Electrical and Electronic Engineering - Research Publications

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Author: Nirmalathas, Ampalavanapillai × Type: Journal Article ×

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Now showing 1 - 10 of 44
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    Investigation on Orbital Angular Momentum Mode-Based Beam Shaping for Indoor Optical Wireless Communications
    Li, J ; Yang, Q ; Dai, X ; Lim, C ; Nirmalathas, A (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2022-12-15)
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    Comparison of Adaptive Equalization Methods for Improving Indoor Optical Wireless Communications Employing Few-Mode Based Uniform Beam Shaping
    Li, J ; Lim, C ; Nirmalathas, A (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2022-06-15)
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    Longwave infrared multispectral image sensor system using aluminum-germanium plasmonic filter arrays
    Shaik, NEK ; Widdicombe, B ; Sun, D ; John, SEE ; Ryu, D ; Nirmalathas, A ; Unnithan, RRR (TSINGHUA UNIV PRESS, 2023-07-01)
    Abstract A multispectral camera records image data in various wavelengths across the electromagnetic spectrum to acquire additional information that a conventional camera fails to capture. With the advent of high-resolution image sensors and color filter technologies, multispectral imagers in the visible wavelengths have become popular with increasing commercial viability in the last decade. However, multispectral imaging in longwave infrared (LWIR, 8–14 μm) is still an emerging area due to the limited availability of optical materials, filter technologies, and high-resolution sensors. Images from LWIR multispectral cameras can capture emission spectra of objects to extract additional information that a human eye fails to capture and thus have important applications in precision agriculture, forestry, medicine, and object identification. In this work, we experimentally demonstrate an LWIR multispectral image sensor with three wavelength bands using optical elements made of an aluminum (Al)-based plasmonic filter array sandwiched in germanium (Ge). To realize the multispectral sensor, the filter arrays are then integrated into a three-dimensional (3D) printed wheel stacked on a low-resolution monochrome thermal sensor. Our prototype device is calibrated using a blackbody and its thermal output has been enhanced with computer vision methods. By applying a state-of-the-art deep learning method, we have also reconstructed multispectral images to a better spatial resolution. Scientifically, our work demonstrates a versatile spectral thermography technique for detecting target signatures in the LWIR range and other advanced spectral analyses.
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    Demonstration of Spatial Modulation Using a Novel Active Transmitter Detection Scheme with Signal Space Diversity in Optical Wireless Communications
    Song, T ; Nirmalathas, A ; Lim, C (MDPI, 2022-11)
    Line-of-sight (LOS) indoor optical wireless communications (OWC) enable a high data rate transmission while potentially suffering from optical channel obstructions. Additional LOS links using diversity techniques can tackle the received signal performance degradation, where channel gains often differ in multiple LOS channels. In this paper, a novel active transmitter detection scheme in spatial modulation (SM) is proposed to be incorporated with signal space diversity (SSD) technique to enable an increased OWC system throughput with an improved bit-error-rate (BER). This transmitter detection scheme is composed of a signal pre-distortion technique at the transmitter and a power-based statistical detection method at the receiver, which can address the problem of power-based transmitter detection in SM using carrierless amplitude and phase modulation waveforms with numerous signal levels. Experimental results show that, with the proposed transmitter detection scheme, SSD can be effectively provided with ~0.61 dB signal-to-noise-ratio (SNR) improvement. Additionally, an improved data rate ~7.5 Gbit/s is expected due to effective transmitter detection in SM. The SSD performances at different constellation rotation angles and under different channel gain distributions are also investigated, respectively. The proposed scheme provides a practical solution to implement power-based SM and thus aids the SSD realization for improving system performance.
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    Investigation on repetition-coding and space-time-block-coding for indoor optical wireless communications employing beam shaping based on orbital angular momentum modes
    Li, J ; Yang, Q ; Dai, X ; Lim, C ; Nirmalathas, A (Optica Publishing Group, 2022-06-06)
    In this paper, we propose a novel beam shaping technique based on orbital angular momentum (OAM) modes for indoor optical wireless communications (OWC). Furthermore, we investigate two spatial diversity techniques, namely repetition-coding (RC) and Alamouti-type orthogonal space-time-block-coding (STBC) for indoor OWC employing the new beam shaping technique. The performance of both diversity schemes is systematically analyzed and compared under different beam shaping techniques using different OAM modes with different power ratios of the modes. It is shown that both RC and STBC can improve the system performance and effective coverage and RC outperforms STBC in all the beam shaping techniques regardless of the power ratios of the different modes. In addition, to further understand the performance of RC and STBC schemes against the signal delays induced during OAM mode conversion, the system tolerance of the two schemes to the delay interval is investigated with different OAM mode-based beam shaping techniques. Numerical results show that higher resistance to the delay interval can be achieved in STBC scheme. The advantage is more obvious when employing OAM0 and OAM1 based beam shaping technique.
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    Few-Mode Based Beam Shaping for Multi-User Indoor Optical Wireless Communications With Time-Slot Coding
    Li, J ; Lim, C ; Nirmalathas, A (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2022-02)
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    IoT Device Integration and Payment via an Autonomic Blockchain-Based Service for IoT Device Sharing
    Dawod, A ; Georgakopoulos, D ; Jayaraman, PP ; Nirmalathas, A ; Parampalli, U (MDPI, 2022-02)
    The Internet of Things (IoT) incorporates billions of IoT devices (e.g., sensors, cameras, wearables, smart phones, as well as other internet-connected machines in homes, vehicles, and industrial plants), and the number of such connected IoT devices is currently growing rapidly. This paper proposes a novel Autonomic Global IoT Device Discovery and Integration Service (which we refer to as aGIDDI) that permits IoT applications to find IoT devices that are owned and managed by other parties in IoT (which we refer to as IoT device providers), integrate them, and pay for using their data observations. aGIDDI incorporates a suite of interacting sub-services supporting IoT device description, query, integration, payment (via a pay-as-you-go payment model), and access control that utilise a special-purpose blockchain to manage all information needed for IoT applications to find, pay and use the IoT devices they need. The paper describes aGIDDI's novel protocol that allows any IoT application to discover and automatically integrate and pay for IoT devices and their data that are provided by other parties. The paper also presents aGIDDI's architecture and proof-of-concept implementation, as well as an experimental evaluation of the performance and scalability of aGIDDI in variety of IoT device integration and payment scenarios.
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    Intelligent Radio Resource Allocation for Human-Robot Collaboration
    Feng, Y ; Ruan, L ; Nirmalathas, A ; Wong, E (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2022-01-01)
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    Dynamic scheduling algorithm for LTE uplink with smart-metering traffic
    Amarasekara, B ; Ranaweera, C ; Evans, R ; Nirmalathas, A (WILEY, 2017-10-01)
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    integrated on a CMOS image sensor
    He, X ; Liu, Y ; Beckett, P ; Uddin, H ; Nirmalathas, A ; Unnithan, RR (OPTICAL SOC AMER, 2021-01-15)
    The CMY colour camera is different from the RGB counterpart where the subtractive colours cyan, magenta and yellow are used. The CMY camera performs better than an RGB camera in low light conditions. However, conventional CMY colour filter technology made of pigments and dyes are limited in performance for next generation image sensors with submicron pixel sizes. This is because the conventional CMY filters cannot be fabricated in nanoscale as they use their absorption properties to subtract colours. This paper presents a CMOS compatible nanoscale thick CMY colour mosaic made of Al-TiO2-Al nanorods forming a total number of 0.82 million colour filter pixels with each filter pixel size of 4.4 µm arranged in a CMYM pattern. The colour mosaic was then integrated on a MT9P031 image sensor to make a CMY camera and colour imaging is demonstrated using a 12 colour Macbeth chart. The developed technology will have applications in astronomy, low exposure time imaging in biology, and photography.