Research On Coexistence Of LTE And Wi-Fi In Unlicensed Bands

With the continuous development of wireless communication, spectrum resource scarcity is getting more and more attention. How to deal with the growing data traffic in cellular networks is a hot topic today. To deploy LTE in unlicensed bands can get a more efficient use of resources, increase the system capacity, and provide a new way to solve the traffic problem.In this thesis, the coexistence performance of WLAN and LTE in unlicensed band is discussed. Firstly, the common WLAN system in unlicensed band is introduced, and the principle of the carrier sensing and collision avoidance is reviewed. Because of the competition mechanism, WLAN system gets low spectrum utilization, and is easily interfered. Then it is shown that deploying LTE may cause a serious influence on the unlicensed bands. In order to solve the problem, we discuss the techniques and methods used for reducing interference in heterogeneous networks.The coexistence of WLAN and LTE is modeled and simulated, the performance of each system is observed respectively. While the channel energy detected by WLAN device is higher than the threshold during the LTE transmission period, the WLAN system has to be in the listen mode, and does not to transmit data. The throughput of WLAN decreases rapidly.In order to solve this coexistence problem, were view the eICIC technology used in LTE network first, and then study the technical scheme of almost blank subframe based on the time domain eICIC, We also proposed an improved algorithmusing blank subframe technology in unlicensed bands. It reduces the interference of WLAN system by setting different number of blank subframes during LTE transmission. Finally we simulate the coexistence system, and find that using ABS technology can reduce the impact on the coexistence system.Then we find that using low-power subframer-ABS technology in unlicensed bands at LTE downlink transmission can reduce the interference. We build the system model, use the semi-dynamic simulation,and validate the improved coexistence system’s performance.Finally we study the fractional power control scheme for the uplink of the cellular network, propose an improved uplink power control method to reduce the interference in unlicensed bands considering the unlicensed band interference characteristics.