Electrical and Electronic Engineering - Research Publications

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Author: Nirmalathas, Ampalavanapillai × Author: Lim, Christina × Start date: 2020 × End date: 2022 ×

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Now showing 1 - 10 of 11
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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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    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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    Approaches to improve performance of 60 GHz radio-0verFiber fronthaul links
    Lim, C ; Tian, Y ; Nirmalathas, A ; Lee, KL (OSA Publishing, 2020)
    In this paper, we review the work we have done to improve the performance of users located at the cell boundary of a 60 GHz radio-over-fibre fronthaul using coordinated-multipoint (CoMP) together with non-orthogonal-multiple-access (NOMA).
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    Multi-Level Code NOMA for Radio-over-Fiber based Fronthaul Links
    Lim, C ; Tao, Y ; Nirmalathas, A (IEEE, 2020)
    The inherent centralized control architecture of radio-over-fiber (RoF) enables advanced coordination functionality to be implemented in a RoF-based mobile fronthaul to facility network management and coordination. This advanced coordination functionality enhances the performance of disadvantaged end users located further away from the remote radio head (RRH) or at the cell edges. In this paper, we review our work incorporating multi-level code based non-orthogonal multiple access (NOMA) to improve the performance of users located further away from the RRH with poor channel gain.
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    Novel Spatial Modulation Channel Index Detection in Optical Wireless Communications with Signal Space Diversity
    Song, T ; Wong, E ; Nirmalathas, A ; Alameh, K ; Lim, C ; Wang, K (IEEE, 2020)
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    Indoor Optical Wireless Communications using Few-mode Based Uniform Beam Shaping and LMS Based Adaptive Equalization
    Li, J ; Lim, C ; Nirmalathas, A (IEEE, 2020-09-01)
    An indoor optical wireless communication system employing few-mode based uniform beam shaping and adaptive LMS equalization is demonstrated. Results show that superior uniformity is obtained and LMS equalization with step size of 0.01 and tap length of 45 achieves the best performance.
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    Demonstration of High-speed Indoor Optical Wireless Communications using Few-mode Based Uniform Beam Shaping
    Li, J ; Lim, C ; Nirmalathas, A ; O'Keefe, N ; Lee, KL (IEEE, 2020-10-04)
    A high-speed indoor optical wireless communications link using few-mode based uniform beam shaping is experimentally demonstrated. Results show that high-quality uniform beam can be realized and the BER performance can be improved significantly by combining the signals from different channels supported by different modes.