Research On Relay Selection Scheme Based On Spatial Channel State Information

With the rapid development of wireless communications and the unmanned aerial vehicle(UAV)technology in recent years,UAV communications become attractive to emergency communication network because of various advantages such as low cost,flexible mobility and line-of-sight(Lo S)environment.In many scenarios and network systems,both military and civilian,UAV communications have high research value.As a relay,the UAV participates in the signal forwarding process where the original communication means cannot achieve the signal transmitted from the source node successfully,and with the assistant of the UAV relay,emergency wireless communications can be realized.However,single relay is often subject to some restrictions,so UAV groups formed as a multi-relay communication system can effectively improve communication performance,in which the relay selection options are of great importance.The main research contents and innovation points are as follows.First of all,in the thesis,aiming at the reliability of UAV relay communication,the relay selection schemes based on spatial channel state information are studied.A communication network system is considered that UAVs act as relay nodes to assist wireless transmissions between the source node and destination node,in which the position of each UAV is different relatively.An optimal relay selection scheme is proposed to improve the channel capacity,and the closed-form outage probability expressions are derived over Rician fading channels considering both large-scale fading and small-scale fading.In addition,numerical results show that both the channel capacity and outage probability performance of the proposed relay selection scheme are strictly better than that of the traditional round-robin scheme.Secondly,the thesis studies the UAV multi-relay cooperative communication system with channel estimation errors.As the channel estimation method cannot reach the absolutely ideal situation,the channel state information is inaccurate.On the basis of considering the spatial channel state information with channel estimation error,including large-scale fading and small-scale fading,an optimal UAV multi-relay cooperative precoding scheme is proposed.Meanwhile,the system outage probability under this scheme is derived to obtain a closed-form solution.After simulation verification,the existence of channel estimation error has a certain adverse impact on the communication performance,and the numerical results show that the proposed UAV multi-relay cooperative precoding scheme can effectively improve the communication reliability in this scenario compared to the traditional option.Finally,the physical layer security of the UAV relay communication system with eavesdropping is explored in the thesis.The eavesdropping node leaks the confidential information transmitted,resulting in the deterioration of the physical layer security performance.In this regard,the secrecy channel capacity based on the difference between transmition channel capacity and eavesdropping channel capacity is used as a criterion for the selection of UAV relays.Based on the obtained UAV spatial channel information,a UAV relay selection scheme with the maximum secrecy capacity is proposed with the compare of traditional round-robin scheme.From the secrecy channel capacity and the secrecy outage probability of the UAV system,the communication performance of relay scheduling schemes is discussed.Additionally,the approximate simulation results of secrecy outage probability is derived.Also,the numerical simulation results verify that the proposed UAV relay selection scheme improves the communication transmission reliability and security performance.