OFDM için frekans ve zaman seçici kanallarda düşük karmaşıklı eşleme

In current standards Orthogonal Frequency Division Multiplex -OFDM- is widelyused for its high resistance to multi-path environments and high spectral efficiency. However since the transmission duration is longer, it is affected fromtime variations of the channel more than single carrier systems. Orthogonality ofsub-carriers are lost within an OFDM symbol and intercarrier interference(ICI)occurs as a result of time variation of the channel. Channel estimation and equalizationbecome problematic, because the classical structures like MMSE requirevery complex operations. This thesis studies the channel equalization problem,as separate from the channel estimation problem. The thesis assumes that thechannel coeffcients are perfectly known and focuses on the estimation of datatransmitted on each OFDM carrier. First, a survey of existing algorithms onchannel equalization is given and simulations are provided to compare them interms of complexity and performance under an OFDM system scenario that isconsistent with the present WiMAX system parameters and operating conditions.As a novel contribution, the thesis proposes two new equalization methods byamending existing algorithms and shows that these modified algorithms improve the state-of-the-art in channel equalization in terms of complexity and performanceunder certain high-mobility scenarios. Ultimately it is shown that theintercarrier interference cancellation problem remains a major impediment tothe implementation of OFDM in high-mobility environments.