The design of Medium Access Control (MAC) protocols for wireless sensor networks (WSNs) has been conventionally tackled by assuming battery-powered devices and by adopting the network lifetime as the main performance criterion. While WSNs operated by energy-harvesting (EH) devices are not limited by network lifetime, they pose new design challenges due to the uncertain amount of harvestable energy. Novel design criteria are thus required to capture the trade-offs between the potentially infinite network lifetime and the uncertain energy availability. This paper addresses the analysis and design of WSNs with EH devices by focusing on conventional MAC protocols, namely TDMA, Framed-ALOHA (FA) and Dynamic-FA (DFA), and by accounting for the performance trade-offs and design issues arising due to EH. A novel metric, referred to as delivery probability, is introduced to measure the capability of a MAC protocol to deliver the measure of any sensor in the network to the intended destination (or fusion center, FC). The interplay between delivery efficiency and time efficiency (i.e., the data collection rate at the FC), is investigated analytically using Markov models. Numerical results validate the analysis and emphasize the critical importance of accounting for both delivery probability and time efficiency in the design of EH-WSNs.
Index TermsWireless sensor networks, multiaccess communication, energy harvesting, dynamic framed ALOHA. ). U. Spagnolini is with Politecnico di Milano. O. Simeone is with the CWCSPR, NJIT. Recent advances in low-power electronics and energy-harvesting (EH) technologies enable the design of self-sustained devices that collect part, or all, of the needed energy from the surrounding environment. Several systems can take advantage of EH technologies, ranging from portable devices to wireless sensor networks (WSNs) [1]. However, EH devices open new design issues that are different from conventional battery-powered (BP) systems [2], where the main concern is the network lifetime [3]. In fact, EH potentially allows for perpetual operation of the network, but it might not guarantee short-term activities due to temporary energy shortages [2].This calls for the development of energy management techniques tailored to the EH dynamics.
While such techniques have been mostly studied at a single-device level [4], in wireless scenarioswhere multiple EH devices interact with each other, the design of EH-aware solutions needs to account for a system-level approach [5] [6]. This is the motivation of this work.In this paper, we focus on system-level design considerations for WSNs operated by EHcapable devices. In particular, we address the analysis and design of medium access control (MAC) protocols for single-hop WSNs (see Fig. 1) where a fusion center (FC) collects data from sensors in its surrounding. Specifically, we investigate how performance and design of MAC protocols routinely used in WSNs, such as TDMA [7], Framed-ALOHA (FA) and Dynamic-FA (DFA) [8], are influenced by the discontinuous energy availabi...