Optical Camera Communication Research Articles

Analytical and simulation tools for optical camera communications

The use of LED-to-camera communication opens the door to a wide range of use cases and applications, with diverse requirements in terms of quality of service. However, while analytical models and simulation tools exist for all the major radio communication technologies, the only way of currently evaluating the performance of a network mechanism over LED-to-camera is to implement and test it. Our work aims to fill this gap by proposing a Markov–modulated Bernoulli process to model the wireless channel in LED-to-camera communications, which is shown to closely match experimental results. Based on this model, we develop and validate CamComSim, the first network simulator for LED-to-camera communications.

Increasing symbol rate by ensemble averaging with dual camera in rolling-shutter optical camera communication

Increasing symbol rate by ensemble averaging with dual camera in rolling-shutter optical camera communication

Design and Implementation of the MIMO-COOK Scheme Using an Image Sensor for Long-Range Communication.

Radio-frequency technologies are widely applied in many fields such as mobile systems, healthcare systems, television and radio broadcasting, and satellite communications. However, one major problem in wireless communication based on radio frequencies is its impact on human health. High frequencies adversely impact human health more than low frequencies if the signal power transgresses the permissible threshold. Therefore, researchers are investigating the use of visible light waves (instead of the radio-frequency band) for data transmission in three major areas: visible light communication, light fidelity, and optical camera communication. In this paper, we propose a scheme that upgrades the camera on–off keying (COOK) scheme by using it with the multiple-input multiple-output (MIMO) scheme; COOK has been recommended by the IEEE 802.15.7-2018 standard. By applying technologies, such as matched filter, region of interest, and MIMO, our proposed scheme promises to improve the performance of the conventional scheme by improving the data rate, communication distance, and bit error rate. By controlling the exposure time, the focal length in a single camera and using channel coding, our proposed scheme can achieve the communication distance of up to 20 m, with a low error rate.

High-accuracy scheme based on a look-up table for motion detection in an optical camera communication system.

In this paper, a high-accuracy motion detection (MD) scheme based on a look-up table (LUT) is proposed and experimentally demonstrated in an optical camera communication (OCC) system. The LUT consists of predefined motions and strings that represent the predefined motions. The predefined motions include straight lines, polylines, circles, and number shapes. At the transmitter, the data with on-off keying (OOK) format is modulated on an 8×8 light-emitting diode (LED) array. The motion is generated by the user's finger in the free space link. At the receiver, the motion and data are captured by the mobile phone front camera. The captured motion is expressed as a string indicating directions of motion, then it is matched as a predefined motion in LUT by calculating the Levenshtein distance (LD) and modified Jaccard coefficient (MJC). Using the proposed scheme, four types of motions are recognized accurately and data transmission is achieved simultaneously. Also, 1760 motion samples from 4 users are investigated over the free space transmission. The experimental results show that the accuracy of the proposed MD scheme can reach 98% at the distance without the loss of finger centroids. In addition, as the transmitter is not blocked, the bit error rate (BER) is below 1e-6 at the distance of 80cm.

Some practical constraints and solutions for optical camera communication.

Mobile wireless communication heavily relies on the radio frequency to convey message and data. However, its limited spectrum can hardly meet the demands for the future high data rate applications. Optical wireless communication, in particular visible light communication, opens up vast optical spectrum for communication, and meanwhile can retrofit the light sources as the communication transmitters in the existing working or living environments. In conjunction with the ubiquitous cameras in hand-held consumer electronics such as smartphones and pads, optical camera communication (OCC) further takes advantages of image sensors as the communication receivers and realizes low-cost communication systems. This article first provides an overview of OCC systems. It then addresses some practical constraints, ranging from sensor low frame rate and instability, rolling shutter readout, to visual qualities of displayed images and videos, and link blockage between the transmitter and receiver. Accordingly, it introduces existing and new solutions to deal with those constraints by data modulation, newly developed camera structures, post-processing of sensed signals and non-line of sight OCC as a new form. In particular, indirect paths by either the indoor surface reflection or the outdoor atmospheric scattering are explored for link connectivity under blockage. Finally, some future research directions are suggested.This article is part of the theme issue ‘Optical wireless communication’.

400 m rolling-shutter-based optical camera communications link

In this Letter, we develop a novel technique, to the best of our knowledge, to increase the link span ($ {L_s} $Ls) of a rolling shutter (RS)-based optical camera communications (OCC) system by reducing the spatial bandwidth of the camera in the out-of-focus regions. We demonstrate a 400 m line-of-sight RS-based OCC link, which is to date the longest $ {L_s} $Ls reported in these systems, and develop a detection method to extract the information out of the video frames, successfully. The proposed system relaxes the condition of a large surface area for the transmitter light source. Consequently, we show that at 400 m $ {L_s} $Ls and exposure times of 100-80 µs, a data rate of 450 bps is achieved successfully.

Secured Key Distribution by Concatenating Optical Communications and Inter-Device Hand-Held Video Transmission

Key distribution is a growing concern for symmetric cryptography. Most of the current key-distribution mechanisms assume the use of the Internet and WAN networks, which are exposed to security hazards. To overcome them, the use of comprehensive and robust cryptographic mechanisms such as Diffie–Hellman (DH) and RSA (Rivest–Shamir–Adleman) algorithms are proposed. These solutions are limited. DH and RSA have been under threat since the introduction of quantum computing. Hence, new ideas are required. This paper introduces a new security approach for a safe key transmission using undetected high-speed optical camera communication (OCC), which is based on the rolling shutter effect of modern smart cameras. The key transfer is done by blinking light-emitting diode (LED) lights in a specific sequence and frequency, following an encoding pattern. The receiver decodes the received blinks to a bit string using a corresponding image processing application. This optical media ensures secure transfer without the ability to quote it. We demonstrate in an experiment the feasibility of using basic wireless optical communication for key transmission, eliminating the need for a permanent, long, and costly setup. It is mobile, available everywhere anytime, and requires only simple connections to operate. The results show that this method is feasible, robust, efficient, and implementable.

Complementary Color Barcode-Based Optical Camera Communications

Electronic displays and cameras can provide an intuitive, simple communications interface without dependence on additional wireless interfaces or the Internet infrastructure. In this paper, we design a complementary color barcode-based optical camera communication (CCB-OCC) system to provide an easy-to-use communication capability from an electronic display-to-camera (D2C) link. The proposed method encodes information into specially designed color barcodes and transmits it in a format perceptually invisible to humans but detectable by camera-equipped devices. In addition, we propose a new transmission packet design that contains pilot symbols to synchronize symbol packets and estimate the D2C channel link for calibrating captured images caused by irregular differences between the sending color and the receiving color in the D2C link. Experimental results verify the feasibility of the CCB-OCC scheme for short-range communications to offer additional information which shows a new possibility in designing a D2C communication system with robust to environmental change, easy-to-use, and simple implementation.

Design and analysis of an optical camera communication system for underwater applications

The growing interest in underwater explorations has stimulated considerable interest in advancing the enabling technologies of underwater wireless communication (UWC) systems. The study presents the design and implementation techniques of a short-range unidirectional UWC system which uses optical camera communication (OCC) principles. OCC systems have light emitting diodes at the transmitter, with the receiver being a camera. Overall system design considerations, synchronisation and frame selection, and a novel spatial position-based image processing algorithm to decode data from frames are discussed. Also, the optimisation techniques used in the image processing algorithm are also elaborated. Importance of few of key features of an OCC system, namely camera quality, transmission distance and the threshold value used for image binarisation are demonstrated through numerical results using simulations via synthetically generated images. Further, the bit error rate (BER) performance of the system is evaluated using the experimental proof of concept setup in clear water, muddy water and under turbulence conditions. Overall BER performance in the order of 10 -3 within the communication distance of 1 m is observed, and it shows that the proposed system design and algorithms can be used to realise an UWC link for short-range applications successfully.

Experimentally Derived Feasibility of Optical Camera Communications under Turbulence and Fog Conditions.

Optical camera communications (OCC) research field has grown recently, aided by ubiquitous digital cameras; however, atmospheric conditions can restrict their feasibility in outdoor scenarios. In this work, we studied an experimental OCC system under environmental phenomena emulated in a laboratory chamber. We found that the heat-induced turbulence does not affect our system significantly, while the attenuation caused by fog does decrease the signal quality. For this reason, a novel strategy is proposed, using the camera’s built-in amplifier to overcome the optical power loss and to decrease the quantization noise induced by the analog-digital converter of the camera. The signal quality has been evaluated using the Pearson’s correlation coefficient with respect to a reference template signal, along with the signal-to-noise ratio that has been empirically evaluated. The amplification mechanism introduced allows our system to receive the OCC signal under heavy fog by gradually increasing the camera gain up to 16 dB, for meteorological visibility values down to 10 m, with a correlation coefficient of 0.9 with respect to clear conditions.

The Necessity of LED to Ambient Light Ratio Optimization for Vehicular Optical Camera Communication.

In vehicular optical camera communication (VOCC) systems, LED panels are used to transmit visible light signals which are captured by cameras. The logic bits 1 and 0 are represented by the On and Off status of the LEDs in the panel. The bit error rate (BER) of the system is directly proportional to the distinguishability of the On and Off LEDs in the received LED panel images. The signal quality is commonly believed in telecommunications to improve with a higher transmitted power. Therefore, one might expect to get a lower BER in VOCC systems by simply using more powerful LED lights. However, this is not the case with VOCC systems. This paper shows that the LED distinguishability is simultaneously determined by two factors: The LED extinction ratio and LED interference. The former needs to be kept high and the latter kept low for better LED distinguishability. The problem is that both the extinction ratio and interference increase with the ratio of LED light to ambient light (L2A). Consequently, an optimal L2A ratio exists to achieve the optimal balance between the positive impact of the extinction ratio and the negative impact of the interference. This can bring about the lowest BER without changing the system’s data rate. In addition, this paper shows that the optimal L2A ratio varies according to the interval between the LEDs in a panel. We analyze the effect of the L2A ratio and LED interval on LED distinguishability. We then formulate a constrained optimization problem to find the optimal L2A ratios corresponding to different LED intervals. The simulation results verify the necessity of LED to ambient light ratio optimization as it can bring about the lowest BER without scarifying other aspects of the VOCC system.

The Optical Bar Code Detection Method Based on Optical Camera Communication Using Discrete Fourier Transform

Optical camera communication (OCC) traditionally uses the bright and dark stripes of rolling shutter pattern captured by the complementary metal-oxide-semiconductor (CMOS) image-sensor to realize communication. For the reason that these stripes are distributed on plane space of the image, the conventional OCC is based on image space-domain. In this paper, different from the convention, we first introduce a Modulation and Image Frequency-Domain Recognition (M-IFDR) method of OCC. In this approach, LEDs are modulated to assign different frequency characteristics instead of transmitting data. Taking discrete Fourier transform (DFT) of the rolling shutter pattern to obtain the spectrum image, we can recognize the LED according to the characteristics of the spectrum image based on image frequency-domain. The experiment results show that the proposed M-IFDR method has good performance, with at least 426 recognizable LEDs and the recognition distance reaching 3m. Therefore, the proposed M-IFDR method can be considered as one of the effective methods of OCC.

Data Rate Enhancement in Optical Camera Communications Using an Artificial Neural Network Equaliser

In optical camera communication (OCC) systems leverage on the use of commercial off-the-shelf image sensors to perceive the spatial and temporal variation of light intensity to enable data transmission. However, the transmission data rate is mainly limited by the exposure time and the frame rate of the camera. In addition, the camera's sampling will introduce intersymbol interference (ISI), which will degrade the system performance. In this paper, an artificial neural network (ANN)-based equaliser with the adaptive algorithm is employed for the first time in the field of OCC to mitigate ISI and therefore increase the data rate. Unlike other communication systems, training of the ANN network in OCC is done only once in a lifetime for a range of different exposure time and the network can be stored with a look-up table. The proposed system is theoretically investigated and experimentally evaluated. The results record the highest bit rate for OCC using a single LED source and the Manchester line code (MLC) non-return to zero (NRZ) encoded signal. It also demonstrates 2 to 9 times improved bandwidth depending on the exposure times where the system's bit error rate is below the forward error correction limit.

Optical Wireless Hybrid Networks: Trends, Opportunities, Challenges, and Research Directions

Optical wireless communication (OWC) is an excellent complementary solution to its radio frequency (RF) counterpart. OWC technologies have been demonstrated to be able to support high traffic generated by massive connectivity of the Internet of Things (IoT) and upcoming 5th generation (5G) wireless communication systems. As the characteristics of OWC and RF are complementary, a combined application is regarded as a promising approach to support 5G and beyond communication systems. Hybrid RF/optical and optical/optical wireless systems offer an excellent solution for recovering the limitations of individual systems as well as for providing positive features of each of the technologies. An RF/optical wireless hybrid system consists both RF and optical-based wireless technologies, whereas an optical/optical wireless hybrid system consists two or more types of OWC technologies. The co-deployment of wireless systems can improve system performance in terms of throughput, reliability, and energy efficiency of individual networks. This study surveys the state of the art and key research directions regarding optical wireless hybrid networks, being the first extensive survey dedicated to this topic. We provide a technology overview of existing literature on optical wireless hybrid networks, such as RF/optical and optical/optical systems. We consider the RF-based macrocell, small cell, wireless fidelity, and Bluetooth, as well as optical-based visible light communication, light fidelity, optical camera communication, and free-space optical communication technologies for different combinations of hybrid systems. Moreover, we consider underwater acoustic communication for hybrid acoustic/optical systems. The opportunities brought by hybrid systems are presented in detail. We outline important challenges that need to be addressed for successful deployment of optical wireless hybrid network systems for 5G and IoT paradigms.

Deep Learning for Optical Vehicular Communication

In this paper, we consider the current status and technical issues involved in the use of optical camera communication (OCC)/visible light communication (VLC) technologies in vehicular communication systems. Hybrid spatial phase-shift keying was introduced in IEEE 802.15.7-2018 as the standard hybrid modulation scheme for vehicular OCC/VLC systems. We herein propose a functional communication system architecture for vehicular systems based on this hybrid waveform, and we also present state-of-the-art research work on an artificial intelligence (AI)-based vehicular OCC system. Every AI module within the proposed system architecture is discussed in detail. Finally, our experimental procedures and results are analyzed to evaluate the performance of the proposed system over a complex channel model in a vehicular environment. We effectively employed the popular You Only Look Once version 2 object detection algorithm for real-time region-of-interest tracking in city driving (at a vehicular velocity of around 30 km/h and highway night driving (at a vehicular velocity of > 60 km/h) scenarios. Moreover, our novel neural-network-based decoder and AI-based error correction proved effective in improving the data decoding accuracy, resulting in a best-case reduction of 2.2 and 9.0 dB, respectively, in the signal-to-noise ratio needed to achieve the desired bit error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> in a vehicular OCC/VLC system.

Design and Implementation of an OCC-Based Real-Time Heart Rate and Pulse-Oxygen Saturation Monitoring System

In this technical paper, we design and implement an optical camera communication system for real-time remote monitoring of patient's heart rate (HR) and oxygen saturation (SpO2) data. The data is collected and transmitted by a patch circuit which comprises a MAX30102 sensor and an RGB LED array. A close circuit television camera is used not only for surveillance but also for receiving the data simultaneously. The LED is modulated using color intensities, and the data can be retrieved regardless of any orientations of the LED array. We propose a neural network (NN) to detect each LED separately, and we implement another NN-based on feature extraction to precisely recognize the colors. The data are also encoded with a unique key, which increases the security of the communication mechanism. System performance of 4.68 kbps with low bit-error-rate (BER) and 1.172 kbps with moderate BER is achieved at 1 and 3 m, respectively.

광학 카메라 통신 시스템의 현실적 시뮬레이션 프레임워크

광학 카메라 통신 (OCC)에서 LED 어레이는 카메라가 수신 할 가시광 신호를 전송하는 데 사용된다. OCC 시스템의 성능은 LED 휘도, 배경 조도, 카메라 노출 설정, LED 및 카메라 이동 속도 등 통신 채널의 많은 매개 변수에 따라 달라진다. 이러한 많은 매개 변수의 영향을 체계적으로 조사하려면 OCC 시스템에 대한 시뮬레이션이 필수적이다. 본 연구에서는 광도 측정, 카메라 형상, 디지털 이미지 획득 및 광학 이미지 통신을 포함한 여러 분야의 기본적인 원리에 대해 서술하고, OCC 시스템을 분석하기 위한 요구 사항을 살펴본다. 이러한 원리와 요구사항에 따라 OCC 시스템의 현실적인 시뮬레이션을 위한 프레임워크를 제안한다.

Simultaneous Data Transmission Using Multilevel LED in Hybrid OCC/LiFi System: Concept and Demonstration

In this letter, a hybrid-encoding scheme is developed for an integrated optical camera communication (OCC)/light-fidelity (LiFi) system. A single multilevel light-emitting diode (LED) is used for transmitting both OCC and LiFi data. Two data streams are transmitted, where each stream is intended for LiFi and OCC. The first stream is transmitted at a very high frequency using the LED. The LED flickers in two different power levels creating consecutive sequences. A smartphone camera receives the sequences as binary successions, wherein the second data stream is modulated. The modulation is referred to as intensity-shift keying. A testbed prototype is implemented to demonstrate the proof-of-concept, which is also used to show the bit-error-rate performance of the proposed scheme.

Experimental DCO-OFDM Optical Camera Communication Systems With a Commercial Smartphone Camera

Modern handheld mobile devices are equipped with a complementary metal-oxide-semiconductor (CMOS) image sensor. These image sensors are capable of perceiving intensity changes in optically modulated signals, driving the rapid development of optical camera communication (OCC). In this study, direct-current offset orthogonal frequency division multiplexing (DCO-OFDM) was developed for a rolling shutter OCC system in order to improve the data transmission rates of OCC systems. Two DCO-OFDM OCC signal detection algorithms, namely the parabolic column vector selection (P-CVS) algorithm and the decomposition of extremely low frequency component (D-ELFC) algorithm, were proposed, along with a frequency-domain downsampling scheme, to eliminate the influence from both the blooming effect and shot noise. The experimental results, obtained after using a self-built DCO-OFDM OCC testbed with a general commercial smartphone camera, demonstrated that the D-ELFC algorithm outperformed in the bit error rate (BER) in comparison to the P-CVS algorithm and achieved a data transmission rate >22 kbps under the conditions of the BER being below the 20% forward error correction (FEC) limit and the illuminance being higher than 510 lux.

Design and Implementation of a Monitoring System using Optical Camera Communication for a Smart Factory

Wireless technologies that are based on radio frequencies are currently widely used, with numerous applications around the world. However, they pose some disadvantages to human health. High frequencies can have potentially harmful effects on children, hospital patients, and even healthy people if the signal power exceeds the permitted standard. Conversely, the use of visible light for data transmission is a trend that presents new options, including optical wireless communication, optical camera communication, and visible light communication. This paper proposes a modulation scheme based on on-off keying in the time domain, which is applied to a monitoring system using optical camera communication. This scheme has various compatible supports for the global-shutter camera and rolling-shutter camera, which are popular commercially available cameras. Furthermore, this scheme facilitates a low-cost monitoring system. By using small light-emitting diodes (LEDs) and controlling the exposure time in a single camera, the camera, as a receiver, can simultaneously detect signals from up to 10 sensor devices in different positions at a maximum distance of up to 50 m, with a low error rate.