Abstract:
The present invention relates to a method for providing services from a content server to a terminal belonging to a discontinuous coverage network, said terminal moving from a first radio coverage zone to a second radio coverage zone over a zone of non radio coverage, said discontinuous coverage network architecture comprising access controllers and radio access points each pair of access controller and radio access point defining a radio coverage zone. According to the present invention, the method comprises the step of: Sending in advance from a first access controller data in a cache memory of at least one radio access point of said second radio coverage zone, when said terminal is outside the coverage of said second radio coverage zone.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention is based on a priority application EP 04291979.5 which is hereby incorporated by reference.  
         [0002]     The present invention relates to a method for improving mobility and service delivery in discontinuous coverage networks.  
         [0003]     Discontinuous coverage networks are radio access networks which do not provide a continuous radio coverage contrary to conventional second or third generation radio access networks as GSM or UMTS. Such discontinuous coverage networks are constituted by islands of coverage supporting very high bit rates and low power cells. Such networks are commonly referred as fourth generation access networks. They provide video/audio streaming services and fast download or upload of large data volumes.  
         [0004]     The islands are nevertheless separated by zones of non-radio coverage so that usual hand over between cells is not to be realized by common techniques.  
         [0005]     In such networks, mobile terminals have a reduced mobility. They cannot leave the radio coverage area without loosing the connection.  
         [0006]     A fast mobile IP solution is currently investigated at the IETF for solving this problem. Mobile IP solutions consists in introducing a home agent between the content server and the access controller. The IP address of the moving terminal is modified during terminal mobility. The current IP address of the moving terminal is stored at the home agent together with a permanent IP address. The mobility is totally transparent for the content server which sends the content to the permanent IP address. The translation is performed at the home agent which in turn identifies the access controller under the coverage of which the moving terminal is currently located. This solution enables it to support mobility in IP networks. Nevertheless, even if the speed of the process is accelerated, such a solution do not provide an efficient answer to the need for providing very high rate streaming services to a moving terminal leaving temporarily the zone of radio coverage.  
         [0007]     A particular object of the present invention is to provide a method for enabling a continuous streaming service provision in the context of discontinuous coverage networks.  
         [0008]     Another object of the invention is to provide an entity of the radio access network supporting the method.  
       SUMMARY OF THE INVENTION  
       [0009]     Introduce the fact that the cache is also needed in the terminal. These objects, and others that appear below, are achieved by a method for providing service to a terminal belonging to discontinuous coverage networks according to claim  1 , an access controller according to independent claim, and a multicast element according to independent claim.  
         [0010]     According to the present invention, the method consists in filling in, in advance, the cache memory of the access controller and/or of the radio access point likely to be visited by the moving terminal in the next future. This method necessitates to anticipate the possible destination of the mobile terminal so that the content necessary for uninterrupted streaming service, or another example non real time service is e.g. file transfer, is available in the appropriate island of radio coverage as soon as the moving terminal enters this island of coverage.  
         [0011]     The method according to the present invention presents the advantage to provide a seamless micro mobility as well as a seamless macro mobility to mobile terminals belonging to discontinuous coverage networks.  
         [0012]     The method according to the present invention further presents the advantage to support continuous streaming services or an other non real time service is e.g. file transfer.  
         [0013]     Further advantageous features of the invention are defined in the dependent claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Other characteristics and advantages of the invention will appear on reading the following description of a preferred embodiment given by way of non-limiting illustrations, and from the accompanying drawings, in which:  
         [0015]      FIG. 1  shows an implementation of the present invention in the context of a discontinuous coverage radio access network supporting micro mobility;  
         [0016]      FIG. 2  shows an implementation of the present invention in the context of a mobile IP based discontinuous coverage radio access network supporting macro mobility;  
         [0017]      FIG. 3  shows an implementation of the present invention in the context of a 4G dedicated discontinuous coverage radio access network supporting macro mobility. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]      FIG. 1  shows an implementation of the present invention in the context of a discontinuous coverage radio access network supporting micro mobility.  FIG. 1  illustrates an example of network architecture for such fourth generation radio access networks where the present invention may be implemented. The radio access network comprises content servers  11 , access controllers  14 , radio access points  161 ,  162  and terminals  17 . Content server  11  and access controller  14  are connected to an IP network  13 , access controller  14  and radio access points  161 ,  162  are connected to a transmission network  15 . Terminals  17  are accessible from radio access points  161 ,  162  through an air interface.  
         [0019]     Each pair (access controller, radio access point) ( 14 ,  161 ), ( 14 ,  162 ) defines a zone of radio coverage. In the example described below the radio coverage is discontinuous so that there remain areas of non radio coverage between two areas of radio coverage ( 14 ,  161 ), ( 14 ,  162 ). It will be understood by the person skilled in the art that the present invention may also apply to mixed continuous and discontinuous networks.  
         [0020]      FIG. 1A  represents the case where terminal  17  is under radio coverage area ( 14 ,  161 ). The terminal inclused a cache memory.  FIG. 1B  represents the case where terminal  17  is not under any radio coverage area.  FIG. 1C  represent the case where terminal  17  is entering coverage area ( 14 ,  162 ). This case illustrates the microdiversity case (i.e. two consecutive coverage areas visited by terminal  17  are serviced by the same access controller  14 ).  
         [0021]     According to the present invention, access controller  14  determines a set of radio access points terminal  17  is likely to enter when moving further. Access controller then duplicate the data received form content server  11  and sends them data to all radio access points  161 ,  162  belonging to the set of radio access points. As a consequence the data are immediately available if terminal  17  enters in the near future one of this radio access points.  
         [0022]     In  FIG. 1A , terminal  17  is under the radio coverage of radio access point  161 , access controller  14  sends the same data to both radio access points  161  and  162 . The data sent to radio access point  161  are used immediately as terminal  17  is under the coverage of this radio access point while the data sent to radio access point  162  are sent in advance in the eventuality that terminal  17  enters the coverage of this radio access point in the near future.  
         [0023]     In  FIG. 1B  where terminal  17  is not under any radio coverage, access controller  14  continues to send the same data to both radio access point  161  and  162 . The data are sent in advance in the eventuality that terminal  17  enters the coverage of one of these radio access points in the near future. The data are not used immediately and stored in a cache memory.  
         [0024]     In  FIG. 1C , terminal  17  is under the radio coverage of radio access point  162 , access controller  14  sends the same data to both radio access point  161  and  162 . The data sent to radio access point  162  are used immediately as terminal  17  is under the coverage of this radio access point while the data sent to radio access point  161  are sent in advance in the eventuality that terminal  17  enters the coverage of this radio access point in the near future.  
         [0025]     The data sent in advance and not immediately used have to be stored in an appropriate cache memory which should be large enough to ensure that the whole data received during the period where terminal  17  is not under any coverage are available in the cache memory. The cache memory should be dimensioned using for example parameter as the average data throughput on the link between access controller  14  and radio access points  161 ,  162  or the average duration of the non coverage period for terminal  17 .  
         [0026]     The present inventions enables it to quickly re-load terminal  17  with the necessary data when terminal  17  enters a new area of coverage after having spent some time in non coverage area. This quick reloading is possible since the needed data are already present in the cache memory of radio access points  161 ,  162 . It will be clear for those skilled in the art that an appropriate cache memory management should be performed, taking especially into account the location of terminal  17 . A cache memory is also present in the terminal.  
         [0027]      FIG. 2  shows an implementation of the present invention in the context of a mobile IP based discontinuous coverage radio access network supporting macro mobility.  FIG. 2  illustrates an example of network configuration for such fourth generation radio access networks where the present invention may be implemented. The radio access network comprises content servers  11 , access controllers  141 ,  142  radio access points  161 ,  162 ,  163 ,  164 . Content server  11  and access controllers  141 ,  142  are connected to an IP network  13  which supports the mobile IP functionality thanks to Home Agent (HA)  12  and thanks to Foreign Agents (FA) each associated to one access controller. The HA is associated to the service provided by content server  11  and provides for a unique IP address for the terminal seen from content server  11 . The FA are adapted to take in charge the mobility of the terminal by sending updated information to a table located in HA which registers under the control of which access controller  141 ,  142 , terminal  17  is currently located. Consequently, a translation between the unique IP address used by content server  11  and the local IP address can take place and the data destined to terminal  17  are routed to the appropriate access controller  141 ,  142 .  
         [0028]     Access controllers  141 ,  142  and radio access points  161 , . . . ,  164  are connected to a transmission network  15 . Terminals  17  accessible from radio access points  161 , . . . ,  164  through an air interface.  
         [0029]     Each pair access controller, radio access point ( 141 ,  161 ), ( 141 ,  162 ), ( 142 ,  163 ), ( 142 ,  164 ) defines a zone of radio coverage. In the example described below the radio coverage is discontinuous so that there remain areas of non radio coverage between two areas of radio coverage. It will be understood by the person skilled in the art that the present invention may also apply to mixed continuous and discontinuous networks.  
         [0030]      FIG. 2A  represents the case where the terminal  17  is under the radio coverage of the coverage area ( 141 ,  162 ).  FIG. 2B  represents the case where the terminal  17  has moved to a new coverage area ( 142 ,  163 ). This case illustrates the macrodiversity case (i.e. the consecutive coverage areas visited by terminal  17  are serviced by different access controller  141 ,  142 ).  
         [0031]     According to the present invention, the serving access controller  141  determines a set of access controllers terminal  17  is likely to be controlled by when moving further.  
         [0032]     The serving access controller  141  duplicates the data and send them in advance to all access controllers  142  belonging to the set of access controller. Access controller  142  then forward the data to radio access points  163  in order for the data to be immediately available if terminal  17  enters in the near future one of this radio access point.  
         [0033]     In  FIG. 2A  terminal  17  is under the radio coverage of the pair (access controller  141 , radio access point  162 ), access controller  141  sends the same data to both radio access point  161  and  162  (microdiversitiy). Further access controller  141  sends the some data to access controller  142  (macrodiversity) which in turn forwards these data to radio access point  163 . The data sent to radio access point  163  are sent in advance in the eventuality that terminal  17  enters the coverage of this radio access point in the near future.  
         [0034]     The Home Agent is responsible for detecting the change of the serving access controller and to trigger the modification of the send in advance mechanism.  
         [0035]     In  FIG. 2B , the Home Agent has detected that the serving access controller has been modified from  141  to  142  because terminal  17  has moved to the radio coverage of radio access point  163  controlled by access controller  142 . Access controller  142  is informed that it should control the “send in advance” mechanism. Consequently it determines the set of access controller  141  to which it should send duplicated data in advance.  
         [0036]     The data sent in advance and not used immediately have to be stored in an appropriate cache memory at the access controller  141 ,  142  which should be large enough to ensure that the whole data received during the period where terminal  17  is not under any coverage are available in the memory. The cache memory should be dimensioned using for example as parameter an average data throughput on the link between access controller  141 ,  142  and radio access points  161 ,  162  as well as an average duration of the non coverage period for terminal  17 .  
         [0037]     In a preferred embodiment of the present invention, the network topology is stored in a decentralized way in the radio access network so that each access controller has the knowledge of its associated radio access points and the location of the radio access points. Consequently, it can determine the neighbor radio access points to which the data have to be sent in advance (micro diversity). In the case of macro diversity the access controllers should know the identity of its neighbor access controller so as to know to which access controllers it has to send the duplicated data.  
         [0038]     In another embodiment a centralized topology of the network is possible.  
         [0039]      FIG. 3  shows an implementation of the present invention in the context of a 4G dedicated discontinuous coverage radio access network supporting macro mobility.  FIG. 3  represents the some radio access network architecture as  FIG. 2 . The difference is that this embodiment does not rely on the mobile IP functionality but on a 4G dedicated solution comprising a multicast element  12  instead of Home Agent and Foreign Agents entities. The “send in advance” functionality is controlled by multicast element  12  which determines to which access controllers  141 ,  142  it has to send the duplicated data coming from content server  11 .  
         [0040]     This embodiment presents the advantage that the multicast element is a central element in the radio access network which controls the macrodiversity. The access controllers  141 ,  142  may consequently have a reduced complexity. The microdiversity remains nevertheless under the control of access controller  141 ,  142  as in the mobile IP embodiment described in connection with  FIG. 2 .  
         [0041]     Mobile localization information comes from the radio access points. To increase performances, two zones are defined in a cell: 
        a zone where data transfer is possible     a larger zone where presence may be detected        
 
         [0044]     This information is given to higher levels devices (centralized or decentralized architecture) where sending in advance must be done.