OFDM-based Visible Light Communication Research Articles

OFDM-Based VLC Systems: A Systematic Review

Visible Light Communications (VLC) represents a new technology of wireless communications allowing high data rate, high-speed internet access, green and friendly communication system, especially for indoor users, where the use of Light Emitting Diodes (LEDs) is growing as a viable alternative to traditional illumination. Orthogonal frequency division multiplexing (OFDM) is a promising modulation format for optical wireless communication (OWC); however, precise channel estimation is required for synchronization and equalization. Moreover, one of the challenging issues for OFDM is its high Peak-to-Average Power Ratio (PAPR) due to the superposition of all subcarriers; therefore, the system requires a high linearity and dynamic range. This paper provides a systematic overview of OFDM-based VLC systems, highlighting the essential aspects of PAPR reduction and channel estimation techniques. Several technical challenges have been addressed to realize the full potential of OFDM-based VLC technology. Moreover, we provide new insights into the over-explored and under-explored areas, which lead us to identify open research problems of VLC based on OFDM. Concisely, this paper serves as a guide and a starting point for researchers willing to research VLC using OFDM.

Increasing the power and spectral efficiencies of an OFDM-based VLC system through multi-objective optimization.

The nonlinearity induced by light-emitting diodes in visible light communication (VLC) systems presents a challenge to the parametrization of orthogonal frequency division multiplexing (OFDM). The goal of the multi-objective optimization problem presented in this study is to maximize the transmitted power (superimposed LED bias-current and signal amplification) for both conventional and constant envelope (CE) OFDM while also maximizing spectral efficiency. The bit error rate (BER) metric is used to evaluate the optimization using the non-dominated sorting genetic algorithm II. Simulation results show that for a BER of 1×10-3, the signal-to-noise ratio (SNR) required decreases with the guard band due to intermodulation distortions. In contrast to SNR values of approximately 13 and 25dB achieved by traditional OFDM-based systems, the VLC system with CE signals achieves a guard band of 6% of the signal bandwidth with required SNR values of approximately 10.8 and 24dB for 4-quadrature amplitude modulation (QAM) and 16-QAM modulation orders, respectively.

An Adaptive Iterative Symbol Clipping Scheme for OFDM-Based Visible Light Communication

An Adaptive Iterative Symbol Clipping Scheme for OFDM-Based Visible Light Communication

A reduced PAPR hybrid OFDM visible light communication system

Orthogonal frequency division multiplexing (OFDM) is used by visible light communication (VLC) systems. Its main goal is to lessen inter-symbol interference's negative impacts. As a result, a lot of bandwidth and a high data rate are transmitted. Using OFDM-based VLC systems, nonetheless, have a high peak-to-average power ratio (PAPR). This research presents a new VLC system for indoor applications that reduces the PAPR while maintaining an acceptable bit error rate (BER). To achieve this, a hybrid pre-coding technique-based PAPR reduction solution is proposed; Vander-monde like matrix (VLM) combined with Gaussian matrix (GM). This technique takes advantage of both VLM and GM as a two stages for the signal to simultaneously reduce the PAPR and save the BER from damage. According to the results, the proposed solution (VLM in conjunction with GM) lowers the PAPR to 9.5 dB. Our system performs better when compared to other systems like discrete cosine transform (DCT), GM, VLM, DCT&GM, and original OFDM by 27%, 25%, 11%, 20%, and 34%, respectively.

Throughput improvement and PAPR reduction for OFDM-based VLC systems using an integrated STC-IMADJS technique

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.

Performance analysis of novel precoding matrix techniques for optical OFDM-based visible light communication systems

Visible Light Communication (VLC) exploits the renowned modulation scheme like orthogonal frequency division multiplexing (OFDM) to accomplish high data rate transmission. However, the optical OFDM system like DC biased optical OFDM (DCO-OFDM) is vulnerable to high peak to average power ratio (PAPR) which results in detrimental clipping distortion which in turn degrades the overall system performance. The limited dynamic range of the LEDs further agitates this issue. On these grounds, PAPR reduction techniques like precoding matrix schemes have been proposed for reducing the high amount of PAPR in DCO-OFDM system. In this paper, discrete Hartley Matrix transform (DHMT) precoded discrete Hartley transform (DHT)-based DCO-OFDM system is proposed for reducing PAPR. In addition, we comparatively investigate the PAPR performance of a new precoding technique like T- transform which is a hybrid combination of Walsh Hadamard transform (WHT) and Zadoff chu transform (ZCT) with other precoding matrix techniques like discrete cosine matrix transform (DCMT), discrete Fourier matrix transform (DFMT), Walsh Hadamard Matrix transform (WHMT) and DHMT. Furthermore, this paper derives the mathematical analysis corresponding to the time-domain signal formats for the precoded DCO-OFDM system which is exploiting complex Fourier signal processing and real trigonometric transform like DHT. From the simulated results, it can be surmised that when compared with other precoding techniques, DHMT precoded DHT-based DCO-OFDM system not only achieves a significant reduction in PAPR but also achieves a better bit error rate (BER) and spectral efficiency performance. Furthermore, less computational complexity is required to implement it.

BER performance analysis of an OFDM-based visible light communication system using DHT post-coding

BER performance analysis of an OFDM-based visible light communication system using DHT post-coding

Design and verification of SoC for OFDM-based visible light communication transceiver systems and integration with off-the-shelf analog front-end

In this paper, a System-on-Chip (SoC) design for Orthogonally Frequency Division Multiplexing (OFDM)-based Visible Light Communication (VLC) transceiver is presented. The VLC transceiver system comprises the physical (PHY) layer and analog front-end (AFE). The OFDM modulation was implemented in the PHY layer. We design the SoC-based PHY layer using the “reuse methodology”. In this methodology, the Intellectual Property (IP) cores do not necessarily need to be created from scratch as it can be obtained from a 3rd party. Using this methodology, it can increase our productivity during the designing process. This methodology is suitable for developing an OFDM system, especially in VLC system, that requires high complexity blocks. When the IP cores are not available from the 3rd party, they can be designed from scratch. We design the IP cores with the AXI4 protocol standard which is widely used in SoC design. Later, the OFDM system IP cores are integrated by using the AXI4-Stream protocol. In addition, the dual-core ARM Cortex-A9 processor is integrated into the OFDM system IP cores using the AXI4-Lite protocol. The transmitter (TX) and receiver (RX) applications run on Linux OS (Xilinux) can access the OFDM system IP cores with the memory–mapped I/O method. To guarantee the successful design, we have tested our SoC design with the off-the-shelf AFE transceiver integration in a real setting. The analog part for this work was created by available commercially components. Three modulation types were selected for the field test, i.e., BPSK, QPSK, and QAM-16. The maximum data rates of VLC system also have been investigated in a real-time as a proof of concept of the proposed SoC architecture.

Digital Pre-Equalization for OFDM-Based VLC Systems: Centralized or Distributed?

We propose and experimentally demonstrate a distributed digital pre-equalization (DPE) technique for orthogonal frequency division multiplexing (OFDM)-based bandlimited visible light communication (VLC) systems. In the VLC system applying distributed DPE, the subcarriers are divided into two bands, where the bandwidth and the power of each band can be flexibly adjusted to maximize the achievable data rate of the system. Hence, distributed DPE exhibits much higher tolerance against light-emitting diode (LED) nonlinearity than conventional centralized DPE. Experimental results verify the superiority of distributed DPE for OFDM-based bandlimited VLC systems. More specifically, a data rate of 976.6 Mbit/s is achieved by using distributed DPE, which corresponds to an achievable rate improvement of 25% in comparison to centralized DPE.

Joint Resource Allocation for a Novel OFDM-Based Multicolor VLC Network

In this letter, a joint subcarrier and power allocation scheme is proposed for an orthogonal frequency division multiplexing (OFDM) based multi-color visible light communication (VLC) network. Different from the conventional white-light VLC, red, green and blue (RGB) lights are used in the VLC network to transmit OFDM signals. The optimization problem is formulated to maximize the sum rate of the VLC network, which is then solved by an iterative solution algorithm based on the Lagrange multiplier method. Simulation results show that the multicolor VLC network may achieve higher sum rate than the conventional white-light VLC system.

PAPR reduction by combining clipping and piecewise linear companding for OFDM-based VLC systems

A scheme called clipping-piecewise linear companding (C-PLC) was proposed in this paper to address the problem of high clipping noise and peak-to-average power ratio (PAPR) in optical orthogonal frequency division multiplexing (O-OFDM) signal for visible light communication (VLC) systems. The clipping information of the signal could be retained by adding a suffix at its end, which could reduce the clipping noise and PAPR of the VLC system, thus limiting the dynamic range of the signal effectively. In addition, the retained clipping information could be recovered at the receiver, with which the bit error rate (BER) performance could be pronouncedly improved. Furthermore, PLC could map bipolar signals into unipolar signals suitable for VLC and effectively reduce the PAPR of the signals. Simulation results showed that C-PLC system has lower PAPR than that of direct-current biased optical-OFDM and μ-OFDM schemes, and it also demonstrates an improved BER performance. This work will be of good help for the research and development of VLC system.

Combined Envelope Scaling with Modified SLM Method for PAPR Reduction in OFDM-Based VLC Systems

Abstract Orthogonal frequency-division multiplexing technique (OFDM) has been adopted widely as a modulation technique for radio frequency (RF) and optical communication systems such as visible-light communication (VLC) due to its high spectral efficiency and low-complexity implementation. VLC-OFDM is recommended in 5 G mobile communication. However, VLC-OFDM suffer from the high peak to-average power ratio (PAPR). In this paper, a modified selective mapping (MSLM) method is applied to the proposed system followed by a new envelope scaling process for further reductions in PAPR of VLC-OFDM system. Simulation results show that the proposed method reduces the PAPR by about 6.8 and 1.7 dB comparing with the original signal and the traditional SLM with a number of rotation vector U = 8, respectively.

Resource Allocation and Interference Management Techniques for OFDM-Based VLC Atto-Cells

In this paper, a resource partitioning scheme combined with a new multi-carrier optical modulation technique for indoor visible light communication (VLC) system is proposed. In VLC systems, the coverage area is divided into multiple atto-cells. In each atto-cell, multiple LED arrays are used as access points (APs) serving the assigned users. The coverage area of APs might be overlapped to avoid service discontinuity for mobile users. The overlapped coverage zones result in co-channel interference (CCI). We develop a shared frequency reuse (SFR) technique combined with two resource allocation algorithms to minimize interference and maximize the system throughput. This technique divides the overall bandwidth into two parts: the shared and reused bands. The shared band serves the users in the interference area while the reused band serves users in the non-interfering area. Furthermore, we propose a new multi-carrier optical modulation technique called odd clipped optical-OFDM (OCO-OFDM). This technique applies the odd symmetry on the frequency-domain OFDM to enhance the spectral efficiency compared to the asymmetrical clipped optical OFDM (ACO-OFDM) which is currently used. Then we study and evaluate the system performance in terms of the signal-to-interference and noise ratio (SINR), total throughput, and the outage probability. The proposed system achieved total throughput of up to 800 Mbps with 40 dB SINR at the cell edge. Furthermore, the outage probability can be optimized to its minimum value when the receiver field-of-view (FOV) is taken by 40° when the minimum SINR is 10 dB.

Improving Availability and Confidentiality via Hyperchaotic Baseband Frequency Hopping Based on Optical OFDM in VLC Networks

The security in visible-light communication (VLC) networks has recently gained attention. This work presents a hyperchaotic baseband frequency hopping method based on optical orthogonal frequency-division multiplexing (Hyperchaos-BB-FH-OOFDM) that can enhance both confidentiality and availability in VLC networks. A four-dimensional hyperchaotic scheme is employed for chaotic mapping. The proposed method exploits the random feature of the input data and chaotic codes to improve the confidentiality against correlation and statistical attacks and to improve the availability against illumination, disguised, and noise jamming. Using the chaotic scheme, the bipolar real OFDM samples are exploited to create dynamic cypher keys and spreading codes that are updated at each frame throughout the entire session, leading to high security against malicious attacks. The proposed method employs a four-fold encryption approach that involves chaotic frequency/time-domain scrambling of OFDM subcarriers, chaotic phase scrambling of frequency-domain subcarriers, and chaotic spreading of the OFDM signals upon transmission. According to the results, in addition to enhancing the confidentiality and availability, the method supports multiplexing, reduces the peak-to-average-power ratio of the OFDM signal, and improves the bit error rate performance for OFDM-based VLC networks.

Enhanced performance of indoor VLC using anti-periodic asymmetrically clipped OFDM and multiple LEDS

Visible light communication (VLC) systems make use of the available LED lamps to realize a high spatial density of high-speed optical links superposed to their natural illumination function. Orthogonal frequency division multiplexing (OFDM) has been adopted for these intensity modulation/direct-detection optical channels. However, it suffers from low power efficiency or low spectral efficiency. In this paper, we aim to improve the performance of OFDM-based indoor VLC systems. By utilizing the principle of spatial summing, we propose an anti-periodic asymmetrically clipped OFDM scheme to make efficient use of both power and spectrum. In this scheme, the OFDM subcarriers are partitioned into multiple specific groups to form independent unipolar signals. These signals are simultaneously transmitted from different LEDs that are within the same light fixture and are summed in space before being detected by a conventional OFDM receiver. The computer simulation results show that the proposed approach can achieve lower PAPR and more robustness to the clipping distortion caused by the nonlinearities of LED leading to better bit error rate performance for the same spectral efficiency than that of the conventional DCO-OFDM and ACO-OFDM schemes do under both LOS and DOW channels.

Complex Signal Mapping for Improving Spectral Efficiency of Li-Fi Systems

Light fidelity (Li-Fi) systems based on the orthogonal frequency division multiplexing (OFDM) scheme have gained more attention in the communications circles, as a means to provide high spectral efficiency and ensure stricter data rate requirements for visible light communication (VLC) systems. However, common OFDM schemes employ Hermitian symmetry to obtain a real-valued signal which is necessary in intensity modulation and direct detection (IM/DD) optical systems, at the expense of doubling the required bandwidth. In this paper, a novel transmission scheme for an OFDM-based Li-Fi system is proposed to tackle the issue in question. A new approach to complex signal mapping (CSM), based on the pairing function method, has been developed for Li-Fi systems. It does not require Hermitian symmetry and, hence, saves about 50% of the required bandwidth. Unlike existing OFDM-based VLC approaches, the proposed scheme employs CSM to ensure a real and positive signal without Hermitian symmetry in order to fully utilize the bandwidth available to Li-Fi networks. Simulation results show that the proposed scheme significantly outperforms other systems in terms of spectral efficiency. The CSM-OFDM based Li-Fi system also achieves a good peak-to-average power ratio (PAPR) reduction with acceptable bit-error-rate (BER) performance, compared to conventional approaches.

Modelling the OFDM-based PHY Layer in SoC for Visible Light Communication

In this paper, we report a System-on-Chip (SoC) architecture for OFDM-based Visible Light Communication (VLC). The OFDM block was implemented as VLC PHY layer. The OFDM block comprises of transmitter and receiver. In transmitter block, there are Reed-Solomon encoder, modulator, IFFT, and preamble generator. While in receiver block, there are Reed-Solomon decoder, demodulator, FFT, and synchronizer. In SoC, these blocks are designed as IP cores. The industry standard AXI4-Stream protocol was used for data exchange between IP cores. The OFDM model in SoC was verified by comparing with a MATLAB simulation.

Image transmission in an OFDM VLC system using symbol scrambling and chaotic Walsh-Hadamard precoding

An image secure transmission scheme combining symbol scrambling and chaotic Wahsh-Hardmard precoding is proposed in orthogonal frequency division multiplexing (OFDM)-based visible light communication (VLC) system. In the proposed scheme, a two-dimensional (2D) logistic-sine-coupling map (LSCM) is employed to generate two chaotic sequences. One is used to scramble the 16 quadrature amplitude modulation (QAM) symbols, and the other is used to scramble the rows of standard Walsh-Hadamard transform (WHT). The simulation results show that the proposed scheme can not only reduce the peak-average-power ratio (PAPR) but also achieve the image secure transmission over OFDM-based VLC systems.

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.

OFDM-based visible light communication with rotated polarity modulation aided complex color shift keying

High-rate techniques, such as optical orthogonal frequency division multiplexing (OFDM) and color shift keying (CSK), have been proposed for visible light communication (VLC). To fully exploit their advantages, in this Letter, we design a modulation scheme called rotated polarity modulation (RPM) aided complex CSK (CCSK) for OFDM-based VLC systems and derive its theoretical bit error rate and an optimal scaling factor. Analytical and simulation results show that in comparison to the existing schemes, the new RPM-CCSK-OFDM system offers an improved link performance and data rate under a modest complexity. It can also be applied to VLC systems equipped with different types of LED devices, thus enabling flexible deployments.