采用矢量孔技术的新型OFDM信号峰均比降低技术

介绍了一种新颖的OFDM信号峰均比降低技术,不仅削去峰值信号,也削去谷值信号,从而最大程度上降低了信号的峰均比。矢量孔技术可以同时调整信号幅度和相位,使得信号矢量回避零点,信号谷值由此被削去。为了限制峰均比降低技术带来的带内和带外失真,该方法还进一步结合了闲置载波技术。仿真结果表明,经过该方法对QPSK调制的OFDM信号进行降低峰均比处理之后,信号峰均比从10.61dB降低到了7.03dB,EVM值保持为4.93%。该方法可以大幅度提高OFDM通信系统中功率放大器的效率和线性度。     

Conjugate Interleaved Partitioning PTS Scheme for PAPR Reduction of OFDM Signals

The interleaved partitioning partial transmit sequence (IP-PTS) scheme is an attractive technique for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems. But the PAPR performance of IP-PTS is inferior to that of the adjacent partitioning PTS (AP-PTS) scheme because the candidates generated in IP-PTS are not fully independent. This paper analyzes the independence of candidates in IP-PTS in detail and finds the effective phase factor vectors. In order to improve the PAPR performance of IP-PTS, a conjugate IP-PTS (C-IP-PTS) scheme is proposed. By performing the conjugate operations on some sub-blocks, the number of candidates is increased. Because of the conjugate property of the discrete Fourier transform (DFT), the additional inverse DFT can be avoided. By optimizing the conjugate sequence, the complexity can be further lowered. Simulation results show that C-IP-PTS can obtain better PAPR performance compared with AP-PTS; moreover, the computational complexity of C-IP-PTS is not high.     

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.     

A Novel Multi-Points Square Mapping Combined With PTS to Reduce PAPR of OFDM Signals Without Side Information

In this paper, we first propose a novel multi-points square mapping (MSM) scheme. Then, we describe in detail how to combine the proposed MSM scheme with conventional partial transmit sequence (C-PTS) scheme, named as M-PTS, to reduce the PAPR of OFDM signals. Compared with C-PTS, the proposed M-PTS scheme needs not to submit side information while keeping almost the same performance of PAPR reduction as the C-PTS scheme. Extensive simulations are conducted to validate analytical results, showing that the proposed M-PTS scheme has better bandwidth efficiency and bit error ratio (BER) performance compared with the C-PTS scheme.      

一种抑制PAPR信号峰均功率比的有效方法

OFDM技术的应用越来越广泛,但是其发送信号功率的峰均功率比（PAPR）比较大是其主要的缺陷之一。本文提出了一个降低OFDM信号PAPR的有效灵活的技术。该方法是通过恰当的选择OFDM调制中各个子载波的时域脉冲波形。仿真结果表明该方法能够大大降低OFDM信号的PAPR值。该技术与现有的其他方法相比实现复杂度也更低。     

A Selected Mapping Technique Using Interleavers for PAPR Reduction in OFDM Systems

Wireless Personal Communications - In this article, we propose a new selected mapping (SLM) technique using interleavers for reducing high peak-to-average-power ratio (PAPR) in orthogonal frequency...     

一种降低OFDM信号PAPR的新方法

正交频分复用(OFDM)技术的一个缺点是信号的高峰值平均功率比(PAPR)大大降低了系统中线性功放的效率。本文提出一种新的基于Nyquist脉冲成形的PAPR抑制方法。这种方法基于选择适当的Nyquist脉冲波形集合对OFDM的各个子载波进行脉冲成形。分析论证了该方法的PAPR上限值和所用的脉冲成形波形集合。仿真结果表明该方法能有效降低任意子载波数目的OFDM信号的PAPR值,而且与已有方法相比应用更为简单。因此脉冲成形技术不仅能对传输信号进行频谱成形来提高系统的频带利用率,而且还可以减小信号的PAPR值。     

PAPR Reduction of OFDM Signals Using Partial Transmit Sequences and Reed-Muller Codes

This letter proposes a modified PTS technique using binary Reed-Muller (RM) codes for error correction and PAPR control in BPSK OFDM systems. A RM code is divided into the direct sum of a correcting subcode for encoding information bits and a scrambling subcode for encoding PAPR bits. The transmitted signal of the resulting OFDM sequence is selected with minimum PAPR from a number of candidates which are codewords of a coset of the scrambling subcode. We consider the RM codes in natural and cyclic orderings. Numerical results show that RM codes in cyclic ordering achieve better performance in PAPR reduction than RM codes in natural ordering.     

Novel Low-Complexity Partial Transmit Sequences Scheme for PAPR Reduction in OFDM Systems Using Adaptive Differential Evolution Algorithm

A low-complexity partial transmit sequence (PTS) technique for reducing the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing signal is presented. However, the conventional PTS scheme requires an exhaustive searching over all combinations of allowed phase factors. Consequently, the computational complexity increases exponentially with the number of the subblocks. This paper presents a novel approach to the PAPR problem to reduce computational complexity based on the relationship between phase weighing factors and transmitted bit vectors. In this paper, we aim to obtain the desirable PAPR reduction with the low computational complexity. Since the process of searching the optimal phase factors can be categorized as combinatorial optimization with some variables and constraints, we propose a novel scheme, which is based on a stochastic optimization technique called modified differential evolution, to search the optimal combination of phase factors with low complexity. To validate the analytical results, extensive simulations have been conducted, showing that the proposed schemes can achieve significant reduction in computational complexity while keeping good PAPR reduction.     

OFDM无线通信中高峰均比及其抑制算法研究

凭借很强的抗符号间干扰(ISI)和抗衰落能力,采用正交频分信道的OFDM技术的无线通信越来越受到人们的重视。但是作为一种多载波调制方式,OFDM技术同样存在着高峰均比(PAPR)的问题,高的PAPR会导致信号畸变,造成子信道间的相互干扰,从而影响OFDM的性能。针对此,重点介绍了OFDM系统中的PAPR比问题的概念,并对降低PAPR的主要算法进行了论述。     

一种降低正交频分复用调制信号峰平比的融合方法

提出了一种降低峰平比(PAPR)的融合算法,该算法在发射端对正交频分复用(OFDM)调制信号进行两次降低峰值处理,因而降低PAPR的能力远远优于常规的选择性映射法和压扩法,而该新方法传输信号的性能与压扩法相当。     

PAPR Reduction of OFDM Signals Using Partial Transmit Sequences With Low Computational Complexity

Partial transmit sequences (PTS) is one of the attractive techniques to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) system. As conventional PTS technique requires an exhaustive searching over all the combinations of the given phase factors, which results in the computational complexity increases exponentially with the number of the sub-blocks. In this paper, we aim to obtain the desirable PAPR reduction with the low computational complexity. Since the process of searching the optimal phase factors can be categorized as combinatorial optimization with some variables and constraints, we propose a novel scheme, which is based on a nonlinear optimization approach named as simulated annealing (SA), to search the optimal combination of phase factors with low complexity. To validate the analytical results, extensive simulations have been conducted, showing that the proposed schemes can achieve significant reduction in computational complexity while keeping good PAPR reduction.     

降低OFDM信号峰均功率比的压扩方法研究

本文通过理论推导和分析,确定了基于误差函数降低正交频分复用(OFDM)系统峰均功率比的非线性压扩方法中两个关键参数的取值,修正了以前的结果,并在此基础上提出了一种新的压扩函数来降低OFDM系统的峰均功率比.理论分析和仿真结果表明,新的压扩方法能够在保持原信号平均功率不变的情况下使峰均功率比降低到7.8dB以下,并且系统具有较好的误比特率性能.     

A Computationally Efficient Tree-PTS Technique for PAPR Reduction of OFDM Signals

The high peak-to-average power ratio (PAPR) of time domain signals has been a major problem in orthogonal frequency division multiplexing (OFDM) systems, and thus various PAPR reduction algorithms have been introduced. Partial transmit sequence (PTS) is one of the most attractive solutions because of its good performance without distortion. However, it is considered as an impractical solution for the realization of high-speed data transmission systems due to its high computational complexity. In this paper, a novel PAPR reduction algorithm based on a tree-structured searching technique is proposed to reduce the PAPR with low complexity. In the proposed scheme, the computational complexity of searching process is decreased by adjusting the size of tree with two parameters, width and depth, while preserving good performance. The simulation results show that proposed scheme provides similar performance with optimum case with remarkably reduced computational complexity.     

Bit-Based SLM Schemes for PAPR Reduction in QAM Modulated OFDM Signals

In this paper, we propose two bit-based selected mapping (SLM) schemes for reducing peak to average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals with quadrature amplitude modulation (QAM), called bitwise SLM (BSLM) and partial bit inverted SLM (PBISLM). Contrary to the conventional SLM which rotates the phases of QAM symbols in the frequency domain, the proposed schemes change the magnitudes as well as the phases of QAM symbols by applying binary phase sequences to the binary data sequence before mapped to QAM symbols. Simulation results show that the proposed schemes have better PAPR reduction performance with shaping gain than the conventional SLM scheme for the QAM modulated OFDM signals, especially for the small number of subcarriers.      

An Adaptive Clipping and Filtering Technique for PAPR Reduction of OFDM Signals

In recent years, many peak-to-average power ratio (PAPR) reduction techniques have been proposed for orthogonal frequency division multiplexing (OFDM) signals. Among various techniques, the iterative clipping and filtering (ICAF) technique has been considered as a practical scheme, and widely used owing to its non-expansion of bandwidth, low computational complexity, and simplicity in implementation without receiver-side cooperation. However, the performance of conventional ICAF technique is degraded, because the same signals are iteratively clipped with a fixed clipping threshold (CT) in every clipping operation. In this paper, we analyze the performance of conventional ICAF technique, and then propose an adaptive ICAF scheme, which clips the signal with an adaptively modified CT in every clipping operation to achieve enhanced PAPR reduction of OFDM signals. Simulation results show that the proposed scheme significantly outperforms the conventional scheme, in PAPR reduction of OFDM signals at the same number of iterations.     

Performance Analysis of the Clipping Scheme with SLM Technique for PAPR Reduction of OFDM Signals in Fading Channels

Since one of major problems of OFDM-based systems is high peak-to-average-power ratio (PAPR) of its transmitted signal, many PAPR reduction techniques and combined schemes with individual techniques have recently been developed. Among various techniques, the clipping technique has been widely used as a practical scheme owing to its low computational complexity and simplicity in implementation, while the selected mapping (SLM) technique is known to provide good PAPR reduction performance without signal distortion. Generally, the combined scheme of two PAPR reduction techniques, which are the clipping and the SLM, is expected to provide the enhanced performance of PAPR reduction, because the clipping noise of combined scheme would be less than that of single clipping technique, when the SLM technique is employed before clipping. However, the performance of clipping scheme with SLM technique has not been evaluated for practical systems over fading channels. In this paper, the performance of the clipping scheme with the SLM technique is theoretically analyzed and compared with simulation results over fading channels. The performance of combined scheme is analyzed with various clipping ratios, phase sets for SLM, and modulation schemes over flat and frequency selective fading channels. In addition, the effects of the clipping at the receiver and the oversampling on the BER performance are discussed. Based on the results of analysis, therefore, one can design the effective clipping scheme with the SLM technique for the PAPR reduction of OFDM-based systems.     

Novel Conversion Matrices for Simplifying the IFFT Computation of an SLM-Based PAPR Reduction Scheme for OFDM Systems

There have been a set of conversion matrices proposed recently by Wang and Ouyang to simplify the inverse fast Fourier transform (IFFT) computation involved in the selected mapping (SLM) scheme for reduction of the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. As compared to the conventional SLM scheme, the modified approach achieves close PAPR reduction with much lower complexity but degraded bit error rate (BER) performance. In this paper, we propose a new set of conversion matrices for the SLM scheme such that the complexity can be reduced without sacrificing the BER performance. It is shown that the improved SLM method has better BER performance and lower complexity than the previous work by Wang and Ouyang, at the cost of a slight PAPR reduction loss.     

PAPR Reduction in OFDM Signals: An Adaptive-Network-Based Fuzzy Inference Approach

In this paper, an adaptive-network-based fuzzy inference system (ANFIS) based scheme is analyzed and proposed for reducing the peak-to-average power ratio (PAPR) in multicarrier signals under additive white Gaussian noise and multipath fading (Raleigh) channel environment. This scheme involves training of ANFIS structure in time domain using Orthogonal Frequency Division Multiplexing signals with low PAPR, such as those obtained by approximate gradient project–null subcarrier switching (AGP–NCS) method. Once the ANFIS module is trained, the proposed scheme approximately offers similar reduction in PAPR as compared to AGP–NCS method, with significantly less convergence time and computational complexity. he results show that proposed approach is not only less complex but also maintains the data rate and bit error rate performance compared with other conventional schemes.     

Partial Shift Mapping for PAPR Reduction with Low Complexity in OFDM Systems

The high peak‐to‐average power is one of the main drawbacks in OFDM systems. This letter proposes a partial shift mapping (PSM) method for peak power reduction in OFDM systems. By utilizing the properties of the discrete Fourier transform, the proposed method generates a set of candidate signals without additional complex multiplication and selects the one with minimum peak power for transmission. Analyses and simulations confirm that the PSM method achieves satisfactory peak power reduction performance and low complexity compared with other kindred methods, for example, selected mapping and partial transmit sequences.