Now showing 1 - 5 of 5
  • Publication
    On Adaptive Network Deployment for Visible Light Communications
    This work studies adaptive network deployment for visible light communications (VLC), which exploit light wave as signal bearers. In most of the current literature, the VLC user is served by a single access point (AP), called serial transmission. To enhance network flexibility, parallel transmission (PT) was developed for VLC, enabling the user to be served by multiple APs simultaneously. Specifically, each AP consists of different coloured light-emitting diodes (LEDs) and modulates only one of them to mitigate inter-cell interference. The receiver, equipped with wavelength division concentrators, can distinguish signals carried by different wavelengths. To further improve network flexibility, adaptive network deployment is proposed in this paper, by allowing the APs to modulate a dynamic number of LEDs. The adaptive scheme is comprised of three modes of network deployment, and the mode selection is formulated as an optimisation problem to maximise network capacity with proportional fairness. Results show that compared with the original PT method, the new scheme can significantly improve network throughput, especially with an increase of up to 40% for room corner users.
  • Publication
    Physics-Based LED Modeling and Nonlinear Distortion Mitigating With real-Time Implementation
    In this paper, a nonlinear model for Light Emitting Diodes (LEDs) inspired by semiconductor physics, and a corresponding post-compensator are implemented in a Field Programmable Gate Array (FPGA) for real-time Visible Light Communications (VLC). Our experiments demonstrate that the LED model effectively characterizes the dynamic LED nonlinearity, including the memory effects. The output signal of this nonlinear LED model shows a good resemblance with the measured LED output. In addition, a dedicated nonlinear equalizer, say, a post-compensator, inspired by this LED physical model can mitigate the nonlinear distortion substantially. Thereby it facilitates high data rate over the bandwidth-limited LED. It shows that the nonlinear compensator is attractive for practical real-time digital signal processing systems due to its high performance and low complexity.
    Scopus© Citations 3  22
  • Publication
    Hybrid LiFi and WiFi Networks: A Survey
    CCBY In order to tackle the rapidly growing number of mobile devices and their expanding demands for Internet services, network convergence is envisaged to integrate different technology domains. For indoor wireless communications, one promising approach is to coordinate light fidelity (LiFi) and wireless fidelity (WiFi), namely hybrid LiFi and WiFi networks (HLWNets). This hybrid network combines the high-speed data transmission of LiFi and the ubiquitous coverage of WiFi. In this paper, we present a survey-style introduction to HLWNets, starting with a framework of system design in the aspects of network architectures, cell deployments, multiple access and modulation schemes, illumination requirements and backhaul. Key performance metrics and recent achievements are then reviewed to demonstrate the superiority of HLWNets against stand-alone networks. Further, the unique challenges facing HLWNets are elaborated on key research topics including user behavior modeling, interference management, handover and load balancing. Moreover, the potential of HLWNets in the application areas is presented, exemplified by indoor positioning and physical layer security. Finally, the challenges and future research directions are discussed.
      11Scopus© Citations 138
  • Publication
    QoS-Driven Load Balancing in Hybrid LiFi and WiFi Networks
    This work studies the quality of service (QoS) performance of wireless networks that integrate light fidelity (LiFi) and wireless fidelity (WiFi). While the hybrid network is potential for improving network capacity, load balancing becomes essential and challenging due to the nature of heterogeneous access points (APs). A number of studies have been conducted to address this issue, focusing on maximising the network capacity with user fairness constraints. However, in practice, QoS metrics including packet loss ratio and latency are important to network services. In this paper, QoS-driven load balancing is studied for hybrid LiFi and WiFi networks (HLWNets) in two scenarios: single-AP association (SA) and multi-AP association (MA). In each case, an optimisation problem is formulated to minimise the packet loss ratio and latency, and a low-complexity iterative algorithm is proposed to solve the problem. Results show that the novel methods, especially MA, can effectively balance the traffic loads among the APs and improve the QoS performance. In addition, the more subflows the better performance MA provides. Targeting the same level of QoS, MA can achieve a system throughput up to 160% higher than the signal strength strategy and 130% higher than the proportional fairness load balancing.
      12Scopus© Citations 9
  • Publication
    A Novel Method of Combining Decision Making and Optimization for LiFi Resource Allocation
    (IEEE, 2022-12-08) ;
    Light fidelity (LiFi) is a promising wireless communication technology which can be integrated into existing lighting infrastructure, fulfilling illumination and communication requirements simultaneously. Due to the relatively small coverage area of LiFi with a single access point (AP), a number of LiFi APs are usually needed to provide coverage. However, joint access point selection and resource allocation then become challenging. This issue is mainly tackled using optimization, iteration, and decision making methods. However, the current literature fail to balance the complexity and optimality well. In this paper, a novel approach that combines decision making and optimization is proposed to provide a better trade-off between optimality and complexity. Specifically, a distributed optimization is integrated into the decision making process of fuzzy logic, which is adopted to classify the user based on their channel quality and throughput requirements. Simulation results show that the mixed method can reach the near-optimal achievable throughput, reducing runtime by more than 3 orders of magnitude compared with the global optimization benchmark. Besides, the proposed method is capable of saving up to 72% runtime compared with iteration based benchmark.
      17Scopus© Citations 1