Color coded multiple access scheme for bidirectional multiuser visible light communications in smart home technologies

How are people using current smart home technologies, and how do they conceptualize future ones that are more interconnected and more capable than those available today? We deployed an online survey study to 150 participants to investigate use of and opinions about smart speakers, home robots, virtual assistants, and other smart home devices. We also gauged how impressions of connected smart home devices are shaped by the way the devices interact with one another. Through a mixed-methods qualitative and quantitative approach, we found that people mostly use single devices for single functions, and have simple and brief interactions with virtual assistants. However, they imagine their future devices to have more control over the physical environment (i.e., interact with each other) and envision them interacting with people in more socially complex ways. These findings motivate design considerations and research directions for connected smart home technologies.

Driven by the increase in Internet of Things (IoT) devices for smart home technologies, visible light communications (VLC) using multiple light emitting diodes (LEDs) have been attracting much attention in order to cope with depleted radio frequency spectrum. This paper presents a suboptimal LED selection algorithm for distributed multiple-input multiple-output (D-MIMO) VLC systems. When total ceiling LEDs are turned on to send information while illuminating an indoor environment, the problems of low energy efficiency and mutual interference between VLC channels arise. The proposed algorithm begins by selecting the LED associated with the largest VLC channel gain and adds the LED supporting the largest level of uncorrelation with the maximum VLC channel gain in each step. Simulation results showed that the proposed scheme achieves a capacity similar to an optimal selection algorithm with reduced computational complexity. With a larger distance between the light terminals and a shorter distance between the LEDs, better channel capacity performance of the proposed scheme can be achieved.

5G networks have to offer extremely high capacity for novel streaming applications. One of the most promising approaches is to embed large numbers of cooperating small cells into the macro-cell coverage area. Alternatively, optical wireless based technologies can be adopted as an alternative physical layer offering higher data rates. Visible light communications (VLC) is an emerging technology for future high capacity communication links (it has been accepted to 5GPP) in the visible range of the electromagnetic spectrum (~370–780 nm) utilizing light-emitting diodes (LEDs) simultaneously provide data transmission and room illumination. A major challenge in VLC is the LED modulation bandwidths, which are limited to a few MHz. However, myriad gigabit speed transmission links have already been demonstrated. Non line-of-sight (NLOS) optical wireless is resistant to blocking by people and obstacles and is capable of adapting its’ throughput according to the current channel state information. Concurrently, organic polymer LEDs (PLEDs) have become the focus of enormous attention for solid-state lighting applications due to their advantages over conventional white LEDs such as ultra-low costs, low heating temperature, mechanical flexibility and large photoactive areas when produced with wet processing methods. This paper discusses development of such VLC links with a view to implementing ubiquitous broadcasting networks featuring advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) or carrier-less amplitude and phase modulation (CAP) in conjunction with equalization techniques. Finally, this paper will also summarize the results of the European project ICT COST IC1101 OPTICWISE (Optical Wireless Communications - An Emerging Technology) dealing VLC and OLEDs towards 5G networks.

The presence of free fatty acids (FFAs) in edible oil varies and presents challenges in visual quantification due to inconsistent colour transitions during titration. In conventional colourimetric titration, the endpoint is often subjectively identified. As per the Malaysian Palm Oil Board (MPOB) standard, neutralisation occurs when a faint pink hue persists for 30 s. However, this definition lacks an objective reference, which impacts its reproducibility. To address this limitation, this study developed an objective RGB (red, green, and blue) sensor-based multi-wavelength colourimetric titration method for quantifying FFAs in edible oils. Two pH indicators were evaluated: red cabbage extract and phenolphthalein. In the first experiment, red cabbage extract was used with acetic acid (CH3COOH) and sodium hypochlorite (NaClO), and colour changes were monitored using an RGB colour sensor. Data were processed through minimum-maximum normalisation and equal interval classification. In the second experiment, phenolphthalein was employed to detect FFAs in cooking and olive oils, with illumination provided by multi-wavelength lasers and RGB light-emitting diodes (LEDs). RGB changes were recorded to determine the neutralisation point and compute FFA content using MATLAB. Results showed that laser-based illumination produced sharper spectral transitions and reduced signal noise. Linear regression analysis revealed a positive linear correlation between RGB values and FFA concentration in cooking oil, while olive oil displayed weaker yet similar trends. Measured FFA contents were 0.33% for cooking oil and 0.45% for olive oil. The findings confirm that RGB sensor systems, combined with tailored illumination and data analysis, can enhance endpoint accuracy in titration and support the development of low-cost, portable diagnostic tools for oil quality monitoring. This approach shows strong potential for further development into real-time, in situ monitoring platforms for industrial and consumer applications. © 2026 Society of Chemical Industry.

Experimental demonstration of an OFDM based visible light communication system using inter-block precoding and superimposed pilots

Background:Technological advances in the smart home have created new opportunities for supporting digital citizens’ well-being and facilitating their empowerment but have enabled new types of complex online harms to develop. Recent statistics have indicated that ‘smart’ technology ownership increases yearly, driven by lower costs and increased accessibility. Research on smart homes has also grown, focusing on technology perspectives at the expense of a user-centric approach sensitive to the smart home’s harms, risks, and vulnerabilities. Objective:This scoping review addresses the information gap by underscoring the scope of literature that exists regarding complex online harms, vulnerabilities, and risks associated with smart home technologies and citizens’ agency. The goal is to understand the state of knowledge, gaps in the literature, and areas for future study. The importance and originality of this paper lie in its interdisciplinary review and approach. It is hoped that this research will contribute to a deeper understanding of complex online harms in the smart home. Design:Three online databases were utilised to identify papers published between 2017 and 2022, from which we selected 235 publications written in English that addressed harms, risks, vulnerabilities, and agency in the smart home context. This allowed us to map contemporary literature to reveal significant gaps in our understanding of the complex online harms affecting smart home users and identify opportunities for further research. Results:This review identified emerging themes of ‘risks’, ‘vulnerabilities’, and ‘harms’ in that order of frequency within the literature on smart homes. The usage of terms is skewed towards computing science and information security, which comprised the majority of the literature at 54.6%. Human–computer interaction papers contributed 24.4%, while social sciences accounted for 16.2%. Conclusion:Risks, harms and vulnerabilities within smart home ecosystems and IoTs are ongoing issues with complexities that necessitate research. Privacy, security, and well-being are key themes that embody the scope of complex harms affecting smart home devices in the broad literature. This review establishes disciplinary research gaps, especially in user-centred perspectives, due to a heavy technology focus in the existing literature. Therefore, further research is needed to address emergent risks, harms and vulnerabilities of smart home devices and understand how user agency and autonomy can complement the design, interface, and socio-technical aspects of smart home systems.

Modelling of the spatial uniformity of the light output from multicolour light emitting diode (LED)-based lamps can be used to evaluate and optimize LED and reflector configurations. The percentage of the output beam that meets or exceeds a user-selected colour accuracy threshold is used as a figure of merit to compare lamp configurations. Results are presented for various distributions of red, green and blue (RGB) or red, amber, green and blue (RAGB) LEDs in a 4 × 4 square matrix. In general, the distributions with highest (4-fold rotational) symmetry have the most uniform output beams. However, those with least uniformity also have 4- fold symmetry, which indicates the importance of choosing the chip layout carefully. The colour uniformity for RAGB configurations is, in general, higher than the colour uniformity for RGB configurations. The colour uniformity at a correlated colour temperature (CCT) of 7000 K is generally higher than the colour uniformity at 3500 K for the LED spectral characteristics investigated.

Visible light communications (VLC) use modern solid-state light-emitting diodes (LEDs) to broadcast information. Emerging white-light LEDs allow the combination of lighting and optical wireless communication in one optical source. In this paper, a new LED lighting design using one-chip-type white LEDs is proposed for efficient illumination and optical wireless communications under the existence of several obstacles. Lighting and communication performance are analyzed to show the effectiveness of the proposed LED lighting. Specifically, the signal-to-noise ratio considering intersymbol interference and the bit-error rate of variable pulse position modulation (VPPM) with dimming control are considered.

Visible light communication (VLC) systems are inherently signal-to-noise ratio (SNR) limited due to link budget constraints. One favourable method to overcome this limitation is to focus on the pre-log factors of the channel capacity. Multiple-input multiple-output (MIMO) techniques are therefore a promising avenue of research. However, inter-channel interference in MIMO limits the achievable capacity. Spatial modulation (SM) avoids this limitation. Furthermore, the performance of MIMO systems in VLC is limited by the similarities among spatial channels. This limitation becomes particularly severe in intensity modulation/direct detection (IM/DD) systems because of the lack of phase information. The motivation of this paper is to propose a system that results in a multi-channel transmission system that enables reliable multi-user optical MIMO SM transmission without the need for a precoder, power allocation algorithm or additional optics at the receiver. A general bit error performance model for the SM system is developed for an arbitrary number of light-emitting diodes (LEDs) in conjunction with pulse amplitude modulation. Based on this model, an LED array structure is designed to result in spatially separated multiple channels by manipulating the transmitter geometry.This article is part of the theme issue ‘Optical wireless communication’.

Visible light communication (VLC) is a promising and viable optical wireless communication (OWC) system that utilizes light-emitting diodes (LEDs) to achieve high data rates, energy efficiency, and resistance to electromagnetic interference (EMI). Direct-current biased optical orthogonal frequency division multiplexing (DCO-OFDM) is a widely used scheme in VLC due to its high spectral efficiency. However, it suffers from significant challenges related to its elevated peak-to-average power ratio (PAPR), which causes nonlinear distortion and signal clipping due to LED limitations. To address this issue, this paper proposes a combination of Vandermonde-like matrix (VLM) precoding and nonlinear companding transform (NCT) techniques (specifically A-law and μ-law) over DCO-OFDM-based VLC. The VLM precoding minimizes the autocorrelation of the OFDM signal, hence reducing its PAPR, and NCT compresses the dynamic range of the signal. Simulation results indicated that the hybrid techniques achieved a PAPR reduction of around 3.5 dB (by 76 %); this is in the best case reduction compared to the conventional DCO-OFDM while maintaining an acceptable bit error rate (BER), moderately higher signal-to-noise ratio (SNR) is required.

Visible light communication (VLC) offers the opportunity to provide services with new requirements, when compared to the ones offered so far by radio wireless technologies almost exclusively. The idea behind VLC is to re-use the light signal, currently utilized for illumination purposes only, to transfer information wirelessly. Light-emitting diodes (LEDs), which are the natural sources of light for VLC due to their fast time response and high energy-efficiency, are devices with a notable non-linear response. A current trend to improve the achievable data rate of the VLC links relies on the use of linear waveforms, instead of just using On-Off Keying, which is robust against LED non-linearities but difficult to adapt to the variable VLC link conditions. Since having a linear transfer function is important when using efficient waveforms such as orthogonal frequency division multiplexing (OFDM), this paper starts by modelling the voltage-versus-current response of commercial LEDs. Then, the derived model is used to identify the guidelines that new VLC prototypes should fulfill. In particular, this paper focuses on the strength of the communication signal, compared to the light source optical power, and shows the way in which these parameters affect the coverage range of a multi-cell VLC system. The effect that these key design parameters have on the VLC link are identified, based on a real experimental setting, as they are difficult to model accurately due to the complex non-linear nature of LEDs when working in highly energy-efficient regimes.

Artificial general lighting sources are currently evolving through the traditional fluorescent and incandescent sources to the modern energy saving light bulbs and now white light emitting diodes (LEDs). The introduction of solid state LED lighting source has attracted the attention of communications engineer’s worldwide, enabling the achievement of the dual functionality of room illumination whilst simultaneously transmitting wireless data via visible light communication (VLC), or optical wireless communications (OWC) in general, in optical spectrum regime. Although the existing wireless networks are primely dominated by radio-based technology, the emerging OWC will play increasingly important role in future wireless communications landscape. It is anticipated that both spectrum regimes, radio and optical, will eventually contribute equally for the next network generation, especially in nanocell and picocell network structures. This talk will outline the growth of optical wireless communications including VLC, and present the challenges and roadmap of the technology for the future generation of wireless networks..

This chapter discusses techniques on multiple-input multiple-output (MIMO) visible light communications (VLC) system which improved the speed of data communications. It discusses the use of pilot signal in reducing the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM)-based intensity-modulated optical wireless communication system. The introduction of solid-state light-emitting diode (LED) lighting has attracted the attention of communications engineers worldwide, enabling the achievement of the dual functionality of room illumination while simultaneously transmitting wireless data via VLC. A Q factor analysis of the signal between single transmitter and single receiver as function of horizontal displacement beneath the center point of a transmitter was carried out, to investigate at what distance and how fast the quality of the signal degrades. The OFDM technique is attracting a lot of interest in optical wireless communications because of its resilience to multipath propagation-induced intersymbol interference (ISI), high spectral efficiency, and immunity to fluorescent light noise near digital converter (DC) region.

The wireless transmission of home area networks contributes to the vulnerabilities of smart homes. As a result, smart homes are vulnerable to malicious attacks like eavesdropping. To secure the transmissions, secret keys should be established for smart home devices. In practical smart home applications, smart home devices might be resource-constrained devices. Thus, the lightweight key establishment schemes are preferred. Typically, lightweight physical layer key extraction schemes can be employed by the smart home devices. However, the key generation rate of the schemes is low. To improve the key generation rate, in this paper we propose an adaptive physical layer key extraction scheme for smart homes by making use of the Received Signal Strength (RSS). Specifically, in our scheme, two smart home devices collect the RSS measurements by probing with each other. Then, the collected measurements are quantized by running the proposed Self-adaptive Lossless Quantization algorithm. Completing these operations, the two smart home devices can obtain the secret key. In our scheme, we design the self-adaptive lossless quantization algorithm to improve the key generation rate. To show the practicality of the new scheme, we implement it using the Ralink WiFi cards. Additionally, we analyse the performance of our scheme and compare it with that of other related works.

Smart home technology is gaining popularity among end-users, as it allows them to remotely control a variety of devices in their homes. Such systems have obvious benefits in terms of automation, but at the same time pose significant threats to home owners if the underlying communications are not secure. To this end, we introduce a novel security protocol that simplifies the pairwise authentication and key exchange among smart home devices. The protocol leverages identity-based cryptography (IBC), thus relaxing the requirement for storing and managing public key certificates. Furthermore, to mitigate the risks associated with centralized key generation in IBC, we opt to generate the private keys in a distributed manner, involving all smart devices. We implemented our protocol on Raspberry Pi 3 devices and demonstrate its efficiency in terms of both computational and communication cost.