This paper presents a novel indoor visible light positioning (VLP) system utilising one vertical-cavity surface-emitting laser installed at the ceiling centre of a space. The system offers three-dimensional localisation by sweeping through space at one-degree resolution in two dimensions (azimuth and elevation), significantly simplifying hardware. Through incorporating the angle of arrival and received signal strength, this system demonstrates excellent precision in indoor positioning. Simulation results verify that the system attains sub-centimetre precision for most test points, outperforming conventional multi-transmitter VLP schemes in cost-efficiency and simplicity.

The integration of semantic communication (SemCom) with non-orthogonal multiple access (NOMA) presents a promising approach to enhance spectrum efficiency and system capacity. SemCom focuses on accurate meaning delivery with less bits, while NOMA enables simultaneous access for multiple users on the same frequency, maximizing resource utilization. However, power allocation in NOMA-based SemCom systems is quite challenging as it should accommodate not only channel conditions and interference management but also the characteristics of semantic information and service requirements. In this paper, we investigate the power allocation strategy for NOMA-based SemCom systems, with the aim to maximize system throughput in semantic unit (STU). Successive interference cancellation requirements and resource budgets are taken into account as the constraints. To address this problem, we propose a modified water filling-based algorithm enhancing both STU and fairness. Simulation results demonstrate the superiority of our proposed algorithm in terms of STU performance and fairness compared to two existing baseline strategies.

Light-emitting-diode based visible light positioning (VLP) system(s) can provide high-precision positioning accuracy, but require an unobstructed line-of-sight (LoS) environment. Visible light multipath signals are significantly affected by temporal and spatial dispersion, making them less effective for stringent positioning services. This work addresses the LoS limitation by optimizing multipath reflections and creating a sustainable alternative channel, even in a fully blocked LoS scenario. Accordingly, optical intelligent reflecting surfaces (IRS) are proposed to converge incident light toward a desired direction with an optimal energy threshold. Unlike recent multi-step IRS orientation and mismatched alignment techniques for position estimation, this paper aims to improve the positioning accuracy of a deterministic (fixed but unknown) receiver by modeling three types of reflections (i.e., fully diffuse, partially diffuse, and purely directive). In addition, a maximum likelihood estimation technique is proposed to leverage the simplicity and robustness of the received signal strength trilateration and direct positioning techniques within a synchronous indoor VLP system. Our simulation results demonstrate 88% improvement in positioning accuracy for partially diffused reflections over LoS-only case.

The newly emerging concept of intelligent reflecting surfaces (IRSs) is changing how we think about the optical wireless propagation channel. Through controlling the light propagation within indoor settings, it becomes feasible to influence the optical channel characteristics in order for visible light communications (VLC) systems to attain specific key performance metrics. In this paper, we propose a novel physical layer security (PLS) mechanism for IRS-assisted VLC systems based on utilising a secret IRS activation pattern that is only shared with the legitimate users. We show that our approach can enhance the secrecy performance of the system without the need to acquire information about the locations of the eavesdropper, which is a major practical limitation to many PLS techniques.

The rise of intelligent reflecting surfaces (IRSs) is opening the door for unprecedented capabilities in visible light communication (VLC) systems. By controlling light propagation in indoor environments, it is possible to manipulate the channel conditions to achieve specific key performance indicators. In this paper, we investigate the role that IRSs can play in boosting the secrecy capacity of non-orthogonal multiple access (NOMA) VLC systems. More specifically, we propose an IRS-based physical layer security (PLS) mechanism that mitigates the information leakage risk inherent in NOMA. Our results demonstrate that the achieved secrecy capacity can be enhanced by up to 105% for a number of 80 IRS elements. To the best of our knowledge, this is the first paper that examines the PLS of NOMA-based IRS-assisted VLC systems.

The emerging intelligent reflecting surface (IRS) technology introduces the potential of controlled light propagation in visible light communication (VLC) systems. This concept opens the door for new applications in which the channel itself can be altered to achieve specific key performance indicators. In this paper, for the first time in the open literature, we investigate the role that IRSs can play in enhancing the link reliability in VLC systems employing non-orthogonal multiple access (NOMA). We propose a framework for the joint optimisation of the NOMA and IRS parameters and show that it provides significant enhancements in link reliability. For example, the bit-error-rate of the NOMA user in the first decoding order is reduced to the order of 10−6using the proposed framework compared to an error floor of 10−2under fixed power allocation and fixed IRS reflection coefficients. The enhancement is even more pronounced when the VLC channel is subject to blockage and random device orientation.

As a key enabling technology for next generation wireless connectivity, light fidelity (LiFi) is envisioned to support seamless multi-user access. In this paper, we propose a novel time-domain based multiple access scheme referred to as index time division multiple access (I-TDMA). Our results indicate that I-TDMA provides significant spectral efficiency enhancement compared to ordinary TDMA in a two-users scenario, with minimal added hardware and computational complexity.