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 implementations.

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.

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.

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.

The limited bandwidth of optical wireless communication (OWC) front-end devices motivates the use of multipleinput- multiple-output (MIMO) techniques to enhance data rates. It is known that very high multiplexing gains can be achieved by spatial multiplexing (SMX) at the cost of prohibitive detection complexity. Alternatively, in spatial modulation (SM), a single light emitting diode (LED) is activated per time instance where information is carried by both the signal and the LED index. Since only one LED is active, both the transmitter (TX) and receiver (RX) complexity reduce significantly while retaining the information transmission in the spatial domain. However, this simplified TX utilization approach leads SM to suffer from significant spectral efficiency losses compared to SMX. In this paper, we propose a technique that benefits from the advantages of both systems. Accordingly, the proposed flexible LED index modulation (FLIM) technique harnesses the inactive state of the LEDs as a transmit symbol. Therefore, the number of active LEDs changes in each transmission, unlike conventional techniques. Moreover, the system complexity is reduced by employing a linear minimum mean squared error (MMSE) equalizer and an angle perturbed receiver. Numerical results show that FLIM outperforms the reference systems by at least 6 dB in the low and medium/high spectral efficiency regions.

Spatial modulation (SM) is a promising technique that reduces inter-channel interference while providing high power efficiency and detection simplicity. In order to ensure the secrecy of SM, precoding and friendly jamming are widely adopted in the literature. However, neither of those methods can take advantage of SM. In this paper, a novel spatial constellation design (SCD) technique is proposed to enhance the physical layer security (PLS) of optical generalized space shift keying (GSSK), which can retain some benefits of SM. Due to the lack of small-scale fading, the quasi-static characteristics of the optical channel is used to tailor the received signal at the legitimate user's (Bob's) side. The PLS of the system is guaranteed by the appropriate selection of the power allocation coefficients for randomly activated light emitting diodes (LEDs). With the aid of Bob's channel state information at the transmitter, the bit error ratio (BER) of Bob is minimized while the BER performance of the potential eavesdroppers (Eves) is significantly degraded. Monte-Carlo simulation results show that the proposed SCD-zero forcing precoding (ZFP) forces Eve to experience a BER of around 0.5 by outperforming both the conventional and ZFP based GSSK for all practical signal-to-noise-ratio regimes and Bob-Eve separations.

A novel modulation scheme for an indoor optical wireless communication (OWC) system referred to as generalized time slot index modulation (GTIM) is proposed for single-carrier frequency domain equalization (SC-FDE) systems. This scheme is further referred to as SC-GTIM. In SC-GTIM, information bits are flexibly encoded onto both the amplitudes and positions of pulses. A set partitioning algorithm is proposed to construct a codebook for the SC-GTIM system. In this paper, SC-GTIM will be compared with the conventional pulse amplitude modulation-based SC-FDE (SC-PAM) and time slot index modulation-based SC-FDE (SC-TIM). By considering a multipath optical wireless channel and the limited dynamic range of a light emitting diode (LED), a considerable bit error ratio (BER) gain can be achieved by SC-GTIM. It is concluded that SC-GTIM is a promising technique for low to medium spectral efficiency transmission and uplink schemes.

Light fidelity (LiFi), which occupies part of the optical spectrum, is a promising technology to meet the high-speed wireless data demand. For an additional throughput gain along with low energy consumption, index modulation (IM) has begun to be combined with LiFi systems. The main advantage of IM is its ability to encode information in both a conventional transmit signal as well as the index of the transmit entity such as through the transmitter, subcarrier and time-slot domain indexes. Time-slot IM (TIM) offers additional degrees of freedom to single-carrier (SC) single-input-single-output systems to encode information onto pulse activation patterns. In this paper, we propose a generalized TIM (GTIM) transmission method for SC frequency domain equalization (SC-FDE)-based systems to fully harness the benefits of TIM. In GTIM, both the number and locations of active time-slots are flexible such that they are different for each transmit symbol. Moreover, the active time-slots carry pulse amplitude modulation (PAM) symbols in the signal domain. The proposed system also benefits from SC-FDE which simplifies the transmission and detection complexity at both sides. We also propose a set partitioning algorithm that chooses the optimal transmission symbols set and labels them concurrently. The bit error ratio (BER) performance of GTIM is compared to conventional PAM and TIM under a limited dynamic range constraint and frequency-selectivity. It is shown that the proposed GTIM achieves up to a 3 dB BER performance gain.

The performance of visible light communication (VLC) systems are limited by the modulation bandwidth of light emitting diodes (LEDs), despite the availability of the wide optical spectrum. A multiple-input, multiple-output (MIMO) scheme can be employed to further improve the data rate by means of harnessing the spatial multiplexing gain. Nevertheless, it is known that the MIMO VLC channel can be rank-deficient, and consequently its performance can be degraded significantly. The rank of the MIMO VLC channel is highly affected by the geometries of light emitting diodes and photodiodes (PDs). In this paper, the effects of PD configurations on the MIMO performances are investigated. It will be shown that certain PD configurations can lead to a rank-deficient channel. We propose Irregular PD configurations (IPC) to overcome this issue. Moreover, bi-objective problems are formulized to obtain the optimal IPC. A significant gain in terms of the condition number of the channel is shown with respect to regular PD configurations, which further suggests a benefit of IPC in MIMO VLC.

In this paper, a novel LED power control algorithm is proposed for an OSM based communications system. The proposed algorithm constantly controls the power of the LEDs employed at the transmitter side to provide the minimum overall SER for a mobile user. An exact analytical SER expression is obtained for the general MISO OSM system. It is shown that the proposed algorithm solves a convex optimization problem where linear constraints are used to minimize the SER. Finally, a 2x1 MISO-OSM example is presented to prove the effectiveness of the proposed algorithm. The computer simulations show that the power adaptive MISO-OSM system with the proposed algorithm achieves the average SER of 3.87E-6 for 30 dB SNR.

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.

Visible light communications (VLC) is an emerging field in technology and research. Estimating the channel taps is a major requirement for designing reliable communication systems. Due to the nonlinear characteristics of the VLC channel those parameters cannot be derived easily. They can be calculated by means of software simulation. In this work, a novel methodology is proposed for the prediction of channel parameters using neural networks. Measurements conducted in a controlled experimental setup are used to train neural networks for channel tap prediction. Our experiment results indicate that neural networks can be effectively trained to predict channel taps under different environmental conditions.

Visible light communication (VLC) involves the dual use of illumination infrastructure for high speed wireless access. Designing such optical based communication systems, realistic indoor optical channel modeling becomes an important issue to be handled. In this paper, first we obtain new realistic indoor VL channel characterizations and models, in a multiple-input multiple-output (MIMO) transmission scenario, using non-sequential ray tracing approach for the channel impulse responses (CIRs). Practical issues such as number of light emitting diode (LED) chips per luminary, spacing between LED chips, objects inside the room and cabling topology are also investigated. On the other hand, since indoor optical channels exhibit frequency selectivity, multi-carrier communication systems, particularly orthogonal frequency division multiplexing (OFDM) is used to handle the resulting inter-symbol interference in VLC systems. Hence, we propose a new MIMO-OFDM based VLC system, called MIMO enhanced unipolar OFDM (MIMO-eU-OFDM) by combining MIMO transmission techniques with the recently proposed eU-OFDM scheme. The bit error rate (BER) performance of the proposed system is investigated in the presence of the 2 × 2 and 4 × 4 realistic MIMO VLC channels and its BER performance is compared with the reference optical MIMO-OFDM systems.