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Identifier

000375301

Title

Network-Level Cooperation: Throughput, Stability, and Energy Issues

Alternative Title

Συνεργασία σε επίπεδο δικτύου :Θέματα διαμεταγωγής, ευστάθειας και ενέργειας

Author

Παππάς, Νικόλαος Δημήτριος

Thesis advisor

Τραγανίτης, Απόστολος

Abstract

Cooperative communications help overcome fading and attenuation in wireless networks. Its main target is to increase the communication rates across the network and the reliability of time-varying links. It is known that wireless communications can benefit from the cooperation of nodes that overhear the transmissions. Most cooperative techniques studied so far have been on physical layer cooperation. The Network-Level cooperation is plain relaying without any physical layer considerations. There is evidence that network-level cooperation can achieve similar gains with physical-layer cooperation, and at the same time is simpler to implement. In the first part of the thesis, we study the impact of a relay node to a network with a finite number of users-sources and one destination node. We assume that the users have saturated queues and the relay node does not have packets of its own; we have random access of the medium and the time is slotted. The relay node stores a source packet that it receives successfully in its queue when the transmission to the destination node has failed. The relay and the destination nodes have multi-packet reception capabilities. We obtain analytical equations for the characteristics of the relays queue such as average queue length, stability conditions etc. We also study the throughput per user and the aggregate throughput for the network. We study both the cases of a half and a full-duplex relay. For the full-duplex relay, we also study the impact of self interference on the stability, the throughput per user-source as well as the aggregate throughput. Furthermore, we evaluate the benefits of using one user of a two-user random access system to relay traffic of the other user. We introduce the notion of Network-Level Partial Relay Cooperation, and we prove that under certain conditions the optimum cooperation strategy for the relay is to partially cooperate. The second part of the thesis is devoted to energy harvesting wireless networks. We study the impact of energy constraints on a network with a source-user, a relay and a destination. This part studies the impact of energy harvesting on network-level cooperation. Specifically, we provide an exact characterization of the stability region. We also consider the concept of cognitive radio communication (with nodes with different energy constraints) in sharing a common wireless channel. Specifically, we give high-priority to the energy-constrained source-destination pair, i.e., primary pair, and low-priority to the pair which is free from such constraint, i.e., secondary pair. In contrast to the traditional notion of cognitive radio, in which the secondary transmitter is required to relinquish the channel as soon as the primary is detected, the secondary transmitter not only utilizes the idle slots of the primary pair but also transmits along with the primary transmitter with a given probability. We choose that probability to maximize the secondary pairs throughput. We obtain the two-dimensional maximum stable throughput region. The region is obtained for both cases in which the capacity of the battery at the primary node is limited or unlimited. Finally, we investigate the performance that can be achieved by exploiting path diversity through multipath forwarding together with redundancy through linear network coding, in wireless mesh networks with directional links. We capture the tradeoff between packet delay and throughput achieved by combining multipath forwarding and network coding, and compare this tradeoff with that of simple multipath routing where different flows follow different paths, the transmission of multiple copies of packets over multiple paths, and single path routing.

Language

English

Subject

Cognitive Networks

Energy Harvesting Communications

Network Coding

Network-Level Cooperation

Stability Region

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