Adaptive Listen-Before-Talk (LBT) scheme for LTE and Wi-Fi systems coexisting in unlicensed band

Abstract

Listen-Before-Talk (LBT) protocol is an essential mechanism that allows Wi-Fi and LTE systems to share the unlicensed band while maintaining the performance of each individual system. However, a conventional LBT mechanism in this coexisting environment operates with the fixed channel occupancy time (COT) even under the varying traffic load in each system. In practice, if COT is set too short or large, one of two systems becomes inefficient when it is overloaded. Furthermore, Wi-Fi and LTE systems operate with different back-off mechanisms, which may violate the requirement of fair-coexistence. It implies that the operational parameters in LBT protocol must be dynamically adapted to the varying traffic load and back-off window size of Wi-Fi system. Toward this end, we propose an adaptive LBT protocol that can increase the overall system throughput without compromising a performance of the Wi-Fi system in the coexisting environment. Two different adaptation mechanisms, on-off adaptation for COT of LTE system and short-long adaptation for idle time (IT), are designed to implement the adaptive LBT scheme. Our simulation results demonstrate that the overall system throughput can be improved by 30–105% depending on the traffic load, while warranting the performance of the Wi-Fi system.