MXPA99008553A - Broadcast receiving system comprising a computer and a decoder - Google Patents

Abstract

A combined computer and decoder system for receiving broadcast digital data transmissions, characterised in that the decoder (2020) comprises a routing means (2032), broadcast digital data received at the decoder (2020) and destined for the computer (2027) being identified and routed to applications within the computer by said routing means. The computer (2027) may further include control means (2038) for controlling the configuration of the decoder, such as the selected channel frequency of the decoder.

Description

SYSTEM TO RECEIVE A TRANSMISSION THAT COMPRISES A COMPUTER AND A DECODER The present invention relates to a combined computer and decoder system for receiving digital broadcast transmissions. The invention extends in the same way to each of the elements of a computer and a decoder that are adapted for use in this system. The transmission of digital data broadcasting is well known in the field of pay TV systems, where demodulated audiovisual information is sent, usually by means of a satellite or satellite / cable link, to a number of subscribers, each subscriber having one decoder or receiver / decoder that can demodulate the program that was transmitted for a subsequent view. The terrestrial digital transmission systems are also known. More recently, it has been proposed to use this digital transmission technology for the distribution of other types of digital data and information. The broadcast transmission has a number of advantages compared to other telecommunication networks, such as the telephone network, notably in relation to increased bandwidth, transmission reliability, and so on. For this reason, a number of systems that use a cable or satellite link to enable access to the Internet, for example, have been suggested. Currently, the provision of these services is at a very early stage and often the conventional hardware and software systems that have been proposed in this regard, are poorly adapted for the applications in question. In the case of the receiver / decoder of the digital television, for example, the system is usually routed by means of a television style remote controller device. While a remote controller of this type is usually sufficient for television applications (changing channels, selecting guides or program menus), more sophisticated applications such as an internet viewer will usually require a keyboard for simplicity of operation. Similarly, depending on the application in question, the available memory of the decoder might be inadequate for effective operation. For these reasons, a PC / decoder configuration can be contemplated in combination. however, although the theoretical advantages of this combination can be foreseen, the practical details of the implementation of this system can give rise to a number of other problems, in particular with regard to the communication of information between the two, how the decoder to manipulate different types of data, how the decoder changes between different modes of operation (for example, TV / internet modes, etc.). It is an object of the present invention to provide a decoder / computer combination that can be performed in a practical manner, which enables the digital data to be downloaded from the decoder to the computer, while avoiding any potential operational problems arising from the interaction between the decoder and the computer. the elements of the system. In accordance with the present invention, there is provided a combined computer and decoder system for receiving digital broadcast data transmissions, characterized in that the decoder comprises routing means, digital broadcast data that is received in the decoder and intended for the computer that is being identified and routed to the applications within the computer through the routing means. The presence of the routing means within the decoder enables the decoder to simplify and effectively identify the messages that are intended for the applications within the decoder and allows the decoder to reject, for example, the messages having another destination. In a computer / decoder configuration, most of the data that is received through the decoder during operation in this mode will be routed to the computer for further processing. However, in certain cases, the data can be routed to the applications within the decoder itself. For example, the decoder may include an application for monitoring the transmission. In one embodiment, the application can monitor the continuity of the messages that were transmitted, for example, by verifying the arrival of each message in a numbered sequence of messages. In this case, the data representing the message number is passed to the surveillance application. Alternatively, certain standard test messages may be passed to a batch within the decoder memory to allow the decoder to evaluate the quality of the transmission channel based on the composition of the received message. The decoder can also use the broadcast data that was received, based on the applications to modify the routing table, as will be described later. In a particularly preferred embodiment, the decoder further includes an application within the decoder that is adapted to configure the operating parameters of the decoder, including, inter alia, the routing means. You can load this configuration application and its parameters inside the decoder or modify it through the instructions that are received from the computer. Alternatively, or in addition, the configuration application can be stored together with the data representing the parameters of the initial configuration, in the decoder memory during the manufacture of the decoder, to allow self-configuration of the decoder when energized the decoder. Conveniently, the configuration application can be additionally loaded into the decoder or modified by the instructions received in the broadcast data of the transmission. This execution enables the decoder to be reprogrammed remotely, by means of the instructions contained in the data flow of the broadcast. In practice, the routing means can be adapted to identify and route messages in accordance with the characteristics of the data of the message received. In one embodiment, the broadcast data that was received in the MPEG format is routed through the decoder via the routing table, in accordance with the value of the packet ID header. Digital broadcast data that is routed to the computer can simply understand the data to be processed by applications that were previously installed on the computer, for example, applications stored on a diskette and loaded into the computer. However, in one embodiment, the broadcast data may also comprise the applications themselves, which are adapted to be routed to the computer for execution within the computer. In this way, remote downloading of applications can be performed within the computer from a remote server. In the case where the data that was transmitted is not confidential and / or is provided by a free service provider (as may be the case for certain internet applications), free data can be transmitted over the air. However, in the case where the transmitted data that is sent to the computer is proprietary or valuable in any other way, the means to restrict access are desirable.

Preferably, the decoder further includes decryption means for decoding the digital data broadcast in a demodulated form for subsequent routing in deciphered form to the computer. In one embodiment, the demodulated data is transmitted together with a control word to demodulate the data, the word itself being keyed by the call key utilization and transmitted in the encoding form. The decoder has an equivalent of the use key to decipher the control word and un-demodulates the data. These and other known security measures of decoding the television data in the present system can conveniently be used to restrict access to data intended for applications within the computer. In the above embodiments, the operation of the routing means has been discussed mainly in relation to the data that was received via the broadcast transmission link intended for the computer or the decoder. However, as will be appreciated, the routing means may also operate to route the digital data that is received from other sources, such as the applications within the decoder and / or within the computer and the data that was received by any means. of the input ports of the decoder, such as a serial / parallel link, and so on. In the case where the computer / decoder combination is to be used in an interactive application, such as an internet application, the computer can be linked to a modem so that messages can be sent from the computer to a server in the broadcast center or elsewhere to request, for example, the transmission of a defined or similar home page. However, this could increase the cost of the system to the user. Preferably, the decoder further comprises a modem, the routing means being adapted to route the selected messages that were received from an application within the computer to the modem. In practice, almost all the receivers / decoders that are proposed for the digital TV market have a modem link and the cost of the modem is absorbed in the cost of the decoder itself. As mentioned in the preamble of this application, communication problems and conflicting commands may arise with a combination of decoder and computer. In a particularly preferred embodiment of the invention, it is provided that the operation of the decoder is controlled, at least in part, by the control signals that are sent from the control means within the computer. By means of transferring the control of the decoder to the computer, the operation of the system can be handled more easily. For example, in one embodiment, the computer controls the tuner operation within the decoder, to select the channel frequency for reception of the digital data to be downloaded to the computer. Because this information can be known for the application within the computer, but not for the decoder, the automatic selection of the frequency of the channel by the application considerably simplifies the establishment of the system for an operator. Potential conflicts between instructions that are sent to the decoder by other means, such as the remote controller of the decoder, and instructions originating from the computer through this transfer of control can also be avoided. For example, the computer can be adapted to send a control signal to the decoder to make the decoder non-responsive to the selected commands that were received from other selected decoder inputs, such as a channel change command from the remote controller of the decoder. In some embodiments, the decoder can still be enabled to receive the commands from other input sources, for example the commands that are received in the broadcast data stream. As will be understood, the establishment of the computer / decoder of the present invention can be used in a number of commercial applications, ranging from wholesale market-type internet display applications, to more specialized applications that are proposed for corporate organizations, where the broadcast link is used to send property data. An example that is contemplated is for the transmission of financial information, notably the information of the stock price, from a central financial center to a number of remote terminals. In this application, the client benefits from the increased capacity of the channel, in comparison with standard telecom networks together with the secure protection of sensitive data by means of a coded transmission (where provided). In this mode, the decoder - will serve exclusively as a channel for information intended for the computer and will not handle the transmissions of the television. In contrast, where the decoder is to be used in the context of a wholesale market product, it is obviously advantageous that the decoder can also be used in its normal configuration, i.e. receiving and processing digital television signals. In this case, the system additionally comprises a visual display of the television, the decoder being adapted to process the transmitted audiovisual transmission data that was subsequently sent to the visual display of the television. The present invention extends further to a computer and decoder for use in a system as described above. Although the application refers to "receivers / decoders" and "decoders", it will be understood that the present invention applies in the same way to the modalities that have a receiver integrated with the decoder as a decoder unit that works in combination with a receiver separated in a physical way. This decoder may be of a class that is used in any digital satellite, terrestrial, cable, etc. transmission system and may include other capabilities of the multi-media type. An embodiment of the present invention will now be described, by way of example only, in which: Figure 1 shows the general architecture of a digital transmission system, as it is known in the field of digital television; Figure 2 shows a general view of the elements of a receiver / decoder; Figure 3 shows the hardware architecture of a combined receiver / decoder and computer system, in accordance with this embodiment of the invention; Figure 4 shows the software architecture of the system of Figure 3. Figure 1 shows an overview of a system 1000 for transmission and reception of the digital television that can be adapted to the present invention. This includes a mostly conventional digital transmission and reception system 2000, which uses the well-known MPEG-2 compression system to transmit compressed digital signals. In more detail, the 2002 MPEG-2 compressor in a broadcast center receives a digital signal stream, for example, a stream of video signals. The compressor 2002 is connected to a 2004 multiplexer and demodulator via a 2006 link.

The multiplexer 2004 receives a plurality of additional input signals, assembles one or more transport streams and transmits compressed digital signals to a transmitter 2008 of the broadcast center via link 2010, which can of course take a wide variety of forms, including telecom links. The transmitter 2008 transmits electromagnetic signals via the 2012 uplink to a 2014 satellite transmitter-receiver, where they are processed electrically and transmitted via a downlink 216 to the land receiver 2018, conventionally in the form of a dish own or rented by the end user. The signals received by the receiver 2018 are transmitted to a receiver / decoder 2020 integrated itself or rented by the end user and connected to the television 2022 of the end user. The receiver / decoder 2020 decodes the MPEG-2 signal compressed into a television signal for the television set 2022. Although the present application refers to "receiver / decoder", it will be understood that the present invention applies equally to the modes having a receiver integrated with the decoder as a decoder unit operating in combination with a physically separate receiver.

A conditional access system 3000 is connected to the multiplexer 2004 and the receiver / decoder 2020, and is located partially in the center of the broadcast and partially in the decoder. This allows the end user to access digital transmissions from one or more transmission providers. A smart card can be inserted that can decrypt the messages that are related to commercial offers (that is, in, or several television programs or data services sold by the transmission provider), within the receiver / decoder 2020. The transmission of demodulated data is well known in the field of pay TV systems. Typically, the demodulated data is transmitted together with a control word by means of demodulating the data, the control word itself being coded by the so-called harness key and transmitted in the encoding form. Then, the demodulated data and the coded control word in the decoder 2020 having access to an equivalent of the usage key stored in a smart card that was inserted in the decoder are received to decipher the coded control word and demodulate afterwards. of the same the data that was transmitted. A paid subscriber will receive, in an ECM (Message of Control of Accreditation) monthly transmission, the key of use necessary to decipher the codified control word, in order to allow the view of the transmission. An interactive system 4000, which also connects to the multiplexer 2004 and the receiver / decoder 2020, and which is located again partially in the transmission and partially in the decoder, allows the end user to interact with different applications by means of a channel 4002 modulated return-demodulated. The above type of system is more generally known in the context of the transmission of digital audiovisual data that is associated with a broadcast digital television transmission. However, as will be described later in more detail, the system will be used to transmit the data that is ultimately intended to be used in a computer linked to the decoder in question. This data can be transmitted in place of, or as well as the data of the digital television, depending on, for example, if the system is proposed for a consumer or professional market. In the case where TV signals are not to be distributed, the 2002 MPEG compressor that was used to process the digital video stream can be omitted. You can pre-format the information that - passed the server 4000 for multiplexing through the multiplexer 2004 in the MPEG format through the server or is transformed by a dedicated server (not shown) for subsequent transmission. Referring to Figure 2, now the elements of a receiver / decoder 2020 or the upper case for use in a digital transmission system will be described, and adapted for use in the present invention. As will be understood, the elements of this decoder are mostly conventional and their implementation will be within the capabilities of one skilled in the art. As shown, the decoder 2020 is equipped with different interfaces to receive and transmit data, in particular an MPEG tuner and demultiplexer 2040 for receiving broadcast MPEG transmissions, a serial interface 2041, a parallel 2042 interface, and a 2028 modem for sending and receive data through a telephone network. In this embodiment, the decoder also includes first and second smart card readers 2030 and 2031, the first reader 2030 for accepting a smart subscription card containing the decryption keys associated with the system and the second reader 2031 for accepting bank cards. and others. The decoder also includes a receiver 2043 for receiving infrared control signals from a combined handset remote controller 2044 and a Peritel output for sending audio-visual signals to a television 2022 connected to the decoder (if present). The central control unit 2045 handles the processing of the digital signals that were received by means of the interfaces and the generation of the digital output signals. The software architecture of the control unit within the decoder may correspond to that which is used in a known decoder and will not be described here in detail. It can be based, for example, on a virtual machine that interacts by means of an interface layer with an operation system - of a lower level that is implemented in the hardware components of the decoder. In terms of hardware architecture, the decoder will be equipped with a processor, memory elements such as ROM, RAM, FLASH, etc., as in known decoders. The applications that are processed by the control unit 2045 can be resident applications stored in the ROM or FLASH _ of the decoder or application transmission and downloaded via the MPEG interface 2 of the decoder. Applications may include program guide applications, games, interactive services, television sales applications, as well as startup application to allow the decoder to be operational immediately after startup and the applications to configure the decoder. The applications are stored in memory locations in the decoder and are represented as resource files comprising description files of graphic objects, variable block files, instruction sequence files, application files, data files, and so on. In a conventional manner, the applications that are downloaded to the decoder by means of the transmission link are divided into modules, each module corresponding to one or more MPEG tables. It can be divided - each MPEG table into a number of sections. For the transfer of data by means of serial and parallel ports, the modules are also divided into tables and sections, the size of the section depending on the channel that was used. In the case of broadcast transmission, the modules are transported in the form of data packets within the respective types of the data stream, for example, the video data stream, the audio data stream, a current of text data. In accordance with the MPEG standards, each packet is preceded by a 13-bit packet identifier (PID), a PID for each packet that is transported in the MPEG stream. A program map table (PMT) contains a list of the different streams and defines the content of each stream in accordance with the respective PID. A PID can alert the device to the presence of applications in the data stream, the PID being identified through the PMT table. Referring now to Figure 3, the hardware architecture of the decoder / computer combination according to the present invention will now be described. The decoder 2020 includes an input connection from the receiver 2018 and is also connected by means of the connectors 2026, 2027 in series and / or parallel to a computer 2027 in the form of a PC. In alternative modes, the 2027 computer can be defined by any number of different computer devices (Unix workstation, etc.) that can receive the data and run the applications that were installed. Associated with the decoder, there is an integrated 2028 modem device. Although this has been represented in this figure as being a different article, the modem 2028 will normally be integrated into the body of the decoder. The PC computer 2027 may also include a link to a 2029 modem, which is usually provided separately from the computer. As will be discussed, in certain embodiments the modem 2029 may be rendered superfluous by the modem 2028 of the decoder. As described above, the decoder includes smart card reader slots 2030, 2031 for accepting credit or subscription cards associated with the decoder. The data transmission that is sent within the system can be keyed or demodulated, the subscription card associated with the decoder that has the key or keys that are needed to decipher the transmissions. Referring now to Figure 4, the architecture of the system logic will now be described. As will be understood, the internal functional elements of the decoder and the PC are implemented in practice by means of the programmed software modules that are executed by the microprocessor devices, in relation to the data stored in the RAM memory means, EEPROM, FLASH, etc. inside the devices. Alternatively, some functions can be implemented through dedicated hardware ASICs, for example. The digital transmission data they provide - the server 4000 and which the receiver 2018 captures, pass to a routing table application 2032 within the decoder 2020. An access control application 2033 acts to decrypt the demodulated MPEG data, to recover the un-demodulated message packets. These message packets are routed through the routing table either to the applications 2034 within the decoder or to the applications within the PC computer 2027 via a selected parallel or serial channel 2025, 2026. Certain messages can also be sent to a decoder configuration application 2035 which controls, inter alia, the configuration of the routing table, as will be described in more detail below. The selection and subsequent routing of messages can be made on the basis of the PID or the Package ID of the MPEG message packet, or on any other header or indicator section associated with the message packet that was received. The data intended for the computer 2027 is sent via a 2025, 2026 parallel or serial connection to a communication manager 2035 that is adapted to manage communications through the parallel and serial ports in the computer. In the case of the 2034 applications within the decoder 2020, these may include, for example, a transmission surveillance application that is adapted to receive the packet messages corresponding to a standard test format and to evaluate the quality of the message channel. communication that is based on the correct or incorrect reception of all or part of the test package message. This can be used, for example, when the receiver is tuned to the channel frequency on which the data in question is sent. In addition or alternatively, a continuity counter application can be provided to monitor the arrival of each message in a numbered sequence. The data received by the decoder and sent to the computer 2027 may include simple data adapted to be processed in an existing application within the computer, for example data for a 2036 web viewer. In other proprietary commercial applications, the data may be, for example, action data that is adapted to be processed and displayed visually by a specialized application. This data can be updated in response to commands received from the 2027 computer or on an automatic basis at periodic intervals. The configuration of the routing table 2032 is in fact controlled by a configuration application 2037, inside the decoder. Part or all of the configuration application can be installed in the application memory during manufacturing, so that the decoder includes a previously determined set of routing instructions to enable the decoder to handle the routing of the packet messages at the moment of the decoder start. In addition, or alternatively, the configuration application can be installed or modified by the packet messages that were received via the MPEG data stream and forwarded within the decoder by the router 2032 in the first case of • conformance to a configuration of initial routing determined previously. In this way, remote programming and deprogramming of the decoder becomes possible. More significantly, the decoder configuration application 2037 can also be configured by means of the control instructions that are sent from a monitoring application 2038 within the PC 2027 computer. As with all PC applications, it can be loaded this application inside the PC by means of the diskette or by means of the package messages that the decoder receives and are redirected to the PC. Thereafter, the monitoring application can perform the necessary configuration of the routing table 2032 and its parameters to enable the decoder to correctly handle and route the messages that are proposed for the 2035 application of the viewer or any other application within the PC or the decoder. Generally, application 2037 also handles additional aspects of the decoder configuration through application 2037 and can be controlled by control signals from monitoring application 2038. In this way, the PC is enabled to take all the necessary steps to correctly configure the decoder, for the reception of data messages destined for an application within the .PC In particular, the monitoring application 2038 can be adapted to send the control messages to the application 2037 to adjust the tuning of the decoder to receive the messages that are sent on a particular communication frequency. The monitoring application may also configure the decoder so that it will not accept other input signals from some or all of the other sources, for example channel change requests that are received from a remote controller associated with the decoder. Other control parameters can also be adjusted, as desired. The advantages of this particular modality will be understood. In general, in a PC / decoder establishment, the operator will be operating the system from the PC terminal. In this case, the system should be generally not responsive to commands to the system through the decoder (with the possible exception of the commands that are received through the MPEG stream, of course). This embodiment of the invention prevents conflicts from arising and avoids, for example, the possibility that the operator inadvertently changes the channels by means of the remote controller of the decoder, during the operation of a PC application. Likewise, the advantage of controlling the decoder from the PC is that the new application that was loaded on the PC can automatically reconfigure a standard decoder, for example, one that is normally established to receive the television channel known. By means of the monitoring application within the PC, the decoder can be controlled to search the channel associated with the transmission of data for the new application and to download and route this data to the application within the PC computer. In this way, the user is spared - having to set the decoder by itself to the correct channel, since this will be done by the PC automatically. In the modalities of Figures 3 and 4, the system is configured for a type of service that is mostly professional or commercial, in which the decoder is used exclusively to process the data that is related to the applications used within the PC In these services, the decoder will not be used to handle the television data and no visual display of the television will be needed. However, in some embodiments, the decoder can be used to perform its "normal" functions, namely the processing of digital television data, from time to time. In that case, a television will be connected to the decoder within the system. In this establishment, the decoder can change to, and from the modes as desired by the user. As mentioned above, in the case where the PC has taken control of the decoder, for example to receive the data from the web page that was downloaded for use in a viewer application, the decoder will not be responsive to the commands that are receive by means of the remote controller of the decoder, etc., until the moment in which the user has finished the session by means of a command from the PC. The above discussion has concentrated on the routing of the packet data that is received via the MPEG stream. As will be appreciated, the routing table can also be used to direct direct messages that were received from any of the ports of the device. In particular, in the case of interactive applications within the PC, for example, a 2036 viewer on the web, you may also need to send commands from the PC application to the server 4000. In the simplest mode , the PC can be connected by means of a standard modem connection 2029 to the server 4000. The requests for information will be answered from the PC 2027 and will be sent by means of the modem 2029, by means of the information sent by the server through the link 2018 by satellite or transmission. This embodiment presupposes the presence of a modem within or associated with the computer 2027. In an alternative configuration, messages destined for the server 4000 can be sent from PC 2027, by means of lines 2025, 2026 in series / parallel which are to be routed via the routing table 2032 to the integral modem 2028 within the decoder, and, afterwards, sent to the server 4000. Because all the decoders are made in practice with this modem, no There is an extra cost for the consumer with this configuration. Of course, modem 2028 can be used to send messages from applications within the decoder, for example, messages from application 2034 that are used to monitor the quality of transmissions on the selected channel or from the access control application 2033 . Exceptionally, messages can also be sent from the server to the decoder and / or PC through any of the 2028 links, 2029 from the modem.

Claims (21)

1. A combined computer and decoder system for receiving digital broadcast data transmissions, characterized in that the decoder comprises routing means, digital broadcast data that is transmitted in the decoder and intended for the computer being identified and routed to the applications within the computer by means of routing means.

2. A combined computer and decoder system according to claim 1, wherein the routing means is further adapted to route the data to the applications within the decoder.

3. A combined computer and decoder system according to claim 1 or 2, wherein the decoder further includes an application within the decoder, which is adapted to configure the operating parameters of the decoder.

4. A combined computer and decoder system according to claim 3, wherein the configuration application is adapted to configure, inter alia, the routing means.

5. A combined computer and decoder system according to claim 3 or 4, wherein the configuration application is loaded into the decoder or modified by instructions received from the computer.

6. A combined computer and decoder system according to any of claims 3 to 5, in which the configuration application is stored in the decoder memory, during the initial fabrication of the decoder. A combined computer and decoder system according to any of claims 3 to 6, wherein the configuration application is loaded into the decoder or modified by the instructions that are received in the broadcast data that was transmitted. A combined computer and decoder system according to any of the preceding claims, in which the transmission data that was received in the MPEG format is routed through the decoder, by means of the routing table at least in part from conformance with the value of the packet ID header. 9. A combined computer and decoder system according to any of the preceding claims, wherein the digital transmission data that is routed to the computer comprises the data to be processed by the applications that were previously installed in the computer and / or the applications that are going to be installed and run inside the computer. A combined computer and decoder system according to any of the preceding claims, wherein the decoder further includes deciphering means that are adapted to decrypt the digital data that was transmitted in a demodulated form for subsequent routing, in the deciphered form, to the computer. A combined computer and decoder system according to claim 10, wherein the decoder provides an equivalent of a key for deciphering an encoded control word, within the transmission data, the control word being used subsequently. to demodulate the data. A combined computer and decoder system according to any of the preceding claims, wherein the decoder further comprises a modem, the routing means being adapted to route the selected messages that were received from an application within the computer to the modem. A combined computer and decoder system according to any one of the preceding claims, wherein the operation of the decoder is controlled at least in part by the control signals that are sent from the control means within the computer. 14. A combined computer and decoder system according to claim 13, in which the computer controls the operation of the tuner inside the decoder, to select the frequency of the channel for the reception of the digital data that is going to be downloaded to the computer. A combined computer and decoder system according to claim 13 or 14, wherein the computer is adapted to send a control signal to the decoder, to make the decoder not responsive to the selected commands received from the decoder. other selected decoder inputs. 16. A combined computer and decoder system according to any of the preceding claims, wherein the computer includes an internet viewer application that is adapted to receive the data that was routed through the decoder. 1

7. A combined computer and decoder system according to any of the preceding claims, wherein the computer includes an application that is adapted to receive financial data, for example stock price information, which is routed through the decoder. 1

8. A combined computer and decoder system according to any of the preceding claims, characterized in that it additionally comprises a visual display of the television that is connected to the decoder, the decoder being adapted to process the received transmission audiovisual data that is sent from subsequent to the visual display of the television. 1

9. A decoder for a combined computer and decoder system according to any of the preceding claims, the decoder comprising routing means that are adapted to identify and route the digital transmission data that is intended for a connected computer. 20. A computer for a combined computer and decoder system according to any of claims 1 to 18, the computer comprising control means for generating the control signals to control, at least in part, the operation of the decoder. 21. A combined computer and decoder system for receiving broadcast digital data transmissions, substantially as described herein with reference to, and as illustrated in the accompanying drawings.