Digital Audio Broadcasting

1. Unlike analog radio systems, DAB system offers the best sound quality and is immune 10 interference and other effects.

2. DAB uses UHF and VHF frequency hands depending on the regulation of a country.

3. The modulation scheme used in DAB is DQPSK.

4. It uses Coded Orthogonal Frequency Division Multiplexing (COFDM).

5. It uses FEC to reduce the error rate and introduces guard space between signals during transmission.

6. It contains different frequency blocks each with 1.5 MHz.

7. DAB can transmit up to 6 audio programs with a data rate of 192 kbp/sec in each frequency block.

8. It uses two transport mechanisms viz:

1) Main Service Channel (MSC) and

2) Fast Information Channel (FIC)

The MSC carries all user data such as audio, multimedia etc. it is made up of Channel Interleaved Frames (CIF). It offers high data rates of 2.304 mbps.

An FIC carries all control information required for interpreting the contents of MSC.

MSC operates in 2 modes viz:

1. Stream Mode and

2. Packet Mode

In case of Stream Mode, the data is always transmitted at a fixed bit rate is a sub channel.

In case of Packet Mode, data is transmitted in the form of packets. Each DAB frame can have a duration (tf) of 24, 48, 96 ms depending on the transmission mode.

Each frame is made up of 3 parts viz:

1. The Synchronization Channel (SC)

2. The fast Information Channel (FIC) and

3. The Main Service Channel (MSC)

The synchronization channel consists of a null symbol and phrase reference symbol to synchronize the receiver.

The following diagram gives a structure of a Digital Audio Broadcasting:

Digital Audio Broadcasting