Abstract
Frequency offsets or frequency spreads distort theorthogonality between sub-carriers, which results in inter-carrierinterference (ICI), in regular OFDM communication systems. Inorder to combat the impact of ICI on OFDM systems, an ICImitigation technique by jointing symbol shift cancellation (SSC)and adjacent sub-channel interference filter (ASIF) is proposedin this paper. At first, the symbol shift cancellation (SSC) methodis used to cancel the impact of ICI on the far sub-carriers, andthen the adjacent sub-channel interference filter (ASIF) methodis used to cancel the impact of ICI on the adjacent sub-carriersinterference. By analyzing the distribution of the adjacent intercarrierinterference, a pilot-symbol scheme is proposed toimprove the accuracy of channel estimation and simplify theadjacent interference filter method. The proposed algorithm canachieve trade-off between the bandwidth efficiency and thecomplexity of ICI cancellation method. Simulation results showthat the technique proposed in this paper can effectively improveBER (Bit Error Rate) performance of the OFDM system.Keywords: OFDM; ICI; BER; ASIF; SSC
I. INTRODUCTION
Orthogonal frequency division multiplexing (OFDM)technology has already been rapidly developed. OFDM hasalso been accepted for the next generation wirelesscommunication systems, such as B3G, Wimax and so on.Although multi-path propagation and frequency-selectivefading exist in radio channels, OFDM is very robust to radiochannel impairments. The receiver design is also simplifieddue to less complex equalization, and OFDM systems havehigh spectral efficiency due to overlapping sub-carrier spectra.However, one of the major disadvantages of such a multicarriermodulated system is the sensitivity of its performance tofrequency or phase offsets. Frequency offsets can result from aDoppler shift due to a mobile environment, as well as from acarrier frequency synchronization error. Such frequency offsetsresult in a loss of the carriers’ orthogonality, and hence intercarrierinterference (ICI) occur. Currently, several approachesfor reducing ICI have been developed including: ICI selfcancellationscheme [1-2], frequency-domain equalizationscheme [3], time-domain windowing scheme [4], frequencyoffset estimation and compensation technique [5], and Dopplerdiversity [6]. Although the ICI self-cancellation scheme is avery simple way for suppressing ICI in OFDM systems, itresults in seriously loss of bandwidth. However, the methods ofother schemes are complex [7].This paper still focuses on the ICI cancellation scheme andits effect on OFDM communication systems, and presents anICI cancellation scheme. Its main idea is that the symbol shiftcancellation (SSC) method is used to cancel the impact of ICIon the far sub-carriers, and then the adjacent sub-channelinterference filter (ASIF) method is used to cancel the impactof ICI on the adjacent sub-carriers interference. By processingso, the effect of ICI on the OFDM system is reduced aspossible, and its bandwidth efficiency has rare loss.In this paper, a new ICI cancellation scheme and itsarchitecture are presented in Section II. The symbol shiftcancellation (SSC) method and the adjacent sub-channelinterference filter (SSC-ASIF) scheme is respectively discussedin Section III and IV, and then BER performance of the OFDMsystem with the ICI cancellation scheme proposed in this paperis simulated and analyzed in Section V.


Download full report
http://ieeexplore.ieeeiel5/5300798/53007...er=5302708