A systematic review and emerging research directions for multi hop routing protocols in wake up radio driven IoT networks

The constrained energy resources of battery-powered Internet of Things (IoT) devices remains a major limitation for achieving long-term operation in Wireless Sensor Networks (WSNs). Wake-up Radio (WuR) technology addresses this limitation by introducing an on-demand communication mechanism enabling nodes to remain in ultra-low-power sleep states and be activated only when needed, mitigating the substantial energy consumption associated with idle listening and overhearing. This paper begins with an overview of the WuR technology and then examines the suitability of WuR technology for IoT networks, aiming to answer the question of whether WuR technology represents a potential promising solution. The limited sensitivity of WuR technology creates a range mismatch between the WuR the main radio, introducing additional challenges for reliable communication and multi-hop routing. Subsequently, the paper presents a comprehensive literature review of 22 WuR-based multi-hop routing protocols proposed from 2002 to November 2025, highlighting their design principles, performance results and limitations. A taxonomy of the surveyed routing protocols is organized depending on the protocol class, network structure and routing metrics. Furthermore, a comparative analysis is performed to evaluate their strengths and weaknesses and to identify open research directions for future WuR routing protocol designs.