Asymmetric channel characteristics analysis based on wideband channel measurement at 39 GHz in indoor office scenario

Beamforming is an essential part of the fifth-generation (5G) mobile communication technology. And it will continue to play an indispensable role in the sixth-generation (6G) system. Due to unequal numbers of radio frequency (RF) chains between the base station (BS) and the user equipment (UE), asymmetric beam patterns exist between BS and UE. In this case, characteristics of downlink (DL) channel and uplink (UL) channel need to be explored. In this paper, channel measurements have been performed in an indoor office at 39 GHz. In the measurement campaign, a directional antenna and an omni-directional antenna are used to simulate BS and UE respectively. In the line-of-sight (LOS) case, we find that path loss (PL) exponent of UL is 0.3 smaller than DL and intercept of UL is 5 dB larger than DL. The measured PL of UL is higher than DL in most cases. And the difference in measured PL between DL and UL decreases with increasing distance. Meanwhile, the root-mean-square (RMS) delay spread (DS) value of UL is larger than DL under most circumstances and the mean value of the difference is 0.9 ns. In the non-line-of-sight (NLOS) case, PL exponent of UL is 0.2 smaller than DL, and the intercept of UL is 2 dB larger than DL. The difference in measured PL and RMS DS between DL and UL becomes narrowed due to blockage effect. The results of the paper are conductive to get a further understanding of asymmetric channel in millimeter-wave.