| The main works of this thesis are diverse waveforms design for MIMO-OFDM radar,virtual array of MIMO-OFDM radar and transmit-receive beam-forming of MIMO-OFDM radar.The main works are summarized as the following:1.Diverse waveforms design for MIMO-OFDM radar: Waveform diversity is inherent characteristic of MIMO radar.OFDM-Chirp diverse waveforms were designed in this thesis,the waveforms is based on Chirp signal and OFDM signal and it has advantages of Chirp signal and OFDM signal simultaneously.The OFDM-Chirp diverse waveforms has large time-bandwidth product,low peak-average ratio,constant time domain and almost constant frequency-domain modulus and low time-delay and frequency-shift autocorrelation peak sidelobe level.More importantly,this scheme can generate over three orthogonal waveforms with a large time-bandwidth product.The number of OFDM-Chirp diverse waveforms are equal to the number of subcarriers of OFDM-Chirp waveforms.The performances of OFDM-Chirp waveforms are analyzed through the ambiguity function.2.Virtual array analysis of MIMO-OFDM radar.Orthogonal waveforms MIMO radar every element of receiving array receive all echoes corresponding to all transmitting signals,after matched filtering all echoes corresponding to transmitting orthogonal waveforms are separated.The number of separated echoes are equal to M times receiving elements,M is the number of transmitting orthogonal waveforms.Every receiving element extract M echoes,compared with matched filtering of traditional radar,M-1 echoes are ?extra?.The array that make up of elements corresponding to the ?extra? echoes is so called virtual array.Transmitting and receiving array element space have an effect on the size of virtual array aperture and slao fequency diversity in transmitting array.3.Transmit-receive beam-forming.OFDM-Chirp diverse waveforms are used in MIMO-OFDM radar,transmitted energy distributed on all directions uniformly,so there is no beam-forming on transmitting end corresponding to the counterpart phased-array radar.On receiving end transmit-receive two way beam is equivalently forming.Frequency diversity is used in transmitting array of MIMO-OFDM radar.There are two types of frequency diversity: small inter-element frequency offset and large inter-element frequency offset.The distinctions between the small inter-element frequency offset and large inter-element frequency offset lies in the difference of the purpose.The former is for anti-interference and the latter is to enhance the detection ability of targets.Transmitting beampattern is range-angle related,which is the common character of both.A large inter-element frequency offset is applied across the transmitting array in MIMO-OFDM radar of this thesis.Frequency offset is calculated based on echoes decorrelation among elements,which improve detection performance,which is performance's improvement in slow time.The disadvantage of large inter-element frequency offset is slight coupling of range and angle in array echoes,which have an effect on signal processing performance in fast time.Beam-forming is processing in fast time,so it is necessory to eliminate coupling of range and angle.Two methods are used to eliminate effects of range-angle coupling: 1.Range compensation algorithm,after range compensation,beam-forming is performed.2.Decoupling algorithm,taking range-angle coupling effects as object function,using genetic algorithm minimizing object function generates a set of optimal carrier frequency.Simulating transmitting beampattern using optimal carrier frequency,finding that range-angle coupling is negligible,which verify effectiveness of decoupling algorithm.After eliminating coupling of range and angle,beam-forming is performed. |
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