Electrical Engineering
      and Computer Sciences

Electrical Engineering and Computer Sciences


UC Berkeley


2008 Research Summary

Low Power Wireless Design for Asymmetric Sensor Networks

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Yuhui David Chen and Jan M. Rabaey

Research in recent years has demonstrated the possibility of deploying wireless technology in a number of sensor networks [1]. From the perspective of the communication link, a class of these applications possesses extreme asymmetry between receiver and transmitter. While the receiver is allowed to have higher power and larger size, the transmitter (a.k.a. transponder) is typically an integrated part of the sensor node and is subject to stringent power and size constraints. Examples of such applications include automotive [2], object identification, and biology [3].

In terms of size, off-chip passives, particularly the antenna, take up most part of a radio. Small size therefore favors the adoption of high carrier frequencies. Alternatively, smaller antennas can be used when the frequency is chosen so that for the given communication distance the coupling between receiver and transmitter is in the near-field regime. A design tradeoff therefore exists among power, data rate, and receiver sensitivity.

In terms of power, the backscattering approach [4] can ideally realize transmitters with minimum energy. Its data rate is however limited by duty cycle and channelization requirements imposed by various regulations (e.g., FCC, ETSI/ERC). Other approaches, such as ultra-wide band (UWB), permit significantly higher data rate and allow the radio to be turned off after a brief transmission. Since the average power is nearly proportional to the duty cycle, low energy-per-bit can be achieved. Finally, simple modulation schemes (such as OOK) may exceed other alternatives, again to maximize not bandwidth efficiency but energy efficiency [1].

This project seeks to explore the design opportunities presented by link asymmetry. Design parameters at both system and circuit levels are under primitive study. While the choice of architecture may be scaled for a range of other applications, the primary objective is to achieve 2 Mb/s data rate, over an effective distance of 2 m, with less than 100 mW average power.

J. Rabaey et al., "PicoRadios for Wireless Sensor Networks: The Next Challenge in Ultra-Low Power Design," ISSCC Digest of Technical Papers, February 2002, pp. 200-201.
L. Reindl et al., "SAW-Based Radio Sensor Systems," IEEE Sensors Journal, Vol. 1, No. 1, June 2001, pp. 69-78.
L. Schwiebert, S. Gupta, and J. Weinmann, "Research Challenges in Wireless Networks of Biomedical Sensors," Proc. Int. Conf. Mobile Computing and Networking, 2001, pp. 151-165.
K. Finkenzeller, RFID Handbook, 2nd Edition, Wiley & Sons, 2003.