Nonlinear Companding Transform Research Articles

A Novel µ-law Nonlinear Companding with Modified Recoverable Upper Clipping Method for PAPR Reduction in ACO-OFDM VLC Systems

The high Peak-to-Average-Power Ratio (PAPR) is the major challenge that causes signal distortion at the output of a Light-Emitting-Diode (LED) due to the narrow dynamic region of a LED in an Optical Orthogonal Frequency Division Multiplexing (O-OFDM) based Visible Light Communication (VLC) systems. Although a μ-law Nonlinear Companding Transform (μ-NCT) in an Asymmetrically-Clipped O-OFDM (ACO-OFDM) architecture decreases the PAPR degree, generates undesired large signals that can enter the nonlinearity range of a LED. This paper proposes a novel PAPR reduction method referred to as μ-NCT with Modified Recoverable Upper-Clipping (μ-NCT+MoRoC) model. The μ-NCT+MoRoC model benefits from the PAPR reduction of μ-NCT, and later uses all the advantages of the newly designed MoRoC method to reduce the large signals’ amplitudes that rose after the μ-NCT. The MoRoC method stores the large signals without losing information at the transmitter within the existing bandwidth using the asymmetrical structure of ACO-OFDM. To recover the source signal at the receiver, the MoRoC method uses newly generated symbol-based threshold detection and recovery algorithms. Both MoRoC and proposed μ-NCT+MoRoC models provide PAPR reduction and 45% peak amplitude reduction for ACO-OFDM systems without additional bandwidth, loss of information, and extra IFFT/FFT.

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.

Hybrid mapped optical‐OFDM using non‐linear companding technique for indoor visible light communication application

In this study, the authors have developed an analytical model for reducing the peak-to-average-power ratio (PAPR) using non-linear companding transform (NCT) based on inverse hyperbolic sine function. As a consequence of non-linear transform, this study compensates the system bit error rate (BER) degradation with the help of an error efficient hybrid modulation. By means of an inflexion point and companding parameter, more design flexibility is achieved; as a result, a trade-off between PAPR and BER has reasonably been more precise. To the best of the authors’ awareness, no findings have yet been reported on the performance evaluation of the optical orthogonal frequency division multiplexing (OOFDM) system using a hybrid modulation technique. To find out the advantages of hybrid modulation with NCT, the authors inspect the nature of PAPR reduction, and BER improvement through numerical simulations. The numerical BER results exhibit roughly 3 dBm decay in the power efficiency of hybrid modulation with NCT over discrete Fourier transform (DFT) precoding technique. On the other hand, the NCT technique with hybrid modulation has 6 dB less PAPR than the DFT precoding technique.

Novel PAPR Reduction Scheme Based on Piecewise Nonlinear Companding Transform in OFDM Systems

In this letter, a novel nonlinear companding scheme is proposed to reduce the peak-to-average power ratio (PAPR) for orthogonal frequency division multiplexing (OFDM) systems with a low bit error rate (BER) and out-of-band (OOB) radiation of the power spectral density (PSD). This companding scheme does not change the statistics of small-amplitude signals and transforms the statistics of large amplitude signals into a sine function. The proposed scheme can maintain average signal-power constant by appropriately selecting the parameters. We also give the theoretical performance analysis for the proposed companding function. The simulation results indicate that the proposed companding scheme can effectively reduce the PAPR of OFDM systems with both low BER and OOB of PSD.

Generalized frequency division multiplexing system performance with companding transform and pulse shaping filter

Generalized Frequency Division Multiplexing (GFDM) is considered as new candidates for futuristic multicarrier modulation technique. But GFDM suffers from high Peak to Average Power Ratio (PAPR) that leads to severe degradation in Bit Error Rate (BER) performance. In present work, Piecewise Nonlinear Companding Transform (PNCT) along with root raised square pulse shaping performance is analyzed to suppress high PAPR in GFDM system and to improve the BER performance. The pulse shaping filters have significant impact on the PAPR performance in GFDM system. By properly considering the rolloff factor in root raised cosine filter with companding transform can effectively handle the high PAPR of GFDM. The simulation results show that root raised cosine pulse shaping along with companding transform significantly achieves the better BER performance and can avoid distortion that occurs in the nonlinear amplifiers of the transmitter leads to reduced PAPR.

Reduction of Peak-to-Average Power Ratio of OFDM System Using Triangular Distribution Based Modified Companding Scheme

ABSTRACTOrthogonal frequency division multiplexing (OFDM) is an attractive multicarrier modulation technique, which is widely introduced in the present as well as future broadband wireless communication systems due to high data rate, high spectral efficiency, and robustness to the multipath fading channel. Despite its popularity, OFDM system suffers from the critical drawback of large peak-to-average power ratio (PAPR) of the transmitted signal, which may lead to undesired spectral re-growth, poor power efficiency, and overall performance degradation. In this paper, we propose an efficient non-linear companding transform (NCT) technique for reducing the PAPR of OFDM signals. Our proposed scheme coined as triangular distribution (TR) based companding offers an improved bit error rate (BER), better design flexibility, and more degrees of freedom while reducing PAPR effectively compared to the other existing companding schemes. The PAPR reduction performance of our proposed scheme for the different modulation approaches like QPSK, 4QAM, 16QAM, 32QAM, and 64QAM is also presented here. The theoretical analysis of the proposed scheme and comparative study with the existing algorithms are presented. Simulation results demonstrate that our proposed companding scheme can substantially outperform the existing NCT techniques in terms of PAPR reduction, BER performance, and bandwidth efficiency for each of the modulation approaches under different noisy channel conditions.

Triangular Distribution-Based Companding Technique for Reducing PAPR of OFDM Systems

Orthogonal frequency division multiplexing (OFDM) technology promises to be a key technique for achieving high data rates in the present as well as future broadband wireless communication systems. In spite of several advantages, one of the major drawbacks of OFDM system is its high peak to average power ratio (PAPR), which degrades the overall performance and results in many restrictions for practical applications. To reduce the PAPR, a novel PAPR reduction technique is proposed here that provides optimum bit error rate (BER) performance, better design flexibility and more degrees of freedom compared to other existing companding schemes. In this proposed technique, original distribution function of OFDM signal magnitude is transformed into a triangular distribution function for achieving a favorable trade-off between PAPR reduction and BER performance. A theoretical performance study with general formulas of the proposed scheme is presented and a comparative analysis is done with the existing algorithms. Extensive simulation results demonstrate that our proposed scheme can substantially outperform the existing non-linear companding transform (NCT) techniques in terms of PAPR reduction, BER and power spectrum density (PSD) performance.

Estimation and Cancellation of Nonlinear Companding Noise for Companded Multicarrier Transmission Systems

Nonlinear companding transform (NCT) is an efficient method to reduce the high peak-to-average power ratio (PAPR) of multicarrier transmission systems. However, the introduced companding noise severely restrains the bit-error-rate (BER) performance. In this paper, a general and simple companding noise cancellation (CNC) technique is proposed to mitigate the nonlinear companding noise at the receiver. By exploiting the Bussgang theorem and reconstructing the companding process at the transmitter, the estimated approximate companding noise can be used to refine the received signals. Furthermore, by employing the proposed approach to a typical exponential companding (EC), our results indicate that the proposed scheme can greatly relieve the conventional bottleneck, i.e. the so-called trade-off between the PAPR reduction and BER performance, of NCTs. It shows that for a 512-subcarrier and quadrature phase shift keying modulated orthogonal frequency division multiplexing system, the gap of the signal-to-noise ratio is no more than 0.3 dB at $${P_e} = 1 \times {10^{ - 5}}$$ between the ideal performance bound and EC-CNC regardless of the companding degree ( $$d=1$$ or $$d=2$$ ) over additive white Gaussian noise channel.

Efficient Nonlinear Companding Transform Scheme for Reducing PAPR of OFDM Signals

Efficient nonlinear companding transform (NCT) scheme for reducing peak-to-average power (PAPR) of orthogonal frequency division multiplexing (OFDM) signals is proposed. This scheme transforms the Gaussian-distributed signals into the specified statistics form defined as a piecewise function. By adjusting the transform parameters, it enables more design flexibility in companding form so that a favorable trade-off between PAPR and bit error rate (BER) can be offered. Compared to existing techniques, the scheme can achieve an effective reduction in PAPR as well as an improved BER performance simultaneously.

Efficient nonlinear companding scheme for substantial reduction in peak-to-average power ratio of OFDM

Orthogonal frequency division multiplexing (OFDM) produces a high peak-to-average power ratio (PAPR) that ad-versely affects high-speed OFDM data transmission. In order to reduce the high PAPR, an efficient nonlinear companding trans-form (NCT) function is proposed. With the proposed NCT function, the compression and expansion weights can be applied indepen-dently with suitably chosen function parameter values. As a re-sult, the proposed function can easily maintain the average signal power approximately unchanged during the companding process. In this regard, the proposed function is superior to previously pro-posed schemes. Also, the simulations show the outstanding PAPR reduction performance of the proposed function. It is demonstrated that the proposed scheme performs wel with nonlinear transmitter amplifiers and delivers superior error performance, compared with error function and exponential function based schemes.

A Novel Nonlinear Companding Transform for PAPR Reduction in Lattice-OFDM System

AbstractIn this paper, a novel companding scheme is proposed to reduce the peak-to-average power ratio (PAPR) of lattice orthogonal frequency division multiplexing (LOFDM) system. By transforming the statistics of original signals into a specified distribution form, which is defined by a continuous sine function, this scheme can achieve a simple companding form as well as an improved PAPR and bit-error-rate (BER) performance. Moreover, by introducing the variable companding parameters in the desired probability density function (PDF), a great design flexibility in the companding form and an effective trade-off between the PAPR reduction and BER performance can be achieved to satisfy various system demands. The general formulas of the proposed scheme are derived and a theoretical analysis regarding the achievable transform gain and the selection criteria of companding parameters are also conducted. Simulation results show that the proposed scheme can substantially outperform the conventional

PAPR Reduction in OFDM Systems using Non-Linear Companding Transform

In this paper a non-linear companding transform is proposed which can effectively reduce the PAPR value in OFDM systems. High value of PAPR has undesirable effects on the performance of wireless communication systems. Various companding schemes are used to reduce the problem of PAPR in orthogonal frequency division multiplexing schemes. High PAPR drives the power amplifiers used at the transmitter’s side into non-linear region and leads to high power dissipation in hand held devices. The proposed NCT has the capability to transform power and amplitude of the original OFDM signal into a uniform distribution which leads to the reduction of PAPR.

An Efficient Algorithm for Improving Ber and Papr of Ofdm System by Using Nonlinear Companding Transform

One of the challenging issues for OFDM (Orthogonal Frequency Division Multiplexing) systems are its PAPR. Proposed review and analysis of various OFDM PAPR reduction methods are based on computational, complexity, spectral spillage and performance. Our aim is a non linear companding technique is proposed to reduce high PAPR of OFDM. Which can use companding for Peak to Average Power Ration control is explored for linking a nonlinear transmit power amplifier with OFDM. In this article analyses the improvement in Bit Error Rate and overall system performance by employing non linear companding technique for PAPR reduction in Digital Video Broadcasting system. Index-terms: Bit Error Rate (BER), DVB-T, OFDM, PAPR.

Nonlinear Companding Transform for Reduction of Peak-to-Average Power Ratio in OFDM Systems

High peak-to-average power ratio (PAPR) of the transmitted signal is one of the limitations to employing orthogonal frequency division multiplexing (OFDM) system. In this paper, we propose a new nonlinear companding algorithm that transforms the OFDM signals into the desirable statistics form defined by a linear piecewise function. By introducing the variable slopes and an inflexion point in the target probability density function, more flexibility in the companding form and an effective trade-off between the PAPR and bit error rate performances can be achieved. A theoretical performance study for this algorithm is presented and closed-form expressions regarding the achievable transform gain and signal attenuation factor are provided. We also investigate the selection criteria of transform parameters focusing on its robustness and overall performance aspects. The presented theoretical analyses are well verified via computer simulations.

Nonlinear Companding Transform Algorithm for Peak -To- Average Power Ratio Reduction of OFDM Signal.

Orthogonal Frequency Division Multiplexing (OFDM) is digital multicarrier Modulation access system for high data rate transfer .But it has high PEAK To Average Power Ratio which increases complexity of A/D Converter and D/A Converters and lowers the efficiency of power amplifiers. In this paper Repeated Clipping and Filtering (RCF) distortion PAPR Reduction technique of an OFDM signal which is existing technique for reducing high Peak -to -Average Power of an OFDM signal. The basic idea of Repeated Clipping and Filtering(RCF) algorithm is to generate the anti-peak signal for Peak-to-Average Power Ratio (PAPR) reduction by projecting the clipping in-band noise into the feasible extension area while removing the Out-of-Band Interference (OBI), also called as Out-of-Band Distortion with filtering (3). The Clipping and filtering method suffers from the three major problems like in-band distortion, out-of-band radiation & peak re- growth after digital to analog conversion (24). The Nonlinear Companding Transform (NCT) distortion technique is proposed for reducing the high Peak -To -Average Power Ratio This proposed scheme reduces the PAPR by compressing the peak signals and expanding the small while maintaining average power constant selecting transform parameters Finally simulation results show that the proposed technique outperforms than Repeated Clipping and Filtering (RCF) technique in terms of low clipping ratio problem, peak re-growth ,out-of-band interference(OBI),PAPR reduction and BER Performance . Keywords - Orthogonal Frequency Division Multiplexing (OFDM), Peak-to-Average Power Ratio (PAPR), Nonlinear Companding Transform (NCT), Repeated Clipping and filtering (RCF) algorithm Bit Error Rate (BER).

PAPR Reduction in SC-FDMA Using NCT Technique

Abstract Orthogonal Frequency Division Multiplexing (OFDM) technology is undoubtedly the best available option for supporting high data rate in both wired and wireless communication systems. But, the feature of high peak-to-average power ratio (PAPR) restricts its usage in some applications for which single carrier frequency division multiple access (SC-FDMA) technique is usually adopted. In this work, a new scheme using Nonlinear Companding Transform (NCT) technique is proposed for further reducing the peak-to-average power ratio (PAPR) of SC-FDMA. It transforms the SC-FDMA signal by properly choosing the transform parameters for achieving a favorable tradeoff between PAPR reduction and bit error rate (BER) performances. The simulation results show better performance of the proposed scheme as compared to competitive alternatives.

Nonlinear Companding Transform Algorithm for Peak -ToAverage Power Ratio Reduction of OFDM Signal.

Nonlinear Companding Transform Algorithm for Peak -ToAverage Power Ratio Reduction of OFDM Signal.

An Efficient Nonlinear Companding Transform for Reducing PAPR of OFDM Signals

In this paper, an efficient nonlinear companding scheme is proposed to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. By transforming the statistics of original signals into a specified distribution form along with remaining an unchanged average output power level, this scheme can achieve significant reduction in PAPR as well as an improved BER performance simultaneously. Moreover, by properly adjusting the transform parameters, more design flexibility in companding form can also be given by this scheme to satisfy various system requirements. The theoretical analysis results regarding the transform gain, companding distortion and the selection criteria of parameters are derived. It is proved that this scheme may lead to less signal distortion compared to existing companding schemes. Simulation results demonstrate that the proposed scheme can substantially offer better overall performance of OFDM system in terms of PAPR reduction, BER performance and bandwidth efficiency.

Reduction of PAPR of OFDM Signals Using Nonlinear Companding Transform

In this paper, we propose and evaluate a novel nonlinear companding transform (NCT) scheme for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems. The key idea of the proposed scheme is to transform the original Gaussian-distributed OFDM signals into a specific statistics form, whose target probability density function is defined by a piecewise function with an inflexion point. By properly choosing the transform parameters, this scheme can enable more flexibility and freedom in the companding form so that a favorable tradeoff between PAPR reduction and bit error rate (BER) performance can be achieved. Moreover, compared to existing NCT techniques, this scheme dramatically decreases the impact of companding distortion on the BER performance to reach a given PAPR level. The analytical expressions regarding the achievable transform gain in PAPR, complementary cumulative density function, attenuation coefficient, and selection criteria of transform parameters are derived. Simulation results justify the significance and accuracy of the analytical expressions presented.

On the Nonlinear Companding Transform for Reduction in PAPR of MCM Signals

In this paper, we provide the design criteria of the nonlinear companding transforms for reduction in peak-to-average power ratio (PAPR) of multi-carrier modulation (MCM) signals, which can enable the original MCM signals to be transformed into the desirable distribution. As examples, some novel nonlinear companding transforms have been proposed to transform the amplitude or power of the original MCM signals into uniform distribution, which can effectively reduce the PAPR for different modulation formats and subcarrier sizes without any complexity increase and bandwidth expansion. It has been shown by computer simulations that the proposed schemes can significantly improve the performance of MCM systems including bit-error-rate and PAPR reduction.