With the growing demand for mobile communications, multicarrier (MC) schemes are receiving an increasing amount of attention, primarily because they handle frequency selective channels better than ordinary single-carrier schemes. However, despite offering several advantages, MC systems have certain weak points. One is their high sensitivity to interchannel interference (ICI). The influence of Doppler shift and ICI are the focus of this paper. Newly proposed B3G/4G systems are developed for data transmission rates higher than those of the IEEE 801.11. It is then necessary that the bandwidth of the subcarrier be small. Moreover, for a higher carrier frequency and mobile speed, the influence of the Doppler shift will be large; therefore, the influence of ICI becomes severer. Using a Markov chain approach, we synthesized a turbo equalizer (TE) that minimizes ICI when interference affects the arbitrary number M of adjacent subchannels. This approach shows the complexity of the proposed algorithm exhibits linear growth with respect to M and independence with respect to the total number of subchannels in the multicarrier system. The proposed ICI cancellation scheme can also be effective in the case of multiple Doppler frequency offsets. This makes the proposed approach attractive for practical implementations.

With the growing demand for mobile communications, multicarrier (MC) schemes are receiving an increasing amount of attention, primarily because they handle frequency selective channels better than ordinary single-carrier schemes. However, despite offering several advantages, MC systems have certain weak points. One is a high sensitivity to interchannel interference (ICI). Using a Markov chain approach, we synthesized an optimal receiver for a situation where interference affects three adjacent subchannels. Simulation results showed that the proposed 'turbo scheme' provided better BER performance than a conventional receiver, especially at higher signal-to-noise ratios. The implementation of the turbo algorithm is independent of the transmitted signal, providing complete OFDM reception compatibility.

In this paper, a new approach is proposed to improve the channel estimation accuracy with channel tracking capability for adaptive multicarrier equalization systems under time-variant multipath fading channel. The improvement is carried out based on the assumption that the channel is static over a transmitted block period, and slowly linearly changing over several block periods. By applying IFFT to the concatenated channel transfer function derived from different blocks, the noise-averaging improvement is achieved, and a better estimation of the channel coefficients with some delay can be obtained. A multi-step channel predictor and a smoothing filter is utilized to compensate for the delay and make the system more robust in terms of channel tracking performance. Adaptive time domain equalization is jointly performed with this approach to avoid the channel invertibility problem found in the frequency domain approach. A short period of training sequences is utilized resulting in more efficient use of available communication capacity. The effectiveness of the proposed approach is evaluated through simulation for multicarrier systems in time-variant multipath fading channels. Results show improvement over previous channel estimation schemes.