Patent Publication Number: US-7225458-B2

Title: Method and apparatus for ensuring reception of conditional access information in multi-tuner receivers

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is related to the following patent application, which is hereby incorporated by reference herein: 
   U.S. patent application Ser. No. 10/302,416, entitled “METHOD AND APPARATUS FOR MINIMIZING CONDITIONAL ACCESS INFORMATION OVERHEAD WHILE ENSURING CONDITIONAL ACCESS INFORMATION RECEPTION IN MULTI-TUNER RECEIVERS,” by Peter M. Klauss, Raynold M. Kahn, Gregory J. Gagnon, and David D. Ha, attorney&#39;s docket number PD-200184, filed on same date herewith. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to systems and methods for providing video program material to subscribers, and in particular to a method and system for ensuring reception of conditional access information in multi-tuner receivers. 
   2. Description of the Related Art 
   Media programs such as video and audio information can be distributed to households via a variety of methods including terrestrial transmitters, cable, the Internet, and satellites. Each of these media distribution systems implement a large number of channels, and are therefore capable of providing a large number of concurrently broadcast media programs to each household. 
   While existing systems provide a large number of channels, there is a trend towards even greater numbers of channels and greater bandwidth requirements on existing channels to accommodate, for example, HDTV. With regard to satellite-based media program distribution systems, the increased channels and bandwidth demands can be satisfied by the introduction of additional satellites and/or the use of additional transponders on the satellites. 
   In order to receive signals from each of the plurality of satellites, ground stations can include multiple antennae (each directed to a satellite of interest) coupled to a single tuner, multiple receiving elements (referred to as low noise block converters, or LNBs) using a single reflector, or multiple antennae and multiple tuners. 
   At the same time, it is important that the media programs transmitted by the satellites be protected from unauthorized reception and/or reproduction. This is accomplished by encrypting the media programs, and broadcasting data that (along with hardware disposed at the receiver station) is used to decrypt the media programs. 
   Unfortunately, when consumers go from one channel to another, the channel selection may require the receiver to switch from one tuner to the other (since the second channel is being transmitted by a different satellite than the first channel). In some cases, this switching from one tuner to the other can temporarily interrupt the reception of the information required to decrypt the desired media information. This problem is especially notable when the user is rapidly changing channels, or “channel surfing.” 
   What is needed is a system and method for assuring that the information required to decrypt media programs is readily available, even in circumstances when a channel command requires switching tuners from one to another. The present invention satisfies that need. 
   SUMMARY OF THE INVENTION 
   In summary, the present invention describes a system and method for receiving conditional access information (CAI) on one or more of a plurality of tuners while the user is selecting different channels. The method comprises the steps of receiving the CAI on a first tuner tuned to a first channel; identifying the first tuner as the tuner receiving the CAI; and commanding the second tuner to receive the CAI after receiving a command to retune the first tuner from the first channel to a second channel. In one embodiment, the apparatus comprises a receiver for receiving a media program and conditional access information (CAI) for decrypting the media program. The receiver comprises a first tuner tunable to a first channel to receive the CAI; a second tuner tunable to the first channel and the second channel; and a verifier, communicatively coupled to the first tuner and the second tuner, the verifier for decrypting the media program using the conditional access information (CAI), for identifying the first tuner as the tuner receiving the CAI, and for commanding the second tuner to receive the CAI after the receiver is commanded to retune the first tuner from the first channel to a second channel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings in which like reference numbers represent corresponding parts throughout: 
       FIG. 1  is a diagram showing an overview of a video distribution system; 
       FIG. 2  is a block diagram showing a typical uplink configuration showing how video program material is uplinked to a satellite for transmission to subscribers using a single transponder; 
       FIG. 3A  is a diagram of a representative data stream received from a satellite; 
       FIG. 3B  is a diagram illustrating the structure of a data packet; 
       FIG. 4  is a block diagram illustrating a high-level block diagram of the IRD; and 
       FIGS. 5A–5C  are flow charts presenting illustrative process steps that can be used to practice one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   In the following description, reference is made to the accompanying drawings which form a part hereof, and which show, by way of illustration, several embodiments of the present invention. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
   Video Distribution System 
     FIG. 1  is a diagram illustrating an overview of a video distribution system  100 . The video distribution system  100  comprises a control center  102  in communication with an uplink center  104  via a ground link  114  and an integrated receiver/decoder (IRD)  132  at receiver station  130  via a public switched telephone network (PSTN) or other link  120 . The control center  102  provides program material to the uplink center  104 , coordinates with the receiver station  130  to offer subscribers  110  pay-per-view (PPV) program services, including billing and associated decryption of video programs. 
   The uplink center  104  receives program material and program control information from the control center  102 , and using an uplink antenna  106 , transmits the program material and program control information to the satellite  108 . The satellite  108  receives and processes this information, and transmits the video programs and control information to the subscriber  110  at the receiver station  130  via downlink  118 . The subscriber  110  receives this information using the subscriber antenna  112  communicatively coupled to the IRD  132 . 
   The video distribution system  100  can comprise a plurality of satellites  108  in order to provide wider terrestrial coverage, to provide additional channels, or to provide additional bandwidth per channel. In one embodiment of the invention, each satellite comprises 16 transponders to receive and transmit program material and other control data from the uplink center  104  and provide it to the subscribers  110 . However, using data compression and multiplexing techniques the channel capabilities are far greater. For example, two satellites  108  working together can receive and broadcast over 150 conventional (non-HDTV) audio and video channels via  32  transponders. 
   While the invention disclosed herein will be described with reference to a satellite based video distribution system  100 , the present invention may also be practiced with terrestrial-based transmission of program information, whether by traditional broadcasting means, cable, or other means. Further, the different functions collectively allocated among the control center  102  and the uplink center  104  as described above can be reallocated as desired without departing from the intended scope of the present invention. 
   Although the foregoing has been described with respect to an embodiment in which the program material delivered to the subscriber is video (and audio) program material such as a movie, the foregoing method can be used to deliver program material comprising purely audio information or data as well. 
     FIG. 2  is a block diagram showing a typical uplink configuration for a single satellite  108  transponder, showing how video program material is uplinked to the satellite  108  by the control center  102  and the uplink center  104 .  FIG. 2  shows three video channels (which could be augmented respectively with one or more audio channels for high fidelity music, soundtrack information, or a secondary audio program for transmitting foreign languages), and a data channel from a computer data source  206 . 
   The video channels are provided by a program source of video material  200 A– 200 C (collectively referred to hereinafter as video source(s)  200 ). The data from each video program source  200  is provided to an encoder  202 A– 202 C (collectively referred to hereinafter as encoder(s)  202 ). Each of the encoders accepts a program time stamp (PTS) from the controller  216 . The PTS is a wrap-around binary time stamp that is used to assure that the video information is properly synchronized with the audio information after encoding and decoding. A PTS time stamp is sent with each I-frame of the MPEG encoded data. 
   In one embodiment of the present invention, each encoder  202  is a second generation Motion Picture Experts Group (MPEG-2) encoder, but other decoders implementing other coding techniques can be used as well. The data channel can be subjected to a similar compression scheme by an encoder (not shown), but such compression is usually either unnecessary, or performed by computer programs in the computer data source (for example, photographic data is typically compressed into *.TIF files or *.JPG files before transmission). After encoding by the encoders  202 , the signals are converted into data packets by a packetizer  204 A– 204 F (collectively referred to hereinafter as packetizer(s)  204 ) associated with each source  200 . 
   The data packets are assembled using a reference from the system clock  214  (SCR), a control word (CW) generated by the conditional access manager  208 , and a system channel identifier (SCID) that associates each of the data packets that are broadcast to the subscriber with a program channel. This information is transmitted to the packetizers  204  for use in generating the data packets. These data packets are then multiplexed into serial data, encoded, modulated, and transmitted. A special packet known as a control word packet (CWP) which comprises control data including the control word (CW) and other control data used in support of providing conditional access to the program material is also encrypted and transmitted. 
     FIG. 3A  is a diagram of a representative data stream. The first packet segment  302  comprises information from video channel  1  (data coming from, for example, the first video program source  200 A). The next packet segment  304  comprises computer data information that was obtained, for example from the computer data source  206 . The next packet segment  306  comprises information from video channel  5  (from one of the video program sources  200 ), and the next packet segment includes information from video channel  1  (again, coming from the first video program source  200 A). The data stream therefore comprises a series of packets from any one of the data sources in an order determined by the controller  216 . The data stream is encrypted by the encryption module  218 , modulated by the modulator  220  (typically using a QPSK modulation scheme), and provided to the transmitter  222 , which broadcasts the modulated data stream on a frequency bandwidth to the satellite via the antenna  106 . 
   Subscribers  110  receive media programs via a subscriber receiver or IRD  132 . Using the SCID, the IRD  132  reassembles the packets to regenerate the program material for each of the channels. As shown in  FIG. 3A , null packets created by the null packet module  312  may be inserted into the data stream as desired. 
     FIG. 3B  is a diagram of a data packet. Each data packet (e.g.  302 – 316 ) is 147 bytes long, and comprises a number of packet segments. The first packet segment  320  comprises two bytes of information containing the SCID and flags. The SCID is a unique 12-bit number that uniquely identifies the data packet&#39;s data channel. The flags include 4 bits that are used to control whether the packet is encrypted, and what key must be used to decrypt the packet. The second packet segment  322  is made up of a 4-bit packet type indicator and a 4-bit continuity counter. The packet type identifies the packet as one of the four data types (video, audio, data, or null). When combined with the SCID, the packet type determines how the data packet will be used. The continuity counter increments once for each packet type and SCID. The next packet segment  324  comprises 127 bytes of payload data, which is a portion of the video program provided by the video program source  200 . The final packet segment  326  is data required to perform forward error correction. 
   Encryption of Media Programs 
   Media programs are encrypted by the encryption module  218  before transmission to assure that they are received and viewed only by authorized subscribers. Each media program is encrypted according to an conditional access information (CAI). In one embodiment, the conditional access information includes an alphanumeric encryption key referred to hereinafter as a control word (CW). This encryption can be accomplished by a variety of data encryption techniques, including the data encryption standard (DES) and the Rivest-Shamir-Adleman (RSA) algorithm. 
   To decrypt the media programs, the subscriber&#39;s  110  IRD  132  must also have access to the CW. To maintain security, CWs are not transmitted to the IRD  132  plaintext. Instead, CWs are encrypted before transmission to the subscriber&#39;s IRD  132 . The encrypted CW is transmitted to the subscriber&#39;s IRD  132  in a control word (data) packet. 
   In one embodiment, the data in the control word packet (CWP) (which is also hereinafter alternatively referred to as a conditional access packet (CAP)), including the CW, is encrypted and decrypted via what is referred to hereinafter as an input/output (I/O) indecipherable algorithm. 
   An I/O indecipherable algorithm is an algorithm that is applied to an input data stream to produce an output data stream. Although the input data stream uniquely determines the output data stream, the algorithm selected is such that it&#39;s characteristics cannot be deciphered from a comparison of even a large number of input and output data streams. The security of this algorithm can be further increased by adding additional functional elements which are non-stationary (that is, they change as a function of time). When such an algorithm is provided with identical input streams, the output stream provided at a given point in time may be different than the output stream provided at another time. 
   So long as the encryption module  218  and the IRD  132  share the same I/O indecipherable algorithm, the IRD  132  can decode the information in the CWP to retrieve the CW. Then, using the CW, the IRD  132  can decrypt the media program so that it can be presented to the subscriber  110 . 
   To further discourage piracy, the control data needed to decrypt and assemble data packets into viewable media programs may be time-varying (the validity of the control data in a CWP to decode a particular media program changes with time). This can be implemented in a variety of ways. 
   For example, since each CWP is associated with a SCID for each media program, the SCID related to each CWP could change over time. 
   Another way to implement time-varying control data is to associate time stamps with the received data stream and the CWP control data. In this case, successful decoding of the CWP to produce the CW would require the proper relationship between the time stamps for the data stream and the control data in the CWP. This relationship can be defined, for example, by changing the decryption scheme used to generate the CW from the CWP according to the received time stamp for the data stream. In this case, if the time stamp of the received data stream does not match the expected value, the wrong decryption scheme will be selected and the proper CW (to decrypt the program material) will not be produced. If, however, the time stamp of the received data stream matches the expected value, the proper decryption scheme will be selected, and the CWP decryption scheme will yield the proper CW. 
   Subscriber Reception and Decryption of Media Programs 
     FIG. 4  is a simplified block diagram of an IRD  132 . The IRD  132  receives and decrypts the media programs broadcast by the video distribution system  100 . These media programs are streamed to the IRD  132  in real time, and may include, for example, video, audio, or data services. 
   The media programs may be transmitted by a plurality of satellites such as satellite  108 A and  108 B (hereinafter alternatively collectively referred to as satellite(s)  108 , each of which typically includes a plurality of transponders  450 – 456 . 
   The IRD  132  is communicatively coupleable to a conditional access module (CAM)  406 . The CAM  406  is typically implemented in a smart card or similar device, which is provided to the subscriber  110  to be inserted into the IRD  132 . The CAM  406  interfaces with a conditional access verifier (CAV)  408  which performs at least some of the functions necessary to verify that the subscriber  110  is entitled to access the media programs. The CAV is communicatively coupled to the tuner(s)  410  via other elements in the IRD  132 , including the microcontroller and memory  414 . 
   In the illustrated embodiment, the CAV  414  is also communicatively coupled to the tuners  410 . This permits the CAV to receive information from the tuners regarding which satellite/transponder/channel each tuner is tuned to and to supply commands to the tuners  410  to switch channels at appropriate times. In another embodiment, the CAV  414  is not directly coupled to the tuners, but receives information regarding the tuners  410  via the microprocessor and memory  414  (which controls the tuners and receives information from them) and provides commands to the tuners via the microprocessor and memory  414  as well. 
   The CAV  408  may be communicatively coupled to the CAM  406  via a metadata analysis module (MAM)  411 . Using the information such as that which can be stored in a metadata table, the MAM  411  acts as a gate-keeper to determine whether stored media programs will be decrypted and presented to the subscriber  110 . This is accomplished by comparing the metadata values with measured or accumulated values. The CAV  408  and the MAM  411  can be implemented as separate modules from the transport/demux/decryptor  412  and the microcontroller and memory  414  as shown, or may be implemented via software instructions stored in the memory and performed by the microcontroller  414 . 
   In one embodiment, the IRD  132  comprises a plurality of tuners such as first tuner  410 A and second tuner  410 B and nth tuner  410 N (alternatively referred to hereinafter as tuner(s)  410 ), a transport and demultiplexing module (TDM)  412 , which operates under control of a microcontroller and associated memory  414 , a source decoder  416  and communicatively coupled random access memory (RAM)  418 , and a user I/O device for accepting subscriber  110  commands and for providing output information to the subscriber. 
   Each of the tuners  410  receive the data packets from the video distribution system and provides the packets to the TDM  412 . The use of multiple tuners  410  allows the IRD  132  to quickly tune a signal from one of a plurality of satellites without moving the antenna or the antenna reflector. The use of two tuners also allows the IRD  132  to receive media program information at a higher bandwidth by receiving information with both tuners simultaneously. This can be implemented by dedicating each tuner to a different low noise block converter (LNB) or an entirely different antenna than the other tuner  410 . 
   Using the SCIDs associated with each media program, the TDM  412  reassembles the data packets according to the channel selected by the subscriber  110 , and unencrypts the media programs using the CW key. The TDM  412  can be implemented by a single secure chip, and is communicatively coupled to a microcontroller and memory  414 . 
   Once the media programs are unencrypted, they are provided to the source decoder  416  which decodes the media program data according to MPEG or JPEG standards as appropriate. The decoded media program is then provided to a D/A converter (if necessary) and provided to external interfaces  404  which can include a media program presentation device such as a television, an audio system, or a computer. The source decoder  416  makes use of communicatively coupled RAM  418  to perform these functions. 
   The CW key is obtained from the CWP using the CAV  408  and the CAM  406 . The TDM  412  provides the CWP to the CAM  406  via the CAV  408 . The CAM  406  uses the I/O indecipherable algorithm to generate the CW, which is provided back to the TDM  412 . The TDM  412  uses the CW to decrypt the media programs. In most IRDs  132 , the CAV  408  and the CAM  406  are capable of decrypting one video/audio/data media program at a time. 
   As described above, to discourage potential pirates, the control data in the CWP used to decode a particular media program may change with time so that it only produces the proper CW when applied to a media program having the proper time stamp. In this case, the CAM  406  can select and/or control the decryption scheme (e.g. the I/O indecipherable algorithm) according to the time stamp associated with the data stream carrying the media program. If the media program is sufficiently disassociated in time, the improper decryption scheme will be used, and the proper CW to decode the media program will not be produced. 
   Further details regarding the encryption and decryption of media programs can be found in co-pending and commonly assigned U.S. patent application Ser. No. 09/491,959, which application is hereby incorporated by reference herein. 
     FIG. 5A  is a flow chart presenting illustrative process steps that can be used to practice one embodiment of the present invention. Conditional access information (CAI) is received on a first tuner  410 A tuned to a first channel, as shown in block  502 . This CAI is used, for example, to decrypt the media program currently being viewed the user. A command is received to change the channel being viewed by the user, as shown in block  504 . The receiver  132  identifies which of the tuners (e.g.  410 A,  410 B . . .  410 N) is receiving the CAI, as shown in block  506 . This can occur after the receipt of the channel change command (as illustrated in  FIG. 5A ), after the channel change command, or may be determined periodically or on an ongoing basis. A determination is made as to whether the channel change command would require retuning the first tuner (the tuner currently receiving the CAI) away from the current channel (e.g. to another channel), as shown in block  508 . If this is the case, there is the possibility that the receipt of the CAI information will be temporarily interrupted, compromising the user&#39;s ability to surf rapidly from one channel to another. 
   A command is provided to a different tuner (e.g. second tuner  410 B or  410 N) to tune to a channel (and a satellite/transponder combination) to receive the CAI information required to decrypt the media program provided on the selected channel. This is shown in block  510 . The first tuner is the retuned from the first channel to the second channel, as was implicated in the channel command. Since the second tuner is now receiving the CAI, the change in channels can be performed without a temporary interruption in the decryption of the media program, as shown in block  514 . 
   In one embodiment, the first tuner is not retuned from the first channel to the second channel until it is confirmed that the second tuner is receiving the CAI. This is shown in block  512 . This effectively prevents any channel change to be performed until an appropriate CAI is received. 
     FIG. 5B  is flow chart illustrating exemplary process steps that can be used to practice another embodiment of the invention. In this embodiment, the tuning step shown in block  510  includes a determination as to which of the plurality of tuners  410  should be selected to receive the CAI. Of the available tuners, this technique chooses the tuner that is retuned least often, as shown in block  518 . Since this tuner is historically retuned less often than the others, using this tuner to receive the CAI should result in fewer service disruptions (e.g. the decision shown in block  508  will result in a “no” more often than if the other tuners were utilized). 
     FIG. 5C  is a flow chart illustrating another embodiment of the present invention. In this embodiment, in performing the operation of block  510 , each of the tuners  410 A– 410 N are selected in order in a round-robin fashion (e.g.  410 A,  410 B,  410 N,  410 A,  410 B,  410 N . . . ). This is shown in block  520 . Since this only occurs when block  508  determines that the commanded channel change requires that the tuner receiving the CAI information change from one channel to another, the round robin selection of the next succeeding tuner will assure that the tuners that are more typically tuned to the CAI channels remain so. In other words, if a particular channel is dedicated to receiving the CAI information, the round robin technique will eventually select that channel, and no further retuning will be required. Further in cases where a particular tuner is not dedicated to receive CAI information, but infrequently receives anything else, the round robin technique will eventually select that channel for receiving the CAI information, and the tuner will remain tuned to that channel until such time (which is infrequent) as the tuner is required to tune to another. Therefore, using the round robin technique, the channels which are statistically more likely to not require retuning are tuned to statistically more often. 
   The foregoing method steps can be implemented in a number of ways, including by use of software modules and hardware modules having a plurality interconnected circuit elements. In one embodiment of the present invention, the steps shown in  FIGS. 5A–5C  are performed at least in part in the CAV  408 , by a hardware module and/or a software module. The processor for performing the operations defined in the software module may be stored in a CAV  408  dedicated memory coupled to a CAV  408  dedicated processor, or may be performed by the microcontroller and associated memory  414 . Other elements, such as the CAM  406  and/or the microcontroller and memory  414  may perform some or all of the functions described in  FIGS. 5A–5C . 
   CONCLUSION 
   The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. For example, the encryption functions described herein could be performed by separate encryption/decryption modules, or a single multi-purpose encryption/decryption module can be utilized to perform the encryption/decryption functions of many separate modules. 
   It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.