Abstract:
A telecommunication method for a telecommunication network providing discontinuous radio coverage is provided, in which the telecommunication network a plurality of cells, The method includes providing a data stream to a mobile terminal within the coverage of a first one of the plurality of cells, interrupting the data stream when the mobile terminal is moved outside the coverage, determining the location of the mobile terminal outside the radio coverage, predicting a second one of the plurality of cells to be the target cell of the mobile terminal, providing the data stream to a server being assigned to the second one of the plurality of the cells, resuming the data stream to the mobile terminal when the mobile terminal is within the coverage of the second one of the plurality of the cells.

Description:
BACKGROUND OF THE INVENTION  
   The invention is based on a priority application EP03293355.8 which is hereby incorporated by reference. 
   The present invention relates to the field of telecommunications, and more particularly without limitation, to the transmission of a data stream to a mobile terminal. 
   Cellular voice and data networks facilitate ‘anytime, anywhere’ connectivity but they are expensive and offer low bandwidth. Infostation networks have been suggested as a viable alternative to meet the needs of mobile applications (Frenkiel, B. R. Badrinath, J. Borras, and R. Yates. The infostations challenge: Balancing cost and ubiquity in delivering wireless data. IEEE Person. Commun., 7(2):66-71, 2000; Exploiting Data Diversity And Multiuser Diversity In Noncooperative Mobile Infostation Networks (2003) Wing Ho Yuen, Roy D. Yates, Siun-Chuon Mau; Combining Infrastructure and Ad hoc Collaboration for Data Management in Mobile Wireless Networks (2002) Olga Ratsimor, Sethuram Balaji Kodeswaran, Anupam Joshi, Timothy Finin, Yelena Yesha ). 
   An infostation network consists of a set of towers offering short-range high bandwidth radio coverage. They offer high-speed discontinuous coverage, which is inherently low cost. Network access is available to users that are passing in close proximity. In this sense the infostation is similar to a base station coupled with an information server such that the base station provides the network connectivity while the information server handles the data requests. A mobile terminal thus experiences areas of connectivity (when close to an infostation) and areas of disconnection (when there is no infostation nearby). 
   SUMMARY OF THE INVENTION  
   The present invention provides for a telecommunication method and a telecommunication network providing discontinuous radio coverage, such as an infostation network. A data stream is provided to a mobile terminal when it is within the coverage of a cell of the telecommunication network, e.g. in close proximity to an infostation. When the mobile terminal is moved outside the coverage provided by the telecommunication network the data stream is interrupted. 
   While the mobile terminal is outside the coverage of the telecommunication network its location is determined. The corresponding location information is provided to a component of the telecommunication network, e.g. the information server, for prediction of a target cell of the telecommunication network to which the mobile terminal is going to move. The data stream for the mobile terminal is provided to the predicted target cell before the mobile terminal has actually reached the target cell. This way the transmission of the data stream to the mobile terminal can be resumed when the mobile terminal has reached the target cell with minimal latency time. 
   In accordance with a preferred embodiment of the invention the location determination of the mobile terminal is performed by means of a second network, such as a cellular network having global coverage, e.g. GSM, GPRS, UMTS-FDD, or hot sport oriented cellular networks, e.g. WLAN or UMTS-TDD, or a tag based location system. Alternatively a satellite positioning system, such as GPS, or other location determination techniques such as triangulation can be utilised. 
   In accordance with a preferred embodiment of the invention the data stream to the mobile terminal is encrypted, e.g. by means of a licence key. In order to further reduce the latency time for resuming the data stream to the mobile terminal the cryptographic key is transmitted to the target cell prior to arrival of the mobile terminal. This way it is avoided that the target cell requests the cryptographic key when the mobile terminal arrives within the coverage of the target cell and requests resumption of the data stream. 
   In accordance with a further preferred embodiment of the invention a historical movement pattern of the mobile terminal is used as a basis for predicting of the target cell. For example the historical movement pattern comprises a number of typical itineraries of the user. Such typical itineraries can be acquired by tracking movement of the mobile terminal. One of the typical itineraries is identified as the actual itinerary by means of the location information. This way the target cell is identified. 
   In accordance with a further preferred embodiment of the invention the historical movement pattern includes a bifurcation, i.e. two different paths having the same originating cell but alternative target cells. The presence server indicates along which one of the alternative branches the mobile terminal travels which enables the information server to determine the target cell. 
   In accordance with a further preferred embodiment of the invention the information server subscribes to the location information, i.e. the information server continuously receives location information regarding the actual position of the mobile terminal outside the coverage of the telecommunication system. This way the precise trajectory of the mobile terminal&#39;s movement can be determined for making a more precise prediction of the target cell and/or arrival time at the target cell. 
   It is to be noted that the present invention is particularly advantageous as it enables a more precise prediction of a target cell while the mobile terminal is outside the radio coverage in order to prepare resumption of the data streaming. This way latency times for resumption of the data streaming are substantially reduced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
     In the following preferred embodiments of the invention are described in greater detail by way of example only and by making reference to the drawings in which: 
       FIG. 1  is a block diagram of an embodiment of a telecommunication system of the invention, 
       FIG. 2  is a flow chart of a preferred embodiment of a method of the invention, 
       FIG. 3  is illustrative of an application of the present invention. 
   

   DETAILED DESCRIPTION  
     FIG. 1  shows a block diagram of an infostation network that provides discontinuous radio coverage. The infostation network has a number of cells—the so called ‘infostations’— 100 ,  102 , . . . Each one of the cells  100 ,  102 , . . . has an assigned local server. Cell  100  has local server  104  that is coupled to air interface  106  in order to provide radio coverage for cell  100 . Local server  104  has memory  108  for storing a cryptographic key and buffer memory  110 . 
   Likewise cell  102  has an assigned local server  112  that has a similar design as location server  104 . Local server  112  is coupled to air interface  114  and has memory  116  for storage of a cryptographic key and buffer memory  118 . The local servers  104 ,  112 , . . . that are assigned to individual cells  100 ,  102 , . . . are coupled to information server  120  of the infostation network by means of transfer network  122 . 
   Information server  120  is coupled to content server  124  for providing data stream  126  to one of the local servers  104 ,  112 , . . . for transmission to a mobile terminal being within the respective radio coverage. Information server  120  has database  128  for storage of movement patterns on a per user basis. 
   Further information server  120  is coupled to presence server  130  through transport network  132 . Presence server  130  belongs to wireless network  134  that provides continuous coverage and location information regarding the actual location of mobile terminals. For example wireless network  134  is a GSM, GPRS, UMTS-FDD, WLAM, UMTS-TDD or other type of network. 
   The presence server  130  provides the location of an active mobile terminal within the coverage of wireless network  134  on the basis of an appropriate positioning technique, such as by providing a cell ID or tag ID, by triangulation, or other techniques that are used for location based services in such cellular telecommunication networks. Alternatively wireless network  134  is not a telecommunication network but merely serves the purpose of positioning the mobile terminal, as for instance the GPS satellite based positioning system. 
   In operation user  136  having mobile terminal  138  is in position A within the radio coverage of cell  100 . Mobile terminal  138  can be any type of mobile communication device such as a mobile phone, personal digital assistant (PDA), a portable computer having a wireless interface, or a communication device being attached to a vehicle, such as a car. 
   Mobile terminal  138  receives data stream  126  over air interface  106  from local server  104 . Data stream  126  is buffered in buffer memory  110  of local server  104  before transmission to mobile terminal  138 . Data stream  126  is transformed by means of a cryptographic key that is stored in memory  108  before transmission to mobile terminal  138 . 
   Data stream  126  can have any content, such as information, news, audio and/or video data for rendering on mobile terminal  138 . The content is delivered from content server  124  to information server  120  where it is transformed into data stream  126  that is transferred via transport network  122  to local server  104 . 
   Typically the data rate of the data transmission of data stream  126  via air interface  106  to mobile terminal  138  is above the data rate for rendering of data stream  126  on mobile terminal  138 . This enables mobile terminal  138  to fill its buffer with a portion of data stream  126  for rendering while mobile terminal  138  is outside the coverage of one of the cells  100 ,  102 , . . . of the infostation-like network. 
   When user  136  moves mobile terminal  138  outside the radio coverage of cell  100  this is signaled to information server  120  and the transmission of data stream  126  to local server  104  as well as the transmission of the data stream via air interface  106  is interrupted. When user  136  moves from position A to B it is still within the coverage of wireless network  134 . Thus, the location of user  136  at position B is determined by presence server  130  of wireless network  134 . 
   When information server  120  receives signaling information that indicates that mobile terminal  138  has left cell  100  it sends one or more request  140  via transport network  132  to presence server  130  in order to obtain location information  142  regarding the actual location of mobile terminal  138  from presence server  130 . In response to request  140  presence server  130  sends location information  142  back too information server  120  via network  132 . 
   On the basis of location information  142  and user&#39;s  136  movement pattern stored in database  128 , information server  120  predicts target cell  102  to which user  136  is likely to move considering its actual position B and its historical movement pattern stored in database  128 . 
   After cell  102  has been identified as the likely target cell the information server  120  resumes transmission of data stream  126 . As cell  102  has been identified as the likely target cell data stream  126  is transferred to local server  112  over transport network  122  in order to prefetch the data into buffer memory  118 . Further the cryptographic key for transformation of data stream  126  is transferred into memory  116  of local server  112 . Thus, at the time of arrival of user  136  at position C the transmission of data stream  126  to mobile terminal  138  is resumed with minimal delay via air interface  114  as data of data stream  126  is already prefetched in buffer memory  118  and the cryptographic key is already stored in memory  116 . 
     FIG. 2  shows a corresponding flow chart. In step  200  a user with his or her mobile terminal is within the radio coverage of an info-station. Streaming data is transmitted from the info-station to the mobile terminal. 
   In step  202  the user has moved outside the radio coverage of the info-station. This means that the streaming of the data is interrupted. However, the user is still within the coverage of a wireless network that features location determination. The location of the user is determined and entered into the information server of the info-station network in step  202 . 
   On this basis the information server of the info-station network performs a prediction of the consecutive info-station to which the user is likely to move. This can be done by extrapolating the users trajectory on the basis of continuous location information received from the wireless network. Continuous location information also enables to precisely predict the user&#39;s time of arrival in the consecutive info-station radio coverage. Alternatively, or in addition, an historical movement pattern of the user is taken into consideration. This enables to limit the amount of location information that is required by the information server in order to perform the prediction of the consecutive info-station on the users itinerary. 
   For example, the movement pattern consists of a number of alternative paths along which the user usually travels. The location information received from the wireless network enables information server of the infostation network to determine which one of the user&#39;s usual paths is the actual one. The determination of the path implies prediction of the consecutive info-station target cell. 
   Once the prediction of the consecutive target cell has been made, content data and/or the cryptographic key is prefetched into the local server of the predicted consecutive info-station (step  206 ). This way streaming of the data is immediately resumed in step  208  when the user moves within the radio coverage of the predicted info-station. When the user moves on its path outside the radio coverage the same procedure is carried out with respect to the next target cell on the user&#39;s path. In other words the control goes back from step  208  to step  202 . 
     FIG. 3  illustrates an implementation example of a telecommunication network of the invention. Info-stations  2 ,  3 ,  4  and  5  are positioned along roads in an urban area. This urban area is also covered by a cellular telecommunication network having a number of cells  142  that provide continuous coverage. 
   In a fist step a movement pattern of a user is observed. Typically the user moves from info-station  2  to info-station  3  and then onwards to info-station  5  or alternatively to info-station  4 . Hence in the example considered here, the user&#39;s typical movement pattern has a bifurcation and is thus ambiguous. 
   In the preferred embodiment considered here the information server of the info-station network subscribes to location information from the present server of the wireless cellular telecommunication network. The location information is received in terms of cell IDs of cells of the cellular wireless telecommunication network. Hence, when the user moves from info-station  3  to info-station  4  the information server receives the following sequence of cell-IDs: A, B, C, D, E, F, and G. When the user moves on the alternative path from info-station  3  to info-station  5  the information server receives the following sequence of cell IDs: A, B, C, D, H, I, J, K. From this information the information server infers that
         (i) There is a bifurcation at cell D and   (ii) Cells E and H are consecutive to the bifurcation.       

   In the following the information server only requests location information from the presence server of the cellular wireless telecommunication network when the user has moved past info-station  3  on his or hers usual itinerary. The request for location information of information server to the present server is specific to cells H and E. In other words, the information server only requires location information from the presence server when the user has moved to cell E or H, as this is the only information the information server requires in order to determine whether the user moves into to the direction of info-station  5  or alternatively into the direction towards info-station  4 . 
   Hence, the information server requests location information from the presence server indicating the two cell IDs that follow a bifurcation in the users movement pattern in order to receive a notification from the presence server that indicates to which one of the alternative cells that follow the bifurcation the user has actually moved. On this basis the information server removes the ambiguity regarding the user&#39;s itinerary and determines the consecutive target info-station, i.e. info-station  4  in case cell E is indicated by the presence server or info-station  5  in case cell H is indicated by the presence server. This way the data volume of location information that is transmitted from the presence server to the information server is drastically reduced. 
   LIST OF REFERENCE NUMERALS 
   
       
         2  Info-Station 
         3  Info-Station 
         4  Info-Station 
         5  Info-Station 
         100  Cell 
         102  Cell 
         104  Local Server 
         106  Air Interface 
         108  Memory 
         110  Buffer Memory 
         112  Local Server 
         114  Air Interface 
         116  Memory 
         118  Buffer Memory 
         120  Information Server 
         122  Transport Network  124   
         124  Content Server 
         126  Data Stream 
         128  Data Box 
         130  Presence Server 
         132  Transport Network 
         134  Wireless Network 
         136  User 
         138  Mobile Terminal 
         140  Report 
         142  Cell