7/31/2019 Dab Final

1/23

Name- Sourav Chatterjee

Dept.- ECE Section-A

Roll no.-085234

7/31/2019 Dab Final

2/23

What is Digital Audio Broadcasting?

DAB is an advanced digital radio technology bywhich multiple radio programmes can be broadcastin a single channel occupying a minimum bandwidth. By DAB we can select our own radiochannel from a large ensemble of differentprogrammes without even tuning our radio each

time. It offers superior CD quality sound and is alsoimmune to fading, interference and distortion alongwith enhanced security.

7/31/2019 Dab Final

3/23

In a nutshell. Disadvantage of conventional Radio Networks History of DAB Overview of important terms associated with DAB OFDM overview Single Frequency Networks MPEG Audio Coding MPEG Audio Layer-II DAB features and architecture Advantages and Disadvantages of DAB Applications

7/31/2019 Dab Final

4/23

Problems faced by conventional analog radio:-

a) Searching for the particular radio channel in an enormous bandwidth spectrum.

b) Suppression of audio quality and fading.c) Highly susceptible to noise - AM systems are more susceptible to

noise than FM. For improving FM noise behaviour bandwidth hasto be increased.

contd .

7/31/2019 Dab Final

5/23

Problems faced by conventional analog radio:-

d) Attenuation of FM radio signals due to internal reflections from thesurroundings and the resulting degradation of audio quality

e) Distortion and multipath effects shadowing and passive echoes.

f) High power required for transmission- more the range and no. ofstations, more the power.

g) Security concerns- sensitive data cannot be transmitted.

7/31/2019 Dab Final

6/23

Designed in 1981 by IRTand first demonstrated in1985- Germany

Developed as a research project for theEuropean Union(EUREKA) and theMPEG-1 Audio layer-II Codec created Choice of codec,modulation scheme

and error control coding made andfirst trial broadcast in 1990

First public demonstration in1993 in UK. Standardized by1997 and commercial operationby 1999

By 2006 50 millionpeople served with DABand over 1000 stationsworldwide. Strongercoding and FEC schemesadopted giving rise toDAB+

7/31/2019 Dab Final

7/23

7/31/2019 Dab Final

8/23

7/31/2019 Dab Final

9/23

COFDM Performance Analysis

Immune to multipath fading- If the multipath delay is less than guard interval then interference is

constructive

Behaviour to phase noise/jitter- COFDM is sensitive to phase and frequency errors as it destroys

orthogonality- Solution is using a pilot carrier to track phase noise

More immune to impulse noise- The impulse noise threshold for COFDM is 11dB higher than that of single

carrier systems

Peak to average power ratio is lower for COFDM- COFDM has Gaussian amplitude pdf and the probability of the ratio

greater than 6 is less than 1%

More sensitive to nonlinear distortion- Nonlinear distortion leads to spreading of each carrier spectrum and

disturbs orthogonality

7/31/2019 Dab Final

10/23

Single Frequency Networks are the broadcast Networks where several transmitterssimultaneously send the same signal over the same frequency channel or we cansay Single Frequency Network is the name given to a network of transmitters whichhave been specially treated to broadcast on one single frequency.

Requirements for SFN:-a. All the transmitters must be properly synchronized

b. The maximum delay due to multipath effects should be less than the symbolduration

c. The individual subcarriers have to carry the same data, appear at the same time

and should have very high tolerance with respect to phase and frequency

7/31/2019 Dab Final

11/23

High frequency efficiency

Lowpower operation (internal network gain)

High location probability

Easy gapfilling (frequency re use)

Network splitting is not possible

Synchronization is necessary

Feed control is required

7/31/2019 Dab Final

12/23

MPEG Audio is one part of a compression standard that also includes video and

systems.

It mandates the syntax of the coded bitstream, defines the decoding process andprovides compliance tests for assessing the accuracy of the decoder.

Audio Sampling rate can be 32,44.1 or 48khz.

Predefined bit rates from 32 to 224 kbps(compression factor ranging from 2.7 to24).

a) Layer 1 Simplest coding technique with 128 kbps per channel(targetdigital compact disc) .

b) Layer 2 --Intermediate complexity with 128 kbps per channel(targetDAB, storage synchronized video and audio sequences on CDROM.

c) Layer 3Most complex but highest audio quality. Best for bit ratesaround 64kbps per channel(target data transmission over ISDN) .

Error detection and correction means provided by cyclic redundancy check(CRC).Anciliary data can also be included in the bitstream.

7/31/2019 Dab Final

13/23

Encoder

Decoder

7/31/2019 Dab Final

14/23

DAB uses SFN with VHF and UHF frequency bands e.g. the terrestrial TV

channels 5 to 12( 174-1492 MHz ) or the L-band( 1452-1492 MHz ).

The modulation used is DQPSK with transmission using OFDM .

The entire spectrum consists of 192 to 1536 subcarriers each carrier a portionof the original bitstream within a band of 1.5MHz .

Within each block DAB can transmit upto 6 stereo audio programmes with adata rate of 192kbps each.

DAB uses FECand channel coding to increase redundancy.

DAB can benefit from multipath propagation if delay is less than guard interval.

Two types of channels used in DAB Main Service Channel(MSC) which carries all audio and multimedia data. It consists of

Common Interleaved Frames(CIF) with 55296 bits sent every 24ms giving data rate of

2.304Mbps Fast Information Channel(FIC) carries all control information with 256 bits in each block

7/31/2019 Dab Final

15/23

TF=24,48or 96ms Within each frame 76 or 153 symbols are transmitted using 192,384,768 or

1536 different carriers for OFDM

The guard intervals can be 31,62,123 or 246 s

7/31/2019 Dab Final

16/23

7/31/2019 Dab Final

17/23

7/31/2019 Dab Final

18/23

Dynamic Reconfiguration of DAB multiplexing

PAD is the Program Associated Data which can contain program and control information,Text to display on LCD, title display etc.

When reconfiguration is done by the DAB Multiplexer it sends a multiplex configuration

Information(MCI) to the receiver through the FIC

7/31/2019 Dab Final

19/23

7/31/2019 Dab Final

20/23

1) Broadcast websites Complete website transmission to offline users in a digital radio receiver,

equipped with web browser. Application based on MOT protocol (Multimedia Object Transfer) which ensures

the integrity and consistency of the provided information. Currently limited use due to bandwidth considerations and high demand on

decoder resources and user interface functionality on the receiver side.

2) Slideshow Slideshow adds synchronized visual content (slides) to radio broadcasts on DAB. Visuals can be embedded in JPEG,PNG or APNG formats and transmitted over

DAB. Slideshow is transmitted in either X-PAD or MSC, and can be effective at data

rates from 8kbit/s upwards.

7/31/2019 Dab Final

21/23

3) Journaline Journaline is a data service, which was internationally standardized by the

WorldDMB Forum for use in DAB and DRM in fall of 2007.

The listener can access interactively both program related and program independenttextual information.

The textual information can contain background information on the program, currentnews, stock market tickers, sports results, the latest airport arrival and departure times,

etc. It is up to the broadcaster to tailor the content to the needs of his specific audience.

Textual information is selected through an interactive menu structure.

7/31/2019 Dab Final

22/23

4) Electronic Program Guide Display of schedules at varying levels of detail for programmes from a range of services. Navigation and selection of services and programmes.

Timed recording of individual programmes, or of groups of programmes and themed orsimilar programming. Services similar to Internet Podcast

5) Surround Sound Surround-sound effect encompasses the listener from all directions. Compared to the stereo format, surround sound almost triples the volume of data, and

data compression becomes even more crucial for an economic multi-channel

transmission.

7/31/2019 Dab Final

23/23

THANK YOU