Performance evaluation of Ultra-Reliable Low-Latency Communication over unlicensed spectrum

We consider in this paper the transport of Ultra-Reliable Low-Latency Communication (URLLC) uplink traffic over unlicensed spectrum. We specifically consider Licensed Assisted Access (LAA) system and study the feasibility of the strict reliability and delay requirements by the means of an exact formulation which incorporates the use of a timer tracking the lifetime of each packet and identifying delay budget violation. When the delay constraint is too tight and traffic density is high, unlicensed spectrum alone is not sufficient, hence we propose the use of SG licensed spectrum to compensate for the lacking resources. We incorporate this usage of licensed spectrum for delayed packets in the model and show how to calculate performance metrics for a given amount of additional licensed resources using grant-free allocation. We validate our analytical models with simulations and dimension the joint unlicensed/licensed system resources so as to meet both reliability and delay constraints.