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

http://pda.etsi.org/pda/queryform.asp

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

http://www.dvb.org/

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


• 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


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

thank you!

and

questions?

Mats Ek

[email protected]

session 2: network planning aspects

Documents