Best Paper Award

  Wireless sensor and actuator networks (WSANs) play important roles in realizing applications involving network-based monitoring and control in various fields, including industrial monitoring and control, building automation, and smart-grid. WSANs share many key requirements with wireless sensor networks (WSNs), such as energy efficiency that comes from limitations on the lifetimes of batteries. Furthermore, inclusion of actuators into each node brings another key requirement in WSANs, i.e., the low latency needed to realize rapid reactions to control commands transmitted based on real-time monitoring information. The most common approach to realizing energy-efficient operations in WSNs is duty-cycling in which each node employs periodical activations and sleeping of radio interface (IF). However, duty-cycling has an inherent trade-off between energy-efficiency and latency through the duty-cycling period, which makes it difficult to simultaneously offer key requirements on WSANs, i.e., energy-efficiency and low-latency.
   In order to overcome the inherent trade-off of duty-cycling, this paper proposes radio-on-demand sensor and actuator networks (ROD-SAN) that apply wake-up receivers to WSAN nodes. During the idle period, when each node waits for the arrival of communications requests, it switches off its main radio IF, leaving only the wake-up receiver active. The wake-up receiver activates the radio IF only when it detects a wake-up request from the other node, followed by the data exchange through the main radio IF. Thanks to this on-demand operation, latency is minimized while energy efficiency is also guaranteed because the energy consumption of the wake-up receiver is much lower than that of the main radio. ROD-SAN employs wake-up signaling that is compatible with the existing communication standard for WSNs, i.e., IEEE 802.15.4. This paper evaluates the data collection rate, packet delivery latency, and energy efficiency of ROD-SAN and standard duty-cycling modes defined in IEEE 802.15.4e by means of computer simulations which show the superiority of ROD-SAN to duty-cycling modes. Furthermore, all protocols required to realize ROD-SAN, which range from the lowest layer of wake-up signaling to the application layer offering the functionalities of information monitoring and networked control, are designed and implemented. Then, experimental results obtained through a large-scale field trial, in which 20 ROD-SAN nodes are deployed in an outdoor area with the scale of 450 m x 200 m, are presented, proving the effectiveness of ROD-SAN in a practical environment.
   This paper includes a novel proposal for solving a fundamental problem of duty-cycling, an original design for wake-up signaling that is compatible with existing protocols, and extensive investigations on the practicality of the proposed approach through prototype developments and large-scale field trials. Therefore, the paper contributes significantly to realization of energy-efficient and high-response wireless networks, and is deserving of an IEICE Best Paper Award.