Digital Video Broadcasting: Technology, Standards and Regulations
An overview of the technical, political, and market issues relating to digital video broadcast and digital television.
TABLE OF CONTENTS Digital Video Broadcasting: Technology, Standards and Regulations
10.4 DVB terrestrial
Television signals can be provided via terrestrial networks as well. This section first discusses the basic elements of terrestrial communications, then describes the several DVB systems for terrestrial communications at a functional level, and finally explains the specifications for the channel encoding and decoding process.
10.4.1 Elements of terrestrial communications
In case of terrestrial communications, specific elements play an important role. These elements concern typical transmission characteristics which have to be regarded when designing a terrestrial communication system.
10.4.1.1 Transmission medium
Digital terrestrial television services are expected to be provided via the ultra high frequency (UHF) band. The frequencies in this band range from 0.3 GHz to 3 GHz.
In contrast with satellite and cable systems, the terrestrial transmission of signals often suffers from multipath interference. A broadcast signal can be reflected, for example, by high buildings or mountains. The reflections are added to the main signal at the receiving end. Because the reflections travel via a different (and thus longer) route, these signals are delayed and therefore are called echoes. Hence, multipath interference occurs. Additionally, depending on the power used, cochannel interference may be caused when a different station transmits its programs via the same frequency.
In cities with high buildings and in mountain areas, echoes are likely to appear. When terrestrial signals are received by a fixed antenna, the antenna can be aimed at the strongest (main) signal. Hence, the influence of echo signals is minimized. This channel can be seen as a...
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