Deploying Power-Aware Wireless Sensor Agents
Developing sensor agents that can be deployed untethered in the ﬁeld presents signiﬁcant challenges in adapting to hardware, communication, power and environmental limitations. Real-world characteristics dictate agent behavior and operating strategies, sometimes quite differently from often held assumptions and intuitions. In this article, we describe the sensor-agent hardware and blackboard-system software used in CNAS (collaborative network for atmospheric sensing), an agentbased, power-aware sensor network for ground-level atmospheric monitoring. CNAS is representative of a class of battery-powered, wireless sensor networks in which the distance separating deployed sensor agents is near the limit of their WiFi communication range. To conserve battery power, CNAS sensor agents must have their wireless radios turned off most of the time, as even having them turned on consumes signiﬁcant power. This limitation complicates agent interaction and network responsiveness, because an agent cannot simply turn on its radio when it needs to send a message. CNAS agents also must have their radios turned on when others are sending messages to them and to support multi-hop message forwarding. We discuss how CNAS agents collaborate using only periodic radio availability and consider how different hardware and communication capabilities would change CNAS strategies.We also relate challenges that had to be addressed during deployments of CNAS at military exercises held in the summer heat in Wisconsin and in the rain and mud in Queensland, Australia. We conclude with research on improving CNAS responsiveness with limited radio availability and on potential next-generation CNAS hardware.
The concept of distributed sensor networks dates back to at least 1978, when a distributed sensor networks workshop was held at Carnegie Mellon University . Preliminary research on mobile ad hoc networks (termed ‘packet radio’ in 1978) coupled with advances in microprocessors suggested the possibility of creating widely distributed networks of autonomous sensor ‘nodes’ that would organize themselves into an effective and resilient sensing system. Hardware, software and communication technology has come a long way since 1978, enabling cost-effective realization of that vision. Today’s agent-based sensor networks consist of small, battery-powered devices that are physically distributed over a wide area and communicate using wireless communication. Although the technology has changed, developing sensor agents that can be deployed untethered in the ﬁeld still presents signiﬁcant challenges in adapting to hardware, communication, power and environmental limitations. Realworld characteristics dictate agent behavior and operating strategies, sometimes quite differently from often held assumptions and intuitions. In this article, we describe the implementation and deployment challenges associated with an agent-based, poweraware sensor network for ground-level atmospheric monitoring developed for the US Air Force. Although the application domain is atmospheric monitoring, many of the challenges that we faced are representative of a general class of batterypowered, wireless sensor networks in which the distance separating deployed sensor agents is near the limit of their communication range.
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