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Pilot Experiments of Side-Emitting Fiber-Based Optical Camera Communication for Wearable Applications
... OCC links can be implemented with different transmitters, such as single or multiple Light Emitting Diodes (LEDs), screens or side-emitting optical fibers [2], while the receiver is either a rolling-shutter or global-shutter camera, as illustrated in Fig. 1. Rolling shutter image sensors expose and read out pixels sequentially (typically line by line), whereas global shutter image sensors expose all pixels at the same time [3]. ...
... In the field of OCC, few works have been done considering wearables as transmitters. In our previous research, we showcased a wearable LED array [21] and a fiber attached on T-shirt [22] as distributed transmitters. Recently, there has been notable development in various medical applications that focus on using wearable sensors to measure individuals' health conditions. ...
This paper presents an experimental evaluation of a wearable light-emitting diode (LED) transmitter in an optical camera communications (OCC) system. The evaluation is conducted under conditions of controlled user movement during indoor physical exercise, encompassing both mild and intense exercise scenarios. We introduce an image processing algorithm designed to identify a template signal transmitted by the LED and detected within the image. To enhance this process, we utilize the dynamics of controlled exercise-induced motion to limit the tracking process to a smaller region within the image. We demonstrate the feasibility of detecting the transmitting source within the frames, and thus limit the tracking process to a smaller region within the image, achieving an reduction of 87.3% for mild exercise and 79.0% for intense exercise.
We present a design approach for a long-distance optical camera communication (OCC) system using side-emitting fibers as distributed transmitters. We demonstrate our approach feasibility by increasing the transmission distance by two orders up to 40 m compared to previous works. Furthermore, we explore the effect of the light-emitting diode (LED) modulation frequency and rolling shutter camera exposure time on inter-symbol interference and its effective mitigation. Our proposed OCC-fiber link meets the forward-error-correction (FEC) limit of 3.8 · 10⁻³ of bit error rate (BER) for up to 35 m (with BER= 3.35 · 10⁻³) and 40 m (with BER=1.13 · 10⁻³) using 2-mm and 3-mm diameter side-emitting fibers, respectively. Our results at on-off keying modulation frequencies of 3.54 kHz and 5.28 kHz pave the way to moderate-distance outdoor and long-distance indoor highly-reliable applications in the Internet of Things and OCC using side-emitting fiber-based distributed transmitters.
The power coupling between two light diffusing multimodal optical fibers of equal and finite lengths that are parallel oriented, and which are coupled through scattering processes, is investigated both theoretically and experimentally. In particular, a simple analytical model of the inherent coupling coefficient, derived according to a perturbation approach in a weak-coupling regime, is developed. The modelling results have been compared with the measurements performed, as a function of fiber distance and coupling length at three different wavelengths, and a close agreement is proved. The obtained results provide better understanding of the power coupling mechanism and of the inherent functional dependence on the main structural parameters of the two-fiber configuration.
Digital and information technologies are heavily pervading several aspects of human activities, improving our life quality. Health systems are undergoing a real technological revolution, radically changing how medical services are provided, thanks to the wide employment of the Internet of Things (IoT) platforms supporting advanced monitoring services and intelligent inferring systems. This paper reports, at first, a comprehensive overview of innovative sensing systems for monitoring biophysical and psychophysical parameters, all suitable for integration with wearable or portable accessories. Wearable devices represent a headstone on which the IoT-based healthcare platforms are based, providing capillary and real-time monitoring of patient’s conditions. Besides, a survey of modern architectures and supported services by IoT platforms for health monitoring is presented, providing useful insights for developing future healthcare systems. All considered architectures employ wearable devices to gather patient parameters and share them with a cloud platform where they are processed to provide real-time feedback. The reported discussion highlights the structural differences between the discussed frameworks, from the point of view of network configuration, data management strategy, feedback modality, etc.
In rolling shutter-based optical camera communication (OCC), the camera’s exposure time limits the achievable reception bandwidth. In long-exposure settings, the image sensor pixels average the incident received power, producing inter-symbol interference (ISI), which is perceived in the images as a spatial mixture of the symbol bands. Hence, the shortest possible exposure configuration should be selected to alleviate ISI. However, in these conditions, the camera produces dark images with impracticable light conditions for human or machine-supervised applications. In this paper, a novel convolutional autoencoder-based equalizer is proposed to alleviate exposure-related ISI and noise. Furthermore, unlike other systems that use artificial neural networks for equalization and decoding, the training procedure is conducted offline using synthetic images for which no prior information about the deployment scenario is used. Hence the training can be performed for a wide range of cameras and signal-to-noise ratio (SNR) conditions, using a vast number of samples, improving the network fitting and the system decoding robustness. The results obtained in the experimental validation record the highest ISI mitigation potential for Manchester encoded on-off keying signals. The system can mitigate the ISI produced by exposure time windows that are up to seven times longer than the transmission symbol duration, with bit error rates (BER) lower than 10⁻⁵ under optimal SNR conditions. Consequently, the reception bandwidth improves up to 14 times compared to non-equalized systems. In addition, under harsh SNRs conditions, the system achieves BERs below the forward error correction limit for 1dB and 5 dB while operating with exposure times that are 2 and 4 times greater than the symbol time, respectively.
In this Letter, we propose and demonstrate a novel wireless communications link using an illuminating optical fiber as a transmitter (Tx) in optical camera communications. We demonstrate an indoor proof-of-concept system using an illuminating plastic optical fiber coupled with a light-emitting diode and a commercial camera as the Tx and the receiver, respectively. For the first time, to the best of our knowledge, we experimentally demonstrate flicker-free wireless transmission within the off-axis camera rotation angle range of 0–45° and the modulation frequencies of 300 and 500 Hz. We also show that a reception success rate of 100% is achieved for the camera exposure and gain of 200 µs and 25 dB, respectively.
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 (SpO
2
) 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.
Radially light-emitting optical fibers are of increasing interest for applications in medicine, visible aesthetics, and environmental remediation. Optical fibers contain a light guiding core coated by protective polymer layers (cladding and coating), which assure both the strength and flexibility of the optical fiber. This paper examines the feasibility of scattering light radially from fibers by loading the fiber cladding with particle scattering centers during the optical fiber fabrication process. This work uses an in-line full-scale scalable facility to coat the fibers and control the polymer cladding and silica sphere. Loadings up to 2.0 wt. % of 500 nm silica particles on the cladding of the optical fiber led to an average of 80 times higher scattering for visible light and up to 30 times higher in the UVA wavelength range compared against cladding without particle modifications. This study illustrated the feasibility of fabricating broadband light scattering optical fibers for use with modified polymeric cladding.
Research on electronic healthcare (eHealth) systems has increased dramatically in recent years. eHealth represents a significant example of the application of the Internet of Things (IoT), characterized by its cost effectiveness, increased reliability, and minimal human eff ort in nursing assistance. The remote monitoring of patients through a wearable sensing network has outstanding potential in current healthcare systems. Such a network can continuously monitor the vital health conditions (such as heart rate variability, blood pressure, glucose level, and oxygen saturation) of patients with chronic diseases. Low-power radio-frequency (RF) technologies, especially Bluetooth low energy (BLE), play significant roles in modern healthcare. However, most of the RF spectrum is licensed and regulated, and the effect of RF on human health is of major concern. Moreover, the signal-to-noise-plus-interference ratio in high distance can be decreased to a considerable extent, possibly leading to the increase in bit-error rate. Optical camera communication (OCC), which uses a camera to receive data from a light-emitting diode (LED), can be utilized in eHealth to mitigate the limitations of RF. However, OCC also has several limitations, such as high signal-blockage probability. Therefore, in this study, a hybrid OCC/BLE system is proposed to ensure efficient, remote, and real-time transmission of a patient’s electrocardiogram (ECG) signal to a monitor. First, a patch circuit integrating an LED array and BLE transmitter chip is proposed. The patch collects the ECG data according to the health condition of the patient to minimize power consumption. Second, a network selection algorithm is developed for a new network access request generated in the patch circuit. Third, fuzzy logic is employed to select an appropriate camera for data reception. Fourth, a handover mechanism is suggested to ensure efficient network allocation considering the patient’s mobility. Finally, simulations are conducted to demonstrate the performance and reliability of the proposed system.
A wearable electroencephalogram (EEG) is a small mobile device used for long-term brain monitoring systems. Applications of these systems include fatigue monitoring, mental/emotional monitoring, and brain–computer interfaces. However, the usage of wireless wearable EEG systems is limited due to the risks posed by the wireless RF communication radiation in a long-term exposure to the human brain. A novel microwave radiation-free system was developed by integrating visible light communication technology into a wearable EEG device. In this work, we investigated the system’s performance in transmitting EEG data at different illuminance level and proposed an algorithm that functions at low illuminance levels for increased transmission distance. Using a 30 Hz smartphone camera, the proposed system was able to transmit 2.4 kbps of error-free EEG data up to 4 meter, which is equal to ~300 lux using an aspheric focus lens.
Fiber-based cylindrical light diffusers are often used in photodynamic therapy to illuminate a luminal organ, such as the esophagus. The diffusers are often made of plastic and suffer from short diffusion lengths and low transmission efficiencies over a broad spectrum. We have developed FibranceTM, a glass-based fiber optic cylindrical diffuser which can illuminate a fiber from 0.5 cm to 10 meters over a broad wavelength range. With these longer illumination lengths, a variety of other medical applications are possible beyond photodynamic therapy. We present a number of applications for Fibrance ranging from in situ controllable illumination for Photodynamic Therapy to light guided anatomy highlighting for minimally invasive surgery to mitigating hospital acquired infections and more.
Red, green, and blue (RGB) light-emitting diodes (LEDs) are widely used in everyday illumination, particularly where color-changing lighting is required. On the other hand, digital cameras with color filter arrays over image sensors have been also extensively integrated in smart devices. Therefore, optical camera communications (OCC) using RGB LEDs and color cameras is a promising candidate for cost-effective parallel visible light communications (VLC). In this paper, a single RGB LED-based OCC system utilizing a combination of undersampled phase-shift on–off keying (UPSOOK), wavelength-division multiplexing (WDM), and multiple-input–multiple-output (MIMO) techniques is designed, which offers higher space efficiency (3 bits/Hz/LED), long-distance, and nonflickering VLC data transmission. A proof-of-concept test bed is developed to assess the bit-error-rate performance of the proposed OCC system. The experimental results show that the proposed system using a single commercially available RGB LED and a standard 50-frame/s camera is able to achieve a data rate of 150 bits/s over a range of up to 60 m.
The following article presents the results of research connected with modeling lighting optical fibers of the "side-core" type. Distribution of the luminous flux was caused by its emission from the surface of the cladding, which is modified in such a way that its refractive index is larger than the refractive index of the material of the core. Luminous intensity and luminance of the model optical fiber curves were also determined; their suitability for lighting was also evaluated.
Spectroscopic experiments were conducted to characterise commercial side emission optical fibres regarding their emission spectra and the intensity of emitted radiation in the spectral range from UV-A to visible blue. For fibres with silica core and scattering particles embedded in the cladding, the emission spectra are determined by the material of the scattering particles. While Al2O3 particles allow emission of UV-A and visible blue light, ZnO filters most of the UV-A light up to wavelengths of 380 nm. The emitted intensity ideally decays exponentially along the fibre with a decay constant that is correlated to the particle concentration. The absolute values of the emitted intensity increase with increasing fibre radius. For fibres with PMMA core and surface perforation, relatively weak background emission of UV-A and blue light and additional local emission peaks due to the surface treatment were observed. The background emission can be explained by scattering due to the intrinsic non-uniformity of the PMMA core. The surface defects cause highly non-uniform and directional emission at a relatively high intensity. Compared to the silica core fibres, higher emission intensity in the UV-A and visible blue spectrum, albeit at a non-uniform distribution, was observed although the transmission along the fibre over longer distances is significantly lower for PMMA core fibres than for fibres with silica core.
This paper investigates using UV-C side-emitting optical fibers (SEOFs) to prevent growth of pathogenic bacteria (P. aeruginosa and E. coli) on nutrient-rich surfaces. Attaching a SEOF to a single 265 nm light emitting diode (LED) increases irradiation area by >1000x and provides continuous low-irradiance of UV-C light to a large surface area. A zone-of-inhibition protocol was developed to quantify bacterial growth prevention on an agar plate around one SEOF. The inhibition zone increased linearly with irradiance time until achieving a maximum inhibition zone of 2.5 to 3 cm, which received ∼ 4.3 mJ/cm² of 265 nm light in 2 hours. The surviving lawn edge bacterial colonies did not develop UV resistance after two generations of exposure. The agar plate remained bio-available after UV exposure, and bacteria could be grown on pre-illuminated area in the absence of UV-C light. Whereas we previously demonstrated SEOFs can inactivate planktonic bacteria, herein we show the ability of SEOFs to prevent bacteria growth on surfaces. This is the first step towards developing technologies with multiple SEOFs to inhibit biofilm growth on surfaces, which is a ubiquitous challenge across multiple applications from membrane surfaces to surfaces in pipes or water storage systems.
Recent literatures have demonstrated the feasibility and applicability of light-to-camera communications. They either use this new technology to realize specific applications, e.g., localization, by sending repetitive signal patterns, or consider non-line-of-sight scenarios. We however notice that line-of-sight light-to-camera communications has a great potential because it provides a natural way to enable visual association, i.e., visually associating the received information with the transmitter's identity. Such capability benefits broader applications, such as augmented reality, advertising, and driver assistance systems. Hence, this paper designs, implements, and evaluates RollingLight, a line-of-sight light-to-camera communication system that enables a light to talk to diverse off-the-shelf rolling shutter cameras. To boost the data rate and enhance reliability, RollingLight addresses the following practical challenges. First, its demodulation algorithm allows cameras with heterogeneous sampling rates to accurately decode high-order frequency modulation in real-time. Second, it incorporates a number of designs to resolve the issues caused by inherently unsynchronized light-to-camera channels. We have built a prototype of RollingLight with USRP-N200, and also implemented a real system with Arduino Mega 2560, both tested with a range of different camera receivers. We also implement a real iOS application to examine our real-time decoding capability. The experimental results show that, even to serve commodity cameras with a large variety of frame rates, RollingLight can still deliver a throughput of 11.32 bytes per second.
The main role of polymer optical fibers is to transmit light or optical signal to a specified spot. In the case of side emitting plastic optical fibers the light leaks out from their surface. This sidelight can be used for creation of optically active textile structures providing opportunities to highlight people and objects without the need for external exposure. Due to the transmission loss, the intensity of radiation emitted in any direction decays exponentially along the fiber axis with increasing distance from the light source. The main aim of this contribution is evaluation of side emitting plastic optical fibers light intensity in dependence on the distance from light source. The special device for measurement of surface and cross section light intensity in various distances from light source was developed. The dependence of surface and cross section light intensity on the distance from light source will be expressed by the exponential type model with attenuation factor as the rate parameter. The influence of the optical fiber type and diameter on the attenuation factor of surface and cross section light intensity will be quantified.
Recent progress in advanced FECs for optical communications is reviewed. A low-density parity-check code (LDPC) is a promising candidate for 100 Gb/s class systems, potentially yielding a net coding gain of 9dB or more.
The role of forward error correction has become of critical importance in fiber optic communications, as backbone networks increase in speed to 40 and 100 Gb/s, particularly as poor optical-signal-to-noise environments are encountered. Such environments become more commonplace in higher-speed environments, as more optical amplifiers are deployed in networks. Many generations of FEC have been implemented, including block codes and concatenated codes. Developers now have options to consider hard-decision and soft-decision codes. This article describes the advantages of each type in particular transmission environments.
The first experimental demonstration of a forward error correction (FEC) for 10-Gb/s optical communication systems based on a block turbo code (BTC) is reported. Key algorithms, e.g., extrinsic information, log-likelihood ratio, and soft decision reliability, are optimized to improve the correction capability. The optimum thresholds for a 3-bit soft decider are investigated analytically. A theoretical prediction is verified by experiment using a novel 3-bit soft decision large scale integrated circuit (LSI) and a BTC encoder/decoder evaluation circuit incorporating a 10-Gb/s return-to-zero on-off keying optical transceiver. A net coding gain of 10.1 dB was achieved with only 24.6% redundancy for an input bit error rate of 1.98×10-2. This is only 0.9 dB away from the Shannon limit for a code rate of 0.8 for a binary symmetric channel. Superior tolerance to error bursts given by the adoption of 64-depth interleaving is demonstrated. The ability of the proposed FEC system to achieve a receiver sensitivity of seven photons per information bit when combined with return-to-zero differential phase-shift keying modulation is demonstrated.
Experimental demonstration of RGB LED-based optical camera communications
- P Luo
- M Zhang
- Z Ghassemlooy
- H L Minh
- H.-M Tsai
- X Tang