Coded Orthogonal Frequency Division Multiplex (COFDM) has been selected as the standard for terrestrial transmission of DigitalVideoBroadcasting( DVB) and DRM radio in Europe. In America, the ATSC has chosen residual sideband modulation for digital TV.
COFDM has the advantage that propagation delay differences in the transmission of digital video broadcast, which are caused by reflections from buildings or mountains and which are unpleasantly noticeable as ghost images, can be completely compensated.
The insensitivity of DBV-T to propagation time differences is achieved in COFDM by multiple, simultaneous orthogonal broadcasting of the same signal. In this process, the signal is simultaneously modulated onto many carrier frequencies. This can be up to 6,875 individual carriers. The carrier spacing can be reduced to 1 kHz. Due to the orthogonality, in which a maximum of the spectral distribution of a transmitter always coincides with the minimum of the spectral distribution of the neighboring transmitter, there is no interference of neighboring carrier frequencies. This multiple modulation is ideal for terrestrially broadcast digital TV and for mobile TV reception.