On the Impact of Listen-Before-Talk on Ultra-Reliable Low-Latency Communications

In this paper, we study the performance of ultrareliable low latency communication (URLLC) for cellular standalone systems in unlicensed bands. Our focus is on the 5 GHz band, adopting a system model in coherence with the MulteFire standard, which essentially is a variant of LTE (Long Term Evolution) for unlicensed band operation.We show that especially the mandatory Listen Before Talk (LBT) procedure is a challenge for achieving low latency communication. Our theoretical analysis indicated that the impact of the LBT procedure prior to downlink transmissions can be significant, taking values of 3- 25 ms for the considered offered load levels. Furthermore, our advanced dynamic system level simulations show that the time spent performing LBT often accounts for 18%-42% of the packet latency budget, depending on the considered outage level and offered traffic. Therefore LBT represents a major challenge for achieving URLLC-alike performance in unlicensed spectrum.