  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.
