University of Canberra Advanced Communications Topics

1. University of Canberra Advanced Communications Topics Television Broadcasting into the Digital Era Lecture 4 Error Correction, DTTB Planning & System Information by: Neil Pickford

2. 64-QAM - Perfect & Failure

3. COFDM DTTB Block Diagram Error Correction

4. Forward Error Correction (FEC) N bits Encode Tx/Rx Decode N bits N+Code N+Code+Error • Broadcast transmission • One way process - Tx to Rx • Not possible to repeat any errored data • Forward Error Correction is a technique used to improve the accuracy of data transmission • Extra redundant bits are added to the data stream • Error correction algorithms in the demodulator use the extra FEC bits to correct data errors • C OFDM uses a Convolutional FEC code

5. Convolutional Coder 1111001 X Output 1-Bit Delay 1-Bit Delay 1-Bit Delay 1-Bit Delay 1-Bit Delay Data Input 1-Bit Delay Y Output 1011011 6 5 4 3 2 1 0

6. Puncturing Codes (FEC) • The X and Y outputs of the Convolutional coder are selected in a Puncturing pattern

7. Inner Coding X Coded Data Data Y • Convolutional coder generates the X & Y codes • Puncturing operation selects X & Y in sequence • Result then scrambled with an interleaver Convolutional Encoder Puncturing Interleaver

8. Viterbi Decoder • A special type of data decoder designed to work with convolutional FEC codes • Uses the past history of the data to identify valid future data values • Element in the Receiver Only

9. Reed Solomon (RS) • RS is a Block data correcting Code • Hamming type cyclic Polynomial sequence • Code Generator Polynomial: g(x) = (x+l0)(x+l1)(x+l2)...(x+l15), l=02 Hex • Field Generator Polynomial: p(x) = x8 + x4 + x3 + x2 + 1 • Has special ability to correct multiple bursts of errors in a code block • DVB-T uses 204 bytes for each 188 byte Packet(ATSC uses 207 bytes for each 187 byte Packet) • Can correct 8 bytes in each 204 byte packet

10. Error Protection - Order Inner Code FEC (2/3) Data Input Interleaver Interleaver Error Protected Data Mapper 188 Bytes 204 Bytes Outer Code RS (204,188) 306 Bytes 204 Bytes 2448 Bits 6 bits x 1512 Carriers6 bits x 6048 Carriers 64 QAM

11. DVB-T - Bit Rates [2k] 16 - 64 - 16 - 64 - 16 - 64 - QPSK QPSK QPSK QAM QAM QAM QAM QAM QAM 1/2 4.35 8.71 13.06 4.84 9.68 14.51 5.28 10.56 15.83 2/3 5.81 11.61 17.42 6.45 12.90 19.35 7.04 14.07 21.11 3/4 6.53 13.06 19.59 7.26 14.51 21.77 7.92 15.83 23.75 5/6 7.26 14.51 21.77 8.06 16.13 24.19 8.80 17.59 26.39 7/8 7.62 15.24 22.86 8.47 16.93 25.40 9.24 18.47 27.71 D/Tu = 1/4 D/Tu = 1/8 D/Tu = 1/32 7 MHz 64 us 32 us 8 us Code Rate Page 21 Table A1 - AS4599-1999

12. DVB-T - C/N Values 64 - QAM GAUSSIAN RICEAN RAYLEIGH 16 - 16 - 64 - 16 - 64 - Code QPSK QPSK QPSK Rate QAM QAM QAM QAM QAM 1/2 3.10 8.80 14.4 3.60 9.60 14.70 5.40 11.20 16.00 2/3 4.90 11.1 16.5 5.70 11.60 17.10 8.40 14.20 19.30 3/4 5.90 12.5 18.00 6.80 13.00 18.60 10.70 16.70 21.70 5/6 6.90 13.5 19.30 8.00 14.40 20.00 13.10 19.30 25.30 7/8 7.70 13.9 20.10 8.70 15.00 21.00 16.30 22.80 27.90 Simulated Theoretical Thresholds (bandwidth independent)

13. C/N - Signal Level Performance 28 24 20 16 C/N Threshold (dB) 12 8 4 0 10 15 20 25 30 35 40 45 50 55 60 Receiver Signal Level (dBuV)

14. General Parameters - Aust Tests Parameter DVB-T ATSC Data Payload 19.35 Mb/s 19.39 Mb/s Carriers 1705 1 Symbol Time 256 us 93 ns Time Interleaving 1 Symbol 4 ms Reed Solomon code rate 188/204 187/207 IF Bandwidth (3 dB) 6.67 MHz 5.38 MHz 19

15. 8VSB vs COFDM Latest

16. 7 MHz COFDM Modulator Spectrum 0 -10 -20 Power Spectrum Density (dB) -30 -40 8k 1/32 Guard 2k 1/32 Guard -50 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 Frequency Offset (MHz)

17. Frequency Planning • Fundamental Matter - Scarce Resource • Analogue Rules set limit to more Services • No NEW TV Spectrum is Available • Digital Transmission changes Rules • Signals have different behaviour • Digital Signals can occupy unused space- “Taboos” • Digital Needs to fit in with Existing PAL • Eventually Digital Only - but long wait??

18. Digital Has to Fit In With PAL 28 29 30 31 32 33 34 35 28 29 30 31 32 33 34 35 • World TV channel bandwidths vary • USA / Japan 6 MHz • Australian 7 MHz • Europeans 8 MHz • Affects:- tuning, filtering, interference & system performance 28 29 30 31 32 33 34 35

19. Channel Spacing • Existing analog TV channels are spaced so they do not interfere with each other. • Gap between PAL TV services • VHF 1 channel • UHF 2 channels • Digital TV can make use of these gaps Ch 8 Ch 9A Ch 9 Ch 7 Ch 6 Taboo Taboo Taboo VHF Television Spectrum

20. Digital Challenges • Digital TV must co-exist with existing PAL services • DTV operates at lower power • DTV copes higher interference levels • Share transmission infra-structure • DTV needs different planning methods Ch 8 Ch 9A Ch 9 Ch 7 Ch 6 8-VSB COFDM VHF Television Spectrum

21. DTTB & PAL

22. UHF Channels: London Photograph by courtesy and © BBC R&D

23. Planning Issues • Channel Disturbances: • Noise, at edge of area with NO interference • Interference, Co Channel Interference and Adjacent Channel Interference • Multipath, Echoes:How Many, How Large, Moving? • Antenna Pattern? • Static Roof Top? Directional? Wideband? • CCIR Antenna Rec BT-419-3 • Portable Receivers? No Antenna? • Frequency Re-Use Distances • Terrain Data • Propagation Models • Protection Ratios

24. Signal Strength SIGNAL STRENGTH, MicroVolts REGION OF SERVICE FAILURES FOR PERCENTAGE OF TIME MEAN RECEIVER C/N LIMIT TIME

25. Digital Service Area Planning • Analog TV has a slow gradual failure • Existing PAL service was planned for:50 % availability at 50 % of locations • Digital TV has a “cliff edge” failure • Digital TV needs planning for:90-99 % availability at 90-99 % of locations

26. TV System Failure Characteristic Good Quality Edge of Service Area Rotten Far Close Distance

27. TV System Failure Characteristic Good Quality Edge of Service Area Rotten Far Close Distance

28. TV System Failure Characteristic Good HDTV PAL Quality SDTV Edge of Service Area Rotten Far Close Distance

29. Service Area Planning Modulation Typical Choice of C/N Dependent Variation PICTURE QUALITY DIGITAL 5 4 ANALOGUE 3 THRESHOLD OF ACCEPTABILITY 2 ANALOGUE FAILURE C/N 1 NO SERVICE 40 45 35 15 20 25 30 10

30. Service Areas - Current 50 - 100 KILOMETRES TRANSMITTER B TRANSMITTER A

31. Service Areas - SFN 50 - 100 KILOMETRES TRANSMITTER B

32. Digital Provides New Concepts • Single frequency networks (SFNs) can help solve difficult coverage situations • SFNs allow the reuse of a transmission frequency many times in the same area so long asexactly the same program is carried • Allows lower power operation • Better shaping of coverage • Improved service availability • Better spectrum efficiency

33. MPEG Packet

34. System Level Multiplexing Approaches

35. Packetisation Approaches Fixed Length Variable Length

36. Transport Stream Link Header Format

37. System Information (SI) • Required for : • Automatic Tuning of receiver upon selection • Program location • EPG (Electronic Program Guide) • API (Application Programming Interface) • CA (Conditional Access)

38. DVB SI Model Networks Terrestrial Satellite Cable Transport Streams Transponder 1 Transponder 2 Transponder 3 Transponder T Channel 2 Channel C Channel 2 Channel C Channel 1 Channel 1 Services Bouquet Service 1 Service 2 Service S Service 1 Service 2 Service S Service 1 Service 2 Service 3 Service S Components Video Audio 1 Audio 2 Data

39. System Information • The DVB SI structure has it’s derivation in MPEG ISO/IEC 13818-1 and is defined in a set of tables. • The primary link between DVB SI and MPEG is the“PSI” (Program Specific Information) in MPEG and is contained primarily in the “PAT”, “PMT” and “CAT” set of tables

40. What is SI? • SI data provides information for: • Automatic tuning to transport stream • User Information for: • Service selection • “Event” selection • “Component” selection • PSI data provides information for: • Configuration of decoder for selected Service • DVB extensions for non-MPEG components

41. PSI and DVB SI Tables NIT ACTUAL Delivery Sys. PID=0x0010 PID=0x0000 NETWORK INFORMATION. PID=P BOUQUET INFORMATION. PMT BAT SDT ACTUAL TS SERVICE DESCRIPTION. PID=Ox0011 EIT ACTUAL TS EIT OTHER TS PID=Ox0001 CAT EIT ACTUAL TS EVENT INFORMATION. PID=0X0012 PID=0X0002 PCR TSDT TOT PID=0X0012 TDT TIME OFFSET. DVB OPTIONAL MPEG DVBMANDATORY NIT OTHER Delivery Sys. PID=0x0010 PAT PID=Ox0011 SDT OTHER TS PID=Ox0011 ST RST STUFFING TABLE. PROGRAMME CLOCK REF. RUNNING STATUS. TIME AND DATE.

42. MPEG Program PIDs • What is a program ? • MPEG has a definition which is different to that normally understood. • A “program” in broadcasting is a collection of elements with a common time base and the same start and stop times. • A program in MPEG is a collection of elements with a common time base only. That is a collection of elementary streams with same PCR_PID and referenced to the same program_number

43. Virtual Channels & PCR Timing • A conventional Broadcaster of a TV channel or service having one program would be composed of a series of “broadcaster programs” or events with the same program_number and a common PCR_PID. • In other words the PCR time base effectively creates a virtual channel which may be associated with a single or multiple program_numbers. • A TV channel having multiple programs would have multiple program_numbers with either single or multiple PCR_PID between program streams. NOTE : Services with different program_numbers may draw upon the same video as with the case of multilingual services.

44. Decoding the Program • Decoding the correct program (ie “channel”) ? • Where there are several Transport Streams available to a decoder, in order to successfully demultiplex a program, the decoder must be notified of both the transport_stream_id (to find the correct multiplex) and the program_number of the service (to find the correct program within the multiplex). Note again the program here refers to the channel not the event or actual broadcast program. • Now to the various main table purposes :

45. PAT, PMT & CAT Tables • PAT (Program Association Table) • provides the link between the transport_stream_id, the program_number and the program_map_id (PMT). • PMT (Program Map Table) • when pointed to from the PAT, the PMT provides the associated group of elements (video, audio etc) with the program_number. • CAT (Conditional Access Table) • provides the association between CA system(s) and their EMM (Entitlement Management Messages) streams and any special parameters associated with them.

46. DVB SI Features • Data structured as several “Tables” • Structures use “fixed format” for essential data, and descriptors for optional or variable-length data (similar to PSI) • Efficient data transmission • Extensible while maintaining compatibility • Support for “private” extensions • Can provide standard EPG data-stream • “Look and Feel” determined by receiver software • Resident or Downloaded

47. SI Features: NIT • Network Information Table • Identification of transmission as a member of a group of multiplexes - “Network” • Network Name • Tuning parameters with support for various delivery media • List of additional frequencies for terrestrial transmission • Designed for simple transcoding of transport streams

48. SI Features: SDT & BAT • Service Description Table • Identifies all Service names and Service types in TS • Linked Services • Pointer to MPEG Program in PSI • Service_id = MPEG Program Number • Bouquet Association Table (Optional) • Groupings of Services • May convey “logical channel number”

49. SI Features: EIT • Present/Following • Information on current and next events • Schedule (optional) • Up to 64 days ahead - ordered by service and time • Event Information • Title, short description • Start time & duration • Content classification & parental rating • Longer text description • Information on components

50. SI Features: TDT,TOT, RST • Time and Date Table • Transmission of current time for automatic setting of receiver clock • Time Offset Table (optional) • Transmission of time offset by zone - both current, and next offset values, with date at which next occurs • Running Status Table (optional) • Mechanism for signalling status transitions with greater timing precision