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

ITU DTTB model

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)

Coded Orthogonal Frequency Division Multiplex Number of carriers per symbol: 2k - 1705 8k – 6817 Modulation: QPSK 16 QAM (uniform or non-uniform) 64 QAM (uniform or non-uniform)

OFDM Carriers

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

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

Multipath propagation

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)

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

Small area field strength distribution Distance [m]

Percentage of locations 50%

Percentage of locations 70%

Percentage of locations 50% to 70%

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

Cut-off characteristics

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

Ricean Channel

Rayleigh Channel

Required C/N

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

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

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

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

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

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

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

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)

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

Direct path

Multipath

Multipath analogue

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

UPGRADE FROM ANALOGUE TO DIGITAL TV TRANSMITTER

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

Analogue TV Transmitter split amplification