Design and analysis of MAC protocols for wireless multi-hop sensor and terahertz networks
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The contributions of this thesis include designing and analyzing novel medium access control (MAC) protocols for two types of wireless networks: (1) duty-cycling cooperative multi-hop wireless sensor networks (MHWSNs), and (2) single-hop Terahertz networks (TeraNets). For MHWSNs, the specific contributions are two new scalable MAC protocols for alleviating the “energy-hole” problem with cooperative transmission (CT). The energy-hole is known to limit the life of battery-powered MHWSNs. The hole occurs when nodes near the Sink exhaust their energy first because their load is heavier: they must transmit packets they originate and relay packets from and to other nodes farther from the Sink. Effective techniques for extending lifetime in MHWSNs include duty cycling (DC) and, more recently introduced, cooperative transmission (CT) range extension. However, a scalable MAC protocol has not been presented that combines both. From the MAC perspective, conducting CT in an asynchronous duty-cycling network is extremely challenging. On the one hand, the source, the cooperators and the destination need to reach consensus about a wake-up period, during which CT can be performed. This dissertation develops novel MAC protocols that solve the challenge and enable CT in an asynchronous duty-cycling network. On the other hand, the question arises, “Does the energy cost of the MAC cancel out the lifetime benefits of CT range extension?” We show that CT still gives as much as 200% increase in lifetime, in spite of the MAC overhead. The second contribution of this dissertation is a comprehensive analytical framework for MHWSNs. The network performance of a MHWSN is a complex function of the traffic volume, routing protocol, MAC technique, and sensors' harvested energy if sensors are energy-harvesting (EH) enabled. The optimum performance provides a benchmark for heuristic routing and MAC protocols. However, there does not exist such an optimization framework that is able to capture all of these protocol aspects. The problems and performance metrics of non-EH networks and EH networks are different. Because the non-EH nodes depend on a battery, a suitable performance metric is the lifetime, defined as the number of packets delivered upon the first or a portion of nodes' death. Thus, the lifetime is governed by the absorbing states in a controlled dynamic system with finite decision horizon. On the other hand, the lifetime of an EH network is theoretically infinite unless the sensors are broken or destroyed. Therefore, an infinite horizon problem is formulated towards the performance of EH networks. The proposed model departs significantly from past analyses for single-hop networks that do not capture routing and past analyses for multi-hop networks that miss MAC aspects. To our knowledge, this is the first work to model the optimal performance of MHWSNs, by jointly considering MAC layer link admission, routing queuing, energy evolution, and cooperative transmission. The third contribution of this dissertation is a novel MAC protocol for Terahertz (THz) Band wireless networks, which captures the peculiarities of the THz channel and takes advantage of large antenna arrays with fast beam steering capabilities. Communication in THz Band (0.1-10THz) is envisioned as a key wireless technology in the next decade to provide Terabits-per-second links, however, the enabling technology is still in its infancy. Existing MAC protocols designed for classical wireless networks that provide Megabits-per-second to Gigabits-per-second do not scale to THz networks, because they do not capture the peculiarities of the THz Band, e.g., the very high molecular absorption loss or the very high reflection loss at THz Band frequencies. In addition, to overcome the high path loss and extend communication range, the proposed MAC design takes advantage of fast beam steering capabilities provided by the large antenna arrays, in particular, beam-switching at the pulse level.