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![Block diagrams for case a) and case b) As is typical in optical wireless communications; the BER target is set at 10 -6 [9, 19, 20]. Data is driven through the relative LED/OLED into the channel and incident light is absorbed by the relevant OPD/PD. The AWG triggers the DSO as mentioned; where both devices store the received data for offline processing.](profile/Paul-Haigh-2/publication/252931434/figure/fig4/AS:341829653417994@1458509948767/Block-diagrams-for-case-a-and-case-b-As-is-typical-in-optical-wireless-communications.png)
Block diagrams for case a) and case b) As is typical in optical wireless communications; the BER target is set at 10 -6 [9, 19, 20]. Data is driven through the relative LED/OLED into the channel and incident light is absorbed by the relevant OPD/PD. The AWG triggers the DSO as mentioned; where both devices store the received data for offline processing.
Source publication
This paper presents the use of equalization techniques in visible light communication (VLC) systems in order to increase the data rate. Here we investigate two VLC links a silicon (Si) light emitting diode (LED) and an organic photodetector (OPD), and an organic LED (OLED) plus an Si photodetector (PD), together with three equalization schemes of a...
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We present recent progress on visible light communication systems using polymer light-emitting diodes as the transmitters and a commercial silicon photodetector as the receiver. In this work we use transmitters at red, green and blue wavelengths to investigate the maximum on-off keying link performance of each device type as the first steps towards...
In this paper, we experimentally demonstrate for the first time an on off keying modulated visible light communications (VLC) system achieving 170 Mb/s using an artificial neural network (ANN) based equalizer. Adaptive decision feedback (DF) and linear equalizers are also implemented and the system performances are measured using both real time (TI...
Citations
... This fact is mainly attributed to the restrained charge carrier mobility in the organic semiconductors, limiting the applicability of the organic devices [46][47][48][49]. In this context, equalization processes (supply a higher charging voltage to the device for improving the carrier transport) [50] were applied to OLEDs, with one study obtaining a frequency bandwidth up to 10 MHz and a datalink supporting up to 100 Mbps [51]. This performance could be the initial step in the process of fabricating efficient OVLC systems. ...
The growing demand for faster data transference and communication allowed the development of faster and more efficient communication network-based technologies, with wider bandwidth capability, high resilience to electromagnetic radiation, and low latency for information travelling. To provide a suitable alternative to satisfy data transmission and consumption demand, wireless systems were established after a decade of studies on this topic. More recently, visible light communication (VLC) processes were incorporated as interesting wireless approaches that make use of a wide frequency communication spectrum to reach higher bandwidth values and accelerate the speed of data/information transmission. For this aim, light converters, such as phosphor materials, are reported to efficiently convert blue light into green, yellow, and red emissions; however, long carrier lifetimes are achieved to enlarge the frequency bandwidth, thereby delaying the data transference rate. In this review, we focused on recent advances using different luminescent materials based on prominent polymers, organic molecules, and semiconductor nanocrystals with improved photophysical properties and favored carrier recombination dynamics, which are suitable to enhance the VLC process. Here, the main features of the above materials are highlighted, providing a perspective on the use of luminescent systems for efficient optical communication applications.
... c NIR communication: NIR-OPD could transcribe the message accurately from a commercial NIR remote control. Reproduced with permission from Ref. [41] mass data transmission in communication networks have arisen with the explosive growth of big data services [169,170]. Because of the ever-dwindling wireless communication spectrum resources, and emerging demand for wireless communication, visible light communication (VLC) with visible light as the carrier of information, is picking up focus as an alternative communication technology [125,171]. ...
Organic photodiodes (OPDs) have shown great promise for potential applications in optical imaging, sensing, and communication due to their wide-range tunable photoelectrical properties, low-temperature facile processes, and excellent mechanical flexibility. Extensive research work has been carried out on exploring materials, device structures, physical mechanisms, and processing approaches to improve the performance of OPDs to the level of their inorganic counterparts. In addition, various system prototypes have been built based on the exhibited and attractive features of OPDs. It is vital to link the device optimal design and engineering to the system requirements and examine the existing deficiencies of OPDs towards practical applications, so this review starts from discussions on the required key performance metrics for different envisioned applications. Then the fundamentals of the OPD device structures and operation mechanisms are briefly introduced, and the latest development of OPDs for improving the key performance merits is reviewed. Finally, the trials of OPDs for various applications including wearable medical diagnostics, optical imagers, spectrometers, and light communications are reviewed, and both the promises and challenges are revealed.
Graphical Abstract
... However, state-of-the-art devices, especially high-power light-emitting diodes (LEDs), which have been widely adopted as transmitters in VLC systems, suffer from limited bandwidth [4], [5] and thus constrain the achievable data rates. Many equalisation methods have been reported to mitigate this bandwidth limitation [6]. From the position where the equalisers reside, they can be classified into pre-and post-equalisers. ...
... Moreover, in VLC systems, which use RC filter-based pre-equalisers at the transmitter, modulation schemes such as OOK with more power spectral density (PSD) at the DC level are more prominent to cause baseline wandering phenomena (BLW) at the receiver [27]. This could randomly degrade the BER performance of the VLC link based on the transmitting bit sequence. ...
... transmitter, modulation schemes such as OOK with more power spectral density (PSD) at the DC level are more prominent to cause baseline wandering phenomena (BLW) at the receiver [27]. This could randomly degrade the BER performance of the VLC link based on the transmitting bit sequence. ...
The light-based Internet of things (LIoT) concept defines nodes that exploit light to (a) power up their operation by harvesting light energy and (b) provide full-duplex wireless connectivity. In this paper, we explore the LIoT concept by designing, implementing, and evaluating the communication and energy harvesting performance of a LIoT node. The use of components based on printed electronics (PE) technology is adopted in the implementation, supporting the vision of future fully printed LIoT nodes. In fact, we envision that as PE technology develops, energy-autonomous LIoT nodes will be entirely printed, resulting in cost-efficient, flexible and highly sustainable connectivity solutions that can be attached to the surface of virtually any object. However, the use of PE technology poses additional challenges to the task, as the performance of these components is typically considerably poorer than that of conventional components. In the study, printed photovoltaic cells, printed OLEDs (organic light-emitting diodes) as well as printed displays are used in the node implementation. The dual-mode operation of the proposed LIoT node is demonstrated, and its communication performance in downlink and uplink directions is evaluated. In addition, the energy harvesting system’s behaviour is studied and evaluated under different illumination scenarios and based on the results, a novel self-operating limitation aware algorithm for LIoT nodes is proposed.
... Der Grad des Post-Equalizings ist dann ein Optimierungsproblem zwischen Signalamplitude und Rauschen. Bei breitbandig modulierten Signalen konnte ein Mehrwert durch Post-Equalizing nachgewiesen werden[86,155,157]. Bei OFDM-Signalen kommt zum Optimierungsproblem noch der Einfluss der nichtlinearen Verzerrungen hinzu. ...
This thesis investigates the analog optical wireless frontend (AFE) and application-specific freeform lenses for optical wireless communications (OWC). Besides theoretical considerations, design examples are described, implemented at printed circuit board (PCB) level, and investigated metrologically. The design examples include a linear driver that interfaces multiple light-emitting diodes using a transistor precision current source. The receiver design examples compromise an unbalanced differential transimpedance amplifier (TIA) and a single-ended TIA with post-amplifier. The circuits are characterized with respect to their power consumption, transfer function, and linearity. Additionally, the receiver circuit noise is investigated and measured. Signals modulated by orthogonal frequency division multiplexing (OFDM) are transmitted to evaluate the data transmission characteristics of the AFE. This work reports OFDM data rates of up to 1554 Mbit/s. The transmission is studied as a function of received signal strength, transmitter signal level, emitter operating point, bandwidth, and temperature. Thereby, the work quantifies how future transceivers can benefit from features, such as adaptive operating point adjustment, adaptive bandwidth adjustment, and a special type of adaptive power loading. The design examples are integrated into an Ethernet network using a commercial digital signal processor. Data rate measurements in point-to-point, point-to-multipoint, and multipoint-to-multipoint configurations underline the versatility of the transceiver. In addition, a network-based localization algorithm is applied to deliver location-specific content to mobile users within the network. The key feature of this work is the detailed investigation of freeform optics in the context of OWC. The work presents a design framework for freeform lenses, which is so far unique in terms of Li-Fi. By investigating several design examples, this work explores the potential of freeform optics for OWC. The framework uses ray-mapping algorithms to design transmitter lenses. Methods based on the edge ray principle are used to calculate receiver lenses. Using total internal reflection lenses, the optical efficiency and homogeneity within the field of view can be improved. Another design example is a multi-path lens that transforms an elliptical emission profile into a FOV with a rectangular cross section. With respect to eye safety, the lens allows an increase of the optical transmitter power by 13 dB compared to a transmitter without a lens. This result corresponds to a range improvement by a factor of 4.5. Another design example demonstrates how transmitter and receiver lens are combined into a new single hybrid lens to realize contactless data transmission in rotary applications. Finally, a simulative feasibility study investigates the combination of freeform Fresnel lenses with the considered AFE. The lenses extend the communication range to several tens of meters depending on the AFE configuration. In summary, this work demonstrates that discussed design examples can address various applications very well and thus represent a reasonable alternative to commercial radio frequency technologies. Freeform lenses are the key for an efficient solution with high performance.
... Bu nedenle, kablosuz optik haberleşme teknolojisinde uygulanabilen fiziksel optik prensiplerinin görünür ışık haberleşmesinde de kullanılabileceği ifade edilmektedir [39]. Verici taraftan gönderilen modülasyonlu sinyaller, şekildeki sıraya göre alıcı tarafta demodüle edilmektedir [40]. Eğer sinyaller negatif genlik değerleriyle iletiliyorsa, modülasyonlu sinyale, şekilde görüldüğü gibi DC bir gerilim eklenebilmektedir [41]. ...
In the first part of the thesis, a new transmission scheme is proposed by using signal
characteristics of the variable pulse position modulation (VPPM) technique. In the
proposed system, 4 information bits are transmitted every three bits. Therefore, the
proposed system has been observed to have better spectral efficiency than traditional
systems with dimming level lower than 35% and higher than 65%. In the second part
of the thesis, it is aimed to detect the information bits without having the dimming
level information. In the part, two different detection methods have been developed,
and the first method is to generate a hybrid signal using artificial neural networks
(ANN). When the proposed system is compared to the traditional system that doesn’t
know the dimming level information, it has been observed that the proposed system
has better bit error rate performance, but it also gives lower bit error rate performance
than the system with excellent dimming level information. In order to solve this
problem, a second method has been developed to estimate the dimming levels of the
signals. When the dimming levels of the signals are changed at the transmitting side,
it is impossible for the traditional system to have dimming level information at the
receiving side without transmitting information signal. However, assuming that the
traditional system knows all the signal characteristics, the BER performance of the
proposed and traditional systems are almost the same under 10-3
. As a result, thanks to the proposed system, a receiver scheme has been developed that it can estimate the information bits of VPPM signals without the need for the dimming level information.
... Recently, an artificial neural network (ANN) has been theoretically demonstrated to have superior potential compared to traditional equalizers due to its approximation to arbitrary functions [16,17]. ANN equalizers have been proposed in optical camera communication and other low-speed VLC links to improve the data rate which presents a better equalizing and compensation effect in various broadband systems [18][19][20]. Our proposed scheme realizes one direct mapping relation between the received distorted signal to desired original input bits. ...
Visible light communication (VLC) beyond 10 Gbps is an important characteristic that can support the future 6 G high-capacity requirements. On the one hand, in order to break the electro-optics (E-O) bandwidth limitation of the light-emitting diodes (LEDs), we fabricated two high-bandwidth ( ${\gt} {\rm gigahertz}$ > g i g a h e r t z ) single wetting layer micro-LEDs with 50 and 75 µm active regions. On the other hand, for mitigating the nonlinear effects of the VLC system, an artificial neural network equalizer is designed and implemented in offline digital signal processing. Both efforts lead to a breakthrough of data rates at a single VLC link. Using quadrature phase shift keying orthogonal frequency division multiplexing, the data rate of a 1.025 GHz VLC link based on a 75 µm micro-LED can reach 8.75 Gbps with a bit-error-ratio (BER) of $2.73 \times {10^{- 3}}$ 2.73 × 10 − 3 . In addition, the E-O characteristics and communication performances of micro-LED with two diameters are compared and discussed. To the best of our knowledge, the data rate of 8.75 Gbps is the highest record of the VLC link based on a single-pixel blue micro-LED with a BER within the forward error correction citation of $3.8 \times {10^{- 3}}$ 3.8 × 10 − 3 .
... Visible light communication (VLC) has attracted continued research interest [1][2][3], while solid-state lighting has dominated the mass market over the last two decades [4]. The use of solid-state semiconductor devices, such as light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs) [5][6][7], and laser diodes (LDs) [8,9], in the visible range enables intensity modulation of the optical power for communication simultaneously with illumination. Therefore, the VLC technology has the potential to reuse the existing lighting infrastructure to deliver add-on functionality in a cost-effective manner that can be adopted in future smart indoor and outdoor environments. ...
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 cm2. 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.
... Then, we can rewrite (38) and (39) in a single constraint as Optical power constraint: ...
... The bandwidth of color LEDs is usually between 10 and 20 MHz [15,16]. Accordingly, we will assume a bandwidth of 15 MHz for the color LEDs, and 2 MHz for the phosphor-coated LEDs [39]. To make a fair comparison, we have also considered a bandwidth of 15 MHz for the PWLEDs, which could be achieved by suppressing the slow response of the phosphorescent component of the LED but increasing the cost significantly [40]. ...
In this paper, we design linear precoders for the downlink of a visible light communication (VLC) system that simultaneously serves multiple users. Instead of using phosphor-coated white light-emitting diodes (PWLEDs), we focus on Red-Green-Blue light-emitting diodes (RGB-LEDs) that allow modulating three separate data streams on the three primary colors of the RGB-LEDs. For this system, we design a zero-forcing (ZF) precoder that maximizes the weighted sum rate for a multilevel pulse amplitude modulation (M-PAM). The precoding design in RGB-based systems presents some challenges due to the system constraints, such as the limited power, the non-negative amplitude constraints per light-emitting diode (LED), and the need to guarantee white light emission while transmitting with RGB-LEDs. For comparison purposes, we also consider the ZF design for a PWLED-based system and evaluate the performance of both a PWLED- and an RGB-based system.
... schemes including multi-level modulation, multi-carrier modulation and analogue pre-and postequalisers have been investigated [8][9][10][11][12][13][14]. In [11], a first-order post-equaliser (post-EQ) was used at the receiver (Rx) to compensate for the frequency response of the blue component of a white phosphorous LED, to increase B mod from 10 MHz (the blue component bandwidth) to 50 MHz. ...
Visible light communication (VLC) systems are highly constrained by the limited 3-dB bandwidth of light-emitting diodes (LEDs). Analogue pre-equalisers have been proposed to extend the LED's bandwidth at the cost of reduced signal-to-noise ratio (SNR). Compared with the pre-equaliser, the multi-carrier modulation with bit-loading can efficiently use the spectrum beyond the LED's raw 3-dB bandwidth without incuring SNR penalties by employing multiple narrow quasi-flat sub-bands to eliminate the need for equalisation. In this work we show by means of experimental investigation that VLC with multi-band carrierless amplitude and phase modulation with bit-loading can outperform VLC with analogue pre-equalisers.
