1. 1 DTTB Lab Tests Methodology & Results Summary Presentation by: Neil Pickford Communications Laboratory http://www.commslab.gov.au

2. 2 Overview n Digital Television Objectives & Technology n DTTB Transmission Technology n The Australian Test Program n Laboratory Tests - Test Rig n Laboratory Tests - Main Results n Field Test Objectives & Equipment n Summary Field Test Results n Selection Process & Criteria n Selection Result & Future

3. 3 Digital Television Why digital? n Noise free pictures n Higher resolution images Widescreen / HDTV n No ghosting n Multi-channel sound n Other services.

4. 4 Broad Objectives of DTB n Overcome limitations of the existing analog television system n Improved picture u High quality (no interference) u Resolution (HDTV) u Format (16:9) n Enhanced Audio services n Data capacity available for other value added services

5. 5 Enabling Technologies n Source digitisation (Rec 601 digital studio) n Compression technology (MPEG, AC-3) n Data multiplexing (MPEG) n Display technology (large wide screens) n Transmission technology (modulation)

6. 6 Transmission Technology n The transmission system is used to transport the information to the consumer. n The system protects the information being carried from the transmission environment n Current Australian analog television uses the PAL-B AM modulation system

7. 7 Digital TV Transmission Technology n The transmission system is a “data pipe” n Transports data rates of around 20 Mb/s n Transports data in individual containers called packets

8. 8 DTTB Transmission Systems n 3 systems are being developed at present. u USAATSC 8-VSB u EuropeDVB-T COFDM u JapanISDBBand Segmented Transmission OFDM

9. 9 8-VSB - USA n Developed by the advance television systems committee - ATSC n Developed for use in a 6 MHz channel u A 7 MHz variant is possible. n Uses a single carrier with pilot tone n 8 level amplitude modulation system n Single Payload data rate of 19.39 Mb/s n Relies on adaptive equalisation n Existing AM technology highly developed

10. 10 COFDM - Europe n Developed by the digital video broadcasting project group - DVB n Uses similar technology to DRB n Uses 1705 or 6817 carriers n Variable carrier modulation types are defined allowing Payload data rates of 5-27 Mb/s in 7 MHz n Developed for 8 MHz channels u A 7 MHz variant has been produced and tested n Can use single frequency networks - SFNs n New technology with scope for continued improvement & development

11. 11 The Australian DTTB Test Program n Australia is interested in a Digital HDTV Future n Australia has a Unique Broadcasting Environment n Overseas Digital TV Developments were interesting but the results could not be directly related to Australia. n To make informed decisions we needed to collect information relevant to our situation. n We had a few Questions.

12. 12 Aims of Australian DTTB Testing-1 Australia needed to know: n How does DTTB perform with VHF PAL-B? n What Protection does PAL require from the DTTB service for: u Co-Channel? u Adjacent Channel? Subjective Assessment u Is Signal level a factor?

13. 13 Aims of Australian DTTB Testing-2 n How Quickly does the system degrade? n What are the real system thresholds? u Signal Level u Carrier to Noise u Payload Data Rate in 7 MHz n How does DTTB cope with Interference?

14. 14 Aims of Australian DTTB Testing-3 n What Protection does DTTB require from the PAL-B service for: u Co-Channel? u Adjacent Channel? u Is Signal level a factor? n What Protection does DTTB require from other DTTB services?

15. 15 Aims of Australian DTTB Testing-4 n How does DTTB perform in a 7 MHz Channel Environment? n How sensitive is DTTB to practical Transmission Equipment? How important is: u Transmitter Linearity? u Transmitter Precorrection? u Transmitter Output Filtering? u Combined Feeder/Antenna Systems?

16. 16 Aims of Australian DTTB Testing-5 n Is DTTB affected by Multipath Echoes? u Are Pre-Echoes a Problem? u What happens past the Guard interval? n Is DTTB affected by Doppler Shift? n Is DTTB affected by Dynamic Flutter? n Is DTTB affected by Impulsive Interference? n How does DTTB perform in the Field cw PAL Lots of Questions but Few Definitive Answers! Lots of Questions but Few Definitive Answers!

17. 17 Scope of Tests n The test program began with the aim of answering these questions for DVB-T n During the early stages of testing ATSC was floated as a Candidate Digital TV System n The test program’s scope was increased and a comparative focus adopted. n All tests were designed to be as generally applicable as possible to any Digital TV Modulation System.

18. 18 Order of Measurements n FACTS Advanced TV Specialists Group directed the priority of Testing n Laboratory Tests First Ê DTTB into PAL protection Ë DTTB System Parameters Ì PAL into DTTB protection Í Other Interferers & Degradations n Field Tests Later

19. 19 Test Rig - Block Diagram

20. 20 Laboratory Tests - Test Rig EUTC/N Set & AttenuatorsPAL & CW Spectrum AnalysersControl Computer Domestic Television Receiver Modulator Control Computers Plot & Printing

21. 21 Test Rig - Modulation Equipment COFDM Modulator MPEG Mux MPEG Encoder MPEG Mux 8-VSB Modulator RF LO Power Meter PAL & CW Interference Generators

22. 22 Laboratory Tests - Transmitters Tx LO Spectrum Analyser Digital CRO Harris Exciter Power Meter Harris 1 kW Tx NEC 200 W Tx Loads Echo Combiner

23. 23 Digital Transmitters TCN-9 Sydney

24. 24 Lab Tests - VHF/UHF Transposer VHF Input Filter RF Amp Mixer 10 Watt UHF Amplifier RF LO Power Supply Level Adjust UHF Amps UHF BPF Filter

25. 25 COFDM - Commercial Receiver n News Data Systems - System 3000

26. 26 COFDM - Test Rx Hardware

27. 27 8-VSB - Test Rx Hardware

28. 28 Main Results - Lab Tests n C/N ATSC 4 dB better than DVB-T. This Advantage offset by Poor Noise Figure n DVB-T is better than ATSC for Multipath n ATSC is better than DVB-T for Impulse Noise n ATSC cannot handle Flutter or Doppler Echoes n ATSC is very sensitive to Transmission system impairments and IF translation n DVB-T is better at handling Co-channel PAL n DVB-T is better rejecting on channel interference (CW)

29. 29 8-VSB & COFDM - Spectrum 8-VSB COFDM

30. 30 Digital Modulation - 8-AM 3 Bits/Symbol +7 -5 -3 +1 +3 +5 -7 8-VSB - Coaxial Direct Feed through Tuner on Channel 8 VHF Before EqualiserAfter Equaliser

31. 31 Spectrum of COFDM DTTB 6.67 MHz in 7 MHz Channel Almost Rectangular Shape 1705 or 6817 Carriers 7 MHz Carrier Spacing 2k Mode 3.91 kHz 8k Mode 0.98 kHz 5.71 MHz in 6 MHz Channel

32. 32 64-QAM - Perfect & Failure

33. 33 General Parameters - Aust Tests ParameterDVB-TATSC Data Payload19.35 Mb/s19.39 Mb/s Carriers17051 Symbol Time256 us93 ns Time Interleaving1 Symbol4 ms Reed Solomon code rate188/204187/207 IF Bandwidth (3 dB)6.67 MHz5.38 MHz

34. 34 General Parameters ParameterDVB-TATSC IF centre Frequency35.3 MHz44.0 MHz Receiver AFC range11.5 kHz359 kHz Latency including MPEG coding SDTV 8 Mb/s37 Frames

35. 35 C/N, NF & Payload Rate Table

36. 36 AWGN Receiver Performance ParameterDVB-TATSC Carrier to Noise Threshold (in native system BW)19.1 dB15.1 dB Simulated Theoretical C/N for optimum system16.5 dB14.9 dB Minimum Signal Level25.2 dBuV27.2 dBuV Receiver noise figure4.6 dB11.2 dB Rx Level for 1 dB C/N Loss34 dBuV35 dBuV

37. 37 Receiver Parameters n Guard interval u Affects payload data rate and echo performance u No impact on general receiver parameters such as C/N & Signal level. n COFDM Transmission Parameter Signalling (TPS) - receiver automatically determines the modulation type, FEC n Currently Guard interval needs to be entered into the receiver.

38. 38 DTTB System Multipath Character 031525 15 19 35 Multipath Level ( - dB) 8VSB COFDM (64QAM,2/3,1/8) C/N Threshold (dB) Indoor AntennaOutdoor Antenna (Conditions: Static multipath, Equal Rx NF, No Co-channel or impulse interference)

39. 39 AWGN C/N Performance

40. 40 AWGN Performance n C/N 4 dB more power required for DVB-T to achieve the same coverage as ATSC. n Better C/N performance ATSC offset by poor receiver noise figure n ATSC C/N is very close to the theoretical DVB-T implementation is still over 2.5 dB higher than the simulated margin. n Other DVB-T modes have different C/N Thresholds and Data Rates

41. 41 Multipath & Flutter Measurements ParameterDVB-TATSC 7.2 us Coax pre ghost0 dB-13.5 dB 7.2 us Coax post ghost0 dB-2.2 dB Echo correction range32 us +3 to -20 us Doppler single echo performance (-3 dB echoes)140 Hz1 Hz

42. 42 Doppler Echo - 7.5 us Coax Echo Level E/D (dB) Frequency Offset (Hz) 0-500200-200500 -20 -10 -5 0 -15 -25 COFDM 8-VSB

43. 43 Multipath & Flutter - Overview n ATSC system 2 Equaliser modes u Rx Eq switches to fast mode when short variable echoes are detected. u Lab Tests - slow equalisation mode. n 8 VSB degrades more rapidly when multipath echo exceeds -7 dB n COFDM works up to 0 dB in a white noise environment but in this condition is very fragile.

44. 44 Transmitter Performance Sensitivity ParameterDVB-TATSC Transmitter/Translator Linearity & Inter-mod SensitivityLowHigh Group Delay / Combiner / Filter SensitivityLow< 50 ns

45. 45 Transmission Strategies Suggested Transmission System performance maintenance strategy n DVB-T - Manual Maintenance same as PAL n ATSC - Automatic Dynamic pre-corrector Gap Fill coverage - System Strategy n DVB-T - IF Translator, Digital Repeater or SFN n ATSC - Digital Repeater

46. 46 Transmission Performance - 1 n ATSC very sensitive to transmission impairments as it uses up correction capacity in the receiver equaliser. n ATSC equaliser has to correct the response characteristic of the whole channel. n DVB-T equaliser uses pilot carriers spread throughout the spectrum to equalise the channel in small 16-50 kHz sections.

47. 47 Transmission Performance - 2 n ATSC Dynamic Pre-corrector will be difficult to apply in the combined antenna systems used in Australia n Zenith suggest transmission without using a transmitter output filter to avoid group delay problems with 8-VSB. n ATSC 6 MHz system operating in a 7 MHz channel helps this situation.

48. 48 Transmission Performance - 3 n If using existing PAL vision transmitters: u Recalibration of metering will be necessary (Peak to Average) u AGC / AFC and protection systems may require modification

49. 49 Impulse Noise - Results n Impulse Sensitivity (Differential to PAL grade 4) u DVB-T 9 -14 dB u ATSC 17-25 dB n Difficult to measure & characterise. n Mainly affects the lower VHF frequencies n ATSC is 8 to 11 dB better at handling impulsive noise than DVB-T

50. 50 Impulse Noise - Plot

51. 51 Impulse Noise - Overview n n ATSC only has a few data symbols affected by any normal impulsive phenomenon n n The DVB-T COFDM demodulation (FFT) spreads the energy from a broad spectrum impulse across all carriers leading to massive data loss when the impulse is large enough.

52. 52 DTTB into PAL - Subjective

53. 53 DTTB into PAL - Overview n n DVB-T marginally less interference to PAL n n DTTB Co channel signals need to be kept at least 46 dB on average below the Wanted PAL level to ensure Grade 4 reception n n DTTB Adjacent channel signals need to be kept on average at or below the Wanted PAL level to ensure Grade 4 reception

54. 54 PAL into DTTB - Results

55. 55 PAL into DTTB - Plot

56. 56 Co Channel PAL into DTTB - Plot

57. 57 Off Air PAL into DTTB - Plot

58. 58 DTTB & PAL - 0 dB Spectrum

59. 59 PAL into DTTB - Overview 1 n n The narrower ATSC system achieves very similar out of band / adjacent channel performance to DVB-T. n n ATSC is nearly 8 dB worse than DVB-T when subjected to interference from Co- Channel PAL transmissions

60. 60 PAL into DTTB - Overview 2 n n In situations where Co-Channel DTTB and PAL signals exist the DTTB into PAL interference will be the dominant factor, providing directional antennas are used. n n If a DTTB frequency offset was being considered for use, the data indicates that moving up in frequency is preferable to moving down.

61. 61 CW into DTTB - Plot

62. 62 CW into DTTB - Summary n n DVB-T is on average 15.5 dB less sensitive across the channel to general CW type interferers than ATSC n n The DVB-T orthogonal carrier spacing is evident for DVB-T in this measurement with a variation of over 8 dB. If known CW interferers are likely then a frequency offset of less than 4 kHz may assist system performance.

63. 63 CW into DTTB centre channel

64. 64 CW into DTTB - Comment n n ATSC has occasional peaks due to critical equaliser responses. n n The DVB-T response above was obtained from the improved equaliser which was provided near the end of the tests.

65. 65 DTTB into DTTB - Overview n Adjacent channel performance of ATSC is better than DVB-T n The Co-channel protection of both digital systems approximates to the system carrier to noise threshold.

66. 66 DTTB into DTTB - Plot

67. 67 DTTB Field Testing Objectives n Investigate the difference in reception character for the two DTTB modulation systems. n Provide information to DTTB system planners n To provide Credible data. A DTTB Field Trial is study of Failure !! In comparison with current PAL television In various reception conditions :

68. 68 Field Testing - Van n A field test vehicle was built in a small van.

69. 69 Field Testing - On the Streets n Over 115 sites were measured

70. 70 Field Test Vehicle Block Diagram NoiseSource 5waysplitSpectrumAnalyser Plisch PAL Demodulator DVB-TReceiver ATSCReceiver Vector Signal Analyser BERMeter CRO PALMonitor VM-700 -20dB 11.5 dB NF 3.6 dB -7 dB Inputlevel NoiseInjection Ch 6-11 VHF Antenna on a 10 m Mast

71. 71 Field Testing - Method n Field tests were conducted in Sydney over a 1 month period on VHF channel 8. n Some simultaneous tests were conducted on VHF channel 6 n Power level for the field test was 14 dB below adjacent analog television channels 7 & 9 n Analog and digital television performance for both systems were evaluated at each site. n Conducted by Independent Consultant & Mr Wayne Dickson of TEN

72. 72 Field Test - Data Collected each Site n Common Masthead Amp used (NF ~ 3.6 dB) n Analog PAL transmission character (7,9 & 10) n Measure level, multipath, quality & Video S/N n Measure DVB & ATSC reception (Ch 8) n Record DTTB & Analog Spectrum n Measure Noise Margin (C/N Margin) n Measure Level Threshold (Signal Margin) n Measure antenna off pointing sensitivity

73. 73 Australian DTTB Field Trial PAL Receive Margin

74. 74 Australian DTTB Field Trial DTTB compared to PAL

75. 75 Australian DTTB Field Trial 8VSB Decoder Margin

76. 76 Australian DTTB Field Trial COFDM Decoder Margin

77. 77 VHF - Band III UHF DOPPLER SHIFT (  Hz) 140 300 0 01000500100200300400600700800900 100 50 200 250 COFDM 2K, 3dB degrade COFDM 2K SPEED (Km/Hr) AIRCRAFT Vehicles Over Cities for current implementations for current implementations ATSC seeseparatecurves see separate curves COFDM implementations will inherently handle post and pre-ghosts equally within the selected guard interval. DTTB Systems Doppler Performance Limits

78. 78 VHF - Band III UHF 0 0 100 8VSB, “Fast Mode”, 3dB degrade SPEED (Km/Hr) Vehicles 8VSB 5 1 10 30231062 Aircraft for current implementations 8VSB implementations of equalisers are likely to cater for post ghosts up to 30 uSec and pre-ghosts up to 3 uSec only. DOPPLER SHIFT (  Hz) ATSC 8-VSB Doppler Performance Limits

79. 79 Field Test - Observations n At -14 dB DTTB power when there was a reasonable PAL picture both 8-VSB & COFDM worked at the vast majority of Sites n When PAL had: u Grain (noise) and some echoes (multipath), both 8-VSB & COFDM failed u Flutter, caused by aircraft or vehicles, 8-VSB failed u Impulsive noise & some grain, COFDM failed

80. 80 Results Conclusion n The assessment of the results presented in this summary depends largely on the specific system requirements of the broadcaster and the viewers. n The implementation and performance of both digital terrestrial transmission systems are still being improved, however the DVB-T system shows more scope for achieving future advances.

81. 81 The Selection Committee n A selection committee was formed from FACTS ATV specialists group Representing: u National broadcasters (ABC and SBS) u The commercial networks (7,9 & 10) u The regional commercial broadcasters u The Department of Communications and the Arts u The Australian Broadcasting Authority

82. 82 Selection Panel - Responsibility n Analysing the comparative tests and other available factual information n Establishing the relevance of the performance differences to Australian broadcasting n Recommending the system to be used

83. 83 Selection Criteria n Derived a set of 50 selection criteria relevant to the Australian transmission environment n Criteria were reduced to final 29 which could impact on the final decision n The criteria were weighted and an overall average used to rank the selection criteria

84. 84 Selection Criteria - Groups n Most Important Criteria Groupings u Coverage u System Design Elements u Operational Modes Supported u Overall System u Receivers

85. 85 Selection Criteria - Analysis n Assessed each of the selection criteria elements for each modulation system k Some criteria were put aside as it was felt there was not enough information to factually score those criteria

86. 86 Criteria - Coverage n Inner and outer service areas n Performance with Roof top antennas n Performance with Set top antennas * n Co-channel & Adjacent channel protection n Mobile Reception n Multipath (Ghosting, Doppler & Flutter) n Immunity to impulse noise

87. 87 Criteria - System Design Elements n Combining & use of common Tx Antenna n Requirements for implementing translators n Suitability for co-channel translators n Ability to use existing transmitters

88. 88 Criteria - Operational Modes Support n HDTV Support n Support for closed captioning n Multiple languages Audio n Surround Sound Audio System

89. 89 Criteria - Overall System n Accepted HDTV system n Performance within 7 MHz channel n Number useful Mb/s in 7 MHz n Ability to fit in existing infrastructure n Overall Modulation System Delay n System Flexibility, Upgrade Capacity & Future Development Capacity

90. 90 Selection Criteria - Receivers n Availability (for HDTV) MP@HL n Receiver Features & Cost n PAL and DTTB capability n Degree of customizing for Australia n Receiver Applications Software n Lock up time n Australian channel selection

91. 91 Selection Criteria Matrix

92. 92 Key Selection Criteria

93. 93 Selection Result - June 1998 n The selection committee unanimously selected the 7 MHz DVB-T modulation system for use in Australia n The criteria that were set aside would, however, not have changed the selection decision

94. 94 Overall Selection Influences n A single system for All Free to Air Broadcasters n Ability to meet Governments objectives for coverage n Able to deliver the HDTV quality objective n Availability of consumer products at acceptable costs n Solid support from proponent n Interoperability with other digital video platforms n Confidence in the system meeting the business objectives

95. 95 More Selections n Sub-committees formed to investigate: u Service information data standard u Multichannel audio system u HDTV video production format n July 1998 3 further recommendations u SI data standard be based on DVB-SI u AC3 multichannel audio is the preferred audio encoding format u 1920/1080/50 Hz interlaced 1125 lines is the preferred video production format

96. 96 DTTB Implementation Notes: n Although SFNs are of interest in Australia they will be of little use during the simulcast period. n Use may be made of Dual Frequency Networks during this period to increase spectrum efficiency n The channel frequency matrix will be adjusted when Analog services cease. Digital provides the capacity to repack the television spectrum.

97. 97 A Future Digital System Concept Hypermedia Integrated Receiver Decoder (IRD) MMDS Satellite Terrestrial Cable B-ISDN XDSL CD, DVD DVC BroadcastInteractivity

98. 98 The End Thank you for your attention Any questions?