A Low-Complexity Turbo Equalizer for OFDM Communication Systems

Alexander N. LOZHKIN  Mitsuhiro AZUMA  Tomohiko TANIGUCHI  

IEICE TRANSACTIONS on Communications   Vol.E89-B   No.1   pp.100-117
Publication Date: 2006/01/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e89-b.1.100
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
OFDM,  DMT,  multicarrier system,  interchannel interference,  turbo-equalizer,  frequency offset,  

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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.