1Lecture B: Digital Media Lecture B: Digital Media BroadcastingBroadcastingISPACS 2005 TutorialC. C. Jay KuoDepartment of Electrical EngineeringUniversity of Southern CaliforniaOutlineOutline• 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• Conclusion2OutlineOutline• 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• ConclusionAnalog Audio Broadcast Analog Audio Broadcast • Frequency Modulation (FM) from 1950s• Amplitude Modulation (AM) from 1920s3Digital Audio Broadcast (DAB)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 PCDAB HistoryDAB 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• HD RadioTMTechnology – Only approved DAB standard in U.S• 2ndfast growing industry after mp3 player with an annual growth of 444% in 2003Evolution of DAB receiverAvailable at www.worlddab.org/images/eureka_leaflet.pdf4DAB WorldwideDAB WorldwideAvailable at http://www.worlddab.org/images/World_map_2004.pdfDAB BenefitDAB 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 next-generation digital broadcasting for radio stations• Added-value system features• Text, graphics and still image transfer5Overview of DAB SystemOverview of DAB SystemAvailable @ http://www.ibiquity.com/technology/hdradio_how.htmStations 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 compressedThe 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 RadioTMor Eureka 147 receivers and analog radios.Generation of a DAB SignalGeneration of a DAB Signal• 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 Concept of DAB distribution networkAvailable at www.worlddab.org/images/eureka_leaflet.pdf6Reception of a DAB SignalReception of a 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 signalsReception of DAB signalAvailable at www.worlddab.org/images/eureka_leaflet.pdfCOFDMTechnique Technique ––MUSICAM Audio MUSICAM Audio CodingCoding•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: • MPEG 1 audio layer II• MPEG 2 audio layer IIPsychoacoustic MaskingAvailable at www.worlddab.org/images/eureka_leaflet.pdf7Technique Technique ––Transmission Transmission Coding and MultiplexingCoding and MultiplexingMultiplexed DAB frame consists of:• Synchronization channel 9 Conveying reference frequency and timing information to synchronize to and decode •Fast information channel9Containing information to extract and decode individual channel• Main service channel9 Carrying the services dataStereoChannel 1StereoChan. 2StereoChan. 3StereoChan. 4StereoChan. 5Mono DataSynchronizationFast information channel- Multiplex configurationinformation- Service informationMain service channel:- Audio services- Data services24 msTStS∆Service dataGuardintervalTotal OFDM symbolTechnique Technique ––ModulationModulation• Coded Orthogonal Frequency Division Multiplexing • Multi-carrier9Traditional: digitally modulated carrier with a very high symbol rate9Multiple carriers: up to 1536, spacing 1k Hz separation9Each 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 figureCOFDM• Against Multi-path9Temporal 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 Available @ http://www.bbc.co.uk/rd/pubs/papers/paper_21/paper_21.shtml8Technique Technique ––TransmissionTransmission• 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 SFNs7681923841536No. of radiated carriers6231563121246Total symbol duration (us)500125250 1,000Useful symbol duration (us)YesNoNoNoSpeed/coverage trade-off 1,5003,0001,500375Nominal frequency range for mobile reception (MHz)48122496Nominal frequency transmitter separations for SFN (km)1233162246Guard interval duration (us)6481683241,297Null symbol duration (us)48242496Frame duration
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