Study On Integrated Radar And Communications Waveform Design Method Based On MIMO

In recent years,with the fast development of MIMO technique,many major breakthroughs have been made in both the radar and communications fields.However,with spectrum resources increasingly stretched,mutual interference between radar and communications systems is also becoming more and more severe.Radar and communications equipment,whether civilian or military,faces problems such as space competition and electromagnetic compatibility,when they are equipped on a single platform.To solve above problem,achieving the radar and communications integration via sharing the same transmit waveform is an effective approach.This dissertation focuses on the key problems and technical difficulties of the shared waveform design and communication information embedding methods for the integrated system of radar and communication based on MIMO radar platform.Based on the problems and difficulties,this dissertation proposes some novel methods for the signal transmission and reception in integrated system,shared waveform design and distance-velocity estimation in MIMO-OFDM system,MIMO shared waveform design combined with constellation mapping to modulate communication information symbols,MIMO radar transmit beamforming and communication information modulation using space-time phase-coding scheme,and space-time phase-coding waveform design in MIMO radar system.The main content of this thesis can be summarized as the following five parts:1.The application scenario for the integrated system of radar and communication based on airborne MIMO radar platforms is described and discussed,and the transmit-receive signal model of the integrated system is developed.According to the characteristics of the transmit waveform,the differences of transmit beamforming between MIMO radar and phased-array radar are discussed.For two different cases of MIMO radar transmit beampattern,i.e.omnidirectional and directional transmit beampattern,the key issues of shared waveform design and communication information embedding are studied.Finally,the conventional MIMO radar and communication signal processing methods are given,and their advantages are discussed.2.In the existing MIMO-OFDM orthogonal waveform design,the equidistantly interleaved OFDM signals increase the frequency interval of OFDM sub-carriers,which results in a decrease of the maximum non-ambiguous radar range.Moreover,OFDM signal has an inherent drawback of time-domain envelope fluctuation which reduces the amplifier efficiency of radar transmitter,affecting the radar detection range.To deal with above problems,a multi-antenna joint optimization waveform design method for MIMO-OFDM is proposed,based on the modified TR(tone reservation)technique.By interleaving the OFDM subcarriers non-equidistantly with constraint of the minimum frequency interval between two adjacent subcarriers,a grouping optimization method is exploited to design the orthogonal interleaved OFDM waveform.Thus it keeps the maximum unambiguous radar range unchanged and obtains the subcarrier interleaving scheme with lower PAPR.Afterwards,the MIMO-OFDM multi-antenna joint optimization combined with the modified TR technique is performed to reduce the PAPR sufficiently by using the low SNR or useless subcarriers as reserved sub-carriers.At the receiver,a distance-velocity estimation algorithm based on compensating the phase-difference is given for the MIMO-OFDM system.Simulation results show the effectiveness of the proposed method.3.As for shared waveform design for the integrated system of radar and communication based on the MIMO radar,the current transmit beamforming and communication information embedding are independent of each other.And the information transmission rate is lower.To solve the above problem,a MIMO transmit waveform design method combined with constellation mapping for embedding information symbols is proposed.By transmitting a weighted sum signal of multiple orthogonal waveforms at each transmit antenna,the information symbols are embedded into each orthogonal waveform via constellation mapping for the communication direction.And the radar transmit beamforming design is optimized by using the minimal ISL criterion.Afterwards,the PAPR upper bound under this transmitting model is derived,and orthogonal waveforms are restructured to reduce the PAPR upper bound.Combined with constellation mapping and transmit beamforming design,the proposed method embedding information symbols into the space domain and meanwhile design the optimal transmit beampattern.Thus it reduces the effect of communication information randomness on the radar mainlobe and obtains lower sidelobe level.For communication,it improves the information transmission rate without changing the radar PRF,has better performance in BER and LPI,and has better tolerance for angular errors.4.For the existing integrated system of radar and communication based on MIMO radar,there is envelope fluctuation of communication equivalent signal among sub-pulses,and the information transmission rate is very dependent on the radar PRF.To solve the above problems,a space-time phase-coding waveform design method for embedding communication information into each sub-pulse is proposed,based on the MIMO radar transmit beamforming.By using the vectorization representation to establish the transmit beamforming model,the constant envelope of communication equivalent signal and of transmit waveform are formulated as constraints.The ADMM algorithm and the SDR method are used to solve the optimization problem for the two design criteria of shape approximation optimization and cumulative power approximation optimization,respectively.Based on the constant emission power among each sub-pulse in the communication direction,the communication information can be embedded on each sub-pulse via using the space-time phase-coding scheme.Afterwards,two information symbol mapping methods are given,namely DCM and PRCM.The DCM method has better performance in BER and LPI,while the PRCM method has better robustness in resisting the phase error of the communication channel estimation.5.The conventional transmit beamforming methods generally focus on integrated power for optimization without constraint on sub-pulse,and the envelope fluctuation of target equivalent signal results in the normalization matching filter loss.To address this problem,a space-time phase-coding waveform design method is proposed.First,at the first emission sub-pulse,the radar transmit beamforming design at the presence of interference is optimized via using the phase-coding waveform.Then,based on the obtained phases,a special space-time phase-coding scheme is exploited to design space-time waveform maintaining the same null depth in interference direction during sub-pulses.Afterwards,the space-time phase optimization model for minimizing the normalization matching filter loss of the target equivalent signal is established,and it is solved by the modified simulated annealing algorithm.The proposed method has better performance in anti-interference and LPI.