Modulation and sleeping strategies for wireless sensor networks

Motivated by the recent and rapidly increasing interest in energy-saving schemes, this paper presents a novel PHY/MAC layer design for wireless sensor networks (WSNs). Capitalizing on the observed rare-event feature of most WSNs, we first design an energy-efficient ternary modulation scheme wherein the modulated symbols can classify (or color) the state of the underlying phenomenon as green, yellow or red. Introducing this new notion of a yellow message (that lies between the binary values represented by green and red) results in great flexibility and energy savings when designing a MAC sleeping scheduler (turning nodes on-and-off). The proposed sleeping protocol enjoys low energy consumption and respects a latency constraint by efficiently using the time-division- multiple-access technique along with the ternary modulation scheme. Numerical results illuminate the energy savings provided by the proposed schemes and quantify the energy-latency tradeoffs.