We illustrate the basic ideas of OFDM transmission and reception in a time invariant channel . Assume that has nonzero support within the interval . The channel frequency response is expressed as
Denote as the transmitted passband signal. The received passband signal after channel transmission is
where is the additive noise.
Given the dispersive nature of the channel, intersymbol interference appears for serially transmitted data streams. Compared to the canonical single-carrier serial transmission scheme, OFDM is a block transmission scheme, which partitions information symbols into blocks, and a guard interval is inserted between consecutive blocks before transmission. There are two different types of guard intervals: one is padding zeros at the end of ...