Performance Analysis of VLC Indoor Positioning and Demonstration

In the design of reconfigurable intelligent surfaces (RISs)-aided visible light communication (VLC) systems, most studies have focused on the deployment of mirror arrays and metasurfaces on walls to influence signal propagation and enhance communication performance. This paper provides a new research direction in the design and performance optimization of RIS-aided VLC systems whereby voltage-controlled tunable liquid crystals (LCs) are deployed as part of the VLC receiver. The purpose of the LC RIS is to provide incident light steering and intensity amplification in order to improve the received signal strength and the corresponding achievable data rate. More specifically, an LC RIS-based VLC receiver design is proposed and its operating principles and the channel model for a VLC system with such a receiver are provided. Since the refractive index of the LC RIS plays a critical role in the wave-guiding and light amplification capabilities of this novel receiver, a rate maximization problem is considered to achieve the optimal refractive index and the required voltage to obtain the best light amplification and data rate performances. This communication design problem is a non-convex optimization problem for which a metaheuristic approach is developed based on the sine-cosine algorithm. Simulation results are used to confirm the considerable data rate improvement by the proposed LC RIS-based VLC receiver and optimization algorithm when compared to a VLC receiver without the LC RIS and a baseline scheme, respectively.

Visible light communications (VLC) can be adopted in lighting infrastructure to provide ubiquitous wireless access in spaces where light is consumed by humans. Unfortunately, the requirement to provide high-quality diffuse illumination reduces the potential capacity of the free space links and we seek ways to accommodate both the lighting and data rate goals. We investigate the combination of multiple VLC transmissions through spatial multiplexing (SM), a MIMO technique, to meet our data rate goals. Specifically, this paper deals with receiver designs intended to receive and decode increasing numbers of SM/MIMO VLC data streams.Conventional imaging (camera) receivers have been used as VLC receivers; however, they are intended to capture frames at relatively low speeds and their architectures do not translate well for receiving multiple high-rate VLC streams. Thus we consider new techniques to optimize imaging receivers to meet the capacity requirements of multiple SM streams.In this paper, we propose token-based pixel selection (TBPS) for CMOS image sensors as a scalable alternative to mitigate this decrease in sampling rate. We show that in many cases, TBPS-based image sensors sample transmissions several times more frequently than windowing image sensors, yielding higher VLC data rates. Assuming the same reset, integration, and read times, TBPS always performs as well as, and often better than, windowing.

Indoor high precision three-dimensional positioning system based on visible light communication using modified genetic algorithm

Indoor positioning systems based on visible light communication (VLC) using white light-emitting diodes (WLEDs) have been widely studied in the literature. In this paper, we present an indoor visible-light positioning (VLP) system based on red–green–blue (RGB) LEDs and a frequency division multiplexing (FDM) scheme. This system combines the functions of an FDM scheme at the transmitters (RGB LEDs) and a received signal strength (RSS) technique to estimate the receiver position. The contribution of this work is two-fold. First, a new VLP system with RGB LEDs is proposed for a multi-cell network. Here, the RGB LEDs allow the exploitation of the chromatic space to transmit the VLP information. In addition, the VLC receiver leverages the responsivity of a single photodiode for estimating the FDM signals in RGB lighting channels. A second contribution is the derivation of an expression to calculate the optical power received by the photodiode for each incident RGB light. To this end, we consider a VLC channel model that includes both line-of-sight (LOS) and non-line-of-sight (NLOS) components. The fast Fourier transform (FFT) estimates the powers and frequencies of the received FDM signal. The receiver uses these optical signal powers in the RSS-based localization application to calculate the Euclidean distances and the frequencies for the RGB LED position. Subsequently, the receiver’s location is estimated using the Euclidean distances and RGB LED positions via a trilateration algorithm. Finally, Monte Carlo simulations are performed to evaluate the error performance of the proposed VLP system in a multi-cell scenario. The results show a high positioning accuracy performance for different color points. The average positioning error for all chromatic points was less than 2.2 cm. These results suggest that the analyzed VLP system could be used in application scenarios where white light balance or luminaire color planning are also the goals.

A novel design of three dimensional optical receiver for visible light communication (VLC) indoor positioning system has been proposed in this paper. We model the optical wireless channel and utilize modified triangulation method to obtain more robust receiver position by using at least two LEDs and one receiver consisting of nine photodetectors (PDs). The main characteristics are as follows: (1) our design of multi-PDs receiver is fully expanded into three dimensions compared with the pyramid structure (PR); (2) based on Multiple-Photodiode-based Indoor Positioning algorithm [1], we improve the indoor positioning algorithm by redefining the optimization problem of obtaining the direction from receiver to LED and using weighted triangulation method to locate receiver position; (3) the improved algorithm is implemented and the simulation results are shown under our three dimensional multi-PDs structure receiver.

A fully differential transimpedence amplifier (TIA) that serves as a receiver front-end for visible light communication (VLC) is proposed. The TIA incorporates an ambient light rejection circuit in the form of a floating active inductor (FAI) which can effectively bypass photocurrent (upto 50μA) and allows the subsequent transimpedence stage to only integrate the modulated photocurrent. This helps to avoid receiver saturation when exposed to excessive optical interference (i.e. large DC photocurrent) in outdoor environment of intelligent transport systems (ITS). Implemented in TSMC 0.18μm CMOS process, the proposed VLC receiver front-end consumes 220 μA bias current and exhibit transimpedence gain of 98dBΩ. Our design is aimed for VLC based receivers in intelligent transport systems by enabling active tracking between VLC transmitter and receiver using the same degree of polarization of light.

Visible light positioning (VLP) is an emerging positioning technique that utilizes indoor light sources to broadcast archer locations through visible light communication (VLC). Benefited by the densely deployed light lamps, VLP holds the promise for more accurate positioning accuracy than RF based approaches, and thus enables interesting applications such as retail navigation and shelf-level advertising in supermarkets and shopping malls. However, we observe that in existing VLP systems, receiving devices are heavily burdened in handling light flickering for VLC. In order to prevent human from being disturbed, the VLC transmitter lamps have to transmit pulses in a high rate (over 1kHz). Since the pulse rate far exceeds the cameras' sampling capability (30fps), receiver design either requires customized light sensor with cumbersome calibration on receiving signal strength [2] or processing high resolution images to leverage rolling shutter effect of the CMOS camera to decode message [1]. The heavy burden on receiving devices motivated us to try getting rid of light flickers. Since human eyes normally can not perceive changes in polarization, the idea is to modulate polarization instead of intensity for communication. In this demo, we demonstrate the VLC system in our VLP design [3] which realizes this idea. It enables lightweight VLC that is even affordable in wearables (Google Glass), without incurring hardware modification or computation off-loading. Moreover, it also makes other types of illuminating light beyond LED light (even sun light) possible to construct communication, therefore eliminates the barrier for deploying future VLC-based applications. As detailed in the full paper [3], our design was inspired by the liquid crystal display (LCD), from which we borrowed polarizer and liquid crystal. Liquid crystal has the property to change the polarization of bypassing polarized light according to the applied voltage. We use polarizer to polarize illuminating light and leverage liquid crystal to modulate bits through changing the light's polarization. The receiver can thus detect changes in polarization with a polarizing film, through which different polarizations result in different intensities. Since the SNR of such communication channel may significantly vary with the mobility of receiving device, we propose to add a dispersion filter to the transmitter. The dispersion filter can cast different frequency of lights into different polarization directions so that SNR in different receiving directions are evened. With the above techniques, VLC transmitter generates signal in low baud rate and mobile devices can perform VLC through camera directly. The communication is long in distance and lightweight enough for resource-constrained devices since the information is carried in intensity changes rather than certain image patterns in rolling shutter approaches. In this demo, we will illustrate the prototype implementation of the VLC communication system. We use incandescent lamps as illuminating light sources. The transmitter consists of a polarizing film, a liquid crystal layer, a dispersor and a control board. The receiver is demonstrated in Android smartphone with polarizing film in front of the camera.

Error compensation in indoor positioning systems based on software defined visible light communication

For an indoor localization system based on visible light communication (VLC) by using received signal strength technique, visible light signals used for estimating the distances between each localization target and reference nodes suffer from non-line-of-sight (NLoS) signal propagation, which could introduce large errors in estimating their locations. Both line-of-sight (LoS) link and NLoS link are taken into account in a noisy VLC channel, and thus the NLoS signal and ambient noise are the sources of localization error. Ricean K factor is introduced to evaluate the relation between the value of NLoS signal and the quality of localization in the proposed system. Analytical expressions for the distance measurement error and the upper bound of localization error are derived by using the least squares method. The simulation results show that the estimation of localization error matches the distribution of Ricean K factor in the noisy overall link. The environmental parameters that can be used to decrease the value of Ricean K factor are also discussed in the simulations, which provide the reference of parameters for building an experimental demonstration of a VLC indoor localization system. A comparison is conducted with the previous works to demonstrate the good performance of our scheme.

Nowadays, with the incursion of solid state lighting technology in our daily life, visible light communication (VLC) systems are becoming more important. This fact has generated a lot of attention on VLC to provide solutions on multiple applications where this technology can be exploited. At the same time, the growing of automation processes has created the necessity of knowing the localization of different objects and devices. Indoor localization based on radio frequency signals is one of the most used techniques (Wi‐Fi, Bluetooth, UWB, RFID, etc); however, VLC is a new and interesting method, which is gaining enormous research attention. Moreover, there are environments where the use of RF technologies is restricted or even prohibited. In such cases, VLC technology becomes an interesting alternative to solve this problem. In this paper, we design and implement a novel VLC‐based indoor localization system that combines the application of a VLC scheme for downlink and an ultrasonic communication for the uplink. Practical localization experiments are carried out in an actual office room environment, and results show a localization accuracy of 4 cm on average for direct links and 10 cm for indirect links.

We propose an electronic label and sensor system using visible light communication (VLC). The downlink signal is transmitted by a white-light light-emitting diode (LED) lamp that can provide lighting, VLC, and energy harvesting for mobile devices. The downlink is received by a solar cell. The uplink can be captured by a surveillance camera image sensor. However, using the camera image sensor as a VLC receiver (Rx) is challenging since the data rate is limited by the frame rate and due to uneven light exposure. The rolling shutter effect of the image sensor can be used to increase the data rate. In this paper, we propose and demonstrate how to demodulate the obtained rolling shutter pattern using a second-order polynomial (SOP) extinction ratio (ER) enhancement scheme, together with iterative and modified quick adaptive thresholding schemes. The ER enhancement scheme can significantly reduce the large ER fluctuation. Experimental results show that by using the proposed SOP ER enhancement scheme, the bit error rate (BER) improvement can be up to two orders of magnitude. We also believe that the proposed electronic label and sensor system may be applicable to Internet-of-Things sensing networks for connecting a number of mobile devices.

White illumination LEDs, with their long lifetimes and energy efficiencies at least 10 times greater than incandescent bulbs, are being massively deployed in illumination applications. Visible light communication (VLC) networks modulate white LEDs at high rates to carry information in a way that is imperceptible to humans. Such communication networks solve the spectrum scarcity problem at RF, are inherently immune to RF interference, and are license-free worldwide. In addition, they inherit the energy efficiency of LED technologies. Indeed, current mobile devices already contain a plethora of optical components, which could be simply modified to be VLC receivers. As many of the 14 billion incandescent bulbs in use worldwide are converted to more energy-efficient LED lighting, a unique opportunity exists to augment them with communications and possible other capabilities.

Using pre-distorted PAM-4 signal and parallel resistance circuit to enhance the passive solar cell based visible light communication

Visible light communication (VLC) with light emitting diodes (LEDs) is an emerging technology for 5G wireless communications. Recently, using complementary metal-oxide-semiconductor (CMOS) image sensor as VLC receiver is developed owing to its flexibility and low-cost. However, two illumination levels such as on-off keying (OOK) signal are used. To improve the system throughput and reduce complexity of the hardware design, in this paper, we propose and experimentally demonstrate a multilevel modulation scheme for VLC system utilizing the overlapping of two light sources for the first time, and the two light sources are modulated by an OOK and a Manchester signal respectively. At the receiver, a CMOS camera can demodulate the Manchester and the OOK signal simultaneously. Meanwhile, a low-pass filter (LPF) is used to enhance the system performance. The experimental results demonstrate that the proposed multilevel modulation scheme can achieve a net data rate of 4.32 kbit/s.

Visible light communication (VLC) reuses illumination devices, particularly light-emitting diodes (LEDs), for communication purposes. It has great potential to alleviate the strain on radio-frequency spectrum in indoor environments. VLC-enabled LED luminaries form VLC attocells that carry downlink data traffic to indoor mobile or stationary terminals. While one of the advantages of indoor VLC is low interference due to natural cell boundaries such as walls, multiple VLC attocells within a room would interfere. This is because illumination requirements often mandate a rich overlap of emissions of luminaries in a room. In this paper, we suggest the coordination of multiple VLC attocells (i.e., VLC-enabled LED luminaries) to turn the problem of overlap and thus interference into an advantage. We stipulate that this coordination can be accomplished through power line communication, which has been considered before as a means to transport data to VLC transmitters. Borrowing from concepts developed for radio-frequency wireless communications, we develop several precoding schemes for the new coordinated VLC broadcasting architecture. These include designs for the case of imperfect channel knowledge at the VLC transmitter, since channel information is usually provided through a low-rate feedback channel. The performance advantages for VLC transmission due to the proposed coordination and precoding designs are demonstrated based on a set of numerical results.