Abstract:
An apparatus and method are disclosed for determining different reverse rates, in accordance with a reverse data transmission state of each mobile station, at a base station having a 1×EV-DO system. The present invention improves the processing capacity of a reverse link by generating a weight based on a comparison result of a present data amount and a previous data amount of each mobile station, calculating a new reverse rate limit by imposing the generated weight onto a predetermined reverse rate limit, and transmitting the newly calculated reverse rate limit to every mobile station within a reverse rate limit message.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a base station apparatus in a 1×EV-DO system and a method thereof that determine different reverse rates for different data transmission situations of each mobile station.  
           [0003]    2. Background of the Related Art  
           [0004]    In general, an IS-95 based mobile communication system provides voice-centered services. Recently, however, thanks to the development of 1×EV-DO wireless protocol, which is a forward link providing the maximum 2.4576 Mbps high speed packet data service, the mobile communication system is now able to provide multimedia services, such as IMT-2000 service as well as high speed packet data service, moving image service, and further packetized voice service.  
           [0005]    The 1×EV-DO system is not focused on providing voice-centered services like IS-95. Rather, it is aiming to provide high speed packet data services only. Specifically, the data source of each mobile station varies depending on the wireless environment. The high speed data in a forward link is first loaded into a time slot that is segmented into 1.67 ms units and is transmitted through time division communication.  
           [0006]    The reverse rates in the 1×EV-DO system are 9.6 Kbps, 19.2 Kbps, 38.4 Kbps, 76.8 Kbps, and 153.6 Kbps. The mobile station often changes the reverse rate to determine an appropriate rate in accordance with a reverse activity bit and a random number. The random number is based on a reverse rate limit that is included in a broadcast reverse rate limit message and transmitted from the base station. The reverse rate limit is pre-defined in a manner that it is designated according to an active call.  
           [0007]    Related art reverse rate limits of the mobile stations are designated according to the number of mobile stations supporting active calls, in a sector where the reverse rate limit message is broadcasted. In other words, if the number of active calls in a sector is low, the base station employing a related art 1×EV-DO system, to maximize reverse link throughput, selects a high reverse rate limit. On the other hand, if the number of active calls in a sector is high, the reverse rate limit is set low to reduce the reverse link loading.  
           [0008]    [0008]FIG. 1 is a block diagram illustrating an apparatus for determining the reverse rate in a related art mobile communication. The device includes a plurality of mobile stations  11  and a base station  12  that generates and transmits a broadcast reverse rate limit message. Base station  12  has a reverse rate generation module  12   a  that generates a broadcast reverse rate limit message by selecting a reverse rate limit per active mobile station using a mapping table (refer to FIG. 2). The mapping table associates reverse rate limits with the numbers of active calls. After a reverse rate limit is selected, reverse rate generation module transmits the broadcast reverse rate limit message to every active mobile station. All mobile stations in the active state receive the same reverse rate limit. Reverse rate generation module  12   a  calculates the number of active calls for each mobile station that transmits reverse data. Then, using the mapping table, reverse rate generation module  12   a  sets the reverse rate limit, corresponding to the calculated number of active calls, and assigns this limit to each mobile station. For instance, suppose the present number of active calls in the sector is 5. Then, based on the associated limit in the mapping table, reverse rate generation module  12   a  designates 38.4 Kbps as the reverse rate limit for each of the five mobile stations. Therefore, the broadcast reverse rate limit message including the reverse rate limit, 38.4 Kbps, is transmitted to the five active mobile stations.  
           [0009]    [0009]FIG. 2 illustrates a mapping table associating the reverse rates with the number of the active calls in the related art mobile communication system. The number of active calls in the mapping table ranges from 1 to 8, and a reverse transmit limit is associated with each number of active calls. For example, if the number of active calls is 1, the reverse rate limit is 153.6 Kbps, which is the maximum value applicable to the 1×EV-DO system. As the number of active calls increases, the reverse rate limit decreases. In this manner, the minimum reverse rate, 9.6 Kbps, is associated with 8 active calls. FIG. 2 is just one example of the mapping table. Thus, even when the number of active calls exceeds 5, it is possible to make a different mapping between the number of active calls and the reverse rate limit.  
           [0010]    [0010]FIG. 3 is a flow chart showing a method for generating a broadcast reverse rate limit message in the related art. Base station  12  calculates the number of active calls based on the active calls requested from each mobile station  11 . Then, base station  12  determines the reverse rate limit corresponding to the calculated number of active calls, using the mapping table (S 31 ).  
           [0011]    Afterwards, base station  12  determines whether an index, having values that identify each mobile station  11  uniquely and that have been assigned to each active state mobile station, is set to identify the maximum reverse power control (RPC) value (S 33 ). Base station  12  repeatedly generates a reverse rate limit message for every index value, using the reverse rate limit determined in the step  31 , until the index reaches the maximum RPC value (S 35 ). Each index value is pre-assigned to a mobile station. Also, the maximum RPC can be designated as  32 . Thus, it is possible to identify each mobile station based on the index value, and when the reverse rate limit message generated is transmitted to every mobile station later, the index can be used for transmitting the reverse rate limit message to each mobile station.  
           [0012]    When the index value exceeds the maximum RPC, base station  12  transmits the reverse rate limit message generated for index values 0 through 31 to each mobile station (S 37 ). The reverse rate limits included in the reverse rate limit messages, transmitted to all mobile stations, hold an equivalent value. Steps  31  through  37  can be repeated for every transmission cycle of the reverse rate limit.  
           [0013]    The above-described method of applying the reverse rate limit, determined according to the number of active calls to all active state mobile stations, does not consider the transmission state of each mobile station. That is to say, although there may be a great number of active calls and some mobile stations may have large volumes of data to transmit, if a low reverse rate limit is applied to every mobile station equally, the mobile stations with large volumes of data to transmit will not be able to secure a transmission rate high enough to transmit all the data. This consequently lowers the usage efficiency of the reverse link greatly.  
           [0014]    The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.  
         SUMMARY OF THE INVENTION  
         [0015]    An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.  
           [0016]    It is, therefore, an object of the present invention to provide a method and apparatus for determining a different reverse rate for each active state mobile station.  
           [0017]    To achieve the above objects, there is provided a method for determining a reverse rate in a mobile communication system, including calculating secondary reverse rate limits for at least one mobile station using weights generated in accordance with reverse data transmission states, taken in from at least one mobile station, and using a predetermined primary reverse rate limit; and transmitting at least one reverse rate limit message, which includes the secondary reverse rate limits for the at least one mobile station, to the at least one mobile station.  
           [0018]    Preferably, the calculation of secondary reverse rate limits continues until an index assigned to a mobile station, transmitting the reverse data, becomes greater than a predetermined index.  
           [0019]    Preferably, the secondary reverse rate limits for the at least one mobile station are calculated differently, depending on an outcome of the weights.  
           [0020]    Preferably, the reverse data transmission state includes a previous reverse data amount and a present reverse data amount, and the previous reverse data amount and the present reverse data amount are compared with each other to generate a weight. Preferably, the weight is increased if the present reverse data amount is greater than the previous reverse data amount and the weight is decreased if the present reverse data amount is less than the previous reverse data amount.  
           [0021]    Also, a weight is preferably generated by comparing the present reverse data amount with an average of reverse data amounts, which are transmitted from mobile stations in an active state at present. Preferably, the weight is increased if the average of the reverse data amounts, which are transmitted from mobile stations in an active state, is greater than the present reverse data amount, and the weight is decreased if the average of the reverse data amounts, which are transmitted from mobile stations in an active state, is less than the present reverse data amount.  
           [0022]    The secondary reverse rate limit is preferably calculated by imposing the predetermined primary reverse rate limit on the weight.  
           [0023]    In addition, the present invention provides a method for determining a reverse rate in a mobile communication system, the method including: (a) measuring a present reverse data amount based on reverse data of a mobile station; (b) comparing the present reverse data amount with a previous reverse data amount; (c) calculating a secondary reverse rate limit by imposing a weight, which is generated according to the comparison result, on a predetermined primary reverse rate limit; (d) including the secondary reverse rate limit with a reverse rate limit message; and (e) transmitting the reverse rate limit message.  
           [0024]    Preferably, every time reverse data is received from the mobile station, steps (a) through (d) are repeatedly performed until an index assigned to the mobile station becomes greater than a predetermined index, thereby calculating a secondary reverse rate limit.  
           [0025]    Additionally, the present invention provides an apparatus for determining a reverse rate in a mobile communication system, which includes a data measurement means for measuring a present reverse data amount, based on reverse data received from at least one mobile station; a weight generation means for generating a weight, by comparing the present reverse data amount with a previous reverse data amount; and a message generation means for calculating a new reverse rate limit, by imposing the generated weight on a predetermined reverse rate limit, and for including the new reverse late limit with a reverse rate limit message.  
           [0026]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein:  
         [0028]    [0028]FIG. 1 illustrates a device for selecting a reverse rate in a mobile communication system of the related art;  
         [0029]    [0029]FIG. 2 illustrates a mapping table associating a reverse rate limit with the number of active calls in a mobile communication system of the related art;  
         [0030]    [0030]FIG. 3 illustrates a flow chart of a method for generating a broadcast reverse rate limit message in the related art;  
         [0031]    [0031]FIG. 4 illustrates an apparatus for selecting a reverse rate in a mobile communication system according to the present invention;  
         [0032]    [0032]FIG. 5 illustrates a table storing a measured amount of reverse data corresponding to each index value, according to the present invention; and  
         [0033]    [0033]FIG. 6 illustrates a method for generating a broadcast reverse rate limit message, according to the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0034]    [0034]FIG. 4 is a block diagram illustrating an apparatus for settling a reverse rate in a mobile communication system, according to the present invention. The apparatus includes a plurality of mobile stations  41  and a base station  43  that generates a reverse rate limit message, including a reverse rate limit that is designated based on a weight. Base station  43  includes a data measurement module  45  that measures an amount of present reverse data, based on reverse data received from the plurality of mobile stations  41 . A weight generation module  47  generates the weight by comparing the present reverse data amount with a previous reverse data amount. Message generation module  49  calculates a new reverse rate limit by imposing the generated weight on a pre-designated reverse rate limit and includes the new reverse rate limit in a reverse rate limit message.  
         [0035]    Base station  43  calculates the number of active calls based on the reverse data received from mobile stations  41  and, using a mapping table, determines a reverse rate limit corresponding to the number of active calls. Therefore, it is possible to calculate a new reverse rate limit by imposing the reverse rate limit on a weight.  
         [0036]    Data measurement module  45  measures a present reverse data amount, based on the reverse data received from mobile stations  41 , and stores the present reverse data amount in a present data field  55  of a table, as shown in FIG. 5. Also, the previous reverse data amount, which was measured in a similar manner previously, is stored in a previous data field  53 , beforehand. Preferably, the previous/present reverse data amount stored in the table identifies the number of packet data packets received. That is, the reverse data received from the mobile stations  41  may be formed of packet data units, and base station  43  may calculate the number of packet data units received from each mobile station  41  to store the number in the table. As a reverse rate transmission cycle restarts in base station  43 , the present reverse data amount is stored in the previous data field  53  and a data amount that is calculated based on newly received reverse data is stored in the present data field  55 .  
         [0037]    Weight generation module  47  first compares the stored present reverse data amount with the stored previous reverse data amount, and based on the comparison result, module  47  generates a weight. More specifically, weight generation module  47  generates ‘+1‘ if the present reverse data amount is greater than the previous reverse data amount and ‘−1’ if the present reverse data amount is smaller than the previous reverse data amount. Of course, if the comparison result indicates a big difference between the present reverse data amount and the previous reverse data amount, different weights, such as +2, +3, or −2, −3, can be generated as well.  
         [0038]    The weight ‘+1’ or ‘−1’ means that the currently designated reverse rate limit is respectively increased or decreased by a single step. For example, suppose that the present number of active calls is 6, as shown in FIG. 2, and the designated reverse rate limit corresponding to this number of the active calls is 19.2 Kbps. In such a case, if the weight generated by weight generation module  47  is ‘+1’, the reverse rate limit becomes 38.4 Kbps, having been increased by one step because of the ‘+1’ weight. Similarly, if the weight is ‘−1’, the new reverse rate limit becomes 9.6 Kbps, having been decreased by one step. More details on this principle are provided below.  
         [0039]    [0039]FIG. 5 illustrates a table storing a measured amount of reverse data corresponding to each index value, according to the present invention. With reference to FIG. 5, suppose that bit values of 1024, 0, 512, and 1024 are stored in the previous data field  53 , and 768, 1024, 0, and 1536 are stored in the present data field  55  for index values 0, 1, 2, and 3, respectively. Weight generation module  47  first compares the reverse data amounts stored in the previous data field  53  with the reverse data amounts stored in the present data field  55  and, based on the comparison result, then generates a weight. For example, when the index value is 0, since the present reverse data amount of 768 bits is less than the previous reverse data amount of 1,024 bits, a ‘−1’ weight is generated. Similarly, the method is applied to the other indexes, and it is found that ‘+1’, ‘−1’, and ‘+1’ weights are generated for indexes values 1, 2, and 3, respectively. Accordingly, in the case where the number of active calls is 4 and the active mobile stations  41  are uniquely identified by index values 0, 1, 2, and 3, respectively, the new reverse rate limits based on the generated weights are 38.4 Kbps, 76.8 Kbps, 38.4 Kbps, and 76.8 Kbps, respectively, given that the previous reverse rate limits were 76.8 Kbps, 38.4 Kbps, 76.8 Kbps, and 38.4 Kbps, respectively, and that no other reverse rate limit exists between the 38.4 Kbps and 76.8 Kbps limits.  
         [0040]    Referring to FIG. 4 again, message generation module  49  can include the newly calculated reverse rate limit, produced by weight generation module  47 , in each reverse rate limit message. In addition, message generation module  49  can transmit each individual reverse rate limit message to its respective mobile station  41 . In this way, the reverse rate limits included in the reverse rate limit messages transmitted to the mobile stations  41  are different from one another and each reverse rate limit is individually applied to its corresponding mobile station  41 . In short, separately determining the reverse rate limit for each mobile station  41  based on its current communication requirements enables the base station to more efficiently manage communication with the mobile stations.  
         [0041]    [0041]FIG. 6 is a flow chart illustrating the method for generating broadcast reverse rate limit messages according to the present invention. Note that steps  61 ,  63  and  75  are not explained here, since they are identical to those described previously in reference to FIG. 3. Referring now to FIG. 6, the number of active calls is calculated based on the number of active calls requested from each mobile station in the active state. Based on the calculated number of active calls, the corresponding reverse rate limit is determined using the mapping table (S 61 ).  
         [0042]    Next, it is decided whether the index is set to indicate the maximum reverse power control (RPC) value (S 63 ). If not, the present reverse data amount and the previous reverse data amount, corresponding to the current index value, are read from the table to determine whether the present reverse data amount is greater than the previous reverse data amount (S 65 ). If the comparison result indicates that the present reverse data amount is greater than the previous reverse data amount, the weight ‘+1’ is generated (S 67 ). On the other hand, if the present reverse data amount is less than the previous reverse data amount, the weight ‘−1’ is generated (S 69 ).  
         [0043]    Thereafter, a new reverse rate limit is calculated using the weights generated either in step  67  or step  69  (S 71 ). The new reverse rate limit is calculated by imposing the weights generated from steps  67  and  69  upon the previous reverse rate limit.  
         [0044]    As explained before, the new reverse rate limit can be either increased or decreased depending on the weights generated in steps  67  and  69 . And, since the weights are generated by comparing the present reverse data amount and the previous reverse data amount, the determination of the new reverse rate limit is influenced by the comparison result. Accordingly, different reverse rate limits may be concurrently assigned to the mobile stations in accordance with the amount of reverse data communicated by the respective mobile stations. The new reverse rate limit calculated from step  73  is included with the corresponding message and a reverse rate limit message is generated therefrom (S 73 ).  
         [0045]    Steps  65  through  73  are repeated until the index indicates the maximum RPC value, and the reverse rate limit message is generated accordingly.  
         [0046]    Particularly in step  63 , if the index value is greater than the maximum RPC, the reverse rate limit messages that have been generated up to this point can be transmitted to each mobile station (S 75 ). At this time, the index assigned to each mobile station can be used to identify the mobile station intended to receive the individual reverse rate limit messages.  
         [0047]    Another preferred embodiment of the present invention is explained with reference to FIG. 5. For each index value, the average amount of present reverse data communicated by all active mobile stations  41  is compared with the amount of present reverse data communicated by the indexed mobile station and a weight is generated, based on the result of the comparison. Preferably, if the present reverse data amount exceeds the average amount, the weight ‘+1’ is generated, and if the present reverse data amount is less than the average amount, the weight ‘−1’ is generated.  
         [0048]    For example, suppose an average value of 832 bits is obtained by averaging the present reverse data amounts communicated by the active mobile stations corresponding to the index values of 0, 1, 2, and 3. In such a case, since the present reverse data amount corresponding to the index value of 0 is 768 bits, which is less than the average value of 832 bits, the weight ‘−1’ is generated. Applying the same method to the other index values 1, 2, and 3, the weights ‘+1’, ‘−1’, and ‘+1’ are sequentially generated. Thus, such a method can be an alternative to step  65  in FIG. 6, though the remaining steps in FIG. 6 may be unchanged.  
         [0049]    In conclusion, the method for settling different reverse rate limits for different mobile stations, according to the reverse data amount communicated by each mobile station, improves the processing efficiency of the reverse link.  
         [0050]    Furthermore, the load of the base station can be considerably reduced by properly adjusting the reverse rate according to the number of active calls.  
         [0051]    The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.