Session 2: Network planning aspects
Transcript of Session 2: Network planning aspects
1
Session 2:
Network planning aspects:
New generation of DTV: DVB-T, DVB-
T2 and DVB-T2 Lite
CoE/ARB Workshop
On
“Transition from Analog to Digital (Digital Terrestrial Television:
Trends, Implementation & Opportunities)
Tunisia – Tunis , 12 – 15 March 2012
2
Contents of DVB-T2 Presentations
1. Session 2: Technical Aspects of DVB-T and DVB-T2
2. Session 4: Coverage aspects: Fixed Portable and Mobile Coverage
3. Session 6: Single Frequency networks
4. Session 11: Implementation of DVB-T2
3
Contents of this Presentation
1. DVB-Commercial requirements of DVB-T2
2. System properties for DVB-T2
3. Improvements in DVB-T2
4. Network planning with T2- Some modes and
parameters
5. DVB-T2 Lite- how does it fit in?
6. Comparison DVB-T, DVB-T2 vs ISDB-T!
7. Future of DVB-T2 /Summary
Main Reference is:
EBU Tech 3348
Frequency and
network aspects of
DVB-T2
4
Some DVB-T2 Commercial Requirements
•T2 transmissions must be able to use existing domestic receive antenna
installations and must be able to re-use existing transmitter
infrastructures. This requirement ruled out the consideration of MIMO
techniques which would involve both new receive and transmit antennas.
•T2 should primarily target services to fixed and portable receivers
•T2 should provide a minimum of 30% capacity increase over DVB-T
working within the same planning constraints and conditions as DVB-T
•T2 should provide for improved single-frequency-network (SFN)
performance compared with DVB-T.
Requirements
5
Some DVB-T2 Commercial Requirements
•T2 should have a mechanism for providing service-specific
robustness; i.e. it should be possible to give different levels of
robustness to some services compared to others. For example,
within a single 8MHz channel, it should be possible to target
some services for roof-top reception and target other services
for reception on portables.
•T2 should provide for bandwidth and frequency flexibility.
•There should be a mechanism defined, if possible, to reduce
the peak-to-average-power ratio of the transmitted signal in
order to reduce transmission costs.
Requirements
The DVB-T2 standard
• Driver: Need for more capacity for HDTV services
• DVB approved the DVB-T2 specification in June 2008
– specifies the physical layer of the air interface (like DVB-T)
– does not address receiver requirements
– Video coding and multiplexing not included but will for digital TV/HDTV
services be MPEG-4 AVC (H.264) over MPEG-2 TS
• ETSI standard September 2009
• DVB/ETSI standards/documents related to DVB-T2
– Main DVB-T2 standard, Ref: ETSI EN 302 755 v.1.2.1 (draft v.1.3.1)
– DVB-T2 Modulator Interface (T2-MI), Ref: ETSI TS 102 773
– Implementation Guidelines, Ref: ETSI TR 102 831
– Transmitter identification in SFNs (TX-SIG), Ref: ETSI TS 102 992
– ETSI standards freely downloadable from ETSI:
http://pda.etsi.org/pda/queryform.asp
6
System properties
DVB-T2 is based upon DVB-T • OFDM based (thousands of orthogonal carriers)
• Same basic OFDM parameters as DVB-T
– FFT size
– Guard interval allows multipath and SFNs
– Pilot patterns- Receiver channel estimation
• But also many new values, other additions and improvements
• A lot of the signal processing in the receiver is similar to DVB-T
Chips/receivers can be developed faster thanks to reuse of knowledge and experience from DVB-T
• From an HW point of view simple to have both DVB-T2 and DVB-T on the same chip (DVB-T comes for “free”)
T2 receivers also support DVB-T and today very small difference in price between T/T2 receivers and DVB-T only receivers
7
System properties
DVB-T och DVB-T2 use OFDM
-60
-50
-40
-30
-20
-10
0
10
-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
frequency relative to centre frequency fc
po
we
r sp
ectr
um
de
nsity
MHz
dB
2 k mode
8 k mode
OFDM spectrum
Representation of OFDM in
the time-frequency plane
Delta= Guard interval
Ts= useful symbol length
8
System properties
9
DVB-T2 Improvements
• 8 Scattered Pilot Patterns
• LPDC error Correction Rates ½, 2/3, ¾ 4/5 and 5/6
• Time interleaving to improve impulse noise robustness
• Extended bandwidth option
• Peak to average power reduction
• Time Frequency interleaving
As answer to the commercial requirements
System properties
10
Comparison DVB-T and DVB-T2
-Summarized
Source: www.dvb.org
System properties
Bandwidths and frequency bands • The DVB-T2 specification as such does not specify any
frequency band
• The system is primarily optimised for: – UHF band IV/V (470-862 MHz),
– But also VHF band III (174-230 MHz),
– L-band (1.5 GHz)
– even higher frequencies are expected to work well
• Specified channel bandwidths (channel raster): o 8 MHz (typically UHF band IV/V)
o 7 MHz (typically VHF band III)
o 1.7 MHz (same as DAB): typically VHF band III and L-band)
o 6 MHz (e.g. South America, USA and Japan, Philippines etc. )
o 5 MHz (L-band 3 x 1.7 MHz frequency block as in MA02 DAB plan)
o Also a 10 MHz mode for non-consumer use
11
System properties
12
DVB-T2 Extended Bandwidth
Theoretical DVB-T2 signal (without filtering) spectrum for guard interval
fraction 1/8 (for 8 MHz channels and with extended carrier mode for 8k, 16k
and 32k)
Extended
BW
Gives
about 400 -
600 kbit/s
extra data
capacity
System properties
13
DVB-T2 Extended BW
Detail of theoretical DVB-T2 spectrum for guard-interval fraction 1/8 (for
8 MHz channels)
• At VHF – Problem to meet spectrum mask for DVB-T
• Insignificant change of Adjacent channel Protection Ratio PR (DVB-T2
to DVB-T
32 k Extended and Normal BW
System properties
14
DVB-T2 Extended BW
SPECTRUM MASK FOR DVB-T according to GE06 agreement UHF
Use of extended Bandwidth for DVB-T2 is not a problem at UHF
System properties
Symbol time (FFT size) and guard interval
• With DVB-T2 the symbol time can be increased by a factor of
– two (16K FFT) and
– four (32K FFT) compared to DVB-T
• Reduces the overhead due to guard interval for a given size of
guard interval (size of SFN) increased capacity
32K-symbol GI
GI 8K-symbol
~6% overhead
in DVB-T2
25% overhead in DVB-T with maximum guard interval
• Increases guard interval length and possible size of SFN for a given
percentage GI fraction
• DVB-T2 may also use the same symbol periods as DVB-T (8K, 4K, 2K) and
also a shorter FFT size (1K)
allows for flexibility for different frequency bands, RF bandwidths, network
types and reception
15
System properties
16
DVB-T2 Guard intervals
GI-Fraction
FFT-
size TU [ms] 1/128 1/32 1/16 19/256 1/8 19/128 1/4
GI [us]
32K 3,584 28 112 224 266 448 532 NA
16K 1,792 14 56 112 133 224 266 448
8 K 0,896 7 28 56 66,5 112 133 224
4 K 0,448 NA 14 28 33,2 56 67 112
2 K 0,224 NA 7 14 16,6 28 33 56
1K 0,112 NA NA 7 8,3 14 17 28
Length of Guard interval for DVB-T2 in an 8 MHz channel raster
RED – Option exist in DVB-T
System properties
Flexibility in pilot pattern
• Pilots are needed for receiver channel estimation
• DVB-T has a fixed pattern of scattered pilot cells
• DVB-T2 has 8 different patterns to choose from, depending on
network type and reception conditions (Rooftop, portable or mobile)
• Minimizes pilot overhead
17
System properties
Flexibility in pilot pattern
• Combination of pilot patterns and modes allowed
18
FFT size Guard interval
1/128 1/32 1/16 19/256 1/8 19/128 1/4
32K PP7 PP4
PP6
PP2
PP8
PP4
PP2
PP8
PP4
PP2
PP8
PP2
PP8 NA
16K PP7
PP7
PP4
PP6
PP2
PP8
PP4
PP5
PP2
PP8
PP4
PP5
PP2
PP3
PP8
PP2
PP3
PP8
PP1
PP8
8K PP7 PP7
PP4
PP8
PP4
PP5
PP8
PP4
PP5
PP2
PP3
PP8
PP2
PP3
PP8
PP1
PP8
4K, 2K NA PP7
PP4
PP4
PP5 NA
PP2
PP3 NA PP1
1K NA NA PP4
PP5 NA
PP2
PP3 NA PP1
System properties
Flexibility in pilot pattern
19
PP1 PP2 PP3 PP4 PP5 PP6 PP7 PP8 Interpretation
DX 3 6 6 12 12 24 24 6 Separation of
pilot-bearing carriers
DY 4 2 4 2 4 2 4 16 Length of sequence
in symbols
1/DXDY 8,33 % 8,33 % 4,17 % 4,17 % 2,08 % 2,08 % 1,04 % 1,04 % Scattered pilots
overhead
System properties
Need to consider when choosing Pilot Pattern (PP):
• Reception mode (fixed, portable or mobile)
• Doppler performance
• Capacity
• FFT size and Guard Interval
• C/N required of selected DT2 mode
• Receiver implementation (PP8 not always implemented in receivers)
Capacity loss for different pilot patterns
Choice of Pilot Pattern (PP) • Rooftop reception:
• Rooftop reception with a directional outdoor antenna
• low Doppler environment with few significant reflections
• PP7 has low overhead but less robust to Doppler can be adopted to
maximise capacity.
• Mobile reception:
• High Doppler frequency need to be considered to provide robust reception,
• PP 2, 4 or 6 should be considered.
• Portable reception:
• Doppler need to be considered but low frequency
• Number of options PP3, 4 and 5 and could be considered depending on
required C/N
• If SFN: PP2 may provide a good compromise
• Large area SFNs:
• Need for longer Guard interval
• Pilot pattern
• Trade off between Doppler and Guard Interval length
• PP2 may provide a good compromise.
20
System properties
Modulation
• T2 has a 256-QAM mode
– Carries 8 bits per data cell(6
bits/data cell for 64-QAM)
– Allows for 33% larger capacity
– The T2 standard also includes
• 64-QAM
• 16-QAM
• QPSK
– … inherited from DVB-T
21
System properties
22
Mobile and portable reception
Example of mobile measurements--250 metre in suburban area !
2500 3000 3500 4000 4500 5000
-66
-64
-62
-60
-58
-56
-54
-52
Level
dBm
Samples
Measurement
every 5 cm
System properties
The Mobile
reception
environment is
very demanding!
0 dB echo – ”kills” some carriers
0 1000 2000 3000 4000 5000 6000 7000-70
-60
-50
-40
-30
-20
-10
0
10
Single path
(0 dB)
TX1
TX2
RX
Hz
23
Can occur in
SFNs or when
there are
reflections
Improved robustness
• DVB-T does not include time interleaving and is therefore sensitive
to impulsive interference and time varying channels
• DVB-T2 has support for deep time interleaving and longer symbol
period (32K FFT), which together radically improve the robustness
against impulsive interference
• Time interleaving also allows for much better performance in time
varying channels
• The type of FEC (LDPC) and modulation (rotated constellation) that
T2 has also allows for much better RF performance in difficult radio
environments
24
System properties
“Rotated constellation”
• Additional modulation stage with so-called
“Rotated Constellation” allows for more
robust reception in extreme radio
environments
• E.g. lots of echoes, part of the signal totally
faded or interfered
• Each constellation point gets unique
projection on both u1 and u2 axes
• Interleaving separates u1 and u2 values
over the air increased diversity
Constellation Rotation angle (in
degree)
QPSK 29.0
16QAM 16.8
64 QAM 8.6
256QAM 3.6
Improvement in C/N is about 1-2 dB
depending on Code rate and modulation and
depending on transmission channel
25
System properties
Forward Error Correction (FEC) • DVB-T has a convolutional code + Reed-Solomon
• DVB-T2 has an LDPC code + BCH code
– Same as in DVB-S2 (satellite) and DVB-C2 (cable)
– 6 code rates: 1/2, 3/5, 2/3, 3/4, 4/5, 5/6
– Flexibility to make desired trade-off between capacity and robustness
– Allows for about 30% more capacity for a given robustness
– FEC block size (Nldpc): 64800 bits or 16200 bits
BBFRAME BCHFEC LDPCFEC
(Nldpc bits)
Kbch Nbch-Kbch
Nbch= Kldpc
Nldpc-Kldpc
26
System properties
Time - freqency Interleaving
• Interleaving is of fundamental importance for the RF
performance on non-AWGN channels i.e. for mobile and
portable reception
• DVB-T2 has several interleavers
– Bit interleaver within a FEC block
– Cell interleaver within a FEC block
– Time interleaving within a PLP (e.g. one TV program)
– Frequency interleaving within an OFDM symbol
• The result is that bit errors caused by the channel are equally
distributed among the FEC blocks, and also within FEC blocks
maximizes error correction ability of the LDPC/BCH code
27
System properties
Kmin=0
TPS pilots and continual pilots between Kmin and Kmax are not indicated
boosted pilot
data
Kmax = 1 704 if 2K
.....
.....
.....
.....
..... .....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
Kmax = 6 816 if 8K
Interleaving in DVB-T and DVB-T2
Kmin=0
TPS pilots and continual pilots between Kmin and Kmax are not indicated
boosted pilot
data
Kmax = 1 704 if 2K
.....
.....
.....
.....
..... .....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
Kmax = 6 816 if 8K
FEC FEC FEC FEC
FEC
FEC
DVB-T
DVB-T2
Single erased OFDM-symbol
Bit errors
Single erased OFDM-symbol
Can be corrected! Time
28
System properties
Performance for modulation and FEC
close to theoretical limits
• Capacity limits for a channel with white noise (AWGN)
– With LDPC coding T2 can come close to the theoretical limit
• Typically a 30% gain in capacity compared to DVB-T for a given required C/N
0,00
1,00
2,00
3,00
4,00
5,00
6,00
7,00
8,00
9,00
10,00
0,0 5,0 10,0 15,0 20,0 25,0 30,0
Eff
ecti
ve b
its p
er
Cell
C/N
Capacity Performance
DVB-T2 QPSK DVB-T2 16-QAM DVB-T2 64-QAM
DVB-T2 256-QAM Shannon Limit BICM Limit
29
System properties
Peak-to-Average Power Ratio (PAPR)
• An OFDM signal is “noise-like” and has large dynamic power
variations (high PAPR)
• Amplifiers have however a maximum peak power level
– Output signals that would normally require a power level above
the maximum level will be clipped!
– This causes intermodulation (in-band distortion + out-of-band
radiation)
• A very significant “back-off” (>10 dB!) is therefore required in
transmitters in order to reduce intermodulation
– Amplification is reduced in order not to cause clipping of the
amplified signal
– Full potential of the transmitter cannot be exploited
30
System properties
PAPR reduction
• Idea: Add a peak compensating waveform that reduces the
peaks
– Transmitted_signal = Original_signal + peak compensating
waveform
• With DVB-T2 there are two different methods available to
reduce the PAPR
– Tone Reservation (TR)
– Active Constellation Extension (ACE)
• Both methods generate a peak-compensating signal, but in
different ways
– TR: 1% of carriers are dedicated for this
– ACE: Border constellation points are “extended” away
• Advantages: Less complex transmitters and/or less
intermodulation in transmitted signal, but some reduction in
data rate (TR) or C/N performance (ACE)
31
Transmitter diversity – MISO/Alamouti • T2 includes a possibility (option) that the transmitters in an SFN transmit
different signals (type A or type B), but with the same information, via so-called MISO-Alamouti coding
• With MISO/Alaomouti coding type A and type B signals add constructively so the frequency selective fading may be avoided
• Without this functionality the channel may look like a strong-echo channel makes reception more difficult
• This improves coverage in areas where both transmitters can be received with similar strength. However...
– ... MISO requires double pilot overhead
– ... does not provide any gain with type A + type A or type B + type B combination
RX TX1 TX2
So, S1 -S1* S0
* h1 h2
Type A Type B
32
Capacity increase in DVB-T2
• DVB-T2 allows for typically about 50% higher capacity for fixed
reception than DVB-T (for a given coverage)
– Exact increase depends on precise configuration of T2 parameters
• Example:
– DVB-T today in Sweden: 22 Mbit/s on UHF (8 MHz bandwidth)
– DVB-T2 can provide about 33 Mbit/s (+50%) on UHF with the same
basic coverage as DVB-T
• Capacity on VHF somewhat lower
– VHF bandwidth is 7 MHz
– VHF has larger SFN areas requires a larger guard interval
– However, VHF has a better link budget may be possible to
increase code rate/capacity (Finland SFN Code Rate 5/6)
– Normal Bandwidth is used at VHF (normally)
33
34
Capacity in DVB-T2
0
10
20
30
40
50
60
1/2 3/5 2/3 3/4 4/5 5/6 1/2 3/5 2/3 3/4 4/5 5/6 1/2 3/5 2/3 3/4 4/5 5/6 1/2 3/5 2/3 3/4 4/5 5/6
4-QAM 16-QAM 64-QAM 256-QAM
Constellation and code-rate
Bit
rate
(M
bit
/s)
Maximum
Recommended
Maximum bitrate and bitrate for recommended configuration
with 8 MHz bandwidth and 32K PP7
35
DVB-T/T2 Parameters - GiraPlan interface
Large number of
options in DVB-T2!
36
DVB-T/T2 C/N values
-About 4-6 dB better than DVB-T
-In particular at difficult Reception environment
Constellation Code
Rate
Gaussian
Raw Values
AWGN)
C/N
Gauss C/N Rice
C/N
Rayleigh
0 dB echo
channel @
90% GI
QPSK 1/2 1.0 3.0 3.2 4.0 4.7
QPSK 3/5 2.2 4.2 4.4 5.5 6.3
QPSK 2/3 3.1 5.1 5.4 6.9 7.9
QPSK 3/4 4.1 6.1 6.4 8.2 9.3
QPSK 4/5 4.7 6.7 7.0 9.1 10.4
QPSK 5/6 5.2 7.2 7.6 9.9 11.5
16-QAM 1/2 6.2 8.2 8.4 9.7 10.4
16-QAM 3/5 7.6 9.6 9.8 11.3 12.2
16-QAM 2/3 8.9 10.9 11.1 12.8 13.8
16-QAM 3/4 10.0 12.0 12.4 14.5 15.8
16-QAM 4/5 10.8 12.8 13.2 15.8 17.3
16-QAM 5/6 11.3 13.3 13.8 16.5 18.4
64-QAM 1/2 10.5 12.5 12.8 14.6 15.5
64-QAM 3/5 12.3 14.4 14.7 16.4 17.5
64-QAM 2/3 13.6 15.7 16.0 17.8 19.2
64-QAM 3/4 15.1 17.2 17.5 19.9 21.5
64-QAM 4/5 16.1 18.2 18.8 21.5 23.5
64-QAM 5/6 16.7 18.9 19.3 22.5 25
256-QAM 1/2 14.4 16.5 16.9 19.0 20.1
256-QAM 3/5 16.7 18.9 19.1 21.2 22.6
256-QAM 2/3 18.1 20.3 20.6 22.8 24.6
256-QAM 3/4 20.0 22.4 22.7 25.3 27.5
256-QAM 4/5 21.3 23.8 24.2 27.3 30.3
256-QAM 5/6 22.0 24.6 25.0 28.8 33.1
C/N QEF Valid for DVB-T2 PP2 32k Normal BW GI 1/8
DVB-T
Without implementation
margin of about 3 dB
Required C/N for
BER=2 10-4 after Viterbi
(quasi error-free after Reed-
Solomon)
Modulation Code
Rate
Gaussian
channel
Ricean
channel
(F1)
Rayleigh
channel
(P1)
QPSK 1/2 3.1 3.6 5.4
QPSK 2/3 4.9 5.7 8.4
QPSK 3/4 5.9 6.8 10.7
QPSK 5/6 6.9 8.0 13.1
QPSK 7/8 7.7 8.7 16.3
16-QAM 1/2 8.8 9.6 11.2
16-QAM 2/3 11.1 11.6 14.2
16-QAM 3/4 12.5 13.0 16.7
16-QAM 5/6 13.5 14.4 19.3
16-QAM 7/8 13.9 15.0 22.8
64-QAM 1/2 14.4 14.7 16.0
64-QAM 2/3 16.5 17.1 19.3
64-QAM 3/4 18.0 18.6 21.7
64-QAM 5/6 19.3 20.0 25.3
64-QAM 7/8 20.1 21.0 27.9
Source EBU Tech 3348
Examples: Fixed Rooftop Reception
Implementation Scenarios
Implementation
Fixed rooftop
reception
MFN
(UK mode)
Fixed rooftop
reception (maximum
coverage area
extension)
Fixed rooftop
reception
Limited area SFN
(GE06 Allotment)
Fixed rooftop
reception
Large area SFN
Scenario 1 2 3a 3b
Bandwidth 8 MHz 8 MHz 8 MHz 8 MHz
FFT mode 32K 32K 32K 32K
Carrier mode Extended Extended Extended Extended
Scattered Pilot
Pattern PP7 PP2 PP4 PP2
Guard interval 1/128
(28 µs)
1/8
(448 µs)
1/16
(224 µs)
1/8
(448 µs)
Modulation 256 QAM 16QAM 256 QAM 256 QAM
Code rate 2/3 2/3 2/3 2/3
C/N 18.9 dB 11.0 dB 19.6 dB 20.0 dB
Data rate 40.2 Mbit/s 16.7 Mbit/s 37 Mbit/s 33.4 Mbit/s
37
Source: EBU Tech 3348: Overview of the Portable and
Mobile Implementation Scenarios
Examples Portable and Mobile Reception
Implemen-
tation
portable
reception
(maximum
date rate)
portable
reception
(maximum
date rate,
alternative)
portable
reception
(maximum
coverage
area
extension)
portable
reception
(optimum
spectrum
usage)
mobile
reception
Band III
mobile
reception
Band III
(alternative)
portable and mobile
reception
(common usage of MUX by
different services)l
Scenario 4a 4b 5 6 7a 7b 8
high data
rate
low data
rate
Bandwidth 8 MHz 8 MHz 8 MHz 8 MHz 1,7 MHz 1,7 MHz 8 MHz
FFT mode 16K 32K 16K 16K 4K 4K 8K
Carrier mode Extended Extended Extended Extended Normal Normal Extended
Scattered
Pilot
Pattern
PP3 PP4 PP3 PP1 PP2 PP1 PP2
Guard
interval
1/8
(224 µs)
1/16
(224 µs)
1/8
(224 µs)
1/4
(448 µs)
1/8
(278 µs)
1/4
(555 µs)
1/4
(224 µs)
Modulation 64 QAM 64 QAM 16 QAM 64 QAM 16 QAM 16 QAM 64 QAM 16 QAM
Code rate 2/3 2/3 1/2 2/3 1/2 1/2 2/3 1/2
C/N 17.1 dB 17.1 dB 9.0 dB 17.5 dB 9.4 dB 9.4 dB 17.5 dB 9.4 dB
Data rate 26,2 Mbit/s 27,7 Mbit/s 13,1 Mbit/s 22,6 Mbit/s 2,5 Mbit/s 2,2 Mbit/s 22,4 Mbit/s
(max)
11,2 Mbit/s
(max)
38
39
DVB-T2 SFN
40
DVB-T2 SFN
Physical Layer Pipes (PLPs) • Input bit streams to DVB-T are always MPEG-2 Transport Streams
• Input streams to DVB-T2 are also always MPEG-2 Transport Streams
– But may also be Generic Streams (arbitrary bit streams)
• Every input stream is carried by the corresponding Physical Layer Pipe
(PLP) in DVB-T2
• The streams carried in the PLPs may have a variable bit rate
• 1-255 input streams/PLP:s (one or more services per PLP)
• Statistical multiplexing over several PLPs is possible
• Every PLP can get its own robustness (code rate + modulation) but not
FFTsize
• PLPs may be sent in a busty way allows for power saving in mobile
devices (“time slicing”)
• Signalling data which is common for several PLPs may be sent in a
dedicated PLP (“Common PLP”)
41
Advantages with multiple PLPs • Possibility to reach different kinds of
receivers and reception conditions with a single RF signal
– HDTV to roof-top directional antennas in PLPs with ”normal” robustness PLPs
– Mobile receivers with robust PLPs
• Possibility to prioritize robustness for selected ”high-priority” services prioritized services (e.g. public service) will ”last longer” in bad reception conditions
• Capacity and coverage can be further improved by Time Frequency Slicing (TFS), which uses multiple PLPs
– Each PLP is frequency hopping over several RF channels increased frequency diversity
• …BUT different FFT size not allowed
42
Flexible frame structure for DVB-T2
Common PLPsL1
sign.
Complete T2-frame
P1
Dummy cells
data PLPs, type 1 data PLPs, type 2auxiliary
streams
• DVB-T has a fixed frame structure without special symbols
• DVB-T2 has a very flexible frame structure
PLP
M1+1 PLPM1+M2
PLP
M1+1
PLP
M1+M2
Complete T2-frame
Cell index
Time
L1-pre signaling
L1-post signaling
Common PLP’s
P1P2K
P21
D1
D2
D3
DL
Dummy cells
PLP
M1+1PLP
M1+M2
OFDM symbols
PLP
1PLP
M1
TYPE 1 data PLP’s (1…M1)
Auxiliary streamsTYPE 2 data PLP’s (M1+1… M1+M2)
Typically 200-250 ms
43
Future Extension Frames (FEFs)
• A mechanism that allows a future system to be sent as “Future Extension frames” in T2 time slots • No restrictions in the allowed content of the FEF
• FEF may use DVB-T2 Lite (mobile, specified subset of DVB-T2)
• Will e.g. allow future transmission of the DVB Next Generation Handheld (DVB-NGH) standard currently developed by DVB
• The FEF mechanism does not exist in DVB-T
• Allows flexible capacity allocation to fixed and mobile services by adjusting the size of T2 frame and FEF
P1 P1 P1 P1 P1 P1
T2 T2 T2 T2 FEF FEF
T2-Lite
or
DVB-NGH
frame
T2-Lite
or
DVB-NGH
frame
44
Mobile reception
• The commercial focus on DVB-T2 is primarily on
stationary reception (and HDTV) , but DVB-T2 is also
designed to work well in mobile/handheld conditions – deep time interleaving
– supports power saving by time slicing
– enables the introduction of “T2-Lite” or DVB-NGH services via Future
Extension Frames (FEF)
– T2-Lite is part of the DVB-T2 standard (from v.1.3.1)
– DVB-NGH is based on DVB-T2
45
DVB-T2 lite
46
DVB-T2 lite – some details
• Reduced complexity smaller silicon size (-50%) and lower power
consumption
DVB-T2-Lite specification include:
• A maximum bitrate of 4 Mbits/sec for each service
• Limitations on the FFT size to exclude the 1K and 32K carrier modes
• Prohibition of the use of rotated constellations in 256-QAM
• Possibility for only short FEC frames (Nldpc = 16200)
• Limitation of the size of the time interleaver memory (approximately
half the size of normal DVB-T2).
• two new LDPC error control code rates, 1/3 and 2/5 more options for
mobile reception
• Through use of FEF allowing different FFT size and Guard interval in
transmissions
• T2 lite signal ignored by normal DVB-T2 receiver
DVB-T2 lite
47
DVB-T2 Lite – Mobile
• Subset of DVB-T2 Basic + new options
• Not better than T2- Basic! (but new options)
• Mix of FFT sizes in different PLPs
• Competitor/Replacement for DVB-H (and possibly DAB using 1.7 MHz
option)
Table I.4: Combinations of modulation, code rate for which
rotated constellations may be used for data with T2-mobile profile
LDPC
Code
identifier
Effective
LDPC Rate
Kldpc/16
200
Modulation
QPSK 16-QAM 64-QAM 256-QAM
1/3 1/3
2/5 2/5
1/2 4/9
3/5 3/5
2/3 2/3 NA
3/4 11/15 NA
NOTE: means that this combination may be used with or without constellation rotation
means that constellation rotation shall not be used for this combination
NA means that this combination shall not be used
DVB-T2 lite
Transmission chain for DVB-T2 with
SS2:
Basic T2-
Gateway
SS1:
Video/
audio
coders and
statistical
multiplexer
SS3:
T2
Modulator
SS4:
T2
Demodulator
Interface A
“TS”
Interface B
“T2-MI”Interface C
“DVB-T2”
RF
channel
Distribution
network
Input
programme
signals
SS3:
T2
Modulator
Decoded
output
programme
signals
Centralised coding,
multiplexing and
distribution
SS5:
MPEG
Decoder
Interface D
“TS”
SS4:
T2
Demodulator
SS5:
MPEG
Decoder
SS4:
T2
Demodulator
SS5:
MPEG
Decoder
T2 receiver
…SS1:
Video/
audio
coders and
statistical
multiplexer
Input
programme
signals
Optional multiple
coding & multiplexing
Centrally positioned
At each
transmitter
site
48
Modulator interface ETSI Specification
This will make it possible to create identical signal and
allow time synchronisation of transmitters in the SFN.
In short the MI specification makes it possible to split the
T2 modulator allowing that the identical bit streams can
be transferred to all the transmitters in the SFN.
The DVB-T2 network
49
DVB-T/T2 vs ISDB-T Parameter ISDB-T (Japan) ISDB-T (Brazil) DVB-T DVB-T2
Standard ARIB STD-B31 ABNT NBR15601 EN 300 744 EN 302 755
Date first
published
May 2001 November 2007 March 1997 September 2009
Modulation COFDM COFDM COFDM COFDM
Modes QPSK, 16QAM,
64QAM, DQPSK
QPSK, 16QAM,
64QAM, DQPSK
QPSK, 16QAM,
64QAM
QPSK, 16QAM,
64QAM, 256QAM
Guard interval 1/4, 1/8, 1/16, 1/32
1/4, 1/8, 1/16, 1/32 1/4, 1/8, 1/16,
1/32
1/4, 19/256, 1/8, 19/128,
1/16, 1/32, 1/128
Bandwidth 6 (8) 6 (8) 5, 6, 7, 8 1.7, 5, 6, 7, 8, 10
FEC Convolutional
Coding + Reed
Solomon
1/2, 2/3, 3/4, 5/6,
7/8
Convolutional Coding
+ Reed Solomon
1/2, 2/3, 3/4, 5/6, 7/8
Convolutional
Coding + Reed
Solomon
1/2, 2/3, 3/4, 5/6,
7/8
LPDC + BCH 1/2,
2/3, 3/4, 5/6, 7/8
Picture coding MPEG 2 MPEG 4 MPEG2 and
MPEG4
MPEG2 and MPEG4
Capacity
increase 0 0 0 +30-67%
Table from Presentation by Multichoice*
DVB-T2 vs ISDB-T
50
DVB-T/T2 vs ISDB-T
• DVB-T2 seem to technically outperform ISDB-T on almost every point
BUT..
• Some “Advantages” of ISDB-T
• Mobile reception in same multiplex use of 1 segment mode
(now of course also possible with T2)
• Mobile Receivers are available today – but of course mobile
receivers for T2 are coming very soon.
• Choice of system is sometimes also political!
• Chinese Digital TV system standard DTMB will present a new
DTMB-A , which is a similar to DVB-T2- but probably has a few years to
implementation
DVB-T2 vs ISDB-T
51
DVB-T2 Future?
•Dual mode Transmitters (DVB-T//T2) are available
•Cost difference T /T2 receivers very small
•DVB-T2 (T2 lite) better than DVB-H for handheld reception!!
•DVB-T2 to “replace” DVB-H?
•DVB-T2 with 1.7 MHz BW to replace T-DAB
•Multiple PLP:s- common infra structure for Radio and TV?
•Countries starting digital should consider DVB-T2, “no point” to start
DVB-T today !
•Only DVB-T2 in GE06 frequency plan in a few years?
DVB-T and DVB-T2 worldwide
52
Source: www.digitag.org