Research On Signal And Data Processing For MIMO-based Sky Wave Over-the-horizon Radar

Caused by the multilayer of the ionosphere, the effect of multipath propagation ormultimode propagation often arises when the signals of the sky-wave over-the-horizonradar (OTHR) transmit in the ionosphere, seriously distorting the performance of thesky-wave OTHR such as target detection, location and so on. In recent years, someOTHR researchers began to propose that applying the technology of MIMO radar(Multi-input Multi-output radar) to the the next generation of sky-wave OTHR, toeliminate the multipath and multimode clutter from different directions of space asmuch as the OTHR could, with the help of flexible beamforming of MIMO radar.Currently, the development of MIMO-OTHR is still at the step of theory andexperiment, so only some fundamental work in the aspect of signal processing and dataprocessing of the MIMO-OTHR is presented in this paper. The detail is as follow:First the ambiguity function of the MIMO waveform set is introduced. Through theanalysis of this ambiguity function, the conclusion that the maximum unambiguous areaof the ambiguity function of the MIMO wave set is much smaller than that of the singlewaveform is drawn. This must be considered when someone wants to design thewaveform set for MIMO-OTHR.Because conventional OTHR is influenced by multipath and multimode clutterfrom different azimuth or elevation angle, the beamforming of MIMO-OTHR isinvestigated to elimate these influences:1) to the array geometry needed for thebeamforming of MIMO-OTHR, a2-D array geometry is introduced, to eliminatemultipath and multimode clutter from any elevation angle and any azimuth angle;2) tothe needed transmitting waveform set, specific waveform sets that can be used inMIMO-OTHR are analyzed;3) to the signal processing needed for the beamforming ofMIMO-OTHR, the fundamental signal processing for MIMO-OTHR is derived. Bychanging the order of the beamforming, the times of matched filtering is reduced. Atlast simulation is presented to prove the signal processing that could be used to elimatethe multipath and multimode clutter.To solve the problem of the association bettwen measurements and propagation paths in data procession of convention OTHR, a method, that could be used to derivethe associations with the elevation of MIMO-OTHR mearsurements, is proposed. Withthe accurate association between the measurements and their propagation path, the dataprocessing of the OTHR would be much easier. Then the method is applied in algorithmMPDA, to improve it as IMPDA algorithm. At last, a simulation for MPDA andIMPDA algorithm is presented to prove similar accuracy of both, but less computationcomplexity of the latter.