Low-complexity PAPR reduction technique for OFDM systems using modified widely linear SLM scheme

In this paper, a modified widely linear selective mapping (MWL-SLM) scheme is proposed to reduce the peak-to-average power ratio (PAPR) of the orthogonal frequency-division multiplexing (OFDM) systems. In the proposed MWL-SLM scheme, through partition one complex signals into two real signals and combining the linear properties of the Fourier Transform, at most 4M² candidate signals can be obtained but only require M inverse fast Fourier transform (IFFT) operations. As a result, the proposed SLM scheme has the ability to generate more candidates when compared with conventional SLM (C-SLM) and widely linear SLM (WL-SLM). Therefore, MWL-SLM outperforms C-SLM and WL-SLM for the same computational cost of IFFT operations. Alternatively, for a given number of candidates, MWL-SLM has slightly inferior PAPR reduction performance to C-SLM and WL-SLM but requires less IFFT operations to be implemented, thus resulting in a lower computational complexity. Simulation results demonstrate the effectiveness of the proposed scheme.     

OFDM峰均功率比降低方法概述

OFDM技术具有抗干扰能力强、频谱效率高、数据传输速率高等优点，但其主要缺点是有很高的峰均功率比（PAPR），影响其的实际应用。现对不同降低OFDM峰均功率比方法分别进行了概述，并给出比较。     

光OFDM系统中削波噪声的建模与研究

针对光正交频分复用(OFDM)系统中峰值平均功率比(PAPR)较高的缺点,研究了削波法降低PAPR的原理;根据这一原理,通过大量数据分析计算,建立了基于MQAM调制下光OFDM系统中的削波噪声模型;由所建立的模型,直接计算得出不同调制下光OFDM系统削波后的误符率。仿真结果表明,每种进制调制下,根据本文建立的削波噪声模型与OFDM具体系统模型仿真所得到的两条曲线基本吻合,并且这两条曲线在不同削波比下的最大均方误差(MSE)不超过1.26×10-2。这充分论证了所建立的削波噪声模型的可行性与适用性。     

Evaluation of Performance Improvement Capabilities of PAPR-reducing Methods

One of the major drawbacks of multicarrier modulation is the large envelope fluctuations which either require an inefficient use of high power amplifiers or decrease the system performance. Peak-to-average power ratio (PAPR) is a very well known measure of the envelope fluctuations and has become the cost function used to evaluate and design multicarrier systems. Several PAPR-reducing techniques have been proposed with the aim to alleviate back-off specifications or increase the system performance. Besides the fact that these techniques have varying PAPR-reduction capabilities, power, bandwidth and complexity requirements, it is interesting to notice that the performance of a system employing these techniques has not been fully analyzed. In this paper we, first, develop a theoretical framework for both PAPR and the distortion introduced by a nonlinearity, and then simulate an OFDM system employing several well known PAPR-reducing techniques from the literature. By means of the theoretical analysis and the simulation results we will show the relation between PAPR and the performance of OFDM systems when a clipping device is present and we will evaluate the real performance improvement capabilities of the PAPR-reducing methods. The agreement between the theoretical and the simulation results demonstrate the validity of the analysis.

A phase scrambling scheme for suppression of peak to average power ratio for OFDM

The complex-valued modulating vectors for the subcarrlers consist of two kinds of components: One is the information-bearing components superposed with pseudo-randomized phases and the other is the suppression components with specified scrambling phases. The pseudorandomized phases are generated according to the predefined polynomial and mapping function whereas the scrambling phases are from a gradient algorithm. The simulation results verify the rationality and validity of the phase scrambling.     

A novel constellation amplitude modification method for PAPR reduction in OFDM systems

In this paper, we propose a constellation amplitude modification (CAM) method to reduce the peak‐to‐average power ratio (PAPR) in orthogonal frequency division multiplexing systems. The key idea of the proposed CAM method is to modify the original constellation amplitude and choose the constellation points with the minimum PAPR as the transmitted constellation points. The CAM method formulates the PAPR reduction as a convex optimization problem, and then, it applies the customized interior‐point method to solve the optimization problem. Compared with the traditional methods, the CAM method does not increase the transmit power, and the receiver has no additional operations. Simulation results show that the CAM method converges fast and offers significant PAPR reduction. Copyright © 2016 John Wiley & Sons, Ltd.     

光OFDM系统中一种改进的SLM峰均比抑制方案

针对光正交频分复用(O-OFDM)系统中峰值平均功 率比(PAPR)较高的缺点,对PAPR抑制技术的选择性 映射法(SLM) 进行了深入研究。基于低复杂度SLM方案的深入研究,提出了一种改进的次PAP R选择的思 想与低复杂度SLM相结合的PAPR抑制方案。改 进的SLM方案能够成倍降低传统SLM方案的计算复杂 度。仿真分析表明,改进的SLM方案在载波数为256的O-OFDM系统中,计算复杂度能降低50%以上,并 且随着子载波数的增加,其复杂度降低程度更为高效;同时,该改进的SLM方案又能使其PAPR抑制性能优于传统的SLM方案,从而进一步提升了低复杂度SLM 方案的实用价值。     

一种改进的低复杂度OFDM峰均比抑制PTS算法

针对正交频分复用系统中的信号峰值平均功率比问题,提出了一种基于时域采样点幅度筛选的低复杂度部分传输序列算法。算法通过设置信号经过逆向傅里叶变换后时域采样点的幅度之和为判别函数,并设置适当的幅度门限,筛选出幅度大于门限的信号采样点集合,利用该集合来搜索信号峰均比抑制相位因子,从而降低算法复杂度。仿真表明,与传统峰均比抑制算法相比,改进算法在保持峰均比抑制性能的同时降低了算法复杂度。     

降低OFDM系统峰均功率比的研究

对载波干涉技术降低OFDM的峰均功率比方法进行改进。先对输入信号进行分组,使系统峰值功率得到明显降低,之后再对分组后的信号进行载波干涉。理论分析及仿真结果表明,提出的方法能使系统峰值功率有明显降低,进而达到了进一步的降低峰均功率比的目的。该方法算法简单、不产生失真,不用传送边带信息,易于与其他降低PAPR的技术相结合使用,具有较好的实用性。     

降低OFDM信号峰均功率比的分段线性压扩变换

为了降低OFDM信号的峰均功率比(PAPR),设计了一种分段线性压扩变换.对小幅度通过数乘变换进行线性放大,而对大幅度先利用数乘变换进行线性缩小,再对缩小后的幅度进行等量放大.得到的压扩变换是分段线性且连续的,用低复杂度的线性运算抑制峰均比,同时用分段的方法减小压扩对系统性能的影响.理论分析和仿真表明,通过数乘因子和增...     

A dual protection scheme for impulsive noise suppression in OFDM systems

Orthogonal frequency division multiplexing (OFDM) can be susceptible to impulsive noise arising from numerous sources in a noisy communications environment. Conventional Reed–Solomon (RS) codes are particularly useful for burst-error corrections and have been employed in OFDM systems to manage impulsive noise. The performance gains, however, have been somewhat limited given the sensitivity to other noise types typically present in a noisy channel. In this regard, a novel scheme utilizing a time-domain pre-processing mean filter in combination with RS coding is proposed for impulsive noise suppression in OFDM systems. This scheme is split into two stages. In the first stage, a proposed mean filter effectively detects and removes the impulsive noise using the measured statistics of the impulsive noise. In contrast to a conventional blanking type filter, the traditional mean replacement value is replaced by a composite comparison value (CCV). This principle creates a more accurate estimate of the original OFDM signal after impulsive noise removal. The residual impulsive noise is then managed by a RS decoder in the second stage. Our results show that this dual faceted approach improves OFDM performance when compared to filtering and coding techniques alone.     

降低OFDM系统高峰均功率比的方法研究

针对OFDM技术具有较高的峰均功率比（peak to average power ration,PAPR）这一主要缺点,提出一种控制OFDM载波信号衍生频谱的迭代算法,在降低系统高峰均功率比的同时,也降低系统的误码率.利用该算法对数据序列长度为64的OFDM信号进行仿真验证,随着迭代次数的增加,衍生频谱系数增大,系统平均功率增加,OFDM信号的峰值功率比得到一定的降低.     

电力线OFDM/OQAM通信系统信道相位预处理均衡算法

针对电力线通信（PLC）正交频分复用（OFDM）系统存在频率掩码和频谱资源利用率低等问题,提出将正交频分复用/偏移正交幅度调制（OFDM/OQAM）技术应用到PLC系统中。该技术通过选用频率选择性较好的滤波器来抑制带外干扰,且不需要循环前缀,但是OFDM/OQAM系统在PLC频域复数信道下会产生严重的自干扰,传统的均衡算法并不能有效地消除OFDM/OQAM系统的固有干扰。针对这种情况提出了一种基于信道相位预处理的均衡算法。该算法的思想是让接收信号乘以一个信道相位调整因子,使等效信道的虚部尽量小,以此来减小接收信号中的干扰分量。仿真结果表明,与传统的均衡算法相比,所提算法在误比特率为1.0×10－6时可以获得0.5dB的性能提升。     

一种基于OPTS的降低OFDM峰均比的低复杂度算法

正交频分技术最主要缺点之一就是传输信号的高峰均值功率比,部分传输序列法是解决高峰均值功率比的最有效方法之一。虽然最优部分传输序列方法性能很好,但其计算复杂度非常大,搜索复杂度随着子块数指数增加,这样降低搜索复杂度显得尤为重要。本文改进TOPTS搜索过程中计算时域矢量的计算方法,使其计算复杂度大大降低,但系统性能不受影响。     

Peak-to-average power ratio of selective mapping technology involving a phase generation mechanism based on polar codes for orthogonal frequency division multiplexing with index modulation systems

In this paper, a novel selective mapping (SLM) method is proposed for reducing the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems. In the proposed method, polar codes are used to construct the SLM phase generation mechanism. This systematic structural design is superior to conventional methods in which phases are randomly generated. Moreover, polar codes and Reed–Muller codes are selected to protect the input data of the OFDM-IM system. The weight distribution of the Reed–Muller codes is then used to determine the location data of the active subcarriers in the OFDM-IM system, and these data are used to determine the error correction capacity. Simulation results indicated that the PAPR improvement achieved using the proposed method is similar to that achieved with conventional SLM methods. Moreover, linear block codes are used to construct the active subcarrier selection and SLM phase generation mechanisms to ensure that both mechanisms have systematic structural designs.     

基于DHT的光OFDM系统PAPR抑制算法

针对光OFDM系统存在高峰均功率比(PAPR),提出了一种基于离散哈特利变换(DHT)的选择映射抑制算法。采用快速哈特利逆变换(IFHT)代替传统的快速傅立叶逆变换(IFFT)和Hermi t i an对称算法,并结合非对称限幅法产生满足光OFDM系统要求的正、实值信号送入光纤信道。     

相干OFDM系统中导引符号功率优化

在瑞利衰落信道下，本文研究了导引符号功率对相干OFDM系统性能的影响，计算了由于不精确信道估计引起的系统性能损失，优化分析了导引符号与数据符号功率比，并给出完整的最优功率分配数学表达式。理论分析和仿真结果给出了各种参数对最优功率比的影响，同时理论结果为系统设计提供了依据。     

A PAPR reduction technique using Hadamard transform combined with clipping and filtering based on DCT/IDCT for IM/DD optical OFDM systems

In Intensity Modulator/Direct Detection (IM/DD) optical OFDM systems, the high peak-to-power average ratio (PAPR) will cause signal impairments through the nonlinearity of modulator and fiber. In this paper, a joint PAPR reduction technique based on Hadamard transformation and clipping and filtering using DCT/IDCT transform has been proposed for mitigating the impairments in IM/DD optical OFDM system. We then experimentally evaluated the effect of PAPR reduction on the bit error rate (BER) performance and the results show the effectiveness of the proposed technique. At a bit error rate (BER) of 1 × 10⁻³, the receiver sensitivity of the proposed 2.5 Gb/s IM/DD optical OFDM system after 100-km standard single-mode fiber transmission has been improved by 0.8 dB, 1.3 dB and 3.1 dB for a launch power of 6.4 dBm, 8 dBm and 10 dBm respectively when compared with the classical system.     

Nonlinear effect mitigation based on PAPR reduction using electronic pre-distortion technique in direct-detection optical OFDM system

The nonlinear effect induced by the Mach–Zehnder modulator (MZM) and optical self-phase modulation (SPM) in the presence of high peak-to-average power ratio (PAPR) is investigated theoretically. We theoretically and experimentally investigate the direct-detection optical orthogonal frequency-division multiplexing (DD-OOFDM) system with an electronic pre-distortion technique of companding transform (CT) to reduce the peak-to-average power ratio (PAPR) of OFDM signals and improve the receiver sensitivity. Experimental results show that the PAPR reduction can reach about 3 dB when the complementary cumulative distribution function is 1 × 10⁻⁴, which means the number of random OFDM signals is 1 × 10⁴, and the receiver sensitivity is improved by 0.7, 1.7, and 2.4 dB for the launch power of 2, 6 and 10 dB m, respectively, at the BER of 1 × 10⁻⁴ after transmission over 100-km single-mode fiber with the μ of 2. It shows that the PAPR reduction can mitigate not only the nonlinearity of MZM, but also the nonlinear phase noise in the fiber link when the optical power into fiber is high.     

Low-cost adaptive directly modulated optical OFDM based on semiconductor optical amplifier

Low cost optical OFDM has great potential for next generation optical access networks and PONs, due to its high flexibility in bandwidth manipulation, and high spectral efficiency. Here, a low cost optical OFDM is proposed, based on adaptive direct modulation semiconductor optical amplifier. Adaptive current loading techniques for PAPR (peak to average power ratio) reduction are proposed and analyzed. Simulations show that the proposed adaptive techniques enable significant BER improvement.