Wireless Relay System Extends High-Speed 5G Coverage Indoors

A new wireless technology could make high-speed 5G networks more accessible in places where signals typically struggle, such as inside buildings or moving vehicles. Researchers have built the first experimental testbed for a system called Wireless Access Backhaul (WAB), which combines different frequency bands to extend coverage without requiring expensive upgrades to existing devices. This approach addresses a key in next-generation networks: high-frequency bands like FR2 (24.25–71 GHz) offer wide bandwidths and multi-gigabit data rates but suffer from severe path loss and penetration issues, making them unreliable in non-line-of-sight conditions. By integrating a wireless relay that uses FR2 for backhaul and FR1 (lower frequencies) for access, the system maintains compatibility with legacy user equipment while improving performance in urban and indoor settings. , detailed in a recent paper, demonstrate that WAB can effectively mitigate the limitations of FR2 links, particularly in uplink transmissions and environments with obstacles.

The core from the experimental campaign is that the WAB architecture successfully extends FR2 coverage while maintaining service transparency for end users. In mobile tests conducted in a vehicular scenario, the system provided reliable connectivity in line-of-sight regions, with end-to-end throughput reaching approximately 50 Mbps in downlink directions. As shown in Figure 3, the throughput strongly correlated with the FR2 backhaul link quality, peaking when the relay had direct visibility of the base station. In non-line-of-sight areas, performance degraded gradually but remained functional where shadowing was not excessively severe, highlighting the system's ability to overcome blockages that would disrupt FR2-only connections. This enables widely available commercial smartphones to access high-frequency networks without costly FR2 modules, a significant advantage for practical deployment.

Ology involved constructing a multi-band WAB testbed using open-source software and commercial off-the-shelf components, assembled without hardware modifications beyond standard 5G parts. The FR2 backhaul segment utilized a commercial customer premises equipment (CPE) operating at 27.2 GHz with 200 MHz bandwidth, connected to a base station installed on a rooftop. The FR1 access link was implemented with an OpenAirInterface gNB on a software-defined radio, providing connectivity to a commercial 5G smartphone. As illustrated in Figure 1, the architecture separated the backhaul and access segments into logically independent networks, with tunneling mechanisms ensuring end-to-end connectivity. This setup allowed the researchers to validate the feasibility of WAB operation in real-world conditions, focusing on vehicular and outdoor-to-indoor scenarios to assess performance under mobility and obstruction.

From the experiments, detailed in Figures 3, 4, and 6, provide concrete data on the system's capabilities. In mobile tests, downlink throughput reached 50 Mbps in line-of-sight zones but dropped to zero in deep non-line-of-sight areas, with block error rates increasing as shown in Figure 4. Uplink throughput averaged around 1 Mbps, limited by the time division duplexing configuration that prioritizes downlink traffic. In outdoor-to-indoor scenarios, the WAB system demonstrated enhanced uplink performance compared to FR2-only configurations, particularly at positions with additional wall attenuation. For instance, at Position 5 in Figure 5, the WAB setup achieved higher uplink spectral efficiency than the FR2 customer premises equipment, as reported in Figure 6a. These confirm that the architecture can mitigate FR2 limitations in challenging indoor environments, offering a practical solution for network densification.

Of this research are significant for the deployment of next-generation wireless networks, as WAB provides a scalable and cost-effective approach to extend high-speed coverage. By enabling multi-band operation, the system allows flexible combinations of FR2's high throughput with FR1's superior penetration and device compatibility, ensuring support for legacy devices. This could accelerate the adoption of 5G-Advanced technologies in dense urban areas, where coverage gaps are common. The testbed's reliance on open-source software and commercial components suggests that widespread implementation may be closer than previously thought, reducing barriers to market deployment. Moreover, the architecture's modular design supports various backhaul technologies, including non-terrestrial networks, enhancing its versatility for future applications.

Despite these promising , the study acknowledges several limitations inherent to the experimental framework. The FR1 access link in the testbed was implemented with prototype software-defined radios operating at low transmit power (20 dBm) and in single-input single-output mode, which constrained downlink performance compared to commercial FR2 systems. As noted in the paper, replacing this with a more powerful, commercial-grade FR1 configuration could improve downlink spectral efficiency, potentially allowing WAB to outperform FR2-only setups in both directions. Additionally, the tests focused on single-hop topologies and did not explore multi-hop scenarios or advanced interference management, areas identified for future work. These limitations highlight the need for further research to optimize resource allocation and integrate additional backhaul technologies for enhanced scalability.