Abstract:
The present invention refers to a method for managing within a global heterogeneous network the transition of a terminal ( 1 ) connected to a first wireless communication network ( 3 ) having a first coverage zone towards a second wireless communication network ( 5 ) having a second coverage zone overlapping at least partially said first coverage zone wherein said method comprises the following steps: determining the terminal ( 1 ) location; determining the networks topology of the surroundings of said terminal ( 1 ); if the terminal ( 1 ) is in a predetermined area corresponding to the coverage border of said first wireless communication network ( 3 ), determining available candidate networks ( 5 ) of the surroundings of said terminal ( 1 ) and, selecting, among said available candidate networks and based on at least one predetermined criterion, said second wireless communication network ( 5 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to the field of wireless communication networks and more specifically to the handover process in heterogeneous networks. 
         [0002]    Heterogeneous network refers to the possibility for a terminal to be connected to different types of networks using different radio frequency bands. Depending on its location and the available networks, a terminal will be connected to one network or another. When a user is moving with its terminal, the terminal is going through different coverage zones corresponding to different types of networks. Thus, at the boundary of such zone, the terminal has to achieve a handover to switch from one network to the other in order to keep or restore its connection. 
         [0003]    Such handover process may require a non-negligible time in order to achieve the different steps of the handover process which may induce, especially in the case of single radio terminal, delays for real-time services. 
         [0004]    One way to detect network boundaries is to scan the surroundings in order to detect new networks signalling but such a permanent scanning is very power consuming and reduces the autonomy of the terminal. 
       SUMMARY OF THE INVENTION 
       [0005]    It is therefore an object of the present invention to overcome the above cited drawbacks of the state of the art and provide a method allowing to reduce handover delays and requiring a limited power consumption. 
         [0006]    Thus, the present invention refers to a method for managing within a global heterogeneous network the transition of a terminal connected to a first wireless communication network having a first coverage zone towards a second wireless communication network having a second coverage zone overlapping at least partially said first coverage zone wherein said method comprises the following steps:
       determining the terminal location;   determining the networks topology of the surroundings of said terminal; if the terminal is in a predetermined area corresponding to the coverage border of said first wireless communication network,   determining available candidate networks of the surroundings of said terminal and,   selecting, among said available candidate networks and based on at least one predetermined criterion, said second wireless communication network.       
 
         [0011]    In another embodiment, said the step of determining available candidate networks comprises a scanning of the surroundings in order to detect said available candidate networks. 
         [0012]    In an additional embodiment, said at least one predetermined criterion is the radio power level. 
         [0013]    In a further embodiment, the terminal is a single radio terminal and wherein it comprises an additional step of pre-attachment to the second wireless communication network. 
         [0014]    In an additional embodiment, the networks topology of the surroundings of the terminal is downloaded from a network repository on the terminal. 
         [0015]    In a supplementary embodiment, a new download is achieved when the terminal is getting close to or out of the border of the networks topology area covered by the previous download. 
         [0016]    In another embodiment, the steps of determining the terminal location and determining the networks topology of the surroundings of the terminal are achieved at the network level by a network process centralized server. 
         [0017]    In an additional embodiment, the step of determination of the terminal location is achieved thanks to the access points (AP) and base stations (BS) crossed by the terminal. 
         [0018]    In a supplementary embodiment, the step of determination of the terminal location is achieved by a global positioning system (GPS). 
         [0019]    The present invention also refers to a single radio terminal comprising:
       a cache memory for saving networks topology data and;   means for:
           determining its location;   downloading networks topology of the surroundings;   determining the available candidate networks;   selecting, among said available candidate networks and based on at least one predetermined criterion, one of said available candidate networks;   determining the optimal instant for triggering a pre-attachment;   requesting to its serving network a pre-attachment to a candidate network;   
               
 
         [0028]    According to another embodiment, said single radio terminal comprises means for:
       determining the optimal instant for launching a scan of the surroundings;   scanning the surroundings in order to determine candidate networks features;       
 
         [0031]    Moreover, the present invention refers to a multiple radio terminal comprising:
       a cache memory for saving networks topology data and;   means for:
           determining its location;   downloading networks topology of the surroundings;   determining the available candidate networks;   
               
 
         [0037]    According to a further embodiment, said multiple radio terminal comprises means for:
       determining the optimal time for launching a scan of the surroundings;   scanning the surroundings in order to determine candidate networks features;       
 
         [0040]    In addition, the present invention refers to a network process server comprising means for:
       receiving a request of pre-attachment triggering service from a single radio terminal;   receiving a request of scanning triggering service from a multiple radio terminal;   checking the connection authorization of the terminal requesting a service;   determining the location of a terminal;   determining networks topology in the surroundings of a terminal;   sending a scanning triggering notification to a terminal;   sending a pre-attachment triggering notification to a single radio terminal.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0048]      FIG. 1  is a diagram of the organization of a terminal oriented embodiment of the present invention in the case of a single radio terminal; 
           [0049]      FIG. 2  is a diagram of an example of heterogeneous network comprising two different network structures; 
           [0050]      FIG. 3  is a diagram of the organization of a network oriented embodiment of the present invention in the case of a single radio terminal; 
           [0051]      FIG. 4  is a possible network architecture of a network oriented solution according to the present invention in the case of a single radio terminal; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0052]    As used herein, the term “single radio terminal” refers to a terminal being able to be connected to only one radio frequency band at a time; 
         [0053]    As used herein, the term “multiple radio terminal” refers to a terminal being able to be connected to several radio frequency bands at a time; 
         [0054]    As used herein, the term “heterogeneous network” refers to a network comprising different types of structure in order to provide radio connection, for example WIMAX and LTE structures; 
         [0055]    As used herein, the term “MIIS” refers to the acronym Media Independent Information Service; 
         [0056]    As used herein, the term “GPS” refers to the acronym Global Positioning System; 
         [0057]    As used herein, the term “LTE” refers to the acronym Long Term Evolution; 
         [0058]    As used herein, the term “WIMAX” refers to the acronym Worldwide Interoperability for Microwave Access; 
         [0059]    As used herein, the term “HSS” refers to the acronym Home Subscriber Server; 
         [0060]    As used herein, the term “AAA” refers to the acronym Authentication, Authorization and Accounting; 
         [0061]    As used herein, the term “scanning of the surroundings” refers to a network level scanning which is used to determine the bandwidth frequency of a possible candidate network. 
         [0062]    The idea of the present invention is to determine, based on the terminal location and the networks topology, the right instant for launching the procedures preceding and leading to a handover such as a available candidate networks determination or candidate network pre-attachment. 
         [0063]    According to the invention, two different approaches are described herein, one is terminal oriented and the other is network oriented. Moreover, two different embodiments are described with respect to two types of terminals, a single radio type and a multiple radio type. 
         [0064]    Therefore, the following description will be divided into two parts, a first part related to the single radio type solution and a second part related to the multiple radio type solution. 
       Single Radio Type Terminal 
       [0065]    The present invention requires the determination of two parameters:
       the location of the terminal and,   the topology of the networks in the surroundings of the terminal location.       
 
         [0068]    Said terminal location can be determined, for example, thanks to the access points and base stations to which the terminal is connected to while moving within a network coverage zone or thanks to a global positioning system (GPS). Nevertheless, any other adapted method can be performed for said location determination. 
         [0069]    Concerning the topology of the surroundings of the terminal, such topology can be downloaded from a network data repository and saved in a dedicated cache memory of the terminal. Such network data repository can be a Media independent Information Service (MIIS) which provides networks cells positioning. Moreover, the size of the area covered by the downloaded topology data file will depend on the terminal cache memory capacity. Thus, when the terminal gets close to the border of the area covered by the network topology file located in the terminal memory, a new downloading of the network topology corresponding to the new terminal location is requested from the MIIS. 
         [0070]    Knowing its location and the topology of the networks in its surroundings, the terminal can therefore determine the optimal instant for launching a scan of the surroundings and a pre-attachment to a candidate network. Such instant corresponds to the instant when the terminal gets close to the border of the area or zone covered by the network to which the terminal is connected. In the case of a single radio terminal, a pre-attachment is required before achieving the handover from one network type to the other. 
         [0071]      FIG. 1  represents the mechanisms previously described between the different entities of the networks: a terminal or mobile node  1 , a serving network  3 , a candidate network  5  and a MIIS  7 . The terminal  1  requests networks topology information to the MIIS  7  and downloads the corresponding file in its cache memory  2  (arrow  11 ). 
         [0072]    Then, the terminal  1  is able to determine the networks possibilities in its surroundings. Thus, when the terminal is getting close to a network coverage border, a pre-attachment process  13  is triggered in order to determine the features of the available candidate networks and to select one in order to achieve said pre-attachment. 
         [0073]      FIG. 2  represents an example of network topology comprising two different networks N 1  and N 2 . N 1  being a WIMAX network whereas N 2  is a LTE network. The terminal is initially positioned at location L 1 . Then, the user is moving towards N 2  according to the trajectory represented by the dotted line. When said user arrives at location L 2 , its terminal has determined that the coverage border of N 1  is approaching and therefore launches a pre-attachment process  13 . During said process  13 , the terminal  1  looks at its cache memory  2  in order to determine the candidate network  5 . If the information concerning the bandwidth frequency of the candidate network  5  is not available in the cache memory  2 , a scanning of the surroundings is achieved in order to determine said bandwidth frequency. Then, the terminal, after having optionally checked that the level of emission power provided by the candidate network  5  matches the expected connection quality, sends a pre-attachment request to the serving network  3  (arrow  15 ) that, in turn, forwards the request to the candidate network  5  (arrow  17 ). 
         [0074]    In the example of  FIG. 2 , the serving network is N 1  and the candidate network is N 2 . Thus, when the user arrives at location L 3  which is the border of the coverage zone of network N 1 , the pre-attachment to network N 2  has already been achieved and the handover processing time required to switch from one network to the other is reduced which decreases the risk of delay in real-time service applications. 
         [0075]    In a second embodiment, corresponding to a network oriented solution, the terminal location monitoring and the networks topology analysis are achieved at the network level instead of being achieved by the terminal. Such process is represented in  FIG. 3  and can be divided into three phases. The first phase P 1  corresponds to a service request phase. The terminal  1  sends a request  20  to a network process unit  9 , said request comprising, for example, the subscriber identity and the involved networks, that is to say, the networks to which the terminal user has subscribed to (possible candidate networks). 
         [0076]    Said network process unit  9  corresponds to the additional equipment required for the present embodiment with respect to classical networks. 
         [0077]    At reception of the request  20 , the network process unit  9  asks the HSS/AAA server  10  the authorization status for the terminal  1  with respect to the candidate networks  5 . 
         [0078]    The network process unit  9  sends back a service acceptance/refusal notification  22  to the terminal  1 . Said notification comprising the accepted networks. 
         [0079]    The second phase P 2  corresponds to the network processing. 
         [0080]    The network process unit  9  receives information about the terminal  1  location (arrow  24 ). Having terminal  1  location details, the network process unit communicates with the MIIS server  7  (arrow  26 ) in order to get the network topology in the surroundings of the terminal. 
         [0081]    Then, data processing to determine a need for scanning and/or pre-attachment is achieved in the network process unit  9 . 
         [0082]    This phase P 2  is achieved periodically which allows the network process unit  9  to track the terminal  1  position and the candidate networks in order to trigger pre-attachment or handover at the convenient time on behalf of the terminal  1 . 
         [0083]    The third phase P 3  refers to the pre-attachment triggering. 
         [0084]    When the network process unit  9  determines that the terminal is in an area close to the border of the serving network coverage zone, a triggering notification comprising the authorized candidate network(s) is sent to the terminal (arrow  28 ). 
         [0085]    Then, as in the terminal oriented embodiment, the terminal  1 , after having optionally checked that the level of emission power provided by the candidate network  5  matches the expected connection quality, sends a pre-attachment request  30  to the serving network  3 , said request being forwarded to the candidate network (arrow  32 ). 
         [0086]      FIG. 4  represents a possible architecture of the network according to this second embodiment wherein the dotted lines represent the additional equipments and connections necessary for the present invention. 
         [0087]    The terminal  1  is connected to the serving network  3  through a base station  31  and an Access Service Network GateWay (ASN-GW)  33  which is itself connected to a Packet Data Network GateWay/Home Agent (PDN GW/HA)  40 . 
         [0088]    For requesting pre-attachment, the terminal  1  sends a request to the centralized network process unit  9 . Said network process unit  9  is connected to the MIIS  7  and the HSS/AAA server  10 . Thus, the network process unit  9  can achieve the pre-attachment determination. Moreover, said network process unit  9  is connected to the ASN-GW  33  of the serving network  3  and to the Mobility Management Entity (MME)  51  of the candidate network  5 . Said MME  51  managing the eNode Bs  53  and the serving gateway  55 . Thus the network process unit  9  may also achieved the handover from the serving network  3  to the candidate network  5 . 
       Multiple Radio Type Terminal 
       [0089]    In the case of multiple radio type terminal, no pre-attachment is necessary, nevertheless the terminal needs to detect the available networks in its surroundings in order to achieve the connection to these available networks. 
         [0090]    In the same way as for the single radio configuration, the terminal location and the topology of the networks in the surroundings are determined either at the terminal level or at the network level. The difference is that no pre-attachment process are triggered but only a scanning of the surroundings in order to detect the available candidate networks and/or to achieve the radio power level assessment of said network candidates. Thus, the scanning of the surroundings is achieved only when the terminal gets close to the border of the coverage zone of the serving network or when the terminal enters the coverage zone of a new candidate network. 
         [0091]    Thus, the present invention allows to reduce the pre-attachment delays in the case of single radio terminals and to reduce the power consumption in any cases by reducing the scanning time. Moreover, the present invention can work without impacting the functioning of present access networks.