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  • PUBLICATION NOTICE: Preliminary Measurements on the Geography of Urban VHF Radio-Frequency Noise

    Abstract: Radio-frequency (RF) noise has typically been measured at a handful of fixed, representative locations within the urban environment (Achatz, Lo, Papazian, Dalke, & Hufford, 1998; Achatz & Dalke, 2001; Dalke, Achatz, Lo, Papazian, & Hufford, 1997; Wepman & Sanders, 2011; Wagstaff & Merricks, 2005; Spaulding & Disney, 1974). In this work, we discuss the development of a mobile RF noise measurement system and the necessary geospatial and statistical post-processing techniques required to characterize the variations in noise on the street-scale in the VHF sections (60 – 300 MHz) of the spectrum. We discuss the design of our mobile noise measurement system, with special focus on the choice and calibration of preselection filters and preamplifiers necessary to reliably measure low RF noise levels while avoiding intermodulation distortion problems that arise in an environment with many strong emitters. Additionally, we describe post-processing techniques developed to reliably merge and interpolate the RF data with geolocation data which are collected on two very different (microsecond and multisecond, respectively) timescales. We use a preliminary urban dataset from Boston, MA to show that the geo-statistical properties of RF noise power can vary appreciably over street-scale distances, and that these spatial variations are repeatable over tactically relevant times.
  • PUBLICATION NOTICE: Isarithmic mapping of radio-frequency noise in the urban environment

    Abstract: Radio-frequency (RF) background noise is a spatially-varying and critical parameter for predicting radio communication system and electromagnetic sensor performance in urban environments. Previous studies have measured urban RF noise at fixed, representative locations. The Cold Regions Research and Engineering Laboratory (CRREL) has developed a tunable system for conducting mobile RF noise measurements in the VHF and UHF and shown that urban RF noise characteristics vary significantly and repeatably at a scale of tens of meters (Haedrich & Breton, 2019). CRREL also found high-powered regions in Boston, MA that are persistent over time. However, since previous studies conducted stationary measurements or measurements along linear transects, little is known about the 2-dimensional topography of urban noise and the spatial distribution and characteristics of these high-powered regions. In this paper, we present the results of a dense, block-grid survey of downtown Boston, MA at 142 and 246.5 MHz with measurements taken every meter along each street. We present isarithmic maps of median noise power and describe the spatial distribution, shape and other characteristics of the high-powered regions. We compare the rate of noise power decay around high-powered regions to losses predicted by a power law model of path loss.
  • PUBLICATION NOTICE: The Urban Ground-to-Ground Radio-Frequency Channel: Measurement and Modeling in the Ultrahigh Frequency Band

    ABSTRACT:  Ground-to-ground radio communication and sensing within the urban environment is challenging because line of sight between transmitter and receiver is rarely available. Therefore, radio links are often critically reliant on reflection and scattering from built structures. Little is known about the scattering strength of different buildings or whether such differences are important to the urban ground-to-ground channel. We tested the hypotheses that (1) diffuse scattering from built structures significantly impacts the urban channel and (2) scattering strength of urban structures varies with surface roughness and materials.  We tested these hypotheses by measuring urban channels in Concord, New Hampshire, and Boston, Massachusetts, and via channel-modeling efforts with three-dimensional representations of the urban environment. Direct comparison between measured and modeled channels suggest that both of these hypotheses are true. Further, it appears that ray-tracing approaches underestimate the complexity of urban channels because these approaches lack the physical processes to correctly assess the power incident on and scattered from built structures. We developed a radio-geospatial model that better accounts for incident power on both directly visible and occluded buildings and show that our model predictions com-pare more favorably with measured channels than those channels predicted via typical ray-tracing approaches.