DTTB Transmitter Ratings This presentation seeks to explain

DTTB Transmitter Ratings This presentation seeks to explain the relationship to PAL analogue Transmitters and provides the base for the ratings of DTTB Transmitters. Compiled by Wayne Dickson SMIREE MIEAust. CPEng. Member SMPTE 25 July 1998 WTD

DTTB Transmitter Ratings LINEAR CONSIDERATIONS 25 July 1998 WTD

COFDM Amplitude Distribution ( CDF = 99. 95%) Peak voltage =2. 8 (9 d. B) - COFDM ( for CDF = 95% peak voltage = 1. 7 (4. 7 d. B) ) ( “CDF” - Cumultive Distribution Function ) RMS voltage = 1 (0 d. B) 9 d. B peak to average DIGITAL TV 25 July 1998 WTD

DTTB Peak Amplitude Distribution 25 July 1998 WTD

DTTB Peak Amplitude Distribution (Expanded) 99. 95 % CDF 25 July 1998 WTD

PAL-DTTB Relative Levels Relative Power Levels for PAL/DTTB Ratio = - 6 d. B (in d. B) Peak 3 d. B Average Power 0 d. B(Peak Sync. ) (if continuous) -2. 15 d. B (Black + Sync. ) 6 d. B 0 d. B Difference Analogue PAL 25 July 1998 9 d. B COFDM DTTB WTD Average Power

PAL-DTTB Relative Levels Relative Power Levels for PAL/DTTB Ratio = - 6 d. B (in KW) Peak 20 KW (Instantaneous) Average Power 10 KW (if continuous) 6 KW 20 KW Peak (Instantaneous) (Peak Sync. ) (Black + Sync. ) 6 d. B 0 d. B Difference Analogue PAL 25 July 1998 9 d. B COFDM DTTB WTD Average 2. 5 KW Power

DTTB Rating of a PAL Transmitter • To handle a COFDM signal with a 9 d. B peak to average character, a PAL transmitter needs to be derated by : • 6 d. B • That is, a 10 KW peak sync transmitter is capable of 2. 5 KW COFDM power. – Provided linearity is adequate. – and other parameters are adequate such as : 25 July 1998 » amplitude and group delay response » LO phase noise » noise level WTD 8

DTTB Transmitter Ratings NON - LINEAR CONSIDERATIONS 25 July 1998 WTD

DTTB Transmitter Non - linear considerations • The non - linear performance is shown by the intermodulation character displayed in the transmitted spectrum. • The required intermodulation performance is influenced by the multipath performance of the consumer’s receivers. • The performance of a receiver is influenced by the modulation type eg : – whether 64 QAM, 16 QAM or QPSK – and whether FEC is 7/8, 5/6, 3/4, 2/3, or 1/2 25 July 1998 WTD 10

DTTB Receiver Multipath Performance • An example of a receiver’s performance operating with modulation of 64 QAM and a FEC of 2/3 follows. Differences will occur from : • • 25 July 1998 other receiver implementations complex static multipath dynamic multipath eg flutter impulse noise WTD 11

DTTB System Multipath Performance (Conditions: Static simple multipath, No Co-channel or impulse interference) C/N Threshold (d. B) Indoor Antennas 35 COFDM (64 QAM, 2/3, 1/8) (Nov. 1997) 25 COFDM Current implementations (April 1998) Picture (above curve) 19 0 25 July 1998 Outdoor Antennas 3 15 Multipath Level ( - d. B) WTD 30 No Picture (Below curve) W. T. Dickson 16 April 98

DTTB System Multipath Performance under typical reception conditions C/N Threshold (d. B) Indoor Antennas 35 COFDM (64 QAM, 2/3, 1/8) Complex multipath (approximate median) 25 19 Simple multipath 0 25 July 1998 Outdoor Antennas 3 15 Multipath Level ( - d. B) WTD 30 Picture (above curve) No Picture (Below curve) W. T. Dickson 16 April 98

DTTB COFDM Decoder Threshold C/N 25 July 1998 WTD W. T. Dickson 16 April 98

DTTB Transmitter Performance requirements • By knowing the worse threshold C/N required by the receiver, the required transmission C/N may be derived. • The transmission C/N will be determined by the combination of : – the noise floor at the transmitted power level – the intermodulation at the transmitted power level 25 July 1998 WTD 15

DTTB Transmission C/N requirements • By observing the previous examples, of a receiver operating in a typical to a worse reception condition, the required C/N by the receiver is varies from approximately 20 d. B to 35 d. B. • Hence the transmitted C/N has to be such that the reception conditions determine the decoding performance, not the transmission conditions. • The following plot will be used to derive the required transmission C/N requirements. 25 July 1998 WTD 16

Transmitter C/N interaction with decoder threshold C/N Hence transmission C/N should be more than 6 d. B below decoder C/N for less than 1 d. B degrading of decoder C/N 0. 2 d. B influence results from a 13 d. B difference. 25 July 1998 WTD

The required DTTB Transmitter C/N • Considering : – (A) @ 35 d. B required decode C/N, an influence of 1 d. B by the Transmitted C/N is acceptable. (as such high C/N will not be common the high 1 d. B influence maybe acceptable) – (B) @ 25 d. B required decode C/N, an influence of 0. 2 d. B by the Transmitted C/N is acceptable. (as a 25 d. B decoder C/N requirement will be potentially common a small influence is demanded) • The Transmitted C/N needs to be : – for (A) 41 d. B for (B) 38 d. B – Hence 41 d. B Transmitted C/N appears to be indicated. 25 July 1998 WTD 18

Transmitter C/N versus Spectrum regrowth • Although the spectrum regrowth is a reflection of what is occurring within the band of data, there is a 1 to 2 d. B higher level of “N” within the data area. Hence the regrowth level should be allowed to be 2 d. B higher than the required Transmitted C/N. • Aim for a Transmitted C/N of 43 d. B. • A Transmission C/N of 22 d. B is likely to ensure failure of all decoders ! • These requirements are for 64 QAM @ FEC of 2/3. 25 July 1998 WTD 19

DTTB Transmission Spectrum Transmission regrowth C/N level Commonly called : “spectrum regrowth” or “spectrum spread”. Notes : 1. 2. 3. 4. 5. COFDM Intermod. Noise Intermod. level increases at double the rate the input level is increasing. Noise level increases at the same rate the input level is increasing. As COFDM is the same as noise, the display of C/N is independent of the resolution B/W. The shape of the sidebands is influenced by the transmitter’s response. Either noise or intermod. may dominate. 25 July 1998 WTD

DTTB Transmission Implementations • Spectrum “regrowth” or “spectrum spread” is a mirror into what is happening within the modulated spectrum. • Although filtering of the spectrum spread is required for the control of adjacent channel interference, such filtering does not change the level of intermodulation or noise. • Implementations must ensure that under conditions of maintenance or partial failure that the maximum allowable Transmission C/N of 43 d. B is not exceeded. 25 July 1998 WTD 21

COFDM - PAL Spectrum Analyser Display Spectrum Analyser display : Vision Carrier Dependent upon Resolution B/W setting. eg. If Res. B/W = 300 KHz “A”= D + 10 Log (6. 6 / 0. 3) = 23. 5 d. B Chroma DTTB PAL (COFDM) Note : It is usually less than this value as resolution B/W shape collects more power than the ideal rectangular filter. When Res. B/W approaches or is less than the separation between the carriers of COFDM : A = D + 10 Log (No. of Carriers) 25 July 1998 Sound Carriers A D = DTTB to PAL ratio ( eg D = 10 d. B ) DTTB power = average heating power PAL power = the equivalent CW power of peak sync Vision Carrier power WTD

DTTB Transmission Spectrum Mask Requirements PAL ADJACENT CHANNEL CONSIDERATIONS 25 July 1998 WTD

DTTB to PAL Adjacent Channel requirements • DTTB power and out of band levels will impact upon the interference into the PAL lower and upper adjacent channels. • The required Transmission C/N of 43 d. B for properation of DTTB will provide some inherent protection of the PAL service if it is guaranteed. • Deduction from the plot following provides some worse case figures. 25 July 1998 WTD 24

Protection Ratio D/U (d. B) DTTB to PAL Interference Vision (3 d. B) Co-channel (45 d. B) SCM 40 Avg SCM 40 Max LOP-10 d. B DTTB Frequency Offset (MHz) 25 July 1998 WTD Sound (8 d. B)

DTTB Power Levels • Without considering spectrum spread from the DTTB, the power which may exist between DTTB and PAL without causing interference is : – for adjacent channel operation • limited by sound in lower adjacent, DTTB 8 d. B below PAL • limited by vision in upper adjacent, DTTB 3 d. B below PAL – for co - channel operation • limited by vision, DTTB 45 d. B below PAL 25 July 1998 WTD 26

DTTB Power Levels • Allowing for a variation of +/- 2 d. B in the DTTB to PAL ratio (>4 Km from the two tower transmissions in Sydney), and combining with the previous -8 d. B restriction, a -10 d. B DTTB to PAL ratio can be allowed without interference into PAL. • This is cautious worse case analysis with the information currently available. • Note that the sound of the lower channel is the restricting criteria. If the vision was the limiting factor a -5 d. B DTTB to PAL ratio could be allowed. 25 July 1998 WTD 27

DTTB Side Bands • The side bands generated from the spectrum spread or regrowth (from noise or intermod. ) may be limited by the “Co - channel” restrictions imposed upon the DTTB to PAL ratio. • As shown the co - channel DTTB to PAL ratio without causing interference is - 45 d. B. (flat spectrum across PAL) • As the side bands only need to be down this far, the DTTB to PAL ratio can be deducted from this figure to arrive at the Transmission C/N which will produce PAL interference. • Hence with a DTTB to PAL ratio of 10 d. B, the side band level may be - 35 d. B. ( ie 35 d. B Transmission C/N) • Hence the side band levels are controlled by the DTTB decoding requirements of 43 d. B Transmission C/N. 25 July 1998 WTD 28

Braodcast Spectrum Vision Carrier (peak sync) DTTB to PAL eg -10 d. B Carrier only no modulation Sound Carriers -13 d. B Chroma PAL (Lower) 25 July 1998 DTTB COFDM WTD PAL (Upper) -20 d. B

DTTB Spectrum Mask Base • Based upon DCA Comms. Laboratory subjective testing using the SCM 40 method for vision interference levels and a deduction from the LOP method for sound interference levels. • Adjacent channel operation with matching coverage patterns of DTTB and PAL, transmitted from the same area. • DTTB to PAL ratio of -10 d. B required for adjacent channel protection of PAL from DTTB. • The DTTB side bands are required to be 45 d. B below PAL vision to protect PAL. • The mask is conservative allowing for the introduction of DTTB into a 100 % PAL market. 25 July 1998 WTD 30

DTTB Spectrum Mask P- 42 d. Bm/4 KHz (P-10 -10 Log. B/W) -3. 5 MHz @ D = - 10 d. B & P = 10 KW +3. 5 MHz 28 d. Bm/4 KHz 43 d. B * P- 77 d. Bm/4 KHz Intermod. - 7 d. Bm/4 KHz (P-10 Log. B/W- 45 d. B) 10. 5 MHz -10. 5 MHz (- 15 d. Bm/4 KHz) * dependent upon modulation parameters D = DTTB to PAL ratio (DTTB average power to equivalent peak sync average power) = - 10 d. B B/W = -1 d. B Bandwidth of COFDM = 6. 6 MHz 25 July 1998 WTD P = 10 KW (70 d. Bm)

DTTB Spectrum Mask PAL “peak sync” vision carrier power Spectral Density (d. B/4 k. Hz) DTTB “single” carrier power Frequency relative to centre of DTTB channel (MHz) 25 July 1998 WTD