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, unlicensed spectrum alone is not sufficient when the traffic density is high and we propose the use of 5G 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 the performances for a given amount of additional 5G resources for a grant-free or a grant-based allocation. We validate our analytical models numerically and dimension the joint licensed/unlicensed system resources so as to meet both reliability and delay constraints.
We study in this paper the coexistence of Ultra Reliable Low Latency Communications (URLLC) and enhanced Mobile Broadband (eMBB) services in unlicensed spectrum for the uplink transmission in a 5G smart-factory scenario. We first model the medium access for both services coexisting in unlicensed spectrum and evaluate their performance metrics: high reliability and stringent delay budget for URLLC and throughput for eMBB. The results show that URLLC requirements cannot be met even for low eMBB traffic load. In order to cope with this, we explore a preemptive approach where URLLC packets are transmitted with high power when their delay approaches the delay constraint, increasing their chance of being successfully received. This approach enhances URLLC performance, with a little impact on that of eMBB. We finally show that with a good calibration of some system parameters can lead to an optimal performance for both services.
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