Recent attention to wireless machine-to-machine (M2M) communications may portend the next big revolution for the wireless industry. Automatic and ad ho c communications between machines, particularly in industrial settings, will provide new ways of remotely monitoring, measuring, and tracking both fixed and mobile systems. Self-forming, self-healing wireless mesh networks make it simple and cost effective to poll, monitor, adjust, and control systems that once required either laborious and expensive manual processes or expensive cabling or wiring. Until recently wireless alternatives to these networks were limited to point-to-point, low-bandwidth, stationary sensors. However, the crossover of high-performance (i.e., mobile broadband) meshing technology into the wireless sensor space is opening up a whole new set of applications and capabilities that were beyond the reach of traditional wireless sensor solutions.
Sensors are a vital part of modern manufacturing process control. An M2M communications system enables sensors to provide critical data for real-time process control applications. By automatically collecting and analyzing process data, these systems lessen the burden on plant technicians and operators.
Early attempts to wirelessly network sensors and controllers with cellular or 802.11 technologies have met with mixed results. Smaller-scale and light industrial deployments have generally been successful since traditional wireless technologies can manage both the physical scope and radio interference in these settings. However, large-scale and heavy industrial settings have proven far more problematic for wireless solutions; long distances, thick concrete walls, extensive metal structures, and machines that generate radio frequency noise create interference and "non-line-of-sight" issues that thwart reliable end-to-end radio communications. It is in these types of facilities that high-performance wireless mesh networking is gaining acceptance.
A wireless mesh is different from the typical point-to-point and centralized radio solutions used for networking sensors today. In a mesh network, each node (in this case, the sensor and its mesh-enabled radio) can send and receive its own information and can also function as a router/repeater to relay messages for neighboring nodes. This ability to "hop" signals through neighboring nodes offers several critical benefits. Peer-to-peer connectivity and hopping between nodes means signals can automatically be routed around obstructions, interference, congestion, and node failures. The ability of nodes to create multi-hop non-line-of-sight connections simplifies deployment and engineering of the network. Since each node regenerates and strengthens the signal as it is passed along, wireless coverage and reliability are enhanced. Multi-hop systems also allow the mesh network to offer very high bandwidth at lower radio power levels. Finally, meshing enables these wireless networks to support end-to-end broadband data rates to more than just sensors; video, imaging, and other bandwidth-intensive applications can be wirelessly networked to infield and remote users. Since the mesh network communication protocol is IP based, mesh networks can extend existing wired network applications to field personnel laptops and PDAs, giving field technicians real-time seamless access to their existing networks and applications.
Some mesh networks also offer self-forming, self-healing features. In these networks, each node maintains a continuously updated dynamic routing table. This enables the network to adapt to changing electromagnetic noise and environmental conditions by dynamically changing network connections. Meshing also creates redundant communication paths throughout the network, so if a node or link fails, the network automatically switches to new routes via alternate paths. This intelligent routing allows for automatic network capacity balancing because the signals will automatically hop away from congested routes. This ensures continued connectivity, increased network utilization, and enhanced end-to-end reliability. Self-forming and self-healing routing also means that additional mesh-enabled devices will automatically join the network when they are powered up.
Because of its inherent advantages, many mesh-based sensor products are appearing on the market. Some products, particularly those adapted from wide-area mobile broadband technology, offer interesting possibilities for process and security use. In contrast to low-bandwidth wireless meshes designed with near-zero power consumption in mind (which leads to short range and low data speeds), the higher-powered, broadband mesh technologies are aimed at applications where performance, coverage, and reliability are paramount. With burst data rates of up to 6 Mbps, these more powerful networking systems can enable bandwidth-intensive applications, such as real-time video monitoring, which could allow facility staff to check environmental and equipment conditions at remote locations. Perimeter security monitoring is another possibility. Technicians can use the same wireless mesh network to connect to central parts inventories, repair manuals, maintenance records, Internet-based help systems, and reporting systems from their laptops and PDAs. Support for these high-speed "man-to-machine" applications drastically improves a company's ROI for the wireless sensor network. Quality of service management can be used to prioritize the delivery of real-time process data so that they are not impacted by non-time-critical user requests and file downloads. The ability to support mobile technicians, deliver remote video, and prioritize real-time data traffic elevates mobile broadband meshes from a wire or cable replacement to a strategic operational investment.
A Broadband Mesh in Action
Early experiences with meshing sensors over wireless broadband networks show that the technology has a future in many settings. The Orange County Water Reclamation Div. (OCWRD), Orange County, FL, recently conducted tests using mesh-enabled sensors for real-time process control at one of its wastewater reclamation facilities. A number of mesh-enabled wireless sensors were deployed throughout the 40-acre facility. Each bit of data obtained was wirelessly routed back to the control center where performance, efficiency, and other parameters were collected and monitored in real time.
Figure 1. In this photo a mesh-enabled architecture (MEA) wireless sensor modem automatically transmits sludge blanket level data to the control center at the Orange County Water Reclamation Div. in Orange County, FL.
In the case of OCWRD, a number of mesh network radios were deployed and interfaced directly with sensor modules via RS-485 (see Figures 1 and 2). The radio nodes were powered from existing AC lines. The resulting high-performance mesh-based broadband network was deployed and fully operational within a day. The wireless system was integrated into the existing wired IP network based in the control center on the outskirts of the facility.
Figure 2. In this photo an MEA wireless sensor modem (foreground) continuously transmits dissolved oxygen data, eliminating the need for manual data collection.
A water reclamation facility is typical of many multi-acre manufacturing environments in that it poses significant physical and environmental challenges for creating a distributed, cost-effective, and reliable broadband network. For example, the sanitation plant's location near a water supply, with its saturated ground, made deploying a wired network cost prohibitive. These facilities are also generally wireless hostile, preventing Wi-Fi and cellular transmissions from creating reliable high-bandwidth links within these settings.
To maintain quality standards and comply with regulatory mandates, wastewater facilities must continuously monitor and maintain records of a variety of critical process parameters, including temperature, dissolved oxygen, and suspended solids. Typically, this information is collected manually by a technician who must walk around to hundreds of individual sensors. Since the sensors aren't networked, if one of them fails it could be days before anyone would know. With a wireless mesh network, this reporting process becomes completely automated and more efficient, providing real-time data and alarm reporting.
In addition to traditional industrial settings, wide-area M2M mesh-based sensor networks are currently being deployed in a number of mining operations throughout the country. One of these mines is using a mesh network primarily as a communications conduit for a number of vehicle-based PLCs used to monitor the facility's heavy machinery, such as its haulers. The network provides continuous feedback on the condition of the machinery's core electrical and propulsion systems, giving onsite and remote engineers a powerful predictive maintenance and operations control tool. The net result is greater efficiency for the entire mining process due to reduced costs and downtime. In the future the mine plans to fully automate this process by integrating the network with a third-party health and diagnostic software package. The software will constantly analyze all the data collected and provide immediate analysis to determine if any parameter is out of specification.
Another mine is using its mesh network to improve communications from rock element sensors and drilling machinery and so prevent redundant and unproductive drilling. They've found broadband-capable mesh sensor networks offer a 250-fold increase in data transmission rates over their existing wireless systems, allowing tighter integration of the mine-to-mill process. The extra integration, made possible by the self-healing nature of mesh networks, allows the removal of redundant mechanical and wireless communication systems, eliminating capital, operational, and network management costs.
The success and benefits demonstrated at the mines and public works facility are helping high-performance mesh networking to gain traction in a variety of other applications. According to a recent market research report released by Wireless Data Research Group, the worldwide market for M2M communications, including sensors, PDAs, and RFID tags, will grow to $31 billion in 2008. These projections, backed by continued deployment of high-performance mesh networks for real-time sensor monitoring and other mission-critical applications, point to a very promising future for meshed M2M communications.