Effect of spectrally aware tunable front ends and adaptive antennas for a city-wide wireless sensor network
Abstract
A city-wide wireless sewer sensor system becomes "intelligent" by having adaptive manhole cover antennas and spectrally aware tunable filters which adapt to an urban radio environment. 150 wireless sensor nodes have been developed and deployed to monitor the sewer flow and to reduce the frequency of the sewer overflow during heavy storm runoff in the mid-sized city: South Bend, Indiana in the US. The challenge for the wireless designer is to design a radiator which operates below ground as well as to improve the communication performance of the wireless sensor system. In addition, the wireless sensor network was often limited by out-of-band strong interference. Therefore, adaptability to the electrical environment is the key factor for wireless communication. In the first approach, a conventional cast-iron manhole cover was replaced with a composite manhole cover to create a radiator which is not only mechanically strong but also electrically functional. The utilization of parasitic antennas is explored to demonstrate the effect of limited beam scanning on a real sensor network system. The combination of an electronically steerable beamforming capability and an angular diversity technique in this antenna allowed the antenna to adapt to its radio environment and find an optimal receive characteristics. The sensor measurement result indicates that the intelligence of the antenna significantly improves packet reception rate and RSSI (Received Signal Strength Indication). In the second approach, the effect of an adaptive front end is investigated to mitigate these nearby interferers. The sensor motes operated at a fixed band, the unlicensed band of 900MHz, and did not have the frequency adaptability of future cognitive radios. Yet, the effect was demonstrative of the potential benefits of adaptive preselect filtering. The measured result shows substantial improvements over the fixed band system by even slight tuning of the bandwidth and/or the center frequency of the preselect filter. Experimentally and numerically we show that both tuning in the filter bandwidth and/or center frequency can significantly improve the packet reception rate. A guideline for an optimized filtering technique is given to provide broad understanding of how the adaptable preselect filtering can be utilized. The optimal filtering point can be found based on frequency spectrum and filter attenuation response.
Degree
Ph.D.
Advisors
Chappell, Purdue University.
Subject Area
Electrical engineering|Electromagnetics
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