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Beginning of dtv


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DTV, DVB archtecture, DTV standards,ATSC, ISDB, Middleware, MHP

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Beginning of dtv

  1. 1. DTV INTRODUCTION Mrs. M. P. Atre PVG
  4. 4. DVB-SNG: standard for news gathering Multiprotocol Encapsulation, or MPE for short, is a Data link layer protocol defined by DVB which has been published as part of ETSI EN 301 192. It provides means to carry packet oriented protocols (like for instance IP) on top of MPEG transport stream (TS).
  5. 5. STANDARDS FOR BROADCASTING Country: USA India Japan Brazil,Phillipines China Integrated Services Digital Broadcasting (ISDB) SCM(single carrier modulation), MCM(multicarrier modulation) (MCM example: OFDM)
  6. 6. DVB STANDARD ARCHITECTURE **Highlighted blocks represent DVB architecture
  7. 7. TERMINOLOGY  Multimedia Home Platform, or MHP in short  MHEG (the Multimedia and Hypermedia Information Coding Experts Group) running over DVB-T in the UK
  8. 8. @ MHP  The Multimedia Home Platform has been provided in DVB as supplementary service for MHP-enabled receivers  Two versions which are MHP 1.1. and MHP 1.2.  MHP used for transmitting HTML (Hypertext Multimedia Language) files familiar from the Internet, and Java applications. Continued…
  9. 9. @ MHP  Starting the HTML and Java applications requires special software (or middleware) in the receiver.  MHP-capable receivers are more expensive and not available in great numbers on the market.  MHP applications are broadcast in many countries but are currently really successful only in Italy
  10. 10. CONTENTS BROADCAST BY MHP ARE: • Games • Electronic programme guides • News • Interactive program-associated services • "Modern" teletext
  11. 11. DVB STANDARD SCHEME Encoding Stage Transport Stage Transmission Stage For Encoding and Transport stage, both stages use MPEG-2
  12. 12. MMDS MMDS stands for Multichannel Multipoint Distribution Service. It is used as replacement of cable TV service provider. MMDS is used to cover rural areas where it is not possible to reach by broadcast and cable TV operators.
  13. 13. LMDS LMDS stands for Local Multipoint distribution service. It is used for providing TV and 2-way internet service similar to MMDS. NOC: Network Operation Centre
  17. 17. PAT
  18. 18. PMT
  22. 22. VIDEO ENCODING STANDARDS  MPEG-1 standard  MPEG-2 standard  MPEG-4 standard  H.264 standard
  23. 23. INTRODUCTION TO VIDEO ENCODING STANDARDS  Motion Picture Experts Group (MPEG) was established in January 1988 as a work group to create international standards of audio and video encoders/decoders (codec)  MPEG-1 standard was published in 1989 and approved as the international standard in 1992  MPEG-2 approved in 1994  New improvements, which would have lead to the MPEG-3 standard, were later incorporated in the MPEG-2. This caused the acronym MPEG-3 not to be used
  24. 24. INTRODUCTION….. CONTINUED..  Structure of the MPEG-4 standard was set out in 1993 and the standard was approved in 1998  Work on MPEG-7, which covered audio and video content, began in 1997 and the standard was approved in 2002  The group is developing the MPEG-21 standard, which is called the multimedia framework  This group is also working with other standards related to the use of audio and video standards mentioned, such as the Intellectual Property Management Protection (IPMP)  MPEG is a member of the International Standards Organization (ISO)
  25. 25. 1. MPEG 1 STANDARD  Aims at the compression of audio and video images previously digitized  USES : Short video clips made available on the Internet, video compact disks (VCDs), and videos distributed on disks of the CD-ROM type use this standard  MP3 audio compression is layer 3 of the MPEG-1, thus the acronym MP3  Compression rate is variable and it’s possible to reach a compression rate of 200:1
  26. 26. MPEG1 CONTINUED..  With the maximum rate the images become distorted, because the compression introduces artifacts in the image  It depends on the quality of the compression algorithm and the compression rate used.  Thus, most of the videos compressed with the MPEG-1 use a compression rate lower than 50:1  Even at this rate, the horizontal resolution obtained after the compression is low, circa 320 lines, and similar to the VHS format.  The compression used is the multi frame type
  27. 27. MPEG-2 STANDARD  MPEG-2 was developed in conjunction with the Video Coding Experts group from the International Telecommunications Union (ITU-T)  Also known in the ITU-T community as H.262  USES :DVDs and digital TV broadcasting use this standard, which is more advanced than MPEG-1  Produces better quality images  The compression rate, just like in the MPEG-1, is variable but normally values of around 40:1 are used
  28. 28. MPEG-2 ..CONTINUED..  More efficient at compressing, without apparent quality loss, than MPEG-1  Demands higher computational effort in the process, requiring more powerful hardware than that needed for MPEG-1  The horizontal resolution obtained after the compression is superior to that of the VHS format  Compression used is the multi frame type  Assembling process of the group of pictures (GOP) used by the multi frame technique, it is more complex to compress MPEG-2 content than to retrieve it
  29. 29. 3. MPEG-4 STANDARD  Standard created by the MPEG group for the compression of audio and video images previously digitized  Used on videos transmitted by the Internet, as well as on cell phones that use images  Common on several standards of digital TV broadcasting, especially HDTV in its advanced video coding (AVC) version  MPEG-4 accepts different profiles  HDTV broadcasting systems use it as the encoding standard, as an alternative to MPEG-2
  30. 30. Video Quality Compression Ratio Bandwidth (bits/sec) Motion JPEG Broadcast 7–27 : 1 10 – 26 Mbps MPEG-2 Broadcast/HDTV 30–100 : 1 3 – 16 Mbps MPEG-1 VCR/Business 25–100 : 1 .5 – 4 Mbps H.261/H.263 Video Conf 24–200 : 1 128 K – 1 Mbps MPEG-4 Video Phone 50–1000 : 1 4.8 K – 64 Kbps
  31. 31. Spatial arrangement for mono, stereo, Dolby surround, and surround 5.1 audio
  32. 32. ATSC DTV Advanced Television Systems Committee, USA
  33. 33. INTRODUCTION  ATSC stands for the Advanced Television Systems Committee, which developed the standards for DTV used in the United States (as well as in Canada, Mexico, and Korea)  The principal standards comprise ATSC documents A/53 for digital television and A/52 for AC-3 audio compression  ATSC DTV signals are not compatible with NTSC  One fundamental difference between digital ATSC and analog NTSC television is that NTSC transmits complete pictures, but the ATSC system effectively sends the pictures broken down into many small parts, with a set of instructions to put them back together again  So, what is produced and seen in the studio may or may not be exactly what all receivers produce, depending on how they interpret the instructions  This is the base for video compression
  34. 34. FEATURES  8-VSB Modulation  Transmitted bit rate  FEC  Cliff effect
  35. 35. 8-VSB MODULATION  Type of Digital Modulation  8-VSB is a special form of AM modulation using a single carrier modulated to eight different amplitude levels  The carrier is modulated with a compressed bitstream signal carrying all the information needed for the channel  This modulation occurs at the transmitter in a piece of equipment called an exciter
  37. 37.  The compressed bitstream input to the DTV exciter is processed and converted into digital symbols  The output of the exciter is a series of pulses of carrier wave, each with one of eight different amplitude levels that are assigned to eight symbols  These symbols are output at a rate of 10.76 million every second.
  38. 38. TRANSMITTED BIT RATE  Each symbol is able to carry 3 bits of digital data  Therefore, the 10.76 million symbol per second output of a DTV exciter can represent 10.76 * 3 = 32.28 Mbps (megabits per second) of digital data  It is important to understand that the “data” being transmitted may represent video, audio, or other types of ancillary data information  Once in the bitstream, it is all referred to as data  Information bit rate for an ATSC bitstream is 19.39 Mbps but data rate coming out of a DTV exciter so much higher than the actual data rate of the video, audio, and ancillary information being broadcasted  This is because of additional bits needed for forward error correction ( FEC )
  39. 39. FEC-FORWARD ERROR CORRECTION  Forward error correction (FEC) is used to make the signal more robust and able to withstand distortions in the transmission path  Multipath distortion is a common problem with over-the-air television signals, caused when multiple signals from the same transmitter arrive at the receiver at slightly different times  There may also be various forms of interference such as lightning strikes that create large RF noise pulses, which can affect reception at great distances from the strike.  Smaller RF pulses are created by electric motors, car ignition systems, and many other things. All of these conditions can cause data to be lost.  The special error correction codes added to the DTV signal helps receivers to fix problems with the received signal.  In addition, DTV receivers have special circuitry called adaptive equalizers to help cancel out the effects of unwanted signals
  40. 40. CLIFF EFFECT  With analog television, the received picture can be excellent (in areas of strong signal reception), mediocre, exhibiting “ghosting” and “snow” (in areas of marginal reception), or unwatchable (in areas of poor reception)  ATSC DTV pictures never display ghosts because, so long as the receiver can decode the digital data that describes the picture, it can reconstruct a nearly perfect picture  However, under extreme conditions, with low received signal strength and/or strong multipath interference echoes, the DTV receiver may no longer be able to correctly decode the picture (and/or the sound)  In that case, the picture and/or sound disappear completely. They go from perfect to nothing, with almost no intermediate stage. This is known as the “cliff effect,” which is common to many digital transmission technologies
  42. 42. DESCRIPTION OF ATSC BITSTREAM  The ATSC compressed bitstream, comprising digital video, digital audio, and ancillary data, is known as a transport stream  This is created by the ATSC encoders and multiplexer and delivered to the television station’s transmitter at a rate of 19.39 Mbps  The transport stream is made up of blocks of compressed digital data, known as packets, which carry video, audio, and ancillary data  This is in contrast to the continuous stream of analog information for an NTSC signal
  43. 43.  The ATSC packets contain 188 bytes of data, but the first byte of each packet is used for synchronization, and an additional three packets are used for management of the bitstream, so 184 bytes are actually available for audio, video, data, and PSIP (Program and System Information Protocol Standard)  For comparison with the 19.39 Mbps data rate of the ATSC bitstream, the fastest broadband cable Internet connection available for the home can download data at about 5Mbps, whereas a dial-up 56kbps modem for a personal computer has a data rate of only 0.056Mbps
  45. 45. OTHER COMPRESSION SYSTEMS  Although AC-3 (Audio Coding-3) is widely used for DTV, it is by no means the only compression system for audio encoding.  Several other systems are widely used in radio and elsewhere. These include an earlier Dolby system called AC-2, also MPEG-1 layer 1, MPEG-1/2 layer 3 (usually known as MP3), and the more recent MPEG AAC (Advanced Audio Coding).  The recent systems provide much higher audio quality at lower bit rates. There are continuing developments, and a technique called Spectral Band Replication (SBR) further improves high-frequency audio response in low- bit-rate applications
  46. 46. ADVANCED COMPRESSION SYSTEMS  Recent developments in compression technology allow high quality encoding with much greater efficiency than MPEG-2  The AVC/H.264 system (developed in conjunction with MPEG) and the VC-1 system (based on Microsoft Windows Media 9) provide equivalent picture quality at about half the bit rate or less.  Such systems allow more programs to be transmitted in less bandwidth.  However, because of the necessity not to make existing DTV receivers obsolete overnight, broadcasters must continue to use the MPEG-2 standard for many years to come.  Various proposals are under consideration to allow the new, more efficient codecs to be used in some circumstances
  47. 47. THANK YOU