Dynamic Contention Window Methods for Improved Coexistence Between LTE and Wi-Fi in Unlicensed Bands

Recently, the 3rd Generation Partnership Project (3GPP) announced standards that permit the Licensed-Assisted Access (LAA) of Long Term Evolution (LTE) to operate over unlicensed spectrum bands. This permission, which is a part of the 5G specifications, is due to the scarcity of the licensed spectrum and the increased use of wireless networks and services. However, these unlicensed bands are mainly occupied by 802.11 based WLAN devices. Thus, challenges arise for the efficient coexistence mechanism to share the same unlicensed band by LAA and Wi-Fi to maintain the quality of service and manage the interference among users. In this work, we propose new variable contention window (CW) methods for LAA to enable the coexistence of LTE and Wi-Fi in a fair manner based on the Wi-Fi statistics. The main novelty of this work is that the knowledge of Wi-Fi activity statistics is exploited to adapt the CW of LAA more effectively. These methods are evaluated based on the 3GPP fairness definition for such coexistence mechanisms under various traffic loads. We show that the fairness depends on the LAA CW size. Further, through simulation results, we show that the proposed schemes are more friendly to the existing Wi-Fi network, in particular for the higher traffic loads, compared with the existing Category 4 Listen-Before-Talk (Cat 4 LBT) algorithm defined in the 3GPP standard and provide higher total throughputs for both coexisting networks, improving the overall network performance.