Feasibility of URLLC in Unlicensed Spectrum

Radio spectrum is the most valuable resource for wireless communications. In recent years, due to the proliferation of the wireless communications, spectrum becomes more and more scarce. Thus, more and more initiatives have been taken by standards for shared use of unlicensed spectrums to maximize the spectral efficiency. For shared spectrum access in the unlicensed bands, there is no guaranteed immediate availability for users with packet transmission demands. Also, transmission may be interfered by signals from other users. Thus, the communication latency and reliability would become unpredictable. Ultra-reliability low latency communication (URLLC) is one of three pillars in the fifth generation (5G) communications. Thus, the feasibility of URLLC in unlicensed spectrum is of special interests to the 5G community. In this paper, we first discuss the conventional approaches for URLLC in licensed spectrum. Then we study the possibility of achieving the required low latency in unlicensed spectrum, where the latency of listen before talk (LBT) and downlink transmission are analyzed and simulated at different channel availability scenarios. Finally, we propose to use multiple transmissions with multiple channels to enhance reliability and availability, where the gain of multiple channels is quantified.