Abstract:
A soft handover method in a multiple wireless access network environment and a server for the same are provided. The present invention provides a handover method comprising: a first access point registering a user terminal with a registration server; reporting a wireless channel state of the first access point to the registration server; the first access point receiving traffic distributed from the registration server; and determining whether the handover is completed according to the distributed traffic.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2007-0112302, filed on Nov. 5, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a soft handover method in a multiple wireless access network environment and a server for the same, and more particularly, to an Inter-Radio Access Technology handover method in a network environment in which a simultaneous multiple wireless access is possible and a server for the same. 
         [0004]    This work was partly supported by the IT R&amp;D program of MIC/IITA [2006-S-003-02, Research on service platform for the next generation mobile comm.]. 
         [0005]    2. Description of the Related Art 
         [0006]    Various schemes have been studied to minimize delay and packet loss which are generated during a handover procedure in a single wireless access network environment. In a MIPv6 (Mobile IP version 6), which is a typical IP mobility providing protocol, a delay of approximately several seconds is generated upon handover, and therefore, it is difficult to apply the MIPv6 in a real-time application. The handover delay of the protocol is generated in procedures such as movement sensing at an IP level, new address allocations, duplication checks, location registrations, etc. 
         [0007]    In order to overcome such problems of the MIPv6, the working group of the International Engineering Task Force (IETF) Mobile IP Signaling and Handoff Optimization (MIPSHOP) has proposed a Hierarchical Mobile IPv6 (HMIPv6) and a Fast Handover for Mobile IPv6 (FMIPv6). The FMIPv6 uses link information which is triggered in L2 (Layer 2) in order to minimize delay of movement sensing performed by the existing MIPv6. The FMIPv6 is a technology which allows a mobile terminal to sense an L2 handover and to perform part of an L3 handover before the L2 handover is completed through a previous access router and a new access router. Even if the L2 handover is completed already, the FMIPv6 supports a real-time service by allowing the mobile terminal to continuously receive a present progressing service before registering the location of L3 by using a bidirectional tunnel between the previous router and the new router. The HMIPv6 is a protocol which extends Mobile IPv6 and IPv6 Neighbor Discovery Protocol for an in-domain mobility processing. The HMIPv6 improved a location registration speed and reduced signaling overhead between a mobile node, a Home Agent, and a correspondent node by hierarchically controlling the MIPv6 mobility. 
         [0008]    In recent years, new wireless access technologies such as 802.11, 802.16, 802.20 and UMTS (Universal Mobile Telecommunications Systems) have been actively developed. In addition, terminals which have two or more multi-interfaces for supporting various wireless access technologies have appeared. However, the existing-Mobile IPv6 (RFC 3775)-protocol and NEMO Basic Support (RFC 3963) protocol do not support a method capable of simultaneously using the multi-interface. Therefore, MONAMI6 (Mobile Nodes and Multiple Interfaces in IPv6) working group of IETF analyzes and outlines the advantages and problems generated when simultaneously utilizing the multi-interface, and is actively conducting a study in a purpose of establishing Mobile IPv6 and NEMO Basic Support standards which can support the multi-interface. 
         [0009]    In a simultaneous multiple wireless access network environment, various methods for shortening the delay time in a mobility processing and for solving packet loss problem have been studied. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides a soft handover method for minimizing handover seams generated by simultaneously using the multi-interface in a simultaneous multiple wireless access network environment and a server for the same. 
         [0011]    According to an aspect of the present invention, there is provided a handover method comprising: a first access point registering a user terminal with a registration server; reporting a wireless channel state of the first access point to the registration server; the first access point receiving traffic distributed from the registration server; and determining whether the handover is completed according to the distributed traffic. 
         [0012]    According to another aspect of the present invention, there is provided a server, comprising: a control unit, while receiving channel state information from a first access point, for receiving channel state information from a second access point and then receives the channel state information only from the second access point; and a traffic distribution unit which distributes traffic to each channel using the channel state information, and transmits the traffic to the first and second access point before the control unit receives the channel state information only from the second access point. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0014]      FIG. 1  illustrates a configuration of a mobile communication network after the 3 rd -generation network, according to an embodiment of the present invention; 
           [0015]      FIG. 2  illustrates a data flow occurred at handover of a user terminal supporting two multi-interfaces to a new access point, according to an embodiment of the present invention; 
           [0016]      FIG. 3  is a flow chart illustrating a control procedure between network entities upon handover, according to an embodiment of the present invention; 
           [0017]      FIG. 4  illustrates a wireless channel state upon handover, according to an embodiment of the present invention; 
           [0018]      FIG. 5  is an internal block diagram illustrating the user terminal of  FIG. 2 , according to an embodiment of the present invention; and 
           [0019]      FIG. 6  is an internal block diagram illustrating a MAP  33 , according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
         [0021]      FIG. 1  illustrates a configuration of a mobile communication network after the 3 rd  generation network, according to an embodiment of the present invention. In the network shown, an IP backbone network  1  is connected to a satellite network  2 , a 4 th  generation network  3 , a 3 rd  generation network  4 , a 2.5 th  generation network  5 , and a wireless local-area network (WLAN or WPAN)  6  etc. A user terminal  7  has various wireless access interfaces, and more particularly, in a next generation 4G mobile communication network  3 , a new mobile RAT (New Mobile Radio Access Technology) which provides a high-speed mobility coexists with a new Nomadic RAT which provides a high data rate. 
         [0022]      FIG. 2  illustrates a data flow occurred at handover of a user terminal supporting two multi-interfaces to a new access point, according to an embodiment of the present invention 
         [0023]    When the user terminal  7  is handovered from an existing access point (RAT A     —   AP)  31  to a new access point (RAT B     —   AP)  32  while the user terminal  7  communicates with the correspondent node  8 , the user terminal  7  exists in an overlapping domain between the two access points  31  and  32 . 
         [0024]      FIG. 5  is an internal block diagram illustrating the user terminal  7 , according to an embodiment of the present invention. 
         [0025]    As shown in  FIG. 6 , the user terminal  7  comprises a control unit  71 , a RAT A     —   AP interface (IF)  72 , and a RAT B     —   AP interface (IF)  73 . 
         [0026]    The control unit  71  is multi-connected via the RAT A     —   AP interface (IF)  72  and the RAT B     —   AP interface (IF)  73  to the RAT A     —   AP  31  and the RAT B     —   AP  32  respectively so that it can be registered on a mobile anchor point (MAP)  33 . Furthermore, the control unit  71  simultaneously receives traffic transmitted via each of the access points  31  and  32  from the MAP  33 . 
         [0027]    The MAP  33  conceptually serves as a home agent (HA), and handles handover based on the terminal movement between access points within an MAP domain, whereby the movement within the same MAP domain is concealed from a correspondent node  8  or the HA  9 . Herein, the HA  9  has registration information for the mobile terminals  7  and  8 . 
         [0028]      FIG. 6  is an internal block diagram illustrating the MAP  33 , according to an embodiment of the present invention. The MAP  33  comprises a control unit  331  and a traffic distribution unit  332 . 
         [0029]    The control unit  331  registers the user terminal  7  according to registration information which is received from each of the access points  31  and  32 , and outputs channel state information which is received from each of the access points  31  and  32  to the traffic distribution unit  332 . 
         [0030]    The traffic distribution unit  332  dynamically distributes traffic according to the wireless channel state of each of the access points  31  and  32  when simultaneously transmitting the traffic to each of the access points  31  and  32  according to the channel state information. 
         [0031]      FIG. 3  is a flow chart illustrating a control procedure between network entities upon handover, according to an embodiment of the present invention. As illustrated in  FIG. 3 , the user terminal  7  is handovered via the RAT A  AP IF  72  and the RAT B  AP IF  73  from the RAT A     —   AP  31  to the RAT B     —   AP  32 . Before the handover, user data is transmitted from the correspondent node  8  to the HA  9  according to an IP routing mechanism, and the HA  9  tunnels the corresponding data to the MAP  33 . The data received at the MAP  33  is transmitted via the RAT A     —   AP  31  to the user terminal  7  according to an intra-domain mobility management protocol of the corresponding access system (STEP  41 ). 
         [0032]    The user terminal  7  and the RAT A     —   AP  31  determine a time point when the handover should be started and a target access point (Target AP) periodically or through an event-based wireless channel measurement control (STEP  43 ). When the handover start time point is determined, the RAT A     —   AP  31  reports a wireless channel state of RAT A  to the MAP  33  (STEP  44 ). Next, the user terminal  7 , the RAT A     —   AP  31 , and the RAT B     —   AP  32  transfer the context to each other to prepare the handover (STEP  45 ), wherein the context is an information for address or protocol which is possessed by the user terminal  7 , and is usually transferred to a target AP, the RAT B     —   AP  32 , by the RAT A     —AP 31.      
         [0033]    Next, the RAT B  IF  73  of the user terminal  7  is activated and establishes a layer 2 connection (L2 connection) with the RAT B     —   AP  32  (STEP  46 ). When the layer 2 connection is completed, the RAT B     —   AP  32  registers the user terminal  7  with the MAP  33  (STEP  47 ). The wireless channel state of the RAT B  is measured periodically or by an event-based scheme (STEP  48 ) in the RAT B     —   AP  32 , and is periodically reported to the MAP  33  (STEP  49 ). The MAP  33  distributes the traffic to the multiple registered user interfaces  72  and  73  using a Weighted Round-Robin scheduling algorithm based on the reported channel information (STEP  50 ). The user terminal  7 , the RAT A     —   AP  31  or the RAT B     —   AP  32  determines a preferred AP by estimating the channel state using the distributed traffic. In addition, according to each RAT channel state, just when the user terminal  7  is deviating from an overlapping domain or when the corresponding channel state value is higher than a threshold value, the handover completion is determined (STEP  51 ). The RAT A     —   AP  31 , in which the connection with the user terminal is disconnected, transmits a de-registration message to the MAP  33  (STEP  52 ). The MAP  33  which received the de-registration message releases binding to the RAT A  IF  72  (STEP  53 ). The user terminal  7  communicates via the RAT B  IF  73  and RAT B     —   AP  32  to the correspondent node  9  (STEP  54 ). 
         [0034]      FIG. 4  illustrates a wireless channel state upon handover, according to an embodiment of the present invention. 
         [0035]    In  FIG. 4 , x-axis is a time-axis and y-axis indicates the channel quality. Curves CQ_A and CQ_B illustrate the wireless channel quality of each AP, which is measured on the time-basis, when the user terminal  7  is moved from the RAT A     —   AP  31  to the RAT B     —   AP  32 . The handover is performed in an overlapping domain  60 , and data distribution to the multi-interface which is simultaneously accessed according to the quality and the preference of each channel within the overlapping domain is accomplished. 
         [0036]    Assuming that a specific technology preference is W i , the sum W t  of each wireless access technology preference to which the user terminal is accessible is 1. When CQ i  denotes wireless quality of each channel, a CQ i  value is determined by the following formula: 
         [0000]    
       
         
           
             
               
                 
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         [0037]    If D t  is a total sum of the product of each of the quality value of each wireless access channel and the preference to the wireless access channel, a distribution ratio D i  to the wireless access channel is derived by the following formula: 
         [0000]    
       
         
           
             
               
                 
                   
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         [0038]    A WRR scheduler distributes the traffic to each channel using the D i  value. 
         [0039]    According to the present invention, the data distribution is accomplished according to the quality of each channel and the preference to a wireless access technology upon handover in a simultaneous multi-interface network environment, wherein a stable and seamless service is provided with a user. In addition, ping-pong problems resulting from the user&#39;s frequent movement in an overlapping domain between two APs can be solved. 
         [0040]    The present invention has been particularly shown and described with reference to exemplary embodiments thereof. Herein, specific terms are used, but they are used only for the purpose of illustrating the present invention, and is not used to limit their meanings and the scope of the present invention defined the following claims. Therefore, it will be understood by those of ordinary skill in the art that various changes in form and further equivalent embodiments may be made. Accordingly, the true technical scope of the present invention should be defined by the technical spirit of the following claims.