Channel Equalization Techniques for Amplify-and-Forward Cooperative Diversity Relaying Scheme

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Addis Ababa University


Spatial diversity is a technique used in wireless communication to combat the effect of fading. This diversity scheme generally requires more than one antenna at transmitting and/or receiving node(s). However, many wireless devices are limited to one antenna because of size or hardware complexity. Recently, a new class of method called cooperative communication has been proposed. This method enables single antenna mobiles in a multi-user environment to share their antennas and generate a virtual multiple-antenna transmitter that allows them to achieve transmit diversity. Broadband wireless systems are emerging in order to provide high data rate services. However, the overall system performance will be degraded because of the frequency selectivity nature of the wireless channel. Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation technique which can mitigate inter-symbol interference (ISI) caused by the frequency selective fading. OFDM possesses the advantages of frequency parallel transmission, high speed communication and efficient spectrum usage. By introducing OFDM transmission into the cooperative communication technique, the gains from both sides are combined. However, one prominent problem of OFDM is its sensitivity against carrier frequency offset which results from either Doppler shift or synchronization loss at the transmitter and receiver oscillators. This carrier offset causes inter-carrier interference (ICI). Hence, efficient ICI reduction techniques are necessary to improve system performance. In this thesis, we focus on two methods of ICI reduction techniques; namely, time- and frequency-domain equalizations. In the frequency-domain equalization a correlative polynomial is used in the frequency domain to suppress the ICI. In time-domain equalization technique a window function is employed. MATLAB simulation of the two techniques shows that, the time-domain equalization scheme achieves better performance in ICI suppression compared to the correlative coding technique. In other words, time domain equalization technique offers better carrier-to-interference ratio (CIR) as compared to the correlative coding method. Key words: Cooperative diversity, OFDM, ISI, ICI, CIR.



Cooperative diversity, OFDM, ISI, , ICI, CIR