A Systematic Review on Wake-up Radios Applied to Wireless Sensor Networks

Wireless Sensor Networks (WSNs) are the backbone of many monitoring applications, especially in the Internet of Things (IoT) context. However, efficient power management becomes a critical challenge when sensor nodes rely on disposable batteries. The deployment of WSNs must ensure coverage and connectivity, but the resulting distribution of nodes and underlying protocols directly impact the network’s lifetime. The concept of ideal power consumption, where nodes are active only when strictly required, is fascinating. One innovative way to coordinate node activation is through Wake-up Radios (WuRs), devices that keep listening for an external activation signal while the remaining node’s components stay off. To further extend power savings, a passive WuR variant allows the complete system to remain off: The device captures the activation signal’s energy to initialize the radio, waking the rest of the system up. The active variant provides a way to extend the activation distance range compared to the passive one and its associated energy savings sit between the passive and traditional methods (non-WuR) to toggle a node between active and sleeping modes. This study presents a systematic literature review regarding WuRs applied to WSNs. Our review presents results concerning the works’ primary research outcomes and limitations, the WuRs’ roles, and prospective future works.