Issues: Hệ thống và Thiết bị thông minh Vol 33.3 (09/2023)
1. Proposal for a Doppler Shift Compensation Method Using Non-Uniform FFT with Pilot Carrier Frequency for OFDM-Based Underwater Acoustic Communication Systems

Nguyen Van Duc, Nguyen Thi Hoai Linh, Nguyen Quoc Khuong, Nguyen Tien Hoa

In this paper, we propose a method that uses the non-uniform Fast Fourier Transform (FFT) to compensate for Doppler frequency shifts in OFDM-based underwater acoustic (UWA) communication systems. To estimate the Doppler frequency shift, the paper proposes using a pilot carrier frequency (PCF) that is identified by transmitting with greater power in the frequency domain compared to other subcarriers. This identifier helps estimate both the Doppler frequency shift and the channel. The paper proposes estimating and compensating for the Doppler frequency shift in two steps: Step 1 performs coarse frequency synchronization, where the Doppler frequency shift is determined by using PCF signal. The Doppler shift correction is obtained by re-sampling the received signal, and then interpolating re-sampled signal. However, the Doppler shift compensation in the step 1 cannot correct the phase distortion of the measured PCF signal. Therefore, performing step 2, known as fine frequency synchronization, is necessary. In this step, the correction for the phase distortion is determined based on the phase difference between the two consecutive OFDM signals in one frame. The remaining Doppler frequency shift is adjusted based on the phase deviation, using the non-uniform FFT. By using the non-uniform FFT, the complexity of the ICI compensation is significantly reduced, and the quality of Doppler shift compensation is improved. The experience results show that the transmitted text will be decoded correctly by using the proposed technique.

Article Code:23007

# Pilot Carrier Frequency, Carrier Frequency Offset, Interchannel Interference, ununiform Fast Fourier Transform.

Page: 1-7

Field: Electronics and Telecommunications
2. Multi-band Antenna Design Optimization Using Nature-inspired Evolutionary Algorithm For 5G Wireless Communication

Le Minh Hoang, Nguyen Thanh Huong*, Nguyen Duc Hai

Automation and telecommunication systems are increasingly improving and becoming more easily integrated thanks to wireless communication technology, in which the essential component is the antenna. Designing and optimizing antenna structures still takes a lot of time, especially for complex structures with multiple operating frequency bands or complex material layers. With modern computing power, the speed of computation is increasingly efficient, and combining automated computation for optimization and design is entirely feasible. Many research groups around the world have implemented automated antenna design through optimization algorithms, genetic algorithms, swarm algorithms, collectively referred to as evolutionary algorithms. These algorithms simplify the antenna design process, making it more automated and optimized. In this paper, the Improved Black Hole algorithm is proposed and used to optimize the design of a CPW-Fed slot microstrip antenna.

Article Code:23036

# Nature-inspired optimization, Black Hole algorithm, Antenna design, 5G communication, Multi-band antenna, Sub-6 GHz band

Page: 8-15

Field: Electrical Engineering
3. BK-SAD: A Large Scale Dataset for Student Activity Recognition

Trinh Cong Dong, Nguyen Van Giang*, Nguyen Chan Hung, Nguyen Quang Dich

Skeleton-based human action recognition has emerged as a prominent research topic in the field of artificial intelligence due to its broad applicability in a wide range of domains, including but not limited to healthcare, security and surveillance, entertainment, and intelligent environments. In this paper, we propose a novel data collection methodology and present BK-Student Activity Dataset (BK-SAD), a new 2D dataset for student activity recognition in smart classrooms that outperforms the existing NTU RGB+D 120 dataset, SBU Kinect Interaction dataset. Our dataset contains three classes: hand raising, doze off, and normal activities. The dataset was collected using cameras placed in the real classroom environments and consisted of video data from multiple viewpoints. The dataset contains over 2700 videos of students raising their hands, over 1700 videos of students dozing off during class, and over 8500 videos of normal activities. In addition, to evaluate the effectiveness of the proposed dataset, we give some baseline performance figures for neural network architectures trained and tested for student activity recognition on BK-SAD dataset. These ConvNet architectures demonstrate significant performance improvement on the proposed dataset. The effectiveness of the proposed novel data collection methodology and BK-SAD dataset in this paper will enable further research and development of activity recognition models for classroom environments, with potential applications in the smart education and intelligent classroom management systems. BK-SAD is available at https://visedu.vn/en/bk-sad-dataset

Article Code:23021

# Dataset, Action recognition, Skeleton pose, Student activity recognition, Smart classroom

Page: 16-23

Field: Information and Communication Technology
4. Studying and Realizing the Based-Intelligent IoT System for Pipeline Cathodic Protection

Bui Dang Thanh*, Thi-Phuong Nghiem

Cathodic protection (CP) emerges as the optimal approach for mitigating metal corrosion in pipeline networks. To ensure the continued efficiency of the CP system, monitoring the potential distribution throughout the network is crucial. In distribution networks, the pipeline potential is influenced by time-varying environmental factors, making it challenging to estimate the potential at locations away from the measurement point. This paper presents a proposed cathodic protection system for pipelines, utilizing an intelligent IoT (Internet of Things) system. The sensor nodes of the system designed based on the STM32 microcontroller perform the measurement of voltages from the reference electrodes, process the signal as well as perform wireless communication about the control stations via LoRa communication. Besides, the control stations are designed to implement voltage compensation control through autotransformer and to communicate with the server through GPRS communication. The objective is to deploy an affordable system capable of effectively monitoring and regulating the potential of the pipeline at a designated measurement location in industrial plants.

Article Code:23027

# Electrochemical corrosion, Impressed current cathodic protection, IoT, LoRa

Page: 24-32

Field: Electrical Engineering
5. A Comparative Study of Machine Learning Classifiers in Oil-Immersed Power Transformer Fault Diagnosis

Nguyen Thanh Son*, Pham Minh Tu, Hoang Anh

The most common fault diagnosis method for oil-immersed power transformers is dissolved gas analysis (DGA). Doernenburg ratios, Rogers ratios, IEC ratios, and Duval's triangle are conventional DGA techniques for insulating oil in power transformers. In this study, Scikit-learn known as a popular open-source free machine learning tool for Python programming language has been used to develop different machine learning (ML) classifiers to effectively detect defects in oil-immersed power transformers. These classifiers are Decision Trees, Support Vector Machines, Gaussian Naive Bayes, K-Nearest Neighbours, Random Forests, and Multi-Layer Perceptron. The input vector of each classifier has been formed by Doernenburg ratios, Rogers ratios, IEC ratios, and CSUS. After these classifiers are completely trained, unseen DGA data sets are then used to evaluate their performances. Based on a statistical analysis, the study can indicate the most efffective type of the input vector and ML classfier for precisely detecting faults in power transformers.

Article Code:23004

# Power transformers, dissolved gas analysis, fault diagnosis, machine learning

Page: 33-40

Field: Electrical Engineering
6. Flatness-based Nonlinear Anti-sloshing Control of Liquid Containers

Minh Do Duc, Khanh Nguyen Viet, Thanh Cao Duc, Hieu Ho Thanh, Duc Duong Minh, Lam Nguyen Tung*

The movement of the liquid inside the container, known as sloshing, is usually undesired. Thus, there is the necessity to keep under control the peaks that the liquid free-surface exhibits during motion. This paper aims at providing a solution for suppressing sloshing liquid in horizontally moving cylindrical container. After introducing equivalent discrete models based on a mass-spring-damper system introduced by the literature (non-linear model), the identification and utilization of flat outputs is presented to generate rest-to-rest trajectories in sloshing liquid systems, which is ensure the equilibrium of the sloshing height at both initial and final points. Moreover, a sliding-mode controller is described to solve the trajectory tracking problem. The effectiveness of the proposed approach is demonstrated through numerical simulations comparisons with a model predictive controller (MPC). This research contributes to the advancement of control techniques for anti-sloshing technology systems, enabling enhanced stability, performance, and safety in various engineering applications.

Article Code:23039

# sloshing, flat output, rest-to-rest trajectory, sliding-mode control, model predictive control

Page: 41-48

Field: Electrical Engineering
7. Evolutionary Airfoil Shape Optimization Coupling Parameterization Methods with Lagrangian Vortex Method

Duong Viet Dung*

In the present paper, the evolutionary algorithm for single-objective optimization is developed using a
genetic algorithm and employing polynomial-based (PARSEC) and radial basis function (RBF) functions for NACA
2412 airfoil parameterization. The determination of the objective functions (aerodynamic coefficients) are performed
using the Lagrangian vortex particle method. The results of the lift coefficient at the wide range of angle of attack
using the vortex particle method shows a good agreement with experimental data listed in the literature. For the
optimization results, the lift coefficient obtained from the PARSEC method is optimized to be larger for the whole
range of AoAs; while it still keeps the stall region at the upper surface of the airfoil to be the same as that of the original
airfoil. In addition, the RBF method illustrates the lift coefficients larger at the range of AoA from -5 to 14 but stall occurs earlier than the original airfoil.

Article Code:23010

# optimization, vortex particle method, viscous flow

Page: 49-56

Field: Mechanical Engineering
8. Output Feedback Adaptive Pitch Angle Control for Variable Speed Wind Turbine

Nhat-Minh Le Phan, Tung Thanh Nguyen, Duong Tung Nguyen, Nga Thi-Thuy Vu*

This paper proposes a simple adaptive controller for pitch angle control of the variable speed wind turbine. The aim of the controller is to keep the speed of the generator at the rated value when the wind speed is above the nominal value. The controller contains two components: one is output feedback component for stable purpose, the other is adaptive component to cancel the effect of nonlinearities, system uncertainties, and external disturbances. The controller does not need information of system parameters and wind speed then it is robust to the system uncertainties as well as wind speed varying. Moreover, this controller is quite simple, so it is easy for implementation. The stability of the closed loop and the convergence of the adaptive law is mathematically proven via Lyapunov theory. The effectiveness of the given scheme is verified via simulation under two scenarios: step wind speed and random wind speed. Also, the comparisons are done between proposed adaptive controller, the corresponding nonadaptive controller, and the PID controller. The simulation results show that, for both cases, the given adaptive controller has the best responses with low steady state error of rotor speed, low overshoot, and smooth output power

Article Code:23022

# Adaptive, output feedback, pitch angle control, wind turbine

Page: 57-64

Field: Electrical Engineering
9. Effective Control Strategies for Rotary Inverted Pendulum System: Energy-based, LQR, and HSMC Techniques

Duc-Binh Pham, Quy-Thinh Dao, Thi-Van-Anh Nguyen*

This work presents a comprehensive study of control problem for the rotary inverted pendulum (RIP), a challenging underactuated system with potential applications in robotics and aerospace. The paper develops effective swing-up energy-based control and stabilization task. It also presents two controllers, linear quadratic regulator (LQR) and hierarchical sliding mode control (HSMC), that effectively handle the stabilization problem. System modelling is based on Lagrangian mechanics, and the control strategies are evaluated using simulations and compared in terms of performance and robustness. The results demonstrate that energy-based control is effective for swing-up, while linear quadratic regulator and hierarchical sliding mode control are effective for stabilization. The proposed controllers show promising results and contribute to the development of robust and efficient control strategies for the RIP system. The study has implications for the development of control strategies for other underactuated systems and can potentially lead to advancements in the field of robotics and aerospace.

Article Code:23026

# Rotary inverted pendulum, Swing-up and stabilization control, Energy-based control, Hierarchical Sliding Mode Control, Linear Quadratic Regulator.

Page: 65-73

Field: Electrical Engineering