A Wideband Distributed Massive MIMO Channel Sounder for Communication and Sensing

Channel sounding is a vital step in the design and deployment of wireless communication systems. In this article, we present the design and implementation of a coherent distributed massive multiple-input-multiple-output (MIMO) channel sounder operating at 5 and 6GHz with a bandwidth of 400MHz based on the NI USRP X410. Through the integration of multiple transceiver chains and radio frequency (RF) switches, the design facilitates the use of a larger number of antennas without significant compromise in dynamic capability. Our current implementation is capable of measuring thousands of antenna combinations in tens of milliseconds. Every radio frequency switch is seamlessly integrated with a 16-element antenna array, allowing phase-coherent multinode dual-polarized double-directional dynamic channel measurements for multistatic integrated sensing and communication (ISAC) applications. In addition, the channel sounder features real-time processing to reduce the data stream to the host computer and increase the signal-to-noise ratio. The correct operation of the sounder is demonstrated through two measurements in an indoor laboratory environment. The first measurement entails a single-antenna robot as a transmitter and 128 distributed receiving antennas. The second measurement demonstrates a passive sensing scenario with a walking person. We evaluate the results of both measurements using the super-resolution algorithm space-alternating generalized expectation maximization (SAGE). The results demonstrate the great potential of the presented sounding system for providing high-quality radio channel measurements, contributing to high-resolution channel estimation, characterization, and active and passive sensing in realistic and dynamic scenarios.