Time Domain Equalization For Ofdm Systems In Time Varying Channels

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Orthogonal Frequency Division Multiplexing (OFDM) is an emerging multi-carrierrnmodulation scheme, which has been adopted for several wireless standards such as IEEErn802.11a and HiperLAN2. OFDM as a transmission technique has been known to have a lot ofrnstrengths compared to any other transmission technique due to its high spectral efficiency,rnrobustness to the channel fading, immunity to impulse interference and ability to handle veryrnstrong echoes. The efficacy of OFDM implementation in many areas such as DAB (Digitalrnaudio Broadcasting), DVB (Digital Video Broadcasting) and Wireless LAN has gained itsrnpopularity.rnA well-known problem of OFDM is its sensitivity to frequency offset between therntransmitted and received carrier frequencies. This frequency offset introduces inter-carrierrninterference (ICI) in the OFDM symbol. This thesis investigates time domain equalizationrntechnique by using well designed windows for combating the effects of ICI entitledrnequalization with time domain windowing. This method is compared with other methods likernexisting frequency domain correlative coding and self cancellation methods in terms of bitrnerror rate performance, carrier to interference ratio and bandwidth efficiency. Effects ofrndifferent orders of windowing on the carrier to interference power ratio are investigated forrnvarious normalized frequency offset values. Through simulations, it is shown that the Timerndomain windowing technique is effective in mitigating the effects of ICI. It shows a betterrnperformance in terms of BER and CIR compared to the existing frequency domain correlativerncoding and self cancellation techniques. The designed window of leading coefficient andrncorrelation order value of 1 gives an optimum design based on maximizing CIR.rnOver10 dB performance gain has been obtained with employment of windowing compared tornthe standard OFDM system without any equalization techniques employed at the normalizedrnfrequency offset of É› = 0.15 and BER of 10-3. The time domain windowing scheme showsrnbetter tolerance to frequency offset by considerable reduction of the sensitivity to frequencyrnerror

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Time Domain Equalization For Ofdm Systems In Time Varying Channels

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