(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.
(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.
(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.