Optical Wireless Communications Using Intelligent Walls

This chapter is devoted to discussing the integration of intelligent reflecting surfaces (IRSs), or intelligent walls, in optical wireless communication (OWC) systems. IRS technology is a revolutionary concept that enables communication systems to harness the surrounding environment to control the propagation of light signals. Based on this, specific key performance indicators could be achieved by altering the electromagnetic response of the IRSs. In the following, we discuss the background theory and applications of IRSs and present a case study for an IRS-assisted indoor light-fidelity (LiFi) system. We then highlight some of the challenges related to this emerging concept and elaborate on future research directions

Channel modelling and error performance investigation for reading lights based in-flight LiFi

The new generation of communication technologies are constantly being pushed to meet a diverse range of user requirements such as high data rate, low power consumption, very low latency, very high reliability and broad availability. To address all these demands, fifth generation (5G) radio access technologies have been extended into a wide range of new services. However, there are still only a limited number of applications for radio frequency (RF) based wireless communications inside aircraft cabins that comply with the 5G vision. Potential interference and safety issues in on-board wireless communications pose significant deployment challenges. By transforming each reading light into an optical wireless access point (AP), light-fidelity (LiFi), could provide seamless on-board connectivity in dense cabin environments without RF interference. Furthermore, the utilization of available reading lights allows for a relatively simple, cost-effective deployment with the high energy and spectral efficiency. To successfully implement the aeronautical cabin LiFi applications, comprehensive optical channel characterization is required. In this paper, we propose a novel Monte Carlo ray-tracing (MCRT) channel modelling technique to capture the details of in-flight LiFi links. Accordingly, a realistic channel simulator, which takes the cabin models, interior elements and measurement based optical source, receiver, surface material characteristics into account is developed. The effect of the operation wavelength, cabin model accuracy and user terminal mobility on the optical channel conditions is also investigated. As a final step, the on-board direct-current biased optical orthogonal frequency division multiplexing (DCO-OFDM) performance is evaluated by using obtained in-flight LiFi channels. Numerical results show that the location of a mobile terminal and accurate aircraft cabin modelling yield as much as 12 and 2 dB performance difference, respectively

Intelligent subflow steering in MPTCP-based hybrid Wi-Fi and LiFi networks using model-augmented DRL

A hybrid Wi-Fi and light fidelity (LiFi) network combines the best of two worlds with the ubiquitous coverage of Wi-Fi and the high peak data rate of LiFi as the radio spectrum does not interfere with the light spectrum. This hybrid network might be realized by using multipath TCP (MPTCP), where Wi-Fi and LiFi paths can be simultaneously employed to potentially boost the total throughput of Wi-Fi while increasing the resilience towards network failure of LiFi due to, for example, blockage. However, naively implementing MPTCP in a hybrid Wi-Fi and LiFi network can yield an unexpected result, such as a lower throughput compared to the single-path TCP due to a Head-of-Line delay during the slow start phase of the TCP congestion control. Even though this problem can be avoided by improving the existing flow control or congestion control of TCP, these solutions still lack intelligent decision making that can improve the adaptability of MPTCP. Therefore, in this paper, we propose a model-augmented deep reinforcement learning (DRL) approach to intelligently steer MPTCP subflows (i.e., TCP connections) by using a close-to-reality scenario emulated by considering random orientation, random blockage, and random mobility of Wi-Fi-and-LiFi-enabled mobile devices. As a result, we will show later that a performance gain can be achieved compared to the state-of-the-art while maintaining ease implementation to existing MPTCP implementation

Optical MIMO-OFDM with Generalized LED Index Modulation

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Visible light communications (VLC) is a promising and uncharted new technology for the next generation of wireless communication systems. This paper proposes a novel generalized light emitting diode (LED) index modulation method for multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM)-based VLC systems. The proposed scheme avoids the typical spectrum efficiency losses incurred by time- and frequency-domain shaping in OFDM signals. This is achieved by exploiting spatial multiplexing along with LED index modulation. Accordingly, real and imaginary components of the complex time-domain OFDM signals are separated first, then resulting bipolar signals are transmitted over a VLC channel by encoding sign information in LED indexes. As a benchmark, we demonstrate the performance analysis of our proposed system for both analytical and physical channel models. Furthermore, two novel receiver designs are proposed. Each one is suitable for frequency-flat or selective channel scenarios. It has been shown via extensive computer simulations that the proposed scheme achieves considerably better bit error ratio versus signal-to-noise-ratio performance than the existing VLC-MIMO-OFDM systems that use the same number of transmit and receive units [LEDs and photo diodes (PDs)]. Compared with the single-input single-output (SISO) DC biased optical (DCO)-OFDM system, both spectral efficiency and DC bias can be doubled and removed respectively simply by exploiting a MIMO configuration.European Cooperation in Science and Technology (COST); The Scientific and Technological Research Council of Turkey (TUBITAK) Research; EPSRC under Established Career Fellowshi

Synthetic LiFi channel model using generative adversarial networks

In this paper, we present our research on modeling a synthetic light fidelity (LiFi) channel model that uses a deep learning architecture called generative adversarial networks (GAN). A research in LiFi that requires the generation of many multipath channel impulse responses (CIRs) can benefit from our proposed model. For example, future developments of autonomous (deep learning-based) network management systems that use LiFi as one of its high-speed wireless access technologies might require a dataset of many CIRs. In this paper, we use TimeGAN, which is a GAN architecture for time-series data. We will show that modifications are necessary to adopt TimeGAN in our use case. Consequently, synthetic CIRs generated by our model can track long-term dependency of LiFi multipath CIRs. The Kullback–Leibler divergence (KLD) is used in this paper to measure the small difference between samples of synthetic CIRs and real CIRs. Lastly, we also show a simple demonstration of our model that can run on a small virtual machine hosted over the Internet

A novel mobile multi-user LiFi system

In this paper, a vehicular light-fidelity (LiFi) system, which supports mobility for seamless broadband data transmission is proposed for multipoint-to-point (M2P) communication. To this end, a novel digital mirror device (DMD) based receiver (RX) is investigated that consists of two functionalities, to sense the transmitters and sense mobility. Relying on the proposed hybrid waveform, the proposed RX has the ability to detect and distinguish multiple transmitter (TX) sources under free movement conditions within three-dimensional space. Computer simulation results for the ‘TX sensing platform’ show that a high TX detection and identification performance is achieved at an extremely low channel signal-to-noise-ratio (SNR) of −11 dB and a bit error ratio (BER) of 10−4. Furthermore. the simulation results for the ‘mobility sensing platform’ was able to trace the positions of light sources simultaneously with the error rate of below 2% relative to the diameter of light spots on the DMD for all considered mobility scenarios

OFDM-Based Optical Spatial Modulation

Spatial modulation (SM) has proven to be a promising multiple-input-multiple-output (MIMO) technique which provides high energy efficiency and reduces system complexity. In SM, only one transmitter is active at any given time while the rest of them remain silent. The index of the active transmitter carries information. This spatial information is in addition to the data carried by the constellation symbols in the signal domain. Therefore, SM increases the transmission rate of the communication system compared to single-input-single-output and space-time block coding (STBC)-MIMO. For signal domain data encoding, orthogonal frequency division multiplexing (OFDM) has been widely adopted. The key benefits in multi-carrier intensity-modulation and direct-detection (IM/DD) systems are: i) the capability to achieve high spectral efficiency and ii) the ability to effectively mitigate direct-current (DC) wander effects and the impact of ambient light. However, current off-the shelf light emitting diodes (LEDs) which are used as transmit entities are primarily bandwidth limited. Thus, there are benefits of combining SM and OFDM to enhance transmission speeds while maintaining low complexity. In this paper, the two most common OFDM-based SM types, namely frequency domain SM (FD-SM) and time domain SM (TD-SM), are investigated for optical wireless communications (OWC). Moreover, proof-ofconcept experimental results are presented to showcase practical feasibility of both techniques. The obtained results are also compared with Monte Carlo simulations. The results show that TDSM with an optimal maximum-a-posteriori-probability (MAP) detector significantly outperforms FD-SM. It can be inferred from the results that TD SM is a strong candidate among OFDM-based optical SM systems for future optical IM/DD wireless communication systems

Physical layer security for multi-user MIMO visible light communication systems with generalized space shift keying

We consider the physical layer security (PLS) of multi-user (MU) multiple-input-multiple-output visible light communication (VLC) systems with an eavesdropper (Eve) and propose a novel spatial constellation design technique based on generalized space shift keying (MU-GSSK-SCD). The received signals of the legitimate users are optimized jointly, such that their bit error ratios (BERs) are minimized and Eve's BER is significantly degraded. The emission power of randomly selected light-emitting diodes is adjusted, by exploiting users' channel state information at the transmitter. Our strategy ensures that legitimate users receive confidential messages fully in an undistorted fashion, while any meaningful leakage to Eve is strongly prohibited, without any artificial noise addition. Every user can decode only its information, hence inter-user security is also guaranteed. The PLS improvements are presented in terms of both BERs and achievable secrecy rates in practical VLC scenarios. For various user configurations, it is shown that MU-GSSK-SCD increases the BER at Eve to the 0.5 level, while providing minimized BERs to the legitimate users. The achievable secrecy rate region is derived for MU-GSSK-SCD and it is shown that full secrecy can be achieved at 0 dB signal-to-noise ratio (SNR) level with a user separation as small as 90 cm