dB Peak-to-average Power Ratio Reduction Research Articles

DFT-spread OTFS-NOMA for downlink integrated positioning and communication

In this article, a non-orthogonal multiple-access (NOMA) transmission system that incorporates discrete Fourier transform (DFT) spread orthogonal time-frequency space (OTFS) modulation is proposed for the downlink integrated positioning and communication (IPAC). This system is designed to decrease the Peak-to-Average Power Ratio (PAPR) within the OTFS-NOMA system while simultaneously serving both communication user (CU) and positioning user (PU) within the same time-frequency resources. Firstly, we demonstrate the applicability of the proposed DFT-spread OTFS-NOMA (DFT-s-OTFS-NOMA) system for downlink transmission. It efficiently serves both the CU and PU concurrently within the same time and frequency resources, thereby increasing spectrum utilization. Subsequently, we develop a two-stage parameter estimation algorithm focusing on accurate positioning parameter estimation for PU and precise channel estimation for CU. Then, the position of the PU is estimated using the time of arrival (TOA) model and the linear least squares (LLS) approach. Simulation demonstrates a 9 dB PAPR reduction in the proposed system compared to the existing OTFS-NOMA system. Additionally, the proposed two-stage positioning method for the PU achieves centimeter-level accuracy in position estimation and near millimeter-per-second-level accuracy in velocity estimation. What is more, the performance of channel estimation and symbol detection, aided by the PU signal in the DFT-s-OTFS-NOMA system, demonstrates resilience against Doppler effects without the need for reliance on pilots. This ensures sustained an effective Bit Error Rate (BER) even in time-variant high mobility scenarios.

Spread spectrum OFDM-IM with X-transform

This paper proposes a developed index modulated spread spectrum orthogonal frequency division multiplexing (OFDM) that is based on X-transform (IM-XOFDM-SS). The presented OFDM sends information not only by M-ary data symbols but also by indexes bits that used to select the spreading code from a known set, and applies the X-transform for baseband processing. A theoretical analysis for upper bound bit-error rate (BER) over Rayleigh fading channels is derived for the proposed scheme. Simulations results show that our proposed scheme outperforms the competitive benchmark systems in terms of BER, peak-to-average power ratio (PAPR) and computational complexity. It achieves, at 10−4 BER, about 22 dB and 21 dB SNR gain when spectral efficiency is SE=1 bps/Hz. Additionally, it gains about 5.5 dB PAPR reduction in comparison to IM-OFDM-SS scheme that is based on FFT for baseband processing.

A Novel PAPR Reduction Scheme Based on Joint Traditional Algorithm and Machine Learning for CO-OFDM Systems

The high peak-to-average power ratio (PAPR) deteriorates the performance of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. Machine learning (ML) has evolved into a powerful technology to reduce PAPR with its flexible learning ability. We propose a joint scheme which adopts iterative partial transmission sequence (IPTS) scheme cascading a feedforward neural network (FNN) trained on iterative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pmb {\mu }$ </tex-math></inline-formula> -law companding and filtering (IMCF) algorithm. The proposed scheme greatly reduces the complexity of partial transmission sequence (PTS) scheme, which has excellent PAPR reduction effect and BER performance. Our method achieves a 5.03 dB PAPR reduction for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10\pmb {^{-4}}\,\,\pmb {CCDF}$ </tex-math></inline-formula> and an additional transmission distance of 200 km SMF for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10\pmb {^{-3}}\,\,\pmb {BER}$ </tex-math></inline-formula> , compared with the original OFDM signal. Meanwhile, the computational complexity of proposed scheme is reduced by 32.4%, compared with IPTS cascading IMCF (IPTS-IMCF) scheme.

PAPR-Degraded Secure OFDM-WDM-PON Based on Chaotic Set-Partitioned SLM

This letter proposes and experimentally demonstrates an orthogonal frequency division multiplexing wavelength division multiplexing passive optical network (OFDM-WDM-PON) system based on novel chaotic set-partitioned selective mapping (SP-SLM) scheme. With the implementation of a three-dimensional chaotic system, peak-to-average power ratio (PAPR) reduction and chaotic encryption are simultaneously realized on the process of OFDM signal modulation, so as to enhance the system performance in the presence of PAPR, bit error rate (BER), fiber nonlinear tolerance and security. The experimental results show that, when compared with original OFDM signal, the OFDM signal with SP-SLM can achieve 4 dB PAPR reduction at the complementary cumulative distribution function value of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-4}$ </tex-math></inline-formula> , as well as a 1.1 dB gain in receiver sensitivity at a 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">$10^{-3}$ </tex-math></inline-formula> . For fiber nonlinear tolerance, the optimal launch fiber power of OFDM signal with SP-SLM is 10 dBm, which is better than 9 dBm of original OFDM signal under the same received optical power of −16 dBm. Furthermore, the key space of the proposed scheme can reach up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{98}$ </tex-math></inline-formula> , which is large enough to effectively protect against illegal attackers.

Gaussian orthogonal matrix transform approach for PAPR reduction of optical OFDM signals

Optical orthogonal frequency division multiplexing (O-OFDM) has been widely adopted as a high-speed data transmission technique in visible light communication systems. This technique usually suffers from high peak-to-average-power ratio (PAPR). In this paper, a new PAPR reduction technique is proposed for O-OFDM signals. At the transmitter, a matrix transformation with the Gaussian elements is applied to the time-domain O-OFDM signal and at the receiver, the inverse matrix is used to recover the original signal. We show that the Gaussian orthogonal matrices can reconstruct the original signals without degrading the bit error rate (BER) performance. Gram-Schmidt technique is used to orthogonalize the Gaussian matrices. Computer simulations are conducted for 16-QAM baseband modulated symbols and about 3 dB PAPR reduction gain is achieved by the proposed approach compared with conventional O-OFDM.

Partial Pre-Emphasis for Pluggable 400 G Short-Reach Coherent Systems

Pre-emphasis filters are used to pre-compensate for the transmitter frequency response of coherent systems to mitigate receiver noise enhancement. This is particularly essential for low-cost, low-power coherent transceivers due to having an extremely bandlimited transmitter. However, the pre-emphasis filter also increases the signal peak-to-average power ratio (PAPR), thus posing a higher effective number of bits (ENoB) requirement for the arbitrary waveform generator (AWG). In this paper, we first numerically study the PAPR impact of partial pre-emphasis filters. We show that with partial pre-emphasis, an ENoB reduction from 5 to 4.5 bits is attainable at the same signal-to-noise ratio (SNR) out of the AWG. Next, we experimentally investigate the overall performance penalty of partial pre-emphasis in a 50 Gbaud 16QAM coherent system. A manageable Q factor penalty of around 0.5 dB is found for both single-polarization and dual-polarization systems with a 0.8 dB PAPR reduction.

Adaptive Uniform Entropy Loading for SSB-DMT Systems

In this paper, we proposed a simple uniform entropy loading (UEL) algorithm to adaptively load the same entropy for all the subcarriers according to the channel state information. Thanks to the signal-to-noise ratio (SNR) equalization effect of precoding, only one distribution matcher is used for UEL, maximally reducing the complexity of entropy loading. The proposed algorithm is based on the relationship between the optimal information bits per symbol (IBPS) and SNR for probabilistically shaped quadrature amplitude modulation (PS QAM) under the constraint of normalized generalized mutual information (NGMI) considering the implementation of constant composition distribution matching (CCDM) and off-the-shelf forward error correction (FEC) code. Different from generalized mutual information (GMI), IBPS intuitively represents practical performance. Besides, the relationship between IBPS and SNR for conventional QAM and time domain hybrid QAM (TDHQ) are also calculated to perform the well-known bit power loading (BPL) algorithm, Levin-Campello (LC) algorithm, and TDHQ assisted adaptive loading (AL) algorithm, respectively. Based on theoretical analysis, to our best knowledge, we first found that precoding procedure adopted by TDHQ assisted AL and UEL scheme degrades Shannon capacity compared to water-filling algorithm, the upper limit of BPL algorithms. However, benefiting from shaping gain of PS QAM, the proposed UEL algorithm achieves higher net data rate (NDR) and lower peak-to-average power ratio (PAPR) than the LC algorithm, which is demonstrated by the simulations and experiments in single sideband discrete multi-tone (SSB-DMT) systems. According to the experimental results, up to 3.2% NDR improvement and 0.82 dB PAPR reduction are realized by the UEL algorithm compared to the LC algorithm. The UEL algorithm also outperforms TDHQ assisted AL algorithm by the average NDR gain of up to 8.0%. The simple and effective advantages make the proposed UEL scheme suitable for the short-to-medium reach optical fiber communication systems.

PAPR Reduction of TDCS Based on Chirp Noise Sequence

This letter proposes a transform domain communication system (TDCS) based on chirp noise sequence to deal with its high peak to average power ratio (PAPR). The optimal chirp noise sequence is obtained by the selective mapping to improve PAPR reduction of the proposed TDCS waveform with low complexity. Compared with other PAPR reduction algorithms, such as magnitude weighting selection and complementary peak reducing signal, the proposed TDCS based on optimal chirp noise sequence has about 1.5 dB PAPR reduction gain without extra bit error rate loss.

Performance Analysis of Layered ACO-OFDM

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.

Analysis of an offset modulation transmission

In this article, a method called offset modulation (OM-OFDM) is proposed to control the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. The theoretical bandwidth occupancy of the proposed offset modulated signal is derived. Using these bandwidth occupancy results, a closed-form theoretical bit error rate (BER) expression for an offset modulated transmission is derived and validated. Thereafter, a BER comparison between OM-OFDM and OFDM at a PAPR value of 13 dB shows that both methods offer similar BER characteristics for frequency selective fading channel conditions. The OM-OFDM method in addition is able to accurately control the PAPR of a transmission for a targeted BER. The authors have further proposed a newly applied power performance decision metric, which can be used throughout the PAPR field, in order to compare various methods. By using this power performance decision metric, the authors show that OM-OFDM offers between 4 dB–1.2 dB (60.34%–24.6%) and 4.1 dB–1.2 dB (60.8%–23.6%), net power performance gain (at a BER of 10−4) when compared to a clipped OFDM, OFDM, tone reserved (TR) OFDM and an active constellation extended (ACE) OFDM transmission in a frequency selective fading channel. Finally, by using a complementary cumulative distribution function (CCDF), the OM-OFDM method is shown to offer between 3.2 dB and 2 dB PAPR reduction (at a CCDF of 10−1) when compared to an OFDM, TR, clipped, and ACE OFDM transmission.

Reducing the PAPR of OFDM Signals Based on SCHT Precoding

The precoding scheme based on real Hadamard transform is an effective and flexible way for reducing the peak-to-average power ratio (PAPR) of OFDM signals. However, the reduction capacity of PAPR is limited for real Hadamard transform method. In this paper, the new scheme based on complex Hadamard transform is proposed. The simulation results indicate that the proposed scheme may obtain a 1.2 dB PAPR reduction of OFDM signal with only moderate complexity compared with the real Hadamard transform.

A simple peak-to-average power ratio reduction scheme for all optical orthogonal frequency division multiplexing systems with intensity modulation and direct detection

This paper fundamentally investigates the peak-to-average power ratio (PAPR) theory in all optical orthogonal frequency division multiplexing (OFDM) systems which employ intensity modulation-direct detection (IM-DD) scheme. We propose a low-complexity PAPR reduction scheme based on phase pre-emphasis. Simulations show that the proposed scheme brings about a 3.74 dB PAPR reduction and better nonlinear impairment tolerance in a 16x10Gb/s IM-DD all optical OFDM system.

OFDMA 상향 링크 시스템에서 PAPR 저감을 위한 선택적 DFT Spreading 기법의 설계와 성능 평가

본 논문에서는 OFDMA(Orthogonal Frequency Division Multiple Access) 상향 링크 시스템에서 발생하는 높은 PAPR(Peak to Average Power Ratio) 문제를 해결하기 위한 방법으로 선택적 DFT(Discrete Fourier Transform) spreading 기법을 새롭게 제안한다. 제안된 방법은 기존의 DFT spreading 기법에 선택적 특성을 추가한 것으로, SLM(Selective Mapping) 기법과 DFT spreading 기법이 혼합된 형태를 갖는다. 그러나 제안된 기법은 copy branch를 사용함에 있어 그 복잡도의 증가를 최소화하기 위해 하나의 DFT만을 사용하고, DFT출력 신호에 여러 개의 각기 다른 matrix를 곱함으로써 여러 개의 copy branch를 생성한다. 여기서 사용된 matrix는 DFT 앞에서의 입력 데이터 위상 회전을 선형 변환함으로써 얻어진 것으로, 각각의 matrix는 그 복잡도가 하나의 DFT보다 매우 낮게 설계된다. 성능 분석을 위해 QPSK 변조 및 512 point IFFT의 사용을 가정하고 한 사용자에게 할당된 sub-carrier 수는 각각 75, 100인 두 가지 경우를 고려하였다. 성능 분석 결과에서, 제안된 선택적 DFT spreading 기법은 copy branch 수가 4일 때 약 5.2 dB 이상의 PAPR 저감 효과를 가지며, 이는 기존의 DFT spreading만을 사용하는 경우 보다 약 1.8 dB 이상, 그리고 32 copy branch를 사용하는 SLM보다도 약 0.95 dB 이상의 뛰어난 PAPR 저감 성능이다. 또한 복잡도의 비교에서도 사용자에게 할당된 sub-carrier의 수가 100일 때, 제안된 기법은 기존의 DFT spreading 기법 보다는 증가되었으나 제안된 기법의 성능에 가장 근접하는 32 copy branch의 SLM보다 약 91.79 % 저감된 곱셈 량을 갖는다. 제안된 기법의 효율성을 확인할 수 있으며, 사용자에게 할당된 sub-carrier의 수가 증가되어 단일 사용자가 모든 sub-carrier를 사용하는 경우, 즉 일반적인 OFDM과 같은 상황에서도 유사한 성능적 이득을 예상할 수 있다. In this paper, we propose a selective DFT spreading method to solve a high PAPR problem in uplink OFDMA system. A selective characteristic is added to the DFT spreading, so the DFT spreading method is mixed with SLM method. However, to minimize increment of computational complexity, differently with common SLM method, our proposed method uses only one DFT spreading block. After DFT, several copy branches are generated by multiplying with each different matrix. This matrix is obtained by linear transforming the each phase rotation in front of DFT block. And it has very lower computational complexity than one DFT process. For simulation, we suppose that the 512 point IFFT is used, the number of effective sub-carrier is 300, the number of allowed sub-carrier to each user's is 1/4 and 1/3 and QPSK modulation is used. From the simulation result, when the number of copy branch is 4, our proposed method has more than about 5.2 dB PAPR reduction effect. It is about 1.8 dB better than common DFT spreading method and 0.95 dB better than common SLM which uses 32 copy branches. And also, when the number of copy branch is 2, it is better than SLM using 32 copy branches. From the comparison, the proposed method has 91.79 % lower complexity than SLM using 32 copy branches in similar PAPR reduction performance. So, we can find a very good performance of our proposed method. Also, we can expect the similar performance when all number of sub-carrier is allocated to one user like the OFDM.

Constrained Clipping for Crest Factor Reduction in OFDM

In this paper, we propose a constrained clipping method for reducing the peak to average power ratio (PAR) or crest factor of an orthogonal frequency division multiplexing (OFDM) signal. This is a transmitter-side processing technique that does not impose any modification at the receiver. Specifically, constrained clipping achieves PAR reduction while simultaneously satisfying spectral mask and error vector magnitude (EVM) constraints which are specified by most modern communications standards. Our proposed constrained clipping method consists of two independent processing units, one to satisfy the in-band EVM constraint and the other to satisfy the out-of-band spectral constraint. Achievable PAR reduction results vary depending on the particular standards' requirements, but we show that by using constrained clipping on a QPSK WiMax signal with 256 subcarriers, a 4.5 dB PAR reduction at the 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> complementary cumulative distribution function (CCDF) level can be obtained

A hybrid PAPR reduction scheme for coded OFDM

We consider schemes for reducing the peak-to-average power ratio (PAPR) in coded orthogonal frequency-division multiplexing (OFDM) systems. We develop a new PAPR reduction technique using the label-inserted encoder of a random-like code and the soft amplitude limiter (SAL). Using this hybrid scheme provides 5.5 dB PAPR reduction in an OFDM system with 128 subcarriers, 4-bit selection and 3 dB clipping. Besides the significant PAPR reduction, the scheme also enjoys other advantages such as small overhead, low complexity, no side information transmission, and little performance loss. Among various random-like codes, the irregular repeat accumulate (IRA) code is the best choice for its simple encoder and capacity achieving performance. The scheme can be directly applied to multiple-input multiple-output (MIMO) OFDM systems. The capacity of the clipped MIMO-OFDM systems is analyzed based on a Gaussian approximation of the clipping noise. We consider an iterative receiver with soft MAP MIMO-OFDM detector. For both single antenna and multiple antenna systems, the encoder part is independent in the hybrid scheme, thus no additional constraint is applied to the IRA code optimization. The IRA codes are designed for the ergodic MIMO-OFDM systems with different PAPR reduction settings, more specifically different clipping ratios, based on the extrinsic information transfer (EXIT) charts. Simulation results show that the hybrid scheme with 3 dB clipping can achieve as good PAPR reduction performance as the simple clipping with 0 dB ratio but incurs much less performance loss at the receiver

A PAPR Reduction Method for MIMO-OFDM Systems Using Subband Permutation

In this letter, a simple peak-to-average power ratio (PAPR) reduction method using subband permutation is proposed for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. The proposed method is shown to have a 2-3 dB PAPR reduction gain for 2 transmit antennas, compared with the conventional MIMO-OFDM, and a low computational complexity at the transmitter and receiver.

SLM-PTS 결합기법 및 ETD-Turbo부호를 적용한 OFDM 시스템에서의 PAR 개선에 관한 연구

본 논문에서는 OFDM 방식의 문제점으로 지적되고 있는 송신단에서의 PAR 특성을 고려하여 고속 적응형 PTS 기법과 SLM 기법을 결합한 SLM-PTS 결합기법을 제안하였다. 또한, PAR 저감기법을 적용한 시스템을 평가하기 위하여 ETD-Turbo 부호를 사용한 COFDM 시스템을 구성한 후 성능을 평가하였다. 분석 결과 제안된 SLM-PTS 기법이 연산량을 경감시키며 전반적으로 우수한 PAR 저감성능을 보임을 알 수 있었다. 특히 Combine 3의 경우 10-5 BER을 기준으로 약 <TEX>$3.7\~3.9\;dB$</TEX> 정토의 개선된 PAR 성능을 보였다. 또한, 터보부호를 사용한 경우 전반적으로 우수한 PAR 성능을 보임을 알 수 있었고, ETD-Turbo 부호를 적응한 경우 추가적으로 약 0.5 dB 정도의 성능 개선효과가 있음을 알 수 있었다. In this paper, we propose a high-speed adaptive PTS method which eliminates high PAR (Peak-to-Average Power Ratio) and we compare the proposed method with other conventional methods. In addition, we have designed a combined type SLM-PTS scheme to reduce PAR and evaluate the performance. The system used for evaluating PAR performance can be constructed as COFDM (Coded Orthogonal Frequency Division Multiplexing) applying ETD(Enhabced Time Diversity)-Turbo coding scheme. All the analyses in this paper are focused on the system characteristics according to IFFT's point and modulation method and the performance evaluation are based on the PAR reduction rates. As a result, the SLM-PTS combination method reveals good PAR reduction rate and remarkable reduction in the amount of calculations. Especially, in the case of combine-3 scheme, we can achieve approximately <TEX>$3.7\~3.9$</TEX> dB PAR reduction on a basis of 10-5 BER level. Moreover, we can eliminate the side information in COFDM system because of its adaptive characteristics in evaluating PAR reduction rate, so that the additional errors can be omitted.

Peak power reduction method for multicarrier transmission

A method to reduce the peak-to-average power ratio (PAR) of multicarrier signals has been developed. The method enlarges the quadrature amplitude modulation (QAM) constellation size at tones so that several signal points represent the same information. It chooses a signal point among equivalent signal points that minimises PAR. The method achieved more than 4 dB PAR reduction in a 64-subcarrier system.