Wireless Cable Method for High-Order MIMO Terminals Based on Particle Swarm Optimization Algorithm

Conducted cable setups have been dominantly utilized in the industry for performance testing of multiple-input-multiple-output (MIMO) terminals. The wireless cable method, which can achieve cable connection functionality without actual radio frequency cable connections, is a promising alternative. To date, the wireless method has been only discussed for <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> MIMO terminals in the literature. However, the algorithm is not directly applicable for high-order MIMO terminals, due to the high computation complexity to determine the calibration matrix and high system cost to implement the calibration matrix. In this paper, an efficient particle swarm optimization (PSO) algorithm is proposed to determine the calibration matrix for high-order MIMO systems. Furthermore, a novel implementation of the calibration matrix in the radio channel emulator is proposed, which can significantly reduce the system cost. To validate the proposed algorithm, two MIMO mockups, each equipped with four antennas, were measured in an anechoic chamber. The measured results demonstrated the effectiveness of the PSO algorithm to establish wireless cable connections for <inline-formula> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> MIMO terminals.