Research On Efficient Waveform Technologies For Flying Ad Hoc Network

Flying Ad-Hoc Networks(FANETs)have been widely applied in various mission scenarios due to their high flexibility,simple deployment,and wide coverage range.However,aiming to meet the demands of information exchange and collaboration among FANET devices and the challenges brought by the complex and diverse mission scenarios,FANET transmission waveforms must possess communication and sensing capabilities to ensure high-quality and stable data transmission in constantly changing environments.Specifically,frequent task migration in FANET results in varying environmental scene characteristics such as communication distances between unmanned aerial vehicle(UAV),relative velocities,and positions of channel scatterers,which in turn affect waveform transmission metrics like bit error rate and sensing accuracy.Therefore,research is needed to adapt waveform transmissions to FANET task scenarios.These selected waveforms shall be efficient and suitable for specific task scenarios and further enable optimized transmissions in highly dynamic and complex FANET environments.Furthermore,the selected waveforms shall improve the overall efficiency of communications and sensings in FANET environments.In this regard,this thesis focuses on the efficient waveform technologies for FANETs and conducts the following research work:1)This thesis proposes a sensing-driven and scenario-adaptive waveform selection mechanism for FANET.First,an integrated communication and sensing waveform transmission system for the FANET platform is introduced.Then,a comprehensive performance indicator is proposed to characterize the communication and sensing performance of different waveforms.Further,the transmission environment information collected by unmanned aerial vehicles(UAVs)is employed to drive the waveform decision module to select the waveform with the optimal overall efficiency in specific task scenarios.Specifically,this thesis focuses on the research of Single Carrier Frequency Domain Equalization(SC-FDE)waveform for low communication rate tasks,Orthogonal Frequency Division Multiplexing(OFDM)waveform for high communication rate tasks in low dynamic scenarios,Orthogonal Time Frequency Space(OTFS)waveform for high communication rate tasks in highly dynamic and complex environment,and their optimal switching.In particular,this thesis proposes a reinforcement learning-based waveform selection module to improve the efficiency and accuracy of waveform switching for UAVs in dynamic scenarios.It combines the prior scene information obtained through a small amount of flight scenario simulation of the UAV with waveform mapping and reinforcement learning networks to achieve fast and accurate waveform switching.Finally,simulation results show that the proposed waveform selection approach can improve communication and sensing comprehensive performance in FANETs.2)This thesis proposes a Message Passing Assisted Sparsity Adaptive Matching Pursuit(MPA-SAMP)channel estimation scheme for reliable OTFS waveform transmission in highly dynamic and complex FANET environments.Firstly,the loss of bi-orthogonality due to the practical rectangular OTFS pulses leads to the degradation of the sparsity of the equivalent channel,posing a challenge in FANET for channel estimation.To address this challenge,this thesis presents a pilot-aided MPA-SAMP channel estimation method.At the receiver,the error rate of the estimated pilot sequence is calculated by the Message Passing(MP)symbol detection output,which is then mapped to an estimation of the channel sparsity.With a small number of iterations,the proposed method achieves adaptive tuning of the channel sparsity required by the Generalized Orthogonal Matching Pursuit(GOMP)algorithm.The proposed MPA-SAMP algorithm can achieve approximate ideal channel estimation accuracy without the need for prior knowledge of channel sparsity and it possesses a lower algorithm complexity.Finally,simulation results demonstrate that the proposed algorithm achieves better channel sensing accuracy and symbol transmission performance than the reference schemes.