Downlink Visible Light Communication Research Articles

Enhanced Gain Difference Power Allocation for NOMA-Based Visible Light Communications

With the escalating demand for high-data-rate wireless services, visible light communication (VLC) technology has emerged as a promising complement to traditional radio frequency wireless networks. To further enhance the achievable rate and error performance in non-orthogonal multiple access-based VLC downlinks, an efficient power allocation scheme named enhanced gain difference power allocation (EGDPA) is proposed for a multiple-input multiple-output VLC system. The power factors are determined by considering users’ channel gains and utilizing the residual allocation principle, which focuses on the remaining power available after allocating it to the previous users. In addition, the impacts of the user distribution and transmission power are investigated, and the performance metrics in terms of achievable data rate, energy efficiency, and bit error rate are also analytically presented. Simulation results demonstrate that energy efficiency can be significantly improved and the achievable data rate gain can be enhanced by at least 6.25% with the proposed EGDPA scheme as compared with other traditional methods, confirming its superiority and validity for efficient multi-user accessing.

A novel hybrid radio over fiber visible light communication system combining 5G mmWave and coarse wavelength division multiplex grid

<p>Visible light communication(VLC)has gained attention for enabling gigabitdata transmission over a short-range. Inradio over fiber (RoF), modulatedradio frequency (RF) is carried over optical fiber. Millimeter-wave (mmW)range also offers a vast amount of spectrum and enables integration with RoF.We propose a novel hybrid network using mmWave based RoF backhaulandcoarse wavelength division multiplexed(CWDM)-VLC for indoorcommunication. Three different optical tones were introduced to produce thedesired mmW signal using optical heterodyning with one of them carryingmodulated data and the other two carrying unmodulated data. Opticalsideband signal with the carrier(OSSB+C) is used for uplink communication.Modulated mmWave signal is used for VLC downlink to drive a multi-colorCWDM system. The performance of the VLC downlink is measured usingdifferent optical filters such as Bessel, Trapezoidal, Gaussian, and FabryPerot. A maximum data rate of 2.64 Gb/s and 6.58 Gb/s were achieved with10 and 20channelsoff the shelf LEDs with 16quadrature amplitudemodulation (QAM) with reasonable BER for downlink VLC communication.The uplink communication was carried out using mmW with 2.5 Gb/s datarate usingon-off keying(OOK)modulation and the data from thiscommunication down converted atcentral office(CO) through RoF backhaul.</p>

Performance study of visible light communication through non-orthogonal multiple access (noma) – LI-FI

Li-Fi (Light Fidelity) is a new wireless communication technology that is comparable to Wireless Fidelity (Wi-Fi). However, Li-Fi is supposed to be better than Wi-Fi, and this has been theoretically verified. Li-Fi is also thought to make a significant contribution to wireless networks. The practical application of Li-Fi will be discussed in this study. In this paper we chose NOMA because of its ability and efficiency in simultaneously transporting data, as well as its application in 5G cellular networks. VLC stands for visible light communication, as the name implies. In this section, we will investigate how the data transporting capabilities of Li-Fi make use of the visible light emitted by light emitting diodes (LEDs). In this paper, the effectiveness of a non-orthogonal multiple access (NOMA) protocol used in a downlink visible light communication (VLC) system is evaluated for two distinct situations. On a two-user paired NOMA, we create an analytical expression of the system coverage probability for QoS provisioning and show that optimum power allocation coefficients do exist. Additionally, we establish the existence of optimal power allocation coefficients. Last but not least, the numerical and analytical results illustrated in our work show that the VLC single-cell system throughput obtained with our technique is better than that obtained with the earlier strategy. Additionally, it is shown that the suggested alternative lower bound fits the original NOMA-VLC GRPA objective asymptotically using indoor VLC channels.

Optimal Resource Management for NOMA-Based Visible Light Communication Systems With Shot Noise

In this paper, the problem of power allocation is investigated for downlink visible light communication (VLC) systems with non-orthogonal multiple access. In the system, both input-dependent shot noise and input-independent Gaussian noise are considered due to the properties of practical VLC channels. We consider two scenarios for the transmitter with a single light emitting diode (LED) and multiple LEDs, respectively. For single-LED scenarios, the problem is posed as a joint optimization problem of alternating current and direct current power control, whose goal is to maximize the minimum signal-to-interference-plus-noise-ratio (SINR) of all users. Although the original problem is non-convex, a geometric programming based algorithm is proposed to acquire the global optimal solution. For multi-LED scenarios, the transmit and dimming beamforming vectors are jointly optimized to maximize the minimum SINR of all users. A joint optimization algorithm that alternately optimizes transmit and dimming beamforming vectors is proposed. Particularly, the transmit beamforming problem is converted into a second-order cone programming problem through the successive convex approximation method. The dimming beamforming problem is transformed into a feasibility problem utilizing a low-complexity bisection algorithm. Numerical results reveal the superior performance of the proposed algorithm compared with its orthogonal multiple access counterpart and conventional schemes without shot noise.

Decoding-Order-Based Power Allocation (DOPA) Scheme for Non-Orthogonal Multiple Access (NOMA) Visible Light Communication Systems

Non-orthogonal multiple access (NOMA) is an effective multiple access scheme that can be used to improve considerably the spectral efficiency of indoor downlink visible light communication (VLC) systems. However, NOMA suffers from inevitable multi-user interference which degrades the system performance. In this paper, a NOMA scheme is applied in a downlink VLC system and the impact of the multi-user interference on the system performance is studied. A closed-form expression for the user symbol error rate (SER) is derived and a decoding-order-based power allocation (DOPA) method is proposed to reduce the multi-user interference and find the optimal power allocation that minimizes the SER. The significance of the proposed schemes is demonstrated by simulation. The results show that the proposed DOPA method is able to reduce effectively the multi-user interference and provide more sum rate in comparison with benchmarking schemes such as the gain ratio PA (GRPA) and the normalized gain difference PA (NGDPA) methods.

Effect of Signal-Dependent Shot Noise on Visible Light Positioning

This paper investigates the error bounds for position estimation in downlink visible light communication (VLC) systems. More precisely, we use Cramér-Rao lower bounds (CRLBs) to study the effect of signal-dependent shot noise (SDSN) on the error performance in visible light positioning. We consider synchronous, quasi-synchronous, and asynchronous visible light positioning (VLP) systems. The system performance is assessed based on the position estimation, and uses information from parameters relating to the time of arrival (TOA), time difference of arrival (TDOA), and received signal strength (RSS). The results demonstrate that SDSN has a negative impact on the error bounds in all considered scenarios. Moreover, the level of degradation observed is not uniform among all cases at higher SDSN levels.

Subchannel and Power Allocation in Downlink VLC Under Different System Configurations

Visible light communication (VLC) has attracted a significant amount of research interest due to its ability to support high data-rates. However, the issue of inter-cell interference (ICI) caused by resource sharing and the line-of-sight (LoS) blockage problem are significant challenges that need to be considered in the design and analysis of VLC systems. This paper investigates the resource allocation problem for the downlink of an orthogonal frequency-division multiple access-based multi-cell VLC system, while considering ICI and LoS blockage. This is carried out under various system configurations employing different transmission modes. Specifically, the joint problem of subchannel allocation (SA) and power allocation (PA) to maximize the sum-rate is formulated as a combinatorial and highly non-convex optimization problem due to the binary and continuous optimization variables. To obtain an efficient solution, the original problem is first separated into the SA problem and the PA problem. Two simple, yet efficient, procedures based on the quality of the channel conditions and matching theory are proposed for the SA problem, respectively. Then, the quadratic transform approach is exploited to develop an algorithm for the PA problem. Simulation results demonstrate the effectiveness of the proposed solutions in terms of their fast convergence and overall performance.

Mobility aware of WDM-based CMO OFDM communication system

Abstract The continued increase in several mobile applications forces to replace existing limited spectrum indoor radio frequency wireless connections with high-speed ones. Visible light communications (VLC) technology has gained prominence in the development of high data rate transmission for fifth-generation networks. In optical wireless communications, light-emitting diode (LED) transmitters are used in applications that desire mobility as LED divergence enables larger coverage. Since each VLC access point covers a small area, handovers of mobile users are inevitable. Wavelength division multiplexing (WDM) can be used in VLC systems to tackle the above issue and to meet the increasing demand for indoor connectivity with high bit rates. In this paper, a new system architecture for WDM with coded modulated optical in orthogonal frequency division multiplexing (OFDM) VLC system in conjunction with red, green, blue, and yellow (RGBY) LEDs is proposed to reduce the impact of random receiver orientation of indoor mobile users over VLC downlink channels and improves the system’s bit-error-rate (BER) performance. Simulation results show that the proposed method is not affected by the user’s mobility and hence it performs better than other approaches, in terms of BER for all scenarios and at all positions. This study reveals that using WDM-OFDM-VLC with RGBY LEDs to construct a VLC system is very promising.

Contactless scribe-test monitor with photovoltaic power, VLC downlink and IR-UWB uplink

A contactless scribe-line channel-leakage monitor with relaxed alignment requirement is described. It comprises photovoltaic converters for powering from indoor illumination, a visible light communication downlink for selecting one among multiple monitors, and an ultra-wideband impulse-radio uplink for transmitting the measured leakage data in the form of impulse repetition frequency. Readout is accomplished with an external loop antenna loosely aligned to the scribe-line transmitter antenna. The proposed monitor was implemented in 0.18-μm CMOS with a footprint 4960 μm $$\times $$ 160 μm including the transmitter antenna. It deploys a novel leakage sensor of ring-oscillator topology. All circuit blocks, except for the transmitter, are power-supplied directly by photovoltaic converters without regulation, and consume 64 nW. Transmitter is powered by an integrated storage capacitor charged to 1.8 V by a photovoltaic-powered voltage booster.

Performance analysis of a low-complexity nonorthogonal multiple access scheme in visible light communication downlinks using pulse modulations

Although Successive Interference Cancellation (SIC) decoding is widely adopted in Nonorthogonal Multiple Access (NOMA) schemes for the recovery of user data at acceptable complexity, the imperfect SIC would cause Error Propagation (EP), which can severely degrade system performance. In this work, we propose an SIC-free NOMA scheme in pulse modulation based Visible Light Communication (VLC) downlinks, including two types of users with different data rate requirements. Low bit-rate users adopt on-off keying, where as high bit-rate ones use Multiple Pulse Position Modulation (MPPM). The soft decision decoding scheme is exploited by high bit-rate users to decode MPPM signals, which could fundamentally eliminate the detrimental effect of EP; the scheme is also easier and faster to execute compared with the conventional SIC decoding scheme. Expressions of the symbol error rate and achievable data rate for two types of users are derived. Results of the Monte Carlo simulation are provided to confirm the correctness of theoretical results.

Light-Emitting Commutating Diodes for Optical Wireless Communications Within LED Drivers

Although visible light communication (VLC) systems provide high density links for use in Internet-of-Things (IoT) devices, the design of high rate VLC transmitters that maintain luminaire efficacy is an open problem. In this article, a novel approach to the integration of VLC within light-emitting diode (LED) drivers is proposed through the replacement of freewheeling/blocking diodes with light-emitting devices termed a light-emitting commutating diodes (LECDs). In this manner, communications and illumination can be provided using a simple, cost effective design while employing no additional components. The subtle change of LED driver control signals facilitates the transmission of data from LECDs while simultaneously supporting illumination functions. Lighting controls such as dimming are maintained and combined with modulation through the use of overlapping pulse position modulation (OPPM) and performance is quantified. Prototype buck and boost converters with LECDs are implemented and their efficacy is measured. Though current commercial LEDs are not intended for such signalling applications, we experimentally demonstrate their feasibility in this application and suggest methods to make such converters reliable. It is demonstrated that the addition of an LECD improves the efficacy of the luminaire as compared to conventional LED drivers while simultaneously enabling a VLC downlink.

Optimization of SINR and Illumination Uniformity in Multi-LED Multi-Datastream VLC Networks

Visible Light Communication (VLC), which is a recent technology that operates at the visible light spectrum band, is a very propitious technology complementary to RF in the era of spectrum crisis. Because of the extensive deployment of energy efficient Light Emitting Diodes (LEDs) and the advancements in LED technology with fast nanosecond switching times, VLC has gained a lot of interest recently. In this paper, we consider a downlink VLC architecture which is capable of providing simultaneous lighting and communication coverage across an indoor setting. We design a multi-element hemispherical bulb which transmits multiple data streams from its LEDs to mobile receivers. The architecture employs a Line-of-Sight (LOS) alignment protocol to tackle the hand-off issue caused by the mobility of the receivers in the room. We formulate an optimization problem that jointly addresses the LED-user associations as well as the LEDs’ transmit powers in order to maximize the Signal-to-Interference plus Noise Ratio (SINR) while taking into consideration an acceptable illumination uniformity constraint across the room. We propose a near-optimal solution using Geometric Programming (GP) to solve the optimization problem, and compare the performance of this GP solution to low complexity heuristics.

A multi-user joint constellation design of color-shift keying for VLC downlink broadcast channels

While creating a required illumination, LED luminaries can be used as wireless access points by visible light communication (VLC) technology. Under normal conditions, there is more than one user who needs to be connected to the VLC network. Consequently, multiple access technique, e.g., time division multiple address (TDMA), is required to enable multiple users to share the network without interfering each other. To achieve a more efficient multi-user communication, we propose a multi-user joint constellation (JC) design for color-shift keying (CSK) by utilizing multiple LED luminaries equipped with multi-color LEDs. Unlike traditional multiple-input–multiple-output (MIMO) researches in which the symbols of different transmitters are independently generated from the constellations, the transmitted symbols are jointly generated in our design which takes the advantage of both multi-color and spacial resources in VLC systems. Considering the signal constraints in both optical and electric domains, the JC design is formulated with the objective function of maximizing the minimum Euclidean distance (MED) between different receiving constellation points. To make it easy to solve the non-convex optimization problem, we propose an iterative algorithm with the help of slack variable and Taylor expansion. Afterwards, a method of constellation mapping for the system is provided. In order to analyze the performance of the JC design, conventional TDMA and non-orthogonal multiple access (NOMA) scheme are introduced as comparisons and the simulation results illustrate that JC owns a better performance than both of them.

Mobile channel estimation based on decision feedback in vehicle-to-infrastructure visible light communication systems

Visible light communication (VLC) emerges as a promising candidate in vehicle-to-infrastructure (V2I) networks. For VLC downlink between street lamps and a mobile vehicle, received signals tend to experience a time-varying multi-source and multi-path channel condition. This will affect the effectiveness of channel equalization when assuming constant channel characteristics within each data packet. In this paper, in order to track the time-varying mobile VLC channel effectively, we propose a channel estimation method for V2I downlink based on decision feedback with orthogonal frequency division multiplexing. Considering different system parameters, extensive numerical experiments are carried out. Results show that compared with the conventional scheme using only training sequences, adopting decision feedback can achieve higher channel estimation accuracy, thus improving link performance significantly. For vehicle velocity at 15 m/s, bit error rate (BER) < 10 −4 can be achieved at ∼199 Mbps if transmit power per lamp is > 30 W. Moreover, the proposed method is almost unaffected by the change of vehicle moving state, with stable BER achieved.

LED Half-Power Angle Optimization for Ultra-Dense Indoor Visible Light Communication Network Deployment

Due to limited interference range, the advantage of visible light communication (VLC) over wireless fidelity (WiFi) lies more in the unit-area transmission rate rather than the single-link transmission rate. To characterize the achievable transmission rate per unit area, we consider an indoor downlink VLC network with dense attocell configuration for the transmitters with single-color light-emitting diode (LED) and multi-color LEDs, assuming binomial distributed users. We divide each attocell into central region and boundary region, and propose the transmission protocols based on such attocell division. We optimize the LED half-power angle to maximize the mean achievable transmission rate per unit area. More specifically, we investigate the rates of cell-center and cell-boundary users under fairness consideration for the single LED transmitter system. We characterize the mean achievable transmission rate per unit area under the white light constraints in the multiple LEDs transmitter system. The performance of the proposed transmission protocols is evaluated by numerical results.

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.

Performance Analysis of Cooperative Non-Orthogonal Multiple Access in Visible Light Communication

Nowadays, visible light communication (VLC) systems have become one of the candidate technologies for high data rate indoor communications. However, the main challenge to develop a high data rate VLC system is the narrow modulation bandwidth of light-emitting diodes (LEDs). Power domain non-orthogonal multiple access (PD-NOMA) is a promising scheme to enhance the spectral efficiency of downlink VLC systems. In this paper, we introduce cooperative PD-NOMA to the system to improve the signal reception for the far users. We evaluate the bit error rate (BER) and achievable rate performance of non-cooperative and cooperative PD-NOMA under perfect channel state information (CSI). Moreover, we drive analytic expressions for the BER and provide a Monte Carlo simulation results for verifying the validity of the derived analytical BER results. The results show that cooperative PD-NOMA outperforms non-cooperative PD-NOMA by 8.2 dB at BER 10−6 and by achievable rate 14.1 bit/s/Hz at 45 dB in a two-user scenario.

Enhancing power allocation efficiency of NOMA aided-MIMO downlink VLC networks

In order to enhance the achievable sum rate of indoor non-orthogonal multiple access (NOMA) aided multiple-input multiple-output (MIMO) visible light communication (VLC) downlink networks, in this paper, an efficient low computational complexity power allocation strategy termed as normalized logarithmic gain ratio power allocation (NLGRPA) is proposed, in which the optical channel information of all transmitter light-emitting diodes (LEDs) are exploited and properly ordered to ensure efficient power allocation Numerical results depict that our proposed NLGRPA method exhibits significant improvement in terms of achievable sum rate of NOMA aided MIMO-VLC networks when compared with other conventional power allocation approaches. Specifically, the proposed NLGRPA algorithm attains an achievable sum rate improvement of more than 55% and 33% compared with the gain ratio power allocation (GRPA) method and normalized gain difference power allocation (NGDPA) method in the 4 × 2 MIMO-VLC networks with nine randomly distributed users.

3-D Hybrid VLC-RF Indoor IoT Systems With Light Energy Harvesting

In this paper, a 3-D hybrid visible light communication (VLC)-radio frequency (RF) indoor Internet of Things system with spatially random terminals with one photodiode (e.g., indoor sensors: temperature sensors, humidity sensors, and indoor air quality sensors) is considered. Specifically, homogeneous Poisson point process is adopted to model to the distribution of the terminals, which means that the number of the terminals obeys Poisson distribution, and the positions of the terminals are uniformly distributed. VLC and RF communications are employed over downlink and uplink, respectively. Meanwhile, the terminals are designed to harvest the energy from the light emitted by the light-emitting diode over the downlink, which is used for the transmissions over the uplink. The light energy harvesting model is considered after introducing the line of sight propagation model for VLC. Then, the outage performance has been studied for the VLC downlink and non-orthogonal multiple access schemes over the RF uplink, respectively, by using stochastic geometry theory, while considering the randomness of the number of the terminals, and all terminals are spatially and randomly distributed in the 3-D room and all RF uplinks follow Rician fading. Finally, the approximated analytical expressions for the outage probability are derived and verified through Monte Carlo simulations.

NOMA for VLC Downlink Transmission With Random Receiver Orientation

Visible light communications (VLC) is an emerging technology with a promise of viable solution to spectrum crunch problem in conventional radio-frequency (RF) bands. In this paper, we consider a downlink multiuser VLC network where users randomly change their location and vertical orientation. In order to increase the spectral efficiency, we consider the non-orthogonal multiple access (NOMA) transmission to serve multiple users simultaneously. In particular, we propose individual and group-based user ordering techniques for NOMA with various user feedback schemes. In order to reduce the computational complexity and link overhead, feedback on the channel quality is proposed to be computed using a mean value of the vertical angle (instead of the exact instantaneous value), as well as the distance information. In addition, a two-bit feedback scheme is proposed for the group-based user scheduling, which relies on both the distance and the vertical angle, and differs from the conventional one-bit feedback of the distance only. The outage probability and sum-rate expressions are derived analytically, which show a very good match with the simulation data. Numerical results verify that the practical feedback scheme with the mean vertical angle achieves a near-optimal sum-rate performance, and the two-bit feedback significantly outperforms the one-bit feedback.