An adaptive channel access mechanism for LTE-U and WiFi coexistence in an unlicensed spectrum

Abstract

This paper proposes an adaptive channel access (ACA) mechanism for LTE-U and WiFi coexistence in an unlicensed spectrum. To support the ACA mechanism, we introduce a new time-frequency structure, and a modified listen before talk (MLBT) functionality for channel contention of LTE-U users. Moreover, we also introduce a dynamic channel switch (DCS) sub-mechanism and an adaptive almost blank subframe (AABS) sub-mechanism for LTE-U users to access a channel under different levels of traffic load. The DCS sub-mechanism is intended to avoid an LTE-U user to occupy a channel for too long and thus provide more access opportunities for WiFi users when the traffic load in the network is low. The AABS sub-mechanism is intended to reserve a certain number of subframes in an LTU-U frame for use by WiFi users when the traffic load in the network is high in order to ensure fair access opportunities for WiFi users. To use the DCS and AABS sub-mechanisms, the BS in the LTE-U network and the AP in the WiFi system must report the number of their users to a mobile management entity (MME) in the core network through signaling messages, respectively. Based on the information contained in the received signaling messages, the MME will calculate the current traffic load of LTE-U and WiFi, and based on the traffic load status decide to use different sub-mechanisms in LTE-U. Simulation results show that the proposed ACA mechanism can effectively improve the system performance in terms of average user throughput.