Abstract:
A method and apparatus for receiving a digital cable or digital satellite video signal which contains a composite of several digital video channels and converting a plurality of selected channels to analog CATV formatted channels, producing a single composite analog CATV compliant output signal is described. The composite analog CATV output signal is distributed throughout a users premises to one or m ore standard analog televisions, which enables each television to receive digital video content without the need for a dedicated set top box for each television. The apparatus also includes several novel and unique features which enhance the convenience for the user which include selectable re-mapping of specific digital television channels to analog CATV channels, user and service provider conditional access means, television guide means, symbology overlay means, multiple picture in picture means and S-video output means.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to devices for processing digital video and more particularly relates to a method and device for the demodulation of digital video and conversion to analog video format.  
           [0002]    Digital technology is rapidly becoming the technology of choice for many types of video and audio communications. Efficient data compression techniques and the availability of increased digital signal processing capabilities have enabled more audio and video information to be digitally transmitted in the same bandwidth as analog modulation techniques. Both digital cable and digital satellite television, commonly referred to as DVB take advantage of digital modulation techniques to efficiently deliver an impressive amount of video information to their subscribers.  
           [0003]    Today, the vast majority of televisions in use support receiving and demodulating analog video formats which conform to NTSC, PAL or SECAM. Additionally, most modern televisions support receiving analog cable television (CATV) with up to 200 channels. However, digital satellite television (DVB-S) and digital cable (DVB-C) are becoming more common as an efficient means to distribute large amounts of video content. Digital modulation techniques employed in DVB are typically not directly compatible with the majority of analog televisions. Thus, heretofore, in order to view DVB content on an analog television, it has been most common to utilize a separate digital video demodulator which converts the digital video to an appropriate standard analog format which can then be applied to a television which supports the analog format. The device that performs the demodulation and conversion from digital video to analog video is typically referred to as a set-top-box (STB) or integrated receiver decoder (IRD). Heretofore, each IRD is capable of demodulating only one digital video channel and producing an associated video signal modulated in a standard analog video format such as NTSC, PAL or SECAM for viewing on a standard analog television. Thus, in homes which have either digital cable or digital satellite and multiple televisions, it has been necessary to add an IRD and coax cabling for each television to enable viewing of the digital video content. As a result, the cost of adding an IRD for each television, coupled with the installation cost and complexities and compounded by the physically obtrusive nature of an IRD has resulted in a significant barrier to entry for digital cable or digital satellite television. This barrier to entry significantly limits the popularity and growth of digital television services and also presents a burden to the digital cable and satellite television service providers which typically subsidize IRD equipment and installation costs.  
           [0004]    It is an object of the present invention to provide an economical, accurate, and physically non-intrusive method and apparatus for converting multiple received DVB channels to analog cable TV (CATV) format such that the composite analog CATV video signal may be distributed over the existing coax cable network which exists in most homes, effectively enabling the digital video content to be distributed throughout the home to multiple televisions without the need for additional set top boxes or cabling for each television. It is another object of the current invention for the apparatus to be implemented into Application Specific Integrated Circuit, such that it may be very economically integrated with existing IRD technology.  
         SUMMARY OF INVENTION  
         [0005]    It is a general object of the present invention to provide a method for simultaneously converting multiple digital cable and digital satellite video channels to multiple analog CATV formatted channels. It is a more specific object of the present invention to provide a method for simultaneously converting multiple digital cable and digital satellite television channels to standard analog CATV formatted channels which include NTSC, PAL, and SECAM. The present invention provides an innovational design which incorporates state of the art digital signal processing technology to provide precise action, increased accuracy, lower cost, and added functionality over known existing products. The apparatus also includes several novel and unique features which enhance the convenience for the user which include selectable re-mapping of specific digital television channels to analog CATV channels, user and service provider conditional access means, television guide means, symbology overlay means, multiple picture in picture means and S-video output means.  
           [0006]    Current analog CATV standards typically support less than 200 channels, while current digital cable and satellite television support up to 1000 channels which implies it is necessary to incorporate a means to enable the user to select which of the available DVB channels to re-map to the available analog CATV channels, preferably, these would be the most commonly viewed channels. The symbology overlay means enables text or graphic information or messages to overlay the video signal and convey a message to the user, such as channel re-map information, messages from the service provider and television guide information. The apparatus also includes conditional access functionality which enables either the operator of the device or the service provider to selectively block specific channels form being forwarded as an analog CATV channel. Additionally, conditional access ensures only authorized viewers can access the transported information. This may involve decryption, authentication, signature verification, key distribution, and application of user preferences. To enable the user to rapidly study the content which is currently available, the apparatus includes a picture in picture television guide means which displays on one or more reserved channels, the real time video content of all of the available channels organized as tiled reduced size picture next to picture structure with symbology overlay providing associated channel number, which enables the user to rapidly view all channel content currently available and then select which specific channel to view.  
           [0007]    In one aspect of the invention, a method for performing demodulation of a received digital video broadcast signal, which contains a composite of several time and frequency division multiplexed video channels, and conversion to multiple re-modulated analog television channels, includes demodulation of the received digital signal, synchronizing to the demodulated symbol times, forward bit error detection and correction of the composite sampled digital signal, depacketizing of the error corrected composite digital signal into individual digital video and digital audio channels, conditional access qualification of the individual digital video and digital audio channels, selection of a plurality of conditional access qualified digital video and digital audio channels, source decoding of plurality of selected digital video and digital audio channels, conversion of decompressed plurality of selected digital video and digital audio channels to composite analog video and audio format channels, re-modulation of plurality of composite analog video and analog audio channels to desired analog CATV channels to form a composite multi-channel analog CATV complaint signal.  
           [0008]    In another aspect of the invention an apparatus for performing demodulation of a received digital video broadcast signal which contains a composite of several digital video channels and conversion to multiple re-modulated analog television channels, includes a demodulator which processes the received digital signal and generates a symbol stream, a forward error correction function which removes and detects bit errors of the composite symbol stream, a de-packetizing function which separates the error corrected composite symbol stream into individual digital video and digital audio channels, a gating function which performs conditional access qualification of the individual digital video and digital audio channels, a selector function which selects a plurality of access qualified digital video and digital audio channels, a plurality of source decoding functions which decompress the plurality of selected digital video and digital audio channels, a plurality of converter functions which convert the source decoded plurality of selected digital video and digital audio channels to composite analog video format channels, and a plurality of re-modulator functions which frequency shift and filter the plurality of composite analog video channels to desired analog CATV channels to form a composite multi-channel analog CATV compliant signal.  
           [0009]    Further objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of the preferred embodiment, drawings and claims.  
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0010]    [0010]FIG. 1 Block diagram of the multi-channel digital video to composite analog CATV converter;  
         [0011]    [0011]FIG. 2 Illustration of the received digital television satellite spectrum (DSS);  
         [0012]    [0012]FIG. 3 Illustration of the multichannel modulated analog CATV output;  
         [0013]    [0013]FIG. 4. System diagram; 
     
    
     DETAILED DESCRIPTION  
       [0014]    The preferred embodiment of the present invention with reference to a multiple channel digital video to composite analog video converter will be described in detail in conjunction with the drawings including theoretical foundation and functional block diagram.  
         [0015]    [0015]FIG. 4, presents a system diagram detailing the application of the present invention. More specifically, a modulated digital video signal is received either from cable  300  or satellite  301  and is applied to the multi channel digital video to composite analog CATV remodulator  302 . The multi-channel digital video to composite analog CATV re-modulator  302 , accepts the received digital video signal  300  or  301 , which is comprised of many video channels, and converts a plurality of selected channels to analog CATV formatted channels, producing a single composite analog CATV output signal  303 . The composite analog CATV output signal  303 , is distributed throughout a users premises using the existing cabling  304  which is commonly installed in most homes. The existing cable  304 , terminates at one or m ore televisions  305 ,  306 ,  307 ,  308  within the premises, which enables each television to receive digital video content without the need for a dedicated ICD at each television.  
         [0016]    In FIG. 2, the spectrum of a received DVB compliant modulated digital video signal  100  which is applied to the wideband video transceiver input is presented. The modulated digital video signal  100  is comprised of one or more subbands  101 ,  102 ,  103 , to  107  each of which is individually modulated and frequency division multiplexed (FDM) to form the composite modulated digital video signal  100 . Each subband  101 ,  102 ,  103  to  107  contains source encoded digital television channels that are time division multiplexed (TDM). In a preferred embodiment of the present invention the modulated digital video signal  100  is Digital Video Broadcast (DVB). In the preferred case of DVB, a plurality of 32 subbands  101 ,  102 ,  103  to  107  exist and each subband  101 ,  102 ,  103  to  107  is preferably 24 Mhz in bandwidth. Each subband  101 ,  102 , and  103  to  107  contain a signal which is QPSK modulated, and contains between 4 to 8 broadcast television quality MPEG-2 compressed video channels which are TDM to form the composite transponder signal  101 ,  102 ,  103  to  107 , The total bandwidth of the received DVB signal is approximately 1 GHZ and contains less than 500 compressed video channels.  
         [0017]    The major elements of the Multi-Channel Digital Video Broadcast to Composite Analog Video Converter are presented in FIG. 1. In FIG. 1, modulated digital video signal  100  is received and applied to the tuner function  2  which filters and quantizes the received signal into sampled form  3 . A feature and competitive advantage of present invention includes operating the tuner function  2  at a sampling rate sufficient to quantize the entire spectrum of the received modulated signal  100 . In the preferred embodiment where signal 100 is DVB, the sampling rate would be less than 3 Giga samples per second. The quantized signal  3  is then applied to the wideband demodulator function  4 .  
         [0018]    A feature and advantage of the present invention is that the wideband demodulator function  4  demodulates all subbands  101 ,  102 ,  103  to  107  of the quantized signal  3  and produces a symbol stream  5 ,  6 ,  7 ,  8  for each of the associated sub-bands  101  to  107 . In the preferred embodiment of DVB, there are less than or equal to 32 symbol streams  5 ,  6 ,  7 ,  8 . The demodulated symbol streams  5 ,  6 ,  7 ,  8  are applied to an inverse forward error correction function  9 .  
         [0019]    Inverse FEC removes transmission coding and corrects any errors that can be detected in each symbol streams  5 ,  6 ,  7 ,  8 . The forward error correction function  9  produces an output bit stream  10 ,  11 ,  12 ,  13  associated with each sub-band  101  to  107  which is then applied to a transport de-multiplexer function  14 .  
         [0020]    The transport de-multiplexer function  14  accepts all bitstreams  10 ,  11 ,  12 ,  13 , each of which contain a plurality of TDM source encoded composite digital video channels, and de-packetizes and selects a plurality of channels to he forwarded as output digital video channels  15 ,  16 ,  17  and ultimately converted to analog CATV format. The de-multiplexer function  14  is controlled by the user channel selection function  26  which accepts user channel preferences and produces associated control signals to the de-multiplexer function  14  to forward the user requested channels  15 ,  16 ,  17 . For the preferred emobiment of DVB, the number of compressed composite video channels contained in the bit streams  10 ,  11 ,  12 ,  13  is less than 1000, and the number of output digital video channels  15 ,  16 ,  17  is preferably less than 200 which is limited by the number of analog CATV channels available. The output digital video channels  15 ,  16 ,  17  are then applied to the user conditional access function  18 .  
         [0021]    The user conditional access function  18  performs channel blocking functionality based on user selections and produces the user qualified digital video channels  19 ,  20 ,  21  which is applied to the service provider conditional access function  22 .  
         [0022]    The service provider conditional access function  22  determines which of the video channels  19 ,  20 ,  21  may be viewed and produce access approved video channel output data  23 ,  24 ,  25  for each approved input channel  19 ,  20 ,  21 . The service provider conditional access function  22  performs decryption, authentication, signature verification, key distribution, and application of user preferences. The approved video channel output data  23 ,  24 ,  25  is applied to the source decoding function  27  which is responsible for implementing video and audio decompression which reversed entropy-reducing source coding and produces a raw bit stream for each video channel  28 ,  29 ,  30 . In the preferred DVB embodiment, the video and audio are compressed in compliance with the MPEG standard.  
         [0023]    The source decoder function  27  produces a plurality of decompressed video and audio signals  28 ,  29 ,  30  each corresponding to the plurality of applied compressed video qualified channel input  23 ,  24 ,  25  with a resolution of preferably less than 800×600 pixels. A feature and advantage of the current invention is that the source decoder function  27  supports decompressing a plurality of video channels simultaneously, preferably less than 200 channels. Each decompressed video and audio channels  28 ,  29 ,  30  are applied to the symbology overlay function  31  and picture in picture function  40 .  
         [0024]    The picture in picture function  40  accepts the plurality of decompressed video and audio signals  28 ,  29 ,  30  and produces a plurality of new decompressed summary video signals  41 ,  42 ,  43  that consists of reduced size input decompressed video signals  28 ,  29 ,  30  tiled in a grid form of picture next to picture, which provides a visual real time television guide of the content that is currently available. The summary video channels  41 ,  42 ,  43  and the decompressed video and audio channels  28 ,  29 ,  30  are applied to the symbology overlay function  31 .  
         [0025]    The symbology overlay function  31 , adds unique graphic and text symbology overlay to each decompressed video channel input,  28 ,  29 ,  30 ,  41 ,  42 ,  43  which may include content such as channel remapping information, channel numbers, time, and messaging information. For each decompressed video and audio channel input  28 ,  29 ,  30 ,  41 ,  42 ,  43 , the symbology overlay function  31  produces an associated symbology overlayed output video and audio channel plurality of output video and audio channels  32 ,  33 ,  35 ,  36 ,  37 ,  38  which are applied to the broadband analog CATV re-modulator  34 .  
         [0026]    The broadband analog CATV re-modulator  34 , converts each of the plurality of decompressed digital video input channels  32 ,  33 ,  35 ,  36 ,  37 ,  38  to a unique modulated CATV standard analog channel to form a composite modulated CATV standard analog signal  39 , the frequency spectrum  200  of which is presented in FIG. 3. The frequency spectrum  200  of the composite modulated CATV standard analog signal  39 , consists of the plurality of unique modulated CATV standard analog channels  201 ,  202 , to  209  each of which correspond to the plurality of decompressed digital video input channels  32 ,  33 ,  35 ,  36 ,  37 ,  38 . In the preferred embodiment, the composite modulated CATV standard analog signal  39  is compliant with and indistinguishable from a standard analog NTSC CATV signal. Additionally, the broadband analog CATV re-modulator function  34  preferably supports additional modes of operation, to generate modulated CATV compliant analog signals  39  which conform to PAL and SECAM standards.  
         [0027]    In summary, a significant feature and advantage of the Multi-Channel Digital Video Broadcast to Composite Analog Video Converter described in the present invention, is to accept a received modulated digital video signal  100  which is DVB compliant, and ultimately convert a plurality of the video channels  15 ,  16 ,  17 , contained in the received digitally modulated video signal  100  into standard analog CATV format  200 . In practice, this Multi-Channel Digital Video Broadcast to Composite Analog Video Converter capability provides the advantage of enabling distribution of DVB content over the standard coaxial cabling which is commonly available throughout most homes and the seamless viewing on common televisions which support analog CATV format. This capability, eliminates the need to have a physically obtrusive separate IRD dedicated for each television, eliminates the need for dedicated cabling to each IRD, reduces installation costs, reduces equipment costs, and provides enhanced features and greater convenience for the consumer.