Wireless sensor networks (WSN) operating outdoors or in challenging indoor environments face radio frequency (RF) propagation challenges that lead to issues in signal strength and interference that are difficult to predict when a network is initially designed and provisioned. Multipath effects in particular pose problems because the impact created by the movement of machinery and people is perhaps the most difficult to simulate with today’s predictive models. Multipath is caused by the signal transmissions from the sensors themselves as the signals “bounce around” the environment. Areas with a lot of concrete, glass and steel construction, or equipment, are the most problematic. Real-world data from industrial environments demonstrates just how significant these effects can be, and highlights the importance of accommodating the time-varying effects inherent in any environment to ensure reliable network functionality in the face of this adversity.

Originally developed by Dust Networks as part of its Time Synchronized Mesh Protocol (TSMP), time synchronized mesh networking has become the foundational building block for reliable WSN protocols in the two leading industrial standards, WirelessHART and ISA100, and is now emerging in WSN standards being developed by the IETF.

Unlike ZigBee, which offers no protection against sporadic RF interference or multipath effects, Dust Networks' extremely reliable,  ultra low-power WSN products used in harsh industrial environments utilize a channel-hopping scheme. In an attempt at correcting ZigBee’s deficiencies, ZigBee Pro has added frequency agility, which switches the entire network to another frequency when faced with interference. However, this approach does nothing to prevent multipath effects due to the sensor’s own transmissions. Only a time-slotted channel-hopping technique has proven an efficient means of coordinating node communications and delivering carrier-class communications (typically measured as 99.999% reliability).