Patent Publication Number: US-2007097862-A1

Title: Call admission controlling device and method for providing qos in high-speed portable network

Description:
TECHNICAL FIELD  
      The present invention relates to a call admission controlling device and method in a high-speed portable network. More specifically, the present invention relates to a call admission controlling device and method for providing QoS (quality of service) in a portable network for providing seamless handoff and using optimal radio resources of cells.  
     BACKGROUND ART  
      Most systems for providing Internet access services only provide best effort services. As various multimedia services have appeared, it is required to provide QoS on the Internet, and call admission control on network resources including radio resources is also needed so as to provide distinguishing QoS.  
      Also, call admission control in consideration of mobility is necessary, which must perform reservation of additional resources in consideration of handoff at adjacent cells so as to provide seamless connection services irrespective of movements of mobile subscribers in the respective cells of the HPi (high-speed portable Internet.)  
      The call admission control method in the mobile network checks whether adjacent cells have handover resources, and admits a call only when the adjacent cells have them. That is, resources for new calls and those for handoff calls are classified, and resources reserved in advance for handoff are allocated at the time of performing handoff, thereby providing seamless services.  
      As demands of the QoS including multimedia services on the Internet have increased, new functions of the Internet nodes which previously considered the best effort services have come to be required. The QoS includes guaranteeing the uniform quality from the time of establishing connection to the time of service termination.  
      The above description also applies to the mobile networks in the same manner, that is, seamless QoS is to be provided to a subscriber when they are moving. However, it is needed to reserve the same bandwidth of all the neighboring cells in consideration of handoff so as to provide the seamless connection service to all the subscribers, and accordingly, usage rates of resources are substantially worsened.  
      Therefore, a dropping probability on a predetermined amount of QoS is assumed in the mobile network, and resources for handoff are occupied to thus enhance the usage rates of resources. In this instance, the probability that the QoS may be worsened is referred to as a handoff dropping probability, and it is very important to guarantee the handoff dropping probability in the mobile network.  
      When the static allocation method for reserving the same bandwidth for all adjacent cells by considering the handoff is used so as to provide seamless quality in the case of the subscriber moving, the usage rates of resources are very much lowered when a constant QoS to the connection of the subscriber is provided in the mobile network. In consideration of this, a dropping probability of a specific QoS is assumed, resources for handoff are obtained, and the usage rates of resources are increased, and in this instance, the dropping probability of QoS is referred to as the handoff dropping probability.  
      Usage of the static allocation fails to reflect mobility characteristics which are movements between cells or between regions of the mobile network. Also, when the respective cells reserve additional resources for handoff, the handoff dropping probability is increased when the handoff resources are allocated at less than the generation rates of handoff, and the usage rates of resources are lowered when the allocation of handoff resources is reserved at greater than the generation rates of handoff.  
     DISCLOSURE OF INVENTION  
      Technical Problem  
      It is an advantage of the present invention to guarantee the handoff dropping probability on a call which is currently serviced, and to effectively use network resources.  
      It is another advantage of the present invention to provide a call admission controlling device and method for providing QoS of a portable Internet so that the HPi may provide seamless and excellent QoS.  
      Technical Solution  
      In one aspect of the present invention, in a device for performing data communication with a mobile terminal through a wireless channel, and controlling call admission according to a request of QoS (quality of service) from a terminal provided in a cell which is a communication area, the device being coupled to the cell, a call admission controller for providing QoS in a portable network comprises: a QoS request receiver for receiving a request of QoS requested by the terminal; a mobility characteristic information unit for storing mobility characteristic information on the respective cells; an available bandwidth information unit for storing available bandwidth information on the respective cells; a handoff dropping probability bandwidth calculator for producing a bandwidth for satisfying handoff dropping probabilities required by the respective cells; a calculator, coupled to the mobility characteristic information unit, the available bandwidth information unit, and the handoff dropping probability bandwidth calculator, for generating a default bandwidth for satisfying the QoS required by the terminal so as to determine whether to control call admission, a first bandwidth following the mobility characteristic on the cell in which the terminal is provided, and a second bandwidth for reserving additional resources for the cell; a comparator for comparing the first bandwidth generated by the calculator with the handoff dropping probability bandwidth of the cell, and comparing the second bandwidth with an established bandwidth; and a call admission control signal output unit for determining whether to admit the call following the request of QoS provided from the terminal when the first bandwidth satisfies the handoff dropping probability bandwidth or the second bandwidth is less than or equal to the established bandwidth according to the comparison results. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention:  
       FIG. 1  shows a block diagram of a subsystem for an HPi (high-speed portable Internet) according to a preferred embodiment of the present invention;  
       FIG. 2  shows a configuration block diagram of a PAR according to a preferred embodiment of the present invention;  
       FIG. 3  shows a schematic diagram of mobility characteristics per cell according to a preferred embodiment of the present invention; and  
       FIG. 4  shows a flowchart of a call admission controlling method for providing QoS of the HPi according to a preferred embodiment of the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      In the following detailed description, only the preferred embodiment of the invention has been shown and described, simply by way of illustration of the best mode contemplated by the inventor(s) of carrying out the invention. As will be realized, the invention is capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.  
      In order to provide seamless excellent QoS in the mobile network, when a packet excess router admits a corresponding call at the time of receiving a new QoS, it is determined whether the cells which are currently serviced may receive the seamless QoS when they handoff to other adjacent cells, and the call is admitted according to determination results.  
      To determine the request of admission, each cell periodically measures an average handoff probability and an average stay probability on the serviced calls per service class, and uses the probabilities and the used bandwidth to find overload states of the cells.  
      The present invention periodically measures the handoff dropping probability on the cells, and when a cell is found to have a handoff dropping probability greater than the guaranteed handoff dropping probability, the corresponding cell reserves resources by a specific amount greater than the predicted amount of resources, thereby preventing generation of new calls and increasing success rates of calls that have undergone the handoff. Further, the present invention allows reserving additional resources in proportion to the handoff dropping probability until the handoff dropping probability on the cells may be reduced below the guaranteed handoff dropping probability.  
      Based on the above-described features, a configuration and an operation of a call admission controlling device for providing QoS of the portable Internet according to a preferred embodiment of the present invention will now be described.  
       FIG. 1  shows a block diagram of a subsystem for an HPi (high-speed portable Internet) according to a preferred embodiment of the present invention.  
      Referring to  FIG. 1 , the HPi coupled to a HA (home agent)  130  for IP mobility through the Internet  120  and an AAA (authentication, authorization, and accounting) server  140  for authenticating and billing users comprises a PAR (packet access router)  111  and an AP (access point)  112  in a DS (distributed system)  110  managed by the PAR  111 , and the AP  112  performs data communication with a terminal  113  through a radio channel.  
      The PAR  111  has a hierarchical structure for managing a plurality of APs  112  in a centralized manner, controls wireless resource states of a plurality of cells, and controls call admission for providing seamless QoS.  
       FIG. 2  shows a configuration block diagram of the PAR  111  according to a preferred embodiment of the present invention.  
      Referring to  FIG. 2 , the PAR  111  comprises a QoS request receiver  210 , an available BW (bandwidth) information unit  220 , a handoff dropping probability BW calculator  230 , a mobility characteristic information unit  240 , a calculator  250 , a comparator  260 , and a call admission control signal output unit  270 .  
      The QoS request receiver  210  receives a QoS request from the terminal  113 , and the available BW information unit  220  calculates available BW of the cell to which the corresponding terminal belongs.  
      The handoff dropping probability BW calculator  230  calculates a BW for satisfying the handoff dropping probabilities required by the respective cells, the mobility characteristic information unit  240  stores mobility characteristic information of respective cells coupled to the PAR  111 , and the calculator  250  calculates a BW needed for call admission based on information provided by the available BW information unit  220 , the handoff dropping probability BW calculator  230 , and the mobility characteristic information unit  240 .  
      The comparator  260  compares the BW calculated by the calculator  250  with the established BW. A first comparator  261  of the comparator  260  compares the available BW with a required BW, a second comparator  262  compares the measured handoff dropping probability with the required handoff dropping probability, and a third comparator  263  compares a calculated BW with a compared BW (a summation of available BW of the current cell and the BW used by the same service classes as that required by the terminal.)  
      The call admission control signal output unit  270  outputs admission or rejection on the receipt of the QoS request from the terminal  113  according to comparison results of the comparator  260 .  
      A requested BW calculator  251  of the calculator  250  calculates a BW needed for the QoS request, a mobility characteristic BW calculator  252  calculates BW caused by the mobility characteristic of the cell to which the QoS request is provided, and a compared BW calculator  254  calculates a BW for comparison with a calculated BW calculator  253 . Processes of calculating the respective BW by the calculators 251, 253, and 254 will now be described in detail.  
      Factors for showing the mobility characteristics used for controlling the QoS in the HPi are given as follows.  
       FIG. 3  shows a schematic diagram of mobility characteristics per cell according to a preferred embodiment of the present invention.  
      Referring to  FIG. 3 , the cells  310  to  370  respectively have a probability A for staying in the corresponding cell, a probability B for handing off to an adjacent cell, and a probability C for terminating access in the corresponding cell during a given time T per service class, and the cells respectively have a BW which is currently in use per class.  
      A call admission controlling method for providing the QoS of the HPi according to a preferred embodiment of the present invention will now be described.  
       FIG. 4  shows a flowchart of a call admission controlling method for providing QoS of the HPi according to a preferred embodiment of the present invention.  
      Since the PAR  111  only manages states of the cells in the lower hierarchy, the cell which is provided on the border of the PAR  111  can be provided near the cells in the lower hierarchy of the adjacent PAR. The PAR  111  which has a period of T so as to know status information of the cells in the lower hierarchy of the adjacent PAR, transmits status information including BW usage states of the cells in the lower hierarchy, and call generation rates on the QoS request to the adjacent PAR  111 .  
      When the QoS request receiver  210  of the PAR  111  receives a QoS request from the terminal  113  which is accessed to the adjacent cell in step S 401 , the available BW information unit  220  checks an available BW which is usable in the cell to which the terminal  113  is currently accessed, the requested BW calculator  251  calculates a requested BW for providing a QoS desired by the terminal  113  in the previous step S 401 , and the first comparator  261  compares the available BW with the requested BW to check whether the available BW is greater than or equal to the requested BW in step S 402 .  
      In this instance, when receiving the QoS request from the terminal  113 , the PAR  111  also receives QoS-related factors including a service class on the requested QoS, a maximum BW, an average BW, a minimum BW, and a maximum bucket size, and the minimum BW is used for the requested BW compared in the previous step S 402 , the requested BW being used for call admission control.  
      When the available BW is less than the requested BW according to the comparison result of S 402 , the call admission control signal output unit  270  rejects the QoS request in step S 412  since it is difficult to provide a service which satisfies the requested QoS, and when the available BW is greater than or equal to the requested BW, the calculated BW calculator  253  calculates a BW according to the mobility characteristic of the corresponding cell in step S 403  since it is possible to provide the service.  
      The calculated BW in consideration of the mobility characteristics including handoff of the corresponding cell is found as follows.  
             CalculatedBW   =         BW     i   ,   k       ⨯     PS     i   ,   k         +       ∑     j   =   0     n     ⁢     (       BW     i   ,   j       ⨯     PH     i   ,   jk         )       +       ∑     l   =   0     m     ⁢     (       (       BW     i   ,   l       +       λ     i   ,   l       ⨯   T       )     ⨯     PH     i   ,   lk         )                 MathFigure   ⁢           ⁢   1             
 
      Equation 1 finds a calculated BW when a number of adjacent cells which belong to the k th  cell and the current PAR  111  is n, and a number of PARs  111  which have the k th  cell and the adjacent cells is m in the case that the terminal  113  requests a QoS of service class i.  
      BW i,k  is a summation of total BWs currently in use by the service classes i in the k th  cell, PS i,k  is a probability that the terminal  113  of service classes i in the k th  cell may stay within the given time T, PH i,jk  is a probability that the terminal  113  of service classes i in the j th  cell may move to the k th  cell within the given time T, and PH i,jk  is a handoff probability of from the PAR-L to the PAR to which the k th  cell belongs.  
      When the adjacent cell is not connected to the current PAR  111 , BW i,l  is a bandwidth used by the service class i of the PAR-L in another adjacent PAR which is other than the PAR-L connected to the corresponding cell,  
      λ i,l    
      is an average generation rate at the adjacent PAR  111  of the service class, T is a period for notifying the adjacent PAR of the load status from each PAR  111 , and PH i,lk  is a handoff probability of from the PAR-L to the PAR  111  to which the k th  cell belongs.  
      The second comparator  252  determines whether the measured handoff dropping probability in the cell satisfy the handoff dropping probability required by the current cell in step S 404 , and the calculated BW calculator  253  finds a new calculated BW in step S 405  based on the subsequent equation so as to reserve additional handoff resources when the calculated BW does not satisfy the handoff dropping probability required by the current cell. 
 
NewCalculatedBW=CalculatedBW×(1 +a )   MathFigure 2 
 
      where “a” is a variable of a real number greater than zero and can be established by a user.  
      The third comparator  236  compares the new calculated BW found by Math  FIG. 2  with a summation of the available BWs of the current cell and the BWs in current use by the service classes that correspond to the required service class (referred to as a compared BW hereinafter) in step S 406 .  
      When the new calculated BW is found to be greater than the compared BW, the call admission control signal output unit  270  rejects the corresponding QoS request in step S 312 , and when the new calculated BW is found to be less than the compared BW, the call admission control signal output unit  270  controls the respective units to perform the process of the dotted block  400  of  FIG. 4  to all the adjacent cells.  
      That is, as shown in the block  400 , the calculated BW in consideration of the respective mobility characteristics on the adjacent cells of the QoS requested cell is calculated based on Equation 1 in step S 408 , and it is determined whether the handoff dropping probability required by the corresponding adjacent cell is satisfied by using the calculated BW in step S 409 .  
      When the handoff dropping probability required by the corresponding adjacent cell is not satisfied by the calculated BW of the corresponding adjacent cell, a new calculated BW caused by Equation 2 is calculated in step S 410 , and the new calculated BW is compared with the compared BW of the corresponding adjacent cell.  
      When the new calculated BW is greater than the compared BW in any one of the adjacent cells of the cell which requested the QoS, the QoS request is rejected in step S 412 . In this instance, the process of the block  400  is performed by the PAR  111  shown in  FIG. 2 . However, when the calculated BW or the new calculated BW is less than the compared BW as to all the adjacent cells, the call admission control signal output unit  270  outputs a control signal for accepting the QoS request in step S 413 .  
      A reason for checking all the adjacent cells is to reduce the probability of failed calls handed off and provided in the adjacent cell by receiving a new current QoS.  
      While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.  
      As described, the call admission controlling device and method for providing the QoS in the HPi measures the mobility characteristics including pause probabilities and handoff probabilities of the terminals in each cell at the time of QoS request in the HPi, and controls the call admission by using the measured results, thereby providing more effective resource usage, and guaranteeing the handoff dropping probability when a sudden handoff occurs.  
      Therefore, seamless excellent QoS is provided irrespective of a handoff caused by movement of the terminal.