Extreme-MIMO Field Trials in 7 GHz Band: Unlocking the Potential of New Spectrum for 6G

Abstract

The frequency range around 7 GHz has emerged as a promising upper mid-band spectrum for 6th generation (6G), offering a practical balance between coverage and capacity. To fully exploit this band, however, future systems require substantially stronger beamforming and spatial multiplexing capability than today's 5G 64-port commercial deployments. This article investigates extreme multiple-input multiple-output (X-MIMO) with 256 digital ports as a practical 6G architecture for 7 GHz operation. First, through system-level simulations, we examine the throughput benefits and design trade-offs of increasing the number of base station (BS) and user equipment (UE) digital antenna ports, including comparisons between 128-port and 256-port configurations. We then present a 256-port 7 GHz BS and UE prototype and report field-trial results obtained in urban outdoor environments. The measurements demonstrate the feasibility of 8-layer downlink single-user MIMO over a 100 MHz bandwidth, achieving more than 3 Gbps for a single user under urban outdoor propagation conditions. Channel analysis based on measured data further suggests how the large digital aperture of X-MIMO supports high-order spatial multiplexing even with limited dominant angular clusters. Finally, we identify key challenges and outline research directions toward practical deployment of 7 GHz X-MIMO systems for 6G.

Figures (5)

• Figure 1: Comparison of RU antenna architectures for 5G C-band (e.g., 3.5 GHz) and 6G at 7 GHz. For 6G at 7 GHz, two antenna architecture options are also presented: 256T256R and 128T128R.
• Figure 2: X-MIMO system-level simulation results for MU-MIMO under two ISD scenarios (200 m and 500 m), with two user densities of 10 and 32 UEs per cell.
• Figure 3: X-MIMO testbed showing the BS and UE platforms for 7 GHz field tests.
• Figure 4: Field test setup, where the 7 GHz prototype BS is mounted on rooftops at the Samsung Seoul Campus, South Korea (left) and Samsung Plano Campus, TX, USA (right). Two UE locations are also indicated, where 8-layer peak data rates were achieved, along with the corresponding dominant signal-path clusters. The measured field-test result of 3.05 Gbps (averaged over one minute) and the corresponding constellation maps for 8-layer with 256QAM are presented, captured at the UE.
• Figure 5: Power-angular profile heatmaps and DFT beams used for 8-layer multiplexing at two UE locations across two measurement sites: (a) Seoul and (b) Plano, where a peak downlink data rate of 3 Gbps is achieved with 8-layer SU-MIMO transmission.