SCADA for the Rest of Us: Unlicensed Bands Supporting Long-Range Communications

We are on the cusp of the next big wave in Internet and wireless technology for the mass market: the emergence of ubiquitous smart environments capable of automated sensing and interaction with the physical world around us. A critical ingredient for this future is the deployment and availability of wireless control network infrastructure and services. Most discussions of the future smart environment focus on large systems managed by large corporate or public entities: smart power grids, smart freshwater and wastewater management, and so on. The distributed communications and control mechanisms that automate these infrastructure systems are called SCADA (forsupervisory control and data acquisition). Most work on SCADA has correspondingly considered the focused networks that support a single large system or application. This paper considers the linked technical, economic, and policy issues of making SCADA available for a much larger and more diverse set of systems than have previously been discussed. Examples include the health clinic interested in at-home monitoring of rural diabetes patients; the town interested in deploying sensors to detect icing on dangerous roads; and the farmer who wants to automatically lower a retention pond’s water level when high flow rates are measured miles upstream in a national forest. We describe the requirements for SCADA communications services that will support affordable automated control for a large number of small and distributed systems like these. We briefly survey a range of candidate entities that might seek to meet these requirements. We argue that achieving the desired technical and economic outcome will require both service provider and end-user deployed networks. We propose allocation of a small unlicensed spectrum band of a new type to support growth in this direction. The difference from previous unlicensed allocations is that a few simple limitations on device behavior (a spectrum etiquette) provide predictability for long-range communications, by ensuring that spectrum congestion results in increased delay rather than reduced range. We describe an example of such an etiquette called adaptive duty cycle limit.