A Hybrid Adaptive Channel Access (HyACA) Mechanism for LTE-U and WiFi Coexistence Systems

Abstract

This article proposes a hybrid adaptive channel access (HyACA) mechanism for improving the channel access performance of an LTE-U and WiFi coexistence system. To support the HyACA mechanism, a modified time-frequency channel structure as well as a modified LBT functionality is first introduced for channel access in the coexistence system. To ensure channel access fairness, a dynamic channel switch (DCS) functionality and an adaptive almost-blank-subframe (AABS) functionality are further proposed to control the channel access under different traffic loads. Under low traffic load, HyACA uses the DCS functionality. Under high traffic load, HyACA uses the AABS functionality. To judge the traffic load status of the coexistence system, a criterion based on the average channel occupation time is introduced, and a calculation model is derived to determine the average channel occupation time. Moreover, another calculation model is derived to calculate the number of ABSs to be reserved in each LTE-U frame of a frame block. Through simulation results, it is demonstrated that the proposed HyACA mechanism can achieve better fairness and throughput performance than the static ABS mechanism, and better throughput performance than the LAA Cat.3 LBT mechanism while ensuring access fairness.