CODEC Coder-DECoder Coder-Decoder (CODEC) A function or device that performs compression and decompression, typically on voice or video streams. Codes Exchange (CODEX) A telecommunications Codex specifies how different binary values sent across the telephone network are translated to and from specific sample voltages. See also Codec. CODEX Codes Exchange COFDM Coded Orthogonal Frequency Division Modulation; OFDM used in conjunction with channel coding techniques. As the overhead of doing this in an already digital system is low, and the gains substantial, practical OFDM/DMT systems are all actually COFDM. Although highly complex, COFDM has high performance under even very challenging channel conditions. By combining the OFDM technique with error-correcting codes, adaptive equalization and reconfigurable modulation, COFDM has the following properties: resistant against link dispersion resistant against slowly changing phase distortion and fading resistant against frequency response nulls and constant frequency interference resistant against burst noise COFDM also generally has a nearly 'white' spectrum, giving it benign electromagnetic interference properties with respect to other signals. Some COFDM systems use some of the sub carriers to carry pilot signals, which are used for frequency synchronizations, as frequency shifts during the transmission using the main modulation/demodulation process transform into bit errors in the decoded data. In wide area broadcasting, receivers can benefit from receiving signals from several spatially dispersed transmitters simultaneously, since transmitters will only destructively interfere with each other on a limited number of subcarriers, whereas in general they will actually reinforce coverage over a wide area. This is very beneficial in many countries, as it permits the operation of national single frequency networks, and avoids the replication of program content on different carrier frequencies which is necessary with FM or other forms of radio broadcasting. Also, because effectively the bit rate is slowed down on each sub-carrier, the effects of "ghosting" are much reduced. Such single frequency networks utilize the available spectrum more effectively than existing analog radio networks. Coherent Communications
CODEC Coder-DECoder Coder-Decoder (CODEC) A function or device that performs compression and decompression, typically on voice or video streams. Codes Exchange (CODEX) A telecommunications Codex specifies how different binary values sent across the telephone network are translated to and from specific sample voltages. See also Codec. CODEX Codes Exchange COFDM Coded Orthogonal Frequency Division Modulation; OFDM used in conjunction with channel coding techniques. As the overhead of doing this in an already digital system is low, and the gains substantial, practical OFDM/DMT systems are all actually COFDM. Although highly complex, COFDM has high performance under even very challenging channel conditions. By combining the OFDM technique with error-correcting codes, adaptive equalization and reconfigurable modulation, COFDM has the following properties: resistant against link dispersion resistant against slowly changing phase distortion and fading resistant against frequency response nulls and constant frequency interference resistant against burst noise COFDM also generally has a nearly 'white' spectrum, giving it benign electromagnetic interference properties with respect to other signals. Some COFDM systems use some of the sub carriers to carry pilot signals, which are used for frequency synchronizations, as frequency shifts during the transmission using the main modulation/demodulation process transform into bit errors in the decoded data. In wide area broadcasting, receivers can benefit from receiving signals from several spatially dispersed transmitters simultaneously, since transmitters will only destructively interfere with each other on a limited number of subcarriers, whereas in general they will actually reinforce coverage over a wide area. This is very beneficial in many countries, as it permits the operation of national single frequency networks, and avoids the replication of program content on different carrier frequencies which is necessary with FM or other forms of radio broadcasting. Also, because effectively the bit rate is slowed down on each sub-carrier, the effects of "ghosting" are much reduced. Such single frequency networks utilize the available spectrum more effectively than existing analog radio networks. Coherent Communications
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