OFDM and COFDM
In wideband digital broadcasting, self-interference cancellation is facilitated by the OFDM or COFDM modulation method. OFDM uses a large number of slow low-bandwidth modulators instead of one fast wide-band modulator. Each modulator has its own frequency sub-channel and sub-carrier frequency. Since each modulator is very slow, we can afford to insert a guard interval between the symbols, and thus eliminate the ISI. Although the fading is frequency-selective over the whole frequency channel, it can be considered as flat within the narrowband sub-channel. Thus, advanced equalization filters can be avoided. A forward error correction code (FEC) can counteract that a certain portion of the sub-carriers are exposed to too much fading to be correctly demodulated.
OFDM is utilized in the terrestrial digital TV broadcasting systems DVB-T (used in Europe and many other areas) and ISDB-T (used in Japan and Brazil). OFDM is also widely used in digital radio systems, including DAB, HD Radio, and T-DMB. Therefore these systems are well-suited to SFN operation.
Read more about this topic: Single-frequency Network