Spread Orthogonal Frequency Division Multiplexing Research Articles

Orthogonal Circulant Multiplexing for Bandwidth- Limited Direct-Detected Optical Communication Systems

We propose and investigate a novel orthogonal circulant multiplexing (OCM) technology for bandwidth-limited direct detection (DD) optical systems. We analytically derive that any OCM, i.e. using any orthogonal circulant matrix for multiplexing, can redistribute the noise uniformly across the subcarriers. However, the distribution of inter-symbol interference (ISI) and inter-carrier interference (ICI) strongly depends on the design of OCM. The previously proposed orthogonal chirp division multiplexing (OCDM), although showing better ISI/ICI tolerance than discrete-Fourier-transform spread (DFT-S) orthogonal frequency division multiplexing (OFDM), is a kind of OCM with poorer performance. We propose and analytically reveal that OCM based on chirp-like polyphase sequence (CLPS), general chirp sequence (GCS), sparse CLPS (SCLPS), and sparse GCS (SGCS) can achieve flatter ISI/ICI distribution across subcarriers and so better performance than OCDM in bandwidth-limited DD systems. The optimal parameter vector of the E-parameter CLPS is a Zadoff-Chu sequence while the parameter α in GCS should be larger. The optimal performance can be achieved by either CLPS (or GCS) using a larger E (or α) or SCLPS (or SGCS) with optimized sparsity. ∼110Gbit/s experiments using Mach-Zehnder modulator or electro-absorption modulator and receiver of 10-GHz photodiode or 8-GHz avalanche photodiode are conducted. The results agree with the theory and show that the proposed OCM outperforms conventional OFDM, DFT-S OFDM, and OCDM.

Performance comparison of single-carrier and multi-carrier waveforms over terahertz wireless channels

Terahertz (THz) wireless communication has been recognized as a powerful technology to meet the ever-increasing demand of ultra-high rate services. In order to achieve efficient and reliable wireless communications over THz bands, it is extremely necessary to find an appropriate waveform for THz communications. In this paper, performance comparison of various single-carrier and multi-carrier waveforms over THz channels will be provided. Specifically, first, a system model for terahertz communication is briefly described, which includes amplifier nonlinearity, propagation characteristic, phase noise, etc. Then, the transceiver architectures related to both single-carrier and multi-carrier waveforms are presented, as well as their corresponding signal processing techniques. To evaluate the suitability of the waveforms, key performance metrics concerning power efficiency, transmission performance, and computational complexity are provided. Simulation results are provided to compare and validate the performance of different waveforms, which demonstrate the outstanding performance of Discrete-Fourier-Transform spread Orthogonal Frequency Division Multiplexing (DFT-s-OFDM) to THz communications when compared to Cyclic Prefix-OFDM (CP-OFDM) and other single-carrier waveforms.

A Novel PAPR Reduction Scheme for Low-Cost Terminals in 6G

This paper presents a low peak-to-average power ratio (PAPR) modulation scheme and demodulation method for low-cost terminals in sixth-generation (6G), which is called one plus delay (1 + D) pi/2(N + 1) BPSK. Explicitly, the modulation scheme is first generated based on pi/2 BPSK, then proceeded by interpolation and (1 + D) transformation. Simulation results show that the proposed (1 + D) pi/2(N + 1) BPSK scheme has lower PAPR and smaller out-of-band leakage in discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM). Moreover, better performance can be attained by increasing the value of N. Finally, similar block error ratio (BLER) performance can be obtained at the same spectral efficiency of the conventional pi/2 BPSK scheme.

FDSS-Based DFT-s-OFDM for 6G Wireless Sensing.

Integrated sensing and communications (ISAC) is emerging as a key technology of 6G. Owing to the low peak-to-average power ratio (PAPR) property, discrete Fourier transform spread orthogonal frequency-division multiplexing (DFT-s-OFDM) is helpful to improve the sensing range and suitable for high-frequency transmission. However, compared to orthogonal frequency-division multiplexing (OFDM), the sensing accuracy of DFT-s-OFDM is relatively poor. In this paper, frequency-domain spectral shaping (FDSS) is adopted to enhance the performances of DFT-s-OFDM including sensing accuracy and PAPR by adjusting the correlation of signals. Specifically, we first establish a signal model for the ISAC system, followed by the description of performance indicators. Then, we analyze the influence of amplitude fluctuation of frequency domain signals on sensing performance, which shows the design idea of FDSS-enhanced DFT-s-OFDM. Further, a FDSS-enhanced DFT-s-OFDM framework is introduced for ISAC, where two types of FDSS filters including a pre-equalization filter and an isotropic orthogonal transform algorithm (IOTA) filter are designed. The simulation results show that the proposed scheme can obtain about 4 dB performance gain in terms of sensing accuracy over DFT-s-OFDM. In addition, FDSS-enhanced DFT-s-OFDM can significantly reduce PAPR and improve the power amplifier efficiency.

Sensing Integrated DFT-Spread OFDM Waveform and Deep Learning-Powered Receiver Design for Terahertz Integrated Sensing and Communication Systems

Terahertz (THz) communications are envisioned as a key technology of next-generation wireless systems due to its ultra-broad bandwidth. One step forward, THz integrated sensing and communication (ISAC) system can realize both unprecedented data rates and millimeter-level accurate sensing. However, THz ISAC meets stringent challenges on waveform and receiver design to fully exploit the peculiarities of THz channel and transceivers. In this work, a sensing integrated discrete Fourier transform spread orthogonal frequency division multiplexing (SI-DFT-s-OFDM) system is proposed for THz ISAC, which can provide lower peak-to-average power ratio than OFDM and is adaptive to flexible delay spread of the THz channel. Without compromising communication capabilities, the proposed SI-DFT-s-OFDM realizes millimeter-level range estimation and decimeter-per-second-level velocity estimation accuracy. In addition, the bit error rate (BER) performance is improved by 5 dB gain at the 10°3 BER level compared with OFDM. At the receiver, a deep learning based ISAC receiver with two neural networks is developed to recover transmitted data and estimate target range and velocity, while mitigating the imperfections and non-linearities of THz systems. Extensive simulation results demonstrate that the proposed deep learning methods can realize mutually enhanced performance for communication and sensing, and is robust against Doppler effects, phase noise and multi-target estimation.

Negatively Biased Solar Cell Optical Receiver for Underwater Wireless Optical Communication System With Low Peak Average Power Ratio

Charging batteries in underwater scenarios is generally very expensive and impractical, and solar cell (SC)-based underwater simultaneous lightwave information and power transfer (SLIPT) systems are a powerful solution. However, silicon SC receiver devices have limited bandwidth and are prone to deep signal-to-noise (SNR) degradation during underwater light fading effects. For these problems, this manuscript proposes a negative-biased SC optical receiver scheme to increase the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-3$</tex-math></inline-formula> dB bandwidth of silicon SC from 440 kHz to 780 kHz. For the deep fading of SNR caused by various degradation effects in the water environment, a low peak average power ratio (PAPR) discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) modulation scheme is employed to counteract the deep fading phenomenon in the system. Achieved a communication rate of 15.2 Mbps in a 60 cm underwater environment with a fading factor of 0.403 and a bit error rate (BER) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1.59\times 10^{-3}$</tex-math></inline-formula> under perturbation. Also, the performance of DFT-S-OFDM and orthogonal frequency division multiplexing (OFDM) modulation systems in water environments with different turbidity (absorption characteristics and scattering) and presence of disturbances are compared separately, and the DFT-S-OFDM system is more robust. Finally, we complete the energy harvesting during the communication process, and the experiments show that the total battery power efficiency of the energy harvesting system can be increased by 1.87 times under the white light-emitting diode (LED) continuous irradiation for three hours.

2×2 MIMO Equalizer Enabled Transmitter Side IQ Imbalance Compensation for Optical Single Sideband Direct Detection System

Recently, optical single sideband (SSB) based direct detection (DD) has been considered as a promising candidate for inter data center interconnects (inter-DCIs). Kramers-Kronig (KK) receiver is always applied to eliminate the signal-to-signal beating interference (SSBI) caused by the square law-detection of a single-ended photodiode (PD) in SSB DD system. The electro-to optical (E/O) conversion of the complex signal can be realized by IQ modulator (IQM). However, IQ imbalance exists at the transmitter since the in-phase and quadrature-phase ports of IQM are driven by the real and imaginary parts of the signal, respectively. In this paper, we show the theoretical analysis of the transmitter side (Tx-side) IQ imbalance includes time delay, amplitude mismatch and phase mismatch. Tx-side IQ imbalance will seriously deteriorate the system performance. To deal with the impairment caused by Tx-side IQ imbalance, a 22 real-value multiple-input multiple-output (MIMO) equalizer is proposed and implemented, and the system with the impact of these three factors are investigated in simulation, respectively. Besides, a transmission of 180 Gb/s/ discrete Fourier transform spread (DFT-S) orthogonal frequency division multiplexing (OFDM) signal over 80-km single mode fiber (SMF) is experimentally demonstrated with bit error rate (BER) below the soft-decision forward error correction (SD-FEC) threshold of 210-2 enabled by the proposed 22 MIMO equalizer.

Phase Noise Resilient Three-Level Continuous-Phase Modulation for DFT-Spread OFDM

In this paper, a novel waveform with low peak-to-average power ratio (PAPR) and high robustness against phase noise (PN) is presented. It follows the discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM) signal model. This scheme, called 3MSK, is inspired by continuous-phase frequency shift keying (CPFSK), but it uses three frequencies in the baseband model – specifically, 0 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm f_{symbol}/4$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{symbol}$ </tex-math></inline-formula> is the symbol rate – which effectively constrains the phase transitions between consecutive symbols to 0 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm \pi /2$ </tex-math></inline-formula> rad. Motivated by the phase controlled model of modulation, different degrees of phase continuity can be achieved, allowing to reduce the out-of-band (OOB) emissions of the transmitted signal, while supporting receiver processing with low complexity. Furthermore, the signal characteristics are improved by generating an initial time-domain constant envelope signal at higher than the symbol rate. This helps to reach smooth phase transitions between 3MSK symbols, while the information is encoded in the phase transitions. Also the possibility of using excess bandwidth is investigated by transmitting additional non-zero frequency bins outside the active frequency bins of the basic DFT-s-OFDM model, which provides the capability to greatly reduce the PAPR. The most critical tradeoffs of the oversampled schemes are that improved PAPR is achieved with the cost of somewhat reduced link performance and, in case of excess band, also the spectrum efficiency is reduced. Due to the fact that the information is encoded in the phase transitions, a receiver model that tracks the phase variations without needing reference signals is developed. To this end, it is shown that this new modulation is well-suited for non-coherent receivers, even under strong phase noise (PN) conditions, thus allowing to reduce the overhead of reference signals. Evaluations of this physical-layer modulation and waveform scheme are performed in terms of transmitter metrics such as PAPR, OOB emissions and achievable output power after the power amplifier (PA), using a practical PA model. Finally, coded radio link evaluations are also provided, demonstrating that 3MSK has a similar bit error rate (BER) performance as that of traditional quadrature phase-shift keying (QPSK), but with significantly lower PAPR, higher achievable output power, and the possibility of using non-coherent receivers.

Pilot Symbol Aided Channel Estimation for OCDM Transmissions

Pilot-aided channel estimation allows the receiver to acquire channel state information (CSI) for each multicarrier block by multiplexing data and pilot symbols in the same block, as long as they can be decoupled. This work proposes several frequency-domain pilot multiplexing techniques to enable independent channel estimation and detection at the receiver for orthogonal chirp division multiplexing (OCDM) transmissions in frequency-selective channels. Analysis shows that each of the proposed schemes is able to achieve the mean squared error (MSE) lower bound for channel estimation and has greater spectral efficiency than the existing schemes for OCDM and chirp spread orthogonal frequency division multiplexing (OFDM).

Generation of faster-than-Nyquist coherent optical DFT-spread OFDM signals with high-baud and high-order modulations

In this paper, we successfully demonstrate the generation and reception of faster-than-Nyquist (FTN) orthogonal frequency-division multiplexing (OFDM) signals with coherent detection. We can improve the spectrum efficiency by using higher order QAMs. However, we believe that the realization of super-Nyquist channel has the following advantages to improve spectral efficiency: Firstly, when we use higher order modulation, the requirements for equipment will be increased, such as the linearity of the modulator. Secondly, flexibility. The signal compression ratio can be arbitrarily set within the maximum compression ratio in our experiment. However, if we increase the modulation order, it can only be an integral multiple of 2, such as 4QAM to 8QAM, which can’t fully and effectively use the channel resources. In the FTN OFDM transmission system, frequency shaping is realized by a delay-and-add filter (DAF) at the transmitter to ensure the energy of signal is concentrated at low frequencies, which will make the OFDM much more robust to strong filtering effect to some extent. We generate a quadrature phase-shift keying OFDM (QPSK-OFDM) signal with equivalent baud rate (In this paper, the generation of FTN signal is in the frequency domain since we used M-point DFT and N-point IDFT while M is greater than N. In other words, the high-frequency parts are discarded to increase spectrum efficiency. Hence, we use “equivalent baud rate” instead of a simple “baud rate”) of 100–120 Gbaud, which is much higher than the sampling rate (80 GSa/s) of digital-to-analog converter (DAC). With this FTN Discrete-Fourier transform spread (DFT-spread) OFDM signal generation technique, we achieve the highest equivalent baud rate (120 GBaud) QPSK-OFDM signal generation and transmission over 80 km single mode fiber (SMF) with bit error rate (BER) under soft-decision forward-error-correction (SD-FEC) limitation of 2.4 × 10−2. We also investigate the generation and reception of 32 Gbaud FTN 16-ary quadrature-amplitude modulation OFDM (16QAM-OFDM) with coherent detection to achieve higher spectrum efficiency in this paper. The experimental results show that there is negligible optical signal to noise ratio (OSNR) penalty when 32 Gbaud FTN DFT-spread 16QAM-OFDM is compressed and transmitted within 28 GHz bandwidth with the BER at 2.4 × 10−2 in optical back to back (OBTB).

PAPR reduction using twin symbol hybrid optimization-based PTS and multi-chaotic-DFT sequence-based encryption in CP-OFDM system

Orthogonal frequency division multiplexing (OFDM) is considered as one of the most significant transmission methodologies of the recent past. Moreover, it permits easy demodulation and modulation. To find the new OFDM-based waveform to be used in fifth generation which is one of the foremost open issues for wireless networks of the next generation. In addition, the OFDM is affected by the maximum Peak-to-Average Power Ratio (PAPR). In order to minimize these problems, this paper proposed a Twin Symbol Hybrid Optimization used as a basis of the Partial Transmit Sequence (TSHO-PTS) method of Cyclic Prefix-OFDM (CP-OFDM). This CP-OFDM achieves the requirements of 5G telecommunication standards. Moreover, the exhaustive searching for optimal phase factors might increase the computational cost of PTS. To beat this problem, a hybrid version of slap swarm optimization (SSO) and Bald Eagle Search (BES) algorithm is introduced to investigate the phase factor optimally by the PTS method. Digital chaotic sequences are used to ensure the physical layer security during the data transmission scheme for the Discrete Fourier Transform Spread OFDM (DFT-S-OFDM) subcarrier allocation. The simulation takes place in the MATLAB platform, and the performances are evaluated by several performance metrics like Complementary cumulative distribution function (CCDF), Bit Error Rate (BER), and computational complexity. The performance of the proposed model is compared with various existing approaches and previous works. From the implemented results, the proposed strategy achieved less (5 dB) PAPR, minimum (10–8) BER, less processing time (0.18 s) than the existing schemes, and hence the complexity also very low (7%) than others.

Chirp-Convolved Data Transmission

We propose a multicarrier chirp waveform, which can be generated by a circular convolution between data modulation symbols and a transmit filter, and show that it can equivalently be represented as discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM) with frequency domain chirp filter. The chirp is defined by a complex exponential function where the phase follows a second-degree polynomial and its coefficients can be chosen to maximize the performance on a fading channel and to generate sets of orthogonal signals. The results show that the waveform outperforms OFDM and DFT-s-OFDM in terms of bit error rate (BER) and block error rate (BLER) on a time-frequency selective channel.

DFT-s-OFDM With Enhanced Time-Domain Spreading for B-IFDMA

Enhanced time-domain spreading is proposed for block-interleaved frequency division multiple access (B-IFDMA) with discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM). By repeating each consecutive modulation symbol prior to the spreading, we show that the DFT of the spreading sequence becomes a window function, which compared to the existing method of repeating the whole block of modulation symbols, offers a signal with both lower cubic metric (CM) and block error rate (BLER). Modulation symbol-specific spreading sequences are further shown to improve the BLER. The new transmission scheme is supported by both time- and frequency domain despreaders, as well as by two channel estimation methods for B-IFDMA.

LTE‐DSRC hybrid vehicular communication system using DFT‐spread OFDM in uplink

SummaryTechnologies are advancing at a rapid rate in the current era. People are advancing with the advancement of technologies, be it in education industry, health industry, and providing luxury. With the advent of autonomous luxury‐in‐motion car that provides in‐car‐entertainment (ICE), vehicular communication is the prerequisite towards achieving this goal. Dedicated short range communication (DSRC) is a matured vehicular communication standard, and Long‐Term Evolution (LTE) is the most competing technologies in the cellular communication. In this paper, we focus on the uplink performance of the LTE‐DSRC hybrid infrastructure. The basic transmission scheme for uplink direction is based on single carrier transmission in the form of discrete Fourier transform (DFT)‐spread Orthogonal Frequency Division Multiplexing (OFDM) with a minimum mean square error (MMSE) receiver at the LTE Evolved Node B (eNodeB) and a DSRC OFDM transmitter. A comprehensive bit error rate (BER) performance simulative study has been made on a color image transmission in uplink hybrid LTE‐DSRC system, and the results obtained are encouraging that the proposed convergence is possible, as it provides a substantial decrease in the BER with a gradual increase in the signal ‐to‐ noise ratio Signal to Noise Ratio (SNR).

DFTs-OFDM based quantum noise stream cipher system

Abstract Quantum noise stream cipher (QNSC) is a physical layer encryption technique based on quantum noise. Discrete-fourier-transform spread orthogonal frequency division multiplexing (DFTs-OFDM) is a widely studied technology with excellent transmission performance. As best as we know, the transmission and security performance of QNSC in DFTs-OFDM transmission has not been studied. This paper introduces DFTs-OFDM into the QNSC system to combine the characteristics of both techniques. Simulation results show that PSK-based QNSC (PSK/QNSC) has better transmission and security performance than QAM-based QNSC (QAM/QNSC) under the same constellation size. As the constellation size increases, obtained security can be upgraded. We also investigate the effects of quantization and clipping noise on the performance of DFTs-OFDM based QAM/QNSC system. We experimentally demonstrate a 10-Gbit/s DFTs-OFDM based PSK/QNSC and QAM/QNSC transmission over a single span 200-km fiber link.

A Reliable OFDM-Based MMW Mobile Fronthaul With DSP-Aided Sub-Band Spreading and Time-Confined Windowing

Performance of digital signal processing (DSP) aided sub-band spreading orthogonal frequency division multiplexing (S-OFDM) implemented with the well-defined, time-located window is evaluated and compared with the cyclic prefix (CP) OFDM signal under severe interference circumstances. A four-quadrature amplitude modulation (QAM) mobile fronthaul over 20 km fiber link and 1 m millimeter wave 60-GHz wireless channel is demonstrated experimentally. The bit-error rate performance of applying time windowing on OFDM and S-OFDM are measured in the single channel scenario. In such simplified system, CP-OFDM is found to be a widely adopted waveform. While, as it suffers from the unexpected external interference, the received error vector magnitude (EVM) would be degraded dramatically for typical OFDM signals. By applying the Hanning window, the impact on the EVM performance can be alleviated as the interference is at the edge of the desired signal band and resulting a 2.5% EVM enhancement. However, an irrecoverable 20% data loss is obtained if the interference is totally immersed in the victim signal. In contrast, S-OFDM exhibits a frequency diversity property by grouping OFDM subcarriers into several sub-bands and spreading them into whole available bandwidth. Thus, as S-OFDM suffers from strong interference inside the signal band, about 12.61% and 43.53% EVM improvements of the average and the worst subcarrier performance with respect to the ordinary OFDM can be achieved via applying the spreading codes orthogonality restoring equalizer. All subcarriers in the S-OFDM are generated to meet the forward error correction threshold with reasonably flat performance. Therefore, the S-OFDM shows its superiority in an MMW mobile fronthaul for better reliability in data transmission.

Analysis of Variable Bit Rate WH/CI‐Spread OFDM based Integrated Satellite‐Terrestrial Broadcast System

In this study, the exact closed-form signal-to-interference-noise ratio (SINR) expression, for the impact of Doppler frequency shift on minimum mean square error receiver is derived for Walsh Hadamard (WH) and polyphase carrier interferometry (CI) code based multicarrier spread orthogonal frequency division multiplexing (SOFDM) transmission scheme over integrated satellite–terrestrial broadcast system. Additionally, bit error rate and spectral efficiency are analysed based on the obtained SINR expression. To examine that, three-state Fontan land mobile satellite, and six-path typical urban and rural area terrestrial channel models are employed. This analysis is performed to substantiate variable bit rate (VBR) quality of service at the physical layer of digital video broadcast satellite handheld (DVB-SH)-A architecture, the provision of which is absent in DVB-SH standard. VBR is assumed for SOFDM. The results illustrate that WH-SOFDM outperforms CI-SOFDM under both performance measures in all the three channel environments. Further, pilot-based channel estimation technique is performed and the estimated error variance is evaluated for VBR WH/CI-SOFDM. Later, block-wise system computational complexity of WH/CI-SOFDM schemes is evaluated. It is shown that, CI-SOFDM is a relatively more complex system than WH-SOFDM. Thus, a trade-off is present between the achieved performance gain and system complexity.

Recursive Carrier Interferometry Aided High Data Rate OFDM Systems With PAPR Suppression, Phase Noise Rejection, and Carrier Frequency Offsets Compensation

In this paper, we propose two groups of recursive codes, namely the Hadamard recursive carrier interferometry (HRCI) codes and diagonal recursive carrier interferometry (DRCI) codes, to simultaneously reduce the peak-to-average power ratio (PAPR) and suppress the phase noises and residual carrier frequency offset (RCFO) for high-speed orthogonal frequency division multiplexing (OFDM) systems. We exploit the recursion property of the Hadamard and diagonal matrices to constitute the proposed HRCI code and DRCI code using the carrier interferometry (CI) code, and present the system model in details to spread OFDM symbols in the frequency domain. Then, we prove that both HRCI and DRCI generation matrices keep their invertibility during the recursions. As a direct result of the new code design, the phase intervals are enlarged and the signals are shifted in the time domain, thus both the PAPR and the phase noises are reduced, and the RCFO can be mitigated. Moreover, the enlarged phase intervals enable the transceiver blocks including the channel estimator, which estimate the phase noise based on the received signals, to improve the performance. Furthermore, we present the expressions for the HRCI and DRCI embedded transmitted and received signals, and derive the analytical signal-to-interference-plus-noise ratio (SINR) expressions for bit error rate (BER) performance analysis. Then, we analyze the effects of presented codes on the phase differences and provide the computational complexity analysis. Numerical simulations verify the effectiveness of our theoretical analysis of SINR. Additionally, under different parameter settings, which consider the working conditions of practical systems, we demonstrate that the presented robust HRCI and DRCI coded OFDM systems can suppress the PAPR satisfactorily and better BER performances can be achieved by the recursive CI-aided spread OFDM systems with phase noise rejection and RCFO compensation when compared with counterpart systems.

Convolution neural network-based time-domain equalizer for DFT-Spread OFDM VLC system

Abstract This paper presents a novel time-domain equalizer for visible light communication (VLC) system using machine learning (ML) method. In this work, we employ discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) as modem scheme and convolution neural network (CNN) as kernel processing unit of equalizer. After estimating channel state information (CSI) from training sequence, the proposed equalizer recovers transmitted symbols according to the estimated CSI. Numerical simulations indicate that the equalizer can significantly enhance bit error rate (BER) performance. For example, when signal-to-noise ratio (SNR) is 20 dB and 16/32/64-quadrature amplitude modulation (QAM) is exploited, original BER is about 0.5 while the BER after recovery achieves 1 0 − 5 , which is much lower than forward error correction (FEC) limit 3 . 8 × 1 0 − 3 . This work promotes the application of ML in VLC domain. To the best of our knowledge, this is the first time a CNN-based equalizer has been explored.

Adjustable PAPR reduction for DFT‐s‐OFDM via improved general precoding scheme

An improved and specification-compatible general precoding scheme (GPC) for adjustable peak-to-average power ratio (PAPR) reduction in discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM) is proposed. Through the rearrangement of periodic padding for precoded data symbols in the GPC precoding matrix, the proposed algorithm does not increase any computational complexity compared to the original GPC. The LTE-based simulation shows the proposed algorithm has a better improvement of PAPR reduction especially in low-order modulations and the performances can be scaled to the other transmission bandwidth. These works contribute to the flexibility of DFT-s-OFDM for supporting 5G transmission over miscellaneous power amplifiers.