Enhancing NR Physical-Layer Key Generation via Beamwidth Adaptations

The fifth-generation new radio (NR) cellular communication introduces numerous advancements over Long Term Evolution and earlier technologies. It enables more flexible resource scheduling across multiple dimensions, with beamspace transmissions and time-frequency numerology selection as representative techniques. However, lightweight physical-layer secure transmission in NR remains under investigation, particularly taking NR beamspace into account. In this study, we propose an efficient beamwidth adaptation scheme for NR physical-layer wireless key generation (KG). Given the pivotal role of NR beamspace in determining the channel probing window in the spatial dimension, it directly influences channel probing results and, consequently, KG efficiency. To address this issue, we study NR beamwidth adaptation for enhancing KG performance. Specifically, we optimize NR beamwidth to maximize secrecy-delay efficiency, revealing the tradeoff involved in adapting beamwidth, where smaller beamwidth improves channel estimation accuracy but increases beam sweeping delay.