Effect of Space Diversity for Fading Mitigation at 40 and 60 GHz Indoor Channels Miguel Riob´ o Prieto * , Rob Hofman *† , Manuel Garc´ ıa S´ anchez * , ´ I˜ nigo Cu´ ı˜ nas * , Isabel Exp´ osito P´ erez * , Jo Verhaevert † , * AtlanTTic Research Center, Universidade de Vigo, Vigo, Spain, manuel.garciasanchez@uvigo.es* † IDLab, Department of Information Technology, Ghent University-imec, Ghent, Belgium, Jo.Verhaevert@Ugent.be* Abstract—Measurements at 5G Frequency Range 2 (FR2) and beyond (41.5 GHz and 60.5 GHz) were carried out in order to study how space diversity can be applied to compensate for the challenging conditions at those frequencies. Several indoor scenarios were analyzed, including Line-Of-Sight (LOS) and Non-Line-Of-Sight (NLOS). When considering an outage of 1%, space diversity was found to be a suitable impairment mitigation technique. Improvements in signal signal levels with increments from 7.98 dB up to 15.18 dB, depending on the case study in question were observed. Index Terms—propagation, measurements, 5G, space diversity. I. I NTRODUCTION With the recent release of 5G, more and more internet providers are switching to it in order to provide better data rates and thus, better service to their customers. Of the two Frequency Ranges (FR) under investigation, only one is currently in use: FR1, which goes from 450 MHz to 6 GHz. However, there are plans to implement the Frequency Range 2 (FR2) allocated between 24.25 and 52.6 GHz, and even beyond. It is well-known that fadings at such frequencies are not neg- ligible as not only the path losses are higher when compared with the frequencies on FR1, but also people crossing the radio link will affect it to a greater extent. All these impairments will challenge mobile network designers as they search for the optimal cellular coverage. One of the possible solutions for this problem is the use of diversity. Having more than one signal path helps in raising the overall signal level when the conditions are not ideal. Polarization diversity with two antennas has already been considered in the past [1] at these frequencies, showing that it can be a good option to improve the signal’s level. Space diversity has also been studied at 40 GHz and 60 GHz in [2] and [3] respectively. However, the envelope of the signal to compute the diversity gain was not obtained simultaneously with several antennas, but in different measurements with the same antenna. This limits the validity of the study as coupling among antennas is not considered. By using a setup with one transmitting antenna and three receiving ones, this work aims at filling the gaps left by those previous reasearchs and complement them in order to have a greater understanding of the radio channel at such frequencies. This paper is structured as follows: An explanation of the Fig. 1. Representation of the rail used to move the receiving antennas. measurement setup and environment is given in Section II. Diversity and processing procedure are explained in Section III and the results are presented in Section IV, while final conclusions are given in Section V. II. MEASUREMENT SETUP AND ENVIRONMENT In this section of the paper both the measurement setup and environment are discussed. A. Measurement setup In order to measure the channel response, a Rohde & Schwarz ZVA67 4-port Vector Network Analyzer (VNA) was used. As we wanted a three antenna system to observe the diversity, three S-parameters, to simulate three different branches, were simultaneously obtained: S 21 , S 31 and S 41 ; connecting the transmitting antenna to port 1 and the three receiving ones to ports 2, 3 and 4. The experiment was performed in wideband with two different central frequencies: 41.5 GHz and 60.5 GHz, both with a 3 GHz bandwidth and 1001 measured frequency points, which let us with a frequency resolution of 3 MHz. Aside from the frequency, the setup was very similar for both experiments, having one directive antenna transmitting on the ceiling with a 3 dB beamwidth of 20º and three receiving ones on a moving rail on the floor (see Figure 1). The antennas at the receiving end were omnidirectional for both cases and allocated on a plastic support with the shape of a triangle, so that the distances between the antennas centers were 3.75 cm and 2.5 cm for the 40 GHz and 60 GHz mea- surement respectively. This is five times their corresponding wavelengths. The parameters were measured according to the labels on Figure 2, being S 21 the one corresponding to antenna number 2 and so on.