next wave tech.ppt
Transcript of next wave tech.ppt
-
7/27/2019 next wave tech.ppt
1/26
http://www.dvb.org
technicaloverview
-
7/27/2019 next wave tech.ppt
2/26
Digital vs Analogue TV
1 1
0 1
1 0
0 0
1 0
1 1
1 1
1 1 0 1 1 0 0 0 1 0 1 1 1 1
1 1
0 1
1 0
0 0
1 0
1 11 1
MPEG-2
DVB
Encoder
Transmission medium
MPEG-2
DVB
Decoder
SourceTelevision
Television
Source
Transmitter
-
7/27/2019 next wave tech.ppt
3/26
Why is Digital TV different?
Digital TV squeezes the information that the viewer cant
see or hear out of a standard analogue TV
DVB uses:
Video compression - MPEG-2
Audio compression - MPEG Layer II
That means you can fit much more TV into the same
channel capacity as analogue TV
A satellite transponder using DVB can contain 6-8 times
more TV programmes than analogue TV
DVB is also completely digital, opening up the world of
EPGs, Internet, data broadcasting, advanced interactive
TV ..
-
7/27/2019 next wave tech.ppt
4/26
Source video compressed
Source audio compressed
Data information prepared
Video, Audio and Data
streams multiplexed
Transmission by cable / satellite /
MMDS / terrestrial
Demultiplexing
Decoding
View on TV
The DVB System
1 10 1
1 0
0 0
1 0
1 1
1 1
1 1 0 1 1 0 0 0 1 0 1 1 1 1
1 1
0 1
1 0
0 0
1 0
1 1
1 1
MPEG-2
DVB
Encoder
Transmission medium
MPEG-2
DVB
Decoder
Source
Television
-
7/27/2019 next wave tech.ppt
5/26
DVB-S Satellite Transmission
Designed to cope witha range of transponder
bandwidths (26MHz - 72 MHz)
Single carrier system
DVB-S is like an onion: centre: payload
series of layers to ensure error protection
adapt the payload for broadcasting implemented
satellite chain
MPEG-2
Transport
Stream
Q
I
IF
Inner
Convolu
-
tional
Coder
Baseband
Shaping
Modulator
MPEG-2
TS MUX
Adaption
& Energy
Dispersal
Outer
Reed -
Solomon
Coder
Convolu-
tional
Interleaver
RF
Up
Converter
-
7/27/2019 next wave tech.ppt
6/26
DVB-C Cable Transmission
Same core as satellite system to facilitate
interworking
No inner convolutional code
System based around 64 QAM, but higher andlower order systems possible
8MHz channel, with 64 QAM can accommodate
about 38.5 Mbits/s
MPEG-2Transport
StreamTuner
RF
ModulatorBaseband
Shaping
Convolu-
tional
Inter-
leaver
Outer
Reed -
Solomon
Coder
MPEG-2
TS MUX
Adaption
& Energy
Dispersal Q
I
IF
-
7/27/2019 next wave tech.ppt
7/26
DVB-T terrestrial transmission
Adaptation
of the trans-
mission
frame
Inner
FEC
Encoder
Sync
Inversion,
Energy
dispersal
(without hierarchical modulation)
Baseband
Interface,
Sync
Separator
Outer
FEC
Encoder
l =12
Inner
Inter-
leaver
Symbol
mapping,
Modulator
COFDMIntroduction
of guardinterval
Digital to
AnalogueTransmitter
To
Aerial
Data Clock
Generation of reference
symbols, pilots and TPS data
MPEG-2
Transport
Stream
-
7/27/2019 next wave tech.ppt
8/26
Common circuitry in the DVB
Receiver
RF &
QAM
demod
Differential
Decoder
Convolutional
de-interleaver
Reed-
Solomon
Decoder
Carrier & clock sync recovery
Matched
Filter &
equaliser
Sync inversion &
Energy dispersal
removal
Output
interface
Cable
Signal
Data
Clock
RF &
OFDM
demod
RF &
QPSK
demod
Epuncturing
& inner
DecoderMatched
Filter
Terrestrial
Signal
Satellite
Signal
Inner
de-interleaver
Sync
Decoder
OUTPUT
-
7/27/2019 next wave tech.ppt
9/26
The COFDM signal
-
7/27/2019 next wave tech.ppt
10/26
Separation of data streams
-
7/27/2019 next wave tech.ppt
11/26
Multi-resolution QAM
When reception conditions and C/N degrade, 16 points
of the constellation of the 64 QAM can be used as one point
in a QPSK constellation
-
7/27/2019 next wave tech.ppt
12/26
DVB-T 8k non-hierarchical
modulation
Programme 1
Useful data rate: 24.88 Mbit/s in a data container
defined by 8MHz channel B/W and 64-QAM modulation
code rates for inner FEC : 5/6
C/N needed at edge of coverage
typically 20 dB (Ricean channel)
Programme 2
Programme 3
Programme 4
-
7/27/2019 next wave tech.ppt
13/26
DVB-T 8k (hierarchical
modulation)
64 QAM for fragile part
16.59 Mbit/s
QPSK for robust part
4.98 Mbit/s
Useful data rate: 21.57 Mbit/s within a data container
of two levels of robustness
With multiresolution QAM used
code rates for inner FEC : 5/6, 1/2
C/N needed at edge of coverage
(Ricean channel)
22.7 dB for fragile part
7.1 dB for robust part
Programme 1
Programme 2
Programme 3
Baseline
Programme 4
-
7/27/2019 next wave tech.ppt
14/26
The Guard Interval
Guard
Interval
TG
Main Symbol Period
TS
e.g. for a national service Ts = 1ms, TG=0.25ms
-
7/27/2019 next wave tech.ppt
15/26
CurrentEuropean UHF
Spectrum usage
Number of transmitters
per UHF channel
UHF channel No.
200
600
1000
1400
40 50 60 6821 30
-
7/27/2019 next wave tech.ppt
16/26
Implementation Scenario
OFDM DVB-T signal fits between existinganalogue UHF carriers
sound
vision
sound
vision
sound
vision
sound
vision
-
7/27/2019 next wave tech.ppt
17/26
DVB-T: key features
Same core as DVB-S and DVB-C systems
DVB-S punctured convolutional coding
OFDM based QPSK or QAM modulation very rugged
against multipath fading
DVB-T offers a 2k or and 8k OFDM option
Two level hierarchical channel coding and modulation
possible
Hierarchical MPEG-2 source coding not included
Possibility of national or regional signal frequency
networks.
-
7/27/2019 next wave tech.ppt
18/26
Transmission frame for DVB-T
Carrier spacing in 2k-mode - 4464 Hz, in 8k-mode - 1116 Hz
Continual Pilot
TPS-Pilot
Data
Scattered Pilot
Continual Pilot TPS-Pilot Continual Pilot
2k-mode: kmax - 1704
8k-mode: kmax - 6816
f1 + 7.61 MHz
Frequency
Carrier-position kmax
Carrier-position kmin (-0)
f1
Symbol 67Symbol 0Symbol 1Symbol 2Symbol 3
-
7/27/2019 next wave tech.ppt
19/26
The DVB-T Guard Interval
Main signal
Echo 2
Co-channel
Echo 1
received signal
after gain
correction
Tg TwantTs
t
t
t
t
t
-
7/27/2019 next wave tech.ppt
20/26
COFDM offers variable bit-rate
System thresholds for 8-VSB and DVB-T COFDM
25
20
15
10
5
0
0 10 20 30
SNR (dB)
Bit Rate (Mbit/s)
8-VSB
COFDM modes
-
7/27/2019 next wave tech.ppt
21/26
Digital TV is different!
Compared with analogue:
digital TV requires less C/N
digital TV is more tolerant of interference
BUT
digital systems fail more abruptly
Clearly, expect to use new strategies in
frequency planning
-
7/27/2019 next wave tech.ppt
22/26
DVB-T offers choice of
strategies
COFDM in DVB-T tolerates multipath (echoes)
COFDM can also tolerate artificial multipath of a
single-frequency network (SFN) new concept in spectrum planning
spectrally-efficient in right circumstances
multi-frequency networks (MFNs)
can interleave channels amongst analogue
-
7/27/2019 next wave tech.ppt
23/26
Choosing a strategy
Every country has its own scenario ...
different history of broadcasting TV
different aspirations for the new digital service
different existing spectrum usage
different future spectrum availability
different neighbours
... so each country must find its best solution
-
7/27/2019 next wave tech.ppt
24/26
Single-frequency networks
SFNs can offer improved spectrum efficiency
examples for DAB, DVB-T
SFN requires an RF channel free over whole
service area of network
reason why not chosen for UK DVB-T
best results with a dense network of lower-
power transmitters
-
7/27/2019 next wave tech.ppt
25/26
Conclusions (i)
planning digital TV services is different
from analogue TV
countries have different requirements
DVB-T permits choice of planning methods
single-frequency networks (SFNs)
multi-frequency networks (MFNs)
thus uniquely able to satisfy differentneeds of all countries
-
7/27/2019 next wave tech.ppt
26/26
Conclusions (ii)
SFNs can give greater spectrum efficiency
MFNs can be interleaved amongst analogue
European administrations have done a great deal of
work to enable DVB-T introduction
DVB-T is being introduced in Europe
firm plans in place in UK and Sweden for 1998
other countries will follow