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ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY *************** PHAN HONG MINH RESEARCHING METHODS TO IMPROVE THE QUALITY OF AN UNDERWATER SENSOR ARRAY RECEIVING SIGNALS IN SHALLOW WATER A

ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY

***************

PHAN HONG MINH

RESEARCHING METHODS TO IMPROVE THE

QUALITY OF AN UNDERWATER SENSOR ARRAY

RECEIVING SIGNALS IN SHALLOW WATER AREAS

Specialization : Electronic Engineering

Code No : 9 52 02 03

SUMMARY OF TECHNICAL DOCTORAL THESIS

Ha Noi – 2020

Academy of military Science and Technology

Scientific Supervisor:

1 Dr Phan Trong Hanh

2 Dr Vu Van Binh

Reviewer 1: Prof Dr Vu Van Yem

Hanoi University of Science and Technology

Reviewer 2: Assoc Prof Dr Do Quoc Trinh

Military Technical Academy

Reviewer 3: Dr Vu Le Ha

Academy of military Science and Technology The thesis will be defended before approval committee at :

Time , date month year 2020

This thesis may be found at:

- Library of Academy of Military Science and Technology

- The Vietnam National Library

1) Phan Hong Minh, Phan Trong Hanh, Luong Thi Ngoc Tu,

“Configuration of hydrophone array based on ICA pre-processing to enhance accuracy position of multi-targets”, Journal of Military Research and Technology, No 48, 04/2017

2) Phan Hong Minh, Phan Trong Hanh, Vu Van Binh, Nguyen

Cong Dai, “The Solution of configuration 2D hydrophone array based on beamforming option”, Journal of Military Research and Technology, No

54, 04/2018

3) Le Ky Bien, Phan Hong Minh, Tran Hieu Thao, Phan Trong

Hanh, “The solution of signal processing for sonobouy systems detection and identification based on passive sonar”, The National conference

"High-tech applications in practice" 2018, Journal of Military Research and Technology, No Special issue, 08/2018

4) Phan Hong Minh, Phan Trong Hanh, Vu Van Binh,

“Multi-channels blind deconvolution of shallow underwater signals based on Feed-Foword neural networks”, Journal of Military Research and Technology, No 62, 08/2019

INTRODUCTION

1 Necessity of the thesis

The sea is especially important for national defense and security, for socio-economic development and integration with the world All countries having seas must have their own plans and solutions to protect the safety of their waters, islands and territorial waters Safely protecting coastal, military bases and archipelagos, detecting target identification to prevent underwater targets from the sea is necessary

2 Obiectives of the study

Research and develop solutions to improve the signal quality of the underwater sensor array for sonar systems and passive positioning devices to enhance the ability to detect and locate targets as sources underwater sound in the shallow sea

3 The main results, scientific significance and practical meaning of the thesis

3.1 The main results

1) Proposed structural model of the retangular acoustic sensor array, combined with a customized adaptive beamforming solution, increased the gain of the sensor array

2) Proposed a model and solution for complex underwater signal processing on the basis of combining independent component analysis (ICA) and multi-channel blind analysis (MBD) to improve SNR ratio in shallow water areas

3.2 Scientific significance and practical meaning of the thesis

The research to improve the quality of the underwater sensor array for sonar systems, passive positioning devices for underwater acoustic emission targets is carried out on the basis of structural solutions and signal processing for shallow waters is to solves scientific and practical requirements

Research results of the thesis with the proposal of a solution of array structure and adaptive beamforming and a solution of complex acoustic signal processing based on the combination of two signal processing techniques ICA and MBD will contribute more theoretically to the field

of hydrodynamic positioning At the same time, these research results are related to the conditions and characteristics of Vietnam's territorial waters, so it will be a good basis and orientation when designing sonar systems or underwater positioning devices in Vietnamese

CHAPTER1: UNDERWATER SENSOR ARRAY AND PROBLEM

TO IMPROVE QUALITY ARRAY IN THE SHALLOW WATER 1.1 Overview of underwater sensor array

1.1.1 Model of sensor array

The sources of interest in sonar and ultrasound are the narrowband and wideband applications that satisfy the wave transmission equation in [31], [37], and their spatial properties can be independently separated Therefore, the measurement of the 𝑧 𝑟 , 𝑡 is stimulated by negative sources that can determine the time-space response 𝑥 𝑟 , 𝑡 The vector 𝑟 is the relative position of the sensor and

the sound source, t is the time

Figure 1.1 Space-Time Model receiving signal of sensor array

Response output 𝑥 𝑟 , 𝑡 is convolution of 𝑧 𝑟 , 𝑡 and response of sensor array ℎ 𝑟 , 𝑡

𝑥 𝑟 , 𝑡 = 𝑧 𝑟 , 𝑡 ⊗ ℎ 𝑟 , 𝑡 (1.1) There 𝑧 𝑟 , 𝑡 is defined are input of receiver, and is convolution of acoutic souce parameter 𝑦 𝑟 , 𝑡 with underwater environment Ψ 𝑟 , 𝑡

𝑧 𝑟 , 𝑡 = 𝑦 𝑟 , 𝑡 ⊗ Ψ 𝑟 , 𝑡 (1.2)

1.1.2 Sensor array and underwater passive sonar system

Model of structure system

The sonar system is a system of devices that determine the position of the sound source in the space under the sea surface Depending on the application and different characteristics, the system

has the form: mobile or fixed The basic structure model of a passive

sonar system with M sensors can be described according to the progress

of the identification detection information as follows (Figure 1.2):

Figure 1.2: Model of underwater passive sonar system

The accuracy positioning of sound source

𝜎𝑝 𝐷 = 𝜎đ2𝑡 𝐷 + 𝜎𝑚𝑡2 𝐷 + 𝜎𝑡𝑛2 𝐷 𝜎𝑖2 𝐷

𝑖

(1.7)

1.2 Shallow water and characteristic

1.2.1 The concept of shallow sea

1.2.2 Multi-path effect in the shallow sea

Figure 1.3: Multipath trajectories in an isvelocity shallow water configuration (A) direct path; (B) Reflection on the surface; (C)

Reflection on the bottom and surface

For shallow waters the transmission environment is limited by the sea surface and the seabed, the signal propagation is reflected many times before go to the receiver According to the experimental results of Lurton [37] in Figure 1.3a, the path of the negative rays in shallow water

is reflected many times, Figure 1.3b shows the multi-path effect of measuring signals in real time domain

Hình 1.4: Simulate multi-path with 5 acouctic path

Figure 1.5: Receiving pulse in the shallow water

Figure 1.4 illustrates the sound channel in shallow water affected

by the multi-path with 5 rays: sound speed is 1520 m/s, depth of channel

is 100m, source with coordinates [0,0, -60], receiver 1 has coordinates [500,0, -40], receiver 2 has coordinates [500, 1000, -70], isotropic sources and direct and reflected sound at the bottom have a loss of 0.5dB

The isotropic source generates a pulse of 13.2ms width into the

audio channel with 5 rays received at the receiver In Figure 1.5, the

signal receives multiple echoes generated by reflected sound rays, which interfere with each other Thus, in the shallow sea, the effect of multi-path effect on signal quality is enormous

To solve this problem, there are several solutions such as: The first is design the geometric structure of the array to increase the gain of the receiving array The second is beamforming of the sensor array so that the main beam is directed towards the direct beam while the signal coming from the other directions is noise, in order to increase the SNR Thirdly, solution DSP to recontruct signal These solutions are discussed

in detail in the following sections

1.2.3 Parametric effect of shallow sea on the quality of passive sonar

system

1.3 Solutions to improve the quality of sensor array

1.3.1 Optimize the geometric structure of the array

1.3.2 Beamforming sensor array

1.3.3 Signal processing array sensors

Figure 1.7: Block diagram of sensor signal processing array system

Signal processing underwater sensor array is an extended concept including processing sonar sensor, underwater communication network including functional blocks such as ADC conversion, FIR filtering, Adaptive LMS filter, Kalman, adaptive noise suppression, linear adaptive enhancement, DEMON / LOFAR analysis, FFT / MUSIC spectrum analysis, target detection (torpedoes, submarines, strange ships, clones, fish stocks, etc.), target identification, of SNR of the array,

recording, tracking, etc (Figure 1.7)

1.4 The problem of improving the quality of the underwater sensor array and the research direction of the thesis

1.4.1 Related studies have been published

Researches in our country,

International pulication

1.4.2 Requirements and research directions of the thesis

From scientific requirements and practical requirements on the quality of sensor arrays, based on the theory of electronic and engineering, the thesis aims at the following tasks:

- Develop solutions to improve the quality of the underwater sensor array by the method of customized beamforming;

- Develop a solution to improve the receiving signal quality of the underwater sensor array using a customized complex signal processing method (Figure 1.9)

Figure 1.9: Proccesing signal model to impove quality of sensor array

1.4.3 Researching of the thesis

The research problem was raised to propose a solution to improve the quality when working in shallow sea environment, characterized by the multi-path effect and high noise In order to solve the above, it is necessary

to fix the following issues: The first is to study a customized beamforming, combining conventional and adaptive control mail lobe in order to improve the SNR ratio of the sensor array The second is to research a solution processing suitable to the structure of the underwater sensor array based on the combination of ICA technology and the solution

of multi-channel blind deconvolution by neural network into processing sensor signal array to restore original signal

2 CHAPTER 2: SOLUTION TO IMPROVING SIGNAL QUALITY BASED ON CUSTOMIZE BEAMFORMING ARRAY 2.1 Beamforming sensor array

𝑒−𝑗 𝑛−𝑁−12 𝑘 𝑧 𝑑

(2.13)

𝐵𝜓 𝜓 = 𝐰𝐻𝐯𝜓 𝜓 = 𝑒−𝑗 𝑁−12 𝜓 𝑤𝑛∗𝑒𝑗𝑛𝜓,

𝑁−1 𝑛=0

where 1 is the Nx1 unity vector Thus, the frequency-wavenumber

function can be written in ψ –space

𝑥𝑛 =1 − 𝑥

𝑛

1 − 𝑥𝑁−1

We observe that ϒ.𝜓 𝜓 is periodic with period 2π for N odd If N is even, the lobes at ±2π, ±6π are negative and period is 4π The period of

|ϒ.𝜓 𝜓 | is 2π for any value of N

ϒ 𝑤: 𝑘𝑧 =𝑁1𝑠𝑖𝑛 𝑁𝑘𝑧

𝑑 2

𝑠𝑖𝑛 𝑘 𝑧𝑑2 , −∞ ≤ 𝜓 ≤ +∞ (2.34)

ϒ 𝑤: 𝑘𝑧 is periodic with period 2π/d

Note that the response function depends only upon the wavenumber

component kz and is periodic with respect to kz at intervals of 2π/d

So that beam lobe in ψ space is:

𝐵𝜓 𝜓 = 1

𝑁

𝑠𝑖𝑛 𝑁𝜓2 𝑠𝑖𝑛 𝜓2 , −

2𝜋𝑑

𝜆 ≤ 𝑢 ≤

2𝜋𝑑

Simulate uniform linear array beamforming in polar and 3D

Figure 2.6: ULA beamforming ϒ(ψ) in polar (dB)

Figure 2.7: ULA beamforming ϒ(ψ) in 3D space

2.1.2 Beamforming sensor array with different geometry

2.2 Adaptive Beamforming sensor array

2.2.1 Model and method adaptive beamforming

2.2.2 Frost adaptive beamforming

2.3 A solution to solve multi-path based on a customized array of beams

2.3.1 Rectangular customized beamforming

On the basis of rectangular array of NxM hydrophone, building

calculation models and designing beam for arrays based on manifold vectors and weighted arrays [17] The beam of a rectagular array with a

source at position p(r,θ,ϕ) is calculated as follows:

(2.49) Where:

𝜓𝑥 =2𝜋

𝜆 𝑑𝑥𝑠𝑖𝑛𝜃𝑐𝑜𝑠𝜙, 𝜓𝑦 =

2𝜋

𝜆 𝑑𝑦𝑠𝑖𝑛𝜃𝑠𝑖𝑛𝜙

If array is uniform with d x = d y = λ/2 và N x M = 5 x 7 the beam with is

lobe Figure 2.20 The manifold vectors is mth row along the y-axis of the retangular array is calculated:

Figure 2.20: Geometry and5x7 rectangular array beamforming

thus, for the all array, we have a manifold matrix with NxM hydrophone

as follows:

𝑽𝜓 𝜓 = 𝒗0 𝜓 ⋮ ⋯ ⋮ 𝒗𝑀−1 𝜓 T, véc tơ 𝝍 = 𝜓𝜓𝑥

𝑦 (2.51) from this, it is possible to define a generalized vector by folding in turn

to have a vector NM x 1 value

Thus:

𝐵 𝜓 = 𝐵 𝜓𝑥, 𝜓𝑦 = 𝑣𝑒𝑐H[𝑾]𝑣𝑒𝑐 𝑽𝜓 𝜓 (2.55)

is an overview format to design an NxM hydrophone all planar array

2.3.2 Calculate and customize arrays to reduce multi-path effect

- Calculating arrays to enhance signals when the target is approaching

Consider the ULA of 30 hydrophones to observe the target from afar into the array, the array can be customized as follows:

+ A ULA of 30 hydrophone: Array gain G A = 30dBi, The figure shows that the main-lobe is very narrow and pointed, the side-lobe are

suppressed, when looking at the distant target, it is good (Fig.2.25)

Figure 2.25: Linear beamforming 30 hydrophones

+ Three independent linear arrays each with 10 hydrophone arrays: G A =

G 1 + G 2 + G 3 = 30 dBi The simulation shows that the main-lobe are

larger, the side-lobe also increase, but ensuring the gain (Figure 2.6)

Figure 2.26: Linear beamforming 3 arrays each 10 hydrophone

+ one vertical array in the middle and two customizable segments

independently rotated by 10 degrees (Figure 2.27):

Hình 2.27: Beamforming one vertical and two rotated by 10 o

When observing a distant target, the signal field to the array is parallel, the first two cases are well observed When the target comes near, both of the above arrays are much worse To calculate the attenuation, consider the magnitude of the main beam at 3dB (the half-power beamwidth, HPBW)

According to [17] the half-power beamwidth main-lobe:

= 550/sin10O = 3167 m

Thus, when the target near the array to a distance of 3167m, in the case

of 2 the gain will decrease and G A = G 1 /2 + G 2 + G 3 /2 dB, the further

the gain decreases In the case of 3 custom arrays that have been rotated

to 10O, when the target is close, the gain is still constant

- Customized array to optimize reception of the desired signal

Consider the rectangular array of 10x10 hydrphone which assumes that the desired signal comes from the direction of 28O, the noise signal comes from the direction of 62O and the noise comes from the direction of 75O Customizing the planar array into 3 parallel arrays and determining the gain with the 3 main beams turning in the direction

of 28O Simulate 3 different linear arrays of configurations to calculate the 62O and 75O directional gain of the array in the cases to determine

G min , G A (θ o )= G 1 (θ o )+ G 2 (θ o )+ G 3 (θ o ) gain regulation = 10 dBi for each

of 62O G min = 0.95 in the case of Num-14 customized in to 2 linear of 15