OFDM-VLC System Research Articles

Study of PAPR mitigation in OFDM-VLC system by SCMA codebook design

Study of PAPR mitigation in OFDM-VLC system by SCMA codebook design

An efficient PCCM masking scheme for PAPR reduction and encryption in OFDM-VLC system

An efficient PCCM masking scheme for PAPR reduction and encryption in OFDM-VLC system

On the performance of delta sigma modulators for DCO-OFDM based NOMA visible light communication systems

The revolution of the solid-state lighting technology and the looming radio frequency (RF) spectrum crisis enabled the rapid evolution of visible light communication (VLC) in the recent times. To furnish contemporaneous illumination and communication, VLC relies on white light emitting diodes (WLEDs). However, the limited modulation bandwidth of WLEDs poses a threat to VLC as the achievable data rates are drastically minimized. Eventually, to enhance the achievable throughput, the pre-eminent way is to apply orthogonal frequency division multiplexing (OFDM) to a VLC system. Furthermore, a VLC system can also exploit non-orthogonal multiple access (NOMA) scheme to bestow with seamless services to the multiple users. However, much similar to the RF-based OFDM system, the OFDM-VLC system also inherits one of the serious disadvantages like the high peak to average power ratio (PAPR). In addition, the rapid fluctuations of the continuous time-domain signal amplitude in DC-biased optical OFDM (DCO-OFDM) results in much complicated design of the LED driver circuitry for driving the LED. Thus, to overcome such drawbacks, we incorporate delta-sigma modulators (DSM) to the NOMA-VLC system which is making use of DCO-OFDM, and we analyze its performance over VLC channel environment. The stunning advantage imparted by the proposed DSM-based DCO-OFDM-NOMA-VLC system is that the continuous amplitude of the time-domain transmitted signal is converted into two levels for driving the LED. Additionally, with the major goal to maximize the sum throughput of the proposed multiuser VLC system by taking into consideration both the user fairness as well as the intensity constraints, we derived the optimal values for the power allocation coefficients corresponding to the fair power allocation algorithm. Furthermore, the dynamically varying fair power allocation algorithm is compared with the fixed/static power allocation algorithm. The major contribution of this work is of two-fold: firstly, the proposed DCO-OFDM-NOMA-VLC system which is making use of DSM exhibits a remarkable reduction in PAPR when compared with the conventional system without the application of DSM, where the proposed system demonstrates a significant gain of 4.78 dB in terms of PAPR reduction. Secondly, from the simulated results it can affirmed that the proposed system not only achieves enhanced sum rates and better outage performance but also imparts a better bit error ratio (BER) performance corresponding to the far user.

CNN direct equalization in OFDM-VLC systems: evaluations in a numerical model based on experimental characterizations

CNN direct equalization in OFDM-VLC systems: evaluations in a numerical model based on experimental characterizations

A novel sampling frequency offset mitigation scheme based on rotated K-means clustering for OFDM-VLC system

Sampling frequency offset (SFO) between digital-to-analog converter (DAC) and analog-to-digital converter (ADC) will severely degrade the transmission performance of orthogonal frequency division multiplexing (OFDM) based visible light communication (VLC) system. In this paper, a novel SFO mitigation scheme based on rotated K-means clustering is proposed, which differs from traditional SFO compensation based on phase estimation and feedback. When SFO causes the constellation points to deviate from their original positions, this scheme can adaptively update the clustering centroids to achieve the correct symbol demapping without phase estimation and compensation. Experimental results indicate that after 3.5 m free-space transmission, the SFO tolerance of quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16-QAM) can reach ±130 and ±65 ppm with a bit error rate (BER) less than the hard-decision forward error correction (HD-FEC) threshold of 3.8e−3, respectively.

A Simplified Post Equalizer for Mitigating the Nonlinear Distortion in SiPM Based OFDM-VLC System

The silicon photomultiplier (SiPM) based orthogonal frequency division multiplexing (OFDM) system is a promising solution to realize both the longer distance and higher data rate in visible light communication (VLC). However, it suffers from nonlinear distortions induced by SiPM. The Volterra nonlinear equalization (VNLE) is commonly used at the receiver to compensate for the nonlinear distortions, but it has a huge implementation complexity. As an alternative, the memory polynomial based equalization (MPE) offers significantly reduced complexity but at the cost of degrading BER performance. In this paper, we propose and demonstrate a promising simplified VNLE equalizer for SiPM based OFDM-VLC systems according to SiPM's characteristics. Results show that the proposed equalizer outperforms the MPE in terms of BER and significantly reduces the computational complexity of the conventional VNLE. With the proposed equalization scheme, a data rate of 1.35Gbps has been achieved. To the best of the author's knowledge, this is the highest data rate achieved using SiPM in VLC with optical OFDM.

Modulation Classification Method Based on Clustering and Gaussian Model Analysis for VLC System

In the letter, a novel automatic modulation classification (AMC) method is proposed and experimentally demonstrated in orthogonal frequency division multiplexing (OFDM) visible light communication (VLC) system. For the proposed AMC method, the classification feature values are obtained by clustering and Gaussian model analysis. Then these classification feature values are used to classify the modulation format. In addition, the recognition accuracy at different optical signal-noise-ratio (OSNR) is investigated in OFDM-VLC system. The experimental results show that, for 4QAM, 16QAM, 32QAM, and 64QAM with the proposed method, it can be accurately recognized with 2000 symbols at OSNR of 4 dB, 11 dB, 13 dB, and 18 dB, respectively.

Comparison of interpolation-based sampling frequency offset compensation schemes for practical OFDM-VLC systems.

Sampling frequency offset (SFO) is an important issue in the orthogonal frequency-division multiplexing (OFDM)-based visible light communication (VLC) systems with low-cost analog-to-digital or digital-to-analog converters (ADCs/DACs). A digital interpolation or resampling filter can be used to effectively compensate the SFO. In such case, oversampling at the receiver ADC is required to mitigate the aliasing effect due to imperfect DACs and nonlinearity of visible light sources that cause extra frequency components inside/outside the OFDM signal spectrum. The oversampling factor (rate) is mainly determined by the order of the digital interpolation filter and nonlinear VLC links. The design of the OFDM-VLC receiver incorporating the digital interpolation filter is vital as it affects not only the transmission performance but also the complexity of digital signal processing (DSP). To evaluate the feasibility of the digital interpolation-based SFO compensation schemes for cost-sensitive VLC applications, in this paper, a real-time OFDM-VLC receiver incorporating the 2nd/3rd/4th order interpolation filters is experimentally demonstrated. An OFDM frame structure is designed for the synchronization including SFO estimation and compensation, in which the precision and latency of DSP are considered. On the basis of the real-time OFDM-VLC receiver, the comparison in the VLC transmission performance and DSP complexity between different interpolation-based SFO compensation schemes is discussed.

Predistortion and pre-equalization for nonlinearities and low-pass effect mitigation in OFDM-VLC systems.

The orthogonal frequency division multiplexing (OFDM) transmission is a promising candidate for visible light communication (VLC) applications. However, the nonlinearity in the optical power emitted by the high-power light-emitting diode (HPLED) as a function of current and temperature implies drastic OFDM-VLC performance degradation. The first part of this work experimentally confirms and models this degradation due to temperature in a white HPLED. The higher attenuation at high frequencies, which is inherent to the HPLED and which is accentuated by the effect of the intrinsic capacitance of the photodiode, is another factor of degradation due to the reduction in the signal-to-noise ratio (SNR) at the receiver for such frequencies. For the mitigation of these combined effects, we propose a predistortion and a digital pre-equalization scheme using a luminous feedback signal at the transmitter side. The VLC system is modeled so that the operating points are mathematically deduced and evaluated by simulations and by an experimental setup. By allowing the linearization of the transmitted light signal and the maintenance of a uniform SNR among all OFDM subcarriers, the performance improvement is confirmed in comparison with other schemes, such as a VLC system without predistortion, predistortion with fixed parameters, as well as a simple post-equalization.

Performance enhancement of LED-based indoor OFDM-VLC system using digital chaotic scheme

LED based visible light communication (VLC) has become a feasible technology for indoor high-speed access networks. Optical orthogonal frequency division multiplexing (O-OFDM) with high spectrum efficiency is often used to increase the data rate to overcome the limited bandwidth of LEDs. Due to the LED nonlinearity and high peak-to-average-power ratio (PAPR) of OFDM, the indoor broadcasting OFDM-VLC system suffers from not only the performance deterioration, but also the security issue. In this paper, we propose to use digital chaotic sequence pilot-assisted (CSPA) scheme to jointly improve the signal-to-noise-ratio (SNR) performance and the system security. The experimental results indicate that the proposed method can achieve 3 dB PAPR mitigation even up for OFDM 64-QAM signal and 2 dB SNR improvement. Meanwhile, the proposed digital CS offers a key space of ∼10106 for each OFDM symbol to guarantee the secure transmission.

3-D Localization With Multiple LEDs Lamps in OFDM-VLC System

Visible light communication (VLC)-based localization is a potential candidate for a wide range of indoor localization applications. In this paper, we propose a VLC architecture based on orthogonal frequency division multiplexing (OFDM) with multiple functionalities integrated into the same system, i.e., the 3-D receiver location, the control of the room illumination intensity, as well as the data transmission capability. In this paper, we propose an original methodology for LED power discrimination applying spatial optical OFDM (SO-OFDM) structure for position estimation. The hybrid locator initially makes a first estimate using a weighted angle-of-arrival (WAoA)-based locator, which is then used as the starting point of the recursive estimator based on the strength of the received signal. Hence, the first stage is deployed to increase the convergence probability, reducing the root-mean-square error (RMSE) and the number of iterations of the second stage. Also, a performance versus computational complexity comparative analysis is carried out with the parameter variations of these estimators. The numerical results indicate a decade improvement in the RMSE for every two decades of decrement of power noise on the receiver photodiode. The best clipping factor is obtained through the analysis of locator accuracy and transmission capacity for each simulated system. Finally, the numerical results also demonstrate effectiveness, robustness, and efficiency of the proposed architecture.

OFDM VLC System Based on Virtual Instrumentation and SDR

This paper covers our second version of visible light communication system, which was based on orthogonal-frequency division multiplexing. Whole platform is implemented in LabVIEW and is running on National Instruments software defined radios. Its design is thoroughly explained, and a number of measurements is presented. Certain limitations are described, and upgrade paths are mentioned as well.

A BIPCM Scheme Based on OCT Precoding for a 256-QAM OFDM-VLC System

A bit-interleaved polar-coded modulation (BIPCM) scheme based on orthogonal circulant matrix transform (OCT) precoding is proposed and experimentally demonstrated in an orthogonal frequency-division multiplexing (OFDM) visible light communication system. It exhibits the advantages of high reliability, low latency, and low computational complexity. To overcome the fading effect on a mapped bit-level, the scheme employs the Monte Carlo method to jointly design a polar code concatenated with 256-ary quadrature-amplitude modulation. In addition, OCT precoding is used to mitigate the frequency selective fading effect across OFDM subcarriers. The experimental results show that the system can achieve a net data rate of 343 Mb/s over 80-cm free-space transmission with a bit error rate below $1\times 10^{-3}$ . At the receiver, it is the number of complex multiplications is reduced by 33% in comparison with BIPCM using an optimized quadratic polynomial permutation interleaver.

An Enhanced Adaptive Scheme With Pairwise Coding for OFDM-VLC System

For a visible light communication (VLC) system, different modulation formats and coding schemes are considered as the effective way to improve system performance under the limited bandwidth of light emitting diode. In this letter, we propose and experimentally demonstrate an enhanced adaptive scheme with pairwise coding (PWC) for an orthogonal frequency-division multiplexing (OFDM)-VLC system. Due to its no coding overhead and low complexity, it can be used to enhance the performance of the OFDM-VLC system. Through pairing the good and bad subcarriers, the signal-to-noise ratio (SNR) imbalance of this pair subcarrier is mitigated. Hence, it can lower the required SNR for a certain bit error ratio (BER). In the enhanced adaptive scheme with PWC, the low-frequency subcarriers (SCs) are modulated by 16 quadrature amplitude modulation (16QAM), while the high-frequency SCs are modulated by 4QAM, and in the midst of them, 32QAM is used. The experimental results show that, it can achieve 1.1 dB Q 2 factor improvement compared with the conventional adaptive scheme and the BER can be up to 1.66×10 -5 using the proposed adaptive scheme with PWC.

Experimental Demonstration of a Real-Time gigabit OFDM-VLC system with a cost-efficient precoding scheme

We experimentally demonstrated a real-time laser-diode (LD) based orthogonal frequency division multiplexing (OFDM) visible light communication (VLC) system with a cost-efficient precoding scheme. The precoding scheme is based on Hadamard matrix and proposed for combating the fading effect of OFDM-VLC system. Compared with an orthogonal circulant matrix transform (OCT) precoding scheme, the proposed scheme can be realized without multiplier. In the experiment, the OCT scheme and a common pre-emphasis scheme are also implemented in the real-time OFDM-VLC system for comparison. The experimental results show that the effectiveness of the proposed scheme is as same as that of OCT scheme, and compared with the pre-emphasis scheme, the proposed scheme can make a better improvement to the system performance. And when the power of the light received after 3.5-m transmission is beyond 5-mW, by using 32-QAM mapping, the system with the proposed precoding scheme can achieve a data rate at 3.63-Gb/s with a bit-error-rate (BER) at below 3.8e−3.

Image secure transmission for optical orthogonal frequency-division multiplexing visible light communication systems using chaotic discrete cosine transform

A physical encryption scheme for orthogonal frequency-division multiplexing (OFDM) visible light communication (VLC) systems using chaotic discrete cosine transform (DCT) is proposed. In the scheme, the row of the DCT matrix is permutated by a scrambling sequence generated by a three-dimensional (3-D) Arnold chaos map. Furthermore, two scrambling sequences, which are also generated from a 3-D Arnold map, are employed to encrypt the real and imaginary parts of the transmitted OFDM signal before the chaotic DCT operation. The proposed scheme enhances the physical layer security and improves the bit error rate (BER) performance for OFDM-based VLC. The simulation results prove the efficiency of the proposed encryption method. The experimental results show that the proposed security scheme not only protects image data from eavesdroppers but also keeps the good BER and peak-to-average power ratio performances for image-based OFDM-VLC systems.

Secure Image Transmission over DFT-precoded OFDM-VLC systems based on Chebyshev Chaos scrambling

This paper proposes a physical layer image secure transmission scheme for discrete Fourier transform (DFT) precoded OFDM-based visible light communication systems by using Chebyshev chaos maps. In the proposed scheme, 256 subcarriers and QPSK modulation are employed. The transmitted digital signal of the image is encrypted with a Chebyshev chaos sequence. The encrypted signal is then transformed by a DFT precoding matrix to reduce the PAPR of the OFDM signal. After that, the encrypted and DFT-precoded OFDM are transmitted over a VLC channel. The simulation results show that the proposed image security transmission scheme can not only protect the DFT-precoded OFDM-based VLC from eavesdroppers but also improve BER performance.

Realization of OFDM modulation and demodulation for visible light communication based on FPGA

In order to ensure stable, correct and real-time high-speed transmission of indoor visible light communication (VLC), the key modulation and demodulation technologies of orthogonal frequency division multiplexing (OFDM) are studied in this paper. The time-domain synchronization, frequency synchronization and channel equalization of receiver are analyzed and optimized by utilizing short and long training preamble. Moreover, field programmable gate array (FPGA) development board (Xilinx Kintex-7) and Verilog hardware description language are used to realize the design of proposed OFDM-VLC system. Simulation and experiment both verify the feasibility of the hardware designs of this system. The proposed OFDM-based VLC system can process signal in real-time, which can be used in actual VLC application systems.

Efficient coding modulation and seamless rate adaptation for visible light communications

The past decade has witnessed a rapid development of VLC technologies. However, the spectral efficiency has to be improved and the robustness enhanced, especially in dynamic lighting conditions. This article proposes an analog rateless code (ARC) modulation scheme for VLC in a hybrid VLC-RF system. The ARC uses a variable-length low-density random projection matrix to map a block of bits into a virtually unlimited number of modulation symbols. The sender progressively transmits the symbols, which are jointly decoded at the receiver, until an acknowledgment of successful decoding is received. Both the protocol design and coding matrix generation are discussed. Simulations validate that our proposed scheme not only achieves the desired seamless rate adaptation, but significantly outperforms a traditional OFDM VLC system in spectrum efficiency. Furthermore, experimental results demonstrate the feasibility of the proposed ARC scheme in a VLC system.

Performance of color-independent OFDM visible light communication based on color space

In this paper, we propose an orthogonal frequency division multiplexing (OFDM)-based visible light communication (VLC) system that can be color independent by using a color-space-based modulation. Along with all of the promising advantages of OFDM, the proposed system will be applicable for all colors in the visible range. Through the simulation results, we show that the proposed OFDM-VLC system is robust to intersymbol interference (ISI) and a large peak-to-average power ratio (PAPR), and is also color independent.