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Terrestrial and Satellite Digital Sound Broadcasting to Vehicular, Portable and Fixed Receivers in the VHF/UHF Bands

DSB Handbook

image of Terrestrial and Satellite Digital Sound Broadcasting to Vehicular, Portable and Fixed Receivers in the VHF/UHF Bands

This Handbook describes the system and service requirements for digital sound broadcasting (DSB) to vehicular, portable and fixed receivers, the related propagation factors, the techniques employed in the digital sound broadcasting systems, and considers relevant planning parameters and sharing conditions.

English

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Components of DSB Systems

Digital systems can overcome the problems caused by obstruction effects and the presence of multipath propagation which results from specular or diffuse reflections. This occurs on roads in rural areas where the path passes through foliage and in urban areas where there are numerous obstacles. When the fading follows a Rayleigh distribution and is frequency-selective, the error rate of a simple digital system can fall below an unacceptable limit, with resulting poor quality. This can be overcome only by increasing the required link margin and thus the transmitter power. The effects of frequency selectivity can also be overcome through the use of symbol durations which are large with respect to the dispersion of the echo delays. A powerful channel coding mechanism can then be applied (convolutional code with Viterbi decoding), but it is necessary to ensure the independence between successive symbols with respect to channel fades. This is achieved by interleaving the symbols either in time or in frequency (the total bit rate is thereby distributed between several carriers spaced sufficiently far apart in frequency). Temporal interleaving is effective, however, only if the receiver is mounted in a vehicle traveling above a certain speed. If the receiver is stationary, frequency interleaving must be used or, alternatively, space diversity reception. When frequency interleaving is used, carriers modulated with other sound channels may be placed between those carrying the parts of a given channel, using orthogonal frequency division multiplexing (OFDM).

English

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