ICI Reduction Methods in OFDM Systems

The principles of multicarrier modulation have been in existence for several decades. However, in recent years these techniques have quickly moved out of textbooks and into practice in modern communications systems in the form of orthogonal frequency division multiplexing (OFDM). OFDM is a special form of multicarrier modulation technique which is used to generate waveforms that are mutually orthogonal and then distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the "orthogonality" in this technique which prevents the demodulators from seeing frequencies other than their own. In an OFDM scheme, a large number of orthogonal, overlapping, narrow band subcarriers are transmitted in parallel. These carriers divide the available transmission bandwidth. The separation of the subcarriers is such that there is a very compact spectral utilization. With OFDM, it is possible to have overlapping sub channels in the frequency domain (Figure 1), thus increasing the transmission rate.