Performance Enhancement of Secure Image Transmission Over ACO-OFDM VLC Systems Through Chaos Encryption and PAPR Reduction

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.

One of the primary challenges faced by visible light communication (VLC) systems employing optical orthogonal frequency division multiplexing is the peak-to-average power ratio (PAPR). This study is dedicated to designing, simulating, and evaluating bit error rate (BER) and PAPR reduction methods tailored for the VLC broadcasting system. The asymmetric clipped optical orthogonal frequency division multiplexing (ACO-OFDM) scheme is highlighted in this work for its impressive performance. Therefore, the proposed PAPR mitigation methodologies applied to ACO-OFDM. The proposed PAPR reduction strategy involves 5 distinct precoding methodologies. The PAPR was mitigated by 3.485 dB after applying the DST precoding methodology. Still, the WHT precoding methodology can achieve PAPR reduction by 1.131 dB, without BER performance degradation, with respect to the conventional ACO-OFDM system. Furthermore, the work addresses another challenge in VLC systems: the bit error rate (BER). This is accomplished by introducing approaches to Time Domain Noise Cancelation and Frequency Domain Noise Cancelation (FDNC). The BER performance of these 2 receiver models is nearly the same. The simulation results indicate the system performance enhancement after applying noise cancellation approaches by 1.65 dB at the 4-QAM modulation scheme and 2.97 dB at the 1024-QAM modulation scheme. The 16-QAM modulation scheme, after applying DST and WHT methodologies alongside noise cancellation approaches, can enhance both PAPR by 20.83% and 6.76%, but the Eb/N0 performance enhancement by 10.10% and 14.64%, respectively. Additionally, the effectiveness and validity of the proposed schemes are verified by comparing them with relevant literature reviews on PAPR reduction techniques and selecting an optimal choice among them.

Visible Light Communication (VLC) systems are favoured for numerous applications due to their extensive bandwidth and resilience to electromagnetic interference. This study delineates various constructions of Optical Orthogonal Frequency Division Multiplexing (O-OFDM) approaches employed in VLC systems. Various factors are elaborated within this context to ascertain a more effective O-OFDM approach, including constellation size, data arrangement and spectral efficiency, power efficiency, computational complexity, bit error rate (BER), and peak-to-average power ratio (PAPR). This paper seeks to assess these approaches’ BER and PAPR performance across varying modulation orders. Regrettably, in VLC systems based on OFDM methodology, the superposition of multiple subcarriers results in a high PAPR. Therefore, this study aims to diminish the PAPR in VLC systems, enhancing system performance. We propose a non-distorting PAPR reduction technique, namely the Vandermonde-Like Matrix (VLM) precoding technique. The suggested technique is implemented across various O-OFDM approaches, including DCO-OFDM, ADO-OFDM, ACO-OFDM, FLIP-OFDM, ASCO-OFDM, and LACO-OFDM. Notably, this method does not affect the system’s data rate because it does not require the mandatory transmission of side information. Furthermore, this technique can decrease the PAPR without impacting the system’s BER performance. This study compares the proposed PAPR reduction technique against established methods documented in the literature to evaluate their efficacy and validity rigorously.

SummaryThe application of orthogonal frequency division multiplexing (OFDM) in a visible light communication (VLC) system increases the peak‐to‐average power ratio (PAPR) of the system. Owing to high PAPR, the intrinsic nonlinearity of LED is an important issue in an asymmetrically clipped DC‐biased optical OFDM (ADO‐OFDM) system. In this paper, a hybrid scheme is proposed to reduce the PAPR as well as to mitigate the nonlinearity in an ADO‐OFDM system. The proposed method is a combination of two ADO‐OFDM formats: precoded ADO‐OFDM and μ‐ADO‐OFDM. The preprocessing of the input using a predetermined matrix (PM) in the precoder relieves the need for a handshake at the receiver. The compression of the peak values and enhancement of low amplitudes of the precoded signal in the time domain yield a low PAPR of 2.4 dB only. Besides PAPR reduction, the union of precoder and compander boosts the bit error rate (BER) performance of the traditional ADO‐OFDM system for μ≤128. The combination of precoder with compander decreases the power requirements for high bit rate transmission for a reference BER of 10−3. In this work, nonlinearity is quantified in terms of error vector magnitude (EVM) in percent. The hybrid scheme shows an EVM of 17.23% for 0 dB input backoff power (IBO) much less than 66.4% EVM for a simple ADO‐OFDM system. In addition to low PAPR and mitigation of nonlinearity, the proposed method shows the improvement in power spectral density (PSD) of the system.

The high peak to average power ratio (PAPR) was one of the main factors affecting the performance in visible light communication (VLC) system, which was based on the orthogonal frequency division multiplexing (OFDM) technology. This paper analyses the PAPR probability distribution of the OFDM signal in VLC system. In order to reduce the OFDM signal PAPR in VLC system, the Partial Transmit Sequence (PTS) method was modified, which was suitable for transmission in VLC system, and was combined with Discrete fourier transform spread (DFTS) to further reduce the optical OFDM signal PAPR. The simulation results show that, the PAPR of the system is reduced about 3.5dB, 2.7dB, 1.2dB comparing with the original signal, DFTS or PTS method used alone. With increase of system complexity, the method with DFTS combined with PTS has a better PAPR suppression performance.

A joint algorithm, integrating selective mapping (SLM) and restorable clipping (RC), is proposed for the direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) and visible light communication (VLC) system to reduce the nonlinearity impacts of light-emitting diode (LED) aggravated by high peak-to-average power ratio (PAPR) and DC-bias. The performance of DCO-OFDM VLC system is analyzed and discussed with different techniques of LED nonlinearity alleviation. The simulation results show that compared to the original DCO-OFDM VLC system, the system with the proposed scheme can achieve about 4.8 dB improvement of PAPR reduction and 7 dB improvement of bit error rate (BER) performance. The reason is that the signals acquiring the desired shape in LED linear region can be recovered correctly without distortion induced by LED nonlinearity. It is demonstrated that the proposed SLM-RC technique effectively reduces not only PAPR but also the impacts of LED nonlinearity without BER deterioration.

Visible Light Communications (VLC) is a promising communication technology designed to serve as a supplemental system to radio frequency communications for many demanding applications. VLC employs optical orthogonal frequency division multiplexing (O-OFDM) techniques to achieve higher data rates and resist intersymbol interference. Among these, asymmetrically clipped O-OFDM (ACO-OFDM) stands out as one of the most power-efficient and high-performing methods for VLC. However, like other O-OFDM techniques, ACO-OFDM encounters the challenge of a high peak-to-average power ratio (PAPR). VLC utilizes light-emitting diodes (LEDs) for data transmission at the transmitter and photodiodes (PDs) for data reception at the receiver. However, the high PAPR issue can drive LEDs to operate in their nonlinear region, reducing system performance and potentially causing LED damage or burnout. The paper aims to alleviate the high PAPR issue by proposing a hybrid combination of precoding technique and various nonlinear companding techniques. Compared to the standard ACO-OFDM, the proposed methodologies can reduce the PAPR issue by 5.5796 dB without a bit error rate (BER) degradation. The paper also aims to improve another aspect of the BER performance of ACO-OFDM. The paper proposes two noise cancellation receiver models to enhance the performance by 2.275 dB compared to standard ACO-OFDM to attain the same BER performance. The proposed PAPR reduction methodology with noise cancellation receiver model can achieve PAPR reduction by 6.0057 dB and enhanced performance by -0.309 dB to achieve the BER performance relative to standard ACO-OFDM. This paper systematically evaluates the proposed PAPR reduction approach by comparing it with established methods from the literature, ensuring a comprehensive assessment of its effectiveness and reliability.

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.

Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) has been proposed in visible light communication (VLC) systems to overcome the dc-biased optical OFDM power consumption issue at the cost of the available electrical spectral efficiency. Due to the implementation of inverse fast Fourier transform, all the optical OFDM schemes including ACO-OFDM suffer from large peak-to-average power ratio (PAPR), which degrades the performance in VLC systems as the light-emitting diodes used as the transmitter have a limited optical power-current linear range. To address the PAPR issue in ACO-OFDM, we introduce a unipolar-pulse amplitude modulation frequency division multiplexing by adopting the single carrier frequency division multiple access (SC-FDMA). This is achieved by considering a PAM as an SC-FDMA data symbol and inserting a conjugate copy of the middle and first SC-FDMA FFT output subcarriers after the middle and last subcarriers, respectively. Simulation results show that, for the proposed scheme, the PAPR is 3.6 dB lower compared with ACO-OFDM. The PAPR improvement is further analyzed with the simulation results demonstrating that the proposed scheme offers 2.5 dB more average transmitted power compared to ACO-OFDM.

In this paper, the direct current (DC)-biased optical orthogonal frequency division multiplexing (DCO-OFDM) visible light communication (VLC) system using modified μ-law companding is modeled and investigated. The simulation results reveal that the high peak to average power ratio (PAPR) induced by multi-carrier modulation (MCM) and DC bias, can aggravate signal distortion that is caused by the nonlinear characteristic of light emitting diode (LED). Thus, a pre-distortion method based on modification of μ-law companding is proposed for DCO-OFDM VLC system to resolve this problem. With the proposed method, the system can achieve a good performance of PAPR reduction and bit error rate (BER), compared to the original DCO-OFDM VLC system. It is demonstrated that the modified μ-law companding is appropriate to alleviate LED nonlinearity without degradation of the signal quality in DCO-OFDM VLC system.

In visible light communication (VLC), intensity modulation with direct detection (IM/DD) based on DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) is used to transfer data at a high rate. Because OFDM signals are modulated using IM/DD, the peak of the transmitted signals is scaled up, resulting in a high peak-to-average power ratio (PAPR). In this article, the Walsh–Hadamard transform (WHT) is used as a precoder for discrete Hartley transform (DHT) to decrease the PAPR and the DC bias and achieve a good bit error rate (BER) performance in such a system. PAPR reduction results from the decrease of superposition of the transmitted signals owing to the use of WHT as a precoder. The proposed scheme and conventional DCO-OFDM indoor VLC system based on discrete Hartley transform (DHT) are compared to assure the new system’s benefits and efficiency.

Orthogonal frequency-division-multiplexing (OFDM) technology is widely used in visible light communication (VLC) to achieve high data rate transmission. However, the traditional direct-current (DC)-biased optical OFDM (DCO-OFDM) VLC systems suffer from the high peak-to-average power ratio (PAPR) which causes signal clipping distortion, and, thus, performance degradation. Furthermore, severe high-frequency fading due to the limited system bandwidth results in poor bit error rate (BER) performance. Precoding matrix (PM) techniques have been proposed to enhance the performance of VLC OFDM transmission, but a little or no work has been carried out in investigating the theory of PM used in OFDM VLC systems. In this paper, we aim to reveal the theory of PM-DCO-OFDM for a VLC system. To figure out the intrinsic laws of a PM method, we investigate the principles of PAPR reduction, clipping distortion optimization, and signal-to-noise ratio (SNR) distribution equalization. Based on the analysis of PAPR, we theoretically proved the simplicity of PM as a method to reduce the possibility of high PAPR by improving the autocorrelation performance of input symbols. The clipping distortion could be improved due to the reduction of high PAPR. Moreover, the relatively uniform SNR distribution can be achieved by PM through equalizing the clipping and channel noise, which is beneficial to improve the BER performance in high-frequency constrained systems. However, the PM method used in a DCO-OFDM VLC system should consider the transmitting power, modulation format, and transmission distance as a whole to achieve the transmission performance improvement. The simulation results demonstrate the complementary cumulative distribution function of PAPR can be reduced ∼3 dB, while the performance of clipping distortion power and clipping error probability are significantly improved. Furthermore, experiment is carried out with results showing that the PM method can improve the BER performance in the case that VLC OFDM transmission has enough transmitting power, but with the low transmitting power, the PM also can damage the BER performance. The simulation and experiment results are consistent with our theoretical analysis.

Efficient n-M-PAWM hybrid modulation scheme for high data transmission in visible light communication system

Layered asymmetrically clipped optical orthogonal frequency division multiplexing (LACO-OFDM) has been proposed for improving the spectral efficiency of conventional asymmetrically clipped optical OFDM. Multiple base layers that are orthogonal in the frequency domain are sequentially superimposed to form LACO-OFDM, where each superimposed layer fills the empty subcarriers left by the previous layer. As our contribution, the bit error ratio (BER) considering the effect of thermal noise, clipping distortion, inter-layer interference, and the bit rate difference between layers is analysed in this paper. Since the BER performance of LACO-OFDM is closely related to its peak-to-average power ratio (PAPR) distribution, we also provide the analytical expression of the PAPR distribution in this paper, which quantifies how the number of layers in LACO-OFDM reduces the PAPR. As a further advance, we propose a tone-injection aided PAPR reduction design for LACO-OFDM, which in turn improves the BER performance. Simulations are provided for verifying both the analytical BER performance and the PAPR distribution of LACO-OFDM. The results show that the expressions derived match well with the simulations. Furthermore, the PAPR reduction method proposed attains a 5 dB PAPR reduction at the $10^{-3}$ probability-point of the complementary cumulative distribution function, as well as a better BER performance than the original LACO-OFDM scheme.

The performance of indoor visible light communication (VLC) systems using a direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) scheme is investigated in this paper. The impact of nonlinearity of Light Emitting Diode (LED) and its beam angle on the VLC system performance is studied. We later analyze the effect of modulation order, number of subcarriers, signal scaling and biasing operation on the peak to average power ratio (PAPR) which is a major issue in OFDM based VLC system. Simulation results show that the bit error rate (BER) decreases as the degree of nonlinearity increases and a better BER can be achieved as the LED behavior approaches linear model. In addition, it is shown that reducing the QAM order or increasing the number of subcarriers may reduce the effect of the LED nonlinearity, thus improving the BER performance of the VLC system. Moreover, it is demonstrated that PAPR is higher for a large number of subcarriers and modulation order. Finally, the PAPR of the visible light OFDM system can significantly be reduced by employing the signal scaling combined with biasing operation.