digital audio broadcasting

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digital audio broadcasting

  1. 1. Digital Audio Broadcasting (DAB) systems Shahab adin Rahmanian Nov,2005 3/2/2007 Digital Audio Broadcasting systems 1
  2. 2. Outline Introduction DAB species History of DAB DAB specification IBOC DAB OFDM CDMA Future work References 3/2/2007 Digital Audio Broadcasting systems 2
  3. 3. Introduction Replace the existing AM and FM audio broadcast services Very well suited for mobile reception High robustness against Multipath reception High quality digital audio services (near CD quality) 3/2/2007 Digital Audio Broadcasting systems 3
  4. 4. Introduction Ancillary data transmission (e.g. travel and traffic information, still and moving pictures, etc.) Larger coverage area than current FM and AM systems Efficient frequency spectrum use Low transmitting power 3/2/2007 Digital Audio Broadcasting systems 4
  5. 5. DAB species DAB (Eureka 147 project) ETSI standard In Band On Channel (IBOC) DAB (High definition radio project) NRSC standard ISDB Japanese standard Digital TV & audio 3/2/2007 Digital Audio Broadcasting systems 5
  6. 6. History of DAB In 1980s the first digital sound broadcasting systems providing CD like audio quality for satellite delivery. Frequency band 10 to 12GHz Little sound data compression Not aimed at mobile reception In 1987 the Eureka-147 project was born First DAB standard was achieved in 1993 In 1995 the ETSI adopted DAB as the only European standard for digital radio 3/2/2007 Digital Audio Broadcasting systems 6
  7. 7. DAB specification 1.5 MHz bandwidth Frequency band between 30MHz to 3GHz 1.5 Mbit/s signal rate 8-384 kbit/s audio rate Up to 63 mono audio channel or 12 stereo audio channel 3/2/2007 Digital Audio Broadcasting systems 7
  8. 8. Block diagram [6] 3/2/2007 Digital Audio Broadcasting systems 8
  9. 9. Important block 24 or 48 Khz PCM audio signal To RF Unit Mpeg II Encoder 3/2/2007 Energy dispersal scrambler Covoloutio nal Encoder Time Interleaving QPSK symbol Mapper Digital Audio Broadcasting systems OFDM symbol Gernerator 9
  10. 10. DAB World Coverage Map [6] 3/2/2007 Digital Audio Broadcasting systems 10
  11. 11. IBOC DAB Permit a smooth evolution from current analog radio broadcasting to fully digital radio broadcasting. Allow broadcaster to keep current analog transmission No new spectrum required for AM or FM transmission Near CD Quality for FM FM stereo quality sound for AM station No new tower or transmitter site New data capabilities for AM and FM stations 3/2/2007 Digital Audio Broadcasting systems 11
  12. 12. IBOC DAB History 2001 iBiquity was born 2002 IBOC technology approved by the FCC 2003 First AM and FM stations begin broadcasting with HD Radio April, 2005 IBOC DAB Standard (NRSC-5) approved 3/2/2007 Digital Audio Broadcasting systems 12
  13. 13. IBOC DAB RF/transmission subsystem Coding and interleaving Mapping Orthogonal frequency division multiplexing (OFDM) modulation Up-conversion to the AM or FM band Transport and service multiplex Takes the audio and data information Generate stream of packets Audio and data input subsystems Audio source coding 3/2/2007 Digital Audio Broadcasting systems 13
  14. 14. Block diagram [1] 3/2/2007 Digital Audio Broadcasting systems 14
  15. 15. Transmission subsystem Interface Layer Transfer PDU frames Logical Channels specify grade of service Channel Coding Scrambling (Energy dispersal) Channel Encoding Interleaving 3/2/2007 Digital Audio Broadcasting systems 15
  16. 16. Transmission subsystem Subcarrier Mapping and Modulation QPSK, 16QAM,64QAM 2048 OFDM modulation Pulse shaping Up conversion 3/2/2007 Digital Audio Broadcasting systems 16
  17. 17. IBOC DAB Hybrid waveform Extended hybrid waveform [1] 3/2/2007 Digital Audio Broadcasting systems 17
  18. 18. IBOC DAB All digital waveform [1] 3/2/2007 Digital Audio Broadcasting systems 18
  19. 19. Mobile radio channels Attenuation Multipath Effects Doppler Shift [2] 3/2/2007 Digital Audio Broadcasting systems 19
  20. 20. Radio Propagation Effects [3] 3/2/2007 Digital Audio Broadcasting systems 20
  21. 21. Attenuation source Any objects which obstruct the line of sight signal Diffract off the boundaries of obstructions Low frequencies diffracting more than high frequency signals High frequency signals, require line of sight for adequate signal strength 3/2/2007 Digital Audio Broadcasting systems 21
  22. 22. Multipath effects 3/2/2007 Digital Audio Broadcasting systems 22
  23. 23. Fast fading Relative phase of multiple reflected signals can cause constructive or destructive interference at the receiver [3] 3/2/2007 Digital Audio Broadcasting systems 23
  24. 24. Rayleigh Fading Rayleigh distribution describes the probability of the signal level being received due to fading. 3/2/2007 Digital Audio Broadcasting systems 24
  25. 25. Frequency Selective Fading Channel spectral response is not flat Deep nulls in the received signal power For narrow bandwidth entire signal can be lost This can overcome in two ways: Transmitting a spread spectrum as CDMA Split the transmission into many small bandwidth carriers (OFDM) 3/2/2007 Digital Audio Broadcasting systems 25
  26. 26. Delay Spread Time spread between the arrival of the first and last multipath signal Lead to inter-symbol interference ISI can be minimized by CDMA or OFDM [3] 3/2/2007 Digital Audio Broadcasting systems 26
  27. 27. Doppler Shift When a wave source and a receiver are moving relative to one another the frequency of the received signal changed Significant problems If transmission technique is sensitive to carrier frequency offsets (COFDM) Relative speed is very high 3/2/2007 Digital Audio Broadcasting systems 27
  28. 28. OFDM Similar to FDM but OFDM uses the spectrum much more efficiently Multicarrier technique Divides the spectrum into many carriers Sub carrier are orthogonal to each other bandwidth of each channel is typically 10kHz30kHz (for voice communications) Multipath tolerance (by guard interval) 3/2/2007 Digital Audio Broadcasting systems 28
  29. 29. OFDM generation [3] 3/2/2007 Digital Audio Broadcasting systems 29
  30. 30. OFDM Noise performance was depend on the modulation technique used for modulating each carrier Minimum SNR required for BPSK was ~7dB, ~12dB for QPSK and ~25dB for 16PSK Total immunity to multipath delay spread when reflection time is less then the guard period Delay Spreads of up to 100µsec could be tolerated, corresponding to multipath reflections of 30km 3/2/2007 Digital Audio Broadcasting systems 30
  31. 31. OFDM It is very sensitive to frequency, and phase errors between the transmitter and receiver phase noise of the transmitter Frequency offset errors between the transmitter and receiver This problem can be overcome by synchronizing the clocks or by reducing the number of carriers used. 3/2/2007 Digital Audio Broadcasting systems 31
  32. 32. OFDM Clipping of the OFDM signal have little effect on the performance Allowing the peak power of the signal to be clipped up to 6 - 9dB Tolerance to clipping reduces the dynamic range overhead 3/2/2007 Digital Audio Broadcasting systems 32
  33. 33. Adding Guard interval to OFDM Robustness against multipath delay spread The level of robustness, can be increased more by the addition of a guard period Cyclic extension effectively extends the length of the symbol without loss of orthogonality 3/2/2007 Digital Audio Broadcasting systems 33
  34. 34. OFDM system implementation Using general purpose DSPs most of the processing is required in performing the fast fourier transform (FFT) The complexity of performing an FFT is dependent on the size of the FFT. 3/2/2007 Digital Audio Broadcasting systems 34
  35. 35. Complexity of FFT 3/2/2007 Digital Audio Broadcasting systems 35
  36. 36. Required Processing Power Example 3/2/2007 Digital Audio Broadcasting systems 36
  37. 37. CDMA What is CDMA (Code Division Multiple Access) Spread spectrum technique Narrow band message is multiplied by a pseudo random noise code (PN code) All channels use the same frequency band and transmit simultaneously Signal is recovered by correlating the received signal with the PN code used 3/2/2007 Digital Audio Broadcasting systems 37
  38. 38. CDMA DAB [3] Signal hiding and non-interference with existing systems. Accurate Ranging Multiple User Access Multipath tolerance 3/2/2007 Digital Audio Broadcasting systems 38
  39. 39. CDMA generation [3] 3/2/2007 Digital Audio Broadcasting systems 39
  40. 40. CDMA Data to be transmitted is spread by modulating the data using a PN code. Received signal is recovered by multiplying the signal by the original spreading code [3] 3/2/2007 Digital Audio Broadcasting systems 40
  41. 41. Comparison OFDM was found to perform very well compared with CDMA OFDM allow up to 2-10 times more channel than CDMA 3/2/2007 Digital Audio Broadcasting systems 41
  42. 42. Reference 1. 2. 3. 4. 5. NRSC-5 standard: “In-Band on Channel Digital Radio Broadcasting Standard NRSC-5,” April, 2005. H. U. Bilbao, “DAB Transmission System Simulation,”M.Sc Thesis, August 2004. E. Lawrey, “The suitability of OFDM as a modulation technique for wireless telecommunications, with a CDMA comparison” M.SC Thesis S.Y. Yeo, M.S. Beak, M.J. Kim, Y.H. You, "High capacity and reliability techniques for digital audio broadcasting system," IEEE Transactions on Consumer Electronics, vol. 50, no. 2, MAY 2004. H. C. Papadopoulos, C. W. Sundberg, “Postcanceling techniques for simultaneous broadcasting of analog FM and digital data," IEEE Transactions on Communications, vol. 51, no. 1, January 2003[3] 3/2/2007 Digital Audio Broadcasting systems 42
  43. 43. References 6. ETSI EN 300 401 “Radio Broadcasting Systems Digital Audio Broadcasting (DAB) to mobile, portable and fixed receivers” 3/2/2007 Digital Audio Broadcasting systems 43
  44. 44. Questions? 3/2/2007 Digital Audio Broadcasting systems 44

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