Pioneering Scalable Prototyping for Mid-Band XL-MIMO Systems: Design and Implementation

TL;DR

Addresses the validation gap for mid-band XL-MIMO by presenting a real-time prototype operating with up to $N$ antennas and up to $K$ users, at a bandwidth of 200 MHz in the 6.4–7.2 GHz band. Approach: a scalable SDR-FPGA fusion prototype implements TDD operation, modular BS/UE architecture, and synchronized, distributed processing to support up to 256 transceiver chains. Contributions: comprehensive preliminaries, a detailed prototype design (BS, UE, synchronization), and extensive experiments revealing near-field effects, spatial non-stationarities, real-time uplink/downlink transmission, and high throughput (up to 15.81 Gbps for 12 users) with spectral efficiency near 80 bit/s/Hz. Significance: provides a scalable, programmable testbed aligned with future 6G XL-MIMO standardization and ISAC deployment, enabling distributed processing and flexible deployment across varied scenarios.

Abstract

The mid-band frequency range, combined with extra large-scale multiple-input multiple-output (XL-MIMO), is emerging as a key enabler for future communication systems. Thanks to the advent of new spectrum resources and degrees of freedom brought by the near-field propagation, the mid-band XL-MIMO system is expected to significantly enhance throughput and inherently support advanced functionalities such as integrated sensing and communication. Although theoretical studies have highlighted the benefits of mid-band XL-MIMO systems, the promised performance gains have yet to be validated in practical systems, posing a major challenge to the standardization. In this paper, preliminaries are first discussed, followed by an analysis of key challenges in constructing a real-time prototype system. Subsequently, the design and implementation of a real-time mid-band XL-MIMO prototype system are presented. Benefiting from the novel architecture, the proposed prototype system supports metrics aligned with standardization, including a bandwidth of 200 MHz, up to 1024 antenna elements, and up to 256 transceiver chains. Operating in time-division duplexing (TDD) mode, the prototype enables multiuser communication with support for up to 12 users, while retaining standard communication procedures. Built on software-defined radio (SDR) platforms, the system is programmable and allows for flexible deployment of advanced algorithms. Moreover, the modular architecture ensures high scalability, making the system adaptable to various configurations, including distributed deployments and decentralized signal processing. Experimental results with the proposed prototype system demonstrate real-time digital sample processing at 1167.85 Gbps, a peak data throughput of 15.81 Gbps for 12 users, and a maximal spectral efficiency approaching 80 bit/s/Hz.

Figures (14)

• Figure 1: An example of the proposed frame structure for the prototype system under the subcarrier spacing $\Delta f = 60\ \mathrm{kHz}$, which is a simplified version of the 3GPP 5G NR frame structure.
• Figure 2: Mid-band XL-MIMO systems provide opportunities for high-rate data transmission, ultra-dense connectivity, localization and sensing, and multi-band cooperation.
• Figure 3: Time-frequency resource grids in TDD mode.
• Figure 4: An example of the architecture of the BS side in the proposed prototype system with 256 transceiver chains.
• Figure 5: Part of the array consisting of 112 ($28\times 4$) elements and the radiation patterns at 6.75 GHz.

Theorems & Definitions (1)

• Remark 1