Editorial

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5 pages, 219 KiB

Open AccessEditorial

Editorial to the Special Issue on “Visible Light Communications, Networking, and Sensing”

by Stanislav Zvánovec, Zabih Ghassemlooy, Rafael Perez-Jimenez and Luis Nero Alves

Sensors 2021, 21(12), 4004; https://doi.org/10.3390/s21124004 - 10 Jun 2021

Cited by 2 | Viewed by 1985

Abstract

The next generation wireless technology networks and beyond (i [...] Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

Research

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16 pages, 3024 KiB

Open AccessArticle

Impact of Transmitter Positioning and Orientation Uncertainty on RSS-Based Visible Light Positioning Accuracy

by Neha Chaudhary, Luis Nero Alves and Zabih Ghassemlooy

Sensors 2021, 21(9), 3044; https://doi.org/10.3390/s21093044 - 27 Apr 2021

Cited by 11 | Viewed by 2329

Abstract

This paper present simulation-based results on the impact of transmitter (Tx) position and orientation uncertainty on the accuracy of the visible light positioning (VLP) system based on the received signal strength (RSS). There are several constraining factors for RSS-based algorithms, particularly due to [...] Read more.

This paper present simulation-based results on the impact of transmitter (Tx) position and orientation uncertainty on the accuracy of the visible light positioning (VLP) system based on the received signal strength (RSS). There are several constraining factors for RSS-based algorithms, particularly due to multipath channel characteristics and set-up uncertainties. The impact of Tx uncertainties on positioning error performance is studied, assuming a statistical modelling of the uncertainties. Simulation results show that the Tx uncertainties have a severe impact on the positioning error, which can be leveraged through the usage of more transmitters. Concerning a smaller Tx’s position uncertainty of 5 cm, the average positioning errors are 23.3, 15.1, and 13.2 cm with the standard deviation values of 6.4, 4.1, and 2.7 cm for 4-, 9-, and 16-Tx cases, respectively. While for a smaller Tx’ orientation uncertainty of 5°, the average positioning errors are 31.9, 20.6, and 17 cm with standard deviation values of 9.2, 6.3, and 3.9 cm for 4-, 9-, and 16-Tx cases, respectively. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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20 pages, 2081 KiB

Open AccessArticle

Design and Experimental Characterization of a Discovery and Tracking System for Optical Camera Communications

by Antonio Mederos-Barrera, Cristo Jurado-Verdu, Victor Guerra, Jose Rabadan and Rafael Perez-Jimenez

Sensors 2021, 21(9), 2925; https://doi.org/10.3390/s21092925 - 22 Apr 2021

Cited by 6 | Viewed by 2241

Abstract

Visible light communications (VLC) technology is emerging as a candidate to meet the demand for interconnected devices’ communications. However, the costs of incorporating specific hardware into end-user devices slow down its market entry. Optical camera communication (OCC) technology paves the way by reusing [...] Read more.

Visible light communications (VLC) technology is emerging as a candidate to meet the demand for interconnected devices’ communications. However, the costs of incorporating specific hardware into end-user devices slow down its market entry. Optical camera communication (OCC) technology paves the way by reusing cameras as receivers. These systems have generally been evaluated under static conditions, in which transmitting sources are recognized using computationally expensive discovery algorithms. In vehicle-to-vehicle networks and wearable devices, tracking algorithms, as proposed in this work, allow one to reduce the time required to locate a moving source and hence the latency of these systems, increasing the data rate by up to 2100%. The proposed receiver architecture combines discovery and tracking algorithms that analyze spatial features of a custom RGB LED transmitter matrix, highlighted in the scene by varying the cameras’ exposure time. By using an anchor LED and changing the intensity of the green LED, the receiver can track the light source with a slow temporal deterioration. Moreover, data bits sent over the red and blue channels do not significantly affect detection, hence transmission occurs uninterrupted. Finally, a novel experimental methodology to evaluate the evolution of the detection’s performance is proposed. With the analysis of the mean and standard deviation of novel K parameters, it is possible to evaluate the detected region-of-interest scale and centrality against the transmitter source’s ideal location. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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16 pages, 6888 KiB

Open AccessEditor’s ChoiceArticle

The Utilization of Artificial Neural Network Equalizer in Optical Camera Communications

by Othman Isam Younus, Navid Bani Hassan, Zabih Ghassemlooy, Stanislav Zvanovec, Luis Nero Alves and Hoa Le-Minh

Sensors 2021, 21(8), 2826; https://doi.org/10.3390/s21082826 - 16 Apr 2021

Cited by 16 | Viewed by 2965

Abstract

In this paper, we propose and validate an artificial neural network-based equalizer for the constant power 4-level pulse amplitude modulation in an optical camera communications system. We introduce new terminology to measure the quality of the communications link in terms of the number [...] Read more.

In this paper, we propose and validate an artificial neural network-based equalizer for the constant power 4-level pulse amplitude modulation in an optical camera communications system. We introduce new terminology to measure the quality of the communications link in terms of the number of row pixels per symbol

N_{pps}

, which allows a fair comparison considering the progress made in the development of the current image sensors in terms of the frame rates and the resolutions of each frame. Using the proposed equalizer, we experimentally demonstrate a non-flickering system using a single light-emitting diode (LED) with

N_{pps}

of 20 and 30 pixels/symbol for the unequalized and equalized systems, respectively. Potential transmission rates of up to 18.6 and 24.4 kbps are achieved with and without the equalization, respectively. The quality of the received signal is assessed using the eye-diagram opening and its linearity and the bit error rate performance. An acceptable bit error rate (below the forward error correction limit) and an improvement of ~66% in the eye linearity are achieved using a single LED and a typical commercial camera with equalization. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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18 pages, 2831 KiB

Open AccessArticle

Performance of Vehicular Visible Light Communications under the Effects of Atmospheric Turbulence with Aperture Averaging

by Elizabeth Eso, Zabih Ghassemlooy, Stanislav Zvanovec, Juna Sathian, Mojtaba Mansour Abadi and Othman Isam Younus

Sensors 2021, 21(8), 2751; https://doi.org/10.3390/s21082751 - 13 Apr 2021

Cited by 14 | Viewed by 2885

Abstract

In this paper, we investigate the performance of a vehicular visible light communications (VVLC) link with a non-collimated and incoherent light source (a light-emitting diode) as the transmitter (Tx), and two different optical receiver (Rx) types (a camera and photodiode (PD)) under atmospheric [...] Read more.

In this paper, we investigate the performance of a vehicular visible light communications (VVLC) link with a non-collimated and incoherent light source (a light-emitting diode) as the transmitter (Tx), and two different optical receiver (Rx) types (a camera and photodiode (PD)) under atmospheric turbulence (AT) conditions with aperture averaging (AA). First, we present simulation results indicating performance improvements in the signal-to-noise ratio (SNR) under AT with AA with increasing size of the optical concentrator. Experimental investigations demonstrate the potency of AA in mitigating the induced signal fading due to the weak to moderate AT regimes in a VVLC system. The experimental results obtained with AA show that the link’s performance was stable in terms of the average SNR and the peak SNR for the PD and camera-based Rx links, respectively with <1 dB SNR penalty for both Rxs, as the strength of AT increases compared with the link with no AT. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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18 pages, 16220 KiB

Open AccessArticle

Wireless Sensor Networks Using Sub-Pixel Optical Camera Communications: Advances in Experimental Channel Evaluation

by Vicente Matus, Victor Guerra, Cristo Jurado-Verdu, Stanislav Zvanovec and Rafael Perez-Jimenez

Sensors 2021, 21(8), 2739; https://doi.org/10.3390/s21082739 - 13 Apr 2021

Cited by 11 | Viewed by 2832

Abstract

Optical wireless communications in outdoor scenarios are challenged by uncontrollable atmospheric conditions that impair the channel quality. In this paper, different optical camera communications (OCC) equipment are experimentally studied in the laboratory and the field, and a sub-pixel architecture is raised as a [...] Read more.

Optical wireless communications in outdoor scenarios are challenged by uncontrollable atmospheric conditions that impair the channel quality. In this paper, different optical camera communications (OCC) equipment are experimentally studied in the laboratory and the field, and a sub-pixel architecture is raised as a potential solution for outdoor wireless sensor networks (WSN) applications, considering its achievable data throughput, the spatial division of sources, and the ability of cameras to overcome the attenuation caused by different atmospheric conditions such as rain, turbulence and the presence of aerosols. Sub-pixel OCC shows particularly adequate capabilities for some of the WSN applications presented, also in terms of cost-effectiveness and scalability. The novel topology of sub-pixel projection of multiple transmitters over the receiver using small optical devices is presented as a solution using OCC that re-uses camera equipment for communication purposes on top of video-monitoring. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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24 pages, 1281 KiB

Open AccessArticle

Optimized Analog Multi-Band Carrierless Amplitude and Phase Modulation for Visible Light Communication-Based Internet of Things Systems

by Luis Rodrigues, Mónica Figueiredo and Luis Nero Alves

Sensors 2021, 21(7), 2537; https://doi.org/10.3390/s21072537 - 05 Apr 2021

Cited by 8 | Viewed by 2817

Abstract

This paper presents a multi-user Visible Light Communication (VLC)-based Internet of Things (IoT) system using multi band-Carrierless Amplitude and Phase (m-CAP) modulation for IoT applications. The proposed system uses a digital m-CAP modulator embedded in a ceiling LED light fixture and analog receivers, [...] Read more.

This paper presents a multi-user Visible Light Communication (VLC)-based Internet of Things (IoT) system using multi band-Carrierless Amplitude and Phase (m-CAP) modulation for IoT applications. The proposed system uses a digital m-CAP modulator embedded in a ceiling LED light fixture and analog receivers, aiming at low-cost, low-power, and small-sized IoT devices. The performance was evaluated in terms of the filtering stage design and the usage of guard bands. Different pairs of emitter and receiver filters were considered. While Bessel and Butterworth analog filters were tested in the analog receiver, the digital m-CAP modulator pulse shaping filter considered raised cosine filters, as well as digital matched filters for the analog Bessel and Butterworth filters. Regarding the guard bands, two approaches were considered: either by using the raised cosine roll-off factor (bandwidth compression) or by suppressing the even bands. The Bit Error Rate (BER) performance was obtained by simulation. The usage of the Bessel filter in the receiver, along with a digital matched filter, proved to be the best solution, achieving a BER lower than

10^{- 3}

for an Eb/No of 6 dB, using a third-order filter. Furthermore, guard bands should be used in order to mitigate inter-band interference in order to have improved performance when multiple users intend to simultaneously communicate. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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22 pages, 3070 KiB

Open AccessArticle

A Comprehensive Open-Source Simulation Framework for LiFi Communication

by Shakir Ullah, Saeed Ur Rehman and Peter Han Joo Chong

Sensors 2021, 21(7), 2485; https://doi.org/10.3390/s21072485 - 02 Apr 2021

Cited by 13 | Viewed by 5286

Abstract

Light Fidelity (LiFi) is a new candidate for wireless networking that utilizes the visible light spectrum and exploits the existing lighting infrastructure in the form of light-emitting diodes (LEDs). It provides point-to-point and point-to-multipoint communication on a bidirectional channel at very high data [...] Read more.

Light Fidelity (LiFi) is a new candidate for wireless networking that utilizes the visible light spectrum and exploits the existing lighting infrastructure in the form of light-emitting diodes (LEDs). It provides point-to-point and point-to-multipoint communication on a bidirectional channel at very high data rates. However, the LiFi has small coverage, and its optical gain is closely related to the receiver’s directionality vis-à-vis the transmitter, therefore it can experience frequent service outages. To provide reliable coverage, the LiFi is integrated with other networking technologies such as wireless fidelity (WiFi) thus forming a hybrid system. The hybrid LiFi/WiFi system faces many challenges including but not limited to seamless integration with the WiFi, support for mobility, handover management, resource sharing, and load balancing. The existing literature has addressed one or the other aspect of the issues facing LiFi systems. There are limited free source tools available to holistically address these challenges in a scalable manner. To this end, we have developed an open-source simulation framework based on the network simulator 3 (ns-3), which realizes critical aspects of the LiFi wireless network. Our developed ns-3 LiFi framework provides a fully functional AP equipped with the physical layer and medium access control (MAC), a mobility model for the user device, and integration between LiFi and WiFi with a handover facility. Simulation results are produced to demonstrate the mobility and handover capabilities, and the performance gains from the LiFi-WiFi hybrid system in terms of packet delay, throughput, packet drop ratio (PDR), and fairness between users. The source code of the framework is made available for the use of the research community. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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16 pages, 7923 KiB

Open AccessArticle

A 40 Mb/s VLC System Reusing an Existing Large LED Panel in an Indoor Office Environment

by Xicong Li, Zabih Ghassemlooy, Stanislav Zvánovec and Paul Anthony Haigh

Sensors 2021, 21(5), 1697; https://doi.org/10.3390/s21051697 - 02 Mar 2021

Cited by 12 | Viewed by 3187

Abstract

With advances in solid-state lighting, visible light communication (VLC) has emerged as a promising technology to enhance existing light-emitting diode (LED)-based lighting infrastructure by adding data communication capabilities to the illumination functionality. The last decade has witnessed the evolution of the VLC concept [...] Read more.

With advances in solid-state lighting, visible light communication (VLC) has emerged as a promising technology to enhance existing light-emitting diode (LED)-based lighting infrastructure by adding data communication capabilities to the illumination functionality. The last decade has witnessed the evolution of the VLC concept through global standardisation and product launches. Deploying VLC systems typically requires replacing existing light sources with new luminaires that are equipped with data communication functionality. To save the investment, it is clearly desirable to make the most of the existing illumination systems. This paper investigates the feasibility of adding data communication functionality to the existing lighting infrastructure. We do this by designing an experimental system in an indoor environment based on an off-the-shelf LED panel typically used in office environments, with the dimensions of 60 × 60 cm

^{2}

. With minor modifications, the VLC function is implemented, and all of the modules of the LED panel are fully reused. A data rate of 40 Mb/s is supported at a distance of up to 2 m while using the multi-band carrierless amplitude and phase (CAP) modulation. Two main limiting factors for achieving higher data rates are observed. The first factor is the limited bandwidth of the LED string inside the panel. The second is the flicker due to the residual ripple of the bias current that is generated by the panel’s driver. Flicker is introduced by the low-cost driver, which provides bias currents that fluctuate in the low frequency range (less than several kilohertz). This significantly reduces the transmitter’s modulation depth. Concurrently, the driver can also introduce an effect that is similar to baseline wander at the receiver if the flicker is not completely filtered out. We also proposed a solution based on digital signal processing (DSP) to mitigate the flicker issue at the receiver side and its effectiveness has been confirmed. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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25 pages, 25920 KiB

Open AccessArticle

Optical Camera Communication as an Enabling Technology for Microalgae Cultivation

by Cristo Jurado-Verdu, Victor Guerra, Vicente Matus, Carlos Almeida and Jose Rabadan

Sensors 2021, 21(5), 1621; https://doi.org/10.3390/s21051621 - 25 Feb 2021

Cited by 4 | Viewed by 3226

Abstract

Optical Camera Communication (OCC) systems have a potential application in microalgae production plants. In this work, a proof-of-concept prototype consisting of an artificial lighting photobioreactor is proposed. This reactor optimises the culture’s photosynthetic efficiency while transmitting on-off keying signals to a rolling-shutter camera. [...] Read more.

Optical Camera Communication (OCC) systems have a potential application in microalgae production plants. In this work, a proof-of-concept prototype consisting of an artificial lighting photobioreactor is proposed. This reactor optimises the culture’s photosynthetic efficiency while transmitting on-off keying signals to a rolling-shutter camera. Upon reception, both signal decoding and biomass concentration sensing are performed simultaneously using image processing techniques. Moreover, the communication channel’s theoretical modelling, the data rate system’s performance, and the plant distribution requirements and restrictions for a production-scale facility are detailed. A case study is conducted to classify three different node arrangements in a real facility, considering node visibility, channel capacity, and space exploitation. Finally, several experiments comprising radiance evaluation and Signal-to-Noise Ratio (SNR) computation are performed at different angles of view in both indoor and outdoor environments. It is observed that the Lambertian-like emission patterns are affected by increasing concentrations, reducing the effective emission angles. Furthermore, significant differences in the SNR, up to 20 dB, perceived along the illuminated surface (centre versus border), gradually reduce as light is affected by greater dispersion. The experimental analysis in terms of scattering and selective wavelength attenuation for green (Arthrospira platensis) and brown (Rhodosorus marinus) microalgae species determines that the selected strain must be considered in the development of this system. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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9 pages, 646 KiB

Open AccessCommunication

EVM Loss: A Loss Function for Training Neural Networks in Communication Systems

by Scott Stainton, Martin Johnston, Satnam Dlay and Paul Anthony Haigh

Sensors 2021, 21(4), 1094; https://doi.org/10.3390/s21041094 - 05 Feb 2021

Cited by 3 | Viewed by 2310

Abstract

Neural networks and their application in communication systems are receiving growing attention from both academia and industry. The authors note that there is a disconnect between the typical objective functions of these neural networks with regards to the context in which the neural [...] Read more.

Neural networks and their application in communication systems are receiving growing attention from both academia and industry. The authors note that there is a disconnect between the typical objective functions of these neural networks with regards to the context in which the neural network will eventually be deployed and evaluated. To this end, a new loss function is proposed and shown to increase the performance of neural networks when implemented in a communication system compared to previous methods. It is further shown that a ‘split complex’ approach used by many implementations can be improved via formalisation of the ‘concatenated complex’ approach described herein. Experimental results using the orthogonal frequency division multiplexing (OFDM) and spectrally efficient frequency division multiplexing (SEFDM) modulation formats with varying bandwidth compression factors over a wireless visible light communication (VLC) link validate the efficacy of the proposed method in a real system, achieving the lowest error vector magnitude (EVM), and thus bit error rate (BER), across all experiments, with a 5 dB to 10 dB improvement in the received symbols EVM overall compared to the baseline implementation, with bandwidth compressions down to 40% compared to OFDM, resulting in a spectral efficiency gain of 67%. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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16 pages, 4277 KiB

Open AccessArticle

An Indoor Visible Light Positioning System Using Tilted LEDs with High Accuracy

by Neha Chaudhary, Othman Isam Younus, Luis Nero Alves, Zabih Ghassemlooy, Stanislav Zvanovec and Hoa Le-Minh

Sensors 2021, 21(3), 920; https://doi.org/10.3390/s21030920 - 29 Jan 2021

Cited by 24 | Viewed by 4094

Abstract

The accuracy of the received signal strength-based visible light positioning (VLP) system in indoor applications is constrained by the tilt angles of transmitters (Txs) and receivers as well as multipath reflections. In this paper, for the first time, we show that tilting the [...] Read more.

The accuracy of the received signal strength-based visible light positioning (VLP) system in indoor applications is constrained by the tilt angles of transmitters (Txs) and receivers as well as multipath reflections. In this paper, for the first time, we show that tilting the Tx can be beneficial in VLP systems considering both line of sight (LoS) and non-line of sight transmission paths. With the Txs oriented towards the center of the receiving plane (i.e., the pointing center F), the received power level is maximized due to the LoS components on F. We also show that the proposed scheme offers a significant accuracy improvement of up to ~66% compared with a typical non-tilted Tx VLP at a dedicated location within a room using a low complex linear least square algorithm with polynomial regression. The effect of tilting the Tx on the lighting uniformity is also investigated and results proved that the uniformity achieved complies with the European Standard EN 12464-1. Furthermore, we show that the accuracy of VLP can be further enhanced with a minimum positioning error of 8 mm by changing the height of F. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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15 pages, 6769 KiB

Open AccessArticle

Utilization of an OLED-Based VLC System in Office, Corridor, and Semi-Open Corridor Environments

by Zahra Nazari Chaleshtori, Zabih Ghassemlooy, Hossien B. Eldeeb, Murat Uysal and Stanislav Zvanovec

Sensors 2020, 20(23), 6869; https://doi.org/10.3390/s20236869 - 01 Dec 2020

Cited by 20 | Viewed by 2725

Abstract

Organic light emitting diodes (OLEDs) have recently received growing interest for their merits as soft light and large panels at a low cost for the use in public places such as airports, shopping centers, offices, and train or bus stations. Moreover, the flexible [...] Read more.

Organic light emitting diodes (OLEDs) have recently received growing interest for their merits as soft light and large panels at a low cost for the use in public places such as airports, shopping centers, offices, and train or bus stations. Moreover, the flexible substrate-based OLEDs provide an attractive feature of having curved or rolled lighting sources for the use in wearable devices and display panels. This technology can be implemented in visible light communications (VLC) for several applications such as visual display, data communications, and indoor localization. This article aims to investigate the use of flexible OLED-based VLC in indoor environments (i.e., office, corridor and semi-open corridor in shopping malls). We derive a two-term power series model to be match with the root-mean-square delay spread and optical path loss (OPL). We show that, for OLED positioned on outer-wall of shops, the channel gain is enhanced in contrast to them being positioned on the inner-wall. Moreover, the channel gain in empty environments is higher compare with the furnished rooms. We show that, the OPL for a 10 m link span are lower by 4.4 and 6.1 dB for the empty and semi-open corridors compared with the furnished rooms, when OLED is positioned on outer-wall of shops. Moreover, the channel gain in the corridor is higher compared with the semi-open corridor. We also show that, in furnished and semi-open corridors the OPL values are 55.6 and 57.2 dB at the center of corridor increasing to 87.6 and 90.7 dB at 20 m, respectively, when OLED is positioned on outer-wall of shops. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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23 pages, 13774 KiB

Open AccessArticle

Experimental Evaluation of Machine Learning Methods for Robust Received Signal Strength-Based Visible Light Positioning

by Willem Raes, Nicolas Knudde, Jorik De Bruycker, Tom Dhaene and Nobby Stevens

Sensors 2020, 20(21), 6109; https://doi.org/10.3390/s20216109 - 27 Oct 2020

Cited by 17 | Viewed by 2666

Abstract

In this work, the use of Machine Learning methods for robust Received Signal Strength (RSS)-based Visible Light Positioning (VLP) is experimentally evaluated. The performance of Multilayer Perceptron (MLP) models and Gaussian processes (GP) is investigated when using relative RSS input features. The experimental [...] Read more.

In this work, the use of Machine Learning methods for robust Received Signal Strength (RSS)-based Visible Light Positioning (VLP) is experimentally evaluated. The performance of Multilayer Perceptron (MLP) models and Gaussian processes (GP) is investigated when using relative RSS input features. The experimental set-up for the RSS-based VLP technology uses light-emitting diodes (LEDs) transmitting intensity modulated light and a single photodiode (PD) as a receiver. The experiments focus on achieving robustness to cope with unknown received signal strength modifications over time. Therefore, several datasets were collected, where per dataset either the LEDs transmitting power is modified or the PD aperture is partly obfuscated by dust particles. Two relative RSS schemes are investigated. The first scheme uses the maximum received light intensity to normalize the received RSS vector, while the second approach obtains RSS ratios by combining all possible unique pairs of received intensities. The Machine Learning (ML) methods are compared to a relative multilateration implementation. It is demonstrated that the adopted MLP and GP models exhibit superior performance and higher robustness when compared to the multilateration strategies. Furthermore, when comparing the investigated ML models, the GP model is proven to be more robust than the MLP for the considered scenarios. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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28 pages, 10050 KiB

Open AccessArticle

Optical OFDM for SiPM-Based Underwater Optical Wireless Communication Links

by Taha Essalih, Mohammad Ali Khalighi, Steve Hranilovic and Hassan Akhouayri

Sensors 2020, 20(21), 6057; https://doi.org/10.3390/s20216057 - 24 Oct 2020

Cited by 18 | Viewed by 3060

Abstract

Underwater optical wireless systems have dual requirements of high data rates and long ranges in harsh scattering and attenuation conditions. In this paper, we investigate the advantages and limitations of optical orthogonal frequency-division multiplexing (O-OFDM) signaling when a silicon photo-multiplier (SiPM) is used [...] Read more.

Underwater optical wireless systems have dual requirements of high data rates and long ranges in harsh scattering and attenuation conditions. In this paper, we investigate the advantages and limitations of optical orthogonal frequency-division multiplexing (O-OFDM) signaling when a silicon photo-multiplier (SiPM) is used at the receiver in order to ensure high sensitivity. Considering a light-emitting diode (LED) transmitter and taking into account the limited dynamic range imposed by the transmitter and the SiPM receiver, we study the performance of three popular O-OFDM schemes, i.e., DC-biased, asymmetrically-clipped, and layered asymmetrically-clipped O-OFDM (DCO-, ACO-, and LACO-OFDM, respectively). We consider a constraint on transmit electrical power

P_{Txe}

and take into account the required DC bias for the three considered schemes in practice, showing the undeniable advantage of ACO- and LACO-OFDM in terms of energy efficiency. For instance, for the considered SiPM and LED components, a spectral efficiency of ∼1 bps/Hz with a data rate of 20 Mbps, a link range of 70 m, and a target bit-error-rate (BER) of

10^{- 3}

, ACO and LACO allow a reduction of about 10 and 6 mW, respectively, in the required

P_{Txe}

, compared to DCO-OFDM. Meanwhile, we show that when relaxing the

P_{Txe}

constraint, DCO-OFDM offers the largest operational link range within which a target BER can be achieved. For instance, for a target BER of

10^{- 3}

and a data rate of 20 Mbps, and considering

P_{Txe}

of 185, 80, and 50 mW for DCO-, LACO-, and ACO-OFDM, respectively, the corresponding intervals of operational link range are about 81,

74.3

, and

73.8

m. Lastly, we show that LACO-OFDM makes a good compromise between energy efficiency and operational range flexibility, although requiring a higher computational complexity and imposing a longer latency at the receiver. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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19 pages, 49337 KiB

Open AccessArticle

Polarization Differential Visible Light Communication: Theory and Experimental Evaluation

by Jorik De Bruycker, Willem Raes, Stanislav Zvánovec and Nobby Stevens

Sensors 2020, 20(19), 5661; https://doi.org/10.3390/s20195661 - 03 Oct 2020

Cited by 3 | Viewed by 2243

Abstract

Visible Light Communication (VLC) has received substantial research attention in the last decade. The vast majority of VLC focuses on the modulation of the transmitted light intensity. In this work, however, the intensity is kept constant while the polarization direction is deployed as [...] Read more.

Visible Light Communication (VLC) has received substantial research attention in the last decade. The vast majority of VLC focuses on the modulation of the transmitted light intensity. In this work, however, the intensity is kept constant while the polarization direction is deployed as a carrier of information. Demodulation is realized by using a differential receiver pair equipped with mutually orthogonal polarizers. An analytical expression to evaluate the Signal-to-Noise Ratio (

S N R

) as a function of the rotation angle of the receiver is derived. It is demonstrated that the signal quality can deteriorate heavily with receiver orientation when using a single differential receiver pair. A way to overcome this drawback using two receiver pairs is described. The analytical expression is experimentally verified through measurements with two different receiver setups. This work demonstrates the potential of polarization-based modulation in the field of VLC, where receiver rotation robustness has been achieved by means of a dedicated quadrant photodiode receiver. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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27 pages, 44206 KiB

Open AccessArticle

A Comprehensive Study on Light Signals of Opportunity for Subdecimetre Unmodulated Visible Light Positioning

by Sander Bastiaens, Kenneth Deprez, Luc Martens, Wout Joseph and David Plets

Sensors 2020, 20(19), 5596; https://doi.org/10.3390/s20195596 - 29 Sep 2020

Cited by 7 | Viewed by 2336

Abstract

Currently, visible light positioning (VLP) enabling an illumination infrastructure requires a costly retrofit. Intensity modulation systems not only necessitate changes to the internal LED driving module, but decrease the LEDs’ radiant flux as well. This hinders the infrastructure’s ability to meet the maintained [...] Read more.

Currently, visible light positioning (VLP) enabling an illumination infrastructure requires a costly retrofit. Intensity modulation systems not only necessitate changes to the internal LED driving module, but decrease the LEDs’ radiant flux as well. This hinders the infrastructure’s ability to meet the maintained illuminance standards. Ideally, the LEDs could be left unmodulated, i.e., unmodulated VLP (uVLP). uVLP systems, inherently low-cost, exploit the characteristics of the light signals of opportunity (LSOOP) to infer a position. In this paper, it is shown that proper signal processing allows using the LED’s characteristic frequency (CF) as a discriminative feature in photodiode (PD)-based received signal strength (RSS) uVLP. This manuscript investigates and compares the aptitude of (future) RSS-based uVLP and VLP systems in terms of their feasibility, cost and accuracy. It demonstrates that CF-based uVLP exhibits an acceptable loss of accuracy compared to (regular) VLP. For point source-like LEDs, uVLP only worsens the trilateration-based median

p_{50}

and 90th percentile root-mean-square error

p_{90}

from

5.3 c m

to

7.9 c m

(+50%) and from

9.6 c m

to

15.6 c m

(+62%), in the

4 m

×

4 m

room under consideration. A large experimental validation shows that employing a robust model-based fingerprinting localisation procedure, instead of trilateration, further boosts uVLP’s

p_{50}

and

p_{90}

accuracy to

5.0 c m

and

10.6 c m

. When collating with VLP’s

p_{50} = 3.5 c m

and

p_{90} = 6.8 c m

, uVLP exhibits a comparable positioning performance at a significantly lower cost and at a higher maintained illuminance, all of which underline uVLP’s high adoption potential. With this work, a significant step is taken towards the development of an accurate and low-cost tracking system. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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13 pages, 3265 KiB

Open AccessArticle

LDPC-Coded CAP with Spatial Diversity for UVLC Systems over Generalized-Gamma Fading Channel

by Hongyan Jiang, Hongbing Qiu, Ning He, Zhonghua Zhao, Wasiu Popoola, Zahir Ahmad and Sujan Rajbhandari

Sensors 2020, 20(12), 3378; https://doi.org/10.3390/s20123378 - 15 Jun 2020

Cited by 5 | Viewed by 2982

Abstract

In this paper, low-density parity-check (LDPC)-coded carrierless amplitude and phase (CAP) modulation with spatial diversity is proposed to mitigate turbulence-induced fading in an underwater visible-light communication (UVLC) channel. Generalized-gamma (GG) distribution was used to model the fading, as this model is valid for [...] Read more.

In this paper, low-density parity-check (LDPC)-coded carrierless amplitude and phase (CAP) modulation with spatial diversity is proposed to mitigate turbulence-induced fading in an underwater visible-light communication (UVLC) channel. Generalized-gamma (GG) distribution was used to model the fading, as this model is valid for weak- and strong-turbulence regimes. On the basis of the characteristic function (CHF) of GG random variables, we derived an approximated bit-error rate (BER) for the CAP modulation scheme with spatial diversity and equal-gain combining (EGC). Furthermore, we simulated the performance of the CAP system with diversity and LDPC for various turbulence conditions and validated the analysis. Obtained results showed that the combination of LDPC and spatial diversity is effective in mitigating turbulence-induced fading, especially when turbulence strength is strong. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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15 pages, 6208 KiB

Open AccessArticle

Optical Camera Communications for IoT–Rolling-Shutter Based MIMO Scheme with Grouped LED Array Transmitter

by Shivani Rajendra Teli, Vicente Matus, Stanislav Zvanovec, Rafael Perez-Jimenez, Stanislav Vitek and Zabih Ghassemlooy

Sensors 2020, 20(12), 3361; https://doi.org/10.3390/s20123361 - 13 Jun 2020

Cited by 24 | Viewed by 4944

Abstract

In optical camera communications (OCC), the provision of both flicker-free illumination and high data rates are challenging issues, which can be addressed by utilizing the rolling-shutter (RS) property of the image sensors as the receiver (Rx). In this paper, we propose an RS-based [...] Read more.

In optical camera communications (OCC), the provision of both flicker-free illumination and high data rates are challenging issues, which can be addressed by utilizing the rolling-shutter (RS) property of the image sensors as the receiver (Rx). In this paper, we propose an RS-based multiple-input multiple-output OCC scheme for the Internet of things (IoT) application. A simplified design of multi-channel transmitter (Tx) using a 7.2 × 7.2 cm² small 8 × 8 distributed light emitting diode (LED) array, based on grouping of LEDs, is proposed for flicker-free transmission. We carry out an experimental investigation of the indoor OCC system by employing a Raspberry Pi camera as the Rx, with RS capturing mode. Despite the small area of the display, flicker-free communication links within the range of 20–100 cm are established with data throughput of 960 to 120 bps sufficient for IoT. A method to extend link spans up to 1.8 m and the data throughput to 13.44 kbps using different configurations of multi-channel Tx is provided. The peak signal-to-noise ratio of ~14 and 16 dB and the rate of successfully received bits of 99.4 and 81% are measured for the shutter speeds of 200 and 800 µs for a link span of 1 m, respectively. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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17 pages, 5324 KiB

Open AccessArticle

Characterization and Performance of a Thermal Camera Communication System

by Victor Guerra, Jaime R. Ticay-Rivas, Victor Alonso-Eugenio and Rafael Perez-Jimenez

Sensors 2020, 20(11), 3288; https://doi.org/10.3390/s20113288 - 09 Jun 2020

Cited by 12 | Viewed by 3094

Abstract

This work presents a novel communications technology named Thermal Camera Communication (TCC), which is analogous to Optical Camera Communication (OCC). Thermographic cameras and Peltier cells are proposed as receiver and transmitter, respectively, changing completely their usual field of application. Furthermore, a comprehensive characterization [...] Read more.

This work presents a novel communications technology named Thermal Camera Communication (TCC), which is analogous to Optical Camera Communication (OCC). Thermographic cameras and Peltier cells are proposed as receiver and transmitter, respectively, changing completely their usual field of application. Furthermore, a comprehensive characterization of the Peltier–Thermal camera pair is carried out, presenting their bandwidth, achievable data rate under On-Off-Keying (OOK) modulation, noise characteristics, and energy efficiency. A comparison against the current state-of-the-art OCC technology is also provided, showing that TCC is a promising technology suitable for sensor networks. The thorough analysis of TCC performed in this work shows that commercial Peltier cells can be re-thought under a communications viewpoint in order to improve their performance. This novel communication technology can be applied in environments such as the access to public transportation or buildings due to the new health emergency situation. The use of thermographic cameras will become massive and dual measurement and communication purposes could be considered for applications such as sensor networks, using a yet unexploited wavelength range. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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12 pages, 2272 KiB

Open AccessLetter

Advanced Modulation Format of Probabilistic Shaping Bit Loading for 450-nm GaN Laser Diode based Visible Light Communication

by Guoqiang Li, Fangchen Hu, Peng Zou, Chaofan Wang, Gong-Ru Lin and Nan Chi

Sensors 2020, 20(21), 6143; https://doi.org/10.3390/s20216143 - 29 Oct 2020

Cited by 10 | Viewed by 2355

Abstract

Visible light communication is an emerging high-speed optical wireless communication technology that can be a candidate to alleviate pressure on conventional radio frequency-based technology. In this paper, for the first time, the advanced modulation format of probabilistic shaping (PS) bit loading is investigated [...] Read more.

Visible light communication is an emerging high-speed optical wireless communication technology that can be a candidate to alleviate pressure on conventional radio frequency-based technology. In this paper, for the first time, the advanced modulation format of probabilistic shaping (PS) bit loading is investigated in a high data rate visible light communication system based on a 450-nm Gallium Nitride laser diode. The characteristic of the system is discussed and PS bit loading discrete multi-tone modulation helps to raise the spectral efficiency and improve the system performance. Higher entropy can be achieved in the same signal-to-noise ratio (SNR) and modulation bandwidth limitation, comparing to bit and power loading. With PS bit loading, an available information rate (AIR) of 10.23 Gbps is successfully achieved at the signal bandwidth of 1.5 GHz in a 1.2 m free space transmission with normalized generalized mutual information above 0.92. And higher AIR can be anticipated with an entropy-loading strategy that fixes the channel characteristic. Experimental results validate that a PS bit loading scheme has the potential to increase the system capacity. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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12 pages, 3423 KiB

Open AccessLetter

Experimental Characterization of RGB LED Transceiver in Low-Complexity LED-to-LED Link

by Mariam Galal, Wai Pang Ng, Richard Binns and Ahmed Abd El Aziz

Sensors 2020, 20(20), 5754; https://doi.org/10.3390/s20205754 - 10 Oct 2020

Cited by 7 | Viewed by 3262

Abstract

This paper proposes a low-complexity and energy-efficient light emitting diode (LED)-to-LED communication system for Internet of Things (IoT) devices with data rates up to 200 kbps over an error-free transmission distance up to 7 cm. The system is based on off-the-shelf red-green-blue (RGB) [...] Read more.

This paper proposes a low-complexity and energy-efficient light emitting diode (LED)-to-LED communication system for Internet of Things (IoT) devices with data rates up to 200 kbps over an error-free transmission distance up to 7 cm. The system is based on off-the-shelf red-green-blue (RGB) LEDs, of which the red sub-LED is employed as photodetector in photovoltaic mode while the green sub-LED is the transmitter. The LED photodetector is characterized in the terms of its noise characteristics and its response to the light intensity. The system performance is then analysed in terms of bandwidth, bit error rate (BER) and the signal to noise ratio (SNR). A matched filter is proposed, which optimises the performance and increases the error-free distance. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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14 pages, 2659 KiB

Open AccessLetter

Experimental Characterization of Single-Color Power LEDs Used as Photodetectors

by Jan Sticklus, Peter Adam Hoeher and Martin Hieronymi

Sensors 2020, 20(18), 5200; https://doi.org/10.3390/s20185200 - 11 Sep 2020

Cited by 12 | Viewed by 3192

Abstract

Semiconductor-based light emitting diodes can be used for photon emission as well as for detection of photons. In this paper, we present a fair comparison between off-the-shelf power Light emitting diodes (LEDs) and a silicon photodetector with respect to their spectral, temporal, and [...] Read more.

Semiconductor-based light emitting diodes can be used for photon emission as well as for detection of photons. In this paper, we present a fair comparison between off-the-shelf power Light emitting diodes (LEDs) and a silicon photodetector with respect to their spectral, temporal, and spatial properties. The examined LED series features unexpected good sensitivity and distinct optical bandpass characteristic suitable for daylight filtering or color selectivity. Primary application is short range optical underwater communication, but results are generally applicable. Full article

(This article belongs to the Special Issue Visible Light Communication, Networking, and Sensing)

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