Visible Light Communication Scheme Research Articles

A Python-Based Indoor Channel Model with Multi-Wavelength Propagation for Color Shift Keying

Color shift keying is a modulation scheme for visible light communication that uses fixtures with three or more narrow-spectral light-emitting diodes to transmit data while fulfilling the primary function of illumination. When this modulation is used indoors, the reflectivity of the walls strongly affects the inter-channel interference and illumination quality. In this paper, we present an indoor channel model that takes into account multi-wavelength propagation. This model is available as an open-source Python package. The model calculates the inter-channel interference, illuminance, correlated color temperature, and color rendering index at the receiver position. The Python package includes a module for estimating the symbol error rate. To validate the model, we computed the received power at each color photodetector for four different indoor scenarios. The model demonstrated a color rendering index of less than 15 when using IEEE-based color shift keying and non-uniform illumination on a horizontal plane. The simulation determined the required luminous flux to achieve a symbol error rate of less than 10−5 when the photodetector is at the center of the indoor space and vertically below the light source. To maintain a symbol error rate less than 10−5, the luminous flux increases when the photodetector is displaced in a diagonal direction from the center of the plane.

NOMA Visible Light Communications with Distinct Optical Beam Configurations

Visible light communication (VLC) has been viewed as one promising candidate to mitigate the challenging spectrum crisis and radio frequency interference in future 6G mobile communications and networking. Due to the relatively limited baseband modulation bandwidth of VLC light sources—typically, light-emitting diodes—non-orthogonal multiple access (NOMA) techniques have been proposed and explored to enhance the spectral efficiency (SE) of VLC systems. However, almost all reported NOMA VLC schemes focus on well-discussed applications employing a Lambertian light beam configuration and ignore the potential applications with distinct non-Lambertian optical beam configurations. To address this issue, in this work, the performance of non-Lambertian optical beam configuration-based NOMA VLC is comparatively investigated for future 6G mobile networks. The numerical results demonstrate that, for a fundamental two-user application scenario with the far user located at the corner position, a maximum sum rate gain of about 15.6 Mbps could be provided by the investigated distinct non-Lambertian beam-based NOMA VLC, compared with the maximum sum rate of about 93.3 Mbps for the conventional Lambertian configuration with the same power splitting factor.

Study of high-order non-equal probability QAM for visible light communication systems.

In this Letter, we propose and experimentally demonstrate a high-order non-equal probability quadrature amplitude modulation (NEP-QAM) scheme for visible light communication (VLC) systems, where NEP-72QAM is considered as an example. Nonlinear coding is introduced to generate the NEP-18QAM signal in the first quadrant, which is then jointly mapped with the other two bits to obtain the four-quadrant symmetric NEP-72QAM signal. Moreover, a bit-to-symbol labeling scheme is proposed to achieve thorough Gray mapping. The experimental results show that the NEP-72QAM scheme achieves better performance than the traditional 64QAM scheme regardless of whether the light-emitting diode (LED) operates in the linear or nonlinear range. Compared with the probabilistically shaped 72QAM scheme, the available range of the driving peak-to-peak voltage of the NEP-72QAM scheme is only reduced by 20 mV when 0.92 is used as the normalized generalized mutual information threshold, but the complexity is much lower.

Visible light communication-channel-adaptive digital pre-equalization scheme based on a deep learning model

To meet the anticipated future demand for optical wireless high data rates, our study proposed a deep learning model-based adaptive digital pre-equalization scheme for visible light communication (VLC) channels is proposed to increase the data rate. We established the deep learning model to predict pre-equalization parameter (PEP) which is adaptive for various VLC channels. The proposed system is flexible and adaptive for commercial light emitting diode with different channel conditions. It improves the bandwidth of different VLC channels up to 125 MHz and has been validated on a 250-Mbps testbed. Based on the experimental results, the PEP update time is at most 5.1 s, and the bit error ratio is always <1 × 10 − 6 while using the PEP in the deep learning network. Meanwhile, the predicted and optimal values of the PEP correspond at 250 Mbps, and the maximum error between the predicted and optimal values of the PEP are only 7 for various channel conditions, including optical power, data rate, send distance, and send angle. The adaptive pre-equalization capability of the proposed system would be a universal digital solution for high-speed access in 6G scenarios combined with the VLC spectrum.

Improving the spectral efficiency of visible light communications by a super-Nyquist multi-band CAP modulation.

In this Letter, we propose a flexible bandwidth compression scheme for visible light communication (VLC) systems employing multi-band carrierless amplitude and phase (CAP) modulation. The scheme combines a narrow filtering for every subband at the transmitter and an N-symbol look-up-table (LUT) based maximum likelihood sequence estimation (MLSE) at the receiver. The N-symbol LUT is generated by recording pattern-dependent distortions induced by inter-symbol-interference (ISI), inter-band-interference (IBI), and the other channel effects upon the transmitted signal. The idea is experimentally demonstrated on a 1 m free space optical transmission platform. The results show that the proposed scheme can improve the subband overlap tolerance up to 42% in subband overlapping scenarios, that is, 3 bit/s/Hz, which is the highest spectral efficiency (SE) among the experimented schemes.

THO-OFDM scheme for visible light communication with noise suppression and dimming control.

In recent years, visible light communication (VLC) has emerged as a dual-use technique for illumination as well as communication. In VLC system, dimming control is deemed to be an essential functionality for luminous intensity adjusting and energy saving. In this Letter, a noise-suppressed triple-layer hybrid optical orthogonal frequency division multiplexing (NSTHO-OFDM) is proposed and further combined with pulse width modulation (PWM) to achieve the functionality of dimming control. The proposed NSTHO-OFDM can attain a 4.28-dB maximum power gain compared with THO-OFDM with an overall bit error rate (BER) of 1 × 10-4. Moreover, the proposed dimming scheme can achieve a wide dimming range of 89.0% while maintaining a favorable BER below 3.8 × 10-3.

DC-Balanced Even-Dimensional CAP Modulation for Visible Light Communication

Carrierless amplitude and phase (CAP) is a high spectral efficiency (SE) modulation scheme for visible light communication (VLC) systems. For N-dimensional (N-D) CAP, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> pulse shaping filters (PSFs) should satisfy zero inter-symbol interference (ISI) and zero inter-channel interference (ICI) conditions. In a practical VLC system, direct-current-balanced (DC-balanced) CAP PSFs are required to avoid severe low-frequency distortion. In this paper, we discuss the possibility of designing perfect DC-balanced N-D PSFs based on zero ISI and zero ICI conditions. Perfect PSFs should be spectrally efficient and flattened. We first prove that it's impossible to design perfect DC-balanced PSFs if the dimension is odd, but it's possible to design perfect DC-balanced PSFs if the dimension is even. Based on our proposed theories, we use a modified minimax optimization method to design a group of perfect DC-balanced 4-D PSFs. A simulation based on the bandpass VLC channel is set up to compare the bit error rate (BER) performance of odd-dimensional and even-dimensional PSFs. The simulation shows that even-dimensional PSFs outperform odd-dimensional PSFs. Moreover, a VLC system based on a laser diode is demonstrated. The experimental results show that the BER performance of even-dimensional CAP (2-D or 4-D CAP) is much better than that of odd-dimensional CAP (3-D CAP) in the bandpass VLC system. We show that the novel 4-D CAP has the nearly identical BER performance as classical 2-D CAP and it can be a good candidate multiuser modulation scheme for bandpass VLC systems.

Research on multi-color visible light communication system using RZ-4PAM signals with 67% duty cycle

In order to improve the transmission performance of visible light communication (VLC) system and user’s demand for large-capacity and high-speed, one multi-color VLC scheme is proposed. This scheme uses red-green-blue light-emitting diode (RGB-LED) as the sender to transmit 4-ary pulse amplitude modulation (4PAM) signals with 67% return-to-zero (RZ). At the receiver, one optical bandpass filter is used for channel separation. By system simulation, we have measured the time-domain waveforms before and after transmission, eye diagrams of the three colors signals, and the bit error rate (BER) performance has been analyzed. The results show that at receiver power of -11dBm, the BER at back-to-back case is slightly lower than that of the signals transmitted in the 8m channel. Since 4PAM signals have higher spectral efficiency compared with the traditional binary signals, this scheme has potential application value in indoor broadband access system.

Hybrid Adaptive Bias OFDM-Based IM/DD Visible Light Communication System

Conventional optical orthogonal frequency division multiplexing (OFDM) schemes, such as adaptively biased optical OFDM (ABO-OFDM) and hybrid asymmetrically clipped optical OFDM (HACO-OFDM), are unable to tap all the resources of the subcarriers and only achieve relatively high power efficiency. In this paper, a hybrid adaptive bias optical OFDM (HABO-OFDM) scheme for visible light communication (VLC) is proposed to improve spectral efficiency and power efficiency. In the proposed HABO-OFDM scheme, different optical OFDM components are combined for transmission at the same time, and the adaptive bias is designed to ensure the non-negativity, as well as obtaining significantly high power efficiency. Meanwhile, the implementation complexity of the HABO-OFDM receiver is notably lower than the conventional superimposed optical OFDM schemes. Simulation results show that the proposed HABO-OFDM scheme outperforms ABO-OFDM and HACO-OFDM in terms of both peak-to-average-power ratio (PAPR) and power efficiency. The PAPR performance of HABO-OFDM is about 3.2 dB lower than that of HACO-OFDM and 1.7 dB lower than that of ABO-OFDM. Moreover, we can see that the Eb(elec)/N0 required for HABO-OFDM to reach the BER target is lower than the other two schemes at the Bit rate/Normalized bandwidth range of 3.5 to 8.75, which means that the power efficiency of HABO-OFDM is higher in this range.

Coded PWM Based Switching Ripple Communication Applied in Visible Light Communication

Visible light communication (VLC) system integrates LED lighting with wireless communication. Conventionally, power conversion and communication are designed separately. The circuitry added for communication helps to achieve a high bit rate, but increases costs and impacts the efficiency. On the other hand, power conversion and communication can also be designed together by applying switching ripple communication (SRC), where no additional devices are needed. However, SRC is usually achieved by broadband modulation methods, which means that the bandwidth is much lower than the switching frequency. By applying information theory to pulsewidth modulation, this article proposes a novel VLC scheme that applies baseband modulation to SRC in order to achieve a high bit rate with a relatively low switching frequency. In addition, power control and communication are decoupled, so that they do not influence each other. In the experiments, GaN MOSFETs are used to achieve a 1.25 Mb/s VLC system with a code error ratio of less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> . Moreover, the scheme shows good performance under the duty cycle from 70% to 30%, and under the output power from 100% to 7.5% of the rated value.

Flexible NOMA-based NOHO-OFDM scheme for visible light communication with iterative interference cancellation.

In this paper, a flexible non-orthogonal multiple access (NOMA) based optical orthogonal frequency division multiplexing (OFDM) modulation scheme, called non-orthogonal hybrid optical OFDM (NOHO-OFDM), is proposed to increase the achievable data rate of the visible light communication system with high efficiency. In addition, a receiver with iteratively successive interference cancellation (ISIC) is investigated, which can reduce the estimation error. Then, the achievable data rate of the proposed NOHO-OFDM with the ISIC scheme is analyzed. Experiment results show that the bit error rate of the NOHO-OFDM can be significantly reduced by the proposed ISIC scheme, and the NOHO-OFDM is superior than the orthogonal scheme in terms of data rates. Meanwhile, simulation results show that the achievable data rate region of the proposed NOHO-OFDM scheme is larger than that of the orthogonal counterpart.

Deep learning-based detection scheme for visible light communication with generalized spatial modulation.

In this paper, a deep learning-based detection scheme is proposed for the visible light communication (VLC) systems using generalized spatial modulation (GenSM). In the proposed detection scheme, a deep neural network consisting of several neural layers is applied to detect the received signals. By integrating the signal processing modules of the conventional detection schemes into one deep neural network, the proposed scheme is able to extract the information bits from the received signals efficiently. After offline training, the proposed detection scheme can serve as a promising detection method for the VLC system with GenSM. Simulation results validate that the proposed detection scheme is capable of achieving superior detection error performance than conventional detection schemes at acceptable complexity.

Optical encryption for visible light communication based on temporal ghost imaging with a micro-LED

As the great application potential of visible light communication (VLC) in the next generation communication after 5G, study of the transmission security in VLC is high desirable with the rapid growth of wireless network traffic. In this paper, an optical encryption scheme for VLC is proposed based on temporal ghost imaging (TGI) with a micro-light-emitting diode (micro-LED). The target temporal signal is digitally encrypted by a sequence of randomized orthogonal secret key. The micro-LED working at 4 Gbps (over 20 times higher than its bandwidth ~160 MHz) physically encrypts the information in a non-invertible way due to the severe transmission distortion. According to TGI theory, correlation calculation between the integration value of received distorted signal and the secret key can realize the decryption process without error. The integrated encryption of digital algorithm and physical hardware property guarantee the security of this method. We experimentally demonstrate the system can resist attack of up to 40% occlusion or 80% Gaussian noise and obtain error-free signal.

An Effective Mapping Scheme for Visible Light Communication With Smartphone Camera

In this paper, an effective mapping scheme is proposed and experimentally demonstrated for visible light communication (VLC) based on light emitting diode (LED) and smartphone camera. At the transmitter, parking information is mapped to a number of bits using the proposed mapping scheme. Based on the parking information, the parking position can be achieved quickly, and the extra processing time is not required for data reception. In addition, the BER performance of the proposed mapping scheme under different distances and speeds are investigated. Experimental results show that optimum receiving distance range is from 0.5 to 1.0 m when exposure time is 1/12800s and international standard organization (ISO) is 160. Moreover, the bit error rate (BER) performance is not affected by low velocity range of 0.5-0.9 m/s under same conditions. And the transmission time of data takes only 1/15s using the proposed scheme, which is much less than that of traditional picture. As the picture resolution is 360×180, its transmission of data is 225 times more than that of using the proposed scheme.

A Novel Unipolar Transmission Scheme for Visible Light Communication

This paper proposes a novel unipolar transceiver for visible light communication (VLC) by using orthogonal waveforms. The main advantage of our proposed scheme over most of the existing unipolar schemes in the literature is that the polarity of the real-valued orthogonal frequency division multiplexing (OFDM) sample determines the pulse shape of the continuous-time signal and thus, the unipolar conversion is performed directly in the analog instead of the digital domain. Therefore, our proposed scheme does not require any direct current (DC) biasing or clipping as it is the case with existing schemes in the literature. The bit error rate (BER) performance of our proposed scheme is analytically derived and its accuracy is verified by using Matlab simulations. Simulation results also substantiate the potential performance gains of our proposed scheme against the state-of-the-art OFDM-based systems in VLC; it indicates that the absence of DC shift and clipping in our scheme supports more reliable communication and outperforms the asymmetrically clipped optical-OFDM (ACO-OFDM), DC optical-OFDM (DCO-OFDM) and unipolar-OFDM (U-OFDM) schemes. For instance, our scheme outperforms ACO-OFDM by at least 3 dB (in terms of signal to noise ratio) at a target BER of 10−4, when considering the same spectral efficiency for both schemes.

Research and Design of LED Light Suppression Flicker Technology in Visible Light Communication Technology

“Lighting communication integration” is a key technology research for the future application of visible light communication(VLC). However, the bandwidth characteristics, dynamic modulation range and linear modulation performance of existing white LED still do not meet the requirements of high-speed communication. After adding the dimming function, the naked eye It is noticeable that flicker is felt. In order to solve the problem of LED flicker caused by high-speed communication, this paper proposes a “lighting and communication integration” technology scheme based on visible light communication(VLC), which studies from the aspects of suppressing flickering VLC scheme, LED communication dimming, and high-efficiency modulation driving circuit design. A PWM dimming control technology based on optical OFDM system is used for VLC and LED dimming scheme. Finally, the technology is applied to the typical application scenario of the power grid—cable tunnel, which realizes the two-way real-time voice communication of cable tunnel inspection personnel. And accurate positioning to ensure the personal safety of the inspectors and the safety of the grid production.

Colour Light Intensity based Modulation Scheme for Visible Light Communication Employing Turbo Codes

-This paper discusses a modulation scheme based by incorporating the data with the subtle changes in the variation of light intensity for Visible Light Communication (VLC) systems. A modulation scheme named Colour Light Intensity Modulation is proposed on the concept of colour spaces of light where the data can be modulated on the subtle changes in the light signals and transmitted. Firstly, the input data is mapped with the intensities of Light Emitting Diodes and transmitted. The received information is demapped to obtain the estimate of the sent message. The simulation results obtained shows that the proposed concept can be used in the development of more efficient VLC systems.

Optical GFDM: an improved alternative candidate for indoor visible light communication

This paper proposes generalized frequency division multiplexing (GFDM) for indoor visible light communication (VLC). GFDM is a flexible multi-carrier scheme that allows engineering in both time and frequency domain, therefore, making GFDM suitable for various 5G applications. In the literature, different types of optical orthogonal frequency division multiplexing (O-OFDM) have been proposed for VLC including direct current offset optical OFDM (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM), Flip-OFDM, etc. O-OFDM can provide high data rate, but it suffers from the problem of the high peak-to-average power ratio (PAPR) which causes clipping distortion, reduces the illumination-to-communication conversion efficiency and affects the lifetime of the LED. The proposed optical GFDM (O-GFDM) scheme for VLC is analyzed for various performance metrics against the O-OFDM counterpart. The analytical expression for symbol error rate (SER) of O-GFDM is derived and simulation results based on PAPR, SER and subcarrier frequency shift tolerance validate the improved performance of the proposed O-GFDM scheme. It is found that one of the variants of the proposed scheme has better spectral efficiency and lower power consumption compared with O-OFDM counterpart. As GFDM is being considered for 5G wireless systems, it is expected that the GFDM-based VLC system will very well gel with next-generation wireless systems to offer seamless services and will provide greater flexibility using software-defined networking.

Adaptive Modulation Scheme Based on Partially Pre-Distorted LACO-OFDM for VLC System

In this paper, an adaptive modulation scheme for visible light communication (VLC) system based on partially pre-distorted layered asymmetrically clipped optical orthogonal frequency division multiplexing (LACO-OFDM) is proposed. The clipping noise that falls on the higher layers in the conventional LACO-OFDM results in inter layer interference, which can be eliminated by the operation of pre-distortion at the expense of extra power consumption. The proposed partially pre-distorted scheme makes a tradeoff between error propagation and power cost to suit different transmission environments. The probability distribution functions of the conventional and pre-distorted LACO-OFDM schemes are analyzed and compared and the layers that should be pre-distorted in the proposed scheme is decided adaptively by maximizing the achievable rate. The computational complexity of the proposed scheme is also investigated, which is acceptable compared with the previous schemes. Simulation results show that the proposed scheme has a superior bit error rate performance compared with the conventional and pre-distorted LACO-OFDM schemes.

Chaos‐based physical‐layer encryption for OFDM‐based VLC schemes with robustness against known/chosen plaintext attacks

The technology of visible light communication (VLC) is regarded as an appealing technique for upcoming wireless indoor multimedia communications. Considering the broadcast aspect of visible light propagation, the visible light interface is exposed and approachable to both licensed and unlicensed parties settled within the illuminated region. In this study, the authors present a chaos-based physical-layer encryption method for orthogonal frequency division multiplexing (OFDM)-based VLC schemes with the ability to counter known-plaintext attacks (KPAs) and chosen-plaintext attacks (CPAs). A logistic map is utilised for the chaos mapping. The presented method produces dynamic ciphertexts by employing the random quality of the chaotic keys and input data. It uses a multiple-fold encryption protocol which implements chaotic scrambling of the subcarrier distribution in time and frequency domains, as well as chaotic polarity inversion of subcarriers. To generate the secret key, a chaotic key creation approach is introduced by including the position-sensitive and real-valued channel state information of the VLC channel. The presented method provides supreme confidentiality for the OFDM-based VLC schemes to counter KPAs, CPAs, brute-force attacks, and statistical attacks. The secrecy capacity of the presented method is improved by applying a pre-equalisation technique at the transmitter instead of the receiver.