Enabling 5G indoor services for residential environment using VLC technology

In this paper, several Orthogonal frequency division multiplexing (OFDM)-based Visible light Communications (VLC) techniques designed for intensity modulation/direct detection (IM/DD) are evaluated and compared for various optical channels. Evaluations are done for line-of-sight (LOS) and no-line-of-sight (NLOS) channels. The techniques analyzed are asymmetrically clipped optical OFDM (ACO-OFDM), direct-current (DC) biased optical OFDM (DCO-OFDM), and asymmetrically clipped DC biased optical OFDM (ADO-OFDM). These schemes are evaluated and compared for different M-QAM modulations in terms of bit error rate (BER). It is shown that ACO-OFDM, in general terms, presents a better performance compared to the conventional DCO-OFDM and ADO-OFDM schemes.

Visible light communication (VLC) is a promising and viable optical wireless communication (OWC) system that utilizes light-emitting diodes (LEDs) to achieve high data rates, energy efficiency, and resistance to electromagnetic interference (EMI). Direct-current biased optical orthogonal frequency division multiplexing (DCO-OFDM) is a widely used scheme in VLC due to its high spectral efficiency. However, it suffers from significant challenges related to its elevated peak-to-average power ratio (PAPR), which causes nonlinear distortion and signal clipping due to LED limitations. To address this issue, this paper proposes a combination of Vandermonde-like matrix (VLM) precoding and nonlinear companding transform (NCT) techniques (specifically A-law and μ-law) over DCO-OFDM-based VLC. The VLM precoding minimizes the autocorrelation of the OFDM signal, hence reducing its PAPR, and NCT compresses the dynamic range of the signal. Simulation results indicated that the hybrid techniques achieved a PAPR reduction of around 3.5 dB (by 76 %); this is in the best case reduction compared to the conventional DCO-OFDM while maintaining an acceptable bit error rate (BER), moderately higher signal-to-noise ratio (SNR) is required.

Visible light communication (VLC) is a technology that is currently being employed to achieve high data rates. Orthogonal frequency division multiplexing (OFDM) is a powerful scheme for intensity modulation and direct detection (IM-DD) that is becoming increasingly important. OFDM systems based on VLC are accomplished through the implementation of IM-DD constraints, including direct current biased optical OFDM (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM), and asymmetrically clipped DC-biased (ADO-OFDM), among others. The OFDM technique based on VLC is inefficient in terms of spectral efficiency and has a high peak to average power ratio (PAPR). In this article, the symbol time compression-image adjust (STC-IMADJS) technique will be proposed for throughput maximization and PAPR reduction in the DCO-OFDM, ACO-OFDM, and ADO-OFDM systems. Furthermore, the STC technique enables the simultaneous transmission of two sub-carriers through Walsh spreading codes without inference between them. As a result, the OFDM symbol has been reduced by 50%. The IMADJS strategy reduces the high PAPR of transmitted signals by compressing large signals and expanding small signals, as long as the average power level remains constant after compression. Therefore, the proposed STC-IMADJS technique doubles the throughput as well as significantly reduces the PAPR for OFDM systems based on VLC. The simulation results are performed using Matlab-2021a for 1024 sub-carriers. As a result, the simulation results show that the proposed technique reduces the PAPR by 3.7 dB (86%), 8.16 dB (93%), and 1.81 dB (20%) for DCO-OFDM, ACO-OFDM, and ADO-OFDM systems respectively. Furthermore, the technique has a significantly lower computational complexity than conventional OFDM systems based on VLC. Finally, the measures of performance through this article are bit error rate and complementary cumulative distribution function.

Power line communications (PLC) and visible light communications (VLC) are two emerging communication technologies which have several similarities. Among them, the advantage related to cost effectiveness is considered as strong research motivation. These two technologies are also characterized by the fact that each one of them barely form a complete communication system without the need of other supporting technologies. In this paper, based on the positive aspect of VLC technology, we exploit the Hermitian symmetry to design an hybrid system combining PLC and VLC technologies using orthogonal frequency division multiplexing (OFDM). A DC biased optical OFDM (DCO-OFDM), employed in VLC, is investigated when combined with PSK-OFDM (used in PLC). In the hybrid PLC-VLC system proposed in this paper, we exploit the inherent clipping feature of DCO-OFDM to combat impulsive noise found in the PLC channel, where the optimal combination of the DC bias level for optical communication, DC and impulse noise clipping threshold, T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> are investigated through simulations. We also exploit the fact that both DCO-OFDM and PSK-OFDM employ the FFT, to simplify the system.

DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) has been proposed in visible light communication (VLC) to overcome the limited modulation bandwidth of light emitting diode (LED). Due to the implementation of the inverse fast Fourier transform at the DCO-OFDM transmitter, DCO-OFDM suffers from its high peak-to-average power ratio (PAPR), which restricts its use in some VLC applications, especially where the optical power efficiency is a crucial requirement. That is because the LEDs used in VLC systems have a limited optical power-current linear range. To this end, a novel discrete Fourier transform spread-optical pulse amplitude modulation (DFTS-OPAM) signal scheme based on the single carrier-interleaved frequency division multiple access (SC-IFDMA) signal is introduced in this paper to address the high PAPR issue of OFDM. DFTS-OPAM is achieved by considering a PAM as an SC-IFDMA data symbol and duplicate the output vector of the fast Fourier transform at the SC-IFDMA transmitter side. Simulation results show that the PAPR of the proposed scheme is 7 dB lower than that of DCO-OFDM. Furthermore, this significant PAPR improvement is experimentally investigated where the practical results show that the proposed scheme can provide more 2.5 dB reduction in the average transmitted power requirement compared to DCO-OFDM and can subsequently increase the maximum achieved distance between the transmitter and the receiver up to 44%.

Orthogonal frequency division multiplexing (OFDM) has been considered for\nvisible light communication (VLC) thanks to its ability to boost data rates as\nwell as its robustness against frequency-selective fading channels. A major\ndisadvantage of OFDM is the large dynamic range of its time-domain waveforms,\nmaking OFDM vulnerable to nonlinearity of light emitting diodes (LEDs). DC\nbiased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM\n(ACO-OFDM) are two popular OFDM techniques developed for the VLC. In this\npaper, we will analyze the performance of the DCO-OFDM and ACO-OFDM signals in\nterms of error vector magnitude (EVM), signal-to-distortion ratio (SDR), and\nachievable data rates under both average optical power and dynamic optical\npower constraints. EVM is a commonly used metric to characterize distortions.\nWe will describe an approach to numerically calculate the EVM for DCO-OFDM and\nACO-OFDM. We will derive the optimum biasing ratio in the sense of minimizing\nEVM for DCO-OFDM. Additionally, we will formulate the EVM minimization problem\nas a convex linear optimization problem and obtain an EVM lower bound against\nwhich to compare the DCO-OFDM and ACO-OFDM techniques. We will prove that the\nACO-OFDM can achieve the lower bound. Average optical power and dynamic optical\npower are two main constraints in VLC. We will derive the achievable data rates\nunder these two constraints for both additive white Gaussian noise (AWGN)\nchannel and frequency-selective channel. We will compare the performance of\nDCO-OFDM and ACO-OFDM under different power constraint scenarios.\n

Adaptive least squares channel estimation for visible light communications based on tap detection

Visible light communication (VLC) is now used to achieve high data rates. Opticalorthogonal frequency division multiplexing (O-OFDM) is a strong technique for intensity modulation and direct detection (IM-DD). Direct current biased O-OFDM (DCO-OFDM) and asymmetrically clipped O-OFDM are two modern O-OFDM systems that operate with IM-DD constraints (ACO-OFDM). Due to severe out of band interference, the DCO-OFDM and ACO-OFDM systems have a high peak to average power ratio (PAPR) and substantial adjacent channel interference (ACI) (OOB). Furthermore, as compared to bipolar OFDM systems, they obtain a greater chance of bit error. The combination of the STC scheme, symbol extension, and pulse shaping signal is presented in this paper for improving the performance of the O-OFDM system without affecting system throughput. This article also decreases the OOB, PAPR, and bit error rate (BER) of DCO-OFDM and ACO-OFDM systems. Further analytical analyses for the proposed systems, such as OOB, PAPR, and computing complexity, are obtained in this paper. The simulation results verify the analytical study of the proposed methods for OOB reduction and PAPR reduction. As compared to typical O-OFDM systems, the proposed shaped STC-DCO-OFDM scheme and the proposed shaped STC-ACO-OFDM scheme lower the OOB by about 40 dB and the PAPR by about 4 dB at the 10 -3 probability point of the complementary cumulative distribution function (CCDF). The proposed systems outperform existing O-OFDM systems under AWGN for the BPSK modulation scheme in terms of BER, and reduce the computational complexity.

The dual property of LEDs to facilitate illumination and Communication concurrently has driven Visible Light Communication (VLC) as an emerging technology and a promising alternative to Radio Frequency (RF) Communication. The primary objective of VLC is to increase the data rates and to have better performance of the networks especially for indoor applications. In this juncture, for the purpose of increasing the Information Spectral Density (ISD), Fast Optical Orthogonal Frequency Division Multiplexing (FOOFDM) can be exploited. In this work, the performance of FOOFDM is evaluated by employing various channel estimation algorithms and Probability of Error expression is derived for the developed system models. In addition, investigations on channel estimation in DC Biased Optical OFDM (DCO-OFDM) is carried out where, the result analysis emphasize that, FOOFDM is superior in terms of both power efficiency and spectral efficiency when compared to DCO-OFDM. Employing a real-valued transform and its simple one dimensional modulation, makes FOOOFM to exhibit lower computational complexity when compared with hermitian symmetry imposed optical OFDM (DCO-OFDM).

In this paper, a multivariate regression transform (MRT) is proposed for pulse-amplitude-modulated-based hybrid optical orthogonal frequency division multiplexing (PHO-OFDM) visible light communications (VLC). PHO-OFDM is a hybrid modulation scheme that combines pulse amplitude modulated discrete multitone (PAM-DMT) and DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) for simultaneous transmission. The proposed method reduces the peak-to-average power ratio of PHO-OFDM to improve its system performance. Complementary cumulative distribution function simulation results show that the proposed method can effectively mitigate the PAPR of PHO-OFDM under different constellation combinations.

Direct-current-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) is widely used in high-speed visible light communication (VLC). Due to the limited dynamic range of light-emitting diode (LED) and the unipolarity for the intensity modulation (IM), double-sided clipping is inevitably imposed on the time-domain signal in VLC OFDM systems. Consequently, it calls for proper DCO-OFDM signal shaping by selecting an appropriate bias and time-domain signal power to reduce the clipping distortion and achieve a higher transmission rate. In this paper, we deep dive into the signal shaping design problem for double-sided clipping DCO-OFDM over both flat and dispersive channels. We derive the optimal bias for flat and dispersive channels, and explain its optimality from the perspectives of effective signal-to-noise ratio (SNR) and information theory. We then analytically characterize the optimal power for flat channels and propose a useful algorithm for dispersive channels enlightened by the optimal solution to the flat case. Furthermore, we uncover an inherent relationship between the considered double-sided clipping and the downside-clipping only DCO-OFDM regarding signal shaping optimization, and develop an in-depth understanding of the impact of top clipping based on the established connection. Practical simulations are provided to validate the superiority of our proposed signal shaping over the existing shaping schemes.

We address the optimal transmission of LED-based visible light communication (VLC) system using direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) modulation and avalanche photodiode (APD) receiver. The peak-to-average-power ratio (PAPR) characteristic of O-OFDM signal is studied, which reveals that the careful setting of transmission parameters is necessary for O-OFDM signal with high PAPR to avoid the severe nonlinear distortion. We further experimentally investigate the nonlinear distortion caused by the LED clipping and APD module saturation, and define a modified term called signal-to-noise and distortion ratio (SNDR) to measure the influence of nonlinear distortion on system performance. The derived explicit expression of SNDR shows that the performance depends on the transmission parameters of both direct current bias Vdc and peak-to-peak voltage Vpp. Meanwhile the sequential quadratic programming algorithm is applied to maximize SNDR and obtain the optimal transmission parameters. The optimal transmission of the nonlinear LED-VLC system is achieved via both simulations and experiments.

A direct current (DC) bias is required in DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) to enable visible light communication (VLC). However, the addition of the DC-bias leads to electrical and optical power inefficiency. An experimental demonstration of an energy efficient superposition modulation technique is presented based on augmented spectral efficiency discrete multitone (ASE-DMT) transmission. Significant energy savings of up to 14.27 dB are achieved in comparison with DCO-OFDM at low DC bias. The results highlight the potential of ASE-DMT in spectrum and energy efficient light fidelity (LiFi) systems.

The quasi-static nature of the optical wireless channel means that the channel state information (CSI) can be readily available at the transmitter and receiver prior to data transmission. This implies that electrically band-limited optical wireless communication (OWC) systems can make use of optimal channel partitioning or vector coding based multi-channel modulation (MCM) to achieve high throughput by mitigating the non-linearities arising from the optical and electrical channel. This paper proposes a pulse amplitude modulation (PAM) based DC-biased optical vector coding (DCO-VC) MCM scheme for OWC. The throughput performance of DCO-VC is evaluated and compared to the well known DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) over hybrid (line-of-sight and diffuse) and diffuse (non line-of-sight only) visible light communication (VLC) channels with additive white Gaussian noise. For the completeness of the VLC physical layer, the performance comparison is based on an uncoded and a forward error correction transmission mode using well-known convolutional codes with Viterbi decoder. The results show that the coded DCO-VC outperforms DCO-OFDM system by achieving up to 2 and 3 dB signal to noise ratio gains over hybrid and diffuse VLC channels, respectively.

Visible Light Communication (VLC) has emerged as an attractive alternative to radio frequency (RF) communication, due to cost-effectiveness and being license free. It has also proved its applicability in automotive applications, as an alternative and/or a complement to the traditional RF-based communications. We investigate the suitability of VLC in Intelligent Transportation Systems (ITS) and discuss its advantages in terms of safety enhancement and improved efficiency of the ITS. In this thesis, a VLC-based Vehicle-to-Vehicle (V2V) system in practical environments, considering both Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) paths are presented. The thesis investigates robust communication between a Light Emitting Diodes (LEDs) based VLC emitter and Photodiodes (PDs) based VLC receiver. For consideration of a V2V communication system, we consider transmitter on vehicle headlights and receivers on taillight making 2 _ 2 Multiple-Input-Multiple-Output (MIMO) communication link. A closed-form expression of the Channel Impulse Response (CIR) is derived and the effect of various channel parameters is analyzed. Optical-Orthogonal Frequency Division Multiplexing (O-OFDM) with adaptive modulation schemes is proposed for system improvement. Its performance is evaluated in terms of Inter Symbol Interference (ISI) mitigation, and data rate improvement. Moreover, the effect of sunlight on the V2V-VLC Two denoising schemes are proposed and evaluated as a solution to combat the effect of the solar irradiance on the VLC signal. Firstly, we use a differential receiver for denoising purposes followed by k-Nearest Neighbour (kNN) based adaptive _ltering algorithm, which is a supervised Machine Learning (MLE) technique. The shadowing effect is also studied. Moreover, an application of VLC in Foglet based ITS is described. The simulation validation of the VLC-based V2V system is performed under various environmental conditions and scenarios. Obtained results emphasize the suitability of VLC technology for automobile applications,.