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DIGITAL AUDIO BROADCASTING SEMINARPROJECTS
Post: #1

DIGITAL AUDIO BROADCASTING
ABSTRACT:

Digital audio broadcasting, DAB, is the most fundamental advancement in radio technology since that introduction of FM stereo radio. It gives listeners interference — free reception of CD quality sound, easy to use radios, and the potential for wider listening choice through many additional stations and services.

DAB is a reliable multi service digital broadcasting system for reception by mobile, portable and fixed receivers with a simple, non-directional antenna. It can be operated at any frequency from 30 MHz to 3GHz for mobile reception (higher for fixed reception) and may be used on terrestrial, satellite, hybrid (satellite with complementary terrestrial) and cable broadcast networks.

DAB system is a rugged, high spectrum and power efficient sound and data broadcasting system. It uses advanced digital audio compression techniques (MPEG 1 Audio layer II and MPEG 2 Audio Layer II) to achieve a spectrum efficiency equivalent to or higher than that of conventional FM radio. The efficiency of use of spectrum is increased by a special feature called Single. Frequency Network (SFN). A broadcast network can be extended virtually without limit an operating all transmitters on the same radio frequency


INTRODUCTION

Digital audio broadcasting, DAB, is the most fundamental advancement in radio technology since that introduction of FM stereo radio. It gives listeners interference — free reception of CD quality sound, easy to use radios, and the potential for wider listening choice through many additional stations and services.

DAB is a reliable multi service digital broadcasting system for reception by mobile, portable and fixed receivers with a simple, non-directional antenna. It can be operated at any frequency from 30 MHz to 36 MHz for mobile reception (higher for fixed reception) and may be used on terrestrial, satellite, hybrid (satellite with complementary terrestrial) and cable broadcast networks.

DAB system is a rugged, high spectrum and power efficient sound and data broadcasting system. It uses advanced digital audio compression techniques (MPEG 1 Audio layer II and MPEG 2 Audio Layer II) to achieve a spectrum efficiency equivalent to or higher than that of conventional FM radio.
The efficiency of use of spectrum is increased by a special feature called Single. Frequency Network (SFN). A broadcast network can be extended virtually without limit a operating all transmitters on the same radio frequency.
DIGITAL AUDIO COMPRESSION

Digital audio compression allows the efficient storage and transmission of audio date. While quantizing, the number of quantizer levels is typically a power of 2 to make full use of a fixed no: of bits per audio sample to represent the quantized values. With uniform quantizer step spacing, each additional bit has the potential of increasing the signal to noise ratio. The typical number of bits per sample used for digital audio is 8, 16, 32, 64. The audio data on a compact disc (2 channels of audio samp1. at 44.1 KHz with 32 bits per sample) requires a data rate of 32x2x44xlO( megabits per second. Ti) transfer this uncompressed data requires a large data transfer rate and a larger bandwidth. Therefore audio data need to be compressed for efficient storage and transmission.

COMPRESSION TECHNIQUES

The MPEG (Motion Picture Experts Group) audio compression algorithm is an International Standardization Organization (ISO) standard for high fidelity audio compression. The high performance of this compression algorithm is due to the exploitation of auditory masking. This masking is a perceptual weakness of the ear that occurs whenever the presence of a strong audio signal in spectral neighborhood of weaker audio signals makes it imperceptible. This noise-masking phenomenon has been observed and corroborated through a variety of psycho acoustic experiments. Due to the specific behaviour of the inner ear, the human auditory system perceives only a small part of the complex audio spectrum. Only those parts of the spectrum located above the masking threshold of a given sound contribute to its perception, where as any acoustic action occurring at the same time but with less intensity and thus situated under the masking threshold will not be heard because it is masked by the main sound event.

SINGLE FREQUENCY NETWORK CAPABILITY OF THE COFDM

With analogue broadcasting especially when it comes to mobile receivers such as car radio-reception is often disturbed by aggravating interference in the form of distortion, noise or total failure. The losses also occur due to signal shadowing. Therefore more than one transmitter may be needed to avoid signal shadowing. To avoid interference from neighboring transmitters different carrier frequencies are used for the same FM/AM program. This can lead to spectrum overloading, especially, in densely populated areas with a high number of stations.

In Single Frequency Network (SFN) all transmitters are emitting the same station in the same frequency. The receiver cannot distinguish whether the received signal is a reflected one or comes from a second transmitter. The DAB allows the combination of blocks of stations on single DAB channel of 1.5 MHz band width, without leading to interference. In conjunction with a SFN, a block of at least six stations per country can be broadcasted via the same DAB channel. By using one or more additional DAB channels, it is possible to provide further blocks of stations for regional and local programs. Thus SFN provides superior frequency economy.

The system provides 4 transmission mode options which allows a wide range of transmission frequencies between 30 MHZ and 3 0HZ and network configuration. For the normal frequency ranges, the transmission modes have been designed to suffer neither from Doppler spread nor from delay spread, both inherent mobile receptions with multipath echoes.

CONCLUSION

More and more countries across the world are switching on to DAB. Their plan is to gradually terminate the existing AM and FM channels, say by 2008 and to use that spectrum for some other purposes. Any how DAB is going to be the Sound of the future. It is in the path of the growth and development. It is going to replace the present methods, even through it may take time. As a successor of DAB , DTV hams started broadcasting in the UK, the USA etc.




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