Research On Interference Management In Next Generation Wireless Networks

The main features of next generation mobile communication networks include dense deployment and large-scale connections.However,these features will introduce more interference,thus effective interference management technology is very important.This thesis mainly studies the interference management problems in two scenarios: interference problems in densely deployed wireless network systems with random access nature;and interference problems for aerial high-speed mobile UAVs terminal.The specific research results and contributions are summarized as follows:The next generation wireless WLAN network,802.11 ax,aims to improve the spectrum efficiency and system throughput in the hotspots and provide users with stable high-speed data transmission services,which will become part of the 5G network.Dense deployment is one of the effective ways to increase area throughput.However,due to the nature of random access,the 802.11 protocol architecture limits the opportunities for more parallel transmissions.Started from the physical layer,this thesis designed a new control frame format and proposed a signaling transmission mechanism based on OFDM.In the proposed transmission mechanism,the stations that can transmit in parallel are detected based on the RTS/CTS handshake process and the control frame information is mapped to a single subcarrier of the OFDM symbol,so that the originally conflicting control frame can be received correctly,thereby providing more parallel transmission and increasing area throughput.The proposed mechanism was implemented based on the WARP platform.By constructing a 3-node prototype experimental system,the feasibility of proposed mechanism is verified in the real wireless transmission environment.The experimental results show that the proposed transmission mechanism can guarantee that the control frame can still be demodulated under the interference condition.A system-level simulation platform was built based on NS3,which verifies the effectiveness of the proposed mechanism.UAV autonomous flight has broad application prospects.The 5G network provides large connectivity,high throughput,extremely low latency,and high reliability features,which can provide communication services for UAVs.Compared with terrestrial users,aerial users are more seriously interfered,thus the quality of downlink communication cannot be guaranteed.Therefore,this thesis studied the use of millimeter-wave Massive MIMO technology to provide downlink communication services for UAVs,among them,beam tracking and inter-beam interference cancellation are the keys for UAVs applications.This thesis proposed a two-stage hybrid beamforming technique assisted by position information.In the first stage,The base station selects the beam codebook with the largest gain in the direction of UAV according to the position information of UAV;in the second stage,the base station obtains the equivalent digital domain channel matrix according to the position information and the beam selection result of the first stage,and then digital beamforming is performed based on the ZF criterion.The proposed method does not need to obtain accurate channel state information,and is suitable for aerial high-speed moving scenario with a large channel estimation error.The beam tracking performance of the proposed scheme was simulated,in which the UAV is at different distances from the base station and moves at a speed of 20m/s along a circular trajectory.In addition,the performance of the proposed twostage hybrid beamforming algorithm based on position information was simulated.The simulation results show that the multi-level beam tracking scheme assisted by position information can significantly improve the performance of long-range beam tracking,and the two-stage hybrid beamforming algorithm can still achieve better performance under the condition of limited channel information.