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Advances in nanotechnology are paving the way for wireless nanoscale sensor networks (WNSNs), promising radically new applications in medical, biological, and chemical fields. However, the small scale poses formidable challenges for communication. First, small nanomaterial-based antennas communicate in the terahertz band, which coincides with the natural resonance frequencies of many types of molecules causing severe molecular absorption and noise. The problem is particularly complicated if the molecular composition of the channel changes over time, causing time-varying absorption and noise. Second, as it is not practical to fit large batteries or replace batteries in a small device, these devices are expected to power themselves by harvesting ambient energy from the environment. However, the amount of energy that can be harvested is directly proportional to the size of the harvester. A nanodevice therefore can generate only a tiny fraction of its total power consumption, which requires us to rethink the design of communication protocols for self-powering WNSNs. In order to address aforementioned challenges, this thesis makes three fundamental contributions. First, it proposes dynamic frequency and power selection as a means to overcome the first problem, i.e, changing molecular composition problem in a time-varying terahertz channel. The dynamic frequency/power selection problem is modelled as a Markov Decision Process to derive the optimal solutions, while several practical heuristics are proposed that achieve close to optimal solutions. Second, to address the severe power shortage problem in a self-powering nanodevice, this thesis proposes a mechanism to exploit the information contained in the energy harvesting data to detect the energy-dissipating events occurring in the environment. This form of event monitoring makes dual use of the energy-harvesting unit in the nanodevice, i.e., it is used to generate power as well as monitor the environment, thus saving significant energy, which otherwise would have been used to power the onboard sensors. Finally, novel WNSN applications are designed and analysed to monitor and control chemical reactors at the molecular level with the ultimate goal of increasing the selectivity of the reactor. It is shown that using the proposed communication protocols for a time-varying terahertz channel, the selectivity of the reactor can be significantly increased, beyond what can be achieved with conventional solutions. |
