| dc.description.abstract | Due to the steady increase of mobile traffic demand, deploying the 5G New Radio (NR) in unlicensed spectrum is an intuitive approach to solve the bandwidth shortage problem in the Sub-6 GHz licensed spectrum. However, for the requirement of ultra-reliable and low latency communication (URLLC) service, the unreliable transmission and unpredictable delay caused by interference in the unlicensed spectrum are intolerant. This dissertation focuses on unlicensed spectrum. The coexistence problem between the Licensed Assisted Access (LAA) and the WiFi is analyzed firstly and then a solution to promote network performance is proposed. The Listen-Before-Talk (LBT) mechanism adopted by the LAA is not suitable for the URLLC service because the device may suffer a long waiting time before transmission. In literatures, the channel reservation approach with the omnidirectional antenna is a potential solution that continuously occupies channel(s) in the unlicensed spectrum to ensure URLLC transmission at any time. However, this approach is unfair, and in the high interference environment, the success channel reservation probability is unacceptable. Therefore, this dissertation considers the multiple channel reservation approach with beam-based antenna and proposes an analytical model to analyze the performance thoroughly. By introducing the fundamental beamforming antenna technology, the success channel reservation probability is indeed improved and the impact to the WiFi is also reduced. The results show that the success channel reservation probability can reach as high as 100% and the impact on the WiFi can be minimized by a specific antenna combination in high interference environment.
In addition, based on the frame based equipment (FBE) scheme, the 3GPP Release-17 proposes a user equipment-initiated channel occupancy time to increase channel utilization in the unlicensed spectrum. However, the increase of WiFi traffic will degrade the URLLC reliability. Therefore, this dissertation proposes a transmit/receive switching scheme and a fixed frame period offset adjustment scheme to promote the FBE reliability. Considering fairness, four strategies are introduced to balance the FBE reliability and the impact on WiFi. The results show that compared with the legacy FBE, the URLLC reliability is significantly improved by 20% in the high interference environment. | en_US |