subject: A few words about DVB-T [print this page] A few words about DVB-T A few words about DVB-T
The Digital Video Broadcasting Project (DVB) is a consortium gathering over 250 broadcasters, manufacturers, network operators, software providers and regulatory bodies in over 35 countries, established to develop open standards for delivering digital television, multimedia and data services. Services in accordance with DVB standards are available on all continents and accessible with over half a billion receivers.
The consortium is the author of many standards. One of them is the DVB-T standard for digital terrestrial television (NTC), endorsed in December 1995, described in EN 300744. The first transmission that used this standard took place in the UK on September 15, 1998. Since then, much has changed. The current state of standards and their implementation in different countries can be followed on the dvb.org website.
Digital terrestrial television systems transmit compressed digital audio/video transport streams (MPEG-TS). The advantage of this solution is the possibility of broadcasting several programs and providing services such as EPG (Electronic Program Guide) in a single stream. Depending on the standard, the systems use MPEG-2 or more advanced MPEG-4/H.264 compression.
To broadcast a digital signal, DVB-T uses COFDM (Coded Orthogonal Frequency Division Multiplexing) modulation scheme. This scheme has been developed for systems that are susceptible to the effect of multipath propagation (typical for wireless signal transmission in urban areas). It consists in the fact that, due to various reflections, the radio signal reaches the receiver in several copies, which are shifted in time. The greater the throughput of the system, the more noticeable it becomes. COFDM modulation is a way to eliminate this problem. Instead of a single high-bandwidth signal the stream is divided into many sub-streams with much slower data rates, modulating a number of orthogonal subcarriers. The number of the subcarriers amounts to 1705 (2k mode) or 6817 (8k mode). Depending on the standard/version, each subcarrier is modulated using QPSK, 16QAM or 64QAM modulation scheme. The throughput of the entire DVB-T stream is within 4 - 32 Mb/s, depending on the version and method of modulation. This means that one multiplex (the band equivalent of a single analog TV channel) can carry up to eight digital television channels in standard definition (SD) or 3-4 channels in high definition (HD).
