Experimental Evaluation of Simplified Per-Subarray Analog Beam Training for LoS-MIMO with Partial use of Reflective Paths

This research introduces a simplified beam training algorithm designed for line-of-sight (LoS) multi-input and multi-output (MIMO) systems, incorporating subarray-based beamforming capabilities at both the transmitter (Tx) and receiver (Rx), Typically, a conventional beam training algorithm is employed to maximize the signal power of each pair of Tx and Rx subarrays, leading to a scenario where each pair of subarrays directs its beam towards each other. However, in LoS-MIMO scenarios, the selected beams may not always be sufficient to achieve higher channel capacity due to spatial correlation dependency on the distance between Tx and Rx. To address this limitation, we have proposed leveraging reflection paths, such as ground reflection paths, and presented an effective beam training algorithm to implement this concept in real scenarios without requiring knowledge of the distance. In this paper, we propose a simplied beam training algorithm where the reflective direction determined by one subarray is shared with the other subarray. Experimental evaluation demonstrates for the first time that higher spatial multiplexing gain can be achieved without high dependency on the distance between TX and RX by controlling analog beam of each subarray appropriately under the existence of reflective paths.