A Gateway Node with Duty-Cycled Radio and Processing Subsystems for Wireless Sensor Networks

Wireless sensor nodes are increasingly being tasked with computation and communication intensive functions while still subject to constraints related to energy availability. On these embedded platforms, once all low power design techniques have been explored, duty-cycling the various subsystems remains the primary option to meet the energy and power constraints. This requires the ability to provide spurts of high MIPS and high bandwidth connections. However, due to the large overheads associated with duty-cycling the computation and communication subsystems, existing high performance sensor platforms are not efficient in supporting such an option. In this article, we present the design and optimizations taken in a wireless gateway node (WGN) that bridges data from wireless sensor networks to Wi-Fi networks in an on-demand basis. We discuss our strategies to reduce duty-cycling related costs by partitioning the system and by reducing the amount of time required to activate or deactivate the high-powered components. We compare the design choices and performance parameters with those made in the Intel Stargate platform to show the effectiveness of duty-cycling on our platform. We have built a working prototype, and the experimental results with two different power management schemes show significant reductions in latency and average power consumption compared to the Stargate. The WGN running our power-gating scheme performs about six times better in terms of average system power consumption than the Stargate running the suspend-system scheme for large working-periods where the active power dominates. For short working-periods where the transition (enable/disable) power becomes dominant, we perform up to seven times better. The comparative performance of our system is even greater when the sleep power dominates.