OFDM系统中基于压缩感知恢复由限幅和HPA产生的非线性失真研究

正交频分复用（Orthogonal Frequency Division Multiplexing,OFDM）系统的主要缺点之一就是有较高的峰均功率比（Peak to Average Power Ratio,PAPR）,降低了功率放大器（High Power Amplifier,HPA）的工作效率,同时HPA引入的非线性失真,恶化了系统的误比特率（Bite Error Rate,BER）性能.本文所提算法将限幅和HPA引入的非线性失真视为一个整体来考虑,利用与限幅噪声在时域上的近似稀疏性,对整个非线性过程进行建模.发送端通过限幅降低了OFDM信号的PAPR,在接收端,选取受噪声干扰小的可靠性观测向量,最小化信道噪声的影响,基于非线性模型计算得到的参数,利用压缩感知（Compressive Sensing,CS）算法能有效地恢复总的非线性失真信号,提升了系统的BER性能.     

低复杂度OFDM信号峰均功率比压缩技术

本文提出了一种用于减小OFDM信号峰均功率比(Peak-to-Average Power Ratio,PAPR)的压缩扩张变换技术.该技术能够以相对较低的计算复杂度大大降低OFDM信号的PAPR.作为应用实例,本文分析了线性压缩扩张、非线性对称压缩扩张和非线性准对称压缩扩张的PAPR改善幅度、计算复杂度、及其用于OFDM系统时对系统误比特率(BER)的改善等方面的性能.实验仿真表明,与采用传统的限幅滤波方法相比,本文提出的技术可以获得较明显的性能增益.     

降低OFDM系统峰均比的改进方法

正交频分复用（OFDM）系统最主要的一个缺点就是峰值平均功率（PAPR）比过高,选择性映射（SLM）虽然能无失真地降低OFDM信号峰均比PAPR,但不能完全避免OFDM系统高峰值的出现。提出一种新的算法,将SLM法与迭代限幅滤波算法结合,通过迭代限幅滤波（RCF）来进一步提高系统的性能。仿真结果表明,该方法可以在不增加系统误码率性能的基础上,在降低OFDM信号峰均比方面,比限幅法、迭代限幅滤波法和SLM法均有很大的提高。     

OFDM系统中基于压缩感知的非线性失真恢复研究

正交频分复用系统(OFDM)的高峰均比(PAPR)问题降低了系统传输效率,增加了解调难度,使高功率放大器(HPA)满负载工作.该文针对削波与HPA引入的非线性失真问题,提出在接收端采取基于泰勒级数的预处理方式对非线性干扰进行处理,最小化信号畸变影响.在发送端通过削波降低信号的PAPR,并利用削波噪声在时域上的稀疏性特性,将传输过程作为整体考虑,最后利用正交匹配追踪算法(OMP)恢复总的非线性失真信号.仿真结果表明,该文所提方法能够有效抑制系统的干扰信号,减少了有用信号受到的非线性影响,验证了该方案的正确性.     

联合法降低OFDM系统的非线性失真

正交频分复用技术(OFDM,Orthogonal Frequency Division Multiplexing)是一种有效的并行多载波传输方案,然而,OFDM技术存在一个主要缺点,即发送信号存在较高的峰值平均功率比(PAPR,Peak-to-Average Power Ratio)。研究表明高带宽效率的限幅类技术着眼于直接降低OFDM信号的峰均比,而幅度和相位预失真方法则是从放大器的角度出发,对放大器进行预失真处理,增大功率放大器的线性范围。这里提出将限幅类技术和预失真处理进行联合实现,从而在系统PAPR减小、失真补偿和误码率之间取得较好的折中。     

OFDM信号限幅滤波的性能分析

OFDM是一种多载波调制技术,其特有的调制特性决定了它有较高的峰均功率比值PAPR（Peak-to-Average Power Ratio）。高峰均功率比信号会对实际放大器提出很高的线性要求,因此它是限制OFDM技术实用化的主要障碍。目前虽有很多降低OFDM信号的PAPR的方案,但大多是以增加系统的复杂程度为代价的。限幅滤波法是一种计算复杂度较小的算法。文中针对600Mb/s高速数传数据经4路子载波（每路150Mb/s）调制后的OFDM信号的PAPR进行了分析,并对限幅滤波法进行了仿真。     

MIMO-OFDM系统峰均比抑制技术的研究

针对MIMO-OFDM系统的高峰均功率比(PAPR)问题,提出了一种改进的PTS与限幅的联合算法。该联合算法先将MIMO-OFDM信号经过改进的PTS优化算法进行处理从而选出PAPR值最小的那一路信号,然后再将其经过限幅处理进一步降低系统的PAPR。仿真结果显示,该联合算法不仅可以有效地降低系统的PAPR,还可以减小信号经过限幅后引起的非线性失真,从而显著提高系统的整体性能。     

减小OFDM系统PAPR的限幅滤波方法分析

为了减小正交频分复用(OFDM)系统的高峰值平均功率比(PAPR),采用了限幅滤波方法。该方法是一种简单有效的减小PAPR方法,首先对离散时域的过采样(L4)的OFDM信号执行限幅,然后让限幅的信号通过带通滤波器(BPF)和低通滤波器(LPF),最后通过功率谱密度(PSD)观察、PAPR分布和BER性能分析对该方法进行性能评价。仿真结果表明,该方法在减小系统的PAPR的同时,也有效地改善了系统的性能。     

OFDM系统峰平比问题的研究

OFDM技术最主要的缺点是具有较大的峰值平均功率比（PAPR）。本文就目前降低PAPR对OFDM系统影响的主要方法进行了简单的综述，一类是从OFDM信号着手；包括剪波法（限幅法），编码技术，相位旋转方法；另一类方法是对高频率放大器的实现线性化技术，主要是放大器预失真方法。     

一种改进的降低OFDM信号PAPR的虚拟序列插入法

正交频分复用（OFDM）系统在时域上的高峰值平均功率比（PAPR），会导致OFDM信号在传输过程中引入互调噪声，从而严重降低系统的误码率（BER）性能。本文研究了一种改进的虚拟序列插入（DSI）法，可以得到更好的PAPR性能。该方法的特点在于采用时频域交换算法来改变所有时域信号的预定相位系数以优化每一个虚拟子载波的相位，从而降低系统的PAPR。计算机仿真结果表明，与传统的DSI方法相比，该方法可以在降低系统复杂度的同时得到更好的PAPR性能。     

OFDM系统中基于压缩感知的非线性失真恢复研究

正交频分复用系统(OFDM)的高峰均比(PAPR)问题降低了系统传输效率,增加了解调难度,使高功率放大器(HPA)满负载工作。该文针对削波与HPA引入的非线性失真问题,提出在接收端采取基于泰勒级数的预处理方式对非线性干扰进行处理,最小化信号畸变影响。在发送端通过削波降低信号的PAPR,并利用削波噪声在时域上的稀疏性特性,将传输过程作为整体考虑,最后利用正交匹配追踪算法(OMP)恢复总的非线性失真信号。仿真结果表明,该文所提方法能够有效抑制系统的干扰信号,减少了有用信号受到的非线性影响,验证了该方案的正确性。     

Combination of PAPR reduction and linearization for the OFDM communication system

Orthogonal frequency division multiplexing (OFDM) has been widely used in many kinds of communication systems. However, OFDM signal has serious problem of high peak‐to‐average‐power ratio (PAPR) due to so many sub‐carriers. So, OFDM signal has very wide dynamic range. Therefore, the bit error rate (BER) performance may be degraded because of the nonlinear devices like the high power amplifier (HPA). Even if the linearization and large back‐off are used to compensate for the HPA nonlinearity, the power efficiency of the HPA is still very low since the PAPR is very high. Therefore, the PAPR reduction of the OFDM signal before the linearization would be more reasonable to improve the power efficiency and nonlinear compensation at the same time. In this paper, we propose a new combined method of SPW (sub‐block phase weighting) for PAPR reduction and linearization technique for the improvement of the power efficiency and for the nonlinear compensation of HPA. An updated SPW method is proposed to use a novel weighting factor multiplication of the complementary sequence characteristic and PAPR threshold technique. From the simulation results, it can be confirmed that BER performance is significantly improved and out‐of‐band spectrum radiations are much mitigated. Power efficiency of HPA can be enhanced since we can set small IBO (input back‐off) due to the PAPR reduction. The proposed system shows about 3 and 1 dB performance improvement than the LCP (linearized constant peak‐power)‐OFDM and LCP‐OFDM plus SPW at BER = 10⁻⁴. Copyright © 2010 John Wiley & Sons, Ltd.     

影响预失真OFDM系统的关键参数IBO阈值的研究

OFDM系统的一个主要缺陷就是峰平比过高引起的高功率放大器(HPA)的非线性失真.该文研究了当使用预失真器进行补偿时,系统的接收误码率BER随HPA的输入回退IBO值变化而产生的性能改变,从而给出系统性能有效改善时,HPA的IBO阈值.     

PAPR reduction for OFDM‐based visible light communication systems using proposed hybrid technique

Orthogonal Frequency Division Multiplexing (OFDM) is utilized with visible light communication (VLC) systems to decrease the impacts of inter‐symbol interference and to achieve communication with high speed of data transmission and huge bandwidth. In any case, the main problem in OFDM‐based VLC systems is high peak‐to‐average power ratios (PAPRs). This paper proposes a hybrid PAPR reduction technique based on signal transformation combined with clipping. The Hadamard transform is used in the proposed technique to reduce the PAPR without affecting the bit error rate (BER) of the VLC systems. The optimum clipping threshold at which the PAPR is reduced simultaneously with the improvement the BER of the VLC systems is also determined. The performance of the proposed system is assessed in terms of complementary cumulative distribution function and the BER. The obtained results demonstrate that the proposed procedure can simultaneously decrease the PAPR and achieve good BER performance compared to the OFDM‐based VLC system.     

Hybrid Zadoff‐Chu and multilateral piecewise exponential companding transform–based PAPR reduction technique in OFDM systems

The orthogonal frequency‐division multiplexing (OFDM) is a multicarrier modulation system that is used to transmit the large volume of data to the receiver. Reducing the peak‐to‐average power ratio (PAPR) in OFDM system is one of the demanding and crucial task in recent days. For this reason, various precoding and companding mechanisms are developed in the traditional works, but it remains with the limitations of increased complexity, reduced performance, and nonlinear distortion. The reduction of PAPR is achieved by minimizing the companding distortion with the enhancement of the bit error rate (BER) performance significantly. Then, in order to avoid clipping in OFDM, a multilateral piecewise exponential companding transform (MPECT) method has been utilized rather than using piecewise exponential companding transform (PEC) where PAPR is getting reduced. The OFDM is very sensitive to synchronizing error. To overcome this sensitivity, employ the Zadoff‐Chu sequence to carrier frequency offsets. Zadoff‐Chu matrix transform (ZCMT) has numerous merits among the other ODFM systems such as the improvement in the performance of the channels that are fading away and provides an ideal periodic autocorrelation and a constant magnitude periodic cross correlation. Both of these techniques provide improvement in the ODFM systems. To get more efficiency, this paper aims to develop a hybrid technique by integrating the ZCMT and MPECT techniques for reducing the PAPR in OFDM systems. Further, convolutional encoding is applied for better BER and PAPR. The simulation results of the proposed ZCMT‐MPECT technique are evaluated and compared with the conventional OFDM and other precoding methods.     

Transforming the Statistical Distribution of Wireless OFDM Signal for PAPR Reduction

To reduce the high peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signal, a novel nonlinear companding transform (CT) scheme is proposed in this paper. This scheme can reallocate both the amplitude/power as well as statistical distribution of the companded signal more reasonably and flexibly than existing CT methods with low computational complexity. By choosing an appropriate companding parameter, it can provide more effective PAPR reduction but at the price of a minimal amount of bit-error-rate (BER) performance degradation caused by the companding distortion. The closed-form expressions including the achievable PAPR gain, signal attenuation factor, and corresponding selection criteria for the companding parameter were derived. Computer simulations demonstrate that the scheme significantly improves the overall performances of OFDM system in terms of PAPR, BER and bandwidth efficiency under the multipath fading channel or with the high power amplifier.

     

A ZCMT Precoding Based Multicarrier OFDM System to Minimize the High PAPR

This paper presents a Zadoff-Chu matrix transform (ZCMT) precoding based multicarrier orthogonal-frequency-division-multiplexing (OFDM) system to minimize the high peak-to-average power ratio (PAPR). In the proposed system, ZCMT kernel is applied to the constellation symbols which not only reduces PAPR but also improves bit-error-rate (BER) performance. The ZCMT precoded OFDM signals allow the radio-frequency high-power-amplifier (HPA) to operate near its saturation level, thus maximize the power efficiency. Extensive computer simulations have been performed to analyze the PAPR, BER and power-spectral-density (PSD). Simulation results show that the proposed system has excellent PAPR gain and BER performance with no spectral distortion.     

Combining discrete cosine transform with clipping for PAPR reduction in intensity-modulated OFDM systems

In this paper, the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signal is reduced by combining the discrete cosine transform (DCT) with clipping in optical intensity-modulated direct-detection (IM/DD) OFDM systems. First, the data are transformed into new modified data by DCT. Second, the proposed scheme utilizes the clipping technique to further reduce the PAPR of OFDM signal. We experimentally demonstrate that the optical OFDM transmission system with this proposed scheme can achieve significant performance improvement in terms of PAPR and bit error rate (BER) compared with the original optical OFDM systems.