Research On Robust Communication Of Optical Wireless And Millimeter Wave Aggregated System

Driven by the rapid growth of mobile service,a large number of wireless terminal devices are connected to the Internet,making the available wireless spectrum resources increasingly depleted.Optical wireless communication has abundant spectrum resource,and millimeter wave communication also has large bandwidth and high data rate.Aggregated communication system combining optical wireless and millimeter wave can take advantage of their spectrum to cope with the high traffic demand in the future.However,in practice,the channel estimation of the aggregated system will affect the communication performance due to the existence of estimation errors.In this thesis,we address the challenges of bounded estimation error and unbounded estimation error in aggregated system,and investigate beamforming schemes for robust communication in aggregated systems to address the degradation of communication performance caused by channel estimation errors and provide a theoretical basis for further research on aggregated communication system.The main research contents and innovations of this thesis are as following:(1)An outdoor aggregated communication system model based on optical wireless and millimeter wave is proposed,and a robust beamforming scheme under perfect channel state information(CSI)when the aggregated system satisfies quality of service(Qo S)is investigated.To achieve the purpose of robust transmission,the minimum transmit power of the aggregated system to reach the Qo S threshold rate needs to be known,and a robust optimization problem is established with the threshold rate as a constraint.Simulation results show that: the power allocated to the optical wireless link and the millimeter wave link is the same under the optimal power allocation;the optical wireless link will be limited by the maximum operating current of the laser transmitter,and the allocated power will not change after increasing to the threshold value,and the excess power will be allocated to the millimeter wave link;increasing the number of transmitting antennas on either link reduces the total transmit power of the aggregated system,but the power allocated to the optical wireless link and the millimeter wave link remains the same.(2)A robust beamforming scheme for the aggregated system is proposed to address the challenge of bounded estimation errors in the channel of the aggregated system in practical applications.The bounded error in the constraint is first eliminated using Slemma,then the original robust problem is modeled as a convex semidefinite programming(SDP)problem by semidefinite relaxation(SDR),and finally a successive convex approximation(SCA)is used to iterate over the SDP problem to obtain the optimal solution.The simulation results show that the scheme can guarantee the robust transmission of the aggregated system,and the power allocated to the optical wireless link and the millimeter wave link is the same;the change of the number of transmitting antennas does not affect the power allocation ratio between the two links.(3)A robust beamforming scheme for aggregated systems is proposed to address the challenge of unbounded errors in the channels of aggregated system in practical applications.By converting the robust problem into an associated outer optimal value problem and an inner power minimization problem,the probabilistic constraints are then transformed into a combination of convex constraints by using Bernstein-type Inequality(BTI)and Large Deviation Inequality(LDI),respectively.The golden section search(GSS)algorithm is then used to obtain the optimal solution.The simulation results show that the scheme can guarantee the robust transmission of the aggregated system,and the power allocated to the optical wireless link and the millimeter wave link is the same;the change of the number of transmitting antennas does not affect the power allocation ratio between the two links.There are 22 figures,9 tables and 103 references in this thesis.