DTTB Transmitter Ratings

1
DTTB TransmitterRatings
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
2
DTTB TransmitterRatings
LINEAR CONSIDERATIONS
3
COFDMAmplitude Distribution
( CDF 99.95)
Peak voltage 2.8 (9 dB) - COFDM ( for
CDF 95 peak voltage 1.7 (4.7dB) ) (
CDF - Cumultive Distribution Function )

RMS voltage 1 (0dB)
9 dB peak to average
DIGITAL TV
4
DTTB Peak Amplitude Distribution
5
DTTB Peak Amplitude Distribution
(Expanded)
99.95 CDF
6
PAL-DTTB Relative Levels
Relative Power Levels for
PAL/DTTB Ratio - 6 dB
(in dB)
Peak
3dB
Peak
(Peak Sync.)
0dB
Average Power
9 dB
(Black Sync.)
(if continuous)
-2.15dB
6 dB
0 dB
Average Power
COFDM
Difference
Analogue PAL
DTTB
7
PAL-DTTB Relative Levels
Relative Power Levels for
PAL/DTTB Ratio - 6 dB
(in KW)
Peak (Instantaneous)
Peak (Instantaneous)
20KW
20KW
(Peak Sync.)
Average Power
10KW
9 dB
(Black Sync.)
(if continuous)
6KW
6 dB
Average Power
0 dB
2.5KW
COFDM
Difference
Analogue PAL
DTTB
8
DTTB Ratingof a PAL Transmitter

• To handle a COFDM signal with a 9 dB peak to
  average character, a PAL transmitter needs to be
  derated by
• 6 dB
• 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
• amplitude and group delay response
• LO phase noise
• noise level

9
DTTB TransmitterRatings
NON - LINEAR CONSIDERATIONS
10
DTTB TransmitterNon - 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
  consumers receivers.
• The performance of a receiver is influenced by
  the modulation type eg
• whether 64QAM, 16QAM or QPSK
• and whether FEC is 7/8, 5/6, 3/4, 2/3, or 1/2

11
DTTB Receiver Multipath Performance

• An example of a receivers performance operating
  with modulation of 64QAM and a FEC of 2/3
  follows. Differences will occur from
• other receiver implementations
• complex static multipath
• dynamic multipath eg flutter
• impulse noise

12
DTTB System Multipath Performance
(Conditions Static simple multipath, No
Co-channel or impulse interference)
Outdoor Antennas
Indoor Antennas
35
COFDM
(64QAM,2/3,1/8)
COFDM
(Nov. 1997)
Picture
25
C/N Threshold (dB)
(above curve)
Current implementations
(April 1998)
19
No Picture
(Below curve)
15
0
3
30

Multipath Level ( - dB)
W.T.Dickson 16 April 98
13
DTTB System Multipath Performance under typical
reception conditions
Indoor Antennas
Outdoor Antennas
35
COFDM
(64QAM,2/3,1/8)
Complex multipath (approximate median)
Picture
25
(above curve)
C/N Threshold (dB)
19
No Picture
Simple multipath
(Below curve)
15
0
3
30

Multipath Level ( - dB)
W.T.Dickson 16 April 98
14
DTTB COFDMDecoder Threshold C/N

W.T.Dickson 16 April 98
15
DTTB TransmitterPerformance 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

16
DTTB TransmissionC/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 dB to 35 dB.
• 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.

17
Transmitter C/N interactionwith decoder
threshold C/N
Hence transmission C/N should be more than 6 dB
below decoder C/N for less than 1 dB degrading
of decoder C/N
0.2dB influence results from a 13dB difference.
18
The required DTTB Transmitter C/N

• Considering
• (A) _at_ 35dB required decode C/N, an influence of
  1dB by the Transmitted C/N is acceptable. (as
  such high C/N will not be common the high 1dB
  influence maybe acceptable)
• (B) _at_ 25dB required decode C/N, an influence of
  0.2dB by the Transmitted C/N is acceptable. (as a
  25dB decoder C/N requirement will be potentially
  common a small influence is demanded)
• The Transmitted C/N needs to be
• for (A) 41dB for (B) 38dB
• Hence 41dB Transmitted C/N appears to be
  indicated.

19
Transmitter C/NversusSpectrum regrowth

• Although the spectrum regrowth is a reflection of
  what is occurring within the band of data, there
  is a 1 to 2dB higher level of N within the data
  area. Hence the regrowth level should be allowed
  to be 2dB higher than the required Transmitted
  C/N.
• Aim for a Transmitted C/N of 43 dB.
• A Transmission C/N of 22 dB is likely to ensure
  failure of all decoders !
• These requirements are for 64QAM _at_ FEC of 2/3.

20
DTTB TransmissionSpectrum
Spectrum regrowth level
Transmission C/N
COFDM
Intermod.
Commonly called spectrum regrowth or
spectrum spread.
Noise
Notes 1. Intermod. level increases at double
the rate the input level is increasing. 2.
Noise level increases at the same rate the input
level is increasing. 3. As COFDM is the same as
noise, the display of C/N is independent of the
resolution B/W. 4. The shape of the sidebands
is influenced by the transmitters response. 5.
Either noise or intermod. may dominate.
21
DTTB TransmissionImplementations

• 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
  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 dB is
  not exceeded.

22
COFDM - PALSpectrum Analyser Display
Spectrum Analyser display
Vision Carrier
Dependent upon Resolution B/W setting.
Sound Carriers
A
Chroma
eg. If Res. B/W 300KHz A D 10Log (6.6 /
0.3) 23.5 dB
DTTB (COFDM)
PAL
D DTTB to PAL ratio ( eg D 10 dB )
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 10Log (No. of
Carriers)
DTTB power average heating power PAL power
the equivalent CW power of
peak sync Vision Carrier power
23
DTTB TransmissionSpectrum Mask Requirements
PAL ADJACENT CHANNEL CONSIDERATIONS
24
DTTB to PALAdjacent 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 dB for proper
  operation 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
DTTB to PALInterference
Sound (8 dB)
Vision (3 dB)
Co-channel (45 dB)
SCM40 Avg SCM40 Max LOP-10 dB
Protection Ratio D/U (dB)
DTTB Frequency Offset (MHz)
26
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 dB
  below PAL
• limited by vision in upper adjacent, DTTB 3 dB
  below PAL
• for co - channel operation
• limited by vision, DTTB 45 dB below PAL

27
DTTB Power Levels

• Allowing for a variation of /- 2 dB in the DTTB
  to PAL ratio (gt4 Km from the two tower
  transmissions in Sydney), and combining with the
  previous -8 dB restriction, a -10 dB 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 dB DTTB to PAL ratio could
  be allowed.

28
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 dB.(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 dB, the side
  band level may be - 35 dB. ( ie 35 dB
  Transmission C/N)
• Hence the side band levels are controlled by the
  DTTB decoding requirements of 43 dB Transmission
  C/N.

29
Braodcast Spectrum
Vision Carrier (peak sync)
DTTB to PAL eg -10 dB
0 dB
Carrier only no modulation
Sound Carriers
-13 dB
Chroma
-20 dB
DTTB COFDM
PAL (Lower)
PAL (Upper)
30
DTTB SpectrumMask Base

• Based upon DCA Comms. Laboratory subjective
  testing using the SCM40 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 dB required for adjacent
  channel protection of PAL from DTTB.
• The DTTB side bands are required to be 45 dB
  below PAL vision to protect PAL.
• The mask is conservative allowing for the
  introduction of DTTB into a 100 PAL market.

31
DTTB SpectrumMask
P- 42 dBm/4KHz (P-10-10LogB/W)
_at_ D - 10 dB P 10 KW
3.5 MHz
-3.5 MHz
28 dBm/4KHz
43 dB Intermod.
P- 77 dBm/4KHz (P-10LogB/W- 45 dB)
- 7 dBm/4KHz
-10.5 MHz
10.5 MHz
(- 15 dBm/4KHz)
dependent upon modulation parameters
D DTTB to PAL ratio (DTTB average power to
equivalent peak sync average power) - 10 dB B/W
-1dB Bandwidth of COFDM 6.6 MHz P 10
KW (70 dBm)
32
DTTB SpectrumMask
PAL peak sync vision carrier power
DTTB single carrier power
Spectral Density (dB/4 kHz)
Frequency relative to centre of DTTB channel (MHz)