Durgin, Gregory D.
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ItemAntenna Performance in a Corona Plasma(Georgia Institute of Technology, 2011-05) Morys, Marcin M. ; Durgin, Gregory D.The formation of corona discharges at high potentials was studied. Glow coronas were found to be generated when the electric field magnitude is in excess of 3MV/m in general for air at atmospheric pressure. The number density of electrons in the glow corona can only be approximated, but the results obtained from the Boltzmann transport equation promise to be accurate enough to give meaningful wave attenuation results, so long as the number density is below 1019 m-3 electrons. Above this density, the attenuation increases dramatically and approximations for density may no longer be valid. Wave propagation and antenna parameters in a corona plasma can be computed through simulation using dielectric slabs of complex impedance to simulate a plasma sheath.
ItemMultipath Fading Measurements at 5.8 GHz for Backscatter Tags With Multiple Antennas(Georgia Institute of Technology, 2010-11) Griffin, Joshua D. ; Durgin, Gregory D.Multipath fading can be heavy for ultra-high frequency (UHF) and microwave backscatter radio systems used in applications such as radio frequency identification (RFID). This paper presents measurements of fading on the modulated signal backscattered from a transponder for backscatter radio systems that use multiple antennas at the interrogator and transponder. Measurements were performed at 5.8 GHz and estimates of the backscatter channel envelope distributions and fade margins were calculated. Results show that multipath fading can be reduced using multiple transponder antennas, bistatic interrogators with widely separated transmitter and receiver antennas, and conventional diversity combining at the interrogator receiver. The measured envelope distribution estimates are compared to previously derived distributions and show good agreement.
ItemRevisiting the Spread Spectrum Sliding Correlator: Why Filtering Matters(Georgia Institute of Technology, 2009-07) Pirkl, Ryan J. ; Durgin, Gregory D.A wireless channel sounder based upon the conventional spread spectrum sliding correlator implementation uses unfiltered pseudo-random noise (PN) at both the transmitter and receiver to generate a time-dilated copy of the channel’s impulse response. However, in addition to this desired impulse response, the sliding correlator also produces a noise-like, wideband distortion signal that decreases the measurement system’s dynamic range. Careful selection of the sliding correlator’s lowpass filter can significantly reduce this distortion, but no amount of filtering will remove it completely. In contrast, using filtered PNs at both the transmitter and receiver enables one to remove this distortion in entirety and realize a measurement system whose dynamic range closely approximates the theoretical ideal for spread spectrum systems.
ItemQuasi 2-D Field Reconstruction Using the Conjoint Cylindrical Wave Expansion(Georgia Institute of Technology, 2009-04) Pirkl, Ryan J. ; Durgin, Gregory D.Off-the-horizon propagation severely degrades the accuracy of any field reconstruction technique that presupposes a two-dimensional (2-D) wireless channel. Therefore, employing the 2-D cylindrical wave expansion (CWE) to interpolate perimeter channel measurements into a planar region often yields poor results. Here, the CWE is adapted for real-world radio channel measurements by selectively combining the basis functions from two similar CWEs. Using both simulated and experimental measurement data, it is shown that this conjoint CWE yields a more accurate reconstruction than the conventional CWE yet requires no additional measurements. Thereby, this field reconstruction- based channel imaging technique will enable more complete investigations of the wireless channel’s spatial behavior and allow researchers to isolate and characterize the actual mechanisms underlying radio wave propagation.
ItemOptimal sliding correlator channel sounder design(Georgia Institute of Technology, 2008-09) Pirkl, Ryan J. ; Durgin, Gregory D.The sliding correlator technique remains one of the most versatile and effective methods for sounding the radio propagation channel in next-generation wireless systems. Despite their utility, there has never been a comprehensive set of metrics and rules for the design of a sliding correlator channel sounder. This paper presents quantitative guidelines for balancing the many system parameters to achieve optimal levels of temporal resolution, dynamic range, processing. gain, and Doppler resolution. The design procedure presented at the end of the paper will allow researchers to probe the new radioscapes that result as wireless systems are pushed to higher carrier frequencies, wider bandwidths, multiple antennas, and ubiquitous operation.
ItemGains for RF tags using multiple antennas(Georgia Institute of Technology, 2008-02) Griffin, Joshua D. ; Durgin, Gregory D.Backscatter radio systems, including high frequency radio frequency identification (RFID), operate in the dyadic backscatter channel - a two-way pinhole channel that has deeper small-scale fades than that of a conventional one-way channel. This paper shows that pinhole diversity is available in a rich scattering environment caused by modulating backscatter with multiple RF tag antennas - no diversity combining at the reader, channel knowledge, or signaling scheme change is required. Pinhole diversity, along with increased RF tag scattering aperture, can cause up to a 10 dB reduction in the power required to maintain a constant bit-error-rate for an RF tag with two antennas. Through examples, it is shown that this gain results in increased backscatter radio system communication reliability and up to a 78% increase in RF tag operating range.
ItemLink envelope correlation in the backscatter channel(Georgia Institute of Technology, 2007-09) Griffin, Joshua D. ; Durgin, Gregory D.High-frequency backscatter radio systems operate in the dyadic backscatter channel, a pinhole channel whose envelope probability density function and bit-error-rate performance are strongly affected by link envelope correlation – the envelope correlation between the forward and backscatter links of the dyadic backscatter channel. This paper shows that link envelope correlation is most detrimental for backscatter radio systems using co-located reader transmitter and receiver antennas and a single RF transponder antenna. It is shown that using separate reader antennas and multiple RF transponder antennas will decrease link envelope correlation effects and a near maximum bit-error-rate can be achieved with link envelope correlation less than 0.6.
ItemMeasurement of Small-Scale Fading Distributions in a Realistic 2.4 GHz Channel(Georgia Institute of Technology, 2007) Henderson, Alexander H. ; Durgin, Gregory D. ; Durkin, Christopher J.
ItemBroadband Spatio-Temporal Channel Sounder for the 2.4 GHz ISM Band(Georgia Institute of Technology, 2006-08-31) Durkin, Christopher J. ; Pirkl, Ryan J. ; Trzecieski, Alexander J. ; Durgin, Gregory D.This report documents the continuing research efforts of the Propagation Group at Georgia Tech towards the construction of a broadband spatio-temporal channel sounder for the Aerospace Corp. The channel sounder, a valuable research tool in radio frequency (RF) channel and direction finding (DF) measurement, was constructed from the 8-element antenna array receiver setup on loan from Aerospace Corporation to support this collaborative project. Upon completion of the 2006 portion of this on-going collaboration, the following contributions were made to the system: The broadband pseudo-random noise generator was modified for improved operation and wider bandwidth. The vector RF signal generator was improved to be cleaner, more stable, and include onboard programming firmware, obviating the need for an external computer and allowing better transmitter portability. An autonomous self-powered transmitter platform was constructed. Extensive improvements were made to the RF receiver signal chain in order to compensate for near out-of-band interference and amplifier noise. Software improvements included an SQL database interface for captured data and associated metadata in order to facilitate storage and retrieval. In addition to these improvements, field measurements were taken to demonstrate channel sounding operation and direction finding in environments with copious noise and interference. Collectively, these outputs fulfill the research deliverables for the year 2006 collaborative project between Aerospace Corporation and Georgia Tech. Future work for this ongoing collaboration will likely involve more measurements and further miniaturization of the array channel sounder. The ultimate goal of the research should be a single compact receiver box containing all RF components and analog-to-digital conversion hardware. This box could then be plugged into a network or laptop computer and an arbitrary array manifold for portable direction-finding and channel measurement. When coupled with the array processing software developed during the 2004 and 2005 phase of this collaborative project, the end result will be a dynamic, portable unit capable of both spatio-temporal channel sounding and/or accurate DF location of 2.4 GHz radios in a complicated radioscape. Temporal and spatial analysis of the measurements should be able to yield detailed data to assist in detailed channel characterization.
ItemDesign and analysis of direction-finding systems in multipath and ...(Georgia Institute of Technology, 2006-08-31) Durgin, Gregory D. ; Durkin, Christopher J. ; Pirkl, Ryan J. ; Trzecieski, Alexander J.