When Wendell Phillips (an American abolitionist and reformer) told a Boston audience in 1852 that "Eternal vigilance is the price of liberty," he did not anticipate the advent of wireless sensor networks (WSNs). WSNs are a new technology that will help us be vigilant. Wireless networks and sensors are not new. However, deploying very large numbers of very small sensing devices (motes) is new.
WSNs are distributed systems programmed for specific missions, to capture and relay specific data. For example, WSNs can check a vehicle's registered identity, location, and movements. Data recorded by sensors embedded in the vehicle can be cross-correlated with data recorded by sensors embedded in sidewalks and roads. With a vast WSN of this type available to them, authorities could monitor driving conditions and instantly recognize traffic problems. Drivers could benefit from such vigilance and the rapid response that it facilitates.
The obvious downside in this example is a further erosion of our privacy. The cross-correlated data can be a bounty for law enforcement. If roads are seeded with sensors enforcing speed limits, we might expect to receive a ticket every time we exceed them. Authorities will benefit from such vigilance, too. There would be less need for patrolling highways or for pulling anyone over for speeding, because automatically generated fines could be issued to vehicle owners.
Cars and roads are merely the tip of the iceberg for WSN applications. There are already commercially available sensor systems for habitat oversight, environmental surveys, building and structural integrity testing, spotting containers and other shipping cargo, border patrol support, fire and flooding alerts, and many other vigilance situations. Industry analysts predict the market for WSNs will surpass $7 billion by 2010.
Potential uses and benefits of WSNs are difficult to gauge; so are the risks associated with their proliferation. Personal computers 30 years ago and cell phones 15 years ago can serve as templates for what we can reasonably expect. Today, motes are costly and big. Early PCs and mobile phones were heavy and expensive. Eventually sensors will be small enough to go unnoticed and inexpensive enough to be scattered almost anywhere.
Power, storage, and communication range will be challenges for WSNs, just as they are for laptop computers and mobile phones. Security is also a serious concern. Power drain in sensors spawned many clever, cost-effective workarounds, skirting security difficulties. Synchronizing sleep and wake cycles maximizes battery life, but exposes sensors to attacks that can force sensors to sleep (stop working) or stay awake (waste energy).
Sensors are more vulnerable to attack than PCs or cell phones. A standard off-the-shelf serial board can be used to change data via sensors' debugging interface. Data diddling could render a WSN unreliable. WSNs may give governments new tools to watch us, but hackers will relish new ways to spam and phish. Revenue-producing WSNs such as those monitoring traffic must be maintained, periodically tested, and upgraded. Maintaining WSNs deployed in rough terrains or hazardous conditions may not be possible. Motes may have to operate unattended, and those without power may remain unreplaced. Abandoned motes will be opportunities for new forms of data theft. Recovering dead motes to prevent staggering pollution problems will require "sensors sensing sensors"with as yet unknown techniques.
Although power and security problems are not yet solved, it is prudent to begin examining the risks that would be posed by widespread deployment of WSNs. As with all advanced technologies, WSNs compel us to balance what's helpful (enhanced ability to observe) with what's harmful (abuse of this ability or undue expectation of its reliability). Performance of large and complex WSNs may be affected by a few malfunctioning sensors, which might be difficult to discover.
The risks of deployment must be compared with the risks of non-deployment. For some locations, the cost-benefit analysis may be simple and decisive. WSNs will appear wherever it makes economic sense to deploy them, or when political goals justify their deployment. Anti-terrorism efforts will add round-the-clock attention to our already well-documented lives. Phillips warned that if we want to be free, we had to be vigilant. He could not imagine we would risk trading freedom for vigilance; with WSNs, it can happen surreptitiously.
©2008 ACM 0001-0782/08/0300 $5.00
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