Energy and Security Aspects of Wireless Networks: Performance and Tradeoffs
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Energy and security are becoming increasingly important in the design of future wireless communication systems. This thesis focuses on these two main aspects of wireless networks and studies their tradeoffs with other performance metrics such as throughput and delay. The first part of the thesis deals with the energy aspect of wireless networks in which we present several novel joint-physical network layer techniques and either evaluate their energy efficiency or study the energy/delay/throughput tradeoffs. First, we study the energy/delay tradeoffs for the problem of reliable packet transmission over a wireless time-varying fading link and also investigate the effect of having Channel State Information on the resulting tradeoff . Then, we extend the model to a single-hop multicast time varying wireless network. We address energy/delay/throughput tradeoffs by considering the problem of streaming a real time file with a fixed delay and energy constraints where the objective is to maximize the number of packets received by the destinations. Again, the effect of having Channel State Information is studied. Also, the effect of using Random Network Coding as a transmission scheme is studied and compared to traditional transmission schemes such as simple ARQ. Next, we consider the effect of cooperation on the energy efficiency of wireless transmissions in which we propose several joint physical-network layer cooperation techniques. Also, the effect of Random Network Coding is investigated in the context of cooperation in which Random Network Coding based cooperation techniques are investigated and compared to cooperation techniques that rely on simple ARQ solely or combined with superposition Alamouti space-time codes. We then consider the particular case of cellular systems in which we design rate allocation technique that minimizes the consumption energy in a Macro cell. This technique takes into account sleep mode configuration of current base stations. In the second part of the thesis, we focus on security and in particular on privacy. We also study the tradeoff between securing wireless transmissions and the energy/delay overhead due to security by considering the problem of information exchange among adjacent wireless node in the presence of an eavesdropper. The nodes are required to exchange their information while keeping it secret from the eavesdropper. The nodes can choose to transmit either through public channel or though more costly private channels. We express the cost of using the private channels in terms of the extra energy or delay required to transmit through the private channel. We then minimize the security cost subject to a target security level. Also this part presents a deterministic Network Coding based transmission scheme and investigates its effect on the achieved performance. Last, we introduce the problem of minimum energy scheduling of a group of base stations and compare this problem to the standard minimum length scheduling problem. We also discuss the complications and the challenges associated with solving the minimum energy scheduling problem.