Research On Algorithms Of Reference Signal Acquisition And Interference Suppression In DTTB Based Passive Radar

Frequency spectrum is a very valuable and limited resource. With the rapiddevelopment of modern wireless application, the demand for frequency spectrum isincreasing dramatically. How to realize the high efficient sharing of frequency spectrumresource has become a research hotspot around the world. Digital video broadcast (DVB)signal locates at the Ultra High Frequency(UHF), which is suitable for the widebandwireless communication application. Its advantages such as broad bandwidth, transmitpower stability and good coverage in low altitude make it a ideal radar illuminator. So DVBsignal is fit for both militray and civil applications. The DVB based passive bistatic radar(PBR) is studied, which provides the theory and technology support for the fully utilizitionand militray/civil sharing. The program is supported by the National Natural ScienceFoundation and Defence Basic Research Project. The main task of our work includes theanalysis of the feature of the interference in DVB based PBR, the reference signalaccqusition in joint time frequency domain, and the interference suppression in echochannel. The research outcome has the guidance significance to the practical application ofDVB based PBR.The main content of this paper is as follows:1.The mathematical models of interference and target echo are formulated.An in-depthanalysis of the reference channel interference, antenna frequency characteristics, fractionaldelay, interference non-stationary caused by echo antenna rotation and range and Dopplermigration effects on system performance is given. The paper also analyzes of therelationship between signal bandwidthand and computational complexity of adaptivecancellation and cross ambiguity function. It is pointed out that the broad bandwidth ofDVB signal causes a sharp increase in the computational complexity, which makesreal-time processing difficult. It is needed to study an efficient adaptive cancellingalgorithm and cross ambiguity function computation method. The above analysis provides atheoretical basis for the research of the reference signal acquisition and the echo channelinterference suppression algorithm.2.The influence of reference channel interference to the system cancellation gain and coherent integration performance is analyzed, and the reference signal accqusition methodin joint time frequency domain is proposed. For the strong sidelobe interference, digitalbeam forming based on wide null suppression method is used to obtain the referencesignal.Time domain method is used to deal with the mainlobe jamming and sidelobeinterference residual. A reference signal purification method is put forward based ontransmitting signal recovery.3.The limitations of echo channel interference cancellation only using time orfrequency domain is analyzed, and the echo channel interference cancellation method injoint time frequency domain is proposed.According to the different operation modes ofecho antenna,the spatial interference suppression method is different, when the direction ofecho antenna is fixed, the digital beamforming method based on the wide null is used; whenthe echo antenna rotates, the diagonal loading of SMI and the adaptive null broadeningmethod is used.According to different characteristics of interference, three kinds of timedomain adaptive cancellation method is proposed.(1)To deal with the fractional delayeffect and computational complexity problems, a combining LMS and FLMS(fast blockLMS) algorithm with fractional delay adaptive cancelling algorithm is proposed;(2)According to reduction of cancellation gain caused by the different frequencycharacteristics between the reference and echo antenna, non stationary of clutter caused bythe rotation of echo atenna and RLS algorithm computational problems, the combination ofRLS and NLMS adaptive cancelling algorithm based on the subband decomposition is putforward;(3)According to the multipath interference residual in reference channe, themethod considering the existing reference channel multipath interference and fractionaltime delay influence from the adaptive cancelling algorithm is proposed. An improvedbeam focusing method is proposed to improve the accumulation gain while the echoantenna rotating.4.The key factors that influents the system power is analyzed.In order to solve theDVB signal cross ambiguity function computational problems, rapid implementationmethod by pulse compression is adopted, the signal is segmented and equivalent to thepulse signal, the coherent integration is achieved by pulse pressure in segment and FFTamong segments. To solve the influnce to accumulation gain caused by range and Doppler migration in long time coherent integration. The Keystone transform and fractional Fouriertransform are adopted to migration compensation. A fast computation method of crossambiguity function and range migration compensation based on CZT is proposed.Compared with the existing methods, based on the equivalent properties, computation isreduced about50%.The effectivenesses of the proposed algorithms are verified by real data, and thecomprehensive verification results in different echo antenna operation modes is given. It isproved that the proposed algorithms can effectively suppress the interferences in referenceand echo channels, improve the cancellation gain and system detection performance, andgreatly reduce the realtime computational complexity.