Research And FPGA Implementation Of Airborne Passive Long-term Coherent Method Based On C-band High-speed Direct Spread Spectrum Communication Signal

Tactical data link is the cornerstone of the information countermeasure system in modern warfare.High-speed pseudo-code direct spread spectrum and high-speed frequency hopping are two typical anti-jamming technical means that are often used.The airborne passive radar system using such signal as source has the advantages of high resolution,concealment,and no active radiation.Therefore,this paper focuses on the C-band high-speed direct-spread communication signal to carry out research on the target detection of airborne passive radar system.In order to solve the problem of sharp broadening of the doppler frequency domain,frequency diffusion and distance walking lead to the serious mismatch of symbol information between channels and the sharp deterioration of detection performance.A low-complexity,high-performance frequency-domain framing three-dimensional networked coherent accumulation improvement method is proposed,and a field-based The long-term coherent accumulation of the programmable logic gate array hardware real-time processing prototype,and carried out the desktop PC simulation test verification.The main research work of this paper is as follows:Firstly,the key problems and their influencing factors in long-term coherent accumulation are analyzed.From the perspective of signal frame structure,modulation style and its characteristics,the relationship between its processing performance and time-frequency sidelobe is analyzed;from the perspective of system geometric topology model and target motion,the echo frequency domain distortion,signal-to-noise ratio and spatial structure are analyzed.From the perspective of signal processing,two key problem models of walking across distance units and walking across doppler units are established.Then,focusing on these two key issues,the research on the long-term coherent accumulation algorithm for weak high-speed direct-spread signals is carried out,and the comparative analysis of its computational complexity and simulation performance is carried out.After modeling and analyzing the contradiction between the extremely low SNR and the wide doppler domain,two traditional motion compensation algorithms,Radon Fourier transform and Keystone transform,are studied for the problem of walking across distance units.Due to their complexity The accuracy is high and there is performance loss in the scene of this paper.An improved method of three-dimensional networked motion compensation with frequency-domain framing is proposed;and for the problem of cross-doppler unit walking,a frequency-domain framing method is proposed.Multi-channel convolutional network maneuver compensation method;and completed the computational complexity analysis and simulation performance comparison,the results show that compared with the traditional method,the improved method has lower computational complexity and about the cumulative performance improvement.Finally,based on the improved method,a FPGA-based long-time coherent accumulation hardware real-time processing prototype is realized.Under the comprehensive consideration of complexity and performance,the detailed design introduction and function verification of each key processing module are carried out,and the desktop host computer simulation test is carried out on the built hardware real-time processing prototype.The test results show that the hardware real-time processing prototype designed with pipeline structure can complete the long-term coherent accumulation of high-speed direct-spread signals on the order of seconds in real time.