Resumen de Transmission strategies for wireless energy harvesting nodes
María Gregori Casas
Over the last few decades, transistor miniaturization has enabled a tremendous increase in the processing capability of commercial electronic devices, which, combined with the reduction of production costs, has tremendously fostered the usage of the Information and communications Technologies (ICTs) both in terms of number of users and required data rates. In turn, this has led to a tremendous increment in the energetic demand of the ICT sector, which is expected to further grow during the upcoming years, reaching unsustainable levels of greenhouse gas emissions as reported by the European Council. Additionally, the autonomy of battery operated devices is getting reduced year after year since battery technology has not evolved fast enough to cope with the increase of energy consumption associated to the growth of the node¿s processing capability. Energy harvesting, which is known as the process of collecting energy from the environment by different means (e.g., solar cells, piezoelectric generators, etc.), has become a potential technology to palliate both of these problems. However, when energy harvesting modules are placed in wireless communication devices (e.g., sensor nodes or hand-held devices), traditional transmission strategies are no longer applicable because the temporal variations of the node¿s energy availability must be carefully accounted for in the design. Apart from not considering energy harvesting, traditional transmission strategies assume that the transmission radiated power is the unique energy sink in the node. This is a reasonable assumption when the transmission range is large, but it no longer holds for low consumption devices such as sensor nodes that transmit to short distances. As a result, classical transmission strategies become suboptimal in short-range communications with low consumption devices and new strategies should be investigated. Consequently, in this dissertation we investigate and design transmission strategies for Wireless Energy Harvesting Nodes (WEHNs) by paying a special emphasis on the different sinks of energy consumption at the transmitter(s). First, we consider a finite battery WEHN operating in a point-to-point link through a static channel and derive the transmission strategy that minimizes the transmission completion time of a set of data packets that become available dynamically over time. The transmission strategy has to satisfy causality constrains in data transmission and energy consumption, which impose that the node cannot transmit data that is not yet available nor consume energy that has not yet been harvested. Second, we consider a WEHN that has an infinite backlog of data to be transmitted through a point-to-point link in a time-varying linear vector Gaussian channel and study the linear precoding strategy that maximizes the mutual information given an arbitrary distribution of the input symbols while satisfying the Energy Causality Constraints (ECCs) at the transmitter. Next, apart from the transmission radiated power, we take into account additional energy sinks in the power consumption model and analyze how these energy sinks affect to the transmission strategy that maximizes the mutual information achieved by a WEHN operating in a point-to-point link. Finally, we consider multiple transmitter and receiver pairs sharing a common channel and investigate a distributed power allocation strategy that aims at maximizing the network sum-rate by taking into account the energy availability in the different transmitters and a generalized power consumption model.
