Experimental Demonstration of RGB LED-Based Optical Camera Communications

Data rate and communication distance are two important criteria for measuring the performance of optical camera communication (OCC) systems. Intensive researches have been made to find possible solutions to improve these two performance indicators. However, most existing literature either provides solutions which closely related to the experimental parameters of their own designed OCC systems or provides models which are suitable for visible light communication (VLC) and cannot be directly used in OCC. Motivated by this, we propose a simplified system model for OCC in this paper. By jointly applying Lambertian model for the transmitter light-emitting diode (LED), channel direct current (DC) gain for free space channel, and mathematical descriptions for the imaging process of the camera receiver, the proposed model provides the relationship between the optical transmission power and the final pixel values on the image sensor. We specifically explore the parameters of the transmission distance and the exposure time based on the proposed model. Simulation results qualitatively and quantitatively explore the influences of these two parameters on the final pixel values. Our proposed model can provide guidance for the design of a generalized OCC system as well as the selection of demodulating threshold, thus it can help to realize a highperformance OCC system.

As mobile payments become increasingly popular, the security of the transaction process should be taken more seriously. Many mobile phones are equipped with complementary metal-oxide-semiconductor (CMOS) cameras, which can be used as visible light communication (VLC) receivers. An optical camera communication (OCC) system is a special VLC system that uses an optical camera as a receiver. OCC offers acceptable security, but challenges remain. In this paper, we propose an OCC system that uses an optical camera with a rolling shutter as a receiver and a light-emitting diode (LED) panel light as a transmitter. The feature of an LED panel light serving as a surface light source reduces the possibility of overexposure and avoids the blooming effect of the camera. The rolling shutter effect of the CMOS camera is used to increase the data rate, which is numerically much higher than the frame rate. Finally, the results of a symbol error rate (SER) test show that the VLC system exhibits error-free performance. The data rate is approximately 4.2kb/s, while the net data rate is approximately 2.46kb/s due to the redundancy of the 3-9 code bar code and the redundant cycle. This data rate is sufficient for mobile payments, which require only 60bits of data at a time.

Nowadays, underwater activities are becoming more and more important. As the number of underwater sensing devices grows rapidly, the amount of bandwidth needed also increases very quickly. Apart from underwater communication, direct communication across the water–air interface is also highly desirable. Air-to-water wireless transmission is crucial for sending control information or instructions from unmanned aerial vehicles (UAVs) or ground stations above the sea surface to autonomous underwater vehicles (AUVs). On the other hand, water-to-air wireless transmission is also required to transmit real-time information from AUVs or underwater sensor nodes to UAVs above the water surface. Previously, we successfully demonstrated a water-to-air optical camera-based OWC system, which is also known as optical camera communication (OCC). However, the reverse transmission (i.e., air-to-water) using OCC has not been analyzed. It is worth noting that in the water-to-air OCC system, since the camera is located in the air, the image of the light source is magnified due to diffraction. Hence, the pixel-per-symbol (PPS) decoding of the OCC pattern is easier. In the proposed air-to-water OCC system reported here, since the camera is located in the water, the image of the light source in the air will be diminished in size due to diffraction. Hence, the PPS decoding of the OCC pattern becomes more difficult. In this work, we propose and experimentally demonstrate a wide field-of-view (FOV) air-to-water OCC system using CUDA Deep-Neural-Network Long-Short-Term-Memory (CuDNNLSTM). Due to water turbulence and air turbulence affecting the AUV and UAV, a precise line-of-sight (LOS) between the AUV and the UAV is difficult to achieve. OCC can provide wide FOV without the need for precise optical alignment. Results revealed that the proposed air-to-water OCC system can support a transmission rate of 7.2 kbit/s through a still water surface, and 6.6 kbit/s through a wavy water surface; this satisfies the hard-decision forward error correction (HD-FEC) bit-error-rate (BER).

The addition of green light-emitting diodes (LEDs) to a combination of red and blue LEDs, which promote photosynthesis and growth in plants, is known to enhance plant growth in closed-type plant production systems. However, there is limited information on the effects of supplementary green light. This study aimed to determine the effect of red (R), green (G), and blue (B) LED ratios on the growth, photosynthetic, and antioxidant parameters in two lettuce (Lactuca sativa) cultivars, red leaf ‘Sunmang’ and green leaf ‘Grand Rapid TBR’. The seedlings were grown for 18 days and then cultivated in growth chambers equipped with LED lighting systems for 4 weeks. Combinations of six LED lighting sources (R:B = 9:1, 8:2, 7:3; R:G:B = 9:1:0, 8:1:1, 7:1:2) were manufactured to emit red (655 nm), blue (456 nm), or green (518 nm) lights under photosynthetic photon flux density of 173 ± 3 μmol·m-2·s-1. Red LEDs were found to improve growth characteristics such as fresh and dry weights of shoots and roots, and leaf area in combination with blue LEDs. The substitution of blue with green LEDs in the presence of a fixed proportion of red LEDs enhanced the growth of lettuce. In particular, the fresh weights of red leaf lettuce shoots under R8G1B1 were about 61% higher than those under R8B2. Furthermore, analysis of leaf morphology, transmittance, cell division rate, and leaf anatomy under treatments with green LEDs supported the enhanced growth of the two lettuce cultivars tested. Meanwhile, growth under blue LEDs led to the accumulation of antioxidant parameters in ‘Sunmang’. Thus, the results of this study suggest that the percentage of red, green, and blue LEDs is an important factor for the growth, development, and biosynthesis of secondary metabolites in plants and especially the supplemental irradiation of green LEDs based on the combination of red and blue LEDs can improve lettuce growth.

To enable a higher transmission rate in optical camera communication (OCC) systems, severe inter-symbol interference (ISI) occurs owing to the reduction of the number of pixel-row-per-bit (PPB). Therefore, those pixels representing data bit 0 or 1 may have same gray scale values, significantly deteriorating the bit decision when using the conventional thresholding scheme. In this Letter, a simple yet efficient scheme, referred to as nearest neighbor bit assisted decision (NNBAD) scheme, is proposed and experimentally demonstrated for signal decision in OCC systems. NNBAD leverages the nearest neighbor bit to jointly assist bit decision for pixels with severe ISI. Experimental results show that, for OCC systems with on-off keying (OOK) modulation, those pixels with severe ISI cannot be distinguished by the conventional thresholding scheme. Yet, the NNBAD scheme exhibits strong robustness against ISI, remarkably improving the bit error rate (BER) performance. The proposed scheme can achieve a throughput of 8.2 kbps with OOK modulation under an illuminance of 600 lx.

We propose a configuration of a wavelength division multiplexing (WDM)-visible light communication (VLC) system using orthogonal frequency division multiplexing (OFDM) modulation and an adaptive Nyquist windowing of the OFDM signal in the receiver. Based on this configuration, we demonstrate a 750-Mb/s WDM-VLC transmission based on RGB light-emitting diode (LED) with a distance of 70 cm. The measured bit error rate (BER) for all channels are under the pre-forward error correction limit of 3.8 \times 10-3. The BER performances of all the channels of the proposed WDM-VLC system show considerable improvement compared with those of the system without Nyquist windowing.

This paper presents a method for performing traffic light detection using computer vision. Reliable traffic light detection and classification is crucial for automated driving in urban environments. By using big data and artificial intelligence, a complex dataset belonging to an urban area in China is preprocessed to determine the level of vehicular congestion, and then different machine learning algorithms are applied to a dataset of traffic light images in order to validate them in the urban environment to be studied, this process is explained step by step. The models obtained in this work can be applied in optical camera communication (OCC) systems, and also in intelligent transportation systems (ITS), using tracking channels for visible light communication (VLC). The two optical channels, VLC and OCC, are simulated in terms of the quality of information received in order to apply the previously generated datasets. In this work, a traffic light feature dataset has been generated from images and two traffic light classification models present in images and video frames have been generated from their features, obtaining a maximum accuracy of 94.52 %.

In order to increase the data rate of the optical camera communication (OCC) system, the 8-composite-amplitude-shift-keying modulation (8CASK) OCC system is used in this work. However, if the static decision thresholds are employed to demodulate multi-level ASK signal, uneven illumination of LED lamps and LED light-emitting instability lead to the fluctuation of the gray range in the picture and degrade the bit-error-rate (BER) performance. In this work, we propose and demonstrate a demodulation scheme, using the uneven illumination compensation algorithm, the pixel matrix threshold overall update algorithm and the secondary decision algorithm, to mitigate the impact of illumination unevenness and LED light-emitting instability. The BER performance is evaluated and compared with other demodulation schemes. The experimental results demonstrate that the communication rate of our proposed scheme can reach 9kbit/s at a distance of 250 cm where the illumination is 135lux, and the BER is 8.01 × 10−5.

To clarify the response of net photosynthetic rate (Pn), stomatal conductance ( g S ), transpiration rate (Tr), and leaf intercellular CO 2 concentration (Ci) to irradiance on the adaxial and abaxial sides of mature and young strawberry leaves using blue, green, and red light-emitting diodes (LEDs), irradiation from a short distance was investigated using ‘Tochiotome’. Light–photosynthetic response curves of the adaxial side of mature leaves were not different among LED treatments. However, those of the adaxial side of young leaves irradiated with red LEDs were less than those of other LED treatments. Pn of the abaxial side of mature leaves was 42% to 71% of the abaxial side. In young leaves, Pn of the abaxial side was 17% to 68% of the adaxial side. Moreover, light–transpiration response curves were different with LED treatments. Ci and Tr under blue and green LEDs were greater than those under red LEDs. This indicates that blue and green lights affected the stomatal opening. In contrast, red LEDs decreased Ci more than other LED treatments. In addition, reactions of the adaxial side of young leaves under blue and red LEDs were seen not only in ‘Tochiotome’, but also in ‘Sachinoka’ and ‘Eran’, which indicates that the photosynthetic reactions of blue light and red light are common characteristics of the strawberry. Therefore, red LEDs promoted the photochemical reaction and activated the CO 2 fixation system. Based on the results of this study of short-distance lighting with LEDs in strawberry production, irradiance of the abaxial side of leaves by blue or green LEDs might improve more assimilates in young leaves compared with red LEDs to increase strawberry yield.

LEDs are quickly becoming the standard lighting solution. Their ability to be turned on and off fast determined scientists to create novel communication methods, such as Visible Light Communication (VLC), in which the transmitter is commonly represented by LEDs and the receiver is represented by photodetectors. The receiver in Optical Camera Communications (OCC) is an image sensor. Designing a communication system that can use low frame rate cameras (30 frames per second) while preventing light flickering at the transmitter is a specific problem in OCC. This work proposes and experimentally confirms an improvement of an OCC solution that does not cause flickering at the transmitter and does not require synchronization between the transmitter and the receiver, while improving the bit rate.

This paper experimentally investigates the performance of visible light based optical camera communications (OCC) link with motion detection (MD) for the optical Internet of things applications. This efficient MD can be considered another functionality of OCC in addition to traditional features of vision, illumination data communications and sensing. The experiments were conducted in an indoor static downlink OCC system employing a mobile phone front camera is employed as the receiver and an $8\times 8$ red, green, and blue (RGB) light-emitting diode array as the transmitter. The motion is detected by observing the user's finger movement in the form of centroid through the OCC link via a camera. The experiment results demonstrate that, the proposed scheme can detect all considered motions accurately with acceptable bit error rate (BER) performances at a transmission distance of up to 80 cm. We show a BER of $1.7\times 10^{-3}$ below the forward error correction limit of $3.8\times 10^{-3}$ over a transmission distance of up to 1 m. The proposed neuron based MD combined together with OCC can be considered an efficient system, which provides illumination, communications, and motion detection in a convenient smart home environment.

Visible light communication (VLC) technology employing light-emitting diodes (LEDs) as light sources has the advantages of using the license-free spectrum, being power and cost-efficient and having high security. However, common LED devices have the limitations of narrow bandwidths, nonlinear optical and frequency responses over different bias current levels, which cause inter-symbol interference and signal distortion, especially under high order modulation schemes with large current swings. In view of this, a compact PAM-4 VLC transceiver system employing a white LED as the light source with pre- and post-equalization is proposed. The white LED consists of a red, a green and a blue LED unit (RGB LED). Controlled by 3-bit thermometer codes, three separate drivers with feed-forward equalizers (FFEs) drive the RGB LED units to produce the PAM-4 optical signal. The driving currents from the three drivers with FFEs can be calibrated using digital and analog tunings to eliminate the differences in optical and frequency responses of the RGB LED units. A cascaded continuous-time linear equalizer (CTLE) is used at the receiver side as post-equalization to compensate for the narrow bandwidth of LED units. Based on experimental results, the proposed RGB PAM-4 VLC system can improve the highest achievable data rate by 1.67 times from 28 to 75 Mb/s using the pre- and post-equalization scheme.

Spirulina cultivated under different light emitting diodes: Enhanced cell growth and phycocyanin production

Radio frequency (RF) waveforms are widely used in wireless technologies, such as mobile system, smart factory, and smart home systems. Due to its simplicity of installation, wireless communication is better than wire communication. However, the use of high frequencies for data transmission can be harmful to human health. To replace RF waveform for communication system, Optical Wireless Communication (OWC), which deploys visible light waveform for communication, was researched widely by researchers around the world. Visible Light Communication (VLC), Light Fidelity (LiFi), and Optical Camera Communication (OCC) are the three candidates for replacing RF system. In this research, we present an multiple-input multiple-output (MIMO) modulation system based on on-off keying (OOK) modulation in the time domain and a light-emitting diode (LED) array. By adjusting the exposure time, focal length, forward error correction, and Deep learning for object detection, it is still possible to implement this technique with 10 links in various locations at a distance of 20 m with a velocity of 2 m/s.

Real-time implementation of OFDM modulation for an OCC system: UNet-based equalizer for signal denoising and BER optimization