Electrical and Electronic Engineering - Research Publications

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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, 2022-02-01)
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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 (OPTICAL SOC AMER, 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, 2014-07-01)
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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, 2020-01-01)
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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.