Ing. Shivani Rajendra Teli, Ph.D.

Discussions on 6G point to one terabit-per-second as a reasonable goal for the peak bit rate of next-generation wireless systems. To meet this goal, the adoption of the sub-terahertz and terahertz bands (from 100 GHz to 10 THz), which can provide ample bandwidth for both communication and sensing systems, has been proposed by academia and industry. Fortunately, in the last decade, the terahertz technology gaphas been progressively closed through major advancements in electronic, photonic, and plasmonic technologies. In parallel, the propagation of terahertz signals has been studied through both physics-based and data-driven approaches, debunking some of the established myths. Nevertheless, there are several communication roadblocks that need to be overcome to unleash the spectrum above 100 GHz. In this chapter, a bottom-up approach will be followed to high-light unexpected findings, innovative solutions, and open challenges for terahertz communications and sensing systems on the ground, in the air, and in space.

Optical camera communication (OCC) is a rapidly growing research field within optical wireless communication (OWC) technologies that uses light-emitting diodes and cameras to provide wireless communication between devices in the visible light spectrum. Its growth has been propelled by the extensive availability of digital cameras in the consumer market in the form of smartphones, navigation cameras, surveillance systems, and others. Therefore, training new students with the necessary skills to apply and develop this technology is essential. This paper presents a practical teaching tool for the field of OCC aimed at students in undergraduate and postgraduate programs in electronics, telecommunications, and computer engineering. The tool is an interactive demonstrator of the OCC technology based on open-source hardware and software that is easy to reproduce and adjust. The workflow for presenting the tool covers the basic principles of OCC, including modulation techniques and image acquisition and processing techniques. As a core part of the class, students are given hands-on experience with OCC equipment to test the technology in a didactic way. This paper provides a resource for educators interested in adopting experimental learning into their courses on OWC.

This paper presents an asymmetric full-duplex solution based on visible light communications (VLC) for indoor wired and wireless hybrid signal transmission. The signal is distributed by a polymer optical fiber (POF) link and passively radiated. The proposed system includes two VLC links: a low-speed downlink and a high-speed uplink using an image sensor (IS) and photodiode detection (PD) based receivers. PD-based system communication performance is evaluated by means of error vector magnitude (EVM) for different modulation orders quadrature phase shift keying (QPSK), 16- and 64-quadrature amplitude modulation (QAM), while the IS-based system is characterized in terms of the success of reception (SoR). High-speed data transmission up to 160 Mbps with a 16-QAM modulation scheme and low-speed data transmission up to 500 bps with 98.6% of SoR using a non-return zero on–off keying (NRZ-OOK) scheme over a 1.5 m optical wireless link are demonstrated. Finally, simulations of the wireless channel are performed to evaluate the misalignment tolerance of the system; and, to estimate the uplink performance at longer distances.

In this paper, for the first time, to the best of our knowledge, we experimentally demonstrate the use of a curved organic light emitting diode (OLED) as a transmitter (Tx) in the non-line-of-sight (NLOS) optical camera communication (OCC) link for an indoor environment using a camera as a receiver. The proposed NLOS-OCC scheme is evaluated for the signal-to-noise ratio (SNR) and the reception success rates 𝑅rs under key photographic and communication parameters, including exposure times 𝑡exp and gain values 𝐺𝑣 , as well as the transmission frequency 𝑓𝑠 and the distance 𝐿 . The SNR analysis is performed using a binary classification procedure based on a Gaussian mixture model for the first time, to the best of our knowledge, for OLED-based NLOS-OCC links. We also derive and demonstrate that the effect of 𝐺𝑣 on the SNR with respect to 𝐿 is minimal based on the pixel illumination model. The initial analysis suggests that, for a wall reflector-based NLOS-OCC link that is 2 m long, the SNR and 𝑅rs increase by 1 dB and 4% (83–87%) for 𝑓𝑠 of 600 Hz, with an increase in 𝑡exp of 1000–1500 µs and 𝐺𝑣 of 25–45 dB.

This study aims to demonstrate that gamification applied to an environmental behavior can create a habit. For this, it is necessary to determine the connection between traveler satisfaction and the different kinds of stimulus (extrinsic, intrinsic and internalized extrinsic).

This paper outlines the concept of a multilevel bipolar on-off keying hybrid optical wireless communication (OWC) system using a single light-emitting diode (LED) as a transmitter as well as photodiode and camera-based receivers for versatile indoor Internet of Things applications. The proposed system offers simultaneous high- and low-speed transmission capabilities using visible light communication (VLC) and optical camera communication (OCC) links, respectively. By means of experimental implementation, we show that the hybrid OWC system employing a chip LED modulated with a multilevel signal improves the data rate Rb as well as the bit error rate and reception success rate of VLC and OCC links, respectively, by doubling the bandwidth. We show that the proposed scheme can provide an independent link performance, irrespective of significant differences between the operating Rb of VLC and OCC over a range of transmission spans L . We demonstrate that the throughput of the VLC link is improved by up to ∼ 100 Mb/s, which corresponds to twice the LED bandwidth, using direct modulation, different amplitude levels, and optimizing the received optical power of the hybrid OWC link. Error-free data transmission for the OCC link is achieved for all values of Rb , amplitude overlap of 0 and 0.3, and a range of L .

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.

This paper presents a non-line-of-sight optical camera communication link that uses a flexible organic light emitting diode and a camera as the transmitter and receiver, respectively. We conduct an experimental investigation of the proposed system in an indoor environment and evaluate its performance in terms of signal-to-noise (SNR) ratio and the reception success rates R_sr for a range of camera exposure times t_exp and the analog gain Gv . The initial results show an SNR increment of 0.5 dB at the transmission frequency fs of 100 Hz with t_exp of 1000–1250 μs, and the Gv of 25–35 dB. In addition, the R_sr of 98 and 87 % are measured at the fs of 100 and 600 Hz, respectively. Moreover, the SNR variance is negligible with changes in fs and t_exp .

Visible-light communication (VLC) is an emerging technology utilizing light-emitting diodes and photodetectors (PDs) and cameras [i.e., image sensors (ISs)] as the transmitter and receivers (Rx), respectively, for simultaneous data communications, illumination, localization, and sensing in the indoor optical Internet of Things. We propose a single-input–multiple-output (SIMO) hybrid VLC system using PD-based and IS-based Rxs for simultaneous high-speed and low-speed (i.e., Rb−High and Rb−Low ) data transmission. In addition, we propose amplitude overlapping AOL in the modulation format to increase Rb and reduce the attenuation due to the high-pass filter effect of the bias-T. We experimentally evaluate the performance of the proposed scheme considering the interlink impacts. Results show that at AOL of 0–0.2: 1) the measured bit error rate for the PD-based VLC is below the forward error correction limit of 3.8×10−3 for Rb−Low of 2.5 and 5 kb/s at Rb−High of 35 and 60 Mb/s, respectively, and 2) for the IS-based VLC link with the camera gain of 4 dB and Rb−High of up to 70 Mb/s, the reception success rates are >96 and 90% at Rb−Low of 2.5 and 5 kb/s, respectively.

In this paper, we propose the hybrid optical wireless communication system using a single light-emitting diode (LED) as a transmitter (Tx) as well as a photodiode and image sensor-based receivers (Rxs) for an indoor IoT environment. The proposed system utilizing a single LED offers simultaneously high- and low-speed transmission capabilities using visible light communication (VLC) and optical camera communication (OCC) links, respectively. The proposed scheme is intended to provide a versatile IoT environment by giving users the choice to switch between links based on device availability. By means of experimental implementation, we show that using a chip LED modulated with bipolar on-off keying modulation format and biased voltage levels improves signal transmission on both VLC and OCC links and thus the throughput of the system. Furthermore, we propose amplitude overlap AOL in the modulation format to improve the data throughput of VLC link. The results depict that error-free transmission is achieved for the VLC link at a data rate of up to 100 Mb/s which is double the 3-dB bandwidth of LED at AOL values of 0.3 and 0.5, and for the OCC link at a data rate of up to 2 kb/s at AOL values of 0 and 0.3.

We report, for the first time in the literature, an optical camera communications (OCC) link leveraging a near-infrared band at a wavelength of 850 nm that is visible to a standard camera and undetectable by the human eye. An experimental test-bed is developed and evaluated for the proposed system. The quality of the proposed communication link is measured in terms of the eye diagram and the bit error rate (BER) for different signal bandwidths. We demonstrated that, an acceptable BER (below the forward error correction limit) can be achieved with a data rate of ~2 kbps using a single near-infrared light-emitting diode, a commercially available camera with a 30-frame rate. This work paves the way to enable the use of the OCC links to many internet of things applications with low cost and no additional complexity.

In this paper, we present the experimental demonstration of a hybrid visible light communications (VLC) and optical camera communications (OCC) system based on a single centralized light emitting diode (LED) coupled with a plastic optical fiber (POF). Two data streams of SS Mb/s and 4 kb/s are point-to-point transmitted simultaneously and passively distributed over a 20 m POF and 3 m free space optics links (FSO), where high- and low-speed signals detection is provided by a photodiode (PD) and an optical camera-based receivers, respectively. The system aims to provide different services and/or applications to the end-user regardless of the employed devices with the lack of intermediate electro-optic conversions, network simplicity and low cost, as major advantages.

We present a novel concept of visible light communication (VLC) uplink by introducing a distributed receiver (Rx) formed by an illuminating optical fiber (IOF) connected to the photodetector. The major functionality of IOF-distributed Rx is to sense/detect the light signal along the fiber span at a range of modulation frequencies coming from an on-off keying modulated light-emitting diode (LED) transmitter. We show that our proposed proof-of-concept of distributed Rx performs below the forward error correction limit of 3.8⋅10−3 at frequencies up to 400kHz. We unveil the signal-to-noise ratio (SNR) limit of 19dB must be maintained for successful data reception. Higher data rates are predicted once the concept is optimized, especially in terms of SNR. The proposed IOF-based scheme can be considered as a solution to the current challenges of VLC uplink.

We have recently presented a novel concept of optical camera communications (OCC) based on illuminating optical fibers (IOF) as transmitter (Tx). In this paper, we further investigate this concept of IOF-based OCC system by replacing a straight IOF by an L-shaped IOF as the transmitter. An intensity modulated light from a white light emitting diode in the on-off keying format at frequencies of 1800 and 2400Hz is launched into the IOF. We experimentally investigate the impact of IOF bending as well as horizontal and vertical orientations of camera-based receiver on the performance of the IOF-based OCC system. The results depict 100% success of reception is achieved over a transmission distance of 50cm for the IOF bending angle in the range of 0 to 90°, and horizontal and vertical orientations of the camera.

In this paper, we study the novel idea of fiber optic lighting - optical camera communications. We carry out analyses of the proposed scheme employing a light emitting diode (LED) illuminated plastic optical fiber (POF) and a rolling-shutter-based camera as the transmitter and the receiver (Rx), respectively in an indoor static environment. We also provide optical and electrical characterization of the LED and LED coupled POF illumination sources. The experiment results demonstrate that, despite the small diameter of the illuminating POF, flicker-free wireless communications at modulation frequencies of 300 and 600 Hz over the transmission distances of 50 and 75 cm can be achieved. Consequently, we show that a 100 % reception success rate is achieved for the camera-based optical Rx with the exposure time and the gain of 400 µs and 25 dB, 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 Letter, we develop a novel technique, to the best of our knowledge, to increase the link span (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 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 𝐿𝑠 and exposure times of 100–80 µs, a data rate of 450 bps is achieved successfully.

The applications of Optical Camera Communications (OCC) have been tested for vehicular communications, Internet-of-things (IoT), and other outdoor scenarios due to the vast availability of standard camera equipment. The outdoor channel is, however, affected by atmospheric conditions, ranging from the presence of particles or water drops in the air to thermally induced fluctuations of the refractive index (turbulence). In this work, we experimentally investigate the influence of fog on an OCC link exploiting rolling shutter cameras and using redgreen- blue (RGB) channels inside a laboratory chamber featuring a fog machine. The analysis is performed using the Pearson’s correlation coefficient between test and reference signals as a measure of similarity or decay of the signal attenuation of fog associated with atmospheric visibility.

The operation of Optical Camera Communication systems in outdoor conditions is challenged by interfering sources of light and optical attenuation induced by the atmosphere. The low signal power at the receiver is prone to be affected by the quantization noise at the analog-to-digital converter. In this paper, an algorithm for optimizing the camera’s analog gain has been experimentally evaluated under laboratory conditions. The image quality improvement is estimated by Pearson’s correlation coefficient to a template signal, and it is shown to improve the signal-to-noise ratio up to 27.8 dB.

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.

We demonstrate the camera based optical wireless communications using flicker-free multi-channel transmitter orientation that provide 100 % success of reception over orientation angle of up to 30° at 200 and 400μs camera shutter speed.

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.

In this paper, we provide a solution based on spatial frequency 𝑓sf to study the angular behavior of a flicker-free, short-range indoor multiple–input multiple–output (MIMO) optical camera communications (OCC) link. We focus on the experimental investigation of OCC’s performance for the transmitters (Txs) [i.e., light-emitting diode (LED) based arrays] located at the same and different distances from the receiver (Rx) with the off-axis rotation angle 𝜃. We have used two 8×8 distributed LED arrays and a commercial low-cost complementary metal-oxide-semiconductor (CMOS) Raspberry Pi camera with the rolling-shutter capturing mode as the Tx and Rx, respectively. The image and the respective communications link quality metrics are measured in terms of the peak signal-to-noise ratio (PSNR) and the rate of successfully received bits with respect to 𝑓sf for different camera shutter speeds (SS). A CMOS image sensor noise characterization is carried in terms of the signal-to-noise ratio (SNR) and PSNR. The proposed study provides a 100% success rate in data reception at the optimum 𝜃 of 50° at lower captured values of 𝑓sf, which is projected onto the image sensor in the form of pixels. Moreover, the effect of channel saturation over 𝑓sf is studied with respect to 𝜃 and SS and we show that, for 𝜃 exceeding the optimum value along transmission range, the 𝑓sf area of the Txs reduces to less than ∼50% of the captured Tx units at 𝜃 of 0°, where no data can be fully recovered.

In this paper, we propose the first study of MIMO (multiple-input multiple-output) scheme using a simplified design of MIMO transmitter (Tx) based on grouping of light-emitting diodes (LED) within an array for flicker-free transmission in optical camera based communications (OCC) link. We carried out an initial experimental investigation of indoor static downlink OCC using a Raspberry Pi camera as the receiver with rolling-shutter capturing mode and a 7.2 cm × 7.2 cm small 64-neopixel LED array as the Tx. The initial study suggests that, despite the small area of the display, communication links from 20 up to 60 cm can be established.

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 × 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 × 10-3 below the forward error correction limit of 3.8 × 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.

The inclusion of organic light emitting diodes (OLEDs) in high-end devices, such as TVs and smart-phones, along with the insertion of cameras embedded in daily use devices, provides the opportunity to establish optical camera communication (OCC) systems based on OLED emitters for Internet of Things (IoT). This Letter presents an experimental demonstration of this OLED-based OCC system for IoT. The results suggest that despite the low emitted power of OLED devices, long range links can be established based on OCC. One outdoor and two indoor scenarios are tested, validating BER below 10−6 for short range and give just 3.56×10−3 for long range links.

This paper investigates the performance of the neural network (NN) assisted motion detection (MD) over an indoor optical camera communication (OCC) link. The proposed study is based on the performance evaluation of various NN training algorithms, which provide efficient and reliable MD functionality along with vision, illumination, data communications and sensing in indoor OCC. To evaluate the proposed scheme, we have carried out an experimental investigation of a static indoor downlink OCC link employing a mobile phone front camera as the receiver and an 8 × 8 red, green and blue light-emitting diodes array as the transmitter. In addition to data transmission, MD is achieved using a camera to observe user’s finger movement in the form of centroids via the OCC link. The captured motion is applied to the NN and is evaluated for a number of MD schemes. The results show that, resilient backpropagation based NN offers the fastest convergence with a minimum error of 10−5 within the processing time window of 0.67 s and a success probability of 100 % for MD compared to other algorithms. We demonstrate that, the proposed system with motion offers a bit error rate which is below the forward error correction limit of 3.8 × 10−3, over a transmission distance of 1.17 m.

In this paper, we study the effect of smartphone camera exposure on the performance of optical camera communications (OCC) link. The exposure parameters of image sensor sensitivity (ISO), aperture and shutter speed are included. A static OCC link with a 8×8 red, green and blue (RGB) LED array employed as the transmitter and a smartphone camera as the receiver is demonstrated to verify the study. Signal-to-noise ratio (SNR) analysis at different ISO values, the effect of aperture and shutter speed on communication link quality is performed. While SNRs of 20.6 dB and 16.9 dB are measured at 1 m and 2 m transmission distance, respectively for a ISO value of 100, they are decreased to 17.4 dB and 13.32 dB for a ISO of 800. The bit error rate (BER) of a 1 m long OCC link with a camera’s shutter speed of 1/6000 s is 1.3×10 −3 (i.e., below the forward error correction BER limit of 3.8×10 −3 ) and is dropped to 0.0125 at a shutter speed of 1/20 s. This study provides insight of the basic smartphone settings and the exposure adjustment for further complex OCC links.

The fifth generation (5G) telecommunications standards are being developed to meet the growing demands for high-speed wireless networks (i.e., few tens of Gigabits per second). The 5G standard stems largely from an increasing number of users and plethora of different devices, collectively referred to as smart devices, connecting to a network as part of Internet-of-Things (IoT). A few potential technologies have emerged for 5G such as millimeter waves, massive multiple-input multiple-output, and small cell communications. Although these technologies would satisfy the requirements of 5G, there is a complementary alternative wireless technology of optical wireless communications (OWC), which is being considered. As part of OWC, visible light communications (VLC) and optical camera communications (OCC) are the most attractive options for 5G networks and beyond. VLC with huge frequency spectrum integrated with IoT can open up a wide range of indoor and outdoor applications as part of future smart environments. This paper provides an overview of the all-optical IoT (OIoT) focusing on VLC and OCC based potential applications and challenges as part of 5G standards.