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Concepts of Multimedia Processing and Transmission. IT 481, Lecture #9 Dennis McCaughey, Ph.D. 6 November, 2006. Broadcast Environment. Video Transmission System Example. Digital Video Broadcast (DVB). DVB-S: Digital video over satellite DVB-C: Digital video over cable

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Concepts of multimedia processing and transmission l.jpg

Concepts of Multimedia Processing and Transmission

IT 481, Lecture #9

Dennis McCaughey, Ph.D.

6 November, 2006


Broadcast environment l.jpg
Broadcast Environment

IT 481, Fall 2006



Digital video broadcast dvb l.jpg
Digital Video Broadcast (DVB)

  • DVB-S: Digital video over satellite

  • DVB-C: Digital video over cable

  • DVB-T: Digital video over terrestrial links

  • DVB-H: Digital video to the handheld device

IT 481, Fall 2006





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MPEG-2 Multiplexers

IT 481, Fall 2006


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The MPEG Transport Stream

  • First byte of each PES packet must be the first byte of the transport packet payload

  • Each transport packet must contain data from only one PES packet

IT 481, Fall 2006


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Transport Stream Role

  • Transport of all programming information

    • All information that a particular provider transmits (on a particular frequency)

  • Minimize processing required for:

    • Retrieval of coded data from one stream

    • Extraction of transport stream packets of one or more transports and the output of a new transport stream

    • Enabling the transport and recovery of a stream over a lossy environment

IT 481, Fall 2006


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Simple Program Transport Stream (SPTS)

Different PES share a common time base

The different PES could carry video, audio and data

Example would be a movie transmitted with multiple languages

Multiple Program Transport Stream (MPTS)

Carries multiple SPTS

Two Types of Transport Streams

IT 481, Fall 2006


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MPEG-2 Transport Packet Header

Transport packets are 188 bytes because MPEG-2 wanted these packets to carried across ATM (188 bytes = 4 ATM cells)

IT 481, Fall 2006


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MPEG Program Streams

  • A group of tightly coupled PES packets referenced to a common time base

  • Intended for transmission in a relatively error-free environment

    • Enable easy software processing of the received data

  • Used for video playback and some network applications

IT 481, Fall 2006


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Transport Layer PIDs

IT 481, Fall 2006


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MPEG Signaling Tables

  • PAT - Program Association Table

    • Lists the PIDs of tables describing each program. The PAT is sent with the well-known PID value of 0x000.

  • CAT - Conditional Access Table

    • Defines type of scrambling used and PID values of transport streams which contain the conditional access management and entitlement information (EMM). The CAT is sent with the well-known PID value of 0x001.

  • PMT - Program Map Table

    • Defines the set of PIDs associated with a program, e.g. audio, video…,

  • NIT - Network Information Table

    • PID=10, contains details of the bearer network used to transmit the MPEG multiplex, including the carrier frequency

  • DSM-CC - Digital Storage Media Command and Control

    • messages to the receivers

IT 481, Fall 2006


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DVB Signaling Tables

  • BAT- Bouquet Association Table

    • Groups services into logical groups

  • SDT- Service Description Table

    • Describes the name and other details of services

  • TDT - Time and Date Table

    • PID=14, provides present time and date

  • RST - Running Status Table

    • PID=13, provides status of a programmed transmission, allows for automatic event switching

  • EIT - Event Information Table

    • PID=12, provides details of a programmed transmission

IT 481, Fall 2006



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Transport Packet

IT 481, Fall 2006


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Transmission Processes

  • Multiplexing and energy dispersion randomization

  • Outer Reed Solomon Encoding

  • Convolutional Interleaving

  • Inner Convolutional Encoding

  • Baseband shaping

  • QPSK Modulation

IT 481, Fall 2006


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Transport Stream Multiplexer

IT 481, Fall 2006


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DVB Scrambler/Descrambler

p(n-14) +p(n-15)

x(n)

y(n)

y(n) = x(n) + p(n-14) + p(n-15)

Self descrambling:

y(n) = x(n) + p(n-14) + p(n-15) + p(n-14) + p(n-15)

= y(n)

IT 481, Fall 2006


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Purposes of Scrambling

  • It facilitates the work of a timing recovery circuit, by eliminating long sequences consisting of '0' or '1' only.

  • It eliminates the dependence of a signal's power spectrum upon the actual transmitted data,

    • Making it more dispersed to meet maximum power spectral density requirements

    • If the power is concentrated in a narrow frequency band, it can interfere with adjacent channels caused by non-linearities of the receiving tract).

IT 481, Fall 2006


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Randomized Transport Packets

IT 481, Fall 2006


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Reed-Solomon Encoding

  • An RS code is partially specified as an RS(n,k) with m-bit symbols.

    • E.g. the DVB code is RS(204,188) using 8-bit symbols.

    • n refers to the number of encoded symbols in a block,

    • k refers to the number of original message symbols.

  • The difference n-k (usually called 2t) is the number of parity symbols that have been appended to make the encoded block.

IT 481, Fall 2006



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R-S Performance

  • An RS decoder can correct up to (n-k)/2 or t symbols,

  • Any t symbols can be corrupted in any way, and the original symbols can be recovered.

  • The DVB code

    • splits the message into blocks 188 symbols long.

    • 16 parity symbols (2t = 204-188 = 16) are then appended to produce the full 204 symbol long code.

  • Up to 8 (t = 16/2) symbol errors can then be corrected

IT 481, Fall 2006


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R-S Performance

  • The power of Reed Solomon codes lies in being able to just as easily correct a corrupted symbol with a single bit error as it can a symbol with all its bits in error.

  • With the DVB code, a sequence of up to 56 consecutive bits could be corrupted affecting at most 8 symbols, and the original message could still be recovered.

    • However it does mean that RS codes are relatively sensitive to evenly spaced errors

    • i.e. in the DVB code if 9 symbols have a single bit error then no corrections can be made.

    • Therefore the RS encoded block is further encoded in a Convolutional code to try and cope with both burst and random errors.

IT 481, Fall 2006


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Framing Structure

IT 481, Fall 2006



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Convolutional Interleaver

A convolutional interleaver consists of a set of shift registers, each with a fixed delay. In a typical convolutional interleaver, the delays are nonnegative integer multiples of a fixed integer (although a general multiplexed interleaver allows arbitrary delay values). Each new symbol from the input signal feeds into the next shift register and the oldest symbol in that register becomes part of the output signal. The schematic below depicts the structure of a convolutional interleaver by showing the set of shift registers and their delay values D(1), D(2),...,D(N). The blocks in this library have mask parameters that indicate the delay for each shift register. The delay is measured in samples.

IT 481, Fall 2006


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Interleaver

IT 481, Fall 2006


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Convolutional Code Definition

Punctured Code Definition

IT 481, Fall 2006


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Convolutional Encoder

To I Channel

Input Bit Stream

To Q Channel

IT 481, Fall 2006



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Punctured Code

IT 481, Fall 2006



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Baseband Shaping

IT 481, Fall 2006


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QPSK and OQPSK Modulators

Slide: Courtesy of Data and Computer Communications by William Stallings

IT 481, Fall 2006


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QPSK Modulation

IT 481, Fall 2006



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References and SMS.

  • [1] S. N. Baron, M. I. Krivocheev "Digital Image and Audio Communications", Van Nostrand Reinhold 1996.

  • [2] J. L. Mitchell, W. B. Pennebaker, C. E. Fogg, D. J. LeGall "MPEG Video Compression Standard", Chapman & Hall 1997.

  • [3] J. B. Rault, Y. F. Dehery, M. Lever "The ISO/MPEG Audio Musicam Family", IEE Conference held at the IEE, Savoy Place, January 1995.

  • [4] http://www.ebu.ch/dvb_contents.htm

  • [5] http://www.ebu.ch/dvb_standards/dvb_world.htm

  • [6] J. Duran "MPEG-2 Overview", INTELSAT IOM , August 1997.

  • [7]ITU-R 217/11 "Document" 10-11S/28-E22, March 1996

  • [8] C. Elia and E. Colzi "Skyplex: Distributed Up-link for Digital Television via Satellite", IEEE Transactions on Broadcasting, Vol.42, No. 4, December 1996.

  • [9]ETSI "Digital Broadcasting System for Television, sound and Data services; Framing structure, channel coding and modulation for 11/12 GHz satellite services", ETS 300421, June 1994.

  • [10]ETSI "Digital Broadcasting System for Television, sound and Data services; Framing structure, channel coding and modulation for Cable Systems", ETS 300429, December 1994.

  • [11]ETSI "Digital Video Broadcasting (DVB) Specification for conveying ITU-R System B Teletext in DVB bitstreams", ETS 300472, October 1996.

  • [12]ETSI "Digital Broadcasting System for Television, sound and Data services; Satellite Master Antenna Television (SMATV) distribution systems", ETS 300473, May 1995.

  • [13] K. Birdwell "Self-Installer Manual DSS", 1995.

  • [14]ITU "Functional Model of a Conditional Access System" 11-3/66-E, 28 October 1996.

  • [15]M. Buer, J. Wallace "Integrated Security for Digital Video Broadcast", IEEE Transactions on Consumer Electronics, Vol.42, No. 3, August 1996.

  • [16] J. Giachetti, V. Lenoir, A. Codet, D. Cutts, J. Sager "A Common Conditional Access Interface for Digital Video Broadcasting Decoders", ", IEEE Transactions on Consumer Electronics, Vol.41, No. 3, August 1995.

  • [17]M. Cominetti, V. Mignone, A. Morello, M. Visintin "The European System for Digital Multi-Programme Television by Satellite", IEEE Transactions on Broadcasting, Vol.41, No. 2, June 1995.

IT 481, Fall 2006


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