Concepts of Multimedia Processing and Transmission IT 481, Lecture #11 Dennis McCaughey, Ph.D. 16 April, 2007

04/09/2007 IT 481,Spring Broadcast Environment

04/09/2007 IT 481,Spring Video Transmission System Example

04/09/2007 IT 481,Spring 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

04/09/2007 IT 481,Spring Direct Video Broadcast (DVB) Systems

04/09/2007 IT 481,Spring Digital Broadcasting, Service Delivery Model

04/09/2007 IT 481,Spring Processing of The Streams in The Set- Top Box (STB)

04/09/2007 IT 481,Spring MPEG-2 Multiplexers

04/09/2007 IT 481,Spring 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

04/09/2007 IT 481,Spring 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

04/09/2007 IT 481,Spring Two Types of Transport Streams 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

04/09/2007 IT 481,Spring 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)

04/09/2007 IT 481,Spring 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

04/09/2007 IT 481,Spring Transport Layer PIDs

04/09/2007 IT 481,Spring MPEG Signaling Tables PAT - Program Association Table – Lists the PIDs of tables describing each program. The PAT is sent with the 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 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

04/09/2007 IT 481,Spring 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

04/09/2007 IT 481,Spring DVB-S Transmission System Ku Band

04/09/2007 IT 481,Spring Transport Packet

04/09/2007 IT 481,Spring Transmission Processes Multiplexing and energy dispersion randomization Outer Reed Solomon Encoding Convolutional Interleaving Inner Convolutional Encoding Baseband shaping QPSK Modulation

04/09/2007 IT 481,Spring Transport Stream Multiplexer

04/09/2007 IT 481,Spring DVB Scrambler/Descrambler 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) p(n-14) +p(n-15) x(n)y(n)

04/09/2007 IT 481,Spring 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).

04/09/2007 IT 481,Spring Randomized Transport Packets

04/09/2007 IT 481,Spring 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.

04/09/2007 IT 481,Spring Reed Solomon RS(204,188,t=8) error protected packet.

04/09/2007 IT 481,Spring 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 = = 16) are then appended to produce the full 204 symbol long code. Up to 8 (t = 16/2) symbol errors can then be corrected

04/09/2007 IT 481,Spring 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.

04/09/2007 IT 481,Spring Framing Structure

04/09/2007 IT 481,Spring Interleaved Frames (Interleaving depth I=12).

04/09/2007 IT 481,Spring 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.

04/09/2007 IT 481,Spring Interleaver

04/09/2007 IT 481,Spring Interleaving Operation

04/09/2007 IT 481,Spring De-Interleaving Operation

04/09/2007 IT 481,Spring Convolutional Encoder Input Bit Stream To Q Channel To I Channel

04/09/2007 IT 481,Spring Convolutional Code Definition Punctured Code Definition

04/09/2007 IT 481,Spring Punctured Code

04/09/2007 IT 481,Spring Puncturing Pattern & Transmission Sequence Code RatesPuncturing pattern Transmitted sequence (after parallel-to-serial conversion) 1/2 X: 1 Y: 1 X 1 Y 1 2/3 X: 1 0 Y: 1 1 X 1 Y 1 Y 2 3/4 X: Y: X 1 Y 1 Y 2 X 3 5/6 X: Y: X 1 Y 1 Y 2 X 3 Y 4 X 5 7/8 X: Y: X 1 Y 1 Y 2 Y 3 Y 4 X 5 Y 6 X 7

04/09/2007 IT 481,Spring Punctured Convolutional Code Block Diagram

04/09/2007 IT 481,Spring Baseband Shaping

04/09/2007 IT 481,Spring QPSK and OQPSK Modulators Slide: Courtesy of Data and Computer Communications by William Stallings

04/09/2007 IT 481,Spring Conditional Access Scrambling, Encrypted Control Word, EMM and SMS.

04/09/2007 IT 481,Spring References [1] S. N. Baron, M. I. Krivocheev "Digital Image and Audio Communications", Van Nostrand Reinhold [2] J. L. Mitchell, W. B. Pennebaker, C. E. Fogg, D. J. LeGall "MPEG Video Compression Standard", Chapman & Hall [3] J. B. Rault, Y. F. Dehery, M. Lever "The ISO/MPEG Audio Musicam Family", IEE Conference held at the IEE, Savoy Place, January [4] [5] [6] J. Duran "MPEG-2 Overview", INTELSAT IOM, August [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 [9]ETSI "Digital Broadcasting System for Television, sound and Data services; Framing structure, channel coding and modulation for 11/12 GHz satellite services", ETS , June [10]ETSI "Digital Broadcasting System for Television, sound and Data services; Framing structure, channel coding and modulation for Cable Systems", ETS , December [11]ETSI "Digital Video Broadcasting (DVB) Specification for conveying ITU-R System B Teletext in DVB bitstreams", ETS , October [12]ETSI "Digital Broadcasting System for Television, sound and Data services; Satellite Master Antenna Television (SMATV) distribution systems", ETS , May [13] K. Birdwell "Self-Installer Manual DSS", [14]ITU "Functional Model of a Conditional Access System" 11-3/66-E, 28 October [15]M. Buer, J. Wallace "Integrated Security for Digital Video Broadcast", IEEE Transactions on Consumer Electronics, Vol.42, No. 3, August [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 [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.