Abstract:
The present invention relates to receivers such as multi-carrier and cellular receivers.  
     Cellular receivers, in the form of portable radiotelephones are commonplace, and their design and operation is well understood. Such portable radiotelephones can be used for making and receiving telephone calls, sending and receiving messages, and even browsing world-wide computer network such as the Internet. Many standards exist for portable radiotelephones, including global system for mobile communications (GSM), general radio packet service (GPRS)  
     Receivers capable of receiving digital television signals, such as signals according to the terrestrial digital video broadcasting (DVB-T) standard are also commonplace.  
     The present invention provides a method and apparatus for receiving and transmitting signals via multiple communication channels.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to receivers such as multi-carrier and cellular receivers.  
           [0002]    Cellular receivers, in the form of portable radiotelephones are commonplace, and their design and operation is well understood. Such portable radiotelephones can be used for making and receiving telephone calls, sending and receiving messages, and even browsing world-wide computer network such as the Internet. Many standards exist for portable radiotelephones, including global system for mobile communications (GSM), general radio packet service (GPRS)  
           [0003]    Receivers capable of receiving digital television signals, such as signals according to the terrestrial digital video broadcasting (DVB-T) standard are also commonplace.  
           [0004]    The use and operation of consumer set-top-boxes (STB) for receiving digital video broadcasting (DVB-T) transmissions are well known. Such STBs are capable of receiving a large number of digital television channels, data and other interactive services.  
         SUMMARY OF THE INVENTION  
         [0005]    According to a first aspect of the present invention, there is provided a terminal having a first receiver for receiving an encrypted first signal from a first communications network comprising: a second receiver for receiving from a second communications network a second signal conveying information enabling said encrypted signal to be decrypted.  
           [0006]    Advantageously, the present invention provides a receiver having a first and a second receiver for receiving signals from two different communications networks. In a first embodiment of the present invention this results in increased power efficiency, since one of the receivers can be effectively switched off whilst not required. Schedule or configuration data can, however, still be received on the other receiver. The received schedule or configuration data can be used to switch on the other receiver at an appropriate time. This configuration allows the receiver to receive non-scheduled data, such as news flashes, results from sporting events, share prices etc.  
           [0007]    In a second embodiment of the present invention, a receiver is able to receive a broadcast signal via a broadcast network, and to receive additional and complementary information thereto via a second telecommunications network. This is particularly advantageous in security applications, where security keys and other private or sensitive data may be sent via a more private telecommunications network. For example, if a pay-per-view film is being broadcast in encrypted form, the security keys needed to decrypt the film may be sent via the second telecommunications network. This prevents the security keys from unauthorised access of the broadcast network.  
           [0008]    According to a second aspect of the present invention, there is provided apparatus for transmitting an encrypted signal on a first communications network, comprising: a transmitter for transmitting on a second communications network information enabling said encrypted signal to be decrypted.  
           [0009]    According to a third aspect of the present invention, there is provided a method of receiving an encrypted first signal from a first communications network comprising: receiving from a second communications network a second signal conveying information enabling said encrypted signal to be decrypted; and decrypting said encrypted first signal using said received information.  
           [0010]    According to a fourth aspect of the present invention, there is provided a method of transmitting an encrypted signal on a first communications network, comprising: transmitting on a second communications network information enabling said encrypted signal to be decrypted.  
           [0011]    According to a fifth aspect of the present invention, there is provided a terminal having a first receiver for receiving a first signal from a first communications network comprising: a second receiver for receiving a second signal conveying complementary information relating to said first signal from a second communications network.  
           [0012]    According to a sixth aspect of the present invention, there is provided Apparatus for transmitting a signal to a receiver via a first communications network comprising: a transmitter for transmitting complementary information relating to said signal via a second communication network.  
           [0013]    According to a seventh aspect of the present invention, there is provided a method of receiving a first signal from a first communications network comprising: receiving a second signal conveying complementary information relating to said first signal from a second communications network.  
           [0014]    According to a eighth aspect of the present invention, there is provided A method of transmitting a signal to a receiver via a first communications network comprising: transmitting complementary information relating to said signal via a second communication network. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The invention will now be described, by way of example only, with reference to the accompanying diagrams, in which:  
         [0016]    [0016]FIG. 1 is a block diagram of a typical consumer receiver/transmitter arrangement;  
         [0017]    [0017]FIG. 2 is a block diagram of a first embodiment according to the present invention; and  
         [0018]    [0018]FIG. 3 is a block diagram of yet a further embodiment according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    [0019]FIG. 1 is a block diagram of a typical consumer receiver/transmitter arrangement in which a terrestrial digital video broadcasting (DVB-T) transmitter  150  transmits a DVB-T signal to a DVB-T set-top-box receiver  106 .  
         [0020]    In the transmitter  150 , a number of television channels  154  and  156  are multiplexed together with a number of data channels  158  and  160  by a multiplexer  152 . In addition to this, service information (SI)  162 , which contains details of each of the other multiplexed channels, is also input to the multiplexer  152 , provided by a SI generator  164 . The multiplexer creates a single, multiplexed, signal  166  which contains all of the separate channels  154 ,  156 ,  158  and  160 , along with the SI  162 . Further details of the multiplexing and SI may be found in the DVB-T specification (EN  300   468 ) which is incorporated herein by reference. The multiplexed signal  166  is transmitted via an antenna  164 , across a transmission channel, to an antenna  102  of a set-top-box receiver  106 . In the case of DVB-T, the transmission channel is a terrestrial transmission channel. However, the transmission channel could, alternatively, be a satellite, microwave, cable or optical channel.  
         [0021]    The signals received by the antenna  102  are input to a DVB-T receiver  100  which enables the user to select a desired channel. Received data may also be stored in a memory  104 .  
         [0022]    Whilst the set-top-box  106  is switched on, the DVB-T receiver  100  is also powered up and receiving DVB-T signals. The DVB-T receiver is constantly decoding SI information which provides details of the content and location of each of the channels within the received multiplexed signal. The SI information also contain schedule details for each of the multiplexed channels. The schedule details allow a user to watch or record a specific programme of interest. For example, if the set-top-box  106  is connected to a personal computer (not shown), it is possible to receive data transmitted over the DVB-T network for use with the personal computer. In this way, the transmission of large data files can be broadcast, to a large audience, using the high data rates provided by DVB-T transmission. If a data file is due to be transmitted at a certain time on a certain channel, the SI information will contain this information which can be used by the personal computer to ensure that receiver receives the required data.  
         [0023]    SI information may change frequently, to reflect not only changes in program scheduling, but also to reflect re-allocation of frequencies and channels etc by the broadcaster. For example, it is possible for a channel to broadcast on a different frequency to originally scheduled. Since the SI contains details of the frequencies (or changes to the frequencies), a receiver should always be able to receive the desired channel and/or program. Some set-top-boxes store SI information in a memory, thereby allowing users to browse a schedule or program guide. However, due to the nature of SI information, the SI information is updated frequently to ensure that no discrepancies exist between the SI stored by the set-top-box and the SI being transmitted by the broadcaster.  
         [0024]    [0024]FIG. 2 shows a block diagram of a first embodiment according to the present invention. A mobile terminal  200  receives DVB-T transmissions from a DVB-T transmitter  272 . The transmitted DVB-T signal is a multiplexed signal produced by a multiplexer  250 . The multiplexer  250  accepts as inputs a number of channels  252 ,  254 ,  256  and  258  to produce the multiplexed signal. The channels may be television, audio or data channels. Service information (SI) data, which contains details of the multiplexed channels, is also input to the multiplexer  250 . The SI data is generated by a SI generator  260 , which may be a database containing schedule and location details of each of the channels.  
         [0025]    The DVB-T signals are received by an antenna  210  of the mobile terminal  200  and are received and decoded by a DVB-T receiver  202 .  
         [0026]    In addition, and advantageously, the mobile terminal also receives an interactive channel from a cellular or other transmission network  274  at a cellular transceiver  206 . The cellular transceiver  206  allows both the reception and transmission of signals between the mobile terminal  200  and the cellular network  274 . The cellular network may be a GSM network, a general packet radio service (GPRS), third generation (3G) or other suitable network.  
         [0027]    SI data generated by the SI generator  260  is also supplied to a profiler  262  of the cellular network  274 . The profiler contains a database of information about each of the subscribers to the cellular network  274 . The profiler may contain information such as, demographic data, income level, sports leisure interests, etc.  
         [0028]    The operation of a first embodiment of the present invention will now be described by way of example.  
         [0029]    According to the prior art, if a user wishes to receive a video clip each time his favourite football team scores during a football match, it is necessary that the DVB-T receiver  100  in the DVB-T set-top-box  106  is constantly powered up and is constantly receiving SI data. This is since the exact timing of when a goal will be scored is not known in advance. Accordingly, no schedule will exist in the SI data for this event. A DVB-T receiver must therefore wait for the SI data to indicate when the video clip will be broadcast. If the user is only interested in receiving video clips of the football match, this is particularly inefficient in terms of power consumption, especially for mobile terminals, since the DVB-T receiver just waiting, consuming power, for a specific video clip to be broadcast.  
         [0030]    According to a first embodiment of the present invention, as exemplified in FIG. 2, the subscriber registers his interest in receiving video clips with the profiler  262  of the cellular network  274 . The DVB-T receiver  202  of the mobile terminal  200  may then be powered down. When a goal is scored, and a video clip is available for broadcast, the broadcaster must schedule the video clip to be included in the existing DVB-T multiplex signal. This may involve rescheduling existing programs, and updating the SI data accordingly. Once a scheduled time has been established for the broadcast of the video clip, a service announcement is sent by the cellular network  274  to the cellular transceiver  206 . The service announcement is received by the cellular transceiver  206  and is processed by the controller  204 . The controller informs the DVB-T receiver  202  of when the video clip will be broadcast and other relevant associated data, such as channel location, encryption parameters etc. The DVB-T receiver can be powered up and configured in time to receive and decode the video clip. The video clip may also be stored in a memory  208 . Once the desired video clip, or other data, has been received, the DVB-T receiver  202  can be once again powered down.  
         [0031]    The service announcement may be in the form of SI data, or may alternatively be in the form of a special short message service (SMS) message containing the necessary timing and location information required by the DVB-T receiver. Alternative forms of service announcement may be used, both in terms of the data required to be sent and the protocol which is used for sending it.  
         [0032]    In this way, the DVB-T receiver  202  can be powered down when not required for actual reception of data. This can produce large savings in power consumption, compared to the system of the prior art.  
         [0033]    The profiler  262  also controls whether requested information is transmitted to a user via the DVB-T or cellular network. For example, if one million people have requested to see a video clip of goals from a particular football match, it is better to transmit the video clip via the DVB-T network. For such a large number of users, the DVB-T network provides a cost effective delivery means. The alternative would be to individually send the video clip via the cellular network which, with so many users, could impact severely on the operation of the cellular network.  
         [0034]    If the number of users requesting to see a particular video clip is much smaller, it may be more economical to send it individually via the cellular network. The exact threshold levels will vary according to the pricing structure of the DVB-T and cellular networks, as well as the number of users requesting a particular item, and the volume of data required to be sent.  
         [0035]    The cellular transceiver  206  may also be used to send an acknowledgement back to the cellular network  274 , indicating whether the video clip was correctly received. This may be used for billing purposes, or also to request a re-sending of the video clip if it not received due to poor signal strength etc. Re-sending of the video clip may again take place either via the DBV-T or cellular network depending on demand and cost effectiveness.  
         [0036]    A further advantage of the present invention is that, if schedule announcements are sent over the cellular network, it is possible to remove some or all of the SI data from DVB-T network. Since the SI data typically occupies up to 3 Mbits- 1  this redundant bandwidth could be used for providing additional data or video channels.  
         [0037]    In a further embodiment of the present invention, a profiler may be included in the mobile terminal  200 . This may be instead of, or in addition to, the profiler  262  of the cellular network  274 . A profiler on the mobile terminal may be used if the communications network used for the interactive channel supports broadcasting of data, such as via a GPRS network or other packet type network. The profiler can be configured according to user preferences, and will only accept service announcements which comply with the user preferences.  
         [0038]    [0038]FIG. 3 shows yet a further embodiment of the present invention, which makes use of the additional interactive channel to provide increased security.  
         [0039]    A mobile terminal  300 , receives DVB-T signals via an antenna  310  at a DVB-T receiver  302 . The DVB-T signals are provided and transmitted by a DVB-T network  320 , via an antenna  330 . The mobile terminal  300  also comprises a cellular transceiver  306  which can send and receive calls via a cellular network  326 . The mobile terminal  300  also comprises a controller  304  which can either send or receive control information from the cellular transceiver  306 , the DVB-T receiver  300  or a memory  308 . A controller  324  is also provided to provide communication and control between the DVB-T network  320  and the cellular network  326 .  
         [0040]    This embodiment enables DVB-T data to be broadcast from the DVB-T network  320  to the mobile terminal  300 . In addition, data related to the broadcast DVB-T signal may also be transmitted to the mobile terminal  300  via the cellular network  326 .  
         [0041]    For example, at present, when encrypted video or television channels are broadcast to a terminal, security keys are also broadcast over the broadcast channel to enable subscribers to decrypt the encoded data. Although the security keys are hidden in the broadcast signal, it is possible for unauthorised users to gain access to these keys by monitoring the broadcast signals. Using the present invention, the security keys or security data can be sent over the interactive channel, directly to each individual receiver. This makes it increasingly difficult for unauthorised users to obtain access to the security keys, since they are sent via a different path to the encrypted video signals. The security keys may be sent for either currently broadcast signals, or for broadcast signals which have yet to be broadcast. In a still further embodiment, the terminal  300  comprises a subscriber information module (SIM) (not shown) which may contain authorisation or additional security data for use with either the cellular or DVB networks. The authorisation or additional security data contained by the SIM may be used in conjunction with the security data to enable authorisation or decryption of the signals received via the broadcast network.  
         [0042]    In a still further embodiment of the present invention, on-line banking and other customer orientated services can use the present invention to improve the transmission of data, including Internet pages, to subscribers. For example, an on-line bank could broadcast using the DVB-T network pages of information containing high quality graphics, standard texts etc. Each page could then be personalised using personal data transmitted over the interactive channel. For example, a generic ‘balance’ sheet could be broadcast to all users containing the bank logo, background images etc. Personal balance data transmitted over the interactive channel could then be combined with the broadcast ‘balance’ sheet, to present to the user their own personal balance sheet.  
         [0043]    The present invention therefore provides benefits not only in increase power efficiency of such systems, but also provides added security and benefits of being able to broadcast information to multiple users, and to send subscriber specific information related to that broadcast information using a separate, personal, communications link. In yet a further embodiment of the present invention, the interactive channel can used for both transmitting service announcements as well as security or private data.  
         [0044]    Those skilled in the art will appreciate that although the present invention is described above with reference to DVB-T transmissions, the invention is not limited thereto. The same techniques could be applied to DVB (satellite) reception and transmission or any other similar or equivalent standards.  
         [0045]    Equally, references to cellular networks and cellular transmission techniques could be replaced by fixed line, public switched telephone networks, or any other type of suitable communications network.