Transcript Clegg(DTV)

National Science Foundation
Digital TV and Its Impact on
Radio Astronomy
Andrew CLEGG
U.S. National Science Foundation
[email protected]
Third Summer School on Spectrum Management for Radio Astronomy
Tokyo, Japan – June 3, 2010
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Analog Television Terrestrial
Broadcasting Standards
Abbrev
Name
Main Geographic Use
PAL
Phase Alternating Line
Most of Europe, Australia, Parts of
Asia (including India & China), Most of
Africa, Eastern South America
NTSC
National Television System
Committee
North & Central America, Western
South America, Japan, Philippines,
Thailand, Taiwan, South Korea
SECAM
Sequential Color with
Memory
France, Russia & former Soviet
republics, portions of Africa,
Madagascar
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Analog TV Standards Worldwide
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Digital Television Worldwide
•
•
•
•
•
Worldwide, terrestrial TV broadcasts are switching from
analog to digital modulation
> Different countries have different schedules for
switching over (most by 2015)
> Some satellite TV broadcasting has been digital for
more than 15 years
Japan is deploying ISDB-T technology, replacing NTSC
and analog HDTV MUSE standards
> ISDB-T also being widely deployed in South America
North America is deploying ATSC digital TV to replace
NTSC analog standard
> U.S. digital transition is completed for “full-service”
broadcasts; legacy NTSC remains for low-power
stations
Australia and Europe are deploying DVB-T
China is rolling its own (DMB-T)
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Digital TV Terrestrial Broadcasting Standards
Over-the-Air
Modulation Type
Main
Geographic
Use
Abbrev
Name
DVB-T
Digital Video
Broadcasting –
Terrestrial
Coded Orthogonal
Frequency Division
Multiplexing (COFDM)
(QPSK, 16QAM, and
64QAM)
Europe, Russia,
Australia, Parts of
Asia
ISDB-T
Integrated
Services Digital
Broadcasting Terrestrial
Coded Orthogonal
Frequency Division
Multiplexing (COFDM)
(DQPSK, QPSK, 16QAM,
and 64QAM)
Japan, South
America (ISDB-T
International)
ATSC
Advanced
Television
Systems
Committee
8-level Vestigial Sideband
(8VSB)
North America,
South Korea
DMB-T/H
Digital
Multimedia
Broadcast –
Terrestrial/
Handheld
Time Domain Synchronous
Orthogonal Frequency
Division Multiplexing (TDSOFDM)
China only
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Digital TV Standards Worldwide
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Digital Transition Worldwide
Completed, no analog / Completed for full-service stations / In transition /
Planned / No transition planned / No Information
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TV Spectra
Analog
Digital
DVB-T (OFDM)
PAL / SECAM / NTSC Generic
(All have video, chrominance, and audio
carriers. Some differences in total bandwidth
and frequency offset between carriers.)
ISDB-T (Yellow)
(OFDM)
PAL
ATSC
(8-VSB)
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Maximum Transmit Power (U.S.)
Chan
Freq (MHz)
Maximum Analog
EIRP (kW)
Maximum Digital
EIRP (kW)
2–6
54 – 72 & 76 – 88
164
74
7 – 13
174 – 216
518
262
14 – 51
470 – 698
8222
1640
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Fig. 1.14.5: Unwanted Emissions Limits for a Full-Power (1640 kW EIRP)
Digital TV Signal
-40
EIRP Limit for Unwanted Emissions
[dB(W/Hz)]
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DTV Unwanted Emissions Limits (U.S.)
(Assumes full-power 1640 kW EIRP)
-50
-60
-70
-80
-90
-100
-110
0
1
2
3
4
5
6
7
8
9
10
Frequency Offset from Channel Edge (MHz)
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Comparison of Analog (NTSC) and
Digital (ATSC) TV Signal Spectra
Direct comparison of digital (8-VSB modulation, left) and analog (AM-VSB, PM, and FM, right) TV
signals, of the same station from the same tower at the same time. The analog signal has more
power because of the large video carrier, but the digital signal fills in the spectrum completely.
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Comparison of Digital (ATSC) and
Analog (NTSC) Signals
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Ratio of Power Spectral Density of
Digital (ATSC) to Analog (NTSC)
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Detail of DTV/Analog TV
10
9
For equivalent digital and
analog TV signals, the digital
power spectral density
exceeds the analog PSD over
94% of the bandwidth, and by
as much as 3 orders of
magnitude.
8
(DTV PSD)/(Analog TV PSD)
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Ratio of Power Spectral Density of
Digital to Analog (detail)
7
6
5
4
3
2
1
0
0.000
1.000
2.000
3.000
4.000
5.000
6.000
Frequency Offset from Bottom of Channel (MHz)
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How to Identify TV Signal
Technology
Bandwidth
Most dominant spectral characteristic Secondary spectral characteristic
6 MHz
Strong video carrier peaked at 1.25 MHz
above bottom channel edge. When tuned
in AM mode on an appropriate receiver,
sounds like a buzzing sound that
changes with changes in the TV picture.
FM audio carrier 5.75 MHz above
bottom edge of channel (250 kHz
Chrominance carrier (phase and
below top edge). Audio can be clearly amplitude modulated) 4.829545 MHz
monitored in wideband FM mode with above bottom of channel.
appropriate radio receiver.
8 MHz
Strong video carrier peaked at 1.25 MHz
above bottom channel edge. When tuned
in AM mode on an appropriate receiver,
sounds like a buzzing sound that
changes with changes in the TV picture.
FM audio carrier 7.2496 MHz above
bottom edge of channel (250 kHz
Chrominance carrier 5.68361875 MHz
below top edge). Audio can be clearly
above bottom-edge of channel.
monitored in wideband FM mode with
appropriate radio receiver.
7 MHz
Strong video carrier peaked at 1.25 MHz
above bottom channel edge. When tuned
in AM mode on an appropriate receiver,
sounds like a buzzing sound that
changes with changes in the TV picture.
FM audio carrier 6.75 MHz above
bottom edge of channel (250 kHz
Chrominance carrier 5.68361875 MHz
below top edge). Audio can be clearly
above bottom-edge of channel.
monitored in wideband FM mode with
appropriate radio receiver.
ATSC (digital)
6 MHz
Flat spectrum except very narrow pilot
tone carrier approximately 309.4 kHz
above bottom edge of channel. Pilot tone
can be heard in CW mode of an
appropriate radio receiver, otherwise rest
of signal just sounds like gaussian noise.
ISDB-T, DVB-T (digital)
6, 7, & 8 MHz
Flat spectrum, OFDM. No significant
spectral features. Identified by frequency
and bandwidth.
NTSC (analog; System M)
PAL (analog; Southern Africa; System I)
PAL (analog; Australia; System B)
Other spectral characteristic(s)
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Video carrier
(103.25 MHz)
Digital and Analog TV in Mitaka
Color carrier
(106.78 MHz)
Audio carrier
(107.75 MHz)
Japanese NTSC TV broadcast
on channel 3 (102 – 108 MHz).
Channel 25
(542 – 548 MHz)
Channel 26
(548 – 554 MHz)
Channel 27
(554 – 560 MHz)
Japanese ISDB-T broadcasts on
channels 25, 26, & 27 (542 – 560 MHz)
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Observational Comparison of
Digital and Analog TV Interference
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Television Interference Caused by Anomalous
Propagation at the Murchison Widefield Array Site
Digital TV signal in Australian channel 7 (181 – 188 MHz), and narrowband interference from analog
(PAL) luminance, chrominance, and audio carriers of channels 6 (174 – 181 MHz),
8 (188 – 195 MHz), and (partially) 9 (195-202 MHz). The digital TV signal is believed to be arising from
a distance of 290 km during a period of anomalous propagation. Data obtained in March 2010.
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TV Broadcasts and Rec. 769
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VHF
Fig. 1.14.2: U.S. Television Channels After Feb 17, 2009 Digital TV Transition
2
3
4
54
60
66
25.3
22.7
20.5
14
15
5
72
~
6
7
8
9
10
11
12
13
76
82
88
174
180
186
192
198
204
210
216 MHz
18.7 17.7
16.3
15.1
7.2
6.9
6.6
6.4
6.2
6.0
5.8
5.6 z(HI)
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19
16
17
20
21
22
23
24
25
26
27
470
476
482
488
494
500
506
512
518
524
530
536
542
548
554 MHz
2.02
1.98
1.95
1.91
1.88
1.84
1.81
1.77
1.74
1.71
1.68
1.65
1.62
1.59
1.56 z(HI)
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UHF
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Digital TV and Redshifted HI
29
30
31
32
33
34
35
36
38
39
40
41
554
560
566
572
578
584
590
596
602
608
614
620
626
632
638 MHz
1.56
1.54
1.51
1.48
1.46
1.43
1.41
1.38
1.36
1.34
1.31
1.29
1.27
1.25
1.23 z(HI)
42
43
44
45
46
47
48
49
50
51
52
53
54
55
638
644
650
656
662
668
674
680
686
692
698
704
710
716
722 MHz
1.23
1.21
1.19
1.17
1.15
1.13
1.11
1.09
1.07
1.05
1.03
1.02
1.00
0.98
0.97 z(HI)
56
57
58
59
60
61
62
63
64
65
66
67
68
69
722
728
734
740
746
752
758
764
770
776
782
788
794
800
806 MHz
0.97
0.95
0.94
0.92
0.90
0.89
0.87
0.86
0.84
0.83
0.82
0.80
0.79
0.78
0.76 z(HI)
Allocated to radio astronomy. Not used for TV.
Reallocated to mobile and fixed use.
Used for land mobile instead of TV in some major cities.
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Worldwide Lower VHF Channel Plans
Figure from Wikipedia, based on data from “World Analogue Television Standards and Waveforms”
(http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html)
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Worldwide Upper VHF Channel Plans
See color key on
previous slide
Figure from Wikipedia, based on data from “World Analogue Television Standards and Waveforms”
(http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html)
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Comparison of Analog and DTV
Channel Allotments
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•
•
•
Allotments specify which channels are available
for use in each city or market area
> Allotments are based on market size, co- and adjacentchannel interference criteria, geography, frequency, and
other considerations
Given the lucrative nature of a TV license,
virtually all allotted channels are spoken for
There are significant differences between the DTV
allotments after the transition and the analog
allotments prior to the transition
A comparison of the allotment tables provides a
quick snapshot of the imminent changes in the
spectrum landscape.
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Number of Analog TV Allotments Per Channel Prior to DTV Transition
80
Number of Analog TV Station Allotments
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Analog TV Allotments
Before DTV Transition
70
68
Σ = 1756
64
61
60
6161
58
58
56
56
5757
58
50
40
33
32
30 30
30
34
31
30
27 2727
28
26
26
27
25
22
20
25
22
24
21
18
22
22
21
20
17
19
17
16 16
14
18
19
18 18
16
16
15
13
13
12
12
13
10
13
12
10
9
7
11
10
9
7
9
6
6
0
0
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68
TV Channel
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Number of Digital TV Allotments Per Channel After DTV Transition
80
76
Number of Digital TV Station Allotments
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Digital TV Allotments
After DTV Transition
70
68
68
Σ = 1811
63
61
60
5757
50
48
44
40
39
40
36
40
414141
41
42
41
40
39
38
37
35
34
31
37
36
32
33
3434
33
35
35
33
31
29
30
30
31
32
30
27
24
20
13
10
8
7 7
2
0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68
TV Channel
25
Change in TV Allotments Per Channel After DTV Transition
200%
UHF Chs 14 - 51 (470 ~ 698 MHz)
150%
% Change (N DTV - N Analog)/N Analog
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Difference between Digital and Analog
TV Allotments
ΔN = +55
Upper VHF, Chs 7 - 13
(174 - 216 MHz)
100%
50%
0%
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68
-50%
Ch 37 (608 - 614 MHz)
(not used for TV)
-100%
-150%
Lower VHF, Chs 2 - 6 (54 - 72 & 76 - 88 MHz)
No longer used, Chs 52 - 69 (698 - 806 MHz)
-200%
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National Science Foundation
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Summary
The world is switching to digital terrestrial TV
broadcasting
Digital TV produces more apparent interference than
analog TV
Both digital TV and (in some countries) the refarming of
TV broadcast spectrum will make observations using TV
band frequencies more challenging
TV interference is most disruptive to the search for highly
redshifted HI, such as the search for the Epoch of
Reionization (EOR)
TV interference in general, and digital TV interference in
particular, have been shown to impact radio observatories
hundreds of km from the transmitting source
Radio astronomers can generally not expect any
regulatory protections when using TV spectrum for
observing
Future instruments such as the SKA must take TV
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interference into account