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1 MINISTRY OF EDUCATION AND TRAINING MINISTRY OF NATIONAL DEFENCE ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY TRAN CONG TRANG THE RESEARCH OF IMPROVING THE TARGET POSITIONING ACCURACY FOR SHIP’S PASSIVE SONAR SYSTEMS Specialization: Radar Technology and Navigation Code: 52 02 04 SUMMARY OF Ph.D THESIS IN ENGINEERING Hanoi, 2019 This thesis has been completed at: ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY Scientific supervisors: Dr Tran Van Hung Dr Nguyen Thanh Hung Reviewer 1: Assoc Prof, Dr Vu Van Yem Hanoi University of Science and Technology Reviewer 2: Assoc Prof, Dr Le Vinh Ha Academy of Military Science and Technology Reviewer 3: Dr Nguyen Van So 189 Brigade, Vietnam People’s Navy The thesis was defended at the Doctoral Evaluating Council at Academy level held at Academy of Military Science and Technology in 8:00, on ….th August 2019 The thesis can ben found at: - Library of the Academy of Military Science and Technology - Vietnam National Library PUBLICATIONS [1] Luong Van Trinh, Tran Van Hung, Tran Cong Trang, 2016, Hybrid TDOA-AOA positioning algorithm in the passive radar system model with the mobile station, Journal of Military Science and Technology, Special issues radar, 8/2016, pp.137-142 [2] Tran Cong Trang, Nguyen Thanh Hung, Tran Van Hung, 2016, Researching of apply the method of compering the contrast coefficients to detect of low noised targets in passive sonars, Workshop on Maritime Communication and Navigation (ComNavi 2016), Hanoi University of Science and Technology, 10/2016, pp.64-68 [3] Doan Van Sang, Tran Quy Dan, Tran Cong Trang, Nguyen Thanh Hung, Tran Van Hung, 2017, Investigation of localization error in sonar system using triangulation method, Journal of Military Science and Technology No 51, (10/2017), ISSN-1859-1043, pp.58-65 [4] Tran Cong Trang, Doan Van Sang, Nguyen Van Linh, Nguyen Hoai Nhan, Nguyen Thanh Hung, 2017, An Experimental Measurement of Simple Chip AD8302 Implemented in SONAR Interferometer, Integrated Circuits, Design, and Verification (ICDV), 7th International Conference, IEEE Published, ISBN: 978-1-5386-3377-9, 5-6 Oct 2017, Hanoi, Vietnam [5] Sang Van Doan, Jiri Vesely, Trang Cong Tran, Thanh Chi Vu, Hung Thanh Nguyen, 2017, The Measurement of Long Baseline Interferometer, Journal of Science and Technology, Radar Monitoring Systems, Military Technical Academy, No189, April-2018, ISSN- 1859 - 0209, pp.167-176 [6] Tran Cong Trang, Đoan Van Sang, Nguyen Thanh Hung, Tran Van Hung, 2018, Application of the MUSIC algorithm for DOA estimation in passive sonar, Journal of Military Science and Technology No.56, (8/2018), ISSN-1859-1043, pp.105-114 [7] Sang Van Doan, Trang Cong Tran, Van Duc Nguyen, DOA Estimation of Underwater Acoustic Signals By Using Non-uniform Linear Arrays, 4th EAI International Conference: INISCOM 2018, Danang Vietnam 27 August 2018, ID 339568416 INTRODUCTION Urgency of the Thesis Passive sonar systems play an important role in the naval warships, especially in the submarines due to the superiority of operation confidentiality Currently, advances in electronic technology and signal processing allowed to design modern passive sonar systems with superior features In the world, the sonar technology has developed rapidly since the beginning of the 21st century [67], especially, in the United States and the European countries such as United Kingdom, France, Rusia [80] In Asian countries, such as Japan and South Korea achieved success in civil sonar techniques Recently, China has invested heavily and also obtained many achievements in research and development of military sonars [23, 78] These countries have been developing many modern sonar systems, focusing on the research of passive sonar In the world and in Vietnam, the research results of passive sonar in the military application are strictly secuređ, hence it is very difficult to evaluate fully and exactly the situation and tendency development of passive sonar technology The Objective - Theoretical analysis and evaluation of the target positioning methods and DOA estimation methods for ship’s passive sonar systems based on mathematical models and simulation tools - Proposing novel solutions to increase the accuracy of DOA estimation for improvement of target location determination accuracy The proposed algorithm is presented using the mathematical description, simulated using Matlab to validate the theory, and the experimental measurement is performed to validate and evaluate theory and simulation The Subject and Scope This paper studies the positioning methods, measures the angle of arrival of the sonar signal source for the object of passive sonar on ship; builds sound broadcast signal model, evaluates the ability to estimate angle of arrival by simulation It also constructs a negative antenna network configuration using MUSIC algorithm to improve the accuracy of the angle measurement of many different sonar signal sources This paper also simulates, evaluates, compares the ability to determine the angle of incidence according to the MUSIC algorithm with algorithms CB (Conventional Beamforming) and MVDR (Minimum Variance Distortionless Response - meet no distortion of minimum variance), proposes solutions to improve the angle measurement accuracy to DOA to improve the target positioning accuracy for passive sonar objects on ship Scientific and pratical significance of the Dissertation Scientific significance - Contributing the recommendation and conclusion for the applicability of the target positioning methods, and DOA estimation algorithms in passive sonar systems - Establishing the signal model of the arrays ULA, UCA, and NLA for the performance of DOA estimation using CB, MVDR, MUSIC algorithms - Proposing the Spatial Smoothing MUSIC algorithm to estimate DOAs of multiple coherent and non-coherent signal sources with higher accuracy and resolution - Developing the system with a hydrophone NLA combined with proposed Spatial Smooth MUSIC algorithm to estimate DOAs of multiple signals emitted from various coherent and/or non-coherent sources, thereby the accuracy of target positioning determination could be increased Pratical significance - Performance of experiment measurement in lab water tanks to demonstrate and prove the applicability of DOA estimation using phase comparison and TDOA methods - Performance of experiment measurement in Nha Trang Bay to demonstrate and prove the applicability of DOA estimation using MUSIC algorithm Research methodology Using research methods, mathematical analysis of known algorithms on target positioning and DOA estimation; using simulation tool in Matlab environment to verify theory; comparing and evaluating errors for each method Establishing the practical experimental measurements to evaluate and verify the theory and simulation; proving the applicability of the proposed solutions and methods Structure of the Thesis The Ph.D thesis consists of 123 pages, 82 figures, 11 tables Structure of the dissertation includes the introduction, chapters, and the conclusion Chapter 1: Overview of passive sonar and target location methods in ship’s passive sonar systems Chapter 2: Technical solutions for improvement of the accuracy of DOA estimation in ship’s passive sonar systems Chapter 3: Application of MUSIC algorithm for improvement of the angle measurement accuracy in ship’s passive sonar systems Chapter OVERVIEW OF PASSIVE SONAR AND TARGET LOCATION METHODS IN SHIP’S PASSIVE SONAR SYSTEMS 1.1 Review of associated national and international publications From the beginning of the 21st century, projects and scientific research publications for sonar in Vietnam have just been considered more Some studies focused on the tasks of technical mastery, equipment improvement, small-scale testing Since the 2010s, the number of military sonar research has increased significantly, due to the operation urgency of equipped new submarines [12] Currently, there are many research projects on passive sonar in the world to improve detection ability and accuracy of target positioning Most studies focus on proposing target positioning algorithms based on buoy antenna or towed antennae system In particular, the algorithm to improve the accuracy of the direction finding of the signal source is the core factor to improve the accuracy of the target location 1.2 Sound propagation characteristics 1.3 Target positioning methods in passive sonar systems HDPR method is considered by European submarine designer and used in many passive sonar systems because it has the ability to locate targets quickly with a quite high accuracy However, the HDPR method is limited in deployment range and frequency because r must be less than /10 Modern submarines often have sonar systems arranged along the hull to determine the target distance TMA method is a classic method that has been used for a long time for submarines Although it is possible to determine the target position with only the information of the direction But the method accuracy is relatively low In the field of passive sonar, the triangulation method is very effective, especially passive sonar systems arranged by floating buoys or near-shore observation stations or carried by surface vessels For submarines, the triangulation method is applied with an additional towed antenna system 1.4 Formulation of Problem and Research Conditions For the purpose of studying to find solutions to improve the accuracy of angle measurement for improving the accuracy of the sonar target localization, the research problems are considererd under the following conditions: The problem of target positioning of a ship's passive sonar system was studied with the assumption that the signal in acoustic noise was detected Underwater acoustic signal with carrier frequency f0 = kHz was used in the Dissertation for simulation and experimental measurement because the carrier frequency f = kHz is a medium value in frequency detection band of passive sonar systems 1.5 Conclusion of Chapter Through an overview studied, the fundamental of target location methods for passive sonar and the factors affecting the target location problem showed that: Sound waves propagate in a marine environment in a curve They have a variable velocity And there are many factors affecting wave propagation such as reflection, refraction, diffraction, scattering, wave attenuation, Locating the source of sound waves radiated from the target is affected by these factors The error of the target coordinate measurement of the passive sonar device depends on the two main parameters that are the angle measurement error and the time difference measurement (for the HDPR method) Therefore, in the Dissertation, the direction finding is selected to research and the solutions to improve the accuracy of measuring the angle of arrival of the sonar signal source are proposed to achieve the objectives of the Dissertation is to improve the accuracy of target location determination of the ship’s passive sonar system There are two problems of Dissertation that are needed to resolve: Analyzing and evaluating the ability to DOA estimation by amplitude, phase comparison and TDOA (Time Difference Of Arrival) methods, and CB (Conventional Beamforming) algorithm, MVDR (Minimum Variance Distortionless Response) and then going deep in analyzing MUSIC by simulation, aiming to apply MUSIC algorithm to achieve the purpose of improving the angle measurement accuracy of passive sonar system This problem is solved in chapter 2 The studying and proposing an appropriate antenna network configuration with optimum MUSIC algorithm for improving the accuracy the angle of arrival of the sonar signal source by simulation and empirical measurement to elucidate the research results is partially solved in chapters and Chapter TECHNICAL SOLUTIONS FOR IMPROVEMENT OF THE ACCURACY OF DOA ESTIMATION IN SHIP’S PASSIVE SONAR SYSTEMS Estimating the angle of arrival is a very important step in a sonar system, especially in a passive sonar In the thesis, the frequency of kHz is selected to perform the simulations, and practical measurement, because this is a frequency which is consequently used in many passive sonar systems In addition, passive sonars in our submarines and many countries operate on this frequency [6] 2.1 DOA estimation methods in passive sonar The ability to measure the phase of a narrow-band signal has been verified by experimental measurements and has been published in [4] The measurement results show that the phase measurement method could be applied for passive sonar to measure the angle of arrival of a narrow band signal with relatively high accuracy The DOA estimation method by measuring the time difference of arrival was investigated using experiment measurement and published in [3] 2.2 Hydrophone array model 2.3 DOA estimation of underwater acoustic signals 2.3.1 DOA estimation using CB algorithm The CB algorithm with hydrophone ULA reduces the main beamwidth and steers it to various direction electrically to received simultaneously multiple signal sources and distinguish them The power p of the output signal of the ULA is calculated as: (2.28) p( )  a( )x H xa( ) H -5 Power [dB] -10 -15 -20 -25 -80 -60 -40 -20 20 DOA [degrees] 40 60 80 Figure 2.19: CB spectrum of a ULA with 16 elements steering to angle of 20o, SNR = 15 dB The CB algorithm was investigated for various frequencies in the low and ultra-low band Its results were published in [2] 2.3.2 DOA estimation using MVDR algorithm For optimization of the DOA estimation problem, Capon proposed a technical resolution to improve the DOA estimation performance [14] Instead of the finding maximum of response power at the output of hydrophone array, Capon used a weighted vector to make minimum power of noise power at the output, this technique so-called MVDR The MVDR condition can be written as: (2.29) P(w) w H a( )  Thus, the optimal weighted vector is obtained by: w R x 1a( ) a( )  R x1a( ) H (3.30) The output signal power by Capon is presented in: PMVDR ( )  a( )  R x1a( ) H , (2.31) where, R x is inverse matrix of the covariance matrix R x  x H x Capon Power [dB] -5 -10 -15 -20 -25 -80 -60 -40 -20 20 DOA [degrees] 40 60 80 Figure 2.21: MVDR Response spectrum of hydrophone ULA with 16 elements, d = /2, DOA = 20o SNR = 15 dB 2.3.3 DOA estimation using MUSIC algorithm The MUSIC algorithm was firstly presented in 1979 by R O Schmidt, then it was researched and developed in various scientific publications [58], [59], [60] In Vietnam, the development and application of the MUSIC algorithm for DOA estimation of radar, communication, wifi, and sonar signal were still new problems Some recent publications for the direction estimation of radiated signal source by MUSIC algorithm were considerable such as [19], [20], [29], [30], [34], [38], [54], [68] The antenna array parameters were changed to improve 10 10 PP beamforming thong thuong PP MVDR PP MUSIC Do rong bup chinh muc -3 dB [degrees] 10 10 10 -1 10 -2 10 -3 10 -4 10 -10 -5 10 SNR [dB] 15 20 25 30 Figure 3.2: Comparison of beamwidth at level -3 dB using MUSIC algorithm versus CB and MVDR algorithm for hydrophone ULA 70 PP beamforming thong thuong PP MVDR PP MUSIC 60 PPAR [dB] 50 40 30 20 10 -10 -5 10 SNR [dB] 15 20 25 30 Figure 3.3: Dependence of PPAR values on SNR using CB, MVDR and MUSIC algorithm for hydrophone ULA Conclusion: The comparisons and evaluations of the hydrophone ULA indicated that the MUSIC algorithm provided good quality, which achieved higher accuracy and resolution than CB and MVDR algorithms Comparison of DOA estimation ability on Sonar display Figure 3.4: Simulation of tracking angle on Sonar display for hydrophone ULA using CB, MVDR and MUSIC algorithms with SNR =15 dB 11 3.2 Comparison and evaluation of DOA estimation performance of the MUSIC algorithm versus MVDR and CB algorithms for hydrophone UCA CB MVDR MUSIC -10 Spectrum [dB] -20 -30 -40 -50 -60 -60 -40 -20 10 DOA [degrees] 20 40 60 Figure 3.5: Comparison of the response spectra of MUSIC algorithm versus CB andSo MVDR UCA sanh algorithms rong bup song ofor muchydrophone -3 dB giua thuat toan 4.5 CB BeamWidth at -3 dB [degrees] 3.5 MVDR MUSIC 2.5 1.5 0.5 -10 -5 10 15 20 25 30 SNR [dB] Figure 3.6: Comparison of beamwidth at level -3 dB using MUSIC algorithm versus CB and MVDR algorithm for hydrophone UCA 12 So sanh su phu thuoc cua ti so PPAR vao SNR cua thuat toan 35 CB MVDR MUSIC 30 PPAR (dB) 25 20 15 10 -10 -5 10 15 20 25 30 SNR (dB) Figure 3.7: Dependence of PPAR values on SNR using CB, MVDR and MUSIC algorithm for hydrophone UCA Conclusion: The comparisons and evaluations of the hydrophone UCA indicated that the MUSIC algorithm provided good quality, which achieved higher accuracy and resolution than CB and MVDR algorithms 3.3 Experimental measurement using MUSIC algorithm The connection diagram of the experimental measurement model is described in Figure 3.9 The implementation of signal processing and MUSIC algorithm is illustrated in the diagram of Figure 3.11 Signal generator 20 m Transducer hydrophones Oscilloscope channels Computer Signal processing Figure 3.9: Experimental measurement model 13 In this measurement, the transmitting transducer was spaced at angles 0o, 10o and -10o Transmitting signal was sine with frequency f = kHz After 200 times of signal acquisition and processing for each angle, the MUSIC spectrum was presented in figure 3.12, and the measurement results of each signal DOA were shown in figure 3.13 Import data to variable s = importdata() Filter u = filter() Hilbert transform x = hilbert() MUSIC Covariance matrix R =x*x’ Eigenvectors and eigenvalues [a, b] = eig(R) Steering vector a() for angles  = -90o : 90o Subspace matrix of noise E = b() MUSIC spectrum P_MUSIC() = 1/(a()’*E*E’*a()) DOA determination  = arg max{P_MUSIC} Figure 3.11: Diagram of signal processing and MUSIC algorithm in Matlab 14 Figure 3.12: MUSIC spectra in directions of a) 0o; b)10o and c) -10o 15 degree 10 degrees -10 degrees DOA [degrees] 10 -5 -10 -15 20 40 60 80 100 So lan 120 140 160 180 200 Figure 3.13: DOA estimation results of 200 times of measurement for: 0o, 10o,-10o Table 3.3: Statistics table of measurement results for MUSIC algorithm True DOA [o] Mean of DOA estimation [o] Absolute mean error [o] Root mean square error [o] 10 -10 9,77 -0,014 -9,78 0,12 0.16 0,12 0.30 0,63 0,25 15 Figure 3.14: Comparison of response spectra in the measurement of direction 0o using MUSIC, CB and MVDR algorithms for hydrophone array with elements Figure 3.15: Comparison of main beamwidths in the measurement using MUSIC, CB and MVDR algorithms for hydrophone array with elements Figure 3.16: 2D sonar displays for DOA estimation results using CB, MVDR and MUSIC algorithms in practical measurement 16 Figure 3.17: 3D sonar displays for DOA estimation results using CB, MVDR and MUSIC algorithms in practical measurement Conclusion: After processing the measured signals on the UCA with elements, the experimental results are completely consistent with previous theoretical and simulation results Specifically, the MUSIC algorithm for a sharper peak and smaller beam width than two others, this shows that the MUSIC algorithm achieved higher accuracy and resolution than CB and MVDR algorithms under the same measurement conditions Thus, empirical measurements have demonstrated the feasibility of the algorithms for estimating the angle of arrival of the underwater acoustic signals, in which the MUSIC algorithm is most appropriate This is the basis for the PhD student to continue developing the MUSIC algorithm for appropriate sound antenna array configurations to optimize the ability to estimate the angle of the sound signal source 3.4 DOA estimation using MUSIC algorithm for hydrophone NLA In order to investigate hydrophone NLAs, the following 4-element arrays were chosen for analysis and evaluation: d1 = [0 3]/2; d2 = [0 12] /2, d3 = [0 8] /2, d4 = [0 8] /2 and d5 = [0 12 16] /2 17 Uoc luong DOA bang thuat toan MUSIC d1=[0 3]/2 d2=[0 12]/2 d5=[0 12 16]/2 -5 MUSIC Spectrum P() [dB] -10 -15 -20 -25 -30 -35 -40 -100 -80 -60 -40 -20 20 40 60 80 100  [degree] Figure 3.18: MUSIC spectra of arrays d1, d2 and d5 for DOA = 50 Figure 3.19: MUSIC spectra of arrays d1, d3, d4 and d5 Figure 3.20: Root mean square errors of DOA estimation for arrays d1, d3, d4 and d5 18 Figure 3.21: The main beam width of MUSIC spectra for d1, d3, d4 and d5 Figure 3.22: PPAR values of MUSIC spectra for arrays d1, d3, d4 and d5 Conclusion: Hydrophone NLAs provided higher accuracy than ULAs with the same number of elements Moreover, the NLAs have the ability to distinguish the angle of the incoming signals better than the ULA with the same number of transducer elements The NLAs have obtained these two advantages due to the larger size of the array But when the signals are correlated, the conventional MUSIC method cannot them either Therefore, it needs to have a suitable solution to distinguish the correlated and/or non-correlated signals One of the candidate solutions to solve the problem is a combination of MUSIC algorithm with spatial smoothing music technique, so-call Spatial Smoothing MUSIC 3.5 DOA estimation using Spatial Smoothing MUSIC The signal model for Spatial Smoothing MUSIC algorithm for 16-element linear array is explained as shown in Figure 3.23 If Ri is a covariance matrix of the ith subarray, total covariance matrix R will be: 19 R M  m 1  Ri M  m 1 i (3.39) Subarray Subarray Subarray Subarray Subarray 10 Subarray 12 16 10 11 12 13 14 15 Subarray Subarray Subarray Subarray Subarray Subarray 11 Subarray 13 Figure 3.23: Grouping technique for a linear hydrophone array Smoothing MUSIC Normal MUSIC MUSIC-Spectrum [dB] -10 -20 -30 -40 -50 -60 -80 -60 -40 -20 20 40 60 80  [degrees] Figure 3.24: Comparison of Spatial Smoothing MUSIC and conventional MUSIC Matrix Ri has a size of m×m, matrix R has a size of m×m, also Then perform the steps as the conventional MUSIC algorithm to find the directions of the incoming signal sources The simulations in Matlab environment is used to evaluate the performance of the Spatial Smoothing MUSIC algorithm RMSE of DOA [degrees] 0.35 Smoothing MUSIC Normal MUSIC 0.3 0.25 0.2 0.15 0.1 0.05 -10 -5 SNR [dB] 10 15 20 Figure 3.25: Dependence of RMSE on SNR for Spatial Smoothing MUSIC and conventional MUSIC 20 Smoothing MUSIC 0.9 Normal MUSIC Do rong bup chinh [degrees] 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 -10 -5 SNR [dB] 10 15 20 Figure 3.26: Comparison of main beam widths of spectra using Spatial Smoothing MUSIC and conventional MUSIC Smoothing MUSIC Normal MUSIC PPAR 10 10 10 -10 -5 SNR [dB] 10 15 20 Figure 3.27: Dependence of PPAR on SNR for Spatial Smoothing MUSIC and conventional MUSIC Smoothing MUSIC Normal MUSIC MUSIC-Spectrum [dB] -5 -10 -15 -20 -25 -30 -35 -80 -60 -40 -20 20 40 60 80  [degrees] Figure 3.28: Ability to distinguish two correlated signals 21 3.5.3 Spatial Smoothing MUSIC algorithm for hydrophone NLA A simulation was performed to evaluate the DOA estimation ability of an NLA with elements using Spatial Smoothing MUSIC for two coherent signals with SNR = 10 dB in direction of 10 o and 15o The obtained MUSIC spectrum is shown in figure 3.31 The simulation results reveal the effectiveness of the combining hydrophone NLA with Spatial Smoothing MUSIC algorithm The angle measurement system could distinguish two angles of two coherent signal in clarity Figure 3.31: MUSIC spectrum using Spatial Smoothing MUSIC for hydrophone NLA Next, Ph.D student simulated the operation of the angle measurement system using hydrophone NLA consisting of elements and ULA consisting of 16 above-mentioned elements combining Spatial Smoothing MUSIC algorithm to evaluate the dependence of the RMSE of DOA estimation on SNR The simulation results shown in Figure 3.32 indicated that the angle measurement system uses the hydrophone NLA combined with the Spatial Smoothing MUSIC algorithm to achieve higher measurement accuracy (smaller RMSE) than hydrophone ULA with 16 elements in most SNR values 22 Figure 3.32: Dependence of RMSE on SNR for hydrophone ULA and NLA with the same size using Spatial Smoothing MUSIC 3.6 Conlusion of Chapter From the research results in chapter 3, the following conclusions can be summarized as the following: Signal processing using MUSIC algorithm improved accuracy and resolution of DOA estimation that was higher than CB and MVDR algorithm Analyses and comparisons according to criteria of beam width, PPAR, angle measurement accuracy, the ability of display on sonar monitor demonstrated the superiority and potential of the MUSIC algorithm in comparison with CB or MVDR algorithms in the ship’s passive sonar systems The hydrophone NLA was proposed to be used in the passive sonar systems due to the increment of array aperture with a minimum number of array elements, thereby computational complexity could be reduced; the DOA accuracy and resolution is enhanced The Spatial Smoothing technique is the splitting the full hydrophone array into subarrays with a smaller number of elements that make the size of covariance matrix smaller This technique provided enhancing the effectiveness of signal processing for MUSIC algorithm while ensuring the ability to distinguish the correlated and uncorrelated signal sources, simultaneously 23 In Chapter 3, the Spatial Smoothing MUSIC was proposed in order to increase the DOA accuracy, reduce the amount of hardware, eliminate the ambiguity and increase the processing speed for DOA measurement in the passive sonar systems CONLUSION The research content and results of the Dissertation were published in 07 journal and conference papers The results of the investigation, evaluation, and proposal in the Dissertation were not plagiarizing any other previous publications The Dissertation has achieved the following results and new contributions: The Results of the Dissertation - Overview of the target positioning methods, DOA estimation methods used in the passive sonar systems Focusing on the DOA estimation using the MUSIC algorithm Mathematical analysis and evaluation of the ability of the localization methods and DOA estimation method used for the ship’s passive sonar systems - Solution for increasing accuracy of DOA estimation was selected to achieve the purpose of enhancement of the target positioning accuracy for the ship’s passive sonar systems - The classical methods using amplitude, phase and time measurement could be employed to instantaneously determine the direction of a single source The advanced methods such as CB, MVDR, and MUSIC were obtained higher effectiveness for estimating DOA of the multiple sources However, they had two major disadvantages, that are computational complexity and unable to distinguish two or more coherent signals - Experimental measurements were performed in lab water tanks at Naval Academy and at Naval Technical Institute The sample signals used for the measurements were harmonic signals with changeable frequency, so they were less affected by environmental interference in case of phase comparison and TDOA measurement methods - Experimental measurement in realistic sea environmental condition of Nha Trang Bay was performed The measured signals were processed using CB, MVDR and MUSIC algorithms Final measured and processed results indicated that the MUSIC algorithm provided the higher accuracy and resolution of DOA estimation than CB and MVDR - The hydrophone NLA combining with MUSIC algorithm was proposed to enhance DOA estimation accuracy, reduce hardware cost and computational capacity and be able to distinguish multiple coherent and/or non-coherent signals 24 Research results confirmed the applying MUSIC algorithm to solve the purpose of the problem to improve the accuracy of estimating the angle of arrival to improve the accuracy of target positioning for ship’s passive sonar systems The Novel Contribution of the Dissertation: i Proposing the hydrophone NLA configuration combined with Spatial Smoothing MUSIC for enhancing the accuracy of DOA estimation of multiple coherent and non-coherent signals ii Establishment of experimental measurement models for sonar signal in lab water tanks to validate the DOA estimation ability of the phase comparison and TDOA measurement methods; Measuring and processing the sonar signal using MUSIC algorithm for the sectoral array of elements in the particular environmental condition Contributing some evaluation to improve the accuracy of sonar signal source positioning in practice Development in Future: - Completing the configuration of hydrophone arrays; performing experimental measurements to verify the phase comparison method, the TDOA measurement method to determine the direction of underwater acoustic signals on different carrier frequency bands in realistic marine environmental conditions; - The experiment measurement in the marine environment will be performed and the measured signals will be processed using MUSIC algorithm for the ULAs, NLAs, and UCAs with a different number of elements - Designing a passive sonar system that can employ the proposed solutions in the Dissertation for development or new manufacturing the ship’s passive sonar devices PUBLICATIONS REFERENCES APPENDIX ... Cong Tran, Thanh Chi Vu, Hung Thanh Nguyen, 2017, The Measurement of Long Baseline Interferometer, Journal of Science and Technology, Radar Monitoring Systems, Military Technical Academy, No189,... passive sonar systems Chapter 2: Technical solutions for improvement of the accuracy of DOA estimation in ship’s passive sonar systems Chapter 3: Application of MUSIC algorithm for improvement of the... resolution than CB and MVDR algorithms under the same measurement conditions Thus, empirical measurements have demonstrated the feasibility of the algorithms for estimating the angle of arrival