Peak-to-average Power Ratio Reduction In Orthogonal Frequency Division Multiplexing Systems Research Articles

A Novel Alternating μ-Law Companding Algorithm for PAPR Reduction in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) inherits multi-carrier systems’ inevitable high peak-to-average power ratio (PAPR) problem. In this paper, a novel alternating companding technique is proposed to combat the harassment of high PAPR. The sequential μ-law companding (SULC) and a tone with a lower PAPR result in only partial tones needing companding. The SULC scheme’s PAPR and bit error rate (BER) performance has been balanced and improved. However, the computational complexity is still too high to be implemented. Therefore, this study sorted the transmission signals according to their amplitudes. Then, all the tones are divided into two groups by estimating the rough companding amount (around 54% of the subcarriers), using traditional parallel companding for the first group and the other group only by partial μ-law companding. This alternating μ-law companding (AULC) is proposed to improve the PAPR performance and simultaneously reduce complexity. Simulation results show that the proposed AULC method appreciably reduces the PAPR by about 5 dB (around 45%) compared with the original μ-law at complementary cumulative distribution function (CCDF) equal to 10−4. Moreover, it only requires a moderate complexity to outperform the other companding schemes without sacrificing the BER performance in the OFDM systems.

Non-linear companding scheme for PAPR reduction in OFDM systems

Abstract High peak-to-average power ratio (PAPR) is one of the critical drawbacks of orthogonal frequency division multiplexing (OFDM). Companding is an efficient scheme to limit the PAPR. Companding operation distorts the shape of OFDM signal, therefore reducing the PAPR with slight degradation in BER performance of OFDM signal. This paper proposes a non-linear companding transform, which transforms the ‘αth’ power of OFDM signal magnitude into a trigonal distribution. In the proposed scheme, design parameter ‘α’ is used to realize a better trade-off between PAPR and BER performance. Proposed scheme provides improved spectral efficiency and BER performance with a reduction in PAPR. We have also calculated the optimal value of design parameter ‘α’ to achieve the optimal BER.

Curve Fitting Based Piecewise Nonlinear Companding Scheme for PAPR Reduction in OFDM Systems

Peak-to-average power ratio (PAPR) is an important issue for orthogonal frequency division multiplexing (OFDM) systems. In this letter, we derive a new piecewise nonlinear companding scheme for reducing PAPR in OFDM systems. Compared with current state-of-art companding scheme, the new companding scheme improves the power spectral density (PSD) performance. The companding function is derived according to the cumulative distribution function (CDF) of companded OFDM signals’ amplitudes, which is fitted by using several piecewise linear functions to approximate the original Rayleigh distribution CDF. The constraint optimization problem is formulated, and parameter selection method is provided. Simulation results verify that under precondition of similar PAPR reduction levels, the proposed companding scheme could achieve better bit error rate (BER) and PSD performance compared with other typical companding schemes.

A Novel Low Complexity Two-Stage Tone Reservation Scheme for PAPR Reduction in OFDM Systems.

Orthogonal frequency division multiplexing (OFDM) has the characteristics of high spectrum efficiency and excellent anti-multipath interference ability. It is the most popular and mature technology currently in wireless communication. However, OFDM is a multi-carrier system, which inevitably has the problem of a high peak-to-average power ratio (PAPR), and s signal with too high PAPR is prone to distortion when passing through an amplifier due to nonlinearity. To address the troubles caused by high PAPR, we proposed an improved tone reservation (I-TR) algorithm to alleviate the above native phenomenon, which will pay some modest pre-calculations to estimate the rough proportion of peak reduction tone (PRT) to determine the appropriate output power allocation threshold then utilize a few iterations to converge to the near-optimal PAPR. Furthermore, our proposed scheme significantly outperforms previous works in terms of PAPR performance and computational complexity, such as selective mapping (SLM), partial transmission sequence (PTS), TR, tone injection (TI), etc. The simulation results show that in our proposed scheme, the PAPR is appreciably reduced by about 6.44 dB compared with the original OFDM technique at complementary cumulative distribution function (CCDF) equal to 10-3, and the complexity of I-TR has reduced by approximately 96% compared to TR. Besides, as for bit error rate (BER), our proposed method always outperforms the original OFDM without any sacrifice.

A LOW-COMPLEXITY PTS TECHNIQUE–BASED IMPROVED PSO ALGORITHM FOR PAPR REDUCTION IN OFDM SYSTEMS

Partial transmit sequence (PTS) is a potent and distortionless scheme frequently used to lower the high peak-to-average power ratio (PAPR) levels in orthogonal frequency division multiplexing (OFDM) signaling. Although this method effectively reduces the PAPR, its main limitation is the exponential growth in the computational expense caused by the exhaustive search for the optimal complex of rotation factors. This work proposes a suboptimal PTS scheme based on an improved particle swarm optimization (PSO) algorithm. The latter exploits heuristics to find the best-matched weighting factors complex in fewer computations. A comparison against existing techniques ascertains the superior efficiency of the proposed scheme in terms of PAPR mitigation and computational burden.

Variation Approach-Based Nonlinear Companding Scheme for PAPR Reduction in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) continues to find vast deployment in current and next generation wireless communication systems. However, high peak-to-average power ratio (PAPR) is one of the major drawbacks in the OFDM system. In this paper, we develop a variation approach based nonlinear companding (VANC) scheme to reduce the PAPR in OFDM systems. It aims to find the probability density function (PDF) for OFDM signal amplitudes with low PAPR and low distortion compared with their original Rayleigh distribution. The target PDF is found by solving a variation optimization problem model, which is built to find the lowest PDF distortion with both average signal power and probability conservation constraint. To the best of our knowledge, it is the first time that the variation method is used to find companding function to address the high PAPR problem. We then propose an algorithm with companding operation based on quantized levels. Simulation results validate the performance superiorities of the proposed scheme to that of other typical companding schemes.

Generalized Continuous Piecewise Linear Companding Transform Design for PAPR Reduction in OFDM Systems

Linear companding transform (LCT) is one of the most attractive schemes to deal with the inherent problem of high peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems, due to its effectiveness and low complexity. In this paper, a generalized continuous piecewise linear companding (CPLC) transform is proposed. The companding and decompanding functions of the proposed scheme consist of multiple continuous linear segments, and the total number of segments is generalized to be any integer not less than four. These linear segments can provide much adaptability for function shaping, leading to high flexibility for performance tradeoffs among PAPR reduction, bit error rate (BER), out-of-band (OOB) rejection and algorithmic complexity. The continuity of the companding function helps to reduce OOB radiations. Several optimization problems with different targets under the constraint condition of constant average power are constructed. Permissible ranges of key parameters, relationships among these parameters and their influence on algorithmic performance are analyzed. Parameter selecting strategies are also provided. In addition, an iterative receiving method is designed to reduce system BER effectively at the receiver. Simulation results validate the performance superiorities of the proposed scheme to that of other typical companding schemes.

Side information embedding scheme for PTS based PAPR reduction in OFDM systems

Partial transmit sequence (PTS) is one of the well-known probabilistic schemes in reducing peak-to-average power ratio (PAPR) for orthogonal frequency division multiplexing (OFDM) signal. In our paper, we address the two major concerns of the PTS–OFDM system: side information (SI) free transmission from transmitter end and complexity reduction of the generated candidates. In the proposed scheme, side information is embedded on the locations of higher power subcarriers at specific partitions within the data block and at the receiver side extraction of SI is based on the power disparity among data symbols in the partitions. The error performance of the proposed scheme over the AWGN channel is analyzed mathematically. Besides, time efficiency of the proposed algorithm has been estimated in respect of computations required for finding the optimal candidates. Simulation results confirm that our proposed SI free transmission scheme performs well in terms of low BER degradations over the AWGN and Rayleigh fading channels, better SI error detection probability, lesser computations and improved PAPR reductions of the OFDM signals.

Adaptive PTS scheme based on fuzzy neural network for PAPR reduction in OFDM system

High peak-to-average power ratio (PAPR) is one of the major drawbacks of orthogonal frequency division multiplexing (OFDM) communication system, which causes signal distortion and affects communication performance. Partial transmission sequence (PTS) is an effective method to reduce the PAPR, but it cannot adaptively select processing parameters for the signal and has high computational complexity. Aiming at the defects of PTS method, this paper propose an adaptive PTS method based on fuzzy neural network (FNN-APTS). The method considers the signal and system characteristics, combining the learning ability of the neural network with the reasoning ability of the fuzzy control method, to select the processing parameters for the signal adaptively. The simulation results show that the proposed FNN-APTS method can adapt to different OFDM models, reducing the computational complexity and improving the system performance while ensuring the reasonable PAPR.

Novel Linear Companding Transform Design Based on Linear Curve Fitting for PAPR Reduction in OFDM Systems

Peak-to-average power ratio (PAPR) reduction is an important issue for orthogonal frequency division multiplexing (OFDM) systems. In this letter, a novel method of continuous piecewise linear curve fitting (CPLCF) is first proposed to design linear companding transforms (LCTs) for PAPR reduction in OFDM systems. From given nonlinear companding transforms (NCTs), this method can derive corresponding LCTs with similar performance and much lower complexity. The constrained optimization problem is formulated, and parameter selecting method is provided. By employing the CPLCF method, a novel LCT scheme, named ANC-LCF, is derived from newly proposed adjusted nonlinear companding (ANC) prototype. Simulation results verify the validity of the novel design method and the performance superiority of the proposed ANC-LCF scheme.

PAPR Reduction in OFDM Systems Using Hybrid Zadoff-Chu Transform Precoding and Partial Transmit Sequence

Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation (MCM) scheme that plays a significant role in digital wireless communication. As a result of its high data rate capability and immunity to multipath fading effect, among others, OFDM remains an ideal technology for 5G communication systems and beyond. Unfortunately, a major drawback of this technology is the high peak-to-average power ratio (PAPR). Nevertheless, many techniques for reducing PAPR have been proposed in the past to address this problem. However, all the techniques previously used have limitations such as high computational complexity, data rate loss, high signal distortion, increase in bandwidth, increase in transmit power, and memory requirements. In this paper, a hybrid technique that combines Zadoff-Chu Transform (ZCT) precoding and Partial Transmit Sequence (PTS) for reducing high PAPR in OFDM signals is presented. To reduce the data rate loss and computational complexity in PTS when a large subblock is used, a Zadoff-Chu precoding is applied to OFDM symbols to precode the symbol before applying PTS with a fewer number of subblocks. An OFDM model was developed where ZCT and PTS techniques were implemented. The performance of the hybrid model was analyzed using Power Spectral Density (PSD), Complementary Cumulative Distribution Function (CCDF), and Bit Error Rate (BER). The simulation result indicates that the hybrid ZCT-PTS provides a better result than using either Zadoff-Chu precoding technique or Partial Transmit Sequence technique separately. A PAPR of 4.2 dB and BER of 3dB is achieved for hybrid ZCT-PTS. The hybrid technique provides a better system performance when compared with Conventional OFDM systems.

An efficient and improved PTS algorithm for PAPR reduction in OFDM system

ABSTRACT In this research, an improved PTS algorithm is projected for diminishing peak to average power ratio (PAPR) of well accepted and effective orthogonal frequency division multiplexing (OFDM) system. OFDM is also considered as trustworthy method for several wireless communication applications and obtained a lot of research interests but unfortunately, one of the most important concern is very high PAPR in OFDM signals, which deteriorates system performance thus this is the most important drawback. To address this problem, a novel partial transmit sequence (PTS) algorithm is projected based upon centering phase sequences matrix (PTS-CPSM-Algo). These phase sequences are used for optimization of data so that minimum PAPR can be obtained. This algorithm obtains significant reduction in PAPR which leads to the enhancement in performance of OFDM system. From the developed analysis and simulation results, supremacy can be clearly seen for proposed PTS-CPSM-Algo over already existing OFDM system, selected mapping (SLM) and partial transmit sequence (PTS).

A Model-Driven DL Algorithm for PAPR Reduction in OFDM System

Deep learning (DL) has dramatically improved the peak-to-average power ratio (PAPR) performance. However, the high computational complexity and excessive training data constitute a significant hurdle. In this letter, a model-driven deep learning algorithm is proposed for PAPR reduction in orthogonal frequency division multiplexing (OFDM) system. Precisely, an iterative peak-canceling signal generation scheme is unfolded as a layer structure of the DL network. The scheme falls into the category of tone reservation technique. A set of trainable parameters, which optimizes the clipping threshold and weights time-domain kernel function, has been designed and introduced into the iterative scheme. Compared with the existing approaches, the simulation results demonstrate that the proposed algorithm achieves comparable PAPR performance with low complexity and training costs.

Initial Probability Adaptation Enhanced Cross-Entropy-Based Tone Injection Scheme for PAPR Reduction in OFDM Systems

Cross entropy (CE) is a method that can be used to obtain the optimal perturbation signal in tone injection (TI) scheme to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. Since CE is an iterative method, the initial probability of CE plays an important role in converging toward the optimal solution. Thus, we focus on finding a more preferable initial probability for CE in this paper. Firstly, we analyze the perturbation signals of TI scheme. It is found that the number of the subcarriers needed to be perturbed is much smaller than the number of the subcarriers of OFDM systems, which demonstrates the perturbed subcarriers of perturbation signals exhibits the property of sparsity. Secondly, we assign different subcarriers with different perturbation weight defined according to the power of clipping noise. Thirdly, we select a candidate subcarrier set with limited size from the whole subcarrier set according to perturbation weight. Finally, by utilizing sparsity and perturbation weight in the determination of initial probability, we propose an enhanced CE method whose initial probability is problem-dependent and adaptive to OFDM symbols. Simulation results verify that the proposed initial probability adaptation enhanced CE-based TI scheme outperforms the traditional CE-based TI scheme and parametric minimum cross entropy (PMCE) based TI scheme on the PAPR, complexity and BER performance.

Adjustable Nonlinear Companding Transform Based on Scaling of Probability Density Function for PAPR Reduction in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) systems suffer from the inherent problem of high peak-to-average power ratio (PAPR). In this article, a novel adjustable nonlinear companding transform is proposed, which is based on scaling of original probability density function (PDF) of OFDM signal amplitudes. The target PDF consists of two parts. The first part with amplitudes no more than the transition point is same to that of original PDF. The second part with amplitudes larger than the transition point and smaller than the cutoff point is obtained by scaling original PDF in dimensions of ordinate and abscissa concurrently, for guaranteeing the constant average power. Companding and decompanding functions are derived, and constraint equation for solving parameters is formulated. Parameters of the proposed algorithm can be adjusted flexibly to achieve desired tradeoffs among algorithmic complexity, bit error rate (BER), out-of-band (OOB) rejection and PAPR reduction performance. Some key properties of the proposed algorithm are theoretically analyzed and proved, which may be much instructive for practical implementations. To further reduce algorithmic complexity, a piecewise curve fitting scheme employing quadratic polynomials is first proposed to simplify companding and decompanding functions. Simulation results confirm analysis results and verify the superiorities of proposed algorithms to other existing algorithms.

Advanced switching DE algorithm based PTS companding technique for PAPR reduction in OFDM systems

Partial Transmit Sequence (PTS) is an efficient method for diminishing the high Peak to Average Power Ratio (PAPR) for Orthogonal Frequency Division Multiplexing (OFDM) system. However, finding an optimum phase factor among different combinations of phase factors, rigorous searching is required. It ultimately increases the computational complexity. For practical implementation high computational complexity becomes crucial problem when a huge number of subcarriers are used in PTS based PAPR reduction technique for OFDM system. Hence, to reduce computational load an Advanced Switching Differential Evolution (ASDE) algorithm is incorporated in PTS scheme. In the proposed approach an optimized switching DE algorithm enhances computational efficiency. But, the PAPR reduction performance becomes poorer compared to conventional PTS scheme. To further reduce PAPR, two thresholds based $$\mu $$ law companding technique is incorporated along with ASDE PTS for OFDM system. The Matlab simulation revealed that, the proposed scheme performed better PAPR reduction and Bit Error Rate performance with less complexity compared to other relevant techniques.

A Hybrid Companding and Clipping Scheme for PAPR Reduction in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) continues to be deployed in 5G communication systems and is likely to be used in beyond 5G (B5G) communication systems as well, due to its many advantages. However, one major drawback with OFDM systems is its high peak-to-average power ratio (PAPR), especially with large bandwidth transmissions. In this paper, we have provided a regularization optimization based flexible hybrid companding and clipping scheme (ROFHCC) used for PAPR reduction in OFDM systems. To reduce the design complexity, the companding function has two parts. It restrains the signal samples with amplitudes over a given value to a constant value for both peak power reduction and small power compensation. For signals with samples less than a given amplitude, they are expanded by a linear companding function. We build a regularization optimization model to jointly optimize the companding distortion as well as the continuity of the companding function for bit error rate (BER) performance as well as power spectral density (PSD) performance. Simulation results indicate that for the same PAPR performance, the proposed companding scheme has an advantage over the referenced companding schemes. For example, when the average signal power is normalized to be 1, we choose both PAPR for ROFHCC scheme and two-piecewise companding (TPWC) scheme as 4 dB, then we can find that at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$BER=10^{-4}$ </tex-math></inline-formula> , the minimum required <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E_{b}/{N_{0}}$ </tex-math></inline-formula> for ROFHCC scheme is around 2.3 dB lower than TPWC scheme.

PAPR reduction in OFDM system using combined MCS and DHMT precoding

Orthogonal Frequency Division Multiplexing (OFDM) has become a preferable scheme for most high data rate wireless communication standards. However, the non-linear power amplifier effect experienced in the OFDM system has increases the peak-to-average power ratio (PAPR). This paper proposed a Median Codeword Shift (MCS) as a new solution to alleviate the effect of high PAPR. MCS takes advantage of the codeword structure and bit position changes through the manipulation of the codeword structure and permutation process to achieve a low PAPR value. Additionally, the enhanced version of MCS is also being proposed by merging MCS with the Discrete Hartley matrix transform (DHMT) precoding method to boost the PAPR reduction. Simulation results show that MCS is capable of minimizing PAPR of conventional OFDM with 24% improvement and at the same time outperform Selective Codeword Shift (SCS) with a 0.5 dB gap. A remarkable result was also achieved by MCS-DHMT with a 15.1% improvement without facing any bit error rate (BER) degradation.

PAPR reduction in OFDM system using combined MCS and DHMT precoding

Orthogonal Frequency Division Multiplexing (OFDM) has become a preferable scheme for most high data rate wireless communication standards. However, the non-linear power amplifier effect experienced in the OFDM system has increases the peak-to-average power ratio (PAPR). This paper proposed a Median Codeword Shift (MCS) as a new solution to alleviate the effect of high PAPR. MCS takes advantage of the codeword structure and bit position changes through the manipulation of the codeword structure and permutation process to achieve a low PAPR value. Additionally, the enhanced version of MCS is also being proposed by merging MCS with the Discrete Hartley matrix transform (DHMT) precoding method to boost the PAPR reduction. Simulation results show that MCS is capable of minimizing PAPR of conventional OFDM with 24% improvement and at the same time outperform Selective Codeword Shift (SCS) with a 0.5 dB gap. A remarkable result was also achieved by MCS-DHMT with a 15.1% improvement without facing any bit error rate (BER) degradation.

Low‐complexity PTS schemes for PAPR reduction in OFDM systems

For original partial transmit sequence (O-PTS), the conjugate operations can be applied to achieve the purpose of ameliorating the peak-to-average power ratio (PAPR) performance. But in this way, an observation has been found that some of these candidate signals has the same PAPR value that brings about great redundant computations. Based on this, a low-complexity PTS is put forward to abate the PAPR of orthogonal frequency division multiplexing (OFDM) systems, thereby avoiding redundant candidate signals. In proposed scheme, a novel scheme employing conjugate operations for generating candidate signals with different PAPR values is given, which avoids the generation of candidate signals with the same PAPR value and saves the needless computations. Meanwhile, the grouping is involved for further reduction in computational complexity. Simulation results illustrate that our scheme has the similar or superior PAPR performance with the remarkable reduction in computational complexity by comparison with O-PTS.