NR-U and Wi-Fi Unlicensed Spectrum Sharing: Design Challenges and Solutions

This paper presents an in-depth analysis of the Listen-Before-Talk (LBT) procedures required for cellular technologies operating in the unlicensed spectrum. We specifically investigate the 5G New Radio Unlicensed Standalone (NR-U SA) design under the most recent 3GPP standard-compliant Type 1 Channel Access Procedure (CAP). We highlight and address key challenges in adapting the asynchronous Type 1 CAP (i.e., load-based CAP) to NR-U’s synchronous slot-based framework and propose the Scheduled Type 1 CAP, which introduces a novel scheduling mechanism and implementation of additional sensing to facilitate seamless integration. We carry out our performance evaluation using a full-stack end-to-end network simulator and construct a realistic 3GPP-compliant coexistence scenario in which 5G NR-U SA and Wi-Fi networks operate indoors in unlicensed sub-7 GHz bands. The users of the 5G NR-U SA and Wi-Fi networks demand eXtended Reality applications. Through an extensive evaluation study, we analyse the interplay between the NR-U numerologies and the CAPs used in shared channel access and evaluate their impact on the end-to-end performance of both technologies by considering various quality of service metrics. The results reveal some of the main pitfalls of the LBT procedure defined by 3GPP in TS 37.213 and demonstrate the clear advantages of the proposed Scheduled Type 1 CAP. Our work provides valuable insights into CAPs for shared spectrum, proposes standard-compliant solutions, and lays the groundwork for future research by introducing a pioneering open-source network simulation platform for evaluating NR-U SA coexistence scenarios with the Scheduled Type 1 CAP.