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.

A Comprehensive Survey of Spectrum Sharing Schemes from a Standardization and Implementation Perspective

“…NR-U leverages beam-based transmissions, which enhances spatial reuse but complicates interference management. The directional nature of beams in NR exacerbates the hidden node and exposed node problems in the unlicensed bands [149], [150], and therefore, the coexistence framework with other RATs in the unlicensed bands becomes more challenging. NR-U, like LAA and MulteFire, adheres to LBT requirements to access a channel.…”

“…Based on the results in [156], dirLBT performs better than omniLBT when the network density is low, while with higher densities omniLBT performs more efficiently. Another technique was also proposed in [150] to deal with the omniLBT/dirLBT trade-off, called the LBTswitch, which is a dynamic switching method between omniLBT and dirLBT.…”

New Radio Beam-Based Access to Unlicensed Spectrum: Design Challenges and Solutions

“…ETSI regulation has harmonized the requirements for the 5 GHz band (5.15-5.35 GHz and 5.47-5.725 GHz) and the 60 GHz band (57)(58)(59)(60)(61)(62)(63)(64)(65)(66), as included in [36] and [37], respectively. To enable worldwide regulation-compliant access and satisfy a fair coexistence with the unlicensed systems (Wi-Fi, WiGig, radar) and intra-RAT services, NR-U should fulfill the following regulatory requirements:…”

NR-U and IEEE 802.11 Technologies Coexistence in Unlicensed mmWave Spectrum: Models and Evaluation

“…More studies on omnidirectional versus directional sensing may be scheduled in the context of a future work item in Release-17 [43]. Previous studies in omnidrectional versus directional sensing tradeoffs, are discussed here [44], [45]. At the UE side, instead, we focused on directional sensing, i.e., dirLBT, since differently from the gNB, the UE only has to communicate with its gNB.…”