Iterative Clipping And Filtering Research Articles

A novel PAPR reduction scheme based on time-delay neural network for CO-OFDM systems

In this paper, we propose a low-complexity peak-to-average power ratio (PAPR) reduction scheme based on time-delay neural network (TDNN) for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems to reduce the limitation of PAPR on the total power of laser diodes and the impact of fiber nonlinear effects. The proposed scheme is jointly trained on traditional iterative clipping and filtering (ICF) scheme and simplified clipping and filtering (SCF) scheme, and changes the objective function by adjusting the given training weight α. Compared to the original orthogonal frequency division multiplexing (OFDM) signal of existing system, our method achieves an adjustable PAPR reduction of 5.31 dB to 6.12 dB for 10−4 complementary cumulative distribution function (CCDF). When bit error rate (BER) Pe=10−3, the proposed scheme (α=0.5) achieves additional transmission distances of 220 km, 55 km, 105 km, and 100 km, compared to the original OFDM signal, partial transmission sequence (PTS) scheme, ICF scheme, and feedforward neural network (FNN)-based ICF scheme, respectively. Besides, our method achieves 86.3% and 80.0% floating-point operations (FLOPs) reductions, compared with PTS scheme and ICF scheme, respectively, which effectively reduces the complexity of PAPR reduction module, saving the system computational time.

A novel PAPR reduction scheme based on nonlinear real-valued support vector regression for CO-OFDM systems

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems suffer from the high peak-to-average ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals, which leads to the back-off of laser power and fiber nonlinear effects, thereby deteriorating the bit error rate (BER) performance and limiting the transmission distance. Iterative clipping and filtering (ICF) scheme, as a direct, simple and effective PAPR reduction scheme that only processes signals at the transmitter, but requires multiple fast Fourier transform (FFT)/inverse fast Fourier transform (IFFT), resulting in high computational complexity. We propose a novel scheme using the machine learning (ML) technique, which is based on nonlinear real-valued support vector regression (NRSVR) and trained on ICF scheme. The simulation results show that compared with ICF scheme, the proposed scheme has a similar PAPR0 for 10−4 complementary cumulative distribution function (CCDF), an additional 15 km of single mode fiber (SMF) transmission for 16 dB optical signal-to-noise ratio (OSNR) and 10−3BER, and a significant time complexity reduction. Compared with other ML-based schemes, the proposed scheme also achieves better performance and lower computational complexity.

Performance Analysis of Selective Mapping and Clipping based MC-CDMA System

Abstract: The use of orthogonal frequency division multiplexing in high-bit-rate communication systems is appealing. Due to its fast data rate, resilience to delay spread, frequency spectrum efficiency, and other features, it has been widely utilised in current wireless communication. In addition to these benefits, a significant disadvantage of OFDM is the high Peak-to-average-power ratio (PAPR) of the transmitter's output signal, which limits the system's performance. The Iterative Clipping and Filtering (ICF) approach is used in this case because it yields better results than the Clipping method, which is the easiest way to lower the PAPR of the OFDM system. Another strategy that effectively reduces PAPR is selective mapping (SLM), in which the actual transmit signal is chosen from a list of candidates.

Implementation of particle swarm optimization based ICF technique to reduce the PAPR of ACO-OFDM

Abstract Orthogonal frequency division multiplexing (OFDM) is advantageous in terms of the spectral efficiency it offers. However, in OFDM, the bandwidth-efficient multicarrier modulation (MM) is limited by the peak-to-average power (PAPR) problem. Iterative clipping and filtering (ICF) method has been used in this work to address such issue. The ICF is regarded as a practical scheme that has become widely accepted and used due to the fact that it is characterized by low computational complexity. This method is also easily implemented, characterized by non-expansion of bandwidth, and it does not require the support to the receiver side during implementation. Nevertheless, the significant of this work is on further improvement where the method involves the iterative clipping of the same signals with a fixed clipping threshold (CT) in every clipping operation. Particle swarm optimization based ICF-OFDM, which is proposed in this research work, literally finds the most suitable clipping ratio, that eventually solves the problem of output power instability. Subsequently, the proposed method is implemented with asymmetrical clipped optical OFDM (ACO-OFDM) to validate the proposed method through the use of Matlab simulation. The PAPR reduction of the proposed method is then compared with the PAPR of the Hartley transform (DHT)-based ACO-OFDM and the traditional ACO-OFDM and DCO-OFDM. The best BER performance has been investigated via two modulation index. Results indicate that our method outperforms the counterparts in term of PAPR reduction and BER performance.

PAPR Reduction an effective approach for next frontier MIMO-OFDM systems

The ‘Orthogonal frequency division multiplexing (OFDM)’ is a well-accepted and effective technology employed today and in future wireless communication systems. The combinations of OFDM and ‘multiple-input multiple-output (MIMO’) offer high quality of services and better throughput. The multicarrier OFDM system experiences a high ‘peak-to-average power ratio (PAPR’), which is the major issue in the OFDM scheme and must be truncated to achieve trustworthy communication. Due to high PAPR in a signal to be transmitted, the power amplifier in the transmitter section enters into saturation region and amplifies the signal nonlinearly, resulting in loss of orthogonality and ultimately in ‘inter-carrier interference (ICI)’. In this article, the 'iterative clipping and filtering (ICF)' method is proposed to minimize the PAPR in the OFDM system. The simulation is carried out using MATLAB (version 2014b). The result of the proposed ICF method and the ‘selective mapping (SLM)’ scheme is analyzed and compared. From the analysis, it is shown that the proposed ICF technique is more suitable for minimizing the PAPR effectively without affecting ‘bit error rates (BER)’ much and the simplicity of the system. The simulation result of the proposed ICF scheme using ‘Quadrature Phase Shift Keying (QPSK)’, FFT size of 128, and clipping and filtering level up to 6 shows that the proposed ICF scheme for clipping level of 6 reduces PAPR to 5dB. Also, the BER is minimized at the level of 3×10−5 at 12 dB SNR.

Improved ACE and ICF low complexity joint algorithm to reduce PAPR of CO-OFDM system

Active constellation expansion (ACE) and iterative clipping and filtering (ICF) are simple and effective techniques for reducing the peak-to-average ratio (PAPR) in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems, but effective PAPR suppression requires a lot of iterations. To overcome this shortcoming, a joint algorithm based on improved active constellation expansion (IACE) and ICF (IACE-ICF) is proposed. The simulation results show that at the complementary cumulative distribution function (CCDF) of 10−4, the PAPR of IACE-ICF (G=4, iter=4) algorithm is optimized by 1.507 dB, 1.13 dB and 0.204 dB compared with that of the IACE, ICF (iter=4) and ICF-IACE (G=4, iter=4) algorithms, respectively. Meanwhile, when the bit error rate (BER) is 10−3, the optical signal to noise ratio (OSNR) of the proposed scheme is optimized by 2.04 dB, 1.75 dB and 1.4 dB compared with that of clipping, ICF (iter=4) and ICF-IACE (G=4, iter=4) algorithms, respectively. On the other hand, the proposed scheme can reduce the number of complex multiplications by 14.29% and complex additions by 28.57% compared with the ICF (iter=14) scheme.

Peak-to-Average Power Ratio Reduction in Pilot-Embedded OTFS Modulation Through Iterative Clipping and Filtering

In this letter, the method to reduce peak-to-average power ratio (PAPR) is studied in the pilot-embedded orthogonal time frequency space modulation where guard symbols with zero padding are introduced to avoid the interference between data and pilot symbols. By permitting the guard symbols to be padded with signals of small magnitudes, an efficient PAPR reduction method based on the iterative clipping and filtering (ICF) framework is proposed. In the proposed method, first, the clipping noise other than the clipped signal is filtered; second, the filtering coefficients for the clipping noises in the data-plus-pilot region and guard region are set to be different values to achieve good tradeoff between PAPR and bit error rate (BER) performance. Simulation results show that the proposed method can reduce the PAPR efficiently with mild BER performance loss.

Sparsity-Learning-Based Iterative Compensation for Filtered-OFDM With Clipping

This letter is concerned with the high peak-to-average power ratio (PAPR) problem in filtered orthogonal frequency-division multiplexing (f-OFDM) systems. Iterative clipping and filtering (ICF) is adopted as a simple and effective method to suppress PAPR but introduces signal distortion. At the receiver, we propose a sparsity-learning based iterative algorithm for distortion compensation by exploiting the sparsity of the distortion. Specifically, our iterative algorithm consists of a linear estimator, a soft demodulator, and a distortion estimator. The iteration between the three modules is based on turbo message passing. We show that our scheme outperforms the conventional iterative methods in both complexity and performance. Numerical results demonstrate that our algorithm achieves more effective PAPR suppression and better error rate performance.

PAPR Reduction Using Iterative Clipping/Filtering and ADMM Approaches for OFDM-Based Mixed-Numerology Systems

Mixed-numerology transmission is proposed to support a variety of communication scenarios with diverse requirements. However, as the orthogonal frequency division multiplexing (OFDM) remains as the basic waveform, the peak-to average power ratio (PAPR) problem is still cumbersome. In this paper, based on the iterative clipping and filtering (ICF) and optimization methods, we investigate the PAPR reduction in the mixed-numerology systems. We first illustrate that the direct extension of classical ICF brings about the accumulation of inter-numerology interference (INI) due to the repeated execution. By exploiting the clipping noise rather than the clipped signal, the noise-shaped ICF (NS-ICF) method is then proposed without increasing the INI. Next, we address the in-band distortion minimization problem subject to the PAPR constraint. By reformulation, the resulting model is separable in both the objective function and the constraints, and well suited for the alternating direction method of multipliers (ADMM) approach. The ADMM-based algorithms are then developed to split the original problem into several subproblems which can be easily solved with closed-form solutions. Furthermore, the applications of the proposed PAPR reduction methods combined with filtering and windowing techniques are also shown to be effective.

A Hybrid Approach to Reduce the PAPR of OFDM Signals Using Clipping and Companding

Orthogonal frequency division multiplexing (OFDM) is an important technology that has been widely used in broadband wireless communications. However OFDM has some drawbacks, one of which is the high peak-to-average power ratio (PAPR) problem. Many techniques for reducing PAPR thus have been proposed in the literatures, where clipping and companding are effective techniques and have gained a lot of research interest. Based on the study of clipping and companding, this paper proposes a hybrid approach to reduce the PAPR of OFDM signals. An iterative clipping and filtering (ICF) technique and an enhanced nonlinear companding (ENC) scheme are used as the typical clipping and companding techniques in this paper. The results of the analysis show that the computational complexity of the proposed method is slightly higher than that of ENC, but much lower than that of ICF. And the simulation results show that the proposed method has better performance on PAPR reduction and bit error rate (BER) in contrast to ICF. On the other hand, compared to ENC with equal PAPR reduction, the proposed method still achieves better performance on BER.

A Clipping-Noise Compression Method to Reduce PAPR of OFDM Signals

Iterative clipping and filtering (ICF) is widely employed in the orthogonal frequency-division multiplexing (OFDM) systems to reduce the peak-to-average power ratio (PAPR). However, the conventional ICF-based methods usually involve numerous transformations between the frequency domain and the time domain and run into numbers of iteration. This letter proposes a clipping-noise compression method, in which the transmitted OFDM signal is modified in the time domain by clipping and noise compression. The computational complexity is greatly reduced owing to the fact that only one fast Fourier transform is needed in the approach. Furthermore, the proposed method exhibits better PAPR reduction and bit error rate (BER) performance in the simulations compared with the conventional ICF-based methods.

Iterative smoothing filtering schemes by using clipping noise‐assisted signals for PAPR reduction in OFDM‐based carrier aggregation systems

Aggregating a lot of subcarriers will generate high peak-to-average power ratio (PAPR) which makes the overall system performance degradation. Among the existing PAPR reduction methods for orthogonal frequency-division multiplexing (OFDM)-based systems, iterative clipping and filtering (ICF) may be easy to implement, but ICF may cause signal distortion, so that the system cannot approximate the processed signals to the original signals which degrades error rates at receivers. Here, the authors proposed a new method based on ICF with smoothed clipping signals, and find the optimised filter to achieve the minimum error vector magnitude and efficiently reduce PAPR. Owing to the lack of a wide range of continuous bandwidth, the Third Generation Partnership Project proposed carrier aggregation (CA) technology in LTE-advanced systems. CA can aggregate many contiguous or non-contiguous fragment spectrums for supporting larger bandwidth and higher peak data rate. Here, the authors also evaluate the developed PAPR reduction scheme for the use in CA scenarios. The efficacy of the proposed scheme is demonstrated in the simulation results.

Iterative Clipping-Noise Compression Scheme for PAPR Reduction in OFDM Systems

The application of orthogonal frequency division multiplexing (OFDM) has become more and more widespread in recent years. However, the high peak-to-average power ratio (PAPR) problem is still one of the critical issues in the implementation of OFDM systems. Among the techniques of PAPR reduction, iterative clipping and filtering (ICF) is widely used due to its easy implement, and many ICF-based methods have been proposed recently. The optimized ICF (OICF) further has been designed with an optimized filter and achieves faster convergence rate. And the simplified OICF (SOICF) applies Lagrange multiplier method to simplify the problem solving as compared to OICF. The approach saves SOICF from using complicated convex optimization methods. Most recently the clipping-noise compression (CNC) method is proposed to reduce the required number of Fourier transforms by compressing the clipping noise in the time domain. Based on SOICF, this paper adopts clipping and noise compression to replace the calculation of PAPR-reduction vector in each iteration. Analysis shows that the computational complexity of the proposed scheme is lower than SOICF. In addition, we have improved the CNC technique and introduced a compression threshold in the proposed scheme. In each iteration, only the components whose amplitude exceeds the compression threshold are compressed, while the others remain unchanged. To this end, this reduces the amount of information lost, resulting in better BER performance. The simulation results show that the proposed scheme has better BER performance than SOICF, and better PAPR reduction than CNC. When equal amounts of PAPR reduction by the evaluated methods are actually achieved, the BER performance of the proposed scheme is better than SOICF and CNC, especially with high-order modulation or lower clipping ratio.

An Enhanced Iterative Clipping and Filtering Method Using Time-Domain Kernel Matrix for PAPR Reduction in OFDM Systems

Iterative clipping and filtering (ICF) is a straight-forward method for reducing the peak-to-average power ratio (PAPR) of signals in orthogonal frequency-division multiplexing (OFDM) system. Recently, convex optimization has been used to find the optimal filter coefficients that minimize the error vector magnitude (EVM) and meet the PAPR constraint. However, high-computation complexity may be incurred when solving the convex optimization problem. Therefore, we develop an efficient PAPR reduction method that uses the time-domain kernel matrix to generate the PAPR-reduction signal. Besides, we relax the assumption that the clipping noise is a series of uncorrelated parabolic pulses and apply the proposed method to more general cases. Based on the instantaneous observation of clipping noise, the proposed method constructs a simple time-domain kernel matrix and employs the curve fitting approach to optimize the corresponding scaling factors. The simulation results show that the proposed method can achieve very close performance to that using convex optimization in terms of both the PAPR reduction and EVM while the computational cost is reduced greatly. In addition, due to the decrease of iteration numbers and computational complexity, the proposed method is more efficient than some existing clipping and filtering methods.

On the Optimization of Iterative Clipping and Filtering for PAPR Reduction in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) offers spectral efficiency advantage, however, it is limited by peak-to-average power (PAPR) problem. The PAPR can be reduced using iterative clipping and filtering (ICF) scheme but requires that the same signals are iteratively clipped with a fixed clipping threshold at different clipping iterations. This method warrants that fast-Fourier transform (FFT)/inverse FFT (IFFT) blocks must be driven in the order of iterations many times to attain a desired PAPR threshold which expends the system power and expands the processing time. Using a second-order cone program, the number of iterations required to attain the desired PAPR threshold was reduced. This optimized ICF (OICF) was later simplified using Lagrange multiplier (LM). In this paper, we apply an adaptive clipping threshold to the LM scheme to improve the performance of the simplified OICF (SOICF). Our results show significant reduction of the PAPR problem compared with the earlier SOICF scheme albeit with some degradation in the bit error ratio (BER) performance that can be under 1.0 dB depending on the chosen clipping threshold. In addition, we also illustrate the results of the performances and the theoretical relationships between the error vector magnitude (EVM) and PAPR, between clipping ratio (CR) and EVM, and lastly the inter-dependencies of EVM, PAPR, the number of OFDM subcarriers, and the CR.

Neural Network Based Simplified Clipping and Filtering Technique for PAPR Reduction of OFDM Signals

Many iterative clipping and filtering (ICF) based techniques have been proposed that achieve similar peak-to-average power ratio (PAPR) reduction of orthogonal frequency division multiplexing (OFDM) signals as the original ICF, but with lower complexity, such as the simplified clipping and filtering (SCF) technique. However, these low complexity methods require numerous complex fast Fourier transform (FFT) operations and parameter calculations. In this letter, we introduce a novel ICF method that uses an optimized mapper based on artificial neural network and SCF techniques. Compared to the conventional ICF based methods, the proposed scheme offers desirable cubic metric (CM) and bit error rate (BER) simulation results with significantly reduced computational complexity.

PAPR Reduction Techniques Comparison inOFDM System

In recent years, multimedia based application which requires the technology that supports high speed data transmission is growing rapidly. To achieve this high speed communication orthogonal frequency division multiplexing (OFDM) is most widely used technology. OFDM system makes the use of orthogonal subcarriers for data transmission with efficient usage of available bandwidth. However as number of subcarriers goes on increasing, Peak to average power ratio (PAPR) of OFDM signal also increasing. This high PAPR causes significant distortions when passed through non-linear amplifier. A number of promising techniques have been proposed & implemented to reduce PAPR of OFDM signal with expense of transmitted signal power, Bit error rate (BER), complexity etc. In this paper, amplitude clipping and filtering (ACF), Iterative clipping and filtering (ICF) and interleaved OFDM techniques are implemented for PAPR reduction of OFDM signal at transmitter. Comparison of these PAPR reduction techniques is done based PAPR and BER performance of the system.

Iterative companding transform and filtering for reducing PAPR of OFDM signal

In this paper, an efficient Iterative Companding Transform and Filtering (ICTF) technique is proposed for reducing the Peak-to-Average Power Ratio (PAPR) of Orthogonal Frequency Division Multiplexing (OFDM) signal. By means of a specially designed iterative procedure, ICTF is able to obtain both an improved Bit Error Rate (BER) and minimized Out-of-Band Interference (OBI) while reducing the PAPR significantly. A comprehensive theoretical analysis is presented, and some important results such as the achievable PAPR gain, impact of companding distortion, and selection criteria for companding parameters and maximum iteration number are derived. In particular, it is shown that the ICTF without de-companding at the receiver can offer a good BER performance. Simulations show that compared to the classic Iterative Clipping and Filtering (ICF) technique, ICTF can dramatically decrease the number of required iterations to reach the desired PAPR with low complexity. In addition, the companded OFDM symbols by the proposed ICTF technique have less in-band distortion, and lower out-of-band spectral regrowth than traditional companding schemes.

PAPR Reduction of OFDM Signal via Custom Conic Optimized Iterative Adaptive Clipping and Filtering

High peak to average power ratio (PAPR) of OFDM reduces the transmitter power efficiency and increases the complication in hardware implementation. A number of techniques have been developed to minimize PAPR of OFDM. Among these techniques, iterative clipping and filtering (ICF) is an effective recent technique that produces significant results in minimizing PAPR. But, the major limitation of this approach is that it requires several iterations for minimizing PAPR. In order to overcome the above limitation, an optimization based ICF is used in this research work. An efficient custom optimized adaptive clipping and filtering technique is proposed. The proposed method shows a greater reduction in PAPR in lesser iterations with reduced out-of-band distortion and bit error rate when compared over classical clipping techniques. Moreover, the effects of oversampling on the performance of the proposed OFDM system are also evaluated.

Iterative Decoding of Iterative Clipped and Filtered OFDM Signal

A communication system with non-linear power amplifier (PA) is considered. We introduce three major performance criteria of the system: (i) power efficiency of the PA, (ii) spectral purity of the transmitted signal expressed by adjacent channel interference, and (iii) transmission performance expressed by mutual information or symbol error rate. In order to fulfill the first two criteria it is proposed to use iterative clipping and filtering (ICF) at the transmitter together with low input back-off, while the third criterion is obtained by modified iterative receiver (MIR). The proposed MIR is based on the well-known iterative receiver, but with ICF in the feedback path. The obtained results show that the proposed system is better than its competitors when considering the three performance criteria together. The analysis and results are focused on OFDM; however, the proposed approach may be applied to single carrier.