Measurement-Based Channel Characterization for 5G Downlink Based on Passive Sounding in Sub-6 GHz 5G Commercial Networks

Under the impetus of global communications organizations, 5G mobile communications becomes a hot technology and moves towards commercial use. In this paper, we propose an efficient downlink channel characterization scheme based on passive sounding in sub-6 GHz 5G commercial network. We first introduce the framework of passive sounding system containing a space-time-division multiplexing (STDM) sounder. Then we elaborate the extraction procedure for 5G downlink signals including synchronization signal block (SSB) and channel state information reference signal (CSI-RS) according to New Radio (NR) technical specifications proposed by 3GPP. Through a pilot test in the anechoic chamber, we also demonstrate the practice of signal extraction. Besides, we derive a dual-polarimetric space-alternating generalized expectation-maximization (SAGE) algorithm which matches with the passive sounding system for multi-dimensional channel parameter estimation. The estimator performance is analyzed by synthetic channel simulation, and results reveal its high accuracy and robustness. Finally, we verify the feasibility of the proposed scheme through analyzing channel characteristics derived from passive sounding in stationary field measurements respectively conducted in industrial park and parking lot with the 5G commercial network built by China Unicom Communications Corporation (CUCC).