Electrical and Electronic Engineering - Research Publications

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    Evolution of Short-Range Optical Wireless Communications
    Wang, K ; Song, T ; Wang, Y ; Fang, C ; He, J ; Nirmalathas, A ; Lim, C ; Wong, E ; Kandeepan, S (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2023-02-15)
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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)
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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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    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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    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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    Mobility-Aware Energy Optimization in Hosts Selection for Computation Offloading in Multi-Access Edge Computing
    Thananjeyan, S ; Chan, CA ; Wong, E ; Nirmalathas, A (Institute of Electrical and Electronics Engineers (IEEE), 2020-07-15)
    Multi-access edge computing (MEC) has been proposed as an approach capable of addressing latency and bandwidth issues in application computation offloading to extend the capabilities beyond the computational and storage limitations of mobile devices. However, there is a critical challenge in MEC to maintain the service continuity between the offloaded user application that is running on the MEC host and the mobile device when a user is moving from radio node to radio node. Furthermore, energy consumption of application computation offloading is an important consideration for MEC service providers in terms of operational costs. Therefore, we formulate the MEC host selection and user application migration problem as a shortest path problem of network energy minimization. We simulate the problem in a hierarchical MEC network deployment environment. We also propose the metric, computational intensity (CI), that can be used by MEC service providers to address the MEC host selection problem. Our results show that with the increment of CI, the selection of MEC hosts tends to move toward level 3 (central deployment) due to energy efficiency and then return to the deployment at level 1 (radio node level) due to latency constraint of the user application. We show that with high accuracy in predicting the user mobility and the available resources in the MEC network, latency- and mobility-aware MEC host selection and user application migration can be pre-calculated to improve response time and energy efficiency.
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    Gigabit/s Optical Wireless Access and Indoor Networks
    Nirmalathas, TA ; Song, T ; Edirisinghe, S ; Tian, L ; Lim, C ; Wong, E ; Wang, K ; Ranaweera, C ; Alameh, K (OSA - Optical Society of America, 2020)
    Optical wireless networks are being explored as a wireless alternative for provision of multi gigabits/second wireless and this paper presents an overview of recent progress and outstanding challenges. and technologies.
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    Estimating Video Popularity From Past Request Arrival Times in a VoD System
    Wang, T ; Jayasundara, C ; Zukerman, M ; Nirmalathas, A ; Wong, E ; Ranaweera, C ; Xing, C ; Moran, B (Institute of Electrical and Electronics Engineers (IEEE), 2020-01-31)
    Efficient provision of Video-on-Demand (VoD) services requires that popular videos are stored in a cache close to users. Video popularity (defined by requested count) prediction is, therefore, important for optimal choice of videos to be cached. The popularity of a video depends on many factors and, as a result, changes dynamically with time. Accurate video popularity estimation that can promptly respond to the variations in video popularity then becomes crucial. In this paper, we analyze a method, called Minimal Inverted Pyramid Distance (MIPD), to estimate a video popularity measure called the Inverted Pyramid Distance (IPD). MIPD requires choice of a parameter, $k$ , representing the number of past requests from each video used to calculate its IPD. We derive, analytically, expressions to determine an optimal value for $k$ , given the requirement on ranking a certain number of videos with specified confidence. In order to assess the prediction efficiency of MIPD, we have compared it by simulations against four other prediction methods: Least Recency Used (LRU), Least Frequency Used (LFU), Least Recently/Frequently Used (LRFU), and Exponential Weighted Moving Average (EWMA). Lacking real data, we have, based on an extensive literature review of real-life VoD system, designed a model of VoD system to provide a realistic simulation of videos with different patterns of popularity variation, using the Zipf (heavy-tailed) distribution of popularity and a non-homogeneous Poisson process for requests. From a large number of simulations, we conclude that the performance of MIPD is, in general, superior to all of the other four methods.
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    MAC protocol for indoor optical wireless networks
    Edirisinghe, S ; Lim, C ; Nirmalathas, A ; Wong, E ; Ranaweera, C ; Wang, K ; Alameh, K (Institution of Engineering and Technology, 2019-11-03)
    Optical wireless communication has emerged as a promising candidate for future high data rate indoor applications such as virtual reality. Even though physical layer of optical wireless networks has rapidly developed during last decade, upper layer architecture that harness the physical layer capabilities has not yet been developed in the same pace. To this end, the authors develop a novel contention-based medium access control (MAC) protocol that accompanies a service differentiation mechanism and a dynamic contention window tuning algorithm. The proposed service differentiation mechanism can identify the diverse traffic types and facilitate their throughput and delay requirements. To add more robustness to the contention-based MAC protocol which depends on contention windows to avoid collisions, the authors also propose an algorithm that dynamically changes the contention window sizes to suit the congestion level. They analyse the performance of the proposed MAC protocol under diverse network configurations and they show that it is far more effective to use end-user network metrics such as throughput in dynamic adaptation algorithms in addition to collision rate due to the wide range of traffic types present in the network. The proposed results demonstrate that the proposed MAC protocol can handle next-generation traffic types and their stringent latency requirements in an effective manner.
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    Performance Analysis of Repetition-Coding and Space-Time-Block-Coding as Transmitter Diversity Schemes for Indoor Optical Wireless Communications
    Song, T ; Nirmalathas, A ; Lim, C ; Wong, E ; Lee, K-L ; Hong, Y ; Alameh, K ; Wang, K (Institute of Electrical and Electronics Engineers (IEEE), 2019-10-15)
    The benefits of 2 × 1 multiple-inputs-single-output scheme for transmitter diversity in the infrared indoor optical wireless communication link are theoretically investigated. The performance of repetition-coding (RC) and Alamouti-type real-valued space-time-block-coding (STBC) as effective transmitter diversity schemes is systematically compared under conditions of channel gain variation caused by the degradation in the received optical power due to the blocking of one optical beam of the optical wireless channel. It is shown that the linear addition of channel gains in the RC scheme outperforms the root-sum-square of channel gains in the STBC scheme with regards to the bit-error-rate (BER) performance. Proof-of-concept experiments are carried out with both schemes under emulated scenarios of channel blockage. The RC scheme exhibits better BER performance when observed experimentally, validating the proposed theoretical model for the two spatial diversity schemes. To understand the performance of RC and STBC schemes against the optical delay caused by the two optical channel path difference within one-bit interval, both schemes are experimentally investigated using on-off-keying modulation, and results show that RC still outperforms STBC. Both theoretical and experimental results indicate that RC has better robustness to channel blockage and differential channel paths induced optical delay.