COFDM

Coded Orthogonal Frequency Division Multiplexing – a modulation scheme which is used by the DVB digital television system. It allows for the use of either 1705 carriers (usually known as ‘2K’), or 6817 carriers (‘8K’). Concatenated error correction is used. The ‘2K’ mode is suitable for single transmitter operation and for relatively small single-frequency networks with limited transmitter power. The ‘8K’ mode can be used both for single transmitter operation and for large area single-frequency networks (SFN). The guard interval is selectable. The ‘8K’ system is compatible with the ‘2K’ system. At the start of DVB transmissions in the United Kingdom in November 1998, only 2K was possible, but soon after 8K was also possible.

There has been much discussion about the relative merits of COFDM vs the 8-VSB scheme used in the ATSC standard (OFDM may be considered for upcoming ATSC 3). The Japanese ISDB system uses a similar scheme, OFDM, and the Chinese have developed their own transmission scheme the DMB-T/H standard – not to be confused with the T-DMB Korean standard modulation – both significantly different COFDM implementations.

See also: DVB, ISDB, VSB

Website: www.dvb.org