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Sensor nets out to solve real-world problems

Posted: 01 Mar 2007 ?? ?Print Version ?Bookmark and Share

Keywords:wireless sensor? sensor network? wireless? UWB? Wi-Fi?

Advanced modulation and RF transmission schemes are quickly moving from lab to field to solve real-world problems, speakers told the IEEE Radio and Wireless Symposium in January.

In discussions ranging from UWB personal-area networks to Wi-Fi meshes, academic researchers presented concrete examples of advanced wireless data and sensor networks addressing people's needs around the globe.

Deborah Estrin, principal researcher at the University of California, Los Angeles Center for Embedded Networked Sensing, demonstrated river and forest monitoring, showing how wireless sensor nets combine with actuators and robotics to form adaptive eyes for such tasks as precision agriculture and tracking species diversity.

Tailor-made apps
"The heterogeneity and spatial variability common to many environmental problems are almost tailor-made for embedded wireless sensor networks," Estrin said. "If you don't have that fine-grained variability, you don't really need to sense at multiple points."

Estrin said the center's networks have:

  • Measured arsenic contaminant transport in drinking wells in Bangladesh;
  • Conducted seismic monitoring in the aftermath of an October 2005 earthquake in Pakistan;
  • Studied the mixing of the San Joaquin and Merced rivers in California; and
  • Observed the microclimates of several continents using terrestrial-imaging nets.

Small robotic and actuator subsystems are critical in some of these applications, Estrin said, because node mobility can help overcome the inherent undersampling of static nodes on a network. Typically, the center's networks use three tiers: simple, dumb "motes" at the endpoints; microservers to control many motes; and autonomous mobile nodes, many of which use cameras and other sensing devices in much the same way interplanetary missions rely on robotics.

Estrin said this tiered model allowed sufficient local, decentralized participation from citizen-researchers, particularly in tracking natural disasters like earthquakes and floods. But, she said, those in control of such bottom-up networks must realize that privacy concerns demand that local participants can selectively decide whether to share only some of the information they collect.

Many designers at the symposium addressed the design of configurable RF and baseband blocks for cognitive radio systems. But Hiroshi Harada of Japan's National Institute of Information and Communications Technology took configurable-device speculation a step further by relating chip design to government plans for the allocation of spectrum. Harada explained how ending analog TV broadcast in July 2011 poses the same problems and opportunities for opening up spectrum in Japan that now confront the United States, which is scheduled to halt analog telecasts in February 2009.

When designers in industry and academia consider cognitive radio, Harada said, they should look at aspects of the anticipated frequency bands available and how that could influence the dynamic range of the devices under design. This related directly to a multiband SiGe-BiCMOS mixer being developed at the institute, with a range of 0.4-5.3GHz.

This mixer was combined with a two-board baseband DSP system using a 430MIPS micro-iTron processor and a multiband antenna designed to shift among multiple available frequency bands.

A cognitive radio can do more than choose frequency bands, Harada said. He showed how a change in volume of the RF signal started a process in which a base station self-loads WLAN software and shifts from cellular to Wi-Fi operation. "Ideally, a single appliance could serve mobile communications, digital terrestrial TV, WLAN and UWB, and configure its software for the different types of links," he said.

This year's Radio and Wireless Symposium was unique in broadening analysis of wireless networks beyond the PHY characteristics of RF and baseband devices.

Several papers looked at using the characteristics of L2 and L3 bridging and routing for directly influencing the topology of wireless networks. Ozgur Oyman, research scientist at Intel Corp.'s communications technology lab, described multihop routing as a way to increase the diversity of antennas for picocellular broadband orthogonal frequency-division multiplexing (OFDM) services like WiMAX or meshed Wi-Fi. Just as spatial or frequency diversity can optimize broadband networks, multihop routing patterns can themselves influence the topology of broadband OFDM cellular, he said.

Intel's work showed that throughput maximization for wireless WAN is equivalent to familiar minimum-cost routing problems encountered in IP routing networks. Oyman's study also maps into the multihop relay work of the IEEE 802.16j relay study group.

- Loring Wirbel
EE Times

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