Presentation is loading. Please wait.

Presentation is loading. Please wait.

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

Similar presentations


Presentation on theme: "TECHNICAL CHARACTERISTICS OF DIGITAL SYSTEMS Stanko PERPAR Chairman ITU-R TG 6/8."— Presentation transcript:

1 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 k – 6817 Modulation: QPSK 16 QAM (uniform or non-uniform) 64 QAM (uniform or non-uniform)

5 OFDM Carriers

6 Guard interval T s = T u + T g T g = ¼, 1/8, 1/16 or 1/32 T g T s = symbol duration T u = usefull symbol duration T g = 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] [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 2x10 -4 (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 ( dB Rice Channel (1 < < 3 dB) – stationary reception using directional antenna Rayleigh Channel ( > 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 BANDIIIIVV Analogue Digital 70% locations % locations455054

23 Minimum field strengths Portable outside reception 64 QAM 2/3 Rayleigh channel BANDIIIIVV Analogue Digital Locations 70% Locations 95%647175

24 Minimum field strengths Portable inside reception 64 QAM 2/3 Rayleigh channel BANDIIIIVV Analogue Digital Locations 70% Locations 95%738387

25 Minimum field strengths Portable inside reception 16 QAM 1/2 Rayleigh channel BANDIIIIVV Analogue Digital Locations 70% Locations 95%687680

26 Mobile reception - Typical urban 16 QAM 1/2 non diversity BANDIIIIVV Analogue Max.speed Locations 70% Locations 95% Locations 99%687579

27 Mobile reception - Typical urban antenna diversity BANDIIIIVV Analogue Max.speed Locations 70% Locations 95% Locations 99%636973

28 CO - CHANNEL INTERFERENCE ANALOGUE Offset 8/12 Norm.offset 500 Hz Prec. offset 1 Hz Tropospheric3022 Continiuous4027 DIGITALRiceRayleigh 64 QAM 2/ QAM 1/21113 ATSC15 (19)

29 ADJACENT CHANNEL ANALOGUE Adj.channelN - 1N +1 Tropospheric-9-12 Continuous1-2 DIGITAL DVB -T-30 ATSC-27

30 Direct path

31 Multipath

32 Multipath analogue

33

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

37 Analogue TV Transmitter split amplification


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

Similar presentations


Ads by Google