Performance Analysis of LBT with Limited Reservation Signal Duration for Fair LTE-LAA/Wi-Fi Coexistence
Due to increasing demand for throughput of cellular networks, the 3GPP consortium has developed LTE-LAA technology which allows LTE networks to use unlicensed frequency bands in 5 GHz spectrum for data transmission. Since this part of spectrum is already used by Wi-Fi networks, LTE-LAA introduces listen-before-talk (LBT) channel access mechanism for fair channel sharing. LBT is based on CSMA/CA and uses binary exponential backoff similar to Wi-Fi. However, there are some important differences. First, by default, LTE-LAA transmission is longer than Wi-Fi one. Second, due to technology constraints, LTE-LAA data transmission in unlicensed spectrum can only be started at the licensed spectrum slot boundaries (LSSBs). If the LTE-LAA BS remains silent between the end of backoff procedure and LSSB, some Wi-Fi stations may occupy the channel. In many papers, to save the channel for the LTE-LAA transmission, it is proposed to send reservation signal until the closest LSSB after the backoff procedure finish. Because of aforementioned differences, channel resource sharing between LTE-LAA and Wi-Fi devices appears to be unfair. In this paper, we propose to limit the reservation signal duration in order to achieve fair LTE-LAA/Wi-Fi coexistence. We implement the proposed solution in the ns-3 simulator and prove its efficiency in different scenarios.