| Conformal arrays refer to the arrays whose array manifolds conform to the carrier platform due to the limitation of aerodynamics and underwater environment,etc..Conformal arrays not only have the advantages of mechanical structure,but also can provide omnidirectional fast scanning and large spatial coverage,hence outperforming traditional array antennas in certain applications.As a key technology of the future radar and communication systems,millimeter wave(mm Wave)is has been a hot research topic in recent years.Due to its ex-tremely short wavelength and severe path loss,mm Wave is generally used in combination with large-scale arrays.As two current research hotspots in array signal processing,the combination of conformal arrays and mm Wave arrays will become an important research direction in the foreseeable future.Its application scenarios include mm Wave 5G commu-nication networking based on UAV swarms and mm Wave satellite communication systems,etc.,and fast and accurate direction-of-arrival(DOA)estimation is the key and substitute for mm Wave conformal array to give full play to its advantages.According to the characteris-tics of mm Wave large-scale conformal array,this dissertation focuses on developing DOA estimation algorithms with low complexity and high accuracy.1.For large-scale uniform circular arrays(UCAs),a low complexity and accurate single-snapshot DOA estimation method based on sequence correlation and optimal phase compen-sation is proposed.Taking advantage of the excellent auto-correlation property of the array response of a UCA,the coarse-resolution estimation of the DOA is obtained through a cyclic cross-correlation between the matching coefficient sequence and the array received signal.Then the DOA refinement is obtained by searching the optimal phase compensation which maximizes the inner product of matching coefficient sequence and the phase-compensated array received signal.The specific contributions include:(1)It is proved that the array re-sponse of large-scale UCA has good correlation.Based on this,the matching coefficient sequence is designed,and the cyclic cross-correlation operation of two cyclic sequences is developed and turned into cyclic convolution;(2)The idea of fast phase compensation is proposed.It is illustrated that compensating the phases of the matching coefficient sequence is equivalent to performing the same processing on the array response vector,which is due to the reciprocity of the two sequences in correlation.Then,the DOA refinement is obtained by searching the optimal phase compensation;(3)The successive interference cancellation algorithm is introduced to estimate the DOAs of multiple impinging signals;(4)The com-putational complexity of the proposed algorithm is analyzed and compared with numerous existing methods,which shows up to orders of magnitude decrease of the computational complexity;(5)The closed-form expression of the Cramér-Rao lower bound(CRLB)for the proposed algorithm is derived.Extensive simulation results are provided,showing that the RMSE of the proposed method is much better than that of the existing methods and able to approach CRLB in high signal to noise ratio(SNR)regions.2.For large-scale uniform cylindrical array,a low complexity and accurate single-snapshot DOA estimation method based on discrete Fourier transform(DFT),matching correlation and optimal phase compensation is proposed.In this method,the two-dimensional angle estimation is decoupled by using the symmetry of uniform cylindrical array.Firstly,the pre-liminary estimation of elevation DOA based on uniform linear arrays(ULAs)is obtained through DFT and optimal phase compensation.Then the estimation of azimuth DOA is ob-tained through matching correlation and optimal phase compensation.Finally,the accurate elevation DOA is obtained by the estimation of azimuth DOA,and the results of 2D DOA estimation for large-scale uniform cylindrical array are obtained.The specific innovations include:(1)The received signal model of uniform cylindrical array is constructed by space vector operation,and the array response of uniform cylindrical array is decomposed into the Kronecker product of array response of ULA and UCA;(2)The received signals of uniform cylindrical array are reduced to a single virtual UCA by coherent integration to estimate the azimuth DOA by the previous method,which greatly improves the estimation SNR and DOA estimation accuracy;(3)The received signals of uniform cylindrical array are reduced to a single virtual ULA by coherent integration,which further improves the estimation SNR and DOA estimation accuracy;(4)The polarization model of uniform cylindrical array based on dipole antenna and its influence on the proposed algorithm are analyzed;(5)Extensive simu-lation results are provided,showing the high performance and great advantages of proposed method.3.For large-scale hybrid conformal array based on Butler matrix-based transceivers(BMTs),a variety of fast DOA estimation methods based on wide beam combination,fast interval it-eration and binary coding are proposed.Firstly,the detection angle space of array is divided according to the detection ability and arrangement of BMTs.Then,the wide beam synthesis method of BMT is used to synthesize multiple wide beams and cover the whole detection an-gle space.The angle range of DOA is determined by the signal power detected by each wide beam,and the range of angle interval is reduced continuously until DOA is finally located at a specific DFT beam.The specific innovations include:(1)The signal model of conformal array based on BMT is established by space vector operation;(2)The wide beam synthesis method of BMT in spatial angle domain is proposed;(3)The fast interval iteration scheme is proposed,including the close spread wide beam method and the overlapped wide beam method;(4)The principle of free superposition of non-overlapping wide beams of BMT is proposed and proved;(5)A fast DOA location method based on equal length binary coding is proposed,and its iteration speed is calculated and analyzed;(6)Considering the unequal probability distribution of DOA,a fast DOA location method based on Huffman coding is proposed.4.For large-scale hybrid conformal array based on BMTs,an accurate DOA estimation method based on fast DOA location and higher-order DFT beam differential(DBD)and a synthesization method of DOA estimation results based on maximum likelihood estimation method are proposed.Firstly,the fast DOA estimation described above is carried out to lo-cate the DOA on a specific DFT beam.Then,DBD or higher-order DBD method is used to estimate the DOA by each BMT.Finally,the maximum likelihood estimation method is used to synthesize the estimation results of multiple BMTs to obtain the final accurate DOA estimation result.The specific innovations include:(1)By analysing the shortcomings of angle measurement method based on DFT beam,the concept of DBD is proposed,and the closed-form solution of DOA estimation method based on DBD is derived;(2)The concept of higher-order DBD is proposed and its advantages and disadvantages in DOA estimation are discussed;(3)Two forms of second-order DBD that can be easy realized by hardware are analyzed.The closed-form solutions for DOA estimation are derived.The advantages and disadvantages of each method are compared and discussed,as well as the difference in DOA estimation performance with the existing algorithms;(4)The mean square error with different DOA by DBD and higher-order DBD method is analyzed,and a method of synthesizing DOA estimation results of multiple BMTs based on maximum likelihood rule is proposed;(5)The effectiveness of proposed method is verified by simulation experiments.The performance simulations of DBD and higher-order DBD verifies its advantages and characteristics compared with DFT beam. |
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