Lecture B Digital Media Broadcasting ISPACS 2005 Tutorial C C Jay Kuo Department of Electrical Engineering University of Southern California Outline Digital Audio Broadcasting DAB DAB history and current status Technology inside DAB Future develop direction Digital Video Broadcasting DVB History of DVB project DVB worldwide DVB H DVB handheld Comparison of DAB and DVB Conclusion 1 Outline Digital Audio Broadcasting DAB DAB history and current status Technology inside DAB Future develop direction Digital Video Broadcasting DVB History of DVB project DVB worldwide DVB H DVB handheld Comparison of DAB and DVB Conclusion Analog Audio Broadcast Amplitude Modulation AM from 1920s Frequency Modulation FM from 1950s 2 Digital Audio Broadcast DAB Advantages Higher fidelity Greater noise immunity New services Receive radiotext such as song title traffic updates Can use radio card to hear DAB with PC DAB History Europe Eureka 147 Founded in 1987 Aiming to develop and define the digital broadcast system 1992 L and S bands allocated to DAB 1995 WorldDAB forum established 1997 Market introduction of DAB in most European countries 2000 70 80 population in Europe covered by DAB The United States Evolution of DAB receiver HD RadioTM Technology Only approved DAB standard in U S 2nd fast growing industry after mp3 player with an annual growth of 444 in 2003 Available at www worlddab org images eureka leaflet pdf 3 DAB Worldwide Available at http www worlddab org images World map 2004 pdf DAB Benefit Enhanced sound fidelity Improved delivery and reception Upgraded audio quality Digital FM with current CD quality Digital AM with current FM quality Seamless conversion from analog to nextgeneration digital broadcasting for radio stations Added value system features Text graphics and still image transfer 4 Overview of DAB System Stations bundle analog and digital audio signals with textual data such as artist and song information weather and traffic and more The digital signal layer is compressed The combined analog and digital signals are transmitted The most common form of interference multipath distortion occurs when part of a signal bounces off an object and arrives at the receiver at a different time than the main signal The signal will be compatible with HD RadioTM or Eureka 147 receivers and analog radios Available http www ibiquity com technology hdradio how htm Generation of a DAB Signal Concept of DAB distribution network Each service coded individually at source level error protected and time interleaved in the channel coder Services data are multiplexed in Main Service Channel MSC Then services data are multiplexed with service information and multiplex control information to form transmission frames Coded Orthogonal Frequency Division Multiplexing COFDM shaping the DAB signal Available at www worlddab org images eureka leaflet pdf 5 Reception of a DAB Signal COFDM Reception of DAB signal DAB ensemble is selected in the analogue tuner Digitized output from the tuner is fed into OFDM demodulator and channel decoder to eliminate transmission errors Control information information in FIC is passed to user interface for service selection and set up the reception service Audio data further processed in an audio decoder to produce the stereo signals Available at www worlddab org images eureka leaflet pdf Technique MUSICAM Audio Coding Masking Pattern Universal Sub band Integrated Coding And Multiplexing Low bit rate reduced to 1 6 1 12 of conventional PCM coding Sub band coding Enhanced by a psychoacoustic model 32 equally spaced sub bands Quantization quantizing noise matches the masking threshold Sample frequency 24KHz Standards Psychoacoustic Masking MPEG 1 audio layer II MPEG 2 audio layer II Available at www worlddab org images eureka leaflet pdf 6 Technique Transmission Coding and Multiplexing 24 ms Stereo Channel 1 Stereo Chan 2 Stereo Chan 3 Stereo Chan 4 Stereo Chan 5 Fast information channel Multiplex configuration information Service information Main service channel Audio services Data services Synchronization Mono Data Guard interval Service data tS TS Total OFDM symbol Multiplexed DAB frame consists of Synchronization channel 9 Conveying reference frequency and timing information to synchronize to and decode Fast information channel 9 Containing information to extract and decode individual channel Main service channel 9 Carrying the services data Technique Modulation Coded Orthogonal Frequency Division Multiplexing Multi carrier COFDM Against Multi path 9Temporal guard interval TGI as long as the delay of the echo signals is less than the guard interval there will be a constructive benefit for reception 9Single frequency network SFN of transmitters efficient use of the scare RF spectrum available 9Traditional digitally modulated carrier with a very high symbol rate 9Multiple carriers up to 1536 spacing 1k Hz separation 9Each carrier independently modulated using differential quadrate phase shift keying differential QPSK 9Multiplexed data distributed amongst all the carriers spectrum 1 54 M shown as the COFDM figure Available http www bbc co uk rd pubs papers paper 21 paper 21 shtml 7 Technique Transmission DAB transmission mode System Parameters Transmission Mode I II III IV 96 24 24 48 1 297 324 168 648 246 62 31 123 Frame duration ms Null symbol duration us Guard interval duration us Nominal frequency transmitter 96 24 12 48 separations for SFN km Nominal frequency range for 375 1 500 3 000 1 500 mobile reception MHz Speed coverage trade off No No No Yes Useful symbol duration us 1 000 250 125 500 Total symbol duration us 1246 312 156 623 No of radiated carriers 1536 384 192 768 Mode I preferable for terrestrial single frequency network of VHF range Mode II suitable for local radio application in L band Mode III appropriate for cable satellite and complementary terrestrial transmission Mode IV L band too but with more transmitter spacing in SFNs Conditional Access CA Scrambling Descrambling Services incomprehensible to unauthorized users Entitlement check Broadcasting the conditions required to access a service Broadcasting encrypted secret codes to descrambling for authorized receivers Entitlement management Distributing entitlement to subscribers 8 DAB Future Develop Direction Traffic and travel information Traffic messages Traffic navigation Travel information Text transmission Electronic Newspaper Picture transmission Fax Printout Differential GPS TV Transmission to Mobiles
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