Abstract:
There is provided a method and apparatus for tuning a digital television channel. More specifically, in one embodiment, there is provided a method comprising receiving a request to access a first digital television channel, downloading a first program map table associated with a frequency of the first digital television channel, storing the first program map table, receiving a request to access a second digital television channel, determining if the second digital television channel is associated with the frequency of the first digital television channel, and creating a conditional access program map table for the second digital television channel based on the stored program map table if the second digital television channel is associated with the frequency.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Phase 371 Application of PCT Application No. PCT/US06/043455, filed Nov. 6, 2006, entitled “METHOD AND APPARATUS FOR TUNING A DIGITAL TELEVISION CHANNEL”. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an apparatus and method for digital television reception, and in particular, an apparatus and method for caching or storing conditional access information that reduces the time required to change channels in a digital television system. 
       BACKGROUND OF THE INVENTION 
       [0003]    This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
         [0004]    Television transmission and reception systems in the United States and abroad are currently transitioning from analog- to digital-based content delivery mechanisms. Consumer demand for digital television services is driven by the improved resolution and overall quality of the digital content (audio and video) compared to prior analog content, as well as the additional content and services offered with digital television services. 
         [0005]    For the broadcaster, digital television imposes requirements different from its analog predecessor. Among these requirements is the need for access security, to ensure that only paying subscribers are permitted access to subscription content, for example premium channels, pay-per-view (PPV) programs, video-on-demand (VOD) content, personal video recording (PVR) functionality, online gaming, and/or Internet access. Although access security is not a new problem, in that it was implemented in prior analog broadcasting systems, digital content delivery presents a new frontier of piracy and “bootlegging” in which the stakes are much higher for broadcasters and content developers. 
         [0006]    Previously, video and audio content was distributed in analog format, for example using analog video tapes and analog cable television, and unauthorized copies were difficult to produce in quantity and usually substandard in quality. However, current digital techniques have eased the production of high-quality copies to the point that pirates and “bootleggers” are beginning to compete with authorized distributors in the dissemination of content. One solution to this problem is improved access security. 
         [0007]    Digital encryption is one popular type of access security particularly suited to protect digital content. The digital content is “scrambled” during encryption in such a way that only those possessing a “decryption key” are able to descramble and receive the content. For example, a popular form of encryption known as “Data Encryption Standard” (DES) involves the exchange of a “DES key” between a content distributor and intended recipient of the content. The “DES key” is used to encrypt or scramble the digital content one or more times using a particular mathematical method, and only those in possession of the “DES key” (and having knowledge of the mathematical method) can successfully decrypt or descramble the digital content. 
         [0008]    The mathematical method and “DES key” are specifically designed to impose a severe burden on those attempting to “guess” or discover the “DES key” without authorization from the content distributor. For example, the “DES key” may consist of a string of digital bits (i.e. “1” or “0”) in a particular order, in which the string may be 56 or more bits in length. The “DES key” string of bits may be computed using random digital bits in a public-private key exchange, e.g., a Diffie Hellman public key exchange, additional keys may then be derived by applying a secure hash algorithm (SHA), and/or a Dynamic Feedback Arrangement Scrambling Technique (DFAST) engine may be used to generate a 56-bit DES key that is not explicitly shared between distributor and subscriber. In addition, each DES key so computed may be used for only a brief period of time (e.g., 2 seconds), and then the DES key may be changed. In this way, unauthorized persons may find it difficult or impossible to determine many DES keys and descramble the content of an entire program in a reasonable amount of time. 
         [0009]    Digital television distributors, including distributors of digital television content via, for example, terrestrial signal, cable, satellite, internet and digital subscriber line (DSL), use the moniker “conditional access” to describe their implementations of access security such as DES digital encryption. The specifics of “conditional access” usually vary from distributor to distributor, but have the common goal of preventing unauthorized access to designated program content. Recent implementations have involved broadcasting some “conditional access” information along with the digital content to be received, for example public key information in the public-private key exchange may be transmitted in addition to audio and video content. 
         [0010]    In addition to “conditional access” information, digital television distributors usually broadcast a variety of other information that may be necessary for acquiring the program, or complements the audio and video data associated with the program. For example, program map table (PMT), program system information (PSI), program and packet identifiers (PID), electronic program guide (EPG), emergency alert system (EAS), and other command and control messages such as conditional access information may be transmitted in frequency bands inside or outside the frequency band associated with the selected television program (i.e., “in-band” or “out of band” (OOB)). The other information may correspond to data necessary to conform with various digital standards, such as, MPEG-2. This complementary information may provide to the end user information about upcoming programs, “conditional access” program information, and data for use by the receiving equipment in collecting and processing the broadcast digital content for use, e.g., display by a television set. 
         [0011]    Due to the limited capacity or bandwidth of current digital distribution systems, the complementary information including “conditional access” program information may be transmitted or updated at a rate somewhat less than that used for television audio and video content. For example, the program map table (PMT) may be transmitted once every 400 milliseconds, while the audio and video content may be updated more frequently. More specifically, when a user/subscriber selects a “conditional access” program for display, traditional systems require current information included in the PMT in order to acquire the information required to display the “conditional access” program. Therefore, each channel change requires that the current PMT be received, i.e. each such channel change associated with conditional access programming may require at least 400 milliseconds of wait time for display. This wait time may result in an unsatisfactory experience for a user/subscriber. 
         [0012]    Given that the satisfaction of paying subscribers may be jeopardized by the significant wait time required for “conditional access” programming, there is a need for a digital television receiver capable of reducing the amount of time required for channel changes associated with conditional access programming, designed for delivery of a variety of digital content, and may be suitable for use with conventional cable television delivery systems. One approach for reducing the amount of time required for channel changes involves caching (or storing) a complete copy of the PMT on memory within the digital television receiver. Although effective, this approach is not commercially feasible due to the large amount of memory required and its associated cost. 
         [0013]    An improved technique for tuning digital television channels would be desirable. 
       SUMMARY OF THE INVENTION 
       [0014]    Certain aspects commensurate in scope with the disclosed embodiments are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below. 
         [0015]    There is provided a method and apparatus for tuning a digital television channel. More specifically, in one embodiment, there is provided a method comprising receiving a request to access a first digital television channel, downloading a first program map table (“PMT”) ( 109 ) associated with a frequency of the first digital television channel, storing the first PMT, receiving a request to access a second digital television channel, determining if the second digital television channel is associated with the frequency of the first digital television channel, and creating a conditional access PMT ( 108 ) for the second digital television channel based on the stored PMT if the second digital television channel is associated with the frequency 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Advantages of the invention may become apparent upon reading the following detailed description and upon reference to the drawings in which: 
           [0017]      FIG. 1  is a simplified block diagram illustrating an exemplary digital television system in accordance with one embodiment of the present invention; 
           [0018]      FIG. 2  is a flow chart illustrating an exemplary technique for tuning a digital television channel in accordance with one embodiment of the present invention; and 
           [0019]      FIG. 3  is a pictorial block diagram illustrating an exemplary system employing a digital television receiver in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
         [0021]    Looking now to the figures and turning initially to FIG. a simplified block diagram illustrating an exemplary digital television system in accordance with one embodiment is illustrated and generally designated by a reference numeral  100 . As illustrated, the digital television system  100  may include a digital television receiver  101 , which may include a tuner  103  coupled to a network source  102 , a link/demodulation block  104 , an out of band receiver/tuner  105 , a point of deployment (POD) module  107 , a microprocessor system  110  including random access memory (RAM)  111 , and a transport demultiplexer  113 , which outputs a decrypted video stream  114  to a display system  115 . 
         [0022]    In operation, a broadcast carrier modulated with signals carrying audio, video, and associated data representing broadcast program content is received from network source  102  by tuner  103 , which may utilize hardware and/or software components to successfully tune the in-band quadrature amplitude modulated (QAM) channel using any one of a plurality of known modulation techniques. The tuner  103  may then produce an in-band digital output signal, which is coupled to the link/demodulation block  104 , and out of band signals are coupled to the out of band receiver/tuner  105 . “In band” refers to those signals transmitted using a carrier frequency traditionally associated with television transmission and reception (e.g., VHF channel  13 ), while “out of band” (OOB) refers to signals sent via frequencies associated with the selected television program. Information contained in the OOB signals is coupled to the POD module  107  after being tuned/received/demodulated in the OOB receiver/tuner  105 . 
         [0023]    The in-band digital output is demodulated in link/demodulator block  104 . The demodulated output from block  104  includes encrypted digital video signals  106  (as well as other encrypted digital signals, e.g. audio) which are coupled to the POD module  107  for descrambling. The demodulated output from block  104  further includes auxiliary information necessary for tuning and for generating an electronic program guide, including, but not limited to, program system information (PSI), program association table (PAT), and program map table (PMT) information  109 , which are coupled to the microprocessor  110 . The microprocessor system  110 , including software and hardware such as RAM  111 , builds a conditional access program map table (CA_PMT)  108  using the PMT information  109 , including extracting conditional access descriptors and other information in accordance with, for example, EIA-679B Part B, section 8.4.3.4. 
         [0024]    The digital television receiver  101  may also include a PMT cache  120  for storing the PMT information  109  for the most recently accessed digital channel frequency. For example, the PMT cache  120  may include one or more discrete memory devices, or the PMT cache  120  may comprise a set of logical addresses (e.g., in the RAM  111 ). Alternatively, the PMT cache  120  may include one or more special purpose memory devices, for example EEPROM, flash memory, or other volatile or non-volatile memory technology devices known in the art. 
         [0025]    As will be described further with regard to  FIG. 2 , the digital television receiver  101  may be configured to store the PMT information  109  associated with the most recently accessed digital channel frequency in the PMT cache  120 . Consequently, the digital television receiver  101  may be able to generate the CA_PMT  108  for any of the plurality of digital channel carried by the most recently accessed digital channel frequency without having to await the demodulated output from block  104 . In this way, channel change requests for digital channel on the most recently accessed frequency can be fulfilled without incurring the delay associated with receiving new in-band PMT information  109 . Rather, the PMT information  109  corresponding to the requested channel may be retrieved from the cache  120  in a substantially shorter amount of time. 
         [0026]    After the CA_PMT  108  is generated, it may be transmitted to the POD module  107 , which acquires the required information for descrambling the encrypted video signals  106  (as well as other signals, e.g. audio). Following processing in the POD module  107 , a transport datastream consisting of packets of digital data is coupled to the transport demultiplexer block  113 , along with encryption keys (e.g., DES keys)  112 , packet identifiers, and other information. 
         [0027]    At the transport demultiplexer block  113 , decoding of the transport datastream occurs including separation into audio and video signals, for example Motion Picture Expert Group version 2 (MPEG2) decoding may take place. Further decryption of the digital content may occur in the transport demultiplexer block  113 , for example, video and audio descrambling using DES decryption may be used prior to coupling the decrypted video  114  (and other content, e.g. audio) to the display system  115  for final decoding and display. 
         [0028]    It should be appreciated that the digital tuner  103  in accordance with the above-described embodiment is not so limited to the above described operations, but rather the digital tuner  103  may also perform a variety of other suitable processing operations prior to providing in-band digital output signals suitable for use in the link/demodulation block  104 . For example, the digital tuner  103  may perform coding, decoding, scrambling, descrambling, rotating, and/or derotating operations prior to passing the digital output signals to link/demodulation block  104 . 
         [0029]    As described above, the digital television receiver  101  may be configured to store the PMT information  109  for one or more digital television frequencies in order to decrease the time between digital channel changes. Accordingly,  FIG. 2  is a flow chart illustrating an exemplary technique  200  for tuning a digital television channel in accordance with one embodiment. In one embodiment, the digital television receiver  101  may execute the technique  200 . In alternate embodiments, however, other suitable digital television systems may employ the technique  200 . 
         [0030]    As illustrated by block  202  of  FIG. 2 , the technique  200  may begin by receiving a request to access a digital television channel. For example, in one embodiment, the digital television receiver  101  may receive a channel request from a user via a television remote control. After receiving the request to access the digital television channel, the technique  200  may include downloading the PMT information  109  associated with the frequency of the requested digital television channel, as indicated by block  204 . For example, as will be appreciated by those of ordinary skill in the art, a single digital television frequency may carry multiple digital television channels. As such, downloading the PMT information associated with the frequency of the requested digital television channel may include downloading the PMT information  109  for a multitude of digital television channels besides the requested digital television channel. 
         [0031]    After the PMT information  109  associated with the frequency of the requested digital television channel has been downloaded, they may be stored in memory, as indicated by block  206 . For example, in one embodiment, the downloaded PMT information  109  may be stored in the PMT cache  120 . As illustrated, the technique  200  may also include generating a CA_PMT for the requested digital channel based on the stored PMT information  109  for that digital channel, as indicated by block  208 . In one embodiment, generating the CA_PMT may proceed as outlined above with regard to  FIG. 1 . After generating the CA_PMT, the technique  200  may involve displaying the requested digital channel, as indicated by block  209 . 
         [0032]    At some point after displaying the digital channel, the technique  200  may include receiving a request to access another digital television channel, as indicated by block  210 . After receiving the request to access another digital television channel, the technique  200  may involve determining whether the newly requested digital television channel is on the same frequency as the previously accessed digital television channel (block  212 ). If the newly requested digital television channel is on the same digital television frequency as the previously requested digital television channel, the technique  200  may include generating a CA_PMT for the newly requested digital channel based on the stored PMT information  109 , as indicated by block  214 . After generating the CA_PMT for the newly requested digital channel, the technique  200  may display the newly requested channel (block  215 ) and then cycle back to block  210  and await another digital television channel request. 
         [0033]    If, however, the newly requested digital television channel is on a different digital television frequency than the previously requested digital television channel, the technique  200  may include downloading the PMT information  109  associated with the frequency of the newly requested digital television channel, as indicated by block  216 . After downloading the PMT information  109  associated with the frequency of the new digital television channel request, the technique  200  may cycle back to block  206  and proceed as described above. In one embodiment, the technique  200  may then involve overwriting the PMT information  109  associated with the originally requested digital television channel. 
         [0034]    Looking next at  FIG. 3 , a digital television reception system  300  in accordance with one embodiment is illustrated. For simplicity, like reference numerals have been used to designate those features previously described in regard to  FIG. 1 . The digital television reception system  300  includes a source signal reception device  302 , the digital television receiver  101 , a program display device  315 , and a program recording device  316 . The source signal reception device  302  may include, for example, a conventional antenna configured to receive terrestrial or over-the-air (OTA) television signals. Of course, it should be apparent that source signal reception device  302  is not so limited, and may include one or a plurality of reception devices configured for placement at ground level or otherwise and configured to receive analog or digital terrestrial television signals, satellite television signals, cable television signals, or other television signals desired to be received. The source signal reception device  302  may include amplifiers, pre-amplifiers, or other components for television reception as is well known in the art. The source signal reception device  302  may be coupled to the digital television receiver  101  via coaxial cable, fiber optic cable, ribbon cable, high speed data transmission line, or other signal transmission conduit known in the art. 
         [0035]    The digital television receiver  101  includes the tuner  103 , the link/demodulation block  104 , the out of band receiver/tuner  105 , the point of deployment (POD) module  107 , the microprocessor system  110  including the random access memory (RAM)  111  and the PMT cache  120 , and the transport demultiplexer block  113 , configured as described above with reference to  FIG. 1 . The output signals from the receiver  101  are coupled to the program display device  315  and program recording device  316 , respectively. The program display device  315  and the program recording device  316  may include, for example, a wide-screen television display, audio processor/receiver and speakers, personal video recorder (PVR), interactive television device configured to permit Internet browsing, personal computer, or other devices with which descrambled and/or decoded digital television content may be used. 
         [0036]    Although the embodiments described above were described using the environment of reception of digital cable television signals, it should be apparent that the invention may be used in other types of radio-frequency communications systems as well, including reception of digital television channels via satellite, DSL, Internet, and terrestrial television transmission systems. Moreover, while the invention has been described in detail in connection with the preferred embodiments known at the time, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.