Wireless Sensor Networks
Written by Tom Marlowe
The advances are important given the growing military reliance on remote sensing—and in particular the need to monitor and control key locations such as isolated mountain passes along the Afghanistan/ Pakistan border with limited personnel.
About 10 years ago, the Defense Advanced Research Projects Agency began major research and development projects into wireless sensor networks with the programs Sensor Information Technology (SensIT) and then Network Embedded Systems Technology (NEST). At the same time, Department of Defense researchers began to work on the next generation of the Internet Protocol communications standard—Internet Protocol version 6 (IPv6).
Those two forces have come together to provide truly revolutionary networked sensor capability to warfighters, who will benefit from smaller devices that can form quickly communications networks that monitor important areas on and off the battlefield, explained David Culler, chief technology officer and founder of Arch Rock Corp.
“Instead of investing in all sorts of proprietary devices, our company has made everything driven by IPv6,” Culler said. “That’s important because of the DoD mandate to go to IPv6, and it’s fundamental because the technology goes into so many distinct areas even in the military sector, and ultimately it’s about integrating all of those systems together.”
Arch Rock formed to commercialize technology developed by the University of California, Berkeley, which received the NEST contract to develop nodes and an operating system to support wireless sensor networks. From 1999–2005, the technology achieved a basic level of readiness, whereupon Arch Rock formed to apply the research to industrial problems using widely adopted standards—including Six LoPan, the standard for low power personal area networks over IPv6.
IPV6 BENEFITS
Three key forces drove IPv6, all of which benefited wireless sensor networking, Culler described.
The first force is scale, a recognition that the need for IP-enabled devices would grow very quickly, pushing a need to increase the number of addresses and the ease with which they are assigned. Wireless sensors are exactly such devices, Culler said. The second force is management, which recognizes the vast majority of these devices will be unattended by human operators—again, much like wireless sensors that sit around perimeters or in rooms waiting for activity to report upon to occur. The architecture of IPv6 makes it much easier for these sensors to work dynamically and consistently.
The third force is extensibility, which recognizes that the need for IP-enabled devices will continue to grow and that they must interact with each other for maximum effectiveness.
“Today, the number of cell phone users is roughly equal to the number of toothbrush users,” Culler quipped. “Now we have one or two billion IP devices, and there are six billion people on the planet. “When we reach 10 billion IP devices globally, eight of those 10 are going to be embedded devices in the physical world. That’s a large number of devices per person. They have to be self-configuring and easy to manage,” he added.
IPv6 provides sensor networks with a standard that already anticipates a large number of self-managed devices and an accompanying set of applications, so the two are extremely complementary, Culler observed. IPv6 also was focused on the need for mobility among such devices from its creation.
“Part of what was so important about the Six LoPan work is that the regularity and architectural clarity of IPv6 makes it easier to compress and easier to implement. That was not at all obvious when it got started, so in many ways it simplifies the problem of fitting more information on small devices” like wireless sensors, Culler said.
Going forward, the military must pay attention to the challenges of energy, environment and engagement, Culler stated.
Warfighters must monitor a large number of key areas and integrate that information to improve efficiency, to reduce energy use, and to mitigate environmental impact, he said. Advanced wireless sensor technology empowers them to do that.
But personnel must also engage the enemy, and wireless sensors, embedded appropriately, will provide them with the eyes and ears that they require to keep watch on battlefield areas.
“The fronts are so dispersed and very often low intensity. This kind of technology comes into play there when you don’t want to have people there all the time,” Culler remarked.
MESH NETWORKING
Companies like Arch Rock provide key products and services for wireless sensor networking while others, such as Trace Systems, provide important consulting expertise.
The founders of Trace Systems specialize in tactical communications networking and the design of systems to meet different communications requirements, according to Jeff Barrows, vice president of programs. They have been supporting unmanned ground sensor (UGS) testing for use on the battlefield, and have been exposed to a variety of technologies. The company recognizes that a network for 50 sensors in fixed locations distributed over a particular geographic area to monitor movements would be quite different than a network that has 1,000 sensors concentrated in a smaller area and are constantly being re-positioned.
“How long do the devices need to sleep before they wake up and check and see if there is any activity? How many of them need to be in a network? Is mobility a requirement? What is the bandwidth requirement for the data being transported? What does the mesh infrastructure look like?” Barrows queried. “The requirements are so vastly different every time, you often end up engineering a completely different sensor mesh networking solution every time.”
In widely different scenarios, however, the versatility of mesh networking has proven to be key to the success of the mission. Mesh networks are self-forming wireless networks that are often capable of adapting to changes in the topology and connectivity between the nodes, but there is usually still a need to transit information through those nodes in a hierarchal fashion, Barrows explained.
Most tactical wireless mesh networks will have a gateway node with a link back to a different location or processing point, perhaps to a command vehicle located a mile or over even hundreds of miles away in a more secure location via a satellite link. Sensors within the mesh will need to communicate through that gateway. Some sensors will communicate directly to the gateway, but other sensors may need to communicate through their neighboring sensors due to distance or other constraints, forming a communications web that allows every node in the network to have a path back to the gateway node.
So in effect, Barrows noted, the gateway builds a tree, starting with sensors to which it communicates directly. Those sensors have their own tree of sensors they communicate with, and so on. This can introduce complexity associated with the aggregation of traffic as it travels across the mesh to the gateway over links that may be bandwidth constrained. If there are 20 nodes in a mesh and only two of those are currently directly connected to the gateway, traffic from every node in the mesh that is headed to the gateway must traverse those two links. The mesh topology approach used will often need to be optimized based on the requirements, yet needs to be easily adapted to support mobility of the nodes and an underlying mesh structure that changes frequently and converges quickly.
Every scenario that employs sensors over a wireless mesh network comes with its own set of challenges. The design of a network might depend on how far apart the sensors must lie and what information they capture—whether it is video, sound, seismic activity or other information.
“A lot of times these networks are deployed in austere environments where there is no power source, so they will need a battery,” Barrows commented. “Well, how long does the battery have to last? Do you need to deploy something on the border between two countries and have it last for a year? Or is a week OK? How often does it have to power up to check the area to see if there has been any activity? What wakes it up? How often does it check in with its neighbor sensors to communicate back?
“If you start thinking of a mesh of 150 sensors, you have to have a hierarchical layout and aggregation strategy for how they communicate, so that everything funnels back to the necessary location without having congested links to the gateway,” he continued. “As you get further back from the device that is collecting the data, you have to decide what is really important to haul back to the command vehicle or wherever it is going. That’s where you have to make decisions. Maybe I want to transmit things that are only this interesting and I want to drop everything else. Maybe you only want to collect low-bandwidth state information until something significant happens and then streaming video is required.”
Developers must consider factors such as the need for significant bandwidth requirements when transmitting video over a mesh network, Barrows said. Such bandwidth-intensive data can require nodes to be placed closer together, the use of different frequencies, data compression, or other techniques to adapt to limited bandwidth in the wireless mesh.
The goal with wireless sensors is often to monitor a large space with fewer resources or to collect information beyond the capabilities of human senses to distinguish. Such missions come in many different forms, Barrows said.
For example, there are some very innovative vendors that produce platforms that can host any type of wireless sensors on board. One example is similar to a javelin that can be fired from the air and land in a way that is ideal for communicating. Sensors can placed on various form factors to detect anything from temperature to seismic activity or the presence of chemicals in the air. Another company makes wireless sensors that can be shot like ammunition rounds into a location such as every window in a building that is suspected of housing a sniper or hostiles. Once inside, they build a self-forming network that collects information from inside the building, detecting movement, analyzing chemicals in the air, or taking pictures inside the rooms, then tagging it with geo-locational information, and transporting all of this information back to warfighters to improve situational awareness before they enter the building.
“Think of a border between two countries at war,” Barrows suggested. “Hundreds and hundreds of miles of border that are being monitored by scouts driving along the border in a vehicle can now be intelligently monitored by a wide variety of sensors—whether they are motion-detection sensors, sound or even video. A rocky mountain pass or cave that is hard to reach by vehicle can be monitored with sensors fired into the region. These things can also now be monitored at a much larger scale and automated with intelligent systems to identify activity of interest. You can rule out things that might not be enemy combatants, identify friendly forces, or ignore other things that you might not want to track by using computers to do a lot of that work.
RICH DATA COLLECTION
Although Dust Networks has not supported the military directly for several years, its current work with commercial customers has significant implications for the military. Much of the original work that created the company’s products came from military grants, said Steve Toteda, Dust Networks’ vice president of marketing.
“Sensors that are being deployed include sensors for applications like temperature, pressure, level and flow,” Toteda said. “These are typically used in a large industrial space like a refinery or a chemical processing plant—any place where you would need to have a rich collection of sensor data. Whether you are making steel or making pharmaceuticals, you are collecting a great deal of information from the manufacturing environment and, in turn, using that to optimize the process, which drives greater efficiency, or in many cases simply making sure you meet specific compliance requirements, whether they are government mandates or the correct parameters for the product.”
Dust Networks produces wireless networking products for sensors manufactured by companies such as General Electric, Emerson and ABB Sensors.
“These modules fit inside the sensors,” Toteda said. “A company might take their wired sensor, and then we’ll work with them to create a wireless version of that sensor. We also provide the gateway that connects to the sensors and carries information back to a control system.”
Dust Networks strives to make it as easy as possible to make live sensors wireless and connect them quickly and seamlessly, Toteda added.
“We have spent more than two years at this point working with standards bodies in the communications space, such as a group called the Hart Foundation as well as the International Society of Automation,” he elaborated. “Each of those bodies has developed standards-based communications protocols. That is what we use for the actual communication between the sensor devices.”
Dust Networks creates mesh wireless sensor networks with its original equipment manufacturer partners, enabling not only the routing of information between sensors, but also the transfer of information between frequencies. As such, the mesh networks are very resilient, Toteda said.
“When you are hopping from frequency to frequency, you are really hopping around those unseen obstructions. These are things that might cause interference like when a motor starts up or WiFi,” he remarked. A general movement toward collecting information from the physical world and pooling it in the commercial world will yield more and more commercial products that will benefit military applications, Toteda predicted.
“In real time, you are able to sense how much material you have on hand and even sensing the amount of material you might have on a freight car or at a particular customer’s location,” he commented.
One Dust Networks customer is working on deploying sensors inside city streets to detect if cars are parked along them or not. Thus, in real time, operators can optimize the efficiency of parking in a crowded area. Other customers are working on projects that have direct military applications.
“You can think of the same thing with respect to buildings, making sure the HVAC system is operating at optimal performance when people are in a particular office. When people go home at night, it actually senses when people are leaving. It’s not on timers; it actually physically senses the people inside to decrease the load on the HVAC system,” Toteda revealed.
HARSH ENVIRONMENTS
Both military and commercial operations require tough sensors that can withstand harsh environments, noted Wallace Lueders, vice president of sales and marketing for Accutech.
“We really help out with supply operations, utilities and management of material, water and resources that are really important to military operations,” said Lueders. “We have also done a fair amount of work with the Navy with our traditional products on shipboard applications.” Accutech has supported energy efficiency operations in military installations, such as fuel distribution, storage and level monitoring for both fixed and mobile facilities, Lueders said.
“Our space is really that last 1,000 to 1,500 feet from a network access point to various pieces of equipment or process or security that need to be monitored remotely without existing infrastructure,” he explained. “Our devices don’t need any external power. The sensors are all built into them, and it’s a quick and convenient system to deploy, which when coupled with the ruggedness of the devices makes them very suitable for harsh environments.” Much of Accutech’s business deals with monitoring and control of chemicals and wastewater. The U.S. Military Academy at West Point, for example, hired the company to automate its wastewater treatment plant after the New York Department of Environmental Conservation objected to its discharge of unprocessed material into the Hudson River.
“We enable the assembly of standard modules in the systems that don’t take a lot of expertise to implement,” Lueders said. “Our gateways, for example, will interface with existing infrastructure in place. The sensors communicate to the gateway with very little setup required by the users. “There is a secure attachment process to validate that the sensors belong to the system to ensure the security of the overall operation. Other than that, by following very simple guidelines, you can very quickly design and deploy an operating system without a lot of customized engineering,” he added.
In addition to flexibility and portability afforded by Accutech’s approach, customers typically save 90 percent of the cost of automation by eliminating a lot of engineering, infrastructure, permitting and other expenses associated with traditional hardwire approaches, Lueders declared.
The Accutech systems are scalable, portable and self-powered. They are robust and durable, capable of operating in high and low temperatures under extreme weather and corrosive conditions. The Accutech systems have unique power management capabilities, running sensor devices on lightweight batteries for up to 20 years. “We are moving more toward interactive control systems. Most of what we have been doing to date has been associated with monitoring environmental projects and reporting and analysis for process improvement,” Lueders said. “As the technology evolves, we will see greater speed and redundancy and a move toward more supervisory control.” ♦
