Static Contention Window Method for Improved LTE-LAA/Wi-Fi Coexistence in Unlicensed Bands

The 3rd Generation Partnership Project (3GPP) has recently defined a Licensed Assisted Access (LAA) scheme to enable Long Term Evolution (LTE) networks to use unlicensed frequency bands. However, the unlicensed bands are mainly occupied by the Wi-Fi technology. Hence, achieving fairness between LAA using LTE (LTE-LAA) and Wi-Fi in the unlicensed bands is a primary challenge. The 3GPP has recently standardised in Release 13 a Listen Before Talk (LBT) algorithm to ensure the fairness among these two technologies (LTE and Wi-Fi) over the unlicensed bands. In this paper, we focus on the downlink performance of LTE-LAA and Wi-Fi with different traffic loads. To achieve not only better fairness but also higher total aggregated throughputs for the coexisting networks, a static Contention Window (CW) selection method based on the fairness definition is proposed. The main novelty of this work is that the knowledge of Wi-Fi activity statistics is exploited effectively to select the CW of LAA. We show that the fairness between LAA and Wi-Fi networks depends on the LAA CW size adaptation criterion. Simulation results validate that the proposed method is effective in LAA/Wi-Fi coexistence scenario, can improve fairness performance and provide higher total aggregated throughputs for both coexisting networks compared with the current Category 4 LBT (Cat 4 LBT) algorithm defined in the 3GPP standard.