Design And FPGA Implimentation On OFDM Communication System For UAV Video Transmission

With the continuous breakthrough of semiconductor technology,the civil UAV industry has been developing rapidly in recent years.Therefore,Aerial photography system has almost become the standard configuration of Unmanned Aerial Vehicle(UAV),and the video transmission system applied in UAV is an important communication guarantee.However,the UAV video transmission system has the characteristics of large volume of data,high data rate and complex channel conditions,so it is severe demand for wireless communication.Orthogonal frequency division multiplexing(OFDM)has the advantage of high spectral efficiency,and it is an effective method to solve this problem.In this dissertation,the basic technical parameters of the OFDM system are analyzed and determined from the basic product requirements of the demanding UAV image transmission system.Then,through in-depth study of several techniques for OFDM communication system including digital intermediate frequency technology,synchronization,channel estimation and equalization technology,this article focuses on analyzing the principle and advantage of the algorithms of channel estimation and equalization and deducing the mean square error(MSE)of them.According to the UAV product requirements,it finishes the algorithm design for the UAV image transmission with OFDM communication system,and simulates and evaluates the performance of the core algorithms of the system with the software of MATALB.For the design of digital intermediate frequency algorithm,it proposes poly-phase filtering which could greatly reduce the complex of FPGA implementation and the structure of half band filters,the CIC filters combined with pulse-shaping filter for digital up conversion and digital down conversion.For the channel estimation using Wiener filter interpolation algorithm,it proposes the implementation optimization by three ways.Fist,simplify the channel covariance matrix according the classical power delay profile and Doppler spectrum model.Second,design the pilot interval and Wiener interpolation filtering orders by simulation according to the maximum multi-path time delay and Doppler shift frequency.Third,optimize the correla tion matrix according to the working SNR range of the system.Therefore,the optimized Wiener filter interpolation matrix is equivalent to a constant stored in FPGA and the implementation complexity is greatly reduced.For receiver equalization,a simplifi ed noise estimation method is proposed,which is used in LMMSE equalization,and the performance approached perfect equalization demodulation performance.Finally,the core algorithms of OFDM system for transmitting image in UAV mentioned above were implemented in FPGA.After hardware programming,functional simulation and timing verification,circuit layout,the UAV image transmission using OFDM communication system was realized in FPGA hardware board and tested to meet the parameters of product design.