Multiple-input Single-output Visible Light Communication Research Articles

An algorithm to reconstruct the constellations based on the superposed character in the Multi-dimensional transmission VLC system

In the Intensity Modulation and Direct Detection (IM-DD) based Multi-dimensional Visible Light Communication (VLC) system, we display different kinds of constellations by using superposed character. An algorithm named Cyclic Delay Diversity (CDD) is used to reduce the superposed signal order at the transmitter, it improves the data rate to 1.6 Gbps with the Bit Error Rate (BER) under the threshold in the Multiple Input Single Output (MISO) VLC system. Although CDD is a common method used in the Physical Downlink Shared Channel (PDSCH) in Long Term Evolution (LTE), it brings an unexpected result in the VLC system. To our acknowledge, this is the first time to discuss the superposed constellations issue detailly and may provide a bran-new idea in the Multiple Input Multiple Output (MIMO)/MISO VLC system or IM-DD system in the following researches.

Asymptotic Capacity Maximization for MISO Visible Light Communication Systems with a Liquid Crystal RIS-Based Receiver

Combined with reconfigurable intelligent surfaces (RISs), visible light communications (VLCs) can increase the communication performance to a great degree. However, the research into RIS-aided VLC systems has mainly focused on mirror array-based RISs deployed on the wall while neglecting liquid crystal (LC)-based RISs in VLC receivers. With the development of advanced materials, the LC RIS has been gradually attracting attention from researchers. Inspired by the current research into the LC RIS, the applications of the LC RIS in multiple-input single-output (MISO) VLC systems are investigated in this paper. We formulate an optimization problem with asymptotic capacity maximization as the objective function and the refractive index of the LC RIS as the independent variable. As for this nonconvex optimization problem, we propose the particle swarm optimization (PSO) algorithm to determine the configuration of parameters for the LC RIS. The simulation results indicate that the employment of the LC RIS in VLC receivers can raise the communication performance of the MISO-VLC systems; meanwhile, the proposed algorithm is an effective way to deal with the optimization problems for LC RIS-based MISO-VLC systems when compared with the exhaustive search method and a baseline scheme. The LC RIS is also expected to solve the dead zone problem in traditional VLC systems.

Artificial-noise aided secure transmission over visible light communication system under coexistent passive and active eavesdroppers.

In this paper, secure transmission over multiple-input single-output visible light communication system under coexistent passive and active eavesdroppers (Eves) is studied. To enhance the achievable secrecy rate of this system given statistical channel state information (CSI) error model for the passive Eves-related channels, a robust artificial-noise (AN) based transmit strategy is proposed and a secrecy rate maximization problem subject to secrecy-outage-probability constraint, sum power constraint, and peak amplitude constraint is formulated. To solve this non-convex problem, a conservative approximation is presented to replace the probabilistic constraint and unbounded CSI error with worst-case secrecy constraints and spherically-bounded CSI errors, respectively. Then, semi-definite relaxation, S-procedure, and a Golden search-based algorithm are proposed to solve the approximated problem with fast convergence and low complexity. Simulation results show that the proposed method outperforms the other AN-aided and non-AN method for the coexistent active and passive Eves case, especially when the power budget is high.

An Artificial-Noise-Based Approach for the Secrecy Rate Maximization of MISO VLC Wiretap Channel With Multi-Eves

In this paper, we consider improving the secure performance of multiple-input single-output visible light communication channel in the presence of multiple eavesdroppers with multiple photodiodes. Our goal is to design an optimal artificial-noise (AN) aided transmission strategy to maximize the achievable secrecy rate subject to both sum power constraint and peak amplitude constraint. We consider a joint optimization of the transmit covariance and AN covariance for the non-convex secrecy rate maximization (SRM) problem. In order to solve it, the SRM problem is transformed into a series of single-variable semidefinite programming (SDP) problems without losing any optimality, and a one-dimensional search based algorithm is proposed to handle the converted problem, with polynomial complexity. By exploiting Karush-Kuhn-Tucker conditions of the problem, beamforming is found to be optimal for the confidential information transmission. Simulation results show the superior performance of the proposed AN-aided method compared with two other AN-aided methods and no AN-aided method.

Optimization of the Receiving Orientation Angle for Zero-Forcing Precoding in VLC

We study the performance of linear zero-forcing (ZF) precoding in multiuser multiple-input single-output visible light communications (VLC) when we are able to select the receiving orientation angle (ROA) of each user. For radio-frequency communications, the non-line-of-sight rich scattering environment usually ensures the linear independence among user’s channels. However, this condition is less likely to happen in VLC systems, degrading the performance of ZF precoding. In this work, we propose a variable ROA (vROA) photodetector able to modify its orientation vector in order to generate semi-orthogonal channel responses among users. We derive the algorithm for determining the orientation of the vROA photodetector of each user, obtaining optimal and suboptimal solutions with high and low complexity, respectively. Simulation results show that the performance of ZF precoding is improved considerably by managing the users ROA.

Generalized quadrature spatial modulation techniques for VLC

In this paper, generalized quadrature spatial modulation (QSM) techniques are proposed for multiple-input single-output (MISO) visible light communication (VLC) systems using quadrature spatial modulation subcarrier intensity modulation (QSM-SIM). Additionally, realistic channel condition including both line-of-sight (LOS) and non-LOS (NLOS) components up to the third reflection is also considered and channel coherence bandwidths are calculated for varying number of LEDs. Since the indoor MISO VLC channel has strong correlation between coefficients, particle swarm optimization (PSO) and approximated maximum minimum Euclidean distance (AMMD) based precoding on the transmitter side are studied to reduce the channel correlation under illumination constraints. As a performance metric, bit error rate (BER) performance of considered modulation techniques is analyzed for different MISO schemes. The upper bound BER performances are also derived analytically in order to validate the simulation results. According to the results, we reached three important conclusions. First one is that variable length generalized QSM (VGQSM) by having few LED arrays on the transmitter side performs the best BER results compared to other schemes that provide the same spectral efficiency (SE) and the second is that precoding is essential for indoor MISO VLC systems to reduce the channel correlation. Finally, an increase in the number of LED arrays results in a decrease in channel coherence bandwidth.

Performance enhancement using decentralised cooperative transmission in an MISO‐VLC system

In this study, the authors propose a decentralised cooperative transmission in a multiple-input–single-output visible light communication (VLC) system to deal with the co-channel interference (CCI) converting the interference between adjacent light-emitting diode (LED) lamps into the desired signal and to overcome link blockage recovering the data when the obstruction is not severe. VLC uses the LED lamps already installed for illumination and can alleviate the growing data traffic in the existing wireless communications without interfering. However, CCI and link blockage must be considered to improve performance. The proposed scheme decentralises a cooperative transmission employing a randomised coding rule since each LED sends a random linear combination of the columns of a deterministic code matrix whose coefficients are independent and identically distributed and the decoding is performed by ignoring the number of cooperative LEDs that is unknown and time varying at the receiver. Through computer simulations, the proposed scheme outperforms a centralised scheme when the random coefficients are real and positive. Although the performance deteriorates as decreasing the received links, it does not require to exchange information among the LEDs before transmission or receive all data before decoding as in a centralised scheme.

Deep Reinforcement Learning-Enabled Secure Visible Light Communication Against Eavesdropping

The inherent broadcast characteristics of the visible light communication (VLC) channel makes VLC downlinks susceptible to unauthorized terminals in many actual VLC scenarios, such as offices and shopping centers. This paper considers a multiple-input-single-output (MISO) VLC scenario with multiple light fixtures acting as the transmitter, a VLC receiver as the legitimate user, and an eavesdropper attempting to intercept the undisclosed information. To improve the confidentiality of VLC links, a physical-layer anti-eavesdropping framework is proposed to obscure the unauthorized eavesdroppers and diminishes their capability of inferring the information through smart beamforming over the MISO VLC wiretap channel. To cope with the intractable problem of finding the theoretically optimal solution of the secrecy rate and utility for the MISO VLC wiretapping channel, a reinforcement learning (RL)-based VLC beamforming control scheme is proposed to achieve the optimal beamforming policy against the eavesdropper. Furthermore, a deep RL-based VLC beamforming control scheme is proposed to handle the curse of dimensionality for both observation space and action space and avoid the quantization error of the RL-based algorithm. Simulation results show that the proposed learning-based VLC beamforming control schemes can significantly decrease the bit error rate of the legitimate receiver and increase the secrecy rate and utility of the anti-eavesdropping MISO VLC system, compared with the benchmark strategy.

Two input one output visible light communication system based on pulse amplitude modulation

To improve the data transmission rate of the conventional point-to-point single input single output (SISO) visible light communication system, a multiple input multiple output (MIMO) visible light communication system is proposed. Considering the complexity of the receiver system, multiple input single output (MISO) visible light communication systems have attracted attention. This paper studies the MISO visible light communication system based on pulse amplitude modulation (PAM), and experimentally proves the advantages of this system in specific scenes. In addition, there are non-linear effects for key devices such as LED light sources and power amplifiers in visible light communication systems. Based on 2×1 MISO visible light communication system, this paper reports a novel equal probability coding mapping scheme for high-order PAM signals with two low-order PAM signals superposition in the optical domain. The system verification is performed through a net data-rate of 700 Mb/s transmission experiment through a red chip of RGB-LED, which proves the feasibility and superiority of this scheme in practice.

Artificial Noise-Based Beamforming for the MISO VLC Wiretap Channel

This paper investigates the secrecy performance of the multiple-input single-output visible light communication (VLC) wiretap channel. The considered system model comprises three nodes: a transmitter (Alice) equipped with multiple fixtures of LEDs, a legitimate receiver (Bob), and an eavesdropper (Eve), each equipped with one photo-diode. The VLC channel is modeled as a real-valued amplitude-constrained Gaussian channel. Eve is assumed to be randomly located in the same area as Bob. Due to this, artificial noise-based beamforming is adopted as a transmission strategy in order to degrade Eve’s signal-to-noise ratio. Assuming discrete input signaling, we derive an achievable secrecy rate in a closed-form expression as a function of the beamforming vectors and the input distribution. We investigate the average secrecy performance of the system using stochastic geometry to account for the location randomness of Eve. We also adopt the truncated discrete generalized normal (TDGN) as a discrete input distribution. We present several examples through which we confirm the accuracy of the analytical results via Monte Carlo simulations. The results also demonstrate that the TDGN distribution, albeit being not optimal, yields performance close to the secrecy capacity.

Bandwidth and BER Improvement Employing a Pre-Equalization Circuit with White LED Arrays in a MISO VLC System

This paper aims to extend the limited bandwidth of phosphorescent white LEDs for a multiple-input single-output (MISO) visible light communication (VLC) system. A proposed LED arrangement model is presented, resulting in improved results as compared to those previously discussed in the literature. In this paper, the impact of the receiver field of view (FOV) angle, the LED transmission angle, and the number of LED arrays used on the transmission are studied at different speeds. The system performance is measured by the signal to noise ratio (SNR) and the corresponding bit error rate (BER) at different data rates. The obtained results show that the proposed model is able to improve the illumination uniformity across the room with a higher SNR using the same number of LEDs in the investigated indoor environment. The paper also introduces a pre-equalization circuit in the transmitter end in order to extend the limited bandwidth of the used white LEDs. This bandwidth extension using the proposed circuit results in an increased data rate with the aid of a blue filter. A number of experiments are executed to optimize the key parameters for maximum bandwidth enhancement. The proposed circuit offers 28% bandwidth enhancement over the most recent study in this area while eradicating the BER at 200 Mb/s when compared to un-equalized LED circuits.

Distortion compensation with clustering algorithm in a MISO VLC system

In this paper, we propose a modified K-means algorithm to mitigate both linear and nonlinear impairments in the multiple input single output (MISO) visible light communication (VLC) system. By presenting a novel dimming control scheme at the transmitter, various superimposed constellation structures are generated at the receiver end. Meanwhile, a table is generated, after looking up the superimposed signals in this table; we separate them to recover the transmitted signals. Then we can realize the spatial multiplexing. Experiments demonstrate that we achieve a data rate of 1.5 Gb∕s with the measured bit error rates (BERs) is under 7% pre-forward error correction (pre-FEC) limit of 3.8 × 10−3 in 1.3-m indoor.

<italic>SecLight:</italic> A New and Practical VLC Eavesdropping-Resilient Framework for IoT Devices

The blooming of the Internet of Things (IoT) needs a communication infrastructure to allow connecting a wide range of devices. Visible light communication (VLC) provides an attractive solution for these IoT devices. However, the broadcast nature makes the VLC prone to be exposed in the reach of eavesdroppers, which undesirably impairs the IoT system security. The negative factors in practical use, such as light reflection, light intensity, channel correlation, and channel estimation error, remain less touched. In this paper, we propose the SecLight to support both the multiple-input single-output VLC (MISO-VLC) and the single-input single-output VLC (SISO-VLC) IoT devices. A random time reversal scheme is first proposed to automatically steer the SISO-VLC signal to the legitimate receivers by scrambling the eavesdropper's channel. Then, we mathematically analyze the impact of channel correlation and channel estimation error inherent in MISO-VLC system and propose an effective approach to alleviate the decreased secrecy capacity by introducing the Karhunen-LoEve transform and equivalent artificial noise. Through extensive evaluation, the proposed SecLight framework proves to be able to aggravate the bit error rate of eavesdroppers, even when a malicious interception is intended while holding the secrecy capacity above 3 bit/s/Hz. Overall, our results demonstrate that our framework SecLight is a promising solution for enhancing the security of the IoT devices.

Secrecy Performance of Multi-User MISO VLC Broadcast Channels With Confidential Messages

We study, in this paper, the secrecy performance of a multi-user (MU) multiple-input single-output visible light communication broadcast channel with confidential messages. The underlying system model comprises $K +1$ nodes: a transmitter (Alice) equipped with $N$ fixtures of LEDs and $K$ spatially dispersed users, each equipped with a single photo-diode. The MU channel is modeled as deterministic and real-valued and assumed to be perfectly known to Alice, since all users are assumed to be active. We consider typical secrecy performance measures, namely, the max–min fairness, the harmonic mean, the proportional fairness, and the weighted fairness. For each performance measure, we derive an achievable secrecy rate for the system as a function of the precoding matrix. As such, we propose algorithms that yield the best precoding matrix for the derived secrecy rates, where we analyze their convergence and computational complexity. In contrast, what has been considered in the literature so far is zero-forcing (ZF) precoding, which is suboptimal. We present several numerical examples through which we demonstrate the substantial improvements in the secrecy performance achieved by the proposed techniques compared with those achieved by the conventional ZF. However, this comes at a slight increase in the complexity of the proposed techniques compared with ZF.

Equiprobable Pre-Coding PAM7 Modulation for Nonlinearity Mitigation in Underwater 2 × 1 MISO Visible Light Communications

Visible light communication has attracted increasing attention for its cost effective, energy conservation, and high efficiency. Nowadays, underwater visible light communication (UVLC) has drawn more interest in the research community. In order to increase the transmission distance in an underwater environment, a high-power light-emitting diode must be considered. Therefore, the nonlinearity induced by the electrical-to-optical conversion in the transmitter, the underwater channel, and the optical-to-electrical conversion in the receiver will become a challenge. To release the nonlinear restriction, we propose a novel pre-coding pulse amplitude modulation (PAM) 7 modulation for 2 × 1 multiple-input single-output (MISO) system for UVLC. In this scheme, two transmitters with lower modulation level are utilized to reduce the nonlinearity. In comparison with traditional space-time block-coding (STBC) technique, a novel precoding scheme with unique mapping/demapping value is proposed to achieve a equiprobable PAM7 signal. The theoretical analysis and experimental results show the proposed pre-coding method can outperform the traditional STBC MISO system in terms of the mutual information and system capacity. The 2.1-m air-underwater transmission experiment demonstrates an overall 53% capacity improvement, validating the feasibility of the proposed pre-coding PAM7 modulation can be a promising candidate for underwater communications.

Constellation design by High/Low order Bit Interleaving in the MISO visible light communication system

Abstract In this paper, we present a newfound in the two-dimensional Visible Light Communication (VLC) system, i.e., additional modulation orders are generated in the receiver. Meanwhile, an algorithm named High/Low order Bit Interleaving (HLBI) is proposed in a formulated VLC Multiple-Input-Single-Output (MISO) model, which aims to decrease part of these orders. A data rate of 1.24Gbit/s is achieved in 1.3 m indoor Line-Of-Sight (LOS) scenario with the Bit Error Rate (BER) is under 3.8 × 10−3. Since the algorithm also aids STBC decoding, the Q factor can be improved to 1.92dB.

Secrecy performance analysis of MISO visible light communication systems with spatial modulation

In this paper, we investigate the physical layer secrecy (PLS) problem in the multiple-input single-output (MISO) visible light communication (VLC) system aided by the spatial modulation (SM), which is termed as the MISO SM-VLC system. With addressing the characteristics of channel input signals and MISO SM-VLC scheme, the secrecy performance of MISO SM-VLC system is investigated in detail for the first time, when the input signals obey finite discrete distributions. Specifically, aided by the distribution information of the system's input and output signals, the average mutual information of MISO SM-VLC system is derived. The lower bound and an accurate closed-form expression for approximation of the average mutual information are also obtained, which can be utilized for estimating the achievable secrecy rate of MISO SM-VLC systems efficiently. Moreover, we analyzed the pairwise error probability and bit error rate (BER) of MISO SM-VLC systems, and additionally, some closed-form expressions about the BER and pairwise error probability are obtained. Numerical and simulation results verify the accuracy of the derived theoretical results of the secrecy performance for MISO SM-VLC systems.

Power-Efficient Linear Precoding for MU-MISO VLC Systems With Channel Uncertainty

In this letter, we consider a multi-user multiple-input single-output visible light communication system. A power-efficient linear precoding for zero-forcing (ZF) detection is developed with channel uncertainty, i.e., noisy channel state information (CSI) and outdated CSI. With the constraint of a dynamic current range of light-emitting diodes, the proposed method is capable of minimizing total optical power and guaranteeing user performance. Simulation results demonstrate that the proposed precoding can achieve a lower power consumption than the pseudo-inverse ZF precoding with the same user performance.

Multi-User Visible Light Communication Broadcast Channels With Zero-Forcing Precoding

This paper studies zero-forcing (ZF) precoding designs for multi-user multiple-input single-output visible light communication (VLC) broadcast channels. In such broadcast systems, the main challenging issue arises from the presence of multi-user interference (MUI) among non-coordinated users. In order to completely suppress the MUI, ZF precoding, which is originally designed for radio frequency (RF) communications, is adopted. Different from RF counterpart, VLC signal is inherently non-negative and has a limited linear range, which leads to an amplitude constraint on the input data signal. Unlike the average power constraint, obtaining the exact capacity for an amplitude-constrained channel is more cumbersome. In this paper, we first investigate lower and upper bounds on the capacity of an amplitude-constrained Gaussian channel, which are especially tight in the high signal-to-noise regime. Based on the derived bounds, optimal beamformer designs for the max-min fairness sum-rate and the maximum sum-rate problems are formulated as convex optimization problems, which then can be efficiently solved by using standard optimization packages.

Joint Transceiver and Offset Design for Visible Light Communications With Input-Dependent Shot Noise

In this paper, we investigate the problem of the joint transceiver and offset design for point-to-point multiple-input–multiple-output (MIMO) and multiple user multiple-input–single-output visible light communication (VLC) systems. Both uplink and downlink multi-user scenarios are considered. The shot noise induced by the incoming signals is considered, leading to a more realistic MIMO VLC channel model. Under key lighting constraints, we formulate non-convex optimization problems aimed at minimizing the sum mean squared error. To optimize the transceiver and the offset jointly, a gradient projection-based procedure is resorted to. When only imperfect channel state information is available, a semidefinite programming-based scheme is proposed to obtain robust transceiver and offset. The proposed method is shown to non-trivially outperform the conventional scaled zero forcing and singular. value decomposition-based equalization methods. The robust scheme works particularly well when the signal is much stronger than the noise.