Communication Systems 1

Digital Video Broadcasting

The DVB standard

Prof. Davide Dardari

DEI - Università degli Studi di Bologna

Prof. Davide Dardari, University of Bologna

DVB (Digital Video Broadcasting): ETSI 1995-97 standard 2

Main technological aspects

• video compression, coding (higher spectral efficiency and robustness

to thermal noise)
• flexibility in bit rate allocation
• video and data multiplexing
• management of multimedia and interactive applications
• security management
• versions: DVB-S (satellite), DVB-T (terrestrial), DVB-C (Cable), DVB-H
(Handheld) e DVB-SH (satellite services to handheld device)
• recently also DVB-T2, DVB-S2, DVB-C2, ….

Prof. Davide Dardari, University of Bologna

DVB: main services made available by MHP 3

(Multimedia Home Platform)

• EB1 Profile “Enhanced Broadcasting”
- electronic programme guide (EPG)
- super teletext
- applications synchronized with video: e.g., gaming

• IB1 Profile “Interactive Broadcasting”

- home shopping
- home banking
- Remote pooling, quiz
- e-mail
- pay-TV,Video on Demand; Near Video on Demand

• IA Profile “Internet Access”

Prof. Davide Dardari, University of Bologna

DVB-S (Digital Video Broadcasting – Satellite) 4

Compliant with DVB-T (terrestrial) and DVB-C (cable)

at information coding level

Prof. Davide Dardari, University of Bologna

 DVB-S 5

The DVB-T transmitter 10

MPEG-2 (188 bytes) Bit rate=28.1 – 58.3 Mb/s, typical 35.6 Mb/s

Bit rate=3-8 Mb/s Channel coding

Bit rate= from 4.98 to 31.8Mbit/s, typical 20 Mb/s

𝑑$ Low priority stream

𝑏#
Outer Inner
Interleaver
coder coder
𝐵! High priority stream 𝐵!"

Code rate Rc
Information source
Modulatore
Front end
(') OFDM
𝑥% PAM TX antennna
g(t)
𝑏# cos 2𝜋𝑓
4-PSK *𝑡
Bandwidth: 7-8 MHz
()) Power
𝑠(𝑡)
mapper 𝑥% = 𝑥%' +𝑗 𝑥%
amplifier
𝐵!" 𝜋/2
()) Prof. Davide Dardari, University of Bologna
𝑥% PAM
g(t)
𝐵+
Bandwidth 26-54 MHz
QAM typical 33 MHz

Prof. Davide Dardari, University of Bologna

 DVB-T (Digital Video Broadcasting – Terrestrial) 6

• flexible bit-date (from 4.98 to 31.8Mbit/s)

• multimedia services

• high spectral efficiency thanks to powerful video compression techniques

• interoperable (sub)standards DVB-S, DVB-C e DVB-H

• compliant with analog bandwidth allocations of 7-8 MHz in the VHF-UHF bands

• support for HDTV, 4K

• iso-frequency coverage

• robust to thermal noise and multipath

Prof. Davide Dardari, University of Bologna

 DVB-T 7

Interactive DVB-T

Broadcast channel

Broadcast network DVB-T receiver

interface
Multimedia servces
Services formatting
BROADCAST
NETWORK

Uplink channel
Service provider TLC interface
Services Interaction
management management

TLC
NETWORK

The uplink channel can be realized with:

-ADSL, optical fiber
-GSM, GPRS, UMTS, LTE, DVB-RCS

Prof. Davide Dardari, University of Bologna

 The terrestrial radio channel 8

Strong multipath propagation

Adoption of OFDM technique

H( f )

Df

f
B
Prof. Davide Dardari, University of Bologna
 The OFDM Technique 9

Signal Guard
Serial-to-parallel IFFT P/S Interval D/A Up
Serial Data Converter Mapper Insertion
Input Converter
LPF

Channel

Signal
Parallel-to-serial One-tap FFT S/P Guard LPF Down
Converter Mapper Interval
Equalizer Removal Converter
Serial A/D
Data
Output

Cyclic prefix
Td<Tg No ISI

Prof. Davide Dardari, University of Bologna

 The DVB-T transmitter 10

Bit rate=3-8 Mb/s

Bit rate= from 4.98 to 31.8Mbit/s, typical 20 Mb/s

Low priority stream

High priority stream

Modulatore
Front end
OFDM

Bandwidth: 7-8 MHz

Prof. Davide Dardari, University of Bologna

 The DVB-T receiver 11

From aerial

Front End OFDM Inner

demod. De-interleaver

Pb<10-11

Inner Outer Outer Demux

Decoder De-interleaver decoder MPEG-2

Common part with satellite baseline receiver

Pb<2*10-4

Prof. Davide Dardari, University of Bologna

Data structure 12

Prof. Davide Dardari, University of Bologna

 Data structure 13

The transmitted signal is organized in frames. Each frame is composed

of 68 OFDM symbols and each group of 4 frames is called super-frame.

Each OFDM symbol is composed of 2048 (2k mode) or 8192 (8k mode)
subcarriers

Only 1705 (6817) subcarriers out of 2048 (8192 in 8k mode) are active,
the remaining are virtual subcarriers (empty).
Of which:
- 45 (177) are continuous pilot subcariers
- 444 (1849) are “scattered” pilot subcarriers
- 17 (68) are TPS (transmission parameters signaling) subcarriers

Then 1512 (6048) subcarriers are left for data

Prof. Davide Dardari, University of Bologna

 Pilot subcarriers (Pilot tones) 14

Their purpose is to allow for channel estimation, frame, time and

frequency synchronization

They are transmitted at a slightly higher power and are modulated by a

pseudo-noise sequence using a BPSK signaling (higher robustness)

Prof. Davide Dardari, University of Bologna

 Transmission Parameter Signalling (TPS) 15

Parameters mapped on TPS

-Frame number in a super-frame
-Modulation scheme
-Hierarchic information
-Inner code rates
-Guard interval length Each TPS block is transmitted in
parallel on 17 subcarriers (68 in 8k
-Transmission mode mode) to increase the robustness at
the RX.
To this purpose a Differential BPSK
modulation is adopted (equalization is
avoided)

Prof. Davide Dardari, University of Bologna

 Operating modes (numerology) 16

• 2k o 8k (N=2048 or N=8192) (FFT)

Nu=6048 (8k) Nu=1512 (2k) data subcarriers
Df=1116 Hz (8k) Df=4464 Hz (2k)
Tu=896 µs (8k) Tu=224 µs (2k)

• 4-16-64 QAM
optional hierarchic modulation a=2,4

• Code rate convolutional inner coder with code rate 1/2, 2/3,3/4,5/6,7/8

• Guard time
Tg/Tu=1/4,1/8,1/16,1/32
Tg=224µs, 112µs, 56µs, 28µs (8k mode)
Tg=56µs, 28µs, 14µs, 7µs (2k mode)

Prof. Davide Dardari, University of Bologna

 Hierarchic modulation 17

D2
a= D1
• • • • • • • •
• • • • • • • •
• • • • • • • •
• • • • • • • •
• • • • • • • •
• • • • • • • • • • • •
• • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • • •
• • • •

• • • •
• • • •
• • • • • • • •
• • • • • • • •
• • • • • • • •
• • • • • • • • D2
D1

• • • • • • • •
• • • • • • • •
• • • • • • • •
• • • • • • • •

Prof. Davide Dardari, University of Bologna

 Operating modes 18

For each mode we obtain different performance, bit rate

and robustness to multipath.

The constraint on bandwidth is always fixed

(about 6.6 MHz)

Prof. Davide Dardari, University of Bologna

 Computation of the useful bit rate: example 19

(8k N=8192)

2Rcout Rcin log2 L N Nu

Br =
Tc N +D N

Rcout = 0.92 outer code rate RS(188,204,8)

1 2 3 5 7
Rcin = , , , ,
2 3 4 6 8 ✓ ◆
N 4 8 16 32 Tg D 1 1 1 1
= , , , = = , , ,
N +D 5 9 17 33 Tu N 4 8 16 32

Tc = 109 ns (Fixed)
Nu = 6048 Data subcarriers
f = 1116 Hz
Prof. Davide Dardari, University of Bologna
 Computation of the useful bit rate: example 20

(8k N=8192)
Most robust configuration

Tg
L = 2 (QPSK), R cinn = 1
2 , Tu = 1
4

ß
Tu = N × Tc = 896µs Tg = 224µs
Br @ 4.9 Mbit/s Modulation Bits per Inner code Guard time
rate
subcarrier 1/4 1/8 1/16 1/32
2 1/2 4,98 5,53 5,85 6,03
2 2/3 6,64 7,37 7,81 8,04
QPSK 2 3/4 7,46 8,29 8,78 9,05
2 5/6 8,29 9,22 9,76 10,05
2 7/8 8,71 9,68 10,25 10,56
4 1/2 9,95 11,06 11,71 12,06
4 2/3 13,27 14,75 15,61 16,09
16-QAM 4 3/4 14,93 16,59 17,56 18,10
4 5/6 16,59 18,43 19,52 20,11
4 7/8 17,42 19,35 20,49 21,11
6 1/2 14,93 16,59 17,56 18,10
6 2/3 19,91 22,12 23,42 24,13
64-QAM 6 3/4 22,39 24,88 26,35 27,14
6 5/6 24,88 27,65 29,27 30,76
6 7/8 26,13 29,03 30,74 31,67

Prof. Davide Dardari, University of Bologna

 DVB-T: Bit Rate for each configuration 21

Mb/s

Prof. Davide Dardari, University of Bologna

 Performance 22

Performance with QPSK, 16-QAM and 64-QAM

Target Peb: 10-11 QEF (2*10-4 after inner code)

PROBABILITA' DI ERRORE PER BIT

-3
10
64-QAM

16-QAM
-4 QPSK hard
10
Pb

-5
10

QPSK soft
-6
10 Tg=28µsec
Tg=56µsec
Tg=112µsec
-7
Tg=224µsec
10
4 5 6 7 8 9 10 11 12 13 14
Eb/No (dB)

Prof. Davide Dardari, University of Bologna

 Reference signal-to-noise ratio 23

Bitrate (Mbit/s)
modula- code a channel channel channel Guard

interval

- tion rate Gaussian Rice Rayleigh 1/4 1/8 1/16 1/32

P =10-11
1/2 3,1 3,6 5,4 4,98 5,53 5,85 6,03

2/3 4,9 5,7 8,4 6,64 7,37 7,81 8,04 eb

QPSK 3/4 1 5,9 6,8 10,7 7,46 8,29 8,78 9,05

5/6 6,9 8,0 13,1 8,29 9,22 9,76 10,05

7/8 7,7 8,7 16,3 8,71 9,68 10,25 10,56

1/2 14,4 14,7 16,0 14,93 16,59 17,56 18,10

2/3 16,5 17,1 19,3 19,91 22,12 23,42 24,13

64QAM 3/4 1 18,0 18,6 21,7 22,39 24,88 26,35 27,14

5/6 19,3 20,0 25,3 24,88 27,65 29,27 30,16

7/8 20,1 21,0 27,9 26,13 29,03 30,74 31,67

1/2 6,5 7,1 8,7 4,98 5,53 5,85 6,03

QPSK 2/3 9,0 9,9 11,7 6,64 7,37 7,81 8,04

3/4 10,8 11,5 14,5 7,46 8,29 8,78 9,05

in + + + +

1/2 2 16,3 16,7 18,2 9,95 11,06 11,71 12,06

64QAM 2/3 18,9 19,5 21,7 13,27 14,75 15,61 16,09

non 3/4 21,0 21,6 24,5 14,93 16,59 17,56 18,10

uniforme 5/6 21,9 22,7 27,3 16,59 18,43 19,52 20,11

7/8 22,9 23,8 29,6 17,42 19,35 20,49 21,11

Prof. Davide Dardari, University of Bologna

 Iso-frequency coverage 24

Equivalent model

t2
t2-t1=Td
t1

TX2
TX1

TX1 CANALE
TX RX
2 RAGGI
Equivalente

Artificial multipath

It still works if Td<Tg

Prof. Davide Dardari, University of Bologna

 Choice of guard time and N 25

The guard time is used to protect the transmission against natural

(propagation) and artificial multipath (SFN)

In 2k mode the maximum guard time is 56μs

In 8k mode the maximum guard time is 224μs

Typically, 7μs is sufficient to protect the transmission against natural

multipath (mountains excluded)

In SFN networks the design of guard time is critical in relation to the

distance between transmitters and network size.

For instance, a large SFN might require guard time larger than 200us
and hence the 8k mode becomes mandatory.

Prof. Davide Dardari, University of Bologna

 Iso-frequency coverage 26

MFN SFN
Sistema MFN
(Multi-Frequency-Network) Sistema SFN
(Single-Frequency Network)

B A
C A A

C
A
A A
B A
A A
B A A
C

Zona di buio

Gap filler

In the DVB-T standard the guard time can be set up to about 224µs
to which a maximum tolerable path difference of d=60 Km
corresponds.
The link budget and coverage design must account for both the
power level and relative delay.

Prof. Davide Dardari, University of Bologna

 Advantages of SFNs 27

SFN is more spectral efficient than MFN

No new frequency planning is needed when a new TX is added

(e.g., gap filler)

SFN is more efficient also from the energy point of view:

– In MFN a large fading margin in the link budget is necessary to

counteract the large signal variations experimented locally.

– In SFN the signals received from different transmitters are

coherently combined by the FFT operation thus reducing the fading
effect and hence the required fading margin (e.g., less TX power).

Prof. Davide Dardari, University of Bologna

 Service Coverage 28

(Service Coverage Pb=10-11 QEF)

• receiving location 0,5m x 0,5m

(covered if the SNR is satisfied for 99% of the time )

• small area 100m x 100m

Long-term signal variations are typically modeled
as log-normal with std. σ
5m
0,
x
Typically σ=5.5 dB (outdoor) 5m
0,

0m
10
x
0m
10
• Coverage area
good 95%
level of coverage
acceptable 70%

Prof. Davide Dardari, University of Bologna

 Fading margin 29

To obtain the desired level of coverage, a fading margin is added to

the median value of the received power in the link budget

The fading margin (location correction factor) Msh, indicates the

increase of received power which allows the coverage
probability to move from 50% to x% within a small area

100 æ - M sh (dB) ö
x% = erfcçç ÷
2 è 2s dB ÷ø

Prof. Davide Dardari, University of Bologna

 Coverage probability vs fading margin 30

0.95
ssh=4 dB
0.9
ssh=6 dB ssh=7 dB
0.85 ssh=8 dB

0.8 ssh=10 dB
Pc(R)
0.75

0.7

0.65

0.6

0.55

0.5
0 2 4 6 8 10
Msh(dB)

good 95% Msh=9 dB

level of coverage
acceptable 70% Msh=2.9 dB
Prof. Davide Dardari, University of Bologna
 Coverage evaluation: numerical example 31

The reference received power, or received electrical field, depend on:

(example)
• type of installation fixed
• channel model Rice
• modulation OFDM 64-QAM
• number of subcarriers 8k
• code rate 2/3
• carrier frequency 834 MHz
• signal-to-noise ratio C/N 17.1 dB
• quality of service QEF (Pb=10-11)
• coverage percentage 95% (σ=9dB)
• interference protection ratio C/I 20 dB

Emed=57.1 dBµV/m
Prof. Davide Dardari, University of Bologna
 Coverage algorithm 32

Covered
no Td<Tg yes E ³ E med yes
location

no
Location
not covered
C / I > (C / I ) ric no Location
not covered

yes

Covered
E (*) ³ E med yes
location

no
Location
not covered Prof. Davide Dardari, University of Bologna
 33

Received field

Emed=57.1 dBµV/m

Guard time

Tg=28 µsec,
Br=24.13 Mbit/s

Prof. Davide Dardari, University of Bologna

Coverage area 34

Tg=28 µsec,
Br=24.13 Mbit/s
Emed=57.1 dBµV/m

Prof. Davide Dardari, University of Bologna

 Coverage area 35

Emed=57.1 dBµV/m

Tg=56 µsec,
Br=23.42 Mbit/s

Prof. Davide Dardari, University of Bologna

 36

First level coverage

Tg=28 µsec
Br=24.13 Mbit/s

Tg=56 µsec
Emed=57.1 dBµV/m Br=23.42 Mbit/s
Prof. Davide Dardari, University of Bologna
 37

Regional coverage

Tg=28µsec
Br=24.13 Mbit/s

Emed=57.1 dBµV/m Tg=56µsec

Br=23.42 Mbit/s
Prof. Davide Dardari, University of Bologna
 38

Digital Video Broadcasting

Second Generation Terrestrial
DVB-T2 (ETSI 2009)

Prof. Davide Dardari, University of Bologna

 DVB-T2 (ETSI 2009) 39

DVB-T2 uses OFDM modulation and offers a wide range of different modes. The number of carriers,
guard interval sizes and pilot signals can be adjusted, so that the overheads can be optimized for any
target transmission channel.

Enhanced channel coding à LDPC (Low Density Parity Check) + BCH (Bose-Chaudhuri-Hocquengham)
à very robust signal.

Multiple Physical Layer Pipes:

This system transmits compressed digital audio, video, and other data in "physical layer pipes" (PLPs). They allow
separate adjustment of the robustness of each delivered service within a channel to meet the required
reception conditions (for example indoor or roof-top antenna). It also allows receivers to save power by
decoding only a single service rather than the whole multiplex of services.

Alamouti coding: is a transmitter diversity method that improves coverage in small-scale single-frequency
networks

Constellation Rotation: provides additional robustness for low order constellations.

Extended interleaving: including bit, cell, time and frequency interleaving.

Future Extension Frames (FEF): allow the standard to be compatibly enhanced in the future (e.g. T2-lite)

Prof. Davide Dardari, University of Bologna

Comparison with DVB-T 40

Prof. Davide Dardari, University of Bologna

 DVB-T2 lite (ETSI 2011) 41

It was introduced in July 2011 to support mobile and portable TV and to reduce implementation costs.

T2-Lite is the first additional transmission profile type that makes use of the FEF approach.

The new profile is defined as a subset of DVB-T2 with two additional LDPC code rates.

Because only elements relevant for mobile and portable reception have been included in the T2-Lite subset
and the data rate is restricted to 4 Mbit/s per PLP, the implementation (chipset) complexity has been
reduced by 50%.

The FEF mechanism allows T2-Lite and T2-base to be transmitted in one RF channel, even when the two
profiles use different FFT sizes or guard intervals.

Prof. Davide Dardari, University of Bologna

 42

Digital Video Broadcasting

Second Generation Satellite
DVB-S2

Prof. Davide Dardari, University of Bologna

 DVB-S2 43

Key technical characteristics:

Four modulation modes available: QPSK and 8PSK intended for broadcast applications in non-linear
satellite transponders driven close to saturation. 16APSK and 32APSK, requiring a higher level of C/N,
are mainly targeted at professional applications such as news gathering and interactive services.

Enhanced channel coding (same as DVB-T2) à LDPC (Low Density Parity Check) + BCH (Bose-
Chaudhuri-Hocquengham) à very robust signal

Adaptive Coding and Modulation (ACM): it allows the transmission parameters to be changed on a
frame by frame basis depending on the particular conditions of the delivery path for each individual
user. It is mainly targeted to unicasting interactive services and to point-to-point professional
applications.

DVB-S2 offers optional backwards compatible modes that use hierarchical modulation to allow legacy
DVB-S receivers to continue to operate, whilst providing additional capacity and services to newer
receivers.

Prof. Davide Dardari, University of Bologna

 Comparison with DVB-S 44

DVB-S2 delivers excellent performance, coming close to the Shannon limit, the theoretical maximum information transfer rate
in a channel for a given noise level. It can operate at carrier-to-noise ratios from -2dB (i.e., below the noise floor) with QPSK,
through to +16dB using 32APSK. Gains in the useful bitrate of more than 30% in each case.

Prof. Davide Dardari, University of Bologna