Recently, physical-layer encryption was featured as a favorable security method for visible light communications (VLCs). Generally, orthogonal frequency-division multiplexing (OFDM) is the key structure unit for the multicarrier modulation of up-to-date networks, such as vehicularad hocnetworks, 4G/5G systems, and the Internet of Things (IoT). This study proposes a robust lightweight channel-independent (LCI) physical-layer encryption method based on optical OFDM to strengthen the confidentiality of VLC systems. The method is suitable for resource-restricted machines, such as IoT systems. With the help of the hashing and stream cipher schemes, the random characteristics of the input data are exploited to create dynamic cipher keys renewed at every frame. The proposed method achieves a threefold encryption operation that involves substitution, phase encryption for frequency-domain OFDM subcarriers, and permutation for time-domain OFDM subcarriers. The results indicate that the proposed method improves the VLC confidentiality against various attacks, such as statistical attacks, known/chosen plaintexts, and brute-force attacks. Aside from improving confidentiality, the proposed method decreases the peak-to-average power ratio of the signal, enhances the bit-error-rate efficiency, and decreases the communication latency.

A system that employs wavelength division multiplexing (WDM) in conjunction with sub‐carrier multiplexing (SCM) tones is proposed to realise high data rate multi‐user indoor visible light communication (VLC). The SCM tones, which are unmodulated signals, are used to identify each light unit, to find the optimum light unit for each user and to calculate the level of the co‐channel interference (CCI). WDM is utilised to attain a high data rate for each user. In this study, multi‐colour (four colours) laser diodes are utilised as sources of lighting and data communication. One of the WDM colours is used to convey the SCM tones at the beginning of the connection to set up the connection among receivers and light units (to find the optimum light unit for each user). To evaluate the performance of the VLC system, two types of receivers are proposed: an array of non‐imaging receivers and an array of non‐imaging angle diversity receivers. In this study, the effects of diffuse reflections, CCI and mobility on the system performance are considered.

The need for high‐speed local area networks to meet the recent developments in multimedia and video transmission applications has recently focused interest on visible light communication (VLC) systems. Although VLC systems provide lighting and communications simultaneously from light emitting diodes (LEDs), LEDs, the uplink channel design in such a system is a challenging task. In this study, the authors propose a solution in which the uplink challenge in indoor VLC is resolved by the use of an infrared (IR) link. The authors introduce a novel fast adaptive beam steering IR system (FABS‐IR) to improve the uplink performance at high data rates while providing security for applications. The goal of the authors’ proposed system is to enhance the received optical power signal, speed up the adaptation process and mitigate the channel delay spread when the system operates at a high transmission rate. The channel delay spread is minimised from 0.22 ns given by hybrid diffuse IR link to almost 0.07 ns. At 2.5 Gb/s, the authors’ results show that the imaging FABS‐IR system accomplished about 11.7 dB signal to noise ratio in the presence of multipath dispersion, receiver noise and transmitter mobility.

In this paper, we introduce an adaptive optical wireless system that employs a finite vocabulary of stored holograms. We propose a fast adaptation approach based on a divide and conquer methodology resulting in a number of adaptation algorithms: fast angle adaptive holograms (FAA-Holograms), fast power adaptive holograms (FPA-Holograms), and fast angle and power adaptive holograms (FAPA-Holograms) and evaluate these in mobile optical wireless (OW) systems in conjugation with imaging reception. The ultimate goal is to improve the signal-to-noise ratio (SNR), to reduce the effect of intersymbol-interference (ISI), to speed up the adaptation process, and to eliminate the need to calculate the hologram in real-time at each transmitter and receiver location. The system operates at high data rates under the impact of multipath dispersion, background noise and mobility. At a data rate of 2.5 Gb/s and under eye safety regulations, the proposed FAPA-Holograms offers around 20 dB SNR in the presence of background shot noise, receiver noise, multipath dispersion, and mobility. Simulation results show that the proposed system, FAPA-Holograms, can reduce the time required to identify the optimum hologram position from 80 ms in the original beam angle and power adaptive line strip multibeam system (APA-LSMS) to about 13 ms.

In this paper, we propose a novel mobile optical wireless (OW) system that employs for the first time beam delay adaptation, and makes use of angle and power adaptation in a line strip multibeam spot diffusing configuration in conjunction with an imaging receiver (BDAPA-LSMS). Our ultimate goal is to improve the bandwidth, reduce the effect of inter-symbol-interference (ISI), and increase the signal to noise ratio (SNR) when the transmitter operates at a higher data rate under the impact of multipath dispersion, background noise and mobility. An increase in channel bandwidth from 36 MHz, typical in a conventional diffuse system (CDS), to about 9.8 GHz can be achieved when our methods of beam delay, angle and power adaptation coupled with an imaging receiver are employed. At a bit rate of 30 Mbit/s our proposed BDAPA-LSMS achieves about 50 dB signal-to-noise ratio gain over conventional diffuse non-imaging systems. Moreover, our simulation results show that the proposed BDAPA-LSMS at a bit rate of 10 Gbit/s achieves about 32.3 dB signal-to-noise ratio at the worst communication path in the presence of background noise and mobility thus achieving a BER below 10-9.

In this paper, we propose a novel optical wireless (OW) system that employs beam delay and power adaptation in a line strip multibeam spot diffusing configuration in conjunction with an angle diversity receiver (BDPA-LSMS). Our ultimate goal is to improve the signal to noise ratio (SNR), reduce the delay spread and increase the received optical power under multipath dispersion, background noise and mobility. A significant reduction in delay spread from 2.4 ns (conventional diffuse system CDS) to about 0.11 ns can be achieved when our methods of beam delay and beam power adaptation coupled with an angle diversity receiver are employed. Our simulation results show that the proposed BDPA-LSMS at a bit rate of 30 Mbit/s achieves about 13 dB signal-to-noise ratio (SNR) gain over a line strip multibeam system (LSMS). At the worst case scenario our proposed (BDPA-LSMS) system offers SNR improvement of 20 dB over CDS and 10 dB SNR gain over LSMS.

Over the last two decades, indoor optical wireless (OW) systems have operated typically at 30 Mbit/s to 155 Mbit/s. Here, we propose and evaluate for the first time a mobile OW system that operates at 5 Gbit/s and 10 Gbit/s. The improvements in data rates and channel bandwidth are achieved through the introduction of three approaches: angle diversity, beam angle and beam power adaptation. We propose a mobile OW system that employs beam angle and beam power adaptation in a line strip multibeam spot diffusing system configuration in conjunction with an angle diversity receiver (APA-LSMS) to mitigate the degradation due to ambient light noise, multipath dispersion and mobility. The performance of our proposed system was investigated through channel and noise modelling. Our results show that the proposed APA-LSMS at a bit rate of 30 Mbit/s achieves about 45 dB signal-to-noise ratio (SNR) gain over a power adaptive line strip multibeam system (PA-LSMS) and offers 60 dB SNR gain over a conventional diffuse system (CDS) at a 6 m horizontal separation between the transmitter and the receiver. The SNR is independent of the transmitter location and when our methods (angle diversity, beam angle and beam power adaptations) are implemented, the SNR can be maximized at the receiver for every transmitter location. The results show an increase in channel bandwidth from 36 MHz (CDS) to approximately 7.2 GHz in our proposed system (APA-LSMS). These improvements enhance our system and enable it to operate at higher data rates of 5 Gbit/s and 10 Gbit/s.