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The scientific community has long envisioned vast networks of sensors each attached to a small battery operated micro-processor replete with a radio communications transceiver. For these scientists, each of the sensor terminals is called a node and the entirety of nodes is termed a Wireless Sensor Network (WSN). WSN's have proven effective in a plethora of application domains spanning climate science [2] to military operations [10]. In applications where remote long-term operation, broad geographic coverage, low-cost (e.g. expendable hardware), and rapid deployment are vital, the WSN offers a practical and efficient solution. To achieve remote distributed sensing and computation the WSN must achieve synchrony among its component nodes.

But the nature of this problem is more fundamental. Wireless communication among terminals of any creed carries with it inherent synchrony requirements. Data-rate, channel capacity, and communication range are ultimately tied back to synchrony through preamble length, chip-rate, and ISI. Further, the application objectives layer additional synchrony requirements. Even the primordial one-to-one link between a piece of factory automation equipment (such as a bottle filler, conveyor, or robotic arm) and its controller becomes substantially more involved when the link to that controller is wireless (as to a laptop or PDA carried by a technician or plant manager). Despite the substantial performance benefits from increased factory floor space (no cable path planning reserves, restrictions in foot-paths from cable-in-the-way, equipment cabinets to house routers and repeaters, etc) and cost benefits from reduced installation, maintenance, and refitting expenditures, wireless deployments in mass production facilities remain rather limited. In large part, this reflects the industry's lack of confidence in wireless real-time control.

A recently introduced standard, IEEE 1588[5], has experienced wide spread adoption by industrial automation applications on wired Ethernet networks. Although 1588 is ideal for high-performance real-time control applications, as it specifies precision below 100ns, it has yet to be applied successfully over wireless links - let alone the low-power wireless links fundamental to WSN and mobile remote control.

Thomas Schmid 2008-11-14