Network coding: performance analysis and robust design in multi-hop wireless mesh networks

Network coding is an innovative idea to boost the capacity of wireless networks. However, there are not enough analytical studies on throughput and end-to-end delay of network coding in multi-hop wireless mesh network that incorporates the specifications of IEEE 802.11 Distributed Coordination Function. In this dissertation, we utilize queuing theory to propose an analytical framework for bidirectional unicast flows in multi-hop wireless mesh networks. We study the throughput and end-to-end delay of inter-flow network coding under the IEEE 802.11 standard with CSMA/CA random access and exponential back-o↵ time considering clock freezing and virtual carrier sensing, and formulate several parameters such as the probability of successful transmission in terms of bit error rate and collision probability, waiting time of packets at nodes, and retransmission mechanism. Our model uses a multi-class queuing network with stable queues, where coded packets have a non-preemptive higher priority over native packets, and forwarding of native packets is not delayed if no coding opportunities are available. The accuracy of our analytical model is verified using computer simulations. Furthermore, while inter-flow network coding is proposed to help wireless networks approach the maximum capacity, the majority of research conducted in this area is yet to fully utilize the broadcast nature of wireless networks, and to perform e↵ectively under poor channel quality. This vulnerability is mostly caused by assuming fixed route between the source and destination that every packet should travel through. This assumption not only limits coding opportunities, but can also cause bu↵er overflow at some specific intermediate nodes. Although some studies considered scattering of the flows dynamically in the network, they still face some limitations. This dissertation explains pros and cons of some prominent research in network coding and proposes a Flexible and Opportunistic Network Coding scheme (FlexONC) as a solution to such issues. Moreover, this research discovers that the conditions used in previous studies to combine packets of di↵erent flows are overly optimistic and would a↵ect the network performance adversarially. Therefore, we provide a more accurate set of rules for packet encoding. The experimental results show that FlexONC outperforms previous methods especially in networks with high bit error rates, by better utilizing redundant packets permeating the network, and benefiting from precise coding conditions

A Low-Energy Fast Cyber Foraging Mechanism for Mobile Devices

The ever increasing demands for using resource-constrained mobile devices for running more resource intensive applications nowadays has initiated the development of cyber foraging solutions that offload parts or whole computational intensive tasks to more powerful surrogate stationary computers and run them on behalf of mobile devices as required. The choice of proper mix of mobile devices and surrogates has remained an unresolved challenge though. In this paper, we propose a new decision-making mechanism for cyber foraging systems to select the best locations to run an application, based on context metrics such as the specifications of surrogates, the specifications of mobile devices, application specification, and communication network specification. Experimental results show faster response time and lower energy consumption of benched applications compared to when applications run wholly on mobile devices and when applications are offloaded to surrogates blindly for execution.Comment: 12 pages, 7 figures, International Journal of Wireless & Mobile Networks (IJWMN