| Inspired by multiple-input multiple-output (MIMO) communication technique andsynthetic impulse and aperture radar (SIAR), as a new radar, MIMO radar is proposedand becomes the research focus concerned by scholars from many countries. MIMOradar systems transmit different signals via multiple antennas, receive and process targetechoes with multiple receiving antennas. Compared with traditional radar, MIMO radarhas more advantages with waveform diversity. Waveform diversity is an importantfeature of MIMO radar, and waveform design is a mean to achieve the waveformdiversity. New radar systems based on chaotic signal is a main field of radar applyingchaos. With different initial values, a large number of chaotic signals can be produced ina short time. The chaotic signal is sensitive to initial values, with a noise like broadbandspectrum, thumbtacked ambiguity function and sharp auto-correlation andapproximately orthogonal cross-correlation properties.In this dissertation, chaotic waveform design for MIMO radar is investigated, andthe main research focus on the following issues:1) The waveform design and choosing method for MIMO radar are proposed forchaotic discrete frequency coding, chaotic binary phase coding and chaotic four phasecoding. The auto-correlation and cross-correlation properties of four kinds of discretechaotic sequences (Tent sequence, Logistic sequence, Quadratic sequence and Bernoullisequence) are studied and the connections between correlation properties of chaoticsequences and sequence length, free parameter are given. The auto-correlation andcross-correlation properties of discrete frequency coding waveforms, binary phasecoding waveforms and four phase coding waveform from four kinds of chaoticsequences are analyzed and the connections between correlation property of chaoticwaveforms and waveform length, free parameter are given. Chaotic waveform choosingfor MIMO radar accords to the following results, the correlation properties of Tent andBernoulli discrete frequency coding waveforms are good, they are relatively idealtransmitting waveforms for MIMO radar. The correlation properties of four kinds ofchaotic binary phase coding waveforms are the same, all of them are relatively idealtransmitting waveforms for MIMO radar. The correlation properties of Tent, Logisticand Quadratic four phase coding waveforms are good, and better than the binary phasecoding waveforms, they are relatively ideal transmitting waveforms for MIMO radar.2) Signal processing model of multiple pulse compression accumulation for MIMOradar based on chaotic waveforms is established, including chaotic discrete frequency coding waveforms and chaotic phase coding waveforms. Auto-correlation sidelobes andcross-correlation statistical power peak of chaotic waveforms were deduced. Withdifferent waveform length N, auto-correlation sidelobes and cross-correlation statisticalpower peak are approximately1N. From different initial values, the correlationproperties of auto-correlation sidelobes and cross-correlation of chaotic waveforms arestudied, the following results are given: From different initial values, it is uncorrelatedbetween auto-correlation sidelobes of different chaotic waveforms; meanwhile, it isuncorrelated between cross-correlation of different chaotic waveforms too. According tothe results about correlation properties, signal processing model of multiple pulsecompression accumulation for MIMO radar based on chaotic waveforms is established,including chaotic discrete frequency coding waveforms and chaotic phase codingwaveforms. Using multiple pulse compression accumulation can reduce auto-correlationsidelobes and cross-correlation of chaotic waveforms effectively.3) With chaotic discrete frequency coding waveforms, an improvement method onperformance of MIMO radar for target detection is proposed. According to connectionsbetween correlation properties of chaotic discrete frequency coding waveforms andwaveform length, free parameter, longer Tent discrete frequency coding waveforms withgood auto-correlation and cross-correlation are designed and chose. In the clutter andnoise background, output of pulse compression has low peak sidelobe level, and thenthe performance of MIMO radar for point target detection is improved. But, the samemethod can not improve the performance of close small target detection for MIMOradar. Based on the signal processing model for MIMO radar with Tent discretefrequency coding waveforms, multiple pulse compression accumulation can reduceauto-correlation sidelobes and cross-correlation of chaotic waveforms, the output haslow peak sidelobe level, and then the performance of MIMO radar for point targetdetection is improved. Especially in close small target scene, due to multiple pulsecompression accumulation for processing, the sidelobes level from the strong targetecho does not cover up the mainlobe level from the weak target echo, so the detectionperformance of close small target is improved.4) With chaotic phase coding waveforms, an improvement method on performanceof MIMO radar for target detection is proposed. In the clutter and noise background,according to connections between correlation properties of chaotic phase codingwaveforms and waveform length, free parameter, Tent phase coding waveforms aredesigned and chose. Because of good correlation properties for longer Tent phasecoding waveforms, the output of pulse compression has low peak sidelobe level, and then the performance of MIMO radar for point target is improved. This method is validfor close small target detection too.Based on the signal processing model for MIMOradar with chaotic phase coding waveforms, multiple pulse compression accumulationcan reduce auto-correlation sidelobes and cross-correlation of chaotic waveforms, andthen the detection performance of MIMO radar for point target and close small targetare improved. |
PDF Full Text Request