R-SplitC: Collision Minimization for Cellular Communication in Unlicensed Spectrum

Abstract

The 3rd generation partnership project (3GPP) has standardized 5G new radio in unlicensed spectrum (NR-U) that uses a wide unlicensed spectrum as an alternative solution to the insufficient bandwidth problem of the existing NR. NR-U has a listen-before-talk (LBT) operation similar to the carrier sense multiple access with collision avoidance (CSMA/CA) operation of Wi-Fi. It allows nodes to transmit only after LBT success. NR-U suffers from the collision issue because its channel access mechanism is similar to that of Wi-Fi. Wi-Fi solves the collision problem through the request-to-send/clear-to-send (RTS/CTS) mechanism. However, NR-U has no way of solving the collision problem. As a result, NR-U suffers severe performance degradation due to collisions as the number of contending nodes increases. In this paper, we propose to use an extended and split reservation signal (RS) for reservation in NR-U that consists of front RS and rear RS and design a new collision minimization scheme, termed R-SplitC, that contains two components: new RS structure and contention window size (CWS) control. The new RS structure helps to minimize collisions in NR-U transmissions, and CWS control works to protect the performance of other communication technologies such as Wi-Fi. We mathematically analyze and evaluate the performance of our scheme and confirm that R-SplitC improves network throughput by up to 99.3% compared to the baseline RS scheme without degrading Wi-Fi performance.