| Wireless video transmission is an essential function for UVA in the application scenarios of aerial reconnaissance and aerial photography.With the rapid development of UAVs in civil and military fields,mobile high-quality video transmission has become a trend.Based on OFDM technology,this paper develops the research and verification of high-definition video transmission waveforms for UVA.The main work of the dissertation includes the following aspects:First of all,we summarize the wireless channel fading characteristics and OFDM technology.We Introduce the related concepts of large-scale fading and small-scale fading of wireless channels,classify multipath fading channels,and describe the envelope statistical characteristics of fading channels;we elaborate the basic principles of OFDM systems and discuss wireless video transmission based on OFDM technology,which provides a reference for waveform design.Secondly,the demand for and analysis of high-definition video transmissions of UAVs are carried out.After video compression bitstream analysis,we adopt three transmission modes,namely,2Mbps,6.5Mbps,and 20 Mbps,which can meet the requirements for video transmission with different resolutions.We give the downlink budget of the longest transmission distance of 5km,analyze the impact of frequency offset and timing deviation on the system,and provide theoretical basis for waveform design.Then,according to the demand of high-speed,large-capacity,anti-multipath and anti-Doppler frequency offset for UAV video transmission,we design a downlink data transmission waveform.Firstly,the frame format and framing process are given,and a subcarrier mapping scheme adapted to three transmission rates is proposed.Secondly,the key technologies of the receiver are studied,including the time frequency synchronization algorithm using the training sequence,and the pilot-based channel estimation,MRC,and QPSK soft demodulation.Finally,link performance simulation is performed,and point-to-point error performance meets the requirements of the index under UVA channel conditions.In the end,we complete the waveform implementation and preliminary verification on the FPGA hardware platform.Given the implementation details of the key modules,the time-frequency synchronization and point-to-point bit error rate tests were performed in a laboratory environment to verify the feasibility of the design scheme.The variable-rate OFDM data transmission scheme proposed in this paper has theoretical and practical significance and provides a reference for the research of high-definition video transmission technology for UAVs. |
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