Over the last decades, wireless communications has emerged and played an important role in the daily activities of human beings. This is due to the fact that wireless connectivity is making exciting inroad to everywhere, without fixed transmitter/receiver or any physical connection cable. In a wireless channel, the signal from a transmitter interferes with its own copies due to different channel paths leading to Inter Symbol Interference(ISI). So, multipath propagation usually introduces new problems in symbol detection. OFDM, as a multichannel modulation, has the ability to overcome this phenomena by dividing the high-rate data stream into N lower-rate substreams. The substreams are transmitted simultaneously over orthogonal long duration subcarriers causing much less severe ISI, because each subcarrier’s bandwidth is much less than the channel coherence bandwidth. However, OFDM is very vulnerable to channel time variations, especially within one OFDM symbol. In such cases, the orthogonality between subcarriers breaks down easily resulting into Inter-Carrier Interference (ICI). This phenomenon may degrade the performance considerably. On the other hand, when transmitting high-rate data at a high-frequency band, OFDM systems would experience time- and frequency-selective or doubly-selective phenomena in which the duration of an OFDM block is comparable to the coherence time as well as multipath spread of the channel. Time-varying impairments is modeled by Doppler shift. In order to overcome this problem, a number of conventional schemes have been proposed to suppress or subtract out the ICI. Examples are equalization, ICI self-cancellation, coding. Equalization is chosen in many practical cases due to high performance, reliability and implementation only in the receiver. It, substantially, relies on matrix inversion and for fast varying channels and large number of subcarriers requires high computations. To reduce the complexity, applying an iterative ICI equalization, one can exploit channel matrix properties to separate Key Words: Doubly-selective channel, Inter Carrier Interference, OFDM, Kalman filter, channel estimation, equalization
