Patent Abstract:
Disclosed are a handoff system and a method among heterogeneous networks. The handoff system among heterogeneous networks has plural access nodes which supports wireless communication with a mobile terminal; and a crossover node which selects resources of an access node to which a handoff is made without repetitive communications between access modes and the mobile terminal in selecting an access node. The handoff system performs a handoff to a network if resources of the network are sufficient for wireless communication.

Full Description:
CROSS-REFERENCE OF RELATED APPLICATIONS 
     This application claims benefit under 35 U.S.C. §119 from Korean Patent Application No. 10-2005-0010636, filed on Feb. 4, 2005, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Apparatuses and methods consistent with the present invention relate to a handoff system and method among heterogeneous networks, and to a mobile terminal and operation method thereof using the same, capable of performing seamless handoffs to the most appropriate network in aspect of resources of data-link layers and network layers. 
     2. Description of the Related Art 
     Recently, with performance improvements of mobile terminals such as handheld computers and Personal Digital Assistants (PDA&#39;s), more users use the wireless internet, and advancements of wireless communication technologies provide the users with various types of network environments. 
       FIG. 1  is a view for showing environments for heterogeneous networks. 
     The wireless Internet users can use various types of network environments. As shown in  FIG. 1 , heterogeneous network environments can include Institute of Electrical and Electronics Engineers (IEEE) 802.11 20, IEEE 802.16 30, Wideband-CDMA (W-CDMA) 40, and so on, and, in such wireless internet environments, a mobile terminal  10  can frequently move around and change its network connection point. 
     In order to enable the mobile terminal  10  to communicate over the wireless Internet, even though the mobile terminal  10  moves to a certain network area beyond its current network area, the mobile terminal  10  in the certain network area should receive the same high quality Internet services as in the current network area. 
     That is, the mobile terminal  10  has to perform seamless communications, so that a handoff concept is applied. The handoff refers to a function of transferring a process for communications from an access node for the current network area to an access node for another network area. 
     Meanwhile, recently, the developments of Internet technologies generalize real-time multi-media services such as Video On Demand (VOD), Audio On Demand (AOD), videophones, video chatting, and the like. Specifically, the mobile terminal  10  can be used to get real-time multi-media services together with advancements of the wireless Internet technologies and improvements of the data processing capacity of the mobile terminal  10 . 
     Together with the advancements of the technologies as above, users can be provided with real-time multi-media services through the mobile terminal  10  while moving. Accordingly, lots of studies are continuing on methods enabling effective handoffs to be performed as users roam around. 
     Heterogeneous networks support different bandwidths one another, but most of the conventional handoff-processing methods for the mobile terminal  10  do not take into consideration the differences among the transmission bandwidths supported by networks to which the mobile terminal  10  is connected before and after the mobile terminal  10  roams around. 
     For example, if the mobile terminal  10  moves from an area of the Wireless Local Area Network (WLAN) to an area of the 3 Generation Partnership Project (3GPP) network, there exists a transmission bandwidth difference among the two networks since the bandwidth of the WLAN is larger than or equal to 384 Kbps and the bandwidth of the 3GPP network is smaller than 384 Kbps. 
     As above, if the bandwidth supported by a network before the movement is larger than the bandwidth supported by a network after the movement, the loss of data packets caused by the bandwidth difference cannot be compensated for. Accordingly, there exists a problem of degrading the qualities of real-time multi-media services. 
     Further, the conventional handoff-processing method for the mobile terminal  10  can be described as below in brief. That is, when the mobile terminal  10  requests a handoff to the access node in a network area to which the mobile terminal  10  moves, the access node allows the handoff if the resources of the network to which the access node belongs are sufficient. 
     Failing to reserve resources in the network to which the mobile terminal  10  is going to move, the mobile terminal  10  requests again the handoff until finding out another network that has sufficient resources. Thus, there exists a problem that it takes time excessively for retries for resources reservations until the mobile terminal  10  finds out a network having sufficient resources as networks are more overlapped in number. 
     SUMMARY OF THE INVENTION 
     Illustrative, non-limiting embodiments of the present invention have been developed in order to solve the above disadvantages and other problems associated with the conventional arrangement. Also, the present invention is not required to overcome the disadvantages described above, and an illustrative, non-limiting embodiment of the present invention may not overcome any of the problems described above. An aspect of the present invention is to provide a handoff system and method among heterogeneous networks, and a mobile terminal using the same and an operating method therefor, capable of seamlessly performing a handoff to the most suitable network in aspect of resources of data-link layers and network layers by detecting all handoff-available heterogeneous networks and performing a handoff to one of the detected networks that has the best wireless communication quality. 
     According to an aspect of the present invention there is provided a handoff system among heterogeneous networks, comprising: plural access nodes which supports wireless communication; and a crossover node which selects an access node for a handoff among the plural access nodes. In selecting the access node, the crossover node may rely on a predetermined condition comprising at least one of wireless communication quality and a network bandwidth which supports the selected access node. 
     Preferably, but not necessarily, the mobile terminal is configured to generate a handoff request signal which initiates selecting of the access node, wherein the handoff request signal comprises at least one of an identification (ID) of the mobile terminal and the predetermined condition. 
     Preferably, but not necessarily, the access node comprises one of an access point and a Base Transceiver System (BTS). 
     Preferably, but not necessarily, the crossover node selects an access node having best wireless communication quality from an access node list created by the mobile terminal. The access node list comprises accessible access nodes which have been searched for by the mobile terminal. 
     Preferably, but not necessarily, the access node notifies the crossover node of a resources reservation failure if a resources reservation request has been received from the crossover node and resources of a network to which the access node belongs are insufficient. In here, upon receiving the resources reservation failure from the access node, the crossover node selects another access node from the plural access nodes and reserves resources at the selected other access node. 
     Another aspect of the present invention is to provide a handoff method among heterogeneous networks comprising plural access nodes which supports wireless communication. The handoff method comprises: selecting an access node for a handoff among the plural access nodes; and selecting another access node for the handoff among the plural access nodes without sending a selection failure notice to the mobile terminal, if the selected access node is determined to be still inappropriate for the handoff. The operation of selecting of the access node may be performed according to a predetermined condition comprising at least one of wireless communication quality and a network bandwidth which supports the selected access node. 
     Preferably, but not necessarily, the handoff method further comprises generating a handoff request signal by which selecting of the access node is initiated. The handoff signal used in the handoff method may comprise at least one of the identification (ID) of the mobile terminal and the predetermined condition. 
     Preferably, but not necessarily, the access node used in the handoff method comprises one of an access point and a Base Transceiver System (BTS). 
     Preferably, but not necessarily, selecting of the access node comprises reserving resources of a network to which the access node belongs after having selected the access node having a best wireless communication quality. Here, the handoff method may further comprise operations of sending a resource reservation request to the access node, and receiving one of a resource reservation success notice if resources of the network are sufficient and a resource reservation failure notice if resources of the network are insufficient. 
     Preferably, but not necessarily, the handoff method may further comprise operations of selecting another access node out of the plural access nodes for resource reservation if the resource reservation failure notice has been received. 
     Still another aspect of the present invention is to provide a mobile terminal applied to a handoff system among heterogeneous networks. The mobile terminal comprises an access node search unit which searches for accessible access nodes among plural access nodes; a list-creating unit which creates a list of the searched-for access nodes; and a network interface unit which sends a handoff request signal comprising at least one of an identification (ID) of the mobile terminal, a predetermined condition used in selecting an access node from the access node list, and a handoff request signal. 
     There is also provided an operation method for a mobile terminal applied to a handoff system among heterogeneous networks, comprising searching plural access nodes for accessible access nodes; creating a list of the searched-for access nodes; and creating a handoff request signal comprising the created access node list; and requesting for a handoff. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above aspects and features of the present invention will be more apparent by describing certain embodiments of the present invention with reference to the accompanying drawings, in which: 
         FIG. 1  is a view for exemplarily showing heterogeneous network environments; 
         FIG. 2  is a view for explaining a handoff system among heterogeneous networks according to an exemplary embodiment of the present invention; 
         FIG. 3  is a block diagram for showing a mobile terminal according to an exemplary embodiment of the present invention; 
         FIG. 4  is a flow chart for explaining a handoff method among heterogeneous networks according to an exemplary embodiment of the present invention; and 
         FIG. 5  is a flow chart for showing signal flows for performing the handoff method among heterogeneous networks as shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereafter, the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 2  is a view for explaining a handoff system among heterogeneous networks according to an exemplary embodiment of the present invention. 
     In  FIG. 2 , a handoff system among heterogeneous networks according to an exemplary embodiment of the present invention has a mobile terminal  300  roaming around heterogeneous networks, that is, roaming from a first network area  100  to a second network area  200 , and a crossover node  600  for connecting the first and second network areas  100  and  200 . Further, the first and second network areas  100  and  200  contain a first access node  400  and a second access node  500 , respectively. 
     The first and second network areas  100  and  200  are heterogeneous networks supporting different bandwidths respectively. For example, the first network area  100  can be a WLAN area supporting a bandwidth higher than 384 Kbps, and the second network area  200  can be a 3GPP area supporting a bandwidth lower than 384 Kbps. 
       FIG. 2  shows two accessible heterogeneous networks, but the present invention is not limited to  FIG. 2 , but can be applied to all wireless networks of various kinds. 
     The mobile terminal (MT)  300  performs wireless communications with the first and second access nodes  400  and  500  in the first and second network areas  100  and  200 , and the mobile terminal can be any of diverse terminals such as a handheld computer, a PDA and a mobile phone which are capable of performing wireless communications. 
     Such a mobile terminal  300  can roam around at any time under wireless Internet environments and change its own network access point. That is, the mobile terminal  300  performs a handoff. To do so, the mobile terminal  300  according to an exemplary embodiment of the present invention searches access nodes, creates an access node list, and sends a handoff request signal. The mobile terminal  300  will be described in detail with reference to  FIG. 3  to be later described. 
     The first access node (AN)  400  provides a wireless communication interface in the first network area  100 , and sends and receives data to and from the crossover node  600 . In here, the first access node  400  can be either an access point (AP) or a Base Transceiver System (BTS). 
     In the present exemplary embodiment, it is shown that a mobile terminal  300  moves from the first network area  100  to the second network area  200 , so the first access node  400  receives a handoff request signal from the mobile terminal  300  and sends the handoff request signal to the crossover node  600 . 
     The second access node  500  provides a wireless communication interface in the second network area  200 , and sends and receives data to and from the crossover node  600 . In here, like the first access node  400 , the second access node  500  can be either an access point (AP) or a Base Transceiver System (BTS). 
     The second access node  500  in the present exemplary embodiment checks whether resources of its network are sufficient, if it receives a resource reservation request from the crossover node  600 . Next, the second access node  500  notifies the crossover node  600  of a resource reservation success, if the resources are sufficient, and notifies the crossover node  600  of a resource reservation failure, if the resources are insufficient. 
     The crossover node  600  sends and receives data to and from the first and second access nodes  400  and  500 . According to the present exemplary embodiment, upon receiving a handoff request signal from the mobile terminal  300 , the crossover node  600  selects, for resource reservation, an access node from the access node list received together with the handoff request signal. 
     Preferably, but not necessarily, the crossover node  600  can select an access node belonging to a network having the best wireless communication quality out of plural access nodes contained in the access node list. In here, there can be a method using the strength of a received signal and a method using an amount of power of a received signal for checking the wireless communication quality of a network. 
     Further, notified of a resource reservation failure by the second access node  500 , the crossover node  600  selects, for resources reservation, different access nodes in order of wireless communication quality from highest to lowest out of plural access nodes contained in the access node list. 
       FIG. 3  is a block diagram for showing a mobile terminal according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 3 , a mobile terminal  300  according to an exemplary embodiment of the present invention has an access node search unit  310 , a list-creating unit  320 , a network interface unit  340 , and a control unit  330 . 
     The access node search unit  310  searches an accessible access node among the plural access nodes. Preferably, but not necessarily, the access node search unit  310  can use the scanning of data-link layer L 2  in order to search for the accessible access nodes. 
     That is, the access node search unit  310  can detect handoff-available networks and catch their L 2  identifiers, such as a Media Access Control (MAC) address and a Cell ID, using the L 2  scanning. 
     The list-creating unit  320  creates an access node list for the accessible access nodes searched by the access node search unit  310 . 
     The control unit  330  creates a handoff request signal containing the access node list created by the list-creating unit  320 , and controls the network interface  340  so as to send the created handoff request signal. 
     In here, the handoff request signal created by-the control unit  330  can further contain the identifier ID of the mobile terminal  300 , that is, its own ID, and a required transmission bandwidth, in addition to the access node list. Preferably, but not necessarily, the access node list can be created in order of wireless communication quality from highest to lowest. 
     The network interface  340 , according to the control of the control unit  330 , sends the handoff request signal to the crossover node  600  through the access node of the network currently occupied, that is, through the first access node  400 . 
       FIG. 4  is a flow chart for explaining a handoff method among heterogeneous networks according to an exemplary embodiment of the present invention. In here, description will be made on a handoff method among heterogeneous networks with reference to  FIGS. 2 to 4  according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 2 , when a mobile terminal  300  moves from the first network area  100  to the second network area  200 , that is, when in need of performing a handoff, the mobile terminal  300  causes the access node search unit  310  to search the plural access nodes for accessible access nodes (S 700 ). 
     When the accessible access nodes are completely searched for, the mobile terminal  300  causes the list-creating unit  320  to create an access node list for the accessible access nodes (S 710 ). In  FIG. 2 , the access node list contains the ID of the second access node  500 . In here, the mobile terminal  300  preferably, but not necessarily, creates the access node list in order of wireless communication quality from highest to lowest. 
     The mobile terminal  300  causes the control unit  330  to create a handoff request signal containing an access node list and causes the network interface unit  340  to send the hand off request signal to the first access node  400 , and the first access node  400  sends the handoff request signal received from the mobile terminal  300  to the crossover node  600  (S 720 ). 
     The crossover node  600  that has received a handoff request signal from the first access node  400  selects, for resources reservation, the second access node  500  which is an access node belonging to a network having the best quality, out of the access node list contained in the received handoff request signal (S 730 ). In here, if the mobile terminal  300  creates the access node list in order of wireless communication quality from highest to lowest, the crossover node  600  reserves resources of an access node first appearing on the access node list. 
     The second access node  500  that has received a resource reservation request from the crossover node  600  checks whether the resources of the network to which it belongs are sufficient (S 740 ). That is, the second access node  500  checks whether to provide the transmission bandwidth needed for the mobile terminal  300 . 
     If the second access node  500  decides in the step S 740  that the resources of the network to which it belongs are sufficient for the mobile terminal  300 , the second access node  500  notifies the crossover node  600  of sufficient resources and performs the handoff (S 750 ). 
     If the second access node  500  decides in the step S 740  that the resources of the network to which it belongs are insufficient for the mobile terminal  300 , the second access node  500  notifies the crossover node  600  of insufficient resources. 
     Next, the crossover node  600  selects another access node out of the access node list, and reserves resources (S 730 ). These steps are repeated until an access node having sufficient resources is found. 
       FIG. 5  is a flow chart for showing signal flows for a method performing a handoff among heterogeneous networks of  FIG. 4 . In here, description will be made on signal flows for a method performing a handoff among heterogeneous networks with reference to  FIGS. 2 to 5 . 
     However, in here, description will be made on a handoff method for a system having the first access node  400  of the first network  100  area in which the mobile terminal  300  is located and the second access node  500  and third access node of the second network area  200  and the third network area to which the mobile terminal  300  moves. 
     The mobile terminal  300  searches an accessible access node (AN) among the plural access nodes (S 800 ). In here, the accessible access nodes are the second and third access nodes. 
     If the accessible access nodes are completely searched for, the mobile terminal  300  creates an access node list (AN_ID List) of the searched accessible access nodes (S 810 ). 
     The mobile terminal  300  sends a handoff request signal to the first access node  400 , and the first access node  400  sends the handoff request signal to the crossover node  600  (S 820 ). In here, the handoff request signal can contain the identifier of the mobile terminal  300  (MT_ID), that is, its own ID, the access node list (AN_ID List), and a required transmission bandwidth (Required B/W). 
     The crossover node  600  that has received the handoff request signal selects out of the AN_ID List an access node to which the handoff is requested (S 830 ). In here, the second access node is assumed to have the best wireless communication quality among the access nodes contained in the AN_ID List. 
     The crossover node  600  sends to the second access node  500  a signal Resource_Reservation_Request for reserving resources (S 840 ). In here, the resource reservation signal can contain the MT_ID and Required B/W. 
     The second access node  500  receives a resource reservation signal from the crossover node  600 , and checks whether the resources of the network to which it belongs are sufficient. In here, it is assumed that the resources of the network to which the second access node belongs are insufficient (S 850 ). 
     The second access node  500  sends a signal Resource_Reservation_Fail notifying the crossover node  600  of resources reservation failure (S 860 ). In here, the resources reservation failure notification signal can contain the MT_ID, Required B/W, and a cause of the resources reservation failure. 
     The crossover node  600  selects out of the AN_ID List the third access node as an access node to perform the handoff, in which the third access node has the wireless communication quality immediately lower in order than the second access node  500  (S 870 ). 
     If one access node is selected, the crossover node  600  sends again a signal Resource_Reservation_Request for reserving resources to the selected access node, that is, the third access node (S 880 ). In here, the resources reservation signal can also contain the MT_ID and Required B/W. 
     The third access node that has received a resources reservation signal from the crossover node  600  checks whether the resources of the network to which it belongs are sufficient. In here, the resources of the network to which the third access node belongs are assumed to be sufficient for the handoff of the mobile terminal  300  (S 890 ). 
     Since the resources of the network to which the third access node belongs are sufficient, the third access node sends a signal Resource_Reservation_Success notifying the crossover node  600  that the resources reservation has been successful (S 892 ). In here, the resources reservation success notification signal can contain the MT_ID, candidate EP, and allocated transmission bandwidth (Allocated B/W). 
     Next, the crossover node  600  sends a signal Handoff_Success notifying the first access node  400  of the successful handoff, and the first access node  400  sends the mobile terminal  300  the handoff success notification signal received from the crossover node  600 . In here, the handoff success notification signal can contain the MT_ID, selected access node ID, that is, the third access node ID, candidate EP, and allocated transmission bandwidth. 
     As described in  FIG. 4 , the handoff system and method among heterogeneous networks according to an exemplary embodiment of the present invention let the crossover node  600  reserve resources of the third access node automatically if failed to reserve resources of the second access node  500 . 
     Accordingly, the exemplary embodiment of the present invention can omit a step of sending the first access node  400  and the mobile terminal  300  a signal notifying of resources reservation failure if the resources reservation of the second access node  50  failed. Further, the exemplary embodiment of the present invention can omit a step for the mobile terminal  300  to send again the crossover node  600  a signal requesting for a handoff. 
     As described above, the handoff system and method among heterogeneous networks and the mobile terminal employing the same and the operation method thereof let a mobile terminal detect all the heterogeneous networks to which a handoff can be performed, and perform the handoff to one of the detected networks which has the best wireless communication quality, bringing out an advantage capable of seamlessly performing a handoff to the most suitable network in aspect of resources of data-link layers and network layers. 
     Further, as above, the exemplary embodiment of the present invention can reduce the number of times of repeated resource reservation signal transmission for searching for an appropriate wireless heterogeneous network, so it has an advantage capable of remarkably reducing resource reservation time which is likely to increase as the number of heterogeneous networks increases. 
     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. Also, the description of exemplary embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.

Technology Classification (CPC): 7