1

Broadcast Systems

Unidirectional distribution systems

DAB architecture

DVB Container High-speed Internet

2

Typical Client Server Application

Client

IBM Server

Sends a data request

Server sends a huge volume of data

3

Unidirectional distribution systems

Asymmetric communication environments bandwidth limitations of the transmission medium depends on applications, type of information examples

wireless networks with base station and mobile terminals client-server environments (diskless terminal) cable TV with set-top box information services (pager, SMS)

Special case: unidirectional distribution systems high bandwidth from server to client (downstream), but no bandwidth

vice versa (upstream) problems of unidirectional broadcast systems

a sender can optimize transmitted information only for one group of users/terminals

functions needed to individualize personal requirements/applications

4

Typical Personalized Services – Broadcast Services

A user might need a filter as a personal requirement. Starting time of news Disable all rated movie channels Disable all movie channels after 10.00pm

As for the broadcast system goes, the broadcast takes place irrespective of the target user.

MAIN ISSUE : Sender still has the control on when to send and what to send.

HOW TO CIRCUMVENT THIS?

5

Cyclic Repetition

In normal radio kind of broadcast, the receiver gets the packets if it tunes to the channel. Else, it will not.

But in specific situations where the sender has to listen to the program (for ex., emergency weather announcement), data pattern has to be repeated.

6

Unidirectional distribution

service provider service user

sender

receiver

receiver

receiver

.

.

.

unidirectionaldistribution

medium

A

A

A

A

A

A

A B

B

B

B

optimized for expected access pattern

of all users

individual accesspattern of one user

7

Structuring transmissions - broadcast disks

Sender cyclic repetition of data blocks different patterns possible (optimization possible only if the content is known)

Receiver use of caching

cost-based strategy: what are the costs for a user (waiting time) if a data block has been requested but is currently not cached

application and cache have to know content of data blocks and access patterns of user to optimize

A B C A B Cflat disk

A A B C A Askewed disk

A B A C A Bmulti-disk

8

Broadcast Patterns

Flat Disk :

All blocks are repeated at equal intervals Average waiting time to receive the data is the same.

Skewed Disk : Some important blocks are repeated several times in a sequence Will ensure that even if some blocks are corrupted, users will not

miss the data

Multi-Disk : Distribute evenly so that blocks occur at higher frequency Pattern should occur cyclically.

9

Broadcast Patterns

The sender can optimize the broadcast patterns and design the sequence based on the type of programs.

If an user has a prior knowledge of the access patterns, his waiting time is drastically reduced.

10

11

Digital Audio Broadcasting

Why has this come up? higher fidelity more stations and more resistance to

noiseco-channel interference and multipathstronger error correction coding

*** If the bit rates used are less, the performance can be worse than FM

12

Digital Audio Broadcasting

A DVB receiver must support the following modes

Mode I for Band III, Earth Mode II for L-Band, Earth and satellite Mode III for frequencies below 3 GHz,

Earth and satellite Mode IV for L-Band, Earth and satellite

13

Digital Audio Broadcasting

SERVICES Primary services, like main radio stations Secondary services, like additional sports commentaries Data services Electronic Programme Guide (EPG) Collections of HTML pages and digital images (Known as

'Broadcast Web Sites') Slideshows, which may be synchronised with audio broadcasts Video Java Platform Applications IP tunneling Other raw data

14

DAB: Digital Audio Broadcasting

Media access COFDM (Coded Orthogonal Frequency Division Multiplex) SFN (Single Frequency Network) 192 to 1536 subcarriers within a 1.5 MHz frequency band

Frequencies first phase: one out of 32 frequency blocks for terrestrial TV channels

5 to 12 (174 - 230 MHz, 5A - 12D) second phase: one out of 9 frequency blocks in the L-band

(1452- 1467.5 MHz, LA - LI) Sending power: 6.1 kW (VHF, Ø 120 km) or

4 kW (L-band, Ø 30 km) Date-rates: 2.304 Mbit/s (net 1.2 to 1.536 Mbit/s) Modulation: Differential 4-phase modulation (D-QPSK) Audio channels per frequency block: typ. 6, max. 192 kbit/s Digital services: 0.6 - 16 kbit/s (PAD), 24 kbit/s (NPAD)

15

Orthogonal Frequency Division Multiplex (OFDM)

Parallel data transmission on several orthogonal subcarriers with lower rate

k3

f

t

c

Amplitude

f

subcarrier: SI function=

sin(x)x

Maximum of one subcarrier frequency appears exactly at a frequency where all other subcarriers equal zero

superposition of frequencies in the same frequency range

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OFDM II

Properties Lower data rate on each subcarrier less ISI interference on one frequency results in interference of one

subcarrier only no guard space necessary orthogonality allows for signal separation via inverse FFT on receiver

side precise synchronization necessary (sender/receiver)

Advantages no equalizer necessary no expensive filters with sharp edges necessary better spectral efficiency (compared to CDM)

Application 802.11a, HiperLAN2, DAB, DVB, ADSL

17

Real environments

ISI of subsequent symbols due to multipath propagation Symbol has to be stable during analysis for at least Tdata

Guard-Intervall (TG) prepends each symbnol

(HIPERLAN/2: TG= 0.8 µs; Tdata= 3.2 µs; 52 subcarriers)(DAB: Tdata= 1 ms; up to 1536 subcarriers)

OFDM symbolfade out

OFDM symbolfade in

impulse response

OFDM symbol OFDM symbol OFDM symbol

tanalysis window

OFDM symbol

Tdata

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Examples for DAB coverage

19

DAB transport mechanisms

MSC (Main Service Channel) carries all user data (audio, multimedia, ...) consists of CIF (Common Interleaved Frames) each CIF 55296 bit, every 24 ms (depends on transmission mode) Hence Bit Rate is 55296/.024 = 2.304 Mbps ` CIF contains CU (Capacity Units), 64 bit each

FIC (Fast Information Channel) carries control information consists of FIB (Fast Information Block) each FIB 256 bit (incl. 16 bit checksum) defines configuration and content of MSC

Stream mode transparent data transmission with a fixed bit rate

Packet mode transfer addressable packets

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Transmission frame

synchronizationchannelSC

main servicechannel

FIC

MSC

nullsymbol

phase referencesymbol

datasymbol

datasymbol

datasymbol

. . . . . .

symbol Tu

frame duration TF

guard interval Td

L 0 0 12 L-11 L

fast informationchannelFIC

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DAB sender

Trans-mitter

Trans-missionMulti-plexer

MSCMulti-plexer

ODFM

PacketMux

ChannelCoder

AudioEncoder

ChannelCoder

DAB SignalService Information FIC

MultiplexInformation

DataServices

AudioServices

Radio Frequency

FIC: Fast Information ChannelMSC: Main Service ChannelOFDM: Orthogonal Frequency Division Multiplexing

1.5 MHzf

carriers

22

DAB receiver

PacketDemux

AudioDecoder

ChannelDecoder

IndependentDataService

AudioService

Controller

TunerODFM

Demodulator

User Interface

FIC

Control Bus

(partial)MSC

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Audio Coding

Goal audio transmission almost with CD quality robust against multipath propagation minimal distortion of audio signals during signal fading

Mechanisms fully digital audio signals (PCM, 16 Bit, 48 kHz, stereo) MPEG compression of audio signals, compression ratio 1:10 redundancy bits for error detection and correction burst errors typical for radio transmissions, therefore signal

interleaving - receivers can now correct single bit errors resulting from interference

low symbol-rate, many symbols transmission of digital data using long symbol sequences, separated by

guard spaces delayed symbols, e.g., reflection, still remain within the guard space

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Bit Rate Management

a DAB ensemble combines audio programs and data services with different requirements for transmission quality and bit rates

the standard allows dynamic reconfiguration of the DAB multiplexing scheme (i.e., during transmission)

data rates can be variable, DAB can use free capacities for other services

the multiplexer performs this kind of bit rate management, therefore, additional services can come from different providers

maximum bit rate per multiplex of 1152 kbit/s.

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Example of a reconfiguration

D1 D2 D3 D4 D5 D6 D7 D8 D9

Audio 1192 kbit/s

PAD

Audio 2192 kbit/s

PAD

Audio 3192 kbit/s

PAD

Audio 4160 kbit/s

PAD

Audio 5160 kbit/s

PAD

Audio 6128 kbit/s

PAD

DAB - Multiplex

D1 D2 D3 D4 D5 D6 D7 D8 D9

Audio 1192 kbit/s

PAD

Audio 2192 kbit/s

PAD

Audio 3128 kbit/s

PAD

Audio 4160 kbit/s

PAD

Audio 5160 kbit/s

PAD

Audio 796 kbit/s

PAD

DAB - Multiplex - reconfigured

Audio 896 kbit/s

PADD10 D11

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Dynamic Reconfiguration Possibilities

The channels need not be fixed before hand. Dynamic reconfiguration is very much possible.

In the fig, there are six audio channels and nine data channels. Each audio channel as a Program Associated Data (PAD)

At the transmitter, if the system comes to know that there are two additional data packets D10 & D11 and then Channel 3 does not need 192 Kbps bit rate, it can reconfigure to 128 kbps and use the additional BW available for the additional DATA.

27

Multimedia Object Transfer Protocol

The DAB frames have to support the high end receivers that support extended graphics as well as the existing receivers that support simple one-line displays.

This brought in the need for the MOT standards.

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MOT standard Protocol

MOT Object :

Header Core : 7 Byte

- Size of header, Size of Body and type of object.

Header Core Header Extension Body

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MOT standard Protocol

MOT Object :Header Extension : Repetition distance (as explained earlier – skewed, flat

disk etc related) Segmentation info Priority

Body: Contains data as described by the header fields.

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Digital Video Broadcasting (DVB)

1991 foundation of the ELG (European Launching Group)goal: development of digital television in Europe

1993 renaming into DVB (Digital Video Broadcasting)goal: introduction of digital television based on satellite transmission cable network technology later also terrestrial transmission

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Digital Video Broadcasting (DVB)

SDTVEDTVHDTV

Multimedia PC

DVD, etc.

TerrestrialReceiver

Cable

Multipoint Distribution

System

Satellites DVBDigital VideoBroadcastingIntegrated

Receiver-Decoder

DVB-S

DVB-C

DVB-T

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DVB

DVB transmits MPEG-2 container high flexibility for the transmission of digital data no restrictions regarding the type of information DVB Service Information specifies the content of a container

NIT (Network Information Table): lists the services of a provider, contains additional information for set-top boxes

SDT (Service Description Table): list of names and parameters for each service within a MPEG multiplex channel

EIT (Event Information Table): status information about the current transmission, additional information for set-top boxes

TDT (Time and Date Table): Update information for set-top boxes

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Transport Stream

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DVB Container

multimediadata broadcasting

MPEG-2/DVBcontainer

single channelhigh definition television

MPEG-2/DVBcontainer

HDTV

multiple channelsstandard definition

MPEG-2/DVBcontainer

SDTV

multiple channelsenhanced definition

MPEG-2/DVBcontainer

EDTV

35

Example: high-speed Internet access

Asymmetric data exchange downlink: DVB receiver, data rate per user 6-38

Mbit/s return channel from user to service provider: e.g.,

modem with 33 kbit/s, ISDN with 64 kbit/s, DSL with several 100 kbit/s etc.

36

DVB Internet Options

DVB-S adapter

PCInternet

TCP/IP

leased line

serviceprovider

informationprovider

satellite provider

satellite receiver

37

Convergence of broadcasting and mobile comm.

Definition of interaction channels Interacting/controlling broadcast via GSM, UMTS, DECT, PSTN,

…

Example: mobile Internet services using IP over GSM/GPRS or UMTS as interaction channel for DAB/DVB

mobileterminal

DVB-T, DAB(TV plus IP data)

GSM/GPRS,UMTS(IP data)

MUX

Internet

TV broadcaster

ISP

mobile operator

TV

data

broadcast

interaction

channels

38

Classification

DVB-C (Cable) EN 300 800 Digital Video Broadcasting (DVB); DVB interaction channel for Cable TV distribution systems

(CATV) DVB-DSNG (Digital Satellite News Gathering) EN 301 210 TR 101 211 Guidelines EN 201 222 DVB-MC (Multipoint Microwave Video) EN 300 749 Digital Video Broadcasting (DVB); DVB framing structure, channel coding and modulation for

MMDS systems below 10 GHz DVB-MS (Multipoint Microwave Video) EN 300 748 Digital Video Broadcasting (DVB); DVB framing structure, channel coding and modulation for

MVDS at 10 GHz and above DVB-S (Satellite) EN 301 421 Digital Video Broadcasting (DVB); Modulation and Coding for DBS satellite systems at 11/12

GHz ETR 101 198 Implementation of BPSK modulation for DVB-S DVB-SFN (Single Frequency Networks) TS 101 190 Megaframe for Single Frequency Networks DVB-SMATV (Single Master Antenna TV) EN 300 473 Digital Video Broadcasting (DVB); DVB Satellite Master Antenna Television (SMATV) distribution

systems

39

Classification

DVB-T (Terrestrial TV) EN 300 744 Digital Video Broadcasting (DVB); Framing structure,

channel coding and modulation for digital terrestrial television (DVB-T)

TR 101 190 Implementation Guidelines for DVB-T Terrestrial Digital Communication Networks ETS 300 813 Digital Video Broadcasting (DVB); DVB

interfaces to Plesiochronous Digital Hierarchy (PDH) networks ETS 300 814 Digital Video Broadcasting (DVB); DVB interfaces

to Synchronous Digital Hierarchy (SDH) networks ETS 300 818 Broadband Integrated Services Digital Network

(B-ISDN); Asynchronous Transfer Mode (ATM); Retainability performance for B-ISDN switched connections

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HDTV Resolution

Analog TVs : 525 lines for the NTSC with an upfate rate of 25 to 30 frames per second

HDTVs have a Resolution of 1920 x 1080 …………

Much better than the analog TV resolution

Tyoical Data Rates of DVB : 5-30 MBPS

41

Profiles for Data Broadcasting

Data Pipe : Asynchronous end-end delivery of data (directly inserted in MPEG-2 transport packets)

Data Streaming : Can be synchronized with other streams – audio/video, data and clock generation at receiver end possible.

Multi-protocol Encapsulation : Transport of arbitrary network protocols on top of MPEG-2 Transport Stream., support for MAC address, unicast, multicast and broadcast.

Object Corousels : Periodic transmission of Objects : Compatible with CORBA

42

Summary of MPEG-2 Compression Capability

43

Comparison

UMTS DAB DVB

Spectrum bands (depends on national regulations) [MHz]

2000 (terrestrial), 2500 (satellite)

1140-1504, 220-228 (UK)

130-260, 430-862 (UK)

Regulation Telecom, licensed

Broadcast, licensed

Broadcast, licensed

Bandwidth 5 MHz 1.5 MHz 8 MHz

Effective throughput

30-300 kbit/s (per user)

1.5 Mbit/s (shared)

5-30 Mbit/s (shared)

Mobility support Low to high Very high Low to high

Application Voice, data Audio, push Internet, images, low res. video

High res. video, audio, push Internet

Coverage Local to wide Wide Wide

Deployment cost for wide coverage

Very high Low Low