1. Stanko PERPAR Chairman ITU-R TG 6/8
TECHNICAL CHARACTERISTICS OF DIGITAL SYSTEMS
Stanko PERPAR
Chairman ITU-R TG 6/8

2. ITU DTTB model

3. Standards for Digital Terrestrial Television Broadcasting
Digital system A: ATSC
Digital system B: DVB -T
Digital system C: ISDB – T
System A: Single carrier modulation
(8-VSB)
Systems B and C: Multicarrier modulation
(OFDM)

4. Coded Orthogonal Frequency Division Multiplex
Number of carriers per symbol: 2k
8k – 6817
Modulation:
QPSK
16 QAM (uniform or non-uniform)
64 QAM (uniform or non-uniform)

5. OFDM Carriers

6. Guard interval Ts = Tu + Tg Tg = ¼, 1/8, 1/16 or 1/32 Tg
Ts = symbol duration
Tu = usefull symbol duration
Tg = guard interval
Some carriers are pilots used for synchronisation, transmission of parameters and signal recovery purposes

7. Forward Error Correction
Outer code: Reed Solomon (204, 188, 16)
Interleaving
Inner code: convolutional with Viterbi soft decision decoding.
Coding rates: ½, 2/3, ¾, 5/6, 7/8

8. Multipath propagation

9. Reception modes Fixed reception Class A portable reception (outdoor)
Class B portable reception (ground floor indoor)
Mobile reception (moving with such speed that Doppler effect appears)

10. Coverage Location (0,5 x 0,5)m covered for 99% of the time
Small area (100 x 100) m
Good coverage for > 95% of locations
Acceptable for > 70% of locations
Coverage area – sum of individual small areas

11. Small area field strength distribution
Distance [m]

12. Percentage of locations 50%

13. Percentage of locations 70%

14. Percentage of locations 50% to 70%

15. Limit value for planning
Analogue: S/N = 30 dB (unweighted)
Digital: BER 2x (Quasi Error Free)
- 3 dB difference means ½ grade on quality scale in analogue picture, but
no picture in digital

16. Cut-off characteristics

17. Transmission Channels
Gaussian Channel – direct sight, no multipath (s < 1dB)
Rice Channel (1 < s < 3 dB) – stationary reception using directional antenna
Rayleigh Channel (s > 3 dB) – portable reception using omnidirectional antenna

18. Ricean Channel

19. Rayleigh Channel

20. Required C/N

21. Planning parameters Minimum field strengths Protection ratios
Co-channel
Adjacent channel

22. Minimum field strengths Fixed reception - 64 QAM 2/3 Rice channel
BAND
III IV V
Analogue 55 65 70
Digital
70% locations 39 44 48
95% locations 45 50 54

23. Minimum field strengths Portable outside reception 64 QAM 2/3 Rayleigh channel
BAND
III IV V
Analogue 55 65 70
. Digital
Locations 70% 59 69
Locations 95% 64 71 75

24. Minimum field strengths Portable inside reception 64 QAM 2/3 Rayleigh channel
BAND
III IV V
Analogue 55 65 70
Digital
Locations 70% 66 73 77
Locations 95% 83 87

25. Minimum field strengths Portable inside reception 16 QAM 1/2 Rayleigh channel
BAND
III IV V
Analogue 55 65 70
Digital
Locations 70% 59 66
Locations 95% 68 76 80

26. Mobile reception - Typical urban 16 QAM 1/2 non diversity
BAND
III IV V
Analogue 55 65 70
Max.speed
254
102 64
Locations 70% 58 69
Locations 95% 71 77
Locations 99% 68 75 79

27. Mobile reception - Typical urban antenna diversity
BAND
III IV V
Analogue 55 65 70
Max.speed
508
203
127
Locations 70% 52 59 63
Locations 95% 58 69
Locations 99% 73

28. CO - CHANNEL INTERFERENCE
ANALOGUE
Offset 8/12
Norm.offset
500 Hz
Prec. offset
1 Hz
Tropospheric 30 22
Continiuous 40 27
DIGITAL
Rice
Rayleigh
64 QAM 2/3 20 23
16 QAM 1/2 11 13
ATSC
15 (19)

29. ADJACENT CHANNEL ANALOGUE Adj.channel N - 1 N +1 Tropospheric -9 -12
Continuous 1 -2
DIGITAL
DVB -T
-30
ATSC
-27

30. Direct path

31. Multipath

32. Multipath analogue

34. Advantages of DVB-T Flexible approach ( cca 120 possibilities) SFN
Mobile reception
Possible use of TABO channels
Robust to multipath effects
Similarity with DVB-S, DVB-C
Set-top box

35. UPGRADE FROM ANALOGUE TO DIGITAL TV TRANSMITTER

36. Analogue TV Transmitter commom mode amplification
Video input
Video input
Analogue
Analogue
Power
Power
Lowpass
Lowpass
RF output
RF output
exciter
exciter
amplifier
amplifier
filter
filter
Audio input
Audio input
ANALOGUE TV TRANSMITTER
ANALOGUE TV TRANSMITTER
ASI input
ASI input
DVB
DVB - -
T exciter
T exciter
Power
Power
Bandpass
Bandpass
with COFDM
with COFDM
RF output
RF output
MPEG
MPEG - - 2 2
amplifier
amplifier
filter
filter
modulator
modulator
transport stream
transport stream
DIGITAL TV TRANSMITTER
DIGITAL TV TRANSMITTER

37. Analogue TV Transmitter split amplification