Wireless Sensor Networks (WSNs) have traditionally been powered by portable energy sources, viz. batteries, which limit their operational lifetime. To ensure WSN sustainability, researchers have turned to alternative energy sources for power. Harvesting ambient energy to power WSNs is a promising approach but energy harvesting devices of the same footprint as wireless sensors are unable to provide sufficient energy for sustained operation; availability of energy is also highly unpredictable. Harvesting energy from radio waves can provide energy-on-demand using a radio transmitter to broadcast over the sensor network when the sensors need to be powered up to operate. However, only minute amounts of energy can be extracted from radio waves, presenting a monumental constraint in terms of the duty cycle and accomplishable tasks. We present our design of a data delivery scheme which aims to optimize the usage of the minute amounts of harvested energy through a sink synchronized protocol. The design has been implemented and experimentally validated utilizing commercially available RF energy harvesting devices.
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