Robert Poor is CTO of Ember Corporation. He contends that point-to-point or point-to-multipoint networks typical of industrial wireless communications systems have limited scalability and reliability.
Wireless systems for industry have mostly used cellular-phone-style radio links, using point-to-point or point-to-multipoint transmission. But research at MIT’s Media Lab in Cambridge, MA, indicated that traditional wireless formats have liabilities in industrial applications. These include rigid structure, meticulous planning requirements, and dropped signals.
In contrast, wireless mesh networks are multihop systems in which devices assist each other in transmitting packets through the network, especially in adverse conditions. You can drop these ad hoc networks into place with minimal preparation, and they provide a reliable, flexible system that can be extended to thousands of devices.
Here is a diagram of such a network.
In a wireless mesh network, multiple nodes cooperate to relay a message to its destination.
The article is pretty technical and contains several illustrations and a case study about the deployment of a wireless mesh network in a water treatment plant.
Robert Poor concludes.
Multihop mesh technology, however, is inherently reliable and redundant, and it can be extended to include thousands of devices. In addition, these networks can be installed in hours instead of days or weeks. And the network doesn’t require sophisticated planning and site mapping to achieve reliable communications. There’s no need for specialized and costly RF engineering labor to complete the installation.
The network is self-configuring. All devices can transmit from their original position, and they don’t have to be moved. A weak signal or dead zone can be fixed simply by dropping a repeater node into place. The network error rate is low and can be further reduced if occasional re-transmits are allowed.
Industrial systems can now benefit from a wireless format that satisfies the multiple conflicting demands of redundancy, distributed communications, flexibility, and reliability. Furthermore, self-configuring, self-healing networks are inherently less expensive to install and maintain as radios and microprocessors become cheaper. A significant barrier to low-cost connectivity has been removed.
Source: Robert Poor, Ember Corp., for Sensors Online, February 2003
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