MXPA97006116A

MXPA97006116A - Interact satellite television system

Info

Publication number: MXPA97006116A
Application number: MXPA/A/1997/006116A
Authority: MX
Inventors: Harrison David
Original assignee: Thomson Multimedia
Priority date: 1996-08-12
Filing date: 1997-08-11
Publication date: 1998-02-01

Abstract

The invention relates to a system for transmitting data between a distribution center and a subscriber, this system conveys a useful signal to the subscriber and has a return path, characterized in that the carrier signal is transmitted together with the useful signal and in that the frequency The signal transmitted on the return path is synchronized with the frequency of the carrier signal. Application to satellite television. Figure

Description

INTERACTIVE SATELLITE TELEVISION SYSTEM DESCRIPTION OF THE INVENTION The invention relates to a system for transmitting images on satellite television. This relates more particularly to the construction of a connection back to the subscriber level. The systems for receiving satellite television programs are known, for example, the DSS digital system, the initials of the trademark Digital Satellite System. One of the existing solutions to build the connection back from the subscriber to the monitoring center, is the use of the telephone connection. The customer's standard television system consists of an external unit comprising the satellite antenna and the block receiving low noise or LNB (which expects to convert the block into low noise) and the internal unit comprising the demodulators and other decoders. This internal unit therefore needs to be connected to a telephone connection via a modem to provide the specific return channel for each client. This solution is not optimal for the following reasons i - The customer must pay for the use of the line based on the duration of the calls and the distance, and this can raise to high costs, particularly if long distances or international connections are necessary. - A telephone line must be connected to each customer premise, this will not always be possible in isolated areas or developing countries. - The connection to the internal unit requires that the telephone plug be available in the vicinity of the decoder. - Not suitable for moving applications. Another solution is to use the satellite connection as a return path, via the subscriber's satellite dish used for reception. This solution is used in bidirectional satellite communication networks of p r. c? -r ltip r.tc? , for example the terminals of the Gilat Satellite Network Limited company, known under the registered trademark Twoway VSAT (which means Very Small Opening Terminal;. C The applications of such networks are of a semi-professional type, such as debit card authorizations. of bank, the registration of numbers of lottery in the points of sale, transfers of funds leeeríniec =, etc. The cost of these systems is high The exchange protocols, in particular the 5"_ :: r: zac :: These systems are generally unsuitable for a large number of high connections, that is to say several million subscribers, the frequency of transmission has problems that are linked to the number of subscribers. The signals of return must be very stable to the frequency, requiring high construction costs due to the use of high frequency synthesizers, these costs are incompatible with the system. ema of the mass market. The purpose of the present invention is to solve the above drawbacks. For this purpose, the object of the invention is a system for transmitting data between a distribution center and a subscriber, this system has a return path, characterized in that a carrier signal is transmitted at a frequency determined by the distribution center and wherein the frequency of the signal transmitted on the return path is synchronized with the frequency of the carrier signal. This object is also a receiver of a data transmission system, characterized in that it includes at least one mixer that receives the carrier signal and delivers a signal whose frequency is linked to that of the return signal.

By virtue of the invention, the proportion of the return path per satellite that is easily carried out, is of a cost not prohibitive for both the subscriber and the provider and is compatible with the characteristics of the receiving station issuing the satellite . Because all receivers are synchronized on an individual frequency, controlled by the monitoring center, it is possible to regulate this return frequency and allow the use of narrow band-pass receiving stations. The frequency of the return signal is regulated by the operator and the phase noise of the return signal is greatly reduced, allowing better use of the satellite frequency band and high modulation speeds. The construction basket is reduced because it is so necessary to use, in the systems "receivers", the subscriber, oscillators or high frequency synthesizers stable at high frequency. The mass market circuits can be used to implement the invention. The exchange protocols are simplified and transmission conflicts are suppressed due to the "interrogation" subscriber at the base of their subscriber codes. These codes can still be installed: t remotely built.

Also, by virtue of this transmission system, the viewer is not much obliged to subscribe to the telephone network. This is not so necessary to build a connection from the internal unit of the television system to the telephone network. The cost of use is regulated only by the supplier of the program, the Telecom operator will not be so relevant. Other features and advantages of the invention will clearly appear in the following description given by way of non-limiting examples and with respect to the accompanying figures which represent: - Figure 1 is a simplified diagram of a satellite transmission system with a trajectory of he came back; - Figure 2 is a diagram of the external unit of the system that receives the subscriber; - Figure 3 is a diagram of the internal unit of the system that receives the subscript; Figure 1 represents the basic concept of the return path of a satellite transmission system implemented by the invention. A ground station 1 equipped with a large diameter antenna, for example 4 to 6 meters, transmits, via a satellite 2, the information and program made suitable to the subscribers- This information and these Droorapatie collected at each level of the subscriber by the form of a satellite dish linked to reception and processing circuits, the total formative part of the total receiver system 3i installed in the premises of the subscriber i. These small diameter antennas, of the order of 45 to 90 cm between, are, in the invention, also used for the return path. In this way, an envelope of the "client" transmits data back via satellite 2 to the base station 1 which therefore also has the role of collecting and centralizing the data transmitted by the subscribers and received in its large antenna. diameter. This over trajectory operates, for example, in the frequency bands of 14-14.5 GHz, 14.5-14.8 GHz or 17.3-18.1 GHz. The data transmitted on this trajectory is the data that is related to pay television, or payment for event, or more generally interactive television, which allows the subscriber immediate access to movies, interactive games, shopping, downloading of programs and also services such as database surveys, petitions, etc. Due to the large number of subscribers, the access to the clients to the return path must be created. For this purpose, an identification code is located for each unit of the subscriber and later it is authorized to send only under receiving this code transmitted by the monitoring center via the satellite. This identification code can be permanently installed during the manufacturing of the system or also be loaded from the monitoring center via a procedure run when the system is installed and started on the client's premise. In this way, the risks of interference or saturation of the satellite which can occur in the case of simultaneous transmissions of the subscribers are avoided, these transmissions are activated according to a procedure of interrogations of the survey type in the part of the monitoring center. Figure 2 represents a satellite mode of the subscriber that receives the system or "receiver". This system is composed of a satellite antenna 5, an external unit 4 and an internal unit 6. From here, the term "system" that receives the "Subscriber" or "receiver" also implies the sending part of the internal and external units. The external path 4 e = is connected to a parabolic antenna 5 through a first connection over which the signals of miereenda are exchanged. This is also connected to the internal unit 6, which will be described later, through a second connection, for example of the coaxial type. The external unit consists of a receiving path which receives the satellite signals that originate from the antenna and transmits them to an internal unit, and a sending path to transmit signals from the internal unit to the antenna. A microwave connection connects the antenna to the input / output of the external unit, linked by itself to the input / output of a diplexer 7. The signals received by the antenna 5 are thus transmitted to the diplexer 7 whose role is to rotate them , via the output from the receiver side (receiver output), to a low noise block LNB which means low noise block converter. This block consists, in a known manner, of a low noise amplifier LNA 9 followed by a passband filter to eliminate the image frequency 10. This filter is connected to a first input of a mixer 11 whose output drives the input of an intermediate frequency amplifier 13. A local oscillator 12 is connected to the second input of the mixer 11. The output of the amplifier 13 which is the output of the T block, MP, ee * ~ a '' u da sia secunda entry / output of the external unit.

By the form of the example, the signals received by the antenna 5 are in the frequency band of 10.95-11.7 GHz. These signals transmitted as inputs to the low noise amplifier travel through the passband filter 10 whose passband corresponds to this frequency band. The signals are then transposed to the intermediate frequency in the band 950-1700 MHz, the bandpass of the amplifier 13, with the help of the mixer 11 and that of the local oscillator 12 sets a frequency of 10 GHz. The receiving output of the diplexer is also attached to the first inlet of the mixer circuit 14 whose role will be explained later. The signals output by the external unit 4 are transmitted to the input / output of the internal unit 6 by means of a coaxial wire cable. This internal unit is described in Figure 3. The input / output of this unit is linked to the receiver circuit 20 whose role, among others, is to decipher the decrypted video signals of the external unit and transmitted on the coaxial wire cable, in the same way as the conventional internal unit. This receiver circuit also filters the signals exchanged on the coaxial wire cable. The deciphered signals available at the output of this circuit 20 are then transmitted at the internal unit output for which a terminal will be connected, for example a television set. A modulator of type CDMA 21, which means Code Division Multiple Access, and which carries out the modulation of a base signal by a binary train, receives in a first input the useful baseband signal which is the digital signal to be transmitted. This first input is linked to an input of the internal unit, for which the input is placed, for example, to a small card, and / or to an output of a memory of the internal unit not shown in the Figure. Connected to the second input of the modulator is a binary code circuit 22 which delivers a stream of binary words encoded by a pseudo-random code, namely the spread spectrum code according to the conventional CDMA modulation process. The modulator 21 is, for example, an exclusive OR input. The output of the modulator 21 is connected to a first input of a converter 23 and its filter circuits. An oscillator 24 transmits a sinusoidal signal, for example at a frequency of 2.3 GHz to a second input of this converter to receive-emit the signal received at the first input. The send-receive and filtered output signal by this converter feeds a first input of an adder 15. The second input receives the signal from an oscillator 26 that delivers a sinusoidal signal at a frequency of 2.4 GHz. The output of this adder is attached to the input / output of the internal unit and then to that of the external unit by the shape of the coaxial cable. In this way, the signals to be transmitted, among other things the information in the small card, are modulated by the CDMA type modulation. Of course, it is only thus conceivable to connect, to the input receiving these baseband signals, an internal memory to the internal unit 6, the various information to be transmitted, such as screen movies, etc., will then be stored later. The modulated signal is then rßc ciG? -cñiic d? at a rate of 2.-5 n. A reference eenax, at the 2.4 GHz frequency, is connected to this useful signal and the total is transmitted to the input / output of the external unit 4 shown in Figure 2, via the coaxial wire cable. This input / output is connected to the input of a low-pass filter 15. The output of this first filter is connected to a first input of a filter plus a mixer 17. The input / output of the external unit is also connected to the input of a high-pass filter 16. The output of this filter is connected to a first input of a mixer 14. The second input of this mixer receives the signal on the 12.7 GHz frequency that originates from the receiver output of the diplexer 7. The output of the mixer 14 is connected to the second inlet of the mixer 17. The output of this mixer is connected to the input of a high-pass filter 18. The output of the filter is connected to a power amplifier 19., the output of the power amplifier which is in turn connected to the input of the diplexer • 7. The input / output of the diplexer on the side of the antenna is, as indicated above, connected to the input / output of the external unit attached to the antenna. The reference signal at the 2.4 GHz frequency is filtered by the high-pass filter 16 which eliminates the useful signal which is at a low frequency and feeds the first input of the mixer 14. The second input that receives the signal at the frequency of 12.7 GHz, the output of the mixer delivers a reference signal at a frequency of 15.1 GHz. This signal is used to receive-emit the useful CDMA signal recovered at the first input of the receiver-emitter 17, after it has been filtered by the low pass filter 15, subsequently eliminating the reference signal in the 2.4 GHz frequency. This circuit 17 also has the role of filtering the IF band signals coming from the path to eliminate them. The signal modulated in the frequency of 17.4 GHz is filtered in the output of the mixer, then amplified and then transmitted as an output from the external unit per the form of the diplexer to feed the antenna 5. The signals of the internal unit consist of the useful signal received-emitted in frequency by a reference signal whose frequency is external to the intermediate frequency band in reception to allow filtering and extracting it from the IF signals, transmitted by the low noise block 8, the signals exchanged between the internal unit and the external unit travel on the same coaxial wire cable. The oscillators 24 and 26, which deliver the frequencies of 2.3 GHz and 2.4 GHz are generally synthesizers which generally, due to the low band of the generated signal, deliver a very stable signal for a low construction cost. Consequently, the frequency and hence the stability of the signal transmitted at the 17.4 GHz frequency is directly linked to the 12.7 GHz reference signal transmitted by the satellite. It is therefore possible to do this with the use of a synthesizer of the frequency of the return signal in order to retransmit a very stable-frequency signal, where the synthesizer could be very expensive, given the frequency of the order of some ten gigahertz to be generated. The frequencies of 2.3 GHz and 2.4 GHz are given by the indication form and for the purpose of the description. In fact, it is sufficient for the forr to correspond to the difference between the frequency of the received frequency synchronization signal and the frequency of the return signal. These frequencies can originate from the same synthesizer. The information transmitted on the return channel,. as indicated above, it is for example the data related to the video or a demand for PPV (Pay Per View), data related to the consumption of the euscriptor, films and programs on screen, data related to elections of the viewers in the case of Interactive television, etc., data stored on the small card and / or in the memory of the internal unit. A variant and the invention consists in using the reference signal by the receiver to synchronize, in addition to the frequency of the return signal, the oscillators of the. internal unit. In this case, the LNB block has a wide pass band, the mixer 11 also receives the frequency signal 12.7 GKz which is therefore transmitted to the internal unit at a frequency of 2.7 GHz after the reception-emission. This signal is then recovered at an additional input for frequency synchronization of each of the oscillators 24 and 26. In this way, the device is fully monitored in frequency by the 12.7 GHz signals received by the antenna.

Another variant of the invention consists in using the reference signal received by the receiver to carry a code of the subscriber, in this way it being possible to interrogate each receiver of the subscriber in succession. In this case, the LNB block has a wide pass band, the mixer. 11 receives the signal of 12.7 GHz frequency which is transmitted to the internal unit on a frequency of 2.7 GHz after the reception-emission. This signal is filtered, in the delivery path, for example with the aid of a bandpass filter 16 instead of a small pass filter. The signal is demodulated by the receiver circuit 20 which then includes a demodulator to extract the code from it. This circuit transmits a send command to the sending circuits or oscillators of the "receiver", these circuits are activated when the code corresponds to the subscriber. As indicated above, the received reference signal can also be used to program this code when it is installed and fixed on the "receiver" in the subscriber's premises. The two previous variants can, of course, be combined. The transmission system which is the object of the invention can be applied to any type of transmission that requires data exchange by satellite, by radio transmission or even direct transmission by wire key or radio waves.

Claims

1. A system for transmitting data between a distribution center and a subscriber, this system transports a useful signal to the subscriber and has a return path, characterized in that the carrier signal is transmitted together with the useful signal and in which the frequency of the signal transmitted on the return path is synchronized with the frequency of the carrier signal.

2. The transmission system according to claim 1, characterized in that the carrier signal is modulated by a signal which includes a subscriber identification code and in which, when the code is recognized, the receiver sends data on the return path .

3. The receiver of a system for transmitting the data according to claim 1, characterized in that it includes at least one mixer that receives the carrier signal and delivers a signal whose frequency is linked to that of the return signal.

4. The receiver according to claim 3, characterized in that it includes a second mixer to act on the frequency of the return signal, an input of this mixer that receives a modulated useful signal to be transmitted on the return path and the second signal input of the first mixer.

5. The receiver according to claim 3, characterized in that the carrier signal also synchronizes the frequency of a first oscillator that effects the frequency reception-reception of the modulation signal useful to be transmitted on the return path and the frequency of one second. oscillator that effects the reception-emission of this carrier signal.

6. The receiver according to claim 3 characterized in that it includes a circuit for deciphering a subscriber identification code carried by the carrier signal.

7. The system according to claim 1 or 2 characterized in that a signal of the return path is a modulated signal of type CDMA.

8. The system according to any of the preceding claims characterized in that the data are those of images for television and the transmission is made by satellite.