Prof. Lin CAI from Illinois Institute of Technology, Chicago, USA gave a talk entitled “Reinforcement Learning for Efficient and Fair Coexistence of LET-LAA and WiFi” at the Faculty of Science and Technology on the 8th August 2019. At the seminar, Prof. Cai shared her latest research results in the fields of wireless access networks. She introduced the multiple ways to achieve coexistence of Long-Term Evolution over Licensed Assisted Access (LET-LAA) and WiFi. Then she presented the system model and problem formulation to analyze and evaluate the performance of coexistence of LET-LAA and Wi-Fi. Reinforcement learning was introduced to solve the complex problem。Through intelligently turning the contention windows of both LET-LAA users and Wi-Fi users, the efficient and fair coexistence can be achieved. Extensive simulation results have been shown to demonstrate the performance improvement of the proposed method.