Junita Mohd Nordin
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Preferred name
Junita Mohd Nordin
Official Name
Mohd Nordin, Junita
Alternative Name
Junita, M. N.
Nordin, Junita M.
Nordin, J.
Nordin, Junita Mohd
Nordin, Junita
Nordin, J. M.
Main Affiliation
Scopus Author ID
24447788000
Researcher ID
DKQ-9678-2022

Research Output

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Development of a new code for subcarrier-multiplexed optical code division multiple access system

2011 , Junita Mohd Nordin

The growing utilization of bandwidth hungry applications of the internet and multimedia applications has lead to tremendous research development in optimizing the bandwidth capacity in optical communication, particularly in Optical Code Division Multiple Access (OCDMA). In this work, a new code in the family of Spectral Amplitude Coding (SAC) OCDMA has been developed in an attempt to overcome the limitations faced by other existing codes of the same class. This work also contributes to the development of mathematical model of hybrid subcarrier multiplexed OCDMA system based on the new code and its performance evaluations. The combination of Subcarrier Multiplexing (SCM) and OCDMA scheme can be regarded as a new research area which is still in its infancy, since most work on SCM gives privilege to the combination with Wavelength division multiplexing (WDM) scheme. This combination demonstrates an improvement in bandwidth utilization of optical communication. In particular, this thesis begins with an explicit construction of the code, namely the Recursive Combinatorial (RC) code that is designed to have a minimum cross correlation of one, with the flexibility of choosing the code’s parameter, such as the code weight and number of code sequences, with minimum code length. The simple code development are based on the matrix combinatorial method to maintain the cross correlation of one between the code sequences, that reduces the Multiple Access Interference (MAI). The mathematical derivation of this code’s performance is then generated to analyze its performance in the OCDMA system. Simulations are carried out to evaluate and optimize the parameters for best performance in the system. The study focuses on the effect of distance, bit rate, data modulation format and input power on the systems performance. Validations of theoretical results by simulations are also conducted. It is shown from the performance analysis that this codes exhibits better performance compared to other codes in the same class. It is shown in term of cardinality; this code could accommodate up to 105 users simultaneously at a permissible bit error rate of 10-9. In the hybrid SCM OCDMA using RC code, this system could accommodate up to 28 subcarrier channels for BER better than 10-9. On the other hand, the MDW code, as compared, can only accommodate up to 20 subcarrier channels. A simulation model is also developed for the SCM OCDMA system, where some comparisons are being made on its performances. In short, the significant contribution of this thesis lies in the development of a new code exhibiting a very simple code construction, which is suitable for the ease of implementation in a practical network. Adding new users in the network using this code does not require modifying the existing network; nodes can be added at the next available wavelength along the bandwidth occupied. At the same time, adding up the code weight will not change any other parameters. In other words, this code design retains the individuality of each code parameter, hence making it a more flexible code compared to others. Apart from that, the theoretical and simulation model derived for a hybrid system of subcarrier multiplexed OCDMA based on RC code has realized a potential approach in improving the bandwidth utilization efficiency of optical communication.

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Development of Highly Efficient Hybrid Kinetic-Solar Energy Harvesting System

2023-01-01 , Liew Hui Fang , Rosemizi Abd Rahim , Muhammad Izuan Fahmi Romli , Junita Mohd Nordin , `Aini Syuhada Md Zain , Mujahidin N.M.D.Z.

The development of sustainable and efficient energy harvesting systems has become critical in meeting global energy demands. Hence, the goal is to combine the kinetic energy created via footsteps alongside solar energy to maximize energy conversion and develop a sustainable power source. The research entails designing and optimizing the hybrid system, while selecting appropriate materials, and implementing advanced power management techniques for effective energy utilization. Therefore, in order to improve the efficiency of energy harvesting via the system, further research on voltage input for solar panels and piezo buzzer efficiency arrangements on slabs were conducted. Whereby, the tile cells generate electricity when someone walks across it. However, this energy output needs to be regulated using a voltage multiplier and an alternating current into direct current (AC-DC) converter. To accomplish this, an experiment on the outcomes for output parameter with stand-alone photovoltaic (PV) harvesting system in 6 days, piezoelectric (PZ) harvesting system with students weighing 60kg and 70kg in 14 steps and a power hybrid harvesting system was carried out. Overall, the findings of this study indicate that the proposed method is functional and can be verified by the system, with an average output of 9.46 V and 126.6 mA produced. Also, this study demonstrates the significant potential of hybrid kinetic-solar energy harvesting system in improving energy sustainability and promoting self-sufficient power generation for a variety of applications, including remote sensing, wireless sensor networks, and internet of things (IoT) devices, through experimental evaluations and simulations.

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Electrical energy consumption monitoring system over internet of things

2024 , Mohd Shahril Affandi Abdul Majid , Rosemizi Abd Rahim , Junita Mohd Nordin

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Performance enhancement of LACO-OFDM BER and PAPR using a K-means algorithm for a VLC system

2023 , Junita Mohd Nordin , Aymen Abdalmunam Hameed , Anuar Mat Safar , Norizan Mohamed Nawawi

Layered asymmetrical clipped optical-orthogonal frequency division multiplexing (LACO-OFDM) enhances spectral efficiency by mandating the use of a K-means algorithm in LACO-OFDM (KLACO-OFDM), which enables efficiency gains to nearly double by modulating odd and even subcarriers. The traditional receiver is not sufficiently sophisticated enough to exploit the full potential of LACO-OFDM, thereby restricting its performance. In this paper, a K-means algorithm was used to increase the spectral efficiency of LACO-OFDM by integrating machine learning to cluster the inward signal such that the original locations of the received constellations can be retrieved. A K-means algorithm is used for assigning the received constellation points into their clusters of the ordinary quadrature amplitude modulator constellation points. The new mathematical framework in the proposed scheme is structured to analyze the PAPR and BER performance of LACO-OFDM systems that have been derived. The K-means algorithm development in LACO-OFDM (KLACO-OFDM) has also reduced the intersymbol interference, hence improving the spectral efficiency of LACO-OFDM compared with the conventional system in visible light communication (VLC) systems. BER gains were about 1.2–1.6 dB at 10−3 BER value, which rises from 1.4 to 2 dB for a 10−4 BER value because a lower BER facilitates precise estimation.

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A multilayers adaptive ALACO-OFDM for spectral efficiency improvement using PSO algorithm in visible light communication systems

2023 , Aymen Abdalmunam Hameed , Anuar Mat Safar , Montadar Abas , Junita Mohd Nordin , Norizan Mohamed Nawawi

In this paper, we propose a new adaptive layered asymmetrically-clipped optical orthogonal frequency division multiplexing (ALACO-OFDM) technique as a method to improve the spectral efficiency of optical system, especially visible light communication (VLC). Particle swarm optimisation (PSO)-based LACO-OFDM method is used for this purpose and the channel capacities are studied. Simulations using variable layers are carried out to validate the theoretical steps. The simulation results indicate that the ALACO-OFDM technique has significantly improve the spectral efficiency compared to previous techniques such as ACO-OFDM. Moreover, it is shown that channel capacities of different layers are significantly improved when electrical power is increased.

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Comparison between conventional OCDMA and subcarrier multiplexing SAC OCDMA system based on single photodiode detection

2017-12-11 , N. A. A Ahmad , Junita Mohd Nordin , Syed Alwee Aljunid Syed Junid , Mohd Rashidi Che Beson , Rosdisham Endut

This paper demonstrates the comparison between conventional OCDMA system and subcarrier multiplexing (SCM) SAC-OCDMA system by applying Recursive Combinatorial (RC) code based on single photodiode detection (SPD). SPD is used in the receiver part to reduce the effect of multiple access interference (MAI) which contributes as a dominant noise in incoherent SAC-OCDMA systems. From this analysis, the performance of SCM OCDMA network could be improved by using lower data rates and higher received power. The hybrid SCM OCDMA system shows better performance compare to conventional OCDMA system although the number of users involved is very high. This is because, for hybrid SCM OCDMA system, the number of users can be increased by increasing the number of subcarriers without affect the number of code length and optical codes. Increasing the number of subcarriers will enhance the power consumption by applying hybrid SCM system in OCDMA compared to the conventional OCDMA system. This is because increasing the number of users for hybrid SCM system does not affects the number of code length and the number of optical codes but only increase the number of subcarriers. Thus, hybrid SCM OCDMA system has to increase spectral efficiency and produce better performance compared to conventional of OCDMA system

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Review of Active Circuit and Passive Circuit Techniques to Improve the Performance of Highly Efficient Energy Harvesting Systems

2023-06-01 , Liew Hui Fang , Rosemizi Abd Rahim , Muhammad Izuan Fahmi Romli , Junita Mohd Nordin , `Aini Syuhada Md Zain

In piezoelectric energy harvesting systems, energy harvesting circuits are the interface between piezoelectric devices and electrical loads. The conventional view of this interface is based on the concept of impedance matching. In fact, in the power supply circuit can also apply as an electrical boundary conditions, such as voltage and charge, to piezoelectric devices for each energy conversion cycle. The major drawback of piezoelectric power harvesting have low-power relationships in systems within (in the range of μW to mW), then system also have significantly reduced any potential losses in circuits that make up the EH system, whereas other condition into careful selection of circuits and components can enhanced the energy harvesting performance and electricity consumption. In the study of energy harvesting systems, it is an energy harvesting system approach that using active and passive electronic circuit to control voltage and or charge on piezoelectric devices as proposed and review to mechanical inputs for optimized energy conversion. Several factors in the practical limitation of active and passive energy consumption, due to device limitations and the power efficiency of electronic circuits, will be introduced and have played an important role into to enhance optimum and increase efficiency of energy harvesting system.

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Modelling and Analysis of Piezoelectric Cantilever for Kinetic Ambient Energy Harvesting

2024-01-01 , Izzati Kholid N.F. , Junita Mohd Nordin , Rosemizi Abd Rahim , `Aini Syuhada Md Zain , Liew Hui Fang , Alif M.H.

Wide bandwidth of vibration energy harvesters becomes one of most difficulties to their implementation but it is important to have cantilever beam that can tolerate wide variety of input frequency and able to harvest more kinetic energy. In this work, the piezoelectric material i.e. lead-zirconate-titanate (PZT), polyvinylidene fluoride (PVDF) and Aluminum Nitride (AlN) have been chosen to be analyzed. The piezoelectric cantilever beam structure, Unimorph type with dimension length of 40mm, 10mm width and thickness is 0.5mm has been proposed. The Finite Element Method (FEM) in ANSYS which consist of modal analysis, harmonic response analysis and statis structural analysis have been used to analyzed the characteristic of piezoelectric materials. Then, the full-bridge rectifier used to convert A-C to D-C sources using MATLAB Simulink and the experimental setup of the project was designed. The modal analysis result showed that PVDF material can applied greater maximum deformation than AlN and PZT material. The effect of dimension of cantilever beams of PVDF against natural frequency with different mode showed the natural frequency decrease when the dimensions of piezoelectric cantilever beam increase. On static structural analysis showed when the dimensions were increased, then the total deformation was decreased. Based on result of rectifying circuit for piezoelectric energy harvester using MATLAB Simulink, the positive and negative half cycle were conducted as theoretical studied. For the design verification, the experimental study showed the output voltage waveform is well regulated with minimum ripple.

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