Space Diversity Gain in Urban Area Low Elevation Links for Surveillance Applications

In this communication we quantify the carrier-to-noise ratio, CNR, gains achieved using space diversity in a link reproducing the propagation conditions between a surveillance aerial vehicle, manned or unmanned, and a ground control station in an urban area at low elevation angles, in the 1-4 deg. range. The receiver is assumed to be at street level, i.e., it undergoes strong blockage effects. Such link differs from others, e.g., satellite or terrestrial, thus requiring an ad-hoc analysis including comprehensive measurements. Here, we describe a continuous wave, CW, measurement campaign where we used a four-channel receiver, i.e., we analyzed a 1 × 4 SIMO configuration. First, the correlation between branches was studied and then, we went on to verify the incremental CNR gains achieved by increasing the number of diversity branches. We also paid attention to the influence of the elevation angle within the limited elevation range considered. Moreover, for reference, we present a comparison with the theoretical diversity gains corresponding to four uncorrelated Rayleigh fading channels. In this study three usual combining strategies were also assessed: selection, SC, equal-gain, EGC, and maximal ratio, MRC.