Electrical and Electronic Engineering - Research Publications

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End date: 2022 × Author: Lim, Christina ×

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Now showing 1 - 10 of 40
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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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    Design of an On-Chip Plasmonic Modulator Based on Hybrid Orthogonal Junctions Using Vanadium Dioxide
    Tanyi, GB ; Sun, M ; Lim, C ; Unnithan, RR (MDPI, 2021-10)
    We present the design of a plasmonic modulator based on hybrid orthogonal silver junctions using vanadium dioxide as the modulating material on a silicon-on-insulator. The modulator has an ultra-compact footprint of 1.8 μm × 1 μm with a 100 nm × 100 nm modulating section based on the hybrid orthogonal geometry. The modulator takes advantage of the large change in the refractive index of vanadium dioxide during its phase transition to achieve a high modulation depth of 46.89 dB/μm. The simulated device has potential applications in the development of next generation high frequency photonic modulators for optical communications which require nanometer scale footprints, large modulation depth and small insertion losses.
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    Secure multiple access for indoor optical wireless communications with time-slot coding and chaotic phase
    Liang, T ; Wang, K ; Lim, C ; Wong, E ; Song, T ; Nirmalathas, A (OPTICAL SOC AMER, 2017-09-04)
    In this paper, we report a novel mechanism to simultaneously provide secure connections for multiple users in indoor optical wireless communication systems by employing the time-slot coding scheme together with chaotic phase sequence. The chaotic phase sequence is generated according to the logistic map and applied to each symbol to secure the transmission. Proof-of-concept experiments are carried out for multiple system capacities based on both 4-QAM and 16-QAM modulation formats, i.e. 1.25 Gb/s, 2 Gb/s and 2.5 Gb/s for 4-QAM, and 2.5 Gb/s, 3.33 Gb/s and 4 Gb/s for 16-QAM. Experimental results show that in all cases the added chaotic phase does not degrade the legitimate user's signal quality while the illegal user cannot detect the signal without the key.
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    Indoor infrared optical wireless localization system with background light power estimation capability
    Wang, K ; Nirmalathas, A ; Lim, C ; Alameh, K ; Li, H ; Skafidas, E (Optica Publishing Group, 2017-09-18)
    The indoor user localization function is in high demand for high-speed wireless communications, navigations and smart-home applications. The optical wireless technology has been used to localize end users in indoor environments. However, its accuracy is typically very limited, due to the ambient light, which is relatively strong. In this paper, a novel high-localization-accuracy optical wireless based indoor localization system, based on the use of the mechanism that estimates background light intensity, is proposed. Both theoretical studies and demonstration experiments are carried out. Experimental results show that the accuracy of the proposed optical wireless indoor localization system is independent on the localization light strength, and that an average localization error as small as 2.5 cm is attained, which is 80% better than the accuracy of previously reported optical wireless indoor localization systems.
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    An Efficient Resource Allocation Mechanism for LTE-GEPON Converged Networks
    Ranaweera, C ; Wong, E ; Lim, C ; Nirmalathas, A ; Jayasundara, C (SPRINGER, 2014-07)
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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).