Method for broadcasting gradual conditional access programmes with data flow separation, and receiver therefor

METHOD FOR DISTRIBUTION PROGRAM

CONDITIONAL ACCESS AND PROGRESSIVE

A SEPARATION OF THE INFORMATION FLOW

RECEIVER AND CORRESPONDENT

p0005Technical area

p0006The present invention relates to a method of broadcasting programs to access and gradual separation of the flow of information and a corresponding receiver.

p0007It is used in pay television, in radio programs or sounds or data in the transmission and distribution of program material, etc ..

p0008State of the prior art

p0009In conventional program broadcasting systems, access to programs is reserved for a certain population of receivers. If it is possible to distinguish various access rights (a program may for example be simultaneously^• available by subscription and purchase, impulsive), it remains a receiver is or is not allowed depending on whether or not to have a right of access. But to attract the viewer or 1'auditeur discovering voluntarily all or part of the image content or sound of a program during a given period of time is an important commercial asset for any conditional access system. This function currently available on some pay-television systems using a scrambling process does not deeply transforming the image. But digital techniques commonly used scrambling too deeply transform the signal for afford to "guess" the program to the user.

p0010French patent application No. 92 15841 filed on 29 December 1992 and entitled "diffusion process for conditional access programs for gradual access to such programs" or the corresponding US application 08 / 172.817 of 27 December 1993 describes a technique to have a "preview" of some programs. This overview is made possible by the use of a right of access is only partial, instead of the usual right of access, that is total. Thus, next to authorized receivers that can fully access a program and unauthorized receivers that can receive nothing of it, there is, according to this technique, other receivers can preview the program, c that is to say that can access a discernible shape but not usable program. The process described in this patent application comprises the following operations:

p0011- Scrambling information specific to various programs,

p0012- Information is transmitted and scrambled for each program,

p0013- Synchronized with each program transmission takes place of access control messages to each of these programs, these messages being able to permit the descrambling and restoration of programs in receivers having corresponding access rights,

p0014- It also transmits partial access checking messages to at least some of these programs, the partial access checking messages being able to permit the descrambling and partial restoration of the corresponding programs for receivers having a partial access right.

p0015Advantageously, to implement this method, cutting the flow of information corresponding to each program into a first stream said elementary stream corresponding to a program which, once restored in a receiver, will be discernible without being directly usable, and a second stream, said additional flow to complement the first, the ability to fully restore the program.

p0016In this variant, the partial access control messages apply to elementary streams.

p0017The technical problem to be solve this invention is the production of the elementary flow and the complimentary flow that requires technique and this from a single outflow of any encoder.

p0018Disclosure of Invention

p0019The present invention therefore relates in particular to a particular stage of emission programs with progressive conditional access process, namely the forming step of said two elementary and complementary flows. The invention applies in cases where the flow of information out of the encoder is digital, because it is in this case posed the most difficult problems for the progressive conditional access. Furthermore, it is assumed that the information is multiplexed, that is to say, they constitute a "multiplex" formed of a sequence of elements which may be, depending on the nature of the multiplexing, frames, packets, or others, ... Under these conditions and according to the invention, to separate the flow of information multiplexed elementary stream and a complementary flow, it alternately takes groups of m successive elements and p successive elements of the multiplex groups constituting elements m the elementary stream and groups of p elements the additional flow.

p0020Specifically, the present invention therefore relates to a method for broadcasting of programs with progressive conditional access, wherein:

p0021- Separating a flow of information corespondant a component of a program into a first stream or elementary stream and a second stream, said additional flow,

p0022- Scrambling at least the flow .complémentaire using a control word,

p0023- Synchronously with each program, transmits access control message to descramble and restore the flow embroiled in receivers having corresponding access rights, the return of one elementary stream leading to a discernible program component without being directly usable, the descrambling of the complimentary flow making it possible to complete the program component to allow to completely restore the program, this method being characterized in that, the information flow being in the form of digital multiplex constituted by a sequence elements, it is the elementary stream by taking in the multiplex of m successive elements of groups and is the additional flow taking in the multiplex groups of p successive elements, m groups successive elements alternating with the groups of p successive elements.

p0024In a first mode of implementation, the elements are multiplex frames of fixed length, cut into variable length channels, the component of the program to be scrambled being transmitted in a determined rank channel; the elementary flow is then constitutes taking the information in a given rank i channel in the m successive groups of frames and the complimentary flow by the information contained in the same row of channel determined i in p successive groups of frames alternating with said m successive groups of frames. In a first embodiment, scrambling rank determined channel i of m successive frame groups by a first control word CW1 and the same rank of channel i successive frames per group by a second control word CW2. The C 1 control word can be known, local control word of the receiver or a control word conveyed within an access control message.

p0025In another variant, it does not confuse the rank determined channel i of m successive frame groups but confuses the rank of channel i of determined groups of p successive frames by a control word (CW2).

p0026In a second mode of implementation, the multiplex elements are packets and the elementary flow is formed by the information contained in successive m packet groups and the complementary stream by the information contained in p successive packets alternating with the groups of m successive groups of packets.

p0027In a first embodiment, scrambling the packets m successive groups of packets by a first control word CWL and packets of groups of p successive packets by a second control word

p0028CW2.

p0029In a second variant, no scrambles the packet groups of m successive packets, but scrambling the groups of p successive packets by a packet control word (CW2).

p0030The present invention also relates to a receiver adapted to receive programs transmitted by the process which has just been defined. This receiver is characterized in that it comprises:

p0031- Means for separating the flow of information received first stream or elementary stream, consisting of groups of m successive elements, and a second stream, said complementary stream, consisting of p successive elements of groups, group m successive elements alternating with the groups of p successive elements,

p0032- Means for recognizing at least one access control message in the information received and to extract at least one control word and at least one access condition,

p0033- Means for checking if at least said access condition is satisfied, - means for descrambling at least the complimentary flow with the associated control word if the corresponding access condition is satisfied,

p0034- At least one video receiver, audio or data receiving at least the elementary stream signals and, where appropriate, the signals of the descrambled complimentary flow if the corresponding access condition is satisfied.

p0035Brief Description of Drawings

p0036- Figure 1 is a schematic diagram showing a pay-TV broadcast channel;

p0037- Figure 2 is a diagram showing the organization of a multiplex in accordance with the frame multiplexing technique;

p0038- Figure 3 is a diagram showing the organization of a multiplex according to the packet multiplexing technique;

p0039- Figure 4 illustrates the constitution of the elementary flow and the complementary flow in the case of a multiplex frame;

p0040- Figure 5 shows respectively scrambled components, degraded and descrambled in the previous case; - Figure 6 illustrates the means for implementing the method of the invention in the case of multiplexing frames;

p0041- Figure 7 shows the basic structure of the elementary flow and the complementary flow in the case of a packet multiplex;

p0042- Figure 8 shows the components respectively tangled, degraded and descrambled in the previous case;

p0043- Figure 9 illustrates the means for implementing the method of the invention in the case of multiplexing packets;

p0044- Figure 10 shows the block diagram of a receiver adapted to process the broadcast signals according to the method of the invention; - Figure 11 illustrates the operation of die-ultiplexeur descrambler in the case of a frame multiplex;

p0045- Figure 12 illustrates the operation of demultiplexer-descrambler in the case of a packet multiplex.

p0046detailed discussion of embodiments of the invention

p0047Figure 1 shows a conventional chain of broadcasting of pay television programs. This chain includes transmitting side, the source coders, in this case two coders referenced 10 and 10 ', a multiplexer / scrambler 12, and at the receiving end a demultiplexer / descrambler 14 and the source decoder, in this case two decoders referenced 18 and 18 '.

p0048Information flows from the source encoders 10 and 10 'supply the multiplexer / scrambler 12, which is responsible for multiplexing and confuse these flows to deliver a single stream that is broadcast stream.

p0049Scrambling is a reversible operation to convert the signal with a key called control word (CW), to make it unintelligible program for users who do not have this control word.

p0050To enable the descrambling control word is transmitted in encrypted form in the known access control messages ECM. Each ECM also contains the access condition (AC) to be satisfied by the access control module of the user to decrypt the control word (CW) and, therefore, the descrambling signal. The control words have a limited life (typically 10 seconds). To avoid problems of control word changes, both current and future respectively control words are transmitted in the access control message. One is the even control word used for a pair phase and noted CW_e ; the other is the odd control word CW noted₀ used during an odd phase.

p0051Information flows from the source coders are multiplexed porellement you. Two techniques are primarily used in the field of digital broadcasting, the multiplexing frame and multiplexing packets. In multiplexing frames, the multiplex is constituted by a succession of fixed-length frames having all the same organization as shown in the diagram of Figure 2 which shows a frame of rank i and the next frame of rank i + 1 . A frame is divided into n variable length channels. Each channel carries an elementary stream

p0052(Video, sound ...). The same blank is used for all frames (multiplex reconfigurations are possible but rare). The bit rate allocated to a channel rank k is equal to (Lgk) / Tbit / s, where k Lgk is the channel bit length and T is the period of the frame.

p0053For example, mention may be made STERNE multiplex which is a frame multiplex. The length of a frame is 24ms. The bit rate allocated to a channel that would have a length of 1 byte would be approximately equal to 333 bits / s.

p0054Generally, a channel is used to convey a service road describing all the other channels of the frame: channel length, flow description elementary transported in the channel, scrambling and access control settings, ...

p0055The service channel also carries a frame counter used for example to determine the lifetime of the control words and the parity of the phase.

p0056The scrambling of an elementary stream is being done by scrambling, in all frames, all bits conveying the elementary stream channel. In Figure 2, the scrambling is on channel 2 and is symbolized by hatching.

p0057As for multiplexing packets, it is to produce a succession of fixed or variable length packets. Each packet contains the data of an elementary stream. The diagram of Figure 3 provides an example of packet multiplex, conveying three elementary streams A, B and C.

p0058Each packet consists of a header (ET), a data field and a suffix (SFX).

p0059The scrambling of an elementary stream is being done by scrambling all packets of data fields carrying this elementary stream. In the example shown in Figure 3, only the elementary flow B is scrambled (the hatching symbolizing scrambling).

p0060For example, the multiplex MPEG2 is a packet multiplex wherein the packets are all fixed length of 188 bytes. The header contains an identifier of the elementary stream, plus two bits specifying the mode and the scrambling parameters^' for this packet. The values ​​of these two bits are now standardized: 00: no scrambling 01: Reserved 10: scrambling with the even control word

p006111: scrambling with the odd control word.

p0062In the patent application No. 92 15841 (US 08 / 172.817) already mentioned, it is described how to implement a progressive scrambling mechanism in case the component (video or audio) is available in two discernible flows. It is sufficient in this case to apply a control word CWL (associated with a condition of access to the CAD elementary stream and a control word CW2 (associated with an access condition CA2) the additional flow. The condition 'CA1 access and security code to CWL are transported in a ECM1 access control message. the access condition CA2 and CW2 cryptogram are transported in a ECM2 access control message. the only access condition CA1 allow the descrambling of the elementary stream, providing an image or its gradient but understandable for the user. now described how exactly produce two discernible flows, respectively scrambled with CW2 CWL and control words, in the case of a multiplex raster and a packet multiplex.

p0063In the case of the multiplex frame first, the component on which it is desired to apply the progressive scrambling is transmitted in the frame i of each channel. The method of the invention is then to confuse the channel i m successive frames with the word CWL and the same channel p successive frames with CW2, and again the same channel m successive frames with CWL, etc ... as shown in the diagram in Figure 4 where the vertical lines symbolize a scrambling with CWL and horizontal lines scrambling with CW2. Words CW2 and CWL change parity at the same time. This parity is not indicated in the diagram of Figure 4.

p0064m numbers of values ​​and p, specific to each scrambled channels should be known to the decoder implicitly or explicitly. In the latter case, they are transmitted in the service road, along with synchronization information (eg, a particular value of the frame counter) indicating what frame begins with CWL or scrambling with CW2.

p0065On receiving the elementary stream is obtained by descrambling the scrambled frames with CWL. The additional flow is obtained by descrambling the frames scrambled with CW2. Sending the video or audio decoder of a single elementary stream gives an image or its gradient. Sending the video decoder and audio elementary streams accompanied by complementary flow gives a picture or sound quality.

p0066Figure 5 shows, on the first line, blurred component on the second line the degraded component when only the elementary stream has been unscrambled and, on the third line, the completely descrambled component.

p0067The choice of m and p must be fixed depending on the performance of the video or audio decoder and especially depending on its acquisition time. Generally, m is greater than p because it takes very little scrambled frames to greatly disturb the behavior of the video or audio decoder.

p0068The means used at transmission are represented in Figure 6. They comprise a multiplexer 20 with a first output 21 delivering the data in clear, a second output delivering frame synchronization, a third output delivering the numbers m and p and the frame counter and parity, and finally a fourth output 24 delivering two control messages ECM1 of access, ECM2.

p0069The means further comprises a circuit 25 containing control words used (CWL even and odd and even and odd CW2) and e scrambler 26 that uses either of these words. This circuit 25 supplies on a first output 27, the scrambled data on a second output 28, frame synchronization, a third outlet 29, the numbers m, p and the frame counter and parity.

p0070Turning now to the packet multiplex, the case is similar to that of multiplex frames, the difference lying in the transmission timing information between the scrambler and the descrambler. Indeed, in the case of the multiplex packet, the packet header can be used to convey the information that is in the packet header that will be sent scrambling information with CWL or CW2, and the parité.- This allows, in particular, to the scrambler to vary the m and p values.

p0071The number m may for example correspond to the number of packets required to code an intra picture while the number p can be the number of packets between two intra pictures.

p0072It may be noted that the scrambling of the elementary stream with the CWL control word is not mandatory. In a simplified variant, do not confuse the rank of channel i of m successive frame groups; it is confused that the rank of channel i p successive frames and this group with the control word CW2. therefore defines no access conditions CA1 and not using the CWL control word. This amounts to exerting no control over the reception of the elementary flow and offering all receivers access to the degraded picture or sound.

p0073It may be noted again, as above, that the CWL control word can be known, local control word of the receiver or a control word conveyed within an access control message.

p0074Figure 7 shows how one is the elementary stream packets with m groups to be confused with the first CWL control word, and packet p groups to be confused with the second control word CW2. The vertical lines symbolize the scrambling with CWL and horizontal lines scrambling with CW2.

p0075At the reception, the elementary stream will be obtained by descrambling the scrambled packets with CWL. The additional flow is obtained by descrambling the scrambled packet with CW2. Sending the video or audio decoder of a single elementary stream .donnera an image or its gradient. Sending the video decoder and audio elementary streams accompanied by additional flows will give a picture or sound quality.

p0076Figure 8 shows, on the first line, blurred component on the second line, the degraded component corresponding to one elementary stream descrambled, and, on the third line, the completely descrambled component (elementary stream and additional flows). Again, the choice of m and p must be set according to the video decoder and audio performance, especially depending on its acquisition time. Generally, m will be much greater than p, because it takes very little of scrambled packets to greatly disturb the behavior of the video or audio decoder.

p00779 schematically shows the means used to broadcast, in the multiplex variant packets. These means comprise a multiplexer 30 which delivers on a first output 31, the clear packets on a second output 32, packet synchronization, a third output 33, the numbers m and p and the parity and a fourth exit 34, the ECM1 access control messages, ECM 2.

p0078These means further comprises a circuit 35 containing peer CWL control words and odd and even control words CW2 and odd, and the scrambler 36 using those words. The circuit 35 delivers, on a first output 37, and the scrambled packets at a second output 38, a parity signal.

p0079In the packet multiplexing as the multiplexing frame, a particular case of implementation of the process is to set no access condition CA1 and not using the CWL control word. This amounts to exerting no control over the reception of the elementary flow and offering all receivers access to the degraded picture or sound. It can also be used as CWL control word, the known, local control word of the receiver or a control word conveyed within an access control message. Finally, you can specify an implementation of the method of the invention in the case of MPEG2 multiplex said.

p0080In the particular case of MPEG2, clean signal for scrambling in the header of each packet consists of two bits called "Transport- Scrambling Control" (TSC) in the proposed system MPEG2 standard (ISO / IEC CD 13818-1). The values ​​of these two bits are now standard 00: the packet is not scrambled

p008101: reserved

p008210: the packet is scrambled with the even control word

p008311: the packet is scrambled with the odd control word.

p0084To implement the method described above, we need to point out to either two control words decoder (odd or even), but all four control words (CWL par, par CW2, CWL odd, CW2 odd ). We must be able to indicate which of these four control words was used to scramble the packet data field. For this, we can use the value "01" today reserved. The behavior of the decoder is as follows (encoder behavior is easily deduced). It is assumed that the decoder has a parity memory (1 bit is enough) called MEM-PAR:

p0085• Initial state: MEM-PAR = 0 or 1 • Receiving a package with TSC≈'OO "no descrambling action is to be taken

p0086• Receiving a packet with TSC = "10": descrambling of the packet with CW2 even and MEM BY → -0 (that is to say, the store "0" in MEM-PAR)

p0087• Receiving a packet with TSC = "11": descrambling of the packet with CW2 odd and MEM PAR "1 (that is to say, store the value" 1 "in MEM-PAR)

p0088• Receiving a packet with TSC = "01": descrambling of the packet with CWL even if MEM PAR≈O or if MEM-odd CWL PAR≈l.

p0089The connection of the receiver, the contents of the parity memory MEM-PAR has probability 1/2 of being wrong until receipt of the first packet with TSC = "10" or "11". The maximum waiting time before being fully synchronized packet is m. It is therefore necessary, in the implementation of this variant, to ensure that this deadline is not noticeable to the user (m value as low as possible).

p0090Note that the special case of implementation of the process of not define a condition of access CA1 and not using the word CWL control is easily achieved using the TSC value = "00" instead of TSC = "01". - •

p0091The decoder only having access to the degraded image can operate in several modes: - send the video decoder unscrambled the images and the images still confused, - send the video decoder only the descrambled pictures, and the video decoder freezes the last picture received while receiving the scrambled image. 10 schematically illustrates a receiver suitable for receiving transmitted programs according to the method which has been described. In this figure, the receiver is generally indicated 40. This receiver comprises a general input 41, a demodulator 42, a demultiplexer-descrambler 44, a security processor 46, a video decoder 48, an audio decoder 50, a data decoder 52, a display 54, a speaker 56 and a personal computer 58. the signal received on the input 41 is first demodulated in circuit 42 and sent to die ultiplexeur / descrambler 44 that extracts frames or packets of the selected component and descrambles if the user has the required access rights.

p0092The signal is then sent to the video decoder 48 if it is a video signal, audio 50 if it is an audio signal decoder, or the data decoder 52 in the case of a data signal. Once the decoded signal, it is presented to the user on suitable support: 54 screen for video, speaker 56 for audio and computer 58 for data.

p0093In the case of a frame multiplex, the demultiplexer-descrambler 44 is organized according to 11.

p0094The general input E is connected to a frame demultiplexer 60 having three outputs respectively _.61 to 62 the scrambled data for frame synchronization and 63 the numbers m and p, the frame counter and parity.

p0095The - descrambler 64 receives either the even or CWL control words CW2 or the odd control words CWL, CW2 by parity and descrambles signals. The clear signals are available on the output S.

p0096The demultiplexer / descrambler analyzes the service road to get there (if not known implicitly) the values ​​of m, p and the synchronization information indicating what frame begins with the scrambling CWL or CW2.

p0097The Dem ultiplexeur / descrambler recovers ECM1 and ECM2. It sends the ECM to the decoder of the security processor (often a microprocessor card) checks for access conditions CA1 and CA2 and calculating the CWL and control words CW2 if the access conditions are met.

p0098If the user satisfies neither CA1 nor CA2, the component remains completely confused.

p0099If the user satisfies the access condition CA1, but not the condition of access CA2, he has access to a picture or sound or degraded data. The demultiplexer / descrambler descrambles the bursts of frames m confused with CWL. It thus generates a stream consisting of m frames in the clear, then p frames scrambled and again m frames plain, etc ... This stream is sent to the video decoder or audio or data.

p0100If the component is an audio component, audio decoder can decode everything (the decoding scrambled frames will result in noise on the speaker) or may decide not to decode the bursts of p remaining frames scrambled (no sound on speaker during the passage of these tι: .mes).

p0101If - the component is a video component, the video decoder can decode everything (the decoding scrambled frames will result in a noisy picture on the screen) or may decide not to decode bursts of p frames remaining scrambled and freeze on the screen during this time the last image correctly decoded.

p0102If the user meets the CA1 and CA2 access conditions, it has access to a picture or sound or completely unscrambled data.

p0103The demultiplexer / descrambler descrambles the bursts of frames scrambled with CWL and bursts of p frames scrambled with CW2. It thus generates a stream consisting of completely unscrambled frames. This stream is sent to the video or audio or data decoder.

p0104A particular case is not to define a condition of access CA1 and not using the CWL control word (bursts of m frames are light). This amounts to exerting no control over the reception of the elementary flow and offering all receivers access to the degraded picture or sound.

p0105In the case of a multiplex packet, the demultiplexer-descrambler 44 is organized according to Figure 12. The input E is connected to a packet demultiplexer 60 'having three outputs respectively 61' supplying the scrambled packets, 62 ' for packet synchronization and 63 'for m p and numbers and for parity.

p0106Descrambler 64 'receives either the even or CWL control words CW2 or the odd control words CWL, CW2, according to parity, and descrambles signaux.- clear signals are available on the output S'.

p0107The demultiplexer / descrambler retrieves the ECML and ECM2. It sends the ECM to the processor Security Decoder (often a microprocessor card) checks for access conditions CA1 and CA2 and calculating the CWL and control words CW2 if the access conditions are met. If the user satisfies neither CA1 nor CA2, the component remains completely confused.

p0108The demultiplexer / descrambler analyzes the en¬ packet header to know with which CW must descramble the packet (even CWL CWL odd, CW2 even, CW2 odd).

p0109If the user satisfies the access condition CA1, but not the condition of access CA2, he has access to an image or sound data or degraded according to the mechanism below.

p0110The demultiplexer / descrambler descrambles m packet bursts with scrambled CWL. It thus generates a stream consisting of m packets in clear and scrambled packets p and again m packets in clear, etc ... This stream is sent to the video decoder or audio or data.

p0111If the component is an audio component, audio decoder can decode everything (the decoding of scrambled packets will result in noise on the speaker) or may decide not to decode the bursts of p remaining packets confused (no sound on speaker during the passage of these packages).

p0112If the component is a video component, the video decoder can decode everything (the decoding of scrambled packets will result in a noisy picture on the screen) or may decide not to decode remaining packets per burst scrambled and freeze on screen during this time the last image correctly decoded. If the user meets the CA1 and CA2 access conditions, it has access to a picture or sound or completely unscrambled data.

p0113The demultiplexer / descrambler descrambles scrambled packet bursts with CWL and packet bursts scrambled with CW2. It thus generates a stream consisting of completely unscrambled packets. This stream is sent to the video or audio or data decoder.

p0114One particular case of implementation is not to define a condition of access CA1 and not using the CWL control word (m packets of the bursts are clear). This amounts to exerting no control over the reception of the elementary flow and offering all receivers access to the degraded picture or sound.