A Portable 28-GHz Channel Sounder Platform and Measurement Results From Close-to-Ground Field Tests

Abstract

This article describes a novel, bespoke, and low-cost 28 GHz RF TX and RX front end design that has been combined with a commercial Software Defined Radio and Raspberry Pi controller to realize a portable propagation measurement system for the 28 GHz band. The complete sounder system can resolve an impulse from RX powers down to -107 dBm (3 dB impulse SNR) and the sounder TX can generate a signal of -8 dBm. Therefore, using 20 dBi antennas supports path loss measurements of 139 dB. The sounder can resolve time domain reflections to 33 ns in a channel measurement bandwidth of 60 MHz, producing both time domain and frequency domain results. The complete sounding system has been used to perform close-to-ground RF channel measurements, with propagation loss models and time domain impulses extracted. Close-to-ground measurement is an underreported area of propagation research that is relevant for novel use-cases, such as in military applications or for mobile device-to-device communications. A key initial finding from the trials is that the path losses for 28 GHz indoor and outdoor links at circa 70 cm above ground seem close to that of free space, with very few strong reflections with delays exceeding 33 ns.