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Resource Allocation in OFDM Based Wireless Relay Networks ...

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1.5 Contribution and Organization of the Thesis<br />

Figure 1.4: Organization of the thesis.<br />

two hops are jo<strong>in</strong>tly optimized via convex optimization techniques to maximize the<br />

end-to-end system throughput. Secondly, a Time Division Multiple Access (TDMA)<br />

based orthogonal transmission is considered. The power load<strong>in</strong>g at the source/relay<br />

nodes and the sub-carrier match<strong>in</strong>g over the two hops <strong>in</strong> each time slot are optimized<br />

<strong>in</strong> the developed algorithm. F<strong>in</strong>ally, simulation results are provided to corroborate<br />

the proposed studies.<br />

The chapter 5 considers the multi-hop transmission scheme where more than one<br />

<strong>in</strong>termediate relay<strong>in</strong>g nodes are deployed for reliable transmission <strong>in</strong> wireless sensor<br />

networks. The relay nodes <strong>in</strong> the sensor networks are consist of small batteries such<br />

that the replacement or recharg<strong>in</strong>g of batteries is not possible. Thus, we develop<br />

lifetime maximization algorithms where the optimization problem is formulated<br />

consider<strong>in</strong>g both the <strong>in</strong>itial energy and the power constra<strong>in</strong>t at each node. To reduce<br />

the energy utilization for decod<strong>in</strong>g and encod<strong>in</strong>g <strong>in</strong> DF relays and to m<strong>in</strong>imize the<br />

noise enhancement with AF relay transmission, we consider a mixed AF-DF relay<br />

transmission. Convergence and the performance of the proposed iterative algorithm<br />

is shown by simulations.<br />

In chapter 6, we <strong>in</strong>vestigate the resource allocation problem <strong>in</strong> cognitive<br />

13

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