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چكيده انگليسي :

158 Superposition network coding in wireless cooperative communication Ali Fazeli a fazeli@ec iut ac ir Date of Submission 2012 03 13 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Dr Mohammad Javad Omidi omidi@cc iut ac irAbstract Communication over a wireless channel is subject to large and small scale propagation effects includingpath loss shadow fading and small scale multipath fading These effects are the most important sources ofperformance degradation in communication systems Various diversity techniques such as time frequency and spatial diversity are proposed to mitigate the adverse effects of fading Among all diversity techniquesmore attention has been given to spatial diversity Cooperative diversity is an innovative approach toimprove reliability of communication by exploiting spatial diversity However this technology ischallenging in practice In some multi relay cooperative diversity protocols that are based on simultaneoustransmission time and frequency synchronization of relay nodes are very important However realizationof such requirement is difficult The imperfect synchronization in destination is the main reason ofperformance degradation for simultaneous transmission based protocols such as distributed space timecoding DSTC Although separation in transmission time of terminals in traditional time division multipleaccess TDMA method can solve the synchronization problems but it leads to lower spectral efficiency Inaddition to these problems asymmetric nature of wireless networks is another issue that must be consideredin cooperative diversity protocols In practical wireless networks different source nodes are distributed atdifferent positions Therefore various terminals experience different channel conditions and thus somenodes are disadvantageous in their transmission in comparison with others Communication in asymmetricnetworks applying non cooperative protocols results in high aggregate transmit power and uneven powerdistribution among various terminals These issues cause performance degradation of communication Cooperative communication is an approach to improve the performance of communication in asymmetricwireless networks In this thesis after reviewing some of the most important cooperative diversity schemes a cooperative strategy is proposed for asymmetric wireless networks that improves overall wirelesscommunication performance in terms of reducing total power consumption improving error performanceand increasing the network lifetime in comparison with non cooperative protocols on one hand and solvessome problems of current cooperative diversity schemes such as synchronization and low spectralefficiency on the other hand In our proposed scheme we use a combination of superposition coding andnetwork coding to achieve incremental diversity in asymmetric wireless communication networks hencethe name superposition network coding This technique solves the synchronization problems by singletransmission of terminals in TDMA scheme Also applying superposition coding improves spectralefficiency in comparison with traditional TDMA cooperative communication strategies In this thesis it istried to implement the receiver structure as simple as possible In addition the error performance ofsuperposition network coding is analyzed by appropriate approximations and the analytical results arecompared with simulation results Excellent agreement between the derived analytical results andsimulation results demonstrates the accuracy of the proposed scheme in improving system performance Keywords Cooperative diversity relay terminal Symbol Error Rate Selection Combining SER SC Interference Ignorant Detector IID Network coding Superposition coding

فاضلي، علي

كدگذاري انطباقي شبكه در مخابرات همكارانه ي بي سيم

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