Wake-up radio enabled BLE wearables: empirical and analytical evaluation of energy efficiency

The energy efficiency is an important issue for a vast range of the Internet of Things (IoT) applications. However, especially critical is the energy efficiency in the context of wearable and body-area network devices. At the very same time, due to their nature, these use cases often impose stringent latency and reliability requirements. In this study, we provide an insight into the feasibility and the performance of the Bluetooth Low Energy (BLE) 5.0 compatible sensor devices enriched with a wake-up radio (WUR). Introduction of a low-consuming WUR radio equips a sensing device with a mechanism to know when its data are desired, and helps to avoid the unnecessary data transmissions thus saving energy. To investigate the utility of this approach and the associated with it trade-offs, we start by instrumenting and measuring a real-life prototype of a WUR-equipped BLE device. Based on the results of the real-life measurements, we first develop the analytical models, and then analyze how the latency requirements imposed by the application and the number of the wake-up signals affect the energy consumption of the WUR-equipped BLE device and a standalone BLE sensor. Our results show under which conditions each of these architectures outperforms another one and demonstrate that the WUR approach can be more energy efficient in the case if the desired latency for data delivery is below 2.11 s.