Maximum bandwidth of orthogonal frequency division multiplex (OFDM) over multipath fading channel

Orthogonal frequency division multiplex (OFDM) is known as an effective method for high-rate transmission over frequency selective fading channels. However, time variations of the channel within an OFDM symbol leads to a loss of orthogonality between subcarriers, resulting in interchannel interference (ICI). This paper presents the effect of time and frequency selectivity on the performance of OFDM when the total bandwidth increases while the subcarrier bandwidth remains constant. It shows that a maximum bandwidth exists with the use of a frequency domain equalizer assuming the channel path gains at the beginning of each OFDM symbol are known, and further increasing the bandwidth beyond this point will not ensure the guaranteed performance. The performance variation as the total bandwidth increases when coding is used is also discussed.