一种降低CO-OFDM系统PAPR改进的星座图扩展算法

相干光正交频分复用(CO-OFDM)系统中的较大峰值平均功率比(PAPR)问题会导致严重的光纤非线性效应。本文提出了一种改进的星座图扩展(ACE)算法,取得了更好的PAPR抑制效果。研究表明,ACE算法与凸集投影法(POCS)相结合可减少计算复杂度,但存在峰值再生现象等问题。为此,本文利用抛物峰值抵消(PPC)算法改善迭代过程中的峰值再生现象,并采用星座映射预修正技术提高了收敛速度。采用改进算法对4QAM、29 Gb/s的CO-OFDM系统进行了仿真实验,结果表明改进算法使OFDM信号的PAPR降低了4.41 dB,并且具有更快的收敛速度。     

OFDM削波噪声迭代消除算法

高峰均功率比(PAPR)的OFDM信号通过功率放大器的时候会产生非线性干扰,同时降低了放大器的工作效率。传统削波算法可以降低信号的PAPR,但是会带来较大的频谱扩展。作为一种新的削波算法,误差削波可以在降低OFDM信号PAPR值的同时不带来任何频谱扩展。但是这种削波会给信号带来更大的带内干扰噪声。提出了一种OFDM削波噪声迭代估计和消除算法,它能有效的消除由于误差削波带来的噪声。新方法通过建立削波噪声模型,在接收端根据该噪声模型用迭代的方法重新产生削波噪声。仿真结果表明,使用削波噪声消除算法后,使得系统的误码率性能接近未削波信号的水平。     

OFDM系统PAPR和OOB辐射联合抑制算法研究

正交频分复用(OFDM)技术具有频谱效率高和抗多径衰落能力强的优点,但存在高峰值平均功率比(PAPR)和高带外(OOB)辐射的固有缺点。部分PAPR抑制算法会导致OOB辐射升高,因此需要一种联合抑制OFDM系统的PAPR和OOB辐射的算法。本文提出了一种新的结合线性压扩和简化限幅滤波的混合式PAPR和OOB辐射联合抑制算法,该算法采用连续分段线性压扩(CPLC)算法抑制信号PAPR,并对压扩后的信号进行频域滤波;然后采用简化限幅滤波(SCF)算法降低频域滤波导致的峰值再生,保证信号的OOB辐射不再升高。接收端采用迭代接收算法提高系统的误码率性能。仿真结果表明,与CPLC、SCF方案相比,所提算法可以达到更好的PAPR和OOB辐射联合抑制性能,同时通过迭代接收算法获得与原始信号相近的误码率(BER)性能。     

浅谈OFDM系统峰均比降低技术

正交频分复用（OFDM）技术以其频谱利用率高和抗频率选择性衰落强等优点，成为下一代移动通信中最具竞争力的关键技术之一，但存在峰均比值（PAPR）较高的问题。本文简要概述了目前降低峰均比的几种方法。     

针对OFDM系统的信道估计算法分析研究

正交频分复用（OrthogonalFrequencyDivisionMultiplexing,OFDM）技术具有极高的频效率和良好的抗多径干扰能力,受到人们的厂泛萝挑。本论文的第一章简要介绍了OFDM技术的背景和发展历史,指出了OFDM系统中信道估计的意义,接着分析了OFDM系统的信道估计算法和几种插值算法,进行了信道估计时相比。     

RA码在水声OFDM通信系统中的应用研究

正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)技术由于具有频谱利用率高、抗多径能力强等优点,成为当前水声通信的研究重点和热点,但较高的峰均功率比(Peak-to-Average Power Ratio, PAPR)严重影响了水声OFDM通信系统的性能。采用重复累积码(Repeat Accumulate, RA)作为信道编码方案,并用线性反馈移位寄存器(Linear Feedback Shift Registers, LFSR)代替原RA码结构中的累加器,再通过选择映射(Selective Mapping, SLM)方法降低系统的峰均功率比。计算机仿真和水池实验结果表明,采用改进结构的RA码结合SLM技术能有效降低水声OFDM系统的PAPR,提高系统的性能,具有很好的应用前景。     

峰值抵消CFR算法设计及FPGA实现

目前比较先进的无线通信系统,其信号峰均比较高,为保证信号不失真,必须要进行功放回退,从而导致功放效率下降。鉴于此问题,文章首先对波峰因子降低（CFR）算法进行了介绍,根据不同CFR算法性能对比,选择性能较好的峰值抵消CFR（PC_CFR）算法,然后对PC_CFR算法进行了MATLAB仿真及分析,最后对该算法进行了设计,并在FPGA上进行了实现。通过对Modelsim仿真结果的分析和硬件平台的实际测试,在保证EVM指标的条件下,可以获得降低PAPR约2.5 dB的效果,对提高功放效率具有重要的实用价值。     

一种新的OFDM峰均功率比抑制算法

峰均功率比(PAPR)过高是OFDM系统的一个主要缺点,由于OFDM发射端功率放大器的非线性,高的峰均功率比会导致信号的频谱扩展,同时降低了放大器的工作效率。传统的削波算法虽然能够简单有效地降低信号的峰均功率比,但是会带来较大的额外频谱增益。为了克服传统削波算法的缺点,文中提出一种新的削波算法,该算法在降低PAPR的同时做到零频谱增益。并基于传统削波产生误差信号,通过对误差信号的滤波,以牺牲信号的EVM实现了零频谱增益。但又会带来较大的带内干扰,仿真表明配合相应的噪声消除算法,其误码性能接近未削波的原始信号水平。     

基于CFD和试验的商用车高位引气管预滤性能的 分析与优化

为延长恶劣工况下某商用车进气系统空气滤清器滤芯的使用寿命,避免频繁更换滤芯,提出了增加旋流扇的高位引气管方案,并通过优化旋流扇夹角来提高进气系统预滤灰尘和液雾的效率,达到降低成本的目的。首先,采用计算流体力学（computational fluid dynamics,CFD）方法,对进气过程中高位引气管的内部流场进行数值模拟,分析了3款高位引气管的速度流线图和速度梯度云图,得到了高位引气管预滤灰尘和液雾的机理,并基于高位引气管速度流场的变化规律,提出了旋流扇夹角优化方向;其次,利用台架试验对优化后的高位引气管进行灰尘和液雾的预滤试验,并计算出灰尘和液雾的预滤效率;最后,对比不同高位引气管预滤灰尘和液雾的效率,根据两预滤效率的变化趋势,选择旋流扇最优夹角为75°。仿真和试验结果表明：旋流扇夹角对进气系统工作过程中高位引气管的流场及预滤效率有重要影响,优化旋流扇夹角有助于提高进气系统的预滤性能,从而减少进入空气滤清器的灰尘和液雾,达到延长空气滤清器滤芯寿命的目的。     

基于DSP的OFDM峰值抵消算法的研究与实现

1引言 OFDM通信系统使用具有正交关系的一组子载波来调制信号,在二进制比特映射到复信号后使用IFFT进行调制,所以OFDM能有效抑制多径信道引起的深度衰落、抵抗脉冲噪声和具有较高的频谱效率的特点。虽然OFDM子载波的高咯值统计独立,但其缺点是当子载波数目增加时,     

Selective post-IFFT amplitude randomising for peak-to-average power ratio reduction in orthogonal frequency-division multiplexing-based systems

The inherent high peak-to-average power ratio (PAPR) of multicarrier transmission, such as orthogonal frequency-division multiplexing (OFDM) or discrete multi-tone (DMT), can lead to a significant degradation in the transmission power efficiency which is unacceptable especially in battery-powered terminals. Among the most popular PAPR reduction techniques proposed in the literature is the selective mapping (SLM) technique which has been shown to offer PAPR reductions of several decibels. However, the SLM technique requires invoking the inverse fast fourier transform (IFFT) process several times per transmitted OFDM block which increases the system's complexity and hence may result in long latencies and high power consumption. The authors propose a new low complexity post-IFFT PAPR reduction technique that can outperform the SLM technique in terms of PAPR reduction while its operational complexity is orders of magnitude less than that of SLM technique.     

Reducing the PAPR by utilisation of the LDPC code

Peak-to-average power ratio (PAPR) is a major drawback in most multi-carrier communication techniques such as orthogonal frequency division multiplex system (OFDM). OFDM consists of lots of independent modulated subcarriers, as a result the amplitude of such a signal can have very large values. These large peaks increase the amount of intermodulation distortion resulting in an increase in the error rate. The PAPR of an OFDM signal can be reduced in several ways: selective mapping, Golay sequences, cyclic coding, clipping and filtering, and multiple signal representation techniques. The authors have improved the performance of the OFDM system by using low-density parity-check (LDPC) codes as an alternative to turbo coding in mitigating the PAPR problem which has been used in the pervious works of the authors. The authors present the design for the proposed (LDPC) code technique that achieves good error correction performance and is used to lower the PAPR in a multiple-input multiple-output OFDM system. The simulation results show that 6-60- reduction in PAPR over current values in the literature can be achieved depending on the system type.     

Time domain constellation shaping technique for peak-to-average power ratio reduction

A new constellation shaping technique has been proposed, which efficiently and effectively reduces the peak-to-average power ratio (PAPR) of orthogonal-frequency-division-multiplexing (OFDM) systems. Its novelty is based upon a simple transformation in the time domain instead of the commonly used frequency domain. This transformation is shown to ensure PAPR reduction regardless of the OFDM system input. As compared with previously known PAPR reduction methods, the proposed technique requires minimal implementation complexity, while it offers considerable performance gains. Closed form analytical expressions for the distribution of the PAPR and the bit error rate are derived. The accuracy of these analytical expressions is verified via equivalent performance evaluation results obtained by means of Monte Carlo computer simulations. Furthermore, performance comparisons made with other competitive techniques show that the proposed technique is an attractive alternative for PAPR reduction.     

抑制OFDM信号峰均比对直接检测光传输系统的性能影响

高峰均比是OFDM通信系统的主要缺点之一,光OFDM通信系统也存在同样的问题.本文将联合Hadamard变换和限幅(Clipping)方法抑制峰均功率比算法成功应用到直接检测的光正交频分复用光纤传输实验平台,重点研究了算法对系统误码性能的影响.实验中产生的2.5 Gb/s QPSK OFDM光信号在标准单模光纤中传输1...     

Peak-to-average power ratio reduction in OFDM using cyclically shifted phase sequences

Two approaches for reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) are proposed that are relied on a set of cyclically shifted phase sequences (CSPS) and implemented using the time domain circular convolution. After multiplying CSPS with the frequency domain data, the signal candidates can be expressed as weighted sum of the circularly shifted OFDM time domain data in the first method, which is called CSPS method. In the second method, weighted coefficients for generating the signal candidates in CSPS method are optimally selected to improve its performance; thus, the second method is referred to as optimised CSPS (OCSPS) method. The performances of the CSPS and OCSPS methods are evaluated using simulated data and compared with those of selective mapping (SLM) and partial transmit sequences (PTS). The simulation results show that both the CSPS and OCSPS methods can reduce the PAPR effectively, and that the OCSPS performs even better than the CSPS. The OCSPS can achieve the same performance as compared to the PTS. A distinct feature of the proposed methods is that only one inverse discrete Fourier transform is needed, and thus, the candidates can be calculated in time domain directly.     

Concatenated peak-to-average power ratio reduction scheme with threshold limited selection for coded orthogonal frequency-division multiplexing

The authors propose a concatenated scheme to reduce the peak-to-average power ratio (PAPR) in coded orthogonal frequency-division multiplexing (OFDM) systems. First, they employ a label-bits-inserted encoder of a random-like code to achieve selected mapping (SLM). Then they set a threshold at the selector to limit the number of candidate sequences. Both analytical and numerical results show that the complexity of the SLM implemented by the label-bit-inserted encoder can be significantly reduced by threshold limited selection. With the same complexity, the performance of PAPR reduction is improved. The proposed concatenated PAPR reduction scheme enjoys many advantages including low-complexity, small overhead, no side information transmission and no performance loss or additional complexity at the receiver.     

OFDM-CPM系统降低PAPR新方案研究

正交频分复用-连续相位调制(OFDM-CPM)系统通过CPM相关相位状态引入记忆,从而获得比传统调制方式更好的误码性能。降低OFDM-CPM系统中的峰值平均功率比(PAPR)是关键技术之一。利用恒包络的概念提出一种新的CE-OFDM-CPM调制方案,可以把OFDM-CPM系统的PAPR降至零分贝。     

An Efficient Genetic Hybrid PAPR Technique for 5G Waveforms

Non-orthogonal multiple access (NOMA) is a strong contender multicarrier waveform technique for the fifth generation (5G) communication system. The high peak-to-average power ratio (PAPR) is a serious concern in designing the NOMA waveform. However, the arrangement of NOMA is different from the orthogonal frequency division multiplexing. Thus, traditional reduction methods cannot be applied to NOMA. A partial transmission sequence (PTS) is commonly utilized to minimize the PAPR of the transmitting NOMA symbol. The choice phase aspect in the PTS is the only non-linear optimization obstacle that creates a huge computational complication due to the respective non-carrying sub-blocks in the unitary NOMA symbol. In this study, an efficient phase factor is proposed by presenting a novel bacterial foraging optimization algorithm (BFOA) for PTS (BFOA-PTS). The PAPR minimization is accomplished in a two-stage process. In the initial stage, PTS is applied to the NOMA signal, resulting in the partition of the NOMA signal into an act of sub-blocks. In the second stage, the best phase factor is generated using BFOA. The performance of the proposed BFOA-PTS is thoroughly investigated and compared to the traditional PTS. The simulation outcomes reveal that the BFOA-PTS efficiently optimizes the PAPR performance with inconsequential complexity. The proposed method can significantly offer a gain of 4.1 dB and low complexity compared with the traditional OFDM.