Design Of Unmanned Aerial Vehicle Image Transmission System Based On COFDM

With the continuous development of UAV technology,it has been widely used in rescue and disaster relief,power line inspection and so on.The image transmission system,which is an important part of UAVplays an irreplaceable role.At the same time,as the application of COFDM technology in wireless image transmission becomes more and more advanced,applying it to UAV image transmission has become the focus of research.Therefore,a UAV image transmission system based on COFDM is designed in this paper.Firstly,the propagation characteristics of UAV image transmission channelare analyzed briefly,such as large-scale fading,shadow fading,multipath fading,channel time-varying and Doppler Effect.The channel coding technology of core technology COFDM,priciples and key technologies of OFDM are studied.Then it introduces the composition of the UAV image transmission system,including the airborme transmitting part and the ground receiving part,and analyzes the working principle of some modules such as image acquisition,source coding and COFDM modulation,up-conversion,RP and so on.The design scheme of the system is put forward.The image acquisition module is implemented by COMS image sensor OV5640,the source coding module uses the MPEG2 compression standard,the up-conversion module uses the AD9957 chip of ADI,the radio frequency unit uses a special amplifier module.This article has carried on the detailed design to the core module COFDM,has designed the data scrambling,outer coding,outer interleaving,internal coding,inner interleaving,constellation mapping,frame formation,IFFT modulation and protective interval in COFDM through the shift register of different size and a plurality of single-port RAMs.It is designed by FPGA chip 5CSEMA5F31C6.The Verilog HDL language is used to write the code for each module of the system,and the code of each sub-module in COFDM is simulated and tested using Modelsim software.The test results are all satisfied with the design requirements.Finally,a test platform is built to test the UAV image transmission system.It includes system imaging,transmission power,system bandwidth,transmission distance,moving speed and transmission rate.The test results show that the system designed in this paper has stable data transmission and good display effect.It achieves the design requirements of transmission distance up to 2 km and stable transmission under 30Km/H mobile speed.The problems appeared in the test are analyzed and solved,and the further optimization direction of the system is put forward according to the test results.