LBT Switching Procedures for New Radio-Based Access to Unlicensed Spectrum

Abstract

Two channel access procedures are being considered for New Radio-based access to unlicensed spectrum (NR-U) in millimeter-wave (mmWave) bands: omnidirectional Listen-Before-Talk (omniLBT) and directional LBT (dirLBT), which differ on the type of physical carrier sense. Under beam-based transmissions, omniLBT is overprotective and reduces spatial reuse due to exposed node situations, while dirLBT enables spatial reuse, but may create hidden node problems. To address the omniLBT-dirLBT trade-off, this paper proposes LBT switching procedures to dynamically adapt the type of physical carrier sense for LBT in NR-U devices. Switching from dirLBT to omniLBT can be implemented by exploiting already available control messages in NR. Differently, to switch from omniLBT to dirLBT, no information in NR specifications is still available at the time of writing. We define new procedures to measure the overprotection level of spatial reuse provided by omniLBT, and send the switching indication accordingly. Results demonstrate the effectiveness of LBT switching, which enables an independent and dynamic adaptation according to the density and activity of neighboring nodes.