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Browsing by Author "Radie Al-Khayyat, Ahmed Hussein"

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    Master Thesis
    Relay selection and distributed code design for cooperative communication systems
    (2016) Radie Al-Khayyat, Ahmed Hussein
    Despite the advantage of multiple-input multiple-output (MIMO) systems, nevertheless mobility, size, or other constraints of mobile devices prevent the use of such systems. Also the complexity (multiple radio-frequency (RF) front ends at both the transmitter and the receiver), channel estimation in centralized MIMO systems degrade the performance. In such, the alternative would be to option to cooperative communication systems via multiple intermediate relay nodes. Once intermediate nodes work cooperatively, they form a virtual MIMO system. The destination receives multiple copies of the same data signals from the source and one or more relay nodes, and combines these to generate diversity. In cooperative communication systems, the performance of the system degrades significantly. This performance degradation is attributed to assume the relay nodes at favorable location, which cannot be justified in random topology networks. In this thesis we propose a relay nodes selection, which guarantees several goals: higher throughput, less delay, a full diversity order, better BER, and higher spectral efficiency. In this thesis, we propose a multi-relay selection protocol for decentralized wireless networks. The proposed relays selection protocol aim to address some issues: selecting relay nodes within the coverage area of the source and destination to ensure that the relays are positioned one hop away from the destination; ensuring the best node (best relays with less distance and attenuation from the destination) access the channel first; and ensuring that the proposed relays selection is collision free. Furthermore, we consider minimizing spectral efficiency loss and BER. In detail, we propose protocol which reduces the spectral efficiency loss in cooperative communication systems. The destination indicates success or failure by broadcasting a single bit of feedback to the source and best relay node. If the source-destination link quality is sufficiently high compared to source-relay and relay-destination links quality, the feedback indicates success of the direct transmission, and the relay does nothing. Otherwise, the feedback requests send by destination that the best relay node to retransmit what it received from the source. In such, relay node does not always retransmit, which increase the spectral efficiency in cooperative communication systems. Best relay node is determined with maximum link quality from source-relay and relay-destination links quality. We finish this thesis by investigating the optimal power allocation and code rate allocation. The optimal power allocation is done considering the cases such that either the received data at relay includes errors or it does not contain any error. On the other hand, the optimal code rate allocation is done considering the case received data received data at relay includes errors. We show the system performance is better compared to equal power and code rate allocation.