Abstract
Due to narrow beamwidth and channel sparseness, millimeter-wave receivers will detect much less multipath than their microwave counterparts, fundamentally changing the small-scale fading properties. By corollary, the de facto Rayleigh-Rice model, which assumes a rich multipath environment interpreted by the Clarke-Jakes omnidirectional ring of scatterers, does not provide an accurate description of this fading nor of the correlation distance that it predicts. Rather, a model interpreted by a directional ring of scatterers, recently proposed in seminal work by Va et al., theoretically demonstrated a strong dependence of correlation distance on beamwidth. To support Va's model through actual measurement, we conducted an exhaustive measurement campaign in five different environments - three indoor and two outdoor - with our 60 GHz 3D double-directional channel sounder, compiling over 36,000 channel captures. By exploiting the super-resolution capabilities of the channel sounder, we were the first, to our knowledge, to measure correlation distance as a function of continuous beamwidth. We showed that for narrow beamwidth, correlation was maintained for much longer distances than predicted by the Rayleigh-Rice model, validating Va's model. As the beamwidth approached omnidirectionality, with increasing number of multipath detected, the behavior indeed approached the Rayleigh-Rice model.
Highlights
CHANNEL MEASUREMENTSThe receiver features a circular array of 16 horn antennas with 22.5◦ beamwidth, rendering a synthesized azimuth field-of-view (FoV) of 360◦ and 45◦ in elevation
5G millimeter-wave channels experience much greater path loss than sub 6-GHz channels [1], [2]
The autocorrelation function (ACF) is derived from measurements or models for small-scale fading, a phenomenon that refers to fluctuations in the received signal that occur over displacements on the order of several wavelengths due to multipath interference [6]
Summary
The receiver features a circular array of 16 horn antennas with 22.5◦ beamwidth, rendering a synthesized azimuth field-of-view (FoV) of 360◦ and 45◦ in elevation. The transmitter was almost identical except that it featured a semicircular array of only 8 horns, limiting the azimuth FoV to 180◦. The sampled signal was matched filtered with the codeword to generate a complexvalued channel impulse response (CIR) as a function of delay. The codeword was electronically switched through each pair of transmitter and receiver horns in sequence, resulting in 16 × 8 = 128 CIRs, which is referred to as an acquisition. Photograph of the T array and R array of our 60 GHz 3D double-directional switched-array channel sounder collecting measurements in the Laboratory environment. Transmit power of 20 dBm, the maximum measurable path loss of the system was 162.2 dB when factoring in antenna gain, processing gain, system noise, and remaining components of the link budget
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