Research On Uplink Transmission Technology Of Light And Small UAVs Based On FH-OFDM

In recent years,the application scenario of UAV has gradually expanded from mapping and search to many fields such as traffic supervision,emergency medical treatment,security patrol and auxiliary wireless communication.The terrain environment of its application has also changed from field scenario to more complex and changeable urban scenario.The urban population is dense.When the UAV cannot communicate normally with the telecommand station,it is easy to cause personal injury accidents and property losses.Therefore,the research on the uplink transmission technology of telecommand station transmitting flight control signal to UAV in urban scene has great application value and practical significance to improve the reliability and effectiveness of uplink data transmission.According to this research background,the main work of this paper is as follows:The uplink wireless channel characteristics of light and small UAV in urban scene are analyzed.Taking a small and light quad-rotor unmanned aircraft as the research object,the UAV is divided into four flight states,and the channel parameters of each state are calculated and analyzed to provide data support for the subsequent design of baseband link and the construction of simulation platform.According to the dual requirements of UAV channel characteristics and improving link transmission reliability and effectiveness,frequency hopping spread spectrum(FHSS)technology and orthogonal frequency division multiplexing(OFDM)technology are introduced,and their principles and performance indexes are introduced,in addition,using their technical advantages,RF FH-OFDM scheme and RF-Subcarrier FH-OFDM scheme are proposed.The RF FH-OFDM scheme is designed and the simulation platform of the scheme is built.The Latin square sequence is used to construct the frequency hopping sequence on the carrier side.Through simulation and comparison,it is concluded that the four flight states of UAV in the urban scene can improve the bit error rate performance of RF FH-OFDM system compared with OFDM system under the conditions of multi frequency interference,Rayleigh fading channel or rice fading channel.In addition,from the perspective of timefrequency domain,three time-frequency analysis methods are used to obtain the time spectrum of UAV uplink transmitted signal before and after passing through multipath fading channel,so as to realize the analysis of time-varying signal,so as to better reflect the time-varying characteristics of the channel.At the same time,the baseband I/Q signal of a small and light quad-rotor unmanned aircraft is obtained through acquisition and processing,and the time spectrum diagram of the UAV is obtained by using three timefrequency analysis methods,which intuitively shows the time spectrum of the signal transmitted by the link for UAVs.In order to further improve the reliability and effectiveness of uplink transmission,greater frequency diversity is obtained.The RF-Subcarrier FH-OFDM technical scheme is designed and the scheme simulation platform is built.The baseband side frequency hopping adopts the group frequency hopping method to construct the frequency hopping sequence.Through simulation,the four flight states of UAV in urban scene are compared under the conditions of multi frequency interference and Rayleigh fading channel or rice fading channel,Compared with RF FH-OFDM system and OFDM system,the bit error rate performance of RF-Subcarrier FH-OFDM system is improved.