一种降低OFDM系统PAPR的联合压扩算法研究

正交频分复用(OFDM)技术的一个主要缺点是其拥有较高的峰值平均功率比(PAPR),当其通过非线性放大器后将产生很严重的性能失真。在众多的降低PAPR的算法中,压扩变换算法因其实现简单得到了广泛的关注。文中提出了一种联合压扩变换算法,实验仿真表明,该算法具有更好的PAPR抑制效果,提高了OFDM系统的性能。     

一种降低OFDM系统PAPR的改进压扩方法

正交频分复用（OFDM）技术是一种多载波调制方式。作为第四代移动通信系统的核心技术,OFDM己成为当今高速无线通信领域的研究热点。正交频分复用（OFDM）系统存在高峰值平均功率比（PAPR）问题,这一问题会导致系统性能降低,为其实用化设置了障碍。文中研究了一种改进的降低PAPR的非线性压缩与扩展算法,可以得到更好的PAPR性能。该方法的特点在于采用一种计算复杂度较低的非线性压扩函数,同时融合了叠加训练序列方法的改进非线性压扩算法,从而有效地降低系统PAPR。理论研究和仿真结果表明,与传统方法相比,所提出的改进压缩与扩展方法可以在降低系统复杂度的同时得到更好的PAPR性能。     

使用μ-law压扩算法降低OFDM系统PAPR的分析

提出使用μ-law压扩算法降低OFDM系统PAPR(峰值平均功率比),对PAPR概率分布进行了理论分析。理论分析和仿真结果表明采用压扩技术可有效地降低OFDM系统的PAPR,同时还对采用预失真放大器AWGN信道中的OFDM系统的性能进行了仿真。     

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。     

联合限幅和μ律压扩抑制可见光通信系统的峰均功率比北大核心CSCD

直流偏置光正交频分复用(DC-biased optical orthogonal frequency division multiplexing,DCO-OFDM)可见光通信(visible light communication,VLC)系统具有较高的峰均功率比(peak-to-average power ratio,PAPR)。为解决此问题,提出一种联合限幅和归一化μ律压扩算法抑制DCO-OFDM系统的PAPR。首先,该联合算法利用限幅操作对时域信号中的大峰值信号进行削波来降低信号的幅值;其次,对限幅后的信号再进行压扩变换。通过这种联合算法,DCO-OFDM系统的PAPR可以显著降低。实验仿真结果表明,当采用16QAM调制方式,互补累计函数的值为10^(-3)时,相比较于联合限幅和传统μ律压扩算法,此联合算法的PAPR下降了约2.206 dB。     

基于时频子空间投影的LOFDM系统时域相关信道估计算法

Strohmer T与Beaver S于2003年提出了适用于时频散射信道的网格正交频分复用 (LOFDM, Lattice Orthogonal Frequency Division Multiplexing)系统,与传统OFDM系统相比该系统具有更高的频带利用率和更好的误码性能。LOFDM系统发送端需要自适应地调整信号的原形脉冲和其时频分布的参数,使之与信道保持匹配;而接收端则需要准确的信道估计以实现相干解调。本文针对LOFDM 系统由于其信号的时频交错特性接收端无法直接利用接收信号进行时域信道估计的问题,采用一种低复杂度的等效时频子空间投影方法有效分离奇偶子载波,并在此基础上提出了一种LOFDM系统频率选择性块衰落信道条件下的时域信道估计算法。同时还对系统存在的干扰进行了分析,推导得到LOFDM系统信道估计算法的Cramér-Rao理论下界。仿真表明:提出的LOFDM信道估计算法不仅具有较好的均方误差性能,而且近似达到理想信道估计的误符号率性能。      

自适应压扩和IDFT技术降低光OFDM系统的PAPR

在光正交频分复用系统中,由于光功率放大器、调制器和光纤本身的非线性,高峰均功率比会大大降低系统的性能.为抑制光OFDM系统的PAPR,提出一种新的基于线性变换和自适应压扩技术的方案.仿真结果表明,与传统压扩方法相比,该方法既能更加有效地抑制光OFDM的PAPR,又能够使系统得到更好的误码率性能.     

适于硬件实现的降OFDM峰均比的分段压扩法

降低信号的峰均功率比(PAPR)是正交频分复用(OFDM)技术的一个关键问题。μ律压扩法作为降低PAPR的一个重要方法,其非线性的特点难于在硬件上实现。在传统的μ律压扩方法基础上,介绍了一种分段线性压扩方法,并对其效果进行仿真评估,并提出一种新的硬件实现方法,在降低复杂度上有良好的效果。     

联合迭代滤波与压扩参数优化的OFDM信号峰平比抑制

针对现有基于压扩变换处理的信号峰平比抑制方法性能单一且参数固定等缺陷,提出一种联合迭代滤波与自适应压扩参数优化的OFDM信号峰平比抑制方案。该方案能够同时对信号的峰平比PAPR和接收端误码率BER性能进行联合优化,并在迭代过程中有效消除因信号幅度畸变所引起的带外频谱再生;所提信号压扩及解压扩函数形式简单,计算复杂度较小;推导并给出了该方案可获得的PAPR抑制增益和BER理论性能界。仿真结果表明,该方案可同时获得较好的信号PAPR抑制、误码率以及带外功率谱性能,并在迭代过程中对压扩参数进行自适应调整,能够有效提高算法的适用灵活性。     

基于循环平稳的LOFDM系统双散射信道最大多普勒扩展盲估计

Strohmer T与Beaver S于2003年提出了适用于时频散射信道的网格正交频分复用(LOFDM,Lattice Orthogonal Frequency Division Multiplexing)系统,与传统OFDM系统相比该系统具有更高的频带种用率和更好的误码性能.LOFDM系统发送端需要自适应地调整信号的原形脉冲和其时频分布的参数与信道保持匹配,以尽可能地降低符号间干扰和载波间干扰的影响.最大多普勒扩展作为信道时变性的直接反映,是LOFDM系统自适应策略的重要参数之一.本文针对LOFDM系统的信号特性,提出了一种双散射信道条件下基于循环平稳的LOFDM系统最大多普勒扩展盲估计算法,克服了现有估计算法存在频谱效率浪费的不足.理论分析与计算机仿真表明:算法可在信道多径信息未知的情况下实现较大取值范围的多普勒扩展的有效估计,具有良好的归一化均方误差性能,且抗噪声能力较强、收敛速度较快.     

A novel criterion for designing of nonlinear companding functions for peak-to-average power ratio reduction in multicarrier transmission systems

Nonlinear companding transform is a promising technique for the peak-to-average power ratio (PAPR) reduction in multicarrier transmission systems. However, conventional hard piecewise companding schemes often along with serious nonlinear distortion or complex companding parameters optimization embarrassment. In this paper, a novel designing criterion of nonlinear companding functions with more effective system performance is proposed. By transforming the Gaussian-distributed multicarrier signals into desirable statistics forms, we show that the smooth and differentiable concave probability distribution function of companded signals can obtain a better PAPR reduction and less out-of-band radiation as well as more simple companding parameters optimization than the traditional piecewise companding schemes. A detailed theoretical analysis and discussion is formulated, and then based on the analysis results, a novel trigonometric function companding scheme is presented and evaluated. Numerical results demonstrate that the companding schemes which consistent with the proposed criterion may significantly outperform conventional schemes by choosing the companding form and parameters appropriately.     

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.

     

Exponential companding technique for PAPR reduction in OFDM systems

In this paper, a new nonlinear companding technique, called "exponential companding", is proposed to reduce the high Peak-to-Average Power Ratio (PAPR) of Orthogonal Frequency Division Multiplexing (OFDM) signals. Unlike the /spl mu/-law companding scheme, which enlarges only small signals so that increases the average power, the schemes based on exponential companding technique adjust both large and small signals and can keep the average power at the same level. By transforming the original OFDM signals into uniformly distributed signals (with a specific degree), the exponential companding schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Moreover, many PAPR reduction schemes, such as /spl mu/-law companding scheme, cause spectrum side-lobes generation, but the exponential companding schemes cause less spectrum side-lobes. Computer simulations, which consider a baseband OFDM system with Additive White Gaussian Noise (AWGN) channels and a Solid State Power Amplifier (SSPA), show that the proposed exponential companding schemes can offer better PAPR reduction, Bit Error Rate (BER), and phase error performance than the /spl mu/-law companding scheme.     

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.     

Nonlinear companding transform for reducing peak-to-average power ratio of OFDM signals

A new nonlinear companding transform scheme is proposed to reduce the peak-to-average ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) signals. By exploiting statistical distribution of transmitted OFDM signals, the proposed scheme effectively reduces the PAPR by compressing the peak signals and expanding the small signals, while maintaining the average power unchanged by properly choosing transform parameters. The fact that the proposed companding scheme is described by a single-valued function allows to be transformed before amplification and to be restored the signals at the receiver. The proposed scheme can be applicable with any modulation format and subcarriers. Our simulations results confirm that the suggested scheme exhibits a good ability to reduce PAPR and a good BER performance with a solid state power amplifier (SSPA) in an additive white Gaussian noise (AWGN) channel.     

新的低复杂度降低OFDM信号峰均功率比的压缩扩张技术

本文提出了一种新的降低OFDM信号峰均功率比的压缩扩张技术.文中通过与传统压缩扩张技术的对比,详细介绍了新压缩扩张技术的方法和计算复杂度、并从统计角度分析了对峰均功率比及其用于OFDM系统时对系统误比特率的改善等方面的性能.数值仿真说明,与传统压缩扩张技术相比较,新压缩扩张技术不仅具有更低的计算复杂度,而且可以获得更为高效的性能增益.     

降低正交频分复用系统峰均功率比的部分压扩算法

针对现有压扩变换法系统性能差的缺点,提出了一种降低系统峰均功率比的部分压扩算法。该方法根据正交频分复用(OFDM)系统信号幅度服从瑞利分布的统计特性,仅压缩大幅度信号保持了系统信号幅度的分布特征,弥补了现有压扩变换的不足,且具有带外功率小的优点。在M阶调制方式下的系统仿真结果表明,部分压扩方法与选择性映射和部分传输序列等方法相比,可获得相近的峰均功率比压缩效果并且在同样的系统误码率条件下比指数压扩法获得约log2(M)dB信噪比增益。     

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.     

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.     

Threshold-based piecewise companding transform for PAPR reduction in OFDM systems

Piecewise companding transform is a flexible and efficient way to solve the high peak-to-average power ratio (PAPR) problem for orthogonal frequency division multiplexing (OFDM) systems. A novel threshold-based piecewise companding transform is proposed in this paper. Based on the statistical characteristics of amplitudes, OFDM signals are classified into three groups (i.e., small, average and large signals). Different from conventional approaches, two dedicated designed thresholds are set to amplify the small signals and compress the large signals, respectively. Simulation results verify the improvement in PAPR reduction of the proposed scheme. Moreover, a lower bit error rate (BER) performance loss can be obtained by introducing the iterative detection with a moderate increase in complexity.