Research On Key Techniques Of Relay Protocols In UAV Communication Systems

Due to the complexity of warfare forms and the diversity of warfare tasks in modern warfare,the communication is playing an important role during the warfare and the communication quality has become a decisive factor for the war situation.It has become extremely hot to introduce the UAVs into the near space working as communication relays to assist completing the information exchange in the warfare.Under this background,this thesis puts forward some improvements aiming at the key technology of relay protocols for the UAV relay communication system for the purpose of improving the stability and reliability and reducing the transmission time and the complexity of implementation of the system.In this thesis,some key techniques of relay protocols for UAV communication systems are studied:To solve the problem of different forwarding protocol scheduling for variable channel states in relay communication systems,ADMF(Adaptive Demodulation-Forward)and hybrid forwarding protocol is proposed.It combines direct DMF(DemodulationForward)protocol and differential DMF protocol and adaptively chooses the appropriate protocol using the LLRs of the symbols transmitted as the decision criterion through each channel.Furthermore,hybrid forwarding protocol is proposed based on the total channel condition.The simulation results show that the BER performances of ADMF protocol and hybrid forwarding protocol are better than the other two forwarding protocols,and the SNR loss is 5dB less when the SER is 10^-2.SNR-FORS(SNR-Feedback Opportunistic Relay Selection)protocol based on SNR feedback is proposed.It achieves higher transmission rate and system throughput than Timer and Subset protocols within limited time overhead under the assumption of noisy feedback channels,through the utilization of LASSO(Least Absolute Shrinkage and Selection Operator)to estimate the ID and LS(Least Square)to estimate the equivalent SNRs of the strong relays in the subset.Its performance can be close to that achieved by the full feedback scheme.The rate of SNR-FORS is 0.43bps/Hz higher than Timer and 0.33bps/Hz higher than Subset.Based on SNR-FORS selection,simulations of the outage probabilities of ANC,bidirectional DF and ADMF forwarding protocols are carried out.The results show that the ADMF protocol has better performance than the other two protocols.Bi-SWVA(Bidirectional Sliding Window Viterbi Algorithm)selection protocol is proposed for bidirectional multi-hop relay communication systems based on SWVA selection protocol,as well as an information exchanging model involving ADMF.Experimental results show that the outage performance of Bi-SWVA can be close to the optimal selection under limited memory requirements and complexity.Simulation of the above relay protocols in UAV relay communication system is carried out based on the UAV communication channels through the introduction of spread spectrum technique,acquisition and tracking technique.When the system achieves precise synchronization,the proposed relay protocols are proved to be available through simulation.