OFDM系统中降低峰均功率比的研究

正交频分复用技术(Orthogonal Frequency Division Multiplexing,OFDM)非常适合高速通信系统,但存在高峰均功率比(PAPR)的问题。对OFDM系统中如何降低PARR的问题进行了研究,讨论了降低PAPR的主要方法,重点分析了选择性映射法(SLM),并在此基础上提出了一种基于预编码矩阵的改进算法,最后通过matlab进行了算法仿真,仿真结果表明,改进算法在使得OFDM系统在降低峰均功率比的性能上得到了进一步的改善。     

减小WT-OFDM系统PAPR的GA-SLM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),采用了选择映射法(SLM)。SLM方法是一种有效的减小OFDM系统PAPR方法且不会产生信号失真。由于SLM方法需要设置循环前缀,可以通过离散小波变换(WT)改善OFDM系统,然后通过遗传算法(GA)搜索最佳相位旋转因子。仿真结果表明,该方法与传统的GA-SLM与SLM相比,能更有效地减小系统的PAPR。     

用后置IFFT幅度随机选择器降低OFDM的PAPR

OFDM和DMT多载波传输系统固有的高峰均功率比(PAPR)能导致功率传输效率的严重退化,特别是用电池作为电源的终端更为严重.目前文献中最常用的PAPR减少技术是选择性映射(SLM)序列技术,它已经达到能把PAPR减少几dB的程度.尽管SLM技术对减少PAPR表现得不错,但是实际上,每个OFDM数据串进行传输的时候,它都需要进行多次的IFFT(快速傅里叶变换)运算,这就增加了的系统的复杂性.因此SLM方法有较长的计算时间和较高的功率消耗.建议了一种低复杂度的前置IFFT的PAPR减少方法,它在PAPR减少方面能比SLM方法做得更好,与此同时它的计算复杂度比SLM有较大的减小.     

次优化SLM法降低OFDM系统PAPR

正交频分复用（OFDM）系统的主要缺点是发射机输出信号的高峰均功率比（PAPR）。选择性映射（SLM）法能有效地降低OFDM信号的PAPR概率,但它需要一组逆快速傅立叶变换（IFFT）来产生候选传输信号,这将导致高的计算复杂度。本文给出一种低复杂度的次优化SLM算法。仿真结果表明该次优化SLM算法在降低PAPR相似的情况下,具有更小的计算复杂度。     

FrFT-OFDM系统的低复杂度峰均功率比抑制技术研究

针对基于分数阶Fourier变换的OFDM系统(简称FrFT-OFDM系统)的高峰均功率比(PAPR)问题,该文提出一种低复杂度的峰均比抑制算法。通过对随机相位序列采用周期延拓至FrFT-OFDM符号长度,相位因子加权后与子载波调制前的数据相乘的方式,实现对高峰均比的有效抑制。该算法只需要一次逆离散分数阶Fourier变换(IDFrFT),所有备选信号直接通过时域chirp圆周移位的加权和得到。仿真结果表明,当备选信号个数相同时,该算法与选择映射(SeLecting Mapping, SLM)算法的PAPR抑制性能相当,比部分传输序列(Partial Transmit Sequence, PTS)算法具有更好的PAPR抑制性能,同时,该算法较SLM和PTS算法的运算量降低。     

OFDM系统中基于SLM降低PAPR的新算法

SLM(选择性映射)算法能解决OFDM(正交频分复用)系统中的高PAPR(峰均功率比)问题,但是基本的SLM算法具有较高的计算复杂度。提出一种G-SLM(分组SLM)算法,该算法通过将输入信号进行分组的方式来降低其与相位因子结合时的算法复杂度。仿真结果表明,该算法不但保持了较低的算法复杂度,同时又有效地降低了PAPR。     

一种新的相位序列在选择性映射中的应用

正交频分复用（OFDM）和多载波码分多址（MC-CDMA）被广泛认为是未来4G通信的核心技术。但是,OFDM和MC-CDMA信号的高峰均功率比（PAPR）会引起非线性失真并导致误码率性能恶化,这已成为它们实用化的最大障碍。选择性映射（SLM）是一种能有效地降低系统PAPR方法,其中相位序列的选择直接影响降低PAPR的效果。提出将一种新的伪随机扰码作为选择性映射中的相位序列来降低OFDM和MC-CDMA系统的PAPR,仿真得出这种伪随机扰码序列能有效地降低系统的PAPR,且优于传统Walsh-Hadamard、Golay序列。     

OFDM系统中降低峰均功率比技术的研究

作为第四代移动通信系统的核心技术,正交频分复用(OFDM)已成为当今高速无线通信领域的研究热点。但是OFDM调制中存在的高峰均功率比(PAPR),为其实用化设置了障碍。在介绍了峰均功率比(PAPR)概念的基础上,简述了目前降低峰均功率比的几种方法,最后着重讲述了选择映射法(SLM)和部分传递序列法(PTS),并进行了仿真比较。     

一种基于SLM的抑制PAPR的改进算法研究

正交频分复用(OFDM)作为一种特殊的多载波传输(MCM)方案,具有较高的频带利用率和良好的抗多径干扰能力。但较高的峰均功率比(PAPR)是限制其应用的一个主要缺点。选择性映射(SLM)算法是无失真降低OFDM系统PAPR的有效方法,但其复杂度较高。因此提出了一种基于SLM的抑制PAPR的改进算法。仿真结果表明,该方法即有效地降低了SLM实现的复杂度,又大幅降低了PAPR,提高了OFDM系统性能。     

一种降低OFDM系统PAPR联合算法的研究

选择映射法(SLM)和概率类算法都可以降低OFDM(Orthogonal Frequency Division Multiplexing)系统的PAPR(Peak to Average Power Ratio),传统SLM算法自身较为复杂,但由于其优良的性能,弃之可惜。研究表明,SLM算法和限幅类算法在性能上具有一定的互补性。任何一个算法未必能达到抑制PAPR的理想效果,在深入研究了两个算法的基础上,将其优点联合起来,以达到降低OFDM系统PAPR的目的。最后对联合改进算法进行了分析与仿真,并验证了联合改进算法的有效性和可行性     

Peak-to-average power control in OFDM using standard arrays of linear block codes

We propose an efficient scheme to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems by using the standard arrays of linear block codes. Our scheme may be regarded as a modified version of the selective mapping (SLM), which is a probabilistic method to reduce the PAPR by selecting a signal with minimum PAPR from several candidates as the transmit signal. Because the coset leaders of a linear code are used for scrambling in our scheme, no side information is required to be transmitted and the received signal can be easily decoded by syndrome decoding. Simulation results show that our scheme has good performance in PAPR reduction.     

Modified selected mapping technique for PAPR reduction of coded OFDM signal

High peak-to-average power ratio (PAPR) of the transmitted signal is a major drawback of orthogonal frequency division multiplexing (OFDM). In this paper, we propose a modified selective mapping (SLM) technique for PAPR reduction of coded OFDM signal. In this technique, we embed the phase sequence, which is used to lower the PAPR of the data block, in the check symbols of the coded OFDM data block. It is shown that we can achieve both PAPR reduction from the SLM technique as well as error performance improvement from the channel coding with no loss in data rate from the transmission of side information. In addition, approximate expression for the complementary cumulative distribution function (CCDF) of the PAPR of the modified SLM technique is derived and compared with the simulation results.     

OFDM与MIMO-OFDM系统中PAPR问题研究

正交频分复用(OFDM)和MIMO-OFDM技术都存在高峰均比的问题,大多数方法都是把降低OFDM峰均比的方法直接使用MIMO-OFDM系统,但在与MIMO-OFDM系统的匹配上存在较大问题。分析了OFDM和MIMO-OFDM的系统模型及PAPR,从理论上分析了OFDM和MIMO-OFDM两系统的关系,给出了在MIMO-OFDM系统中降低PAPR需要注意的问题,为OFDM和MIMO-OFDM系统的技术实用化做好理论基础。     

An efficient sphere decoding approach for PTS assisted PAPR reduction of OFDM signals

It is well known that one of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the potentially high peak-to-average power ratio (PAPR) of the (OFDM) signal. Partial transmit sequence (PTS) is a widely accepted method in reducing PAPR of OFDM signal. As traditional optimal PTS (OPTS) technique requires an exhaustive search over all the combinations of the allowed phase factors the search complexity increases exponentially with the number of sub-blocks. In this paper, a new precalculated radius sphere decoding (PRSD) is presented. It can achieve the same PAPR performance but at lower computational complexity compared with OPTS and existing sphere decoding (SD) approach at zero decoding failure rate.     

Nonbinary LDPC Coding for Multicarrier Underwater Acoustic Communication

Recently, multicarrier modulation in the form of orthogonal frequency division multiplexing (OFDM) has been shown feasible for underwater acoustic communications via effective algorithms to handle the channel time-variability. In this paper, we propose to use nonbinary low density parity check (LDPC) codes to address two other main issues in OFDM: (i) plain (or uncoded) OFDM has poor performance in fading channels, and (ii) OFDM transmission has high peak to average power ratio (PAPR). We develop new methods to construct nonbinary regular and irregular LDPC codes that achieve excellent performance, match well with the underlying modulation, and can be encoded in linear time and in a parallel fashion. Based on the fact that the generator matrix of LDPC codes has high density, we further show how to reduce the PAPR considerably with minimal overhead. Experimental results confirm the excellent performance of the proposed nonbinary LDPC codes in multicarrier underwater acoustic communications.     

A Modified SLM Scheme With Low Complexity for PAPR Reduction of OFDM Systems

In this paper, we propose a new peak-to-average power ratio (PAPR) reduction scheme of orthogonal frequency division multiplexing (OFDM) system, called a modified selected mapping (SLM) scheme, which considerably reduces the computational complexity with keeping the similar PAPR reduction performance compared with the conventional SLM scheme. The proposed scheme is analytically and numerically evaluated for the OFDM system specified in the IEEE 802.16 standard. For the OFDM system with 2048 subcarriers, the proposed scheme with 4 binary phase sequences can reduce the complex multiplications by 63.5% with the similar PAPR reduction compared with the SLM scheme with 16 binary phase sequences.     

用于SFBC MIMO-OFDM系统的改进SLM算法

在空频编码(SFBC)多输入多输出正交频分复用(MIMO-OFDM)系统中传输符号存在较高峰均功率比(PAPR)问题,采用SLM算法能够有效降低系统峰均功率比,但随着发射天线数的增加,较多的快速傅里叶反变换(IFFT)会增加系统的计算复杂度,因此,构造F矩阵并提出了一种基于F矩阵SFBC MIMO-OFDM系统的改进SLM算法。采用F矩阵作为相位序列组对空频编码信号进行独立处理,获得最优相位序列取共轭,将共轭序列中每两个旋转因子为一个单位交换位置,并扰码SFBC后各天线的信号,以此减少了每根发射天线上的IFFT次数。理论和MATLAB仿真分析表明,该算法获得了良好的峰均比性能,同时也降低了系统的计算复杂度。     

A Low Complexity Selected Mapping Scheme by Use of Time Domain Sequence Superposition Technique for PAPR Reduction in OFDM System

By using the time domain sequence superposition (TDSS) technique, in this paper, we propose a low complexity selected mapping (LC-SLM) scheme for the peak-to-average power ratio (PAPR) reduction of the orthogonal frequency division multiplexing (OFDM) system. Unlike the conventional selected mapping (SLM) scheme which needs several inverse fast Fourier transform (IFFT) operations for an OFDM signal, the proposed scheme requires to implement two IFFT operations only. Thus, it can remarkably reduce the computational complexity. Simulation results show that the proposed scheme can achieve similar PAPR performance as the conventional SLM scheme.      

卫星激光通信中基于Fibonacci数列与GCD序列的非规则QC-LDPC码构造方法

为提高卫星激光通信系统的可靠性,节约其硬件资源,提出一种基于斐波那契(Fibonacci)数列与最大公约数(GCD)序列的非规则准循环低密度奇偶校验(Quasi-Cyclic Low-Density Parity-Check, QC-LDPC)码构造方法。该方法通过由Fibonacci数列与GCD序列组合构造的循环移位矩阵扩展原模图基矩阵,从而得到校验矩阵。所构造的校验矩阵围长至少为6且码长码率可灵活选择,需存储元素少,利于硬件实现,较适用于卫星激光通信系统。仿真结果表明,采用该方法构造的非规则QC-LDPC码与相同码率码长的基于完备差集的非规则Type-I QC-LDPC码、基于消除陷阱集的有限长度非规则FL-QC-LDPC码、基于GCD可快速编译的非规则GL-QC-LDPC码以及基于矩阵扩展的非规则RC-LDPC码相比,其净编码增益均有一定提高。     

Simple construction of OFDM signals with diversity gain and low PAPR

A simplified orthogonal frequency division multiplexing (OFDM) system with low peak-to-average power ratio (PAPR) and frequency diversity is proposed. The considered OFDM system exploits a frequency diversity by using a simple symbol repetition as is the case in previous work (i.e. Ko et al., MILCOM2002). From the presented results, it can be seen that a modified OFDM signal can be easily implemented with low PAPR, still maintaining the same diversity gain at the receiver as in Ko et al. However, a small increase of decoding delay may be expected.