Velocity Based Latency Design For Wireless Sensor And Actuator Networks

Recent technological advances have lead to the emergence of wireless sensor and actuator networks (WSANs) which are capable of observing the physical world, processing the data, making decisions based on the observations and performing appropriate actions. These networks can be an integral part of systems such as battlefield surveillance and microclimate control in buildings, nuclear, biological and chemical attack detection, home automation and environmental monitoring, among many others.In WSANs, the phenomena of sensing and acting are performed by sensor and actuators, respectively. Sensors are low-cost, low power devices with limited sensing, computation, and wireless communication capabilities. Actuators are resource rich nodes equipped with better processing capabilities, higher transmission powers and longer battery life. One of the main requirements of sensor-actuator communication is to consume low energy as in wireless sensor networks. Moreover, in some applications such as in fire, the communication traffic is typically delaying sensitive. Therefore, another main requirement of sensor-actuator communication is to support the real-time traffic.Analyzing the mobile object message delivery mechanism in traditional networks, this paper gives the mechanisms to save energy in wireless sensor networks is the use of the listen-sleep modes at MAC layer, by which nodes are put to sleep as often as possible. However, long sleep time may cause additional latency and lower message delivery ratio, while sensor nodes communicate with mobile actuators in wireless sensor and actuator networks. For a specific period of listen-sleep cycle, this paper presents an approach which determines the proportion of the sleep time to the listen time. The focus is to offer the designers full flexibility in trading latency, message delivery ratio, mobile velocity and bandwidth versus each other. In addition, we propose a communication algorithm of sensor nodes and actuators for distributed wireless sensor and actuator networks, which could track the migrating actuators and forward messages to them. To reduce the energy consumption, sensor nodes turn off and turn on their radio periodically according to the time intervals determined by the evaluated latency.Then theoretical analysis and experimental implements of the stated algorithms are reported. For each definite MDR values, we can save energy at most by adjusting the sleep time. The simulation results show that between 10% to 90% energy savings can be achieved by our technique under different settings of several key system parameters, compared with the no-sleep mode operation.