description, when a WiBro terminal (or Mobile Station (MS)) transmits real-time video data in the WiBro system, the present invention, the present invention adaptively decreases the video bit rate in the poor network situation and increases the video bit rate in the better network situation taking into account not only the physical situation of the local wireless network but also the end-to-end wireless channel status information, thereby providing the best video quality. 
         [0051]    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.