Method for facilitating a dialog between a subscriber to a pay television system and a decoder of the received signals, and a decoder for these signals.

The present invention relates to a method to facilitate a dialogue between a subscriber to a pay-TV system and a decoder of the received signals. It also relates to this decoder.

In a pay-TV system (pay-TV), and in general, the subscriber chooses the programs they want to watch and it pays to receive these programs are transmitted in scrambled form to be unintelligible to non-subscribers or to subscribers who have not chosen or paid for a particular program. The signals can be transmitted by cable, satellite or antenna. advanced pay television systems have also said the possibility "pay-per-view" programs buying just before the start of the program or during transmission, and this in a transmission system Single Lane. In this case, it is necessary to memorize some credit to the location of the user, that credit is available to enable the purchase and the receipt of a pay-per-view broadcast that you want to watch. If the stored credit is sufficient, the issue amount is debited from the credit and the received signal from the transmitting station managed to allow a comfortable reception.

WO 81/02499 relates to a method and a system for scrambling the transmission of video information, particularly for pay television. Portions of the video signal, for example portions or line segments, lines or frames are transmitted in an order different from their natural sequence. The manner of rearranging the sequence of line segments for the transmission can be controlled by a code generator which changes the sequence at each frame or based on other suitable time base. The code, which may be encrypted, varies randomly and can be fully or partially transmitted with the scrambled video signal.

US Patent 4,484,217 relates to a method and a system for charging away from a pay-TV program. The credit available is stored in the subscriber location and a cost signal is transmitted by the transmitter. Pay-per-view is made possible by the fact that a purchase is expected by pulses. A unique code may accompany the transmitted signal for identification purpose. If the subscriber's decoder recognizes the program as a purchase program pulse, the cost of the program is displayed. To view the program, the subscriber between adequate demand in the decoder and it automatically compares the cost of the program with available credit. If the cost does not exceed the credit, the program is managed and the cost is deducted from the credit. However, the above system is not intended to allow the display as teletext information issued on planned programs, in chronological order, or the display of information in the form of instructions for operations to be performed by the user on the decoder in order to facilitate the dialogue between the latter and the user and prevent operation errors.

Accordingly, the object of the present invention is to facilitate and improve the dialogue between a subscriber to a pay-TV system and a decoder of the received signals. In addition, the decoder must allow quick and easy recharge credit by the subscriber without using the management center.

To achieve this object, the method and decoder are constructed as respectively described in claims 1 and 3.

That is stored in the subscriber's decoder teletext information transmitted by for emission programs, such as titles, prices, dates of issue, number or code of expected emissions, etc. and that this information can be selected by menu with the keyboard decoder and displayed by a text generator on the TV screen, there is a possibility of dialogue between the subscriber and the decoder, the latter guiding the user through all what to do.

The invention will be explained below with the description of an embodiment illustrated in the drawing.<ul><li>Figure 1 shows the basic principle of a pay-TV system,</li><li>2 shows the principle of the input and the output of a video signal line in a buffer of 32 lines,</li><li>Figure 3 shows a block diagram of the decoder according to the invention.</li><li>4 shows the principle of interference and descrambling the transmitted video signals,</li><li>5 shows the rotation of a line of the video signal,</li><li>6 shows the inversion of a video signal line, </li><li>7 shows a mirror symmetry of a video signal line,</li><li>Figure 8 shows a block diagram of the CPTV card</li><li>9 shows the physical structure of a video signal line,</li><li>10 shows the structure of the physical data in the Didon data transmission system, and</li><li>11 shows the data structure in the system Dido.</li></ul>

In Figure 1, a microcomputer 1 is provided for generating data according to a teletext screen for projected emissions programs such as title, price, date or period of issuance, etc. as well as other information useful to the user. This data is introduced in 3 by an interface 2 in the video signal supplied by a camera 4 or any other producer of video signal element. The lines of the return of the vertical scanning of the video signal not normally transmit any information are used in the system according to the invention for transmitting teletext data, so that they are transmitted at the same time as the video signal.

9 shows the a return line of the vertical scanning of the video signal structure. It is seen that the line is formed of 32 bytes of teletext data and it further comprises synchronization information and Hamming code addresses for the detection / correction of errors. The 32 bytes of teletext data is protected by 2 bytes of code detection of CRC-16 errors.

The video signal with the teletext data is then delivered to a scrambler 5 which scrambles the image, for example by permutation of rows or by other means. The scrambled signal is transmitted by air, by cable or satellite video receiver 6 of the subscriber. The receiver comprises a descrambler 7 which delivers the signal to the TV managed 8.

The scrambled signal is fully compatible with PAL and SECAM standards (NTSC). The interference can be run in normal version or deep release. In normal version, the video lines are switched between them, only the active part of the line being swapped. In the SECAM system, a line pair is swapped with an even line and an odd line is switched with an odd line. In the PAL system (NTSC), the burst (color carrier frequency) is left unchanged. Each line is sampled and digitized to 8 bits at a sampling frequency f 3 = xf_burst or f = 4 xf_burst the synchronous burst, so that in the PAL (NTSC) system, the color phase is preserved. Each line is thus divided in principle into 3 (or 4) x 256 segments of 8 bits. 4 shows the principle of interference and descrambling of video signals traansmis. On issue a random generator produces 25 real-time code words. 26 information on the identification of the issue to be transmitted is supplied with a transmission key 34 and the code word to a system of chriffrage 27, which delivers real-time encrypted signal 28 to be transmitted. The transmission key 34 can be transmitted in encrypted form. At the reception, the transmitted signal is issued with the transmission key to deciphering system 29, for example according to the system DES which delivers the deciphered code word (provided that the current program was purchased) and information 26. The identification code word controls a pseudo random 30 which delivers turn pointers 31 for a table of 32 256 permutation codes. Each line of the video signal, the table selects among 33 buffers the one which allows the de-permutation of the lines.

It is possible to enter and exit the buffer lines in any order. 2 schematically shows a buffer memory 18 including 3 x 19 256 segments of 8 bits forming a line of the video signal. In this memory, the segments or samples are sequentially introduced in successive positions of memory. The figure shows that the introduction of a new segment 20 into one of the memory locations releases the segment 21 that was stored in this position, so that the memory is always filled with 32 lines and that a buffer is always filled of 256 segments. The scrambling / unscrambling as indicated above, provides excellent security against piracy, for the following reasons: - The number of possible permutations of lines is so large that it is difficult to find the "right combination", either by chance or by correlation. - Code or permutation key is transmitted in real time, so even if a hacker finds the right permutation, it is only for a moment, for example one second. - The permutation code is transmitted encrypted, for example but not exclusively by the DES system, virtually unbreakable. - Deciphering permutation codes is done in a smart card microprocessor (CPTV card), as discussed below, providing all the necessary security. Alternatively, the microprocessor of the card can be one of decoder elements. - Maps CPTV its reprogrammable, which allows to periodically change the encryption keys.

In the deep interference version is carried out in addition to the permutation of the lines as indicated above, the following interference: - According to Figure 5, rotation of the active line on itself, that is to say for example that the active part of the line begins in the middle of the real line and is followed, after the end of the real line , the beginning of that line. - By 6, a polarity reversal of the current line from the level of 50 IRE. This allows an automatic adjustment of the brightness level to keep it constant. This removes the possibility of image recognition by changing the ambient lighting. - According to Figure 7, a mirror symmetry of the video line according to which the active portion of the video line undergoes an axial symmetry axis perpendicular to the black level of the video.

Let us recall that during the interference, only the active part of the line is permuted, including the return lines of the vertical scan, which allows the interference teletext data, but that in all cases the horizontal synchronization remains unchanged. At the output of the buffer, the data is converted into analog signals by a digital / analog converter of 8 bits. Thus a PAL or SECAM signal (NTSC) managed to display on the TV. Let us now examine the decoder of the principle and its possible uses.

FIG 3 shows that the video signal from the head station (transmitter) is supplied to the video buffer memory 9 of 32 lines for performing the de-permutation of the lines as indicated above and a data receiver teletext 10. recall here that the teletext format data is transmitted at the same time and by the same channel as the video signal, said data being transmitted by the return lines of the vertical balayge the video signal. A microprocessor 11 is the central element of the decoder. It comprises dead and vivid memories for any information that may be displayed on the TV, this information which is shaped into teletext data format, is partly transmitted by the headend and stored in a memory of the microprocessor and partially stored in a read only memory of the microprocessor 11. the microprocessor is associated with said security card CPTV (Pay TV card) 12 normally inserted in the decoder and to a keyboard 13 thereof. The microprocessor delivers on call using the keyboard, the teletext data in appropriate digital format text generator 14 controlling the TV display. The microprocessor 11, in conjunction with the CPTV card 12 controls the buffer 9 for dépermuter the lines as indicated above. The video signal unraveled and the text generator are available in 15 to be displayed on the TV. In addition, the microprocessor is also connected to a modem 16 itself connected to a telephone line 17.

Let us now examine in more detail the possibilities of the decoder described above.

The CPTV card is an active card comprising a microprocessor provided internally of a nonvolatile memory (RAM with battery, NVRAM or E2PROM) unreadable from outside (safety) and a clock. According to Figure 8, the card includes two electronic circuits A and B. Circuit A is a safety device with CPU 40 and associated memories such as ROM 41, E2PROM 42, RAM 43, and a memory interface 44, and the Circuit B is a separate E2PROM memory of 2 Kbytes. The map is presented in principle in the form of a credit card. It comprises the following four functions: - Decoding of the transmitted encrypted permutation key, for example using the DES system. The card receives the encrypted key microprocessor 11 and returns when the emission was purchased, the key to unscrambling dépermuter the lines of the video signal. - Save the list of numbers, codes or programming acquired and subscriptions to a particular genre of programming (sports programs, cultural, cinema, cooking, etc.). This storage of the list of purchased emissions allows CPTV card microprocessor will return to the descrambling code if the issue has been purchased. In addition, and for the purpose of statistical and billing, it is possible to know the emissions purchased. - Credit Management. CPTV the card stores information representative of the credit that it can use for the purchase of emissions or abonnemnts. To purchase a program, the user brings up by action on the keyboard 13, the list of scheduled programs received in advance of the headend and stored in the microprocessor 11 of the decoder and which are selected by menu and displayed on the TV screen. The TV shows in addition to the title of the program, number, price, date of issue and other useful information if needed. The user then selects the number of the issue he wants by pressing the corresponding key on the keyboard. If the stored credit available on the card is sufficient for the purchase in question, issue or the purchased subscription is stored in the card on the list of purchased emissions and the amount is deducted from the available credit. When the show airs purchased, it is identified by the card comparaiosn with its registered number or code on the list of purchased emissions and the card returns to the microprocessor code or descrambling key. - The fourth function of the CPTV card is a measure of function of time by a clock. This is used in some programs, such interactive games between the user and the head station as described below.

We see that the map differs from the known maps of the state of the art in that it stores all the confidential or secret information necessary for descrambling the video signal, such as descrambling keys and credit. The card manages the credit, memorizes the emissions purchased and permits the unscrambling of the purchased emissions. It is erasable, all stored data can be modified. It is thus possible to modify the key unscrambling and to reuse the card once filled.

For all the processes, the user is guided by the decoder itself which displays text and handling instructions on the TV via text generator 14. For this purpose, some of the information might be displayed as text is stored permanently in a ROM of the microprocessor 11, which portion corresponds in principle to handling instructions, and the other part of the information is temporarily stored in a RAM of the microprocessor 11, this second information being broadcast by the station and head for particular programs to be broadcast. The following options are available to the user: - Visualization of securities, price, etc. programs to be broadcast, - Guide in buying program schedule, - Guide in buying subscriptions (windows / channel) - Guide in the annexes of the decoder - Dialogue with the decoder transparent to the user - Receiving messages (special / general) - Standard teletext reception.

The above shows that the dialogue between the user and the decoder is greatly facilitated by it.

The decoder is also particularly suitable for purchase by the user directly at him, a dialogue program with the decoder (pay-per-view) without informing the management center, that is ie all purchasing operations are performed in the CPTV card, the decoder interprets the commands given by the user and transmitting the CPTV card. For this purpose, the user simply selects the keyboard the title of the program is interested in introducing this number and activates a button "validation". If the credit contained in the CPTV card is sufficient, the number or code of the selected program is stored in the list of emissions purchased, the amount is deducted from the available credit, and when the program is broadcast, the map delivers to the microprocessor the descrambling code of the issue. This principle prevents overcrowding telephone lines and allows a user to purchase a current program.

If the credit card is contained in the no or insufficient to purchase a subscription or issue a new credit or an increase in credit still available can be inserted in the card according to one of the following: - Purchase by the user to the central management of a code (eg 9 digits) corresponding to the amount of credit to refill and recharge credit by introducing this code in the decoder using the keyboard. When the code is inserted in the decoder, the new credit is stored in the CPTV card. - By postal exchange the card at regular time intervals, allowing the head of the station to know which programs watched (statistical). - Credit Recharge in a store (video club, bank) also to know what programs were watched. - By remote control: the credit card can be charged by antenna or cable on the orders of the show.

Among the possible uses of the decoder according to the invention include still - Display menu to purchase subscription programs with possibility to know at any time purchased programs, these programs are designated by a sign (letter, number) Specifically, the credit still available display of subscriptions deadlines, the overall supply by the headend, that is to say, updated programs that will be released later, changing conditions by group of subscribers , etc. All this information, which are issued by the teletext data receiver (10) are stored in the memory of the microprocessor 11 and displayed on demand on the TV screen with the text generator 14. - Interactive games: This is such a lotto game with the head station to which the user is involved in betting numbers and introducing the amount played using the keyboard 13. The number and amount played are stored in the CPTV card. The drawn out or the issuance number is transmitted by the video signal and encoded form as teletext data, and if it matches the number bet by the user, it is authenticated by the CPTV map using the internal clock in it that exactly determines the time between setting and gain control, to prevent fraud, it being understood that the development must precede the draw at the show. If the player wins, the decoder calls the central transmission via the modem 16 and the gain is enhanced as an increase in the credit card in the CPTV, this increase being controlled by the head station (see below). - Receive personalized messages from the headend. These messages are sent in a teletext decoder format and verifies that it is the one who is to receive the message reliability. To this end, each CPTV card carries a particular stored identification number that is transmitted by the head station with each message. If the decoder is the one to whom the message is addressed, the card allows the message on the TV. - Security code. This is a code to prevent unauthorized persons, such as children make purchases that exceed a predetermined amount or participate in games that are not intended for them. In this case, must be introduced by keypad security code in the decoder as a password. If it is not introduced or if it is not correct, the decoder refuses to execute the order given to it. - Link modem. Thanks to the modem 16 connected to the microprocessor 11 and a telephone line 17, it is possible the decoder into which is inserted the card CPTV, automatically call during the night (thanks to the clock of the card CPTV) the headend to get a credit recharge, if it is sold. At the same time, the decoder sends to the headend all watched programs. Of course, the appeal of the head station by the decoder can also be periodic, fixed dates, if desired. - The decoder can be used as a receiver Teletext standard with all the usual functions of TV channels operators or from PTT.

10 shows as an example of the organization of data in the lines of the video signal the physical data structure in the case of a data transmission system Didon (France). Each frame of the video signal is transmitted as a line L0, L1, L2, L3 or L4. So a group of 5 lines (L0-L4) is transmitted every 5 frames. particulieèrement more we see that the lines L2 and L3 transmit 32 bytes of data pages each. The mappings B0 to B5 to select a group of subscribers among 2²⁴ groups, each 240 subscribers. The mappings include the group number, the action to perform, p. ex. credit recharge, and the list of subscribers affected by this particular action. The synchronization is ensured by a radical of the CRC-16 as indicated. In addition, each line is protected by a CRC-16 which enables error detection and each group of 5 lines is protected by an XOR that corrects an erroneous line. The advantage of organizing data according to 10 is that it enables you to find easily the information where it is in the decoder.

11 shows another example of data structure in the case of the DI-OS (operating system Dido). We see that the data is organized in pages of 32 65'536 bytes each. The first four pages (0-3) of the data structure includes a table which outputs for each channel may be passed the address of the first page of a block of pages for that channel and the block length which is identical with the number of pages of that block and the number of revisions or changes that have been made in that block. The advantage of the organization according to Figure 11 is that it leads to a very flexible structure for transmitting data and a highly flexible future expansion.

The above shows that the decoder according to the invention offers a number of possibilities to the user, especially that facilitates dialogue with the latter thanks to the TV display of projected emissions programs and handling instructions necessary to perform on the keyboard to purchase or for a credit recharge. In addition, CPTV card makes it extremely safe decoder against piracy.