A dual-band wake-up radio for ultra-low power Wireless Sensor Networks

Wake-up radio is an emerging technology for smart sensor networks and the Internet of Things with the ambitious goal of minimizing the power needed to communicate, thus enabling a new generation of applications. Wake-up radios should exhibit low latency coupled with high sensitivity, addressing capabilities with ultra-low power budget. They may be combined with existing radio transceivers and power management units to reduce the overall communication power while maintaining a high performance. This paper presents a 2.45 GHz and 868 MHz wake-up radio with the above mentioned characteristics. Dual band is exploited to increase the flexibility of the wakeup radio, allowing interoperability with the two most common bands used in Wireless Sensors Network and Internet of Things. Simulations results present a system with sensitivity as low as -55 dBm at 868 MHz and -53 dBm at 2.45 GHz.

I. Introduction

Recent advances in digital microelectronics are enabling the development of a large variety of cyber-physical systems. Wireless Sensors Networks (WSN) and Internet of Things (IoT) are one of most promising technologies exploiting these advances to provide a flexible distribution of low-cost and low-energy devices equipped with sensors, which communicate wirelessly. Nowadays WSN is mature enough to be adopted in a wide range of applications such as health-care, implantable devices, environmental and industrial monitoring, surveillance and IoT, among others [1]. However, limited energy availability remains the crucial issue. This limitation reduces the lifetime of the entire network, while emerging WSN applications demand even longer system lifetimes [2]. Since the radio is the node's most power hungry component, reduction in the communication power consumption can significantly improve the node's lifetime [3]. Longer lifetimes can be achieved with aggressive duty cycling, turning the radio off (“power save mode”) and on (“idle listening or transmitting mode”) periodically to save energy. In idle listening three main schemes are possible for power saving, namely pure asynchronous, synchronous and pseudo synchronous. Asynchronous communication is, by far, considered to be the most energy efficient mechanism, which can be achieved by using a wake-up radio receiver (WURx) [4]–[6]. WURx are able to detect short commands or wakeup signals on the communication channel, consuming only few microwatts or less. They are coupled to the main radio or are integrated directly on chip and they should provide a positive balance between power saved and used. The capability of WURs to simultaneously or alternatively listen the channel at the WSN 2.45 GHz and 868 frequencies MHz is exploited in this work. A dual-band antenna is matched to the wake-up radio, and the entire system is designed for best trade-off among power transferred to the WUR, size and dual-band capabilities.