Patent Publication Number: US-2006002296-A1

Title: Controlling transmission rate of reverse traffic channel in wireless communication system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      Pursuant to 35 U.S.C. § 119(a), this application claims the benefit of earlier filing date and right of priority to Korean Application No. 2004-49775, filed on Jun. 29, 2004, the contents of which is hereby incorporated by reference herein in its entirety.  
     FIELD OF THE INVENTION  
      Field of the Invention  
      The present invention relates to an HDR (High Data Rate) system, and particularly, to controlling a transmission rate of a reverse traffic channel of an HDR system in a wireless communication system.  
     BACKGROUND OF THE INVENTION  
      With the provision of various kinds of information and services through the Internet, a high data rate (HDR) system has been introduced to provide high data rate wireless communication services to a user of a mobile communication service.  
      The HDR system is a type of third generation mobile communication system providing high-speed packet data services. The HDR system transmits data such as text messages, videos, music and the like through a network such as the Internet. Particularly, the HDR system has a data processing speed that is much higher than that of an existing wireless data system. Furthermore, the HDR system may be compatible with an existing data transmission device so that an existing system can be easily upgraded.  
      In general, users using the same kind of service in the HDR system should be provided with the same quality of service. Accordingly, data of a reverse channel (terminal→base station) of the HDR system undergoes coherent demodulation using a reverse pilot signal. A transmission rate of the reverse channel is variably controlled per each terminal within a range of 9.5 Kbps˜153.6 Kbps by using data traffic and different characteristics of channel environments.  
       FIG. 1  is a block diagram for controlling a transmission rate of a reverse traffic channel in a mobile communication terminal in accordance with the related art. As shown, the mobile communication terminal in accordance with the related art comprises a receiving unit  10  for receiving, from all base stations in an active set, an RAB (Reverse Activity Bit) indicating whether a reverse traffic channel is congested, a transmission rate control unit  20  for determining a transmission rate of a reverse channel upon receiving the RAB from the receiving unit  10 , a transmission rate adjusting unit  30  for adjusting a transmission rate of data according to control information received from the transmission rate control unit  20 ; and a transmitting unit  40  for transmitting, to a base station, data which has been adjusted by the transmission rate adjusting unit  30 .  
       FIG. 2  is a state transition diagram showing five kinds of transmission rates (9.6 Kbps, 19.2 Kbps, 38.4 Kbps, 76.8 Kbps and 153.6 Kbps) of a reverse traffic channel. On the assumption that each transmission rate of the reverse traffic channel is a state indicating a transmission rate of a mobile communication terminal, a reverse transmission rate of the mobile communication terminal may be controlled as shown in the state transition diagram of  FIG. 2 . The state of the terminal can only be transited from a predetermined state (S 0 , S 1 , S 2 , S 3  or S 4 ) to a neighboring state.  
      Accordingly, when RABs are received through the receiving unit  10  from all base stations of an active set, the transmission rate control unit  20  determines a transmission rate (state transition) based upon the received RAB value and a transition probability (P). The transmission rate control unit  20  then outputs a control signal corresponding to the determined rate to the transmission rate adjusting unit  30 . The transition probability (P) is a value determined by each state, and is determined ultimately to control a transmission rate. For example, P ij  denotes a probability that a state of the terminal is transited from state i to state j.  
      Accordingly, the transmission rate adjusting unit  30  adjusts a transmission rate of data by the transmission rate of the control signal outputted from the transmission rate control unit  20 , and then transmits the data to a base station through the transmitting unit  40 .  
      A method for controlling a transmission rate of a reverse traffic channel by the transmission rate control unit  20  will now be described in detail.  FIG. 3  is a flow chart showing a method for controlling a transmission rate of a reverse traffic channel in a HDR system in accordance with the related art.  
      As shown in  FIG. 3 , when a plurality of RABs are received from the receiving unit  10 , the transmission rate control unit  20  determines the state transition based on the received RABs and the transition probability (P). Namely, assuming that a reverse transmission rate of a current mobile communication terminal corresponds to state i, the transmission rate control unit  20  determines whether every received RAB is zero (S 310 ).  
      If it is determined that every corresponding RAB is zero, then a current reverse channel has capacity. Thus, the transmission rate control unit  20  checks whether the reverse transmission rate, namely, a state of the terminal is S 4  (S 312 ). If the terminal is in the state of S 4 , the current state S 4  is maintained since there is no need to lower the reverse transmission rate (S 314 ). If the terminal is not in the state of S 4 , a random number between “0” and “1” is generated and then the terminal compares the corresponding random number to a next transition probability (P i, i+1 ) (S 316 , S 318 ). If the random number is equal to or greater than the transition probability (P i, i+1 ), the current state S i  is maintained (S 314 ), and if the generated random number is smaller than the transition probability (P i, i+1 ), a state of the terminal is transited to a next state of S i+1  (S 320 ).  
      In contrast, if at least one of the received RABs is not zero, then the current reverse channel is congested. Thus, the transmission rate control unit  20  checks whether the reverse transmission rate, namely, a state of the terminal is S 0  (S 322 ). If the reverse transmission rate is S 0 , then the current state of S 0  is maintained (S 314 ). If the state of the terminal is not S 0 , then a random number between “0” and “1” is generated, and the corresponding random number is compared to a transition probability (P i, i−1 ) (S 324 , S 326 ). If the random number is equal to or greater than the transition probability (P i, i−1 ), the current state S i  is maintained (S 314 ). If the random number is smaller than the transition probability (P i, i−1 ), a state of the terminal is transited to a previous state of S i−1  (S 328 ).  
       FIG. 3  is a flow chart illustrating a situation when packets are consecutively transmitted. When the packet transmission is temporarily stopped and then performed again, the terminal starts transmitting packets in the state of S 0 , namely, at the lowest transmission rate. Also, since each mobile communication terminal has a maximum transmission rate value transmitted from the base station, the terminal cannot transmit at a transmission rate greater than the maximum value (limit value). Preferably, the maximum transmission rate value is included in a limit value message of a transmission rate of the reverse traffic channel and then transmitted.  
      In general, users using the same kind of data service should be provided with the same quality of service. However, the method for controlling the reverse transmission rate of the HDR system in accordance with the related art is limited in providing fairness to users using the same kind of data service.  
      For example, if there are two terminals using the same data service for one base station and a current network is congested, each terminal controls a transmission rate of the reverse traffic channel according to the flow chart shown in  FIG. 3 . Specifically, the transmission rate control unit  20  determines whether to decrease a transmission rate or to maintain a current state according to a random number generated from each terminal.  
      However, if the random numbers generated from one of the two mobile communication terminals are continuously smaller than a transition probability, and the random numbers generated from the other terminal are continuously greater than the transition probability, the former terminal continuously decreases a transmission rate and the latter terminal maintains a current transmission rate. For this reason, fairness in providing users with the same quality of service cannot be achieved due to different transmission rates.  
     SUMMARY OF THE INVENTION  
      The present invention is directed to controlling a transmission rate of a reverse traffic channel of an HDR system in a wireless communication system.  
      Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
      To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention is embodied in a method for controlling a transmission rate of a reverse traffic channel in a wireless communication system, the method comprising determining whether a reverse traffic channel is congested, generating a random number if the reverse traffic channel is congested, comparing the random number to a transition probability, setting a count value according to the comparison between the random number and the transition probability, and comparing the count value to a threshold value if the random number is equal to or greater than the transition probability and setting a transmission rate of the reverse traffic channel according to the comparison between the count value and the threshold value.  
      The random number is generated if the transmission rate is not a lowest possible rate. The count value is reset if the reverse traffic channel is not congested.  
      In one aspect of the present invention, the method further comprises decreasing the transmission rate of the reverse traffic channel if the random number is less than the transition probability. Preferably, the count value is reset prior to decreasing the transmission rate of the reverse traffic channel. Also, the method may further comprise decreasing the transmission rate of the reverse traffic channel if the count value is equal to or greater than the threshold value. Moreover, the method may further comprise maintaining a current transmission rate if the count value is less than the threshold value.  
      Preferably, a congestion control bit received from base stations in active set is used to determine whether a reverse traffic channel is congested. The threshold value is set differently according to a type of service.  
      In another aspect of the present invention, the method further comprises counting the number of times the random number is consecutively equal to or greater than the transition probability, wherein the number of times the random number is consecutively equal to or greater than the transition probability indicates the number of times a current transmission rate is maintained. Also, the transition probability indicates a probability of transition from a current state to a previous state.  
      In another embodiment of the present invention, a method for controlling a transmission rate of a reverse traffic channel in a wireless communication system comprises determining that a reverse traffic channel is congested, generating a random number if the reverse traffic channel is congested, comparing the random number to a transition probability, and decreasing the transmission rate of the reverse traffic channel when the random number is consecutively equal to or greater than the transition probability more than a predetermined number of times.  
      The random number is generated if the transmission rate is not a lowest possible rate. A count value is reset if the reverse traffic channel is not congested. Furthermore, a count value is reset prior to decreasing the transmission rate of the reverse traffic channel.  
      In one aspect of the present invention, the method further comprises counting the number of times the random number is consecutively equal to or greater than the transition probability, wherein the number of times the random number is consecutively equal to or greater than the transition probability indicates the number of times a current transmission rate is maintained.  
      In another aspect of the present invention, the method further comprises maintaining a current transmission rate if the number of times the random number is consecutively equal to or greater than the transition probability is smaller than a threshold value, wherein the threshold value is set differently according to a type of service.  
      Preferably, the method further comprises decreasing the transmission rate of the reverse traffic channel if the random number is less than the transition probability, wherein a count value is reset prior to decreasing the transmission rate of the reverse traffic channel. The transition probability indicates a probability of transition from a current state to a previous state. Furthermore, a congestion control bit received from base stations in an active set is used to determine whether a reverse traffic channel is congested.  
      It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. Features, elements, and aspects of the invention that are referenced by the same numerals in different figures represent the same, equivalent, or similar features, elements, or aspects in accordance with one or more embodiments.  
       FIG. 1  is a related art block diagram illustrating a method for controlling a transmission rate of a reverse traffic channel in a mobile communication terminal.  
       FIG. 2  is a related art state transition diagram illustrating a transmission rate change of the reverse traffic channel in the mobile communication terminal  
       FIG. 3  is a related art flow chart illustrating a method for controlling a transmission rate of the reverse traffic channel in an HDR system.  
       FIG. 4  is a flow chart illustrating a method for controlling a transmission rate of a reverse traffic channel of an HDR system in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The present invention relates to controlling a transmission rate of a reverse traffic channel of an HDR system in a wireless communication system.  
      Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. A basic concept of the present invention is that users requiring the same type of data service are respectively provided with their service in a fair, impartial and reasonable manner. This is done by forcibly decreasing a reverse transmission rate regardless of a generated random number when a state that a current transmission rate of a mobile communication terminal is maintained is repeated more than a certain number of times. Accordingly, the present invention determines (controls) a transmission rate of the reverse traffic channel by setting a count variable and a threshold value (C TH ).  
      Preferably, the count variable is the number of situations in which a channel-congested state (i.e., when at least one of the RABs received from base stations in an active set is not zero) is not transited but is continuously maintained.  
      A method for controlling a transmission rate of the reverse traffic channel in accordance with the present invention may be applied to a block diagram of a mobile communication terminal shown in  FIG. 1 .  
      The method for controlling a transmission rate of the reverse traffic channel in accordance with an embodiment of the present invention will now be described with reference to  FIG. 4 . In the present invention, as shown in  FIG. 2 , it is preferable that each transmission rate of each reverse traffic channel (9.6 Kbps, 19.2 Kbps, 38.4 Kbps, 76.8 Kbps and 153.6 Kbps) is a state showing a transmission rate of the mobile communication terminal, and a transmission rate of a current reverse traffic channel is in a state S i .  
      In such a state, when Reverse Activity Bits (RABs) received from all base stations in the active set through a receiving unit  10  are inputted, a transmission rate control unit  20  determines whether every received RAB is zero (S 410 ).  
      If every RAB is zero, then a reverse traffic channel has capacity. Thus, the transmission rate control unit  20  checks whether the transmission rate (state) of the current reverse traffic channel corresponds to S 4  (S 412 ). If the state of the terminal is S 4 , the current state S 4  is maintained because there is no need for the transmission rate control unit  20  to raise (increase) the reverse transmission rate (S 414 ). In contrast, if the state of the terminal is not S 4 , the transmission rate control unit  20  initializes a count value (S 416 ), generates a random number between zero and one according to the RAB (S 418 ), and compares the generated random number with a transition probability (P i, i+1 ) (S 420 ).  
      If the random number is equal to or greater than the transition probability (P i, i+1 ), a current reverse transmission rate is maintained at the state of S i  (S 414 ). If the generated random number is smaller than the transition probability (P i, i+1 ), the reverse transmission rate is increased to a state of S i+1  (S 422 ).  
      In contrast, if at least one of the RABs is not zero, then the current reverse channel is in a congested state. Thus, the transmission rate control unit  20  preferably lowers the reverse transmission rate. Here, since the transmission rate of the reverse traffic channel cannot be lower than S 0 , the transmission rate control unit  20  checks whether the reverse transmission rate corresponds to the state of S 0  (S 424 ). If the state of the terminal is S 0 , the current state S 0  is maintained (S 414 ) because there is no need for the transmission rate control unit  20  to lower the reverse transmission rate. However, if the state of the terminal is not S 0 , a random number between zero and one is generated (S 426 ), and the generated random value is compared with a transition probability (P i, i−1 ) (S 428 ).  
      If the random value is smaller than the transition probability (P i, i−1 ), a count value is initialized (S 430 ) and the reverse transmission rate is decreased to S i−1  (S 432 ). If the generated random value is equal to or greater than the transition probability (P i, i−1 ), the count value is increased by one (S 434 ) and the increased count value is compared to a preset threshold value (C TH ) (S 436 ).  
      Preferably, the threshold value (C TH ) indicates the degree by which a state of channel congestion is not transited but maintained. Also, the threshold value (C TH ) can be set differently according to the type of service.  
      If the increased count value is smaller than the threshold value (C TH ), the transmission rate is maintained at the current state of S i  (S 414 ). If the increased count value is equal to or greater than a predetermined threshold value (C TH ) for more than a predetermined number of times, the count value is initialized (S 430 ) and the reverse transmission rate is forcibly lowered by one level to be in the state of S i−1  (S 432 ).  
      Accordingly, although the random numbers generated from two mobile communication terminals are different, a transmission rate of the reverse traffic is determined according to a comparison result between a threshold value (C TH ) and a count value which indicate a degree to which a current transmission state is maintained. Accordingly, the transmission rate control unit  20  can fairly maintain the transmission rate of the reverse traffic channel.  
      For reference, if the threshold value (C TH ) is set as an infinite value, the method for controlling a transmission rate of the reverse traffic channel in accordance with the present invention can operate in the same manner as that in accordance with the related art.  
      As so far described, the present invention is advantageous in that a service can be provided fairly to users requiring the same type of data service by using an algorithm that forcibly decreases a reverse transmission rate regardless of a random number generated in a mobile communication terminal when the reverse channel of the HDR system is congested.  
      As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.