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Coherent Distributed Radar for High-Resolution Through-Wall Imaging

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Progress rept. no. 23

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In this reporting period, we continued collecting indoor data and processing the scans for improving the indoor range accuracy. Since the transceivers are very tightly synchronized, the transmission phase and time and the phase use for down conversion are well-controlled and repeatable as we perform the experiments. We are continuing to take more data and develop algorithms for improved range accuracy based on both channel estimation and digital beam forming. To facilitate the collection of data, we have configured the hardware and software to stream the complex correlator output at a rate of 10Hz to the PC. This will allow us to evaluate several algorithms for RF ranging offline. A key parameter for the beam forming algorithms that will be used to improve ranging accuracy and for imaging is the aperture the spatial range over which the multipath environment is sufficiently stationary to be processed coherently. If this aperture is large, a narrow beam can be formed and multipath can be suppressed effectively. One way to estimate this parameter is to compute the spatial correlation length of the range error. In Figure 1, we show the results of an outdoor ranging experiment. This result is specific to the particular outdoor environment carrier, bandwidth, and ranging algorithm used here, but suggest that an aperture of several wavelengths is possible. With beam forming measurements spaced at roughly half wavelength, the potential for beam forming is present. For an indoor environment, due to the higher density of scatters, the error de-correlates faster, and hence the aperture will be smaller, reducing the potential for beam forming to improve the range accuracy. We show the autocorrelation plots for an indoor office environment below. For the indoor environment, the aperture will be reduced to 1-2m, essentially making the beam forming approach, at the used frequencies and bandwidth, not suitable for the indoor environment.

Subject Categories:

  • Electrical and Electronic Equipment
  • Active and Passive Radar Detection and Equipment
  • Radiofrequency Wave Propagation

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