Modeling, Simulation and Fairness Analysis of Wi-Fi and Unlicensed LTE Coexistence

Coexistence of small-cell LTE and Wi-Fi networks in unlicensed bands at $5$ GHz is a topic of active interest, primarily driven by industry groups affiliated with the two (cellular and Wi-Fi) segments. A notable alternative to the 3GPP Rel. 13 defined LTE-Licensed Assisted Access (LTE-LAA) mechanism for coexistence is the unlicensed LTE (LTE-U) Forum \cite{lteuforum} that prescribed Carrier Sense Adaptive Transmission (CSAT) whereby LTE utilizes the unlicensed band as a supplemental downlink unlicensed carrier (to enhance downlink data rate) to normal operation using licensed spectrum. In this work, we provide a new analytical model for performance analysis of unlicensed LTE with fixed duty cycling (LTE-DC) in coexistence with Wi-Fi. Further, the analytical results are cross-validated with ns-3 (www.nsnam.org) based simulation results using a newly developed coexistence stack. Thereafter, notions of {\em fair coexistence} are investigated that can be achieved by tuning the LTE duty cycle. The results show that as the number of Wi-Fi nodes increases, the Wi-Fi network in coexistence with LTE-DC with 0.5 duty cycling achieves a higher throughput than with an identical Wi-Fi network.