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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/2763

Title: TIME DOMAIN EQUALIZATION FOR OFDM SYSTEMS IN TIME VARYING CHANNELS
Authors: AWOKE, ATENA
Advisors: Dr.-Ing. Hailu Ayele
Keywords: OFDM SYSTEMS
CHANNELS
Copyright: Jul-2011
Date Added: 7-May-2012
Publisher: AAU
Abstract: Orthogonal Frequency Division Multiplexing (OFDM) is an emerging multi-carrier modulation scheme, which has been adopted for several wireless standards such as IEEE 802.11a and HiperLAN2. OFDM as a transmission technique has been known to have a lot of strengths compared to any other transmission technique due to its high spectral efficiency, robustness to the channel fading, immunity to impulse interference and ability to handle very strong echoes. The efficacy of OFDM implementation in many areas such as DAB (Digital audio Broadcasting), DVB (Digital Video Broadcasting) and Wireless LAN has gained its popularity. A well-known problem of OFDM is its sensitivity to frequency offset between the transmitted and received carrier frequencies. This frequency offset introduces inter-carrier interference (ICI) in the OFDM symbol. This thesis investigates time domain equalization technique by using well designed windows for combating the effects of ICI entitled equalization with time domain windowing. This method is compared with other methods like existing frequency domain correlative coding and self cancellation methods in terms of bit error rate performance, carrier to interference ratio and bandwidth efficiency. Effects of different orders of windowing on the carrier to interference power ratio are investigated for various normalized frequency offset values. Through simulations, it is shown that the Time domain windowing technique is effective in mitigating the effects of ICI. It shows a better performance in terms of BER and CIR compared to the existing frequency domain correlative coding and self cancellation techniques. The designed window of leading coefficient and correlation order value of 1 gives an optimum design based on maximizing CIR. Over10 dB performance gain has been obtained with employment of windowing compared to the standard OFDM system without any equalization techniques employed at the normalized frequency offset of ɛ = 0.15 and BER of 10-3. The time domain windowing scheme shows better tolerance to frequency offset by considerable reduction of the sensitivity to frequency errors.
URI: http://hdl.handle.net/123456789/2763
Appears in:Thesis - Electrical Engineering

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