Anew method has been developed for the design of a miniature, low-power, low-cost radio node capable of self-organization and communication within an ad-hoc network. The integrated radio transceiver, combined with a backend processor in a single networkable node, offers unique network scalability and low power levels that will enable applications that are not possible with any existing sensor node platform. One unique feature of this radio is that the proposed integrated microchip can be mass produced in a CMOS process without a costly external crystal so that the network formed by a set of homogeneous nodes is robust to network changes or node failure. These characteristics enable formation of reliable, inexpensive ad-hoc networks with group intelligence and long lifetimes.

The node should be essentially disposable and should contain a bi-directional transceiver and a backend processor capable of computation and control. Most importantly, the node should operate at power levels on the order of microwatts, to enable deployment with an ultra-thin battery or harvesting power from the environment. This work focused on low-duty-cycle UWB communication and exploited a natural biological phenomenon of Pulse Coupled Oscillators (PCOs) to provide a low-complexity method of regulating node-to-node communication.

The transceiver front end is a low-power, highly efficient, FCC-compatible channel interface that demonstrates good interference rejection and enables transmissions up to 3 meters. The improved front end design utilizes a dual-band transmission scheme that enables 30-dB separation between the timing pulses and data pulses, significantly reducing error probability, with little cost in area or power. This is due to the design of tunable transceiver circuits that are able to easily switch between the two transmission and receive bands.

Another improvement to the design is the addition of the use of wave shaping. By using wave shaping, the signal power is confined more closely to the intended 500-MHz transmission bands, and wastes less transmission power while staying within FCC limits. Another significant characteristic of this transmitter receiver pair is its ability to be aggressively duty-cycled.

Significant efforts were made in characterizing the PCO system, designing local oscillators and related blocks, and developing error-reduction techniques and synchronization detection schemes to enable nodes to determine if they should proceed with communication. The parameter space was characterized for synchronization of the network, and a set of rules governing required coupling strengths, transmission limits, and jitter limits for the nodes in the network was developed.

Using sub-optimal designs, which can be significantly improved for jitter performance, standard deviations in timing uncertainty of less than 5ns were demonstrated. The initial coupled oscillator designs based upon thresholded relaxation oscillators exhibited too much timing uncertainty, and an improved version will enable synchronization of a larger network.

This work was done by Alyssa Apsel of Cornell University for the Defense Advanced Research Projects Agency. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Electronics/Computers category. DARPA-0010


This Brief includes a Technical Support Package (TSP).
Ultra-Low-Power Radios for Ad-Hoc Sensing Networks

(reference DARPA-0010) is currently available for download from the TSP library.

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This article first appeared in the December, 2010 issue of Defense Tech Briefs Magazine.

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