Practical determination of impulse sample power boosting factor in impulse postfix OFDM systems

An impulse postfix OFDM (IP-OFDM) system, which performs channel estimation in time-domain by exploiting the IP instead of pilot tones, has recently been proposed by Chang et al. Although the proposed system can achieve the enhanced bit error rate (BER) performance compared to that of conventional OFDM systems, there is an important peak-to-average power ratio (PAPR) issue of using the IP that needs to be resolved. In this letter, we propose decision criteria for determining the power boosting factor (PBF) of IP in practical IP-OFDM systems with a high power amplifier (HPA). The analysis is performed with two criteria, the complementary cumulative distribution function of signal PAPR and the input back-off to determine the PBF of IP. The best PBF can be the one which gives an equal power to the IP and the rest of the OFDM symbol. From the analytic results, however, the PBF maximizing the power of the IP out of the HPA turns out to be the best one due to the non-linearities of the HPA. Simulation results demonstrate the effectiveness of the proposed decision criteria for IP-OFDM systems.     

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.     

OFDM系统中基于限幅和压缩感知的非线性失真补偿算法

正交频分复用（Orthogonal Frequency Division Multiplexing,OFDM）信号具有较高的峰均功率比（Peak to Average Power Ratio,PAPR）,不仅影响功率放大器（High Power Amplifier,HPA）的工作效率,而且HPA使得OFDM信号产生严重的非线性失真,导致系统的误比特率（Bite Error Rate,BER）增大.本文基于限幅和压缩感知（Compressive Sensing,CS）提出了改进的补偿算法,发送端采用限幅降低信号的PAPR,接收端首先采用改进的逆模型方式减小HPA引入的非线性失真,再采用CS抵消由限幅引入的信号失真.仿真表明,所提方法不仅明显降低了OFDM信号的PAPR,而且有效提高了系统的BER性能.     

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.     

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.     

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.     

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.     

Power boosting factor determination in impulse postfix‐OFDM‐based positioning system

Based on recently introduced novel impulse postfix‐OFDM scheme, we proposed a joint time‐of‐arrival/angle‐of‐arrival positioning scheme, in which both channel estimation and positioning information can be realized by analyzing the channel impulse response estimated on an access point equipped with a uniform linear antenna array. However, the power boosting factor (PBF) determination of impulse postfix (IP) should be taken as an important issue, because a small PBF will result in imprecise channel estimation and deteriorate the communication quality, as well as positioning accuracy; in contrast, the huge power assignment on IP will lead to insufficient power allocated on date portion, when transmitted power is restricted, which also increases the system BER. In this paper, to obtain the optimal performance of both BER and positioning accuracy, we mathematically analyze the BER and positioning performance with increasing PBFs in the term of signal‐to‐noise ratio and confirm our assumption in the cases of quadrature phase‐shift keying and 16‐quadrature amplitude modulation, with computer simulation. The result applies that, as the PBF is increasing, the system BER is enhanced until PBF reaches 15 and starts deteriorating thereafter. According to the result, the decision criteria for determining PBF of IP should depend on practical preference of BER or positioning. Copyright © 2015 John Wiley & Sons, Ltd.     

基于功放效率的OFDM信号幅度的最佳分布——峰均比抑制

星座图扩展（ACE）技术可以无损地降低OFDM信号的峰均比,本文的论述指出仅追求低峰均比对应的功放效率和效能并不是最好.笔者提出了OFDM信号的最佳互补累积分布函数（OCCDF）峰均比抑制方法,即考虑OFDM信号的幅度分布及出现概率,整体地评估其对放大器失真的影响,以OFDM信号放大器的效率为评估峰均比优劣的标准,在算法上以限定MER条件下得到尽可能低的功放输入功率回退（IBO）为迭代收敛目标,预见了应该存在最高功放效率意义匹配的所谓OFDM信号的最佳幅度分布.实验证实：相比原始OFDM系统,在放大基于OCCDF准则优化后的OFDM信号时,放大器获得了3.15dB的IBO性能改善,对比同等条件下单载波系统仅差0.05dB.     

Threshold IBO of HPA in the predistorted OFDM communication system

Orthogonal frequency division modulation (OFDM) system is very useful for the multi-path channel and highly bandwidth-efficient system. However, OFDM signal shows the high peak to average power ratio (PAPR) so that nonlinear distortion can happen in the high power amplifier (HPA). This paper studies BER performance variation according to input back off (IBO) values when the predistorter is used for the compensation for the HPA nonlinearity. In the case of the solid state power amplifier (SSPA) of nonlinearity parameter p=0.5 and IBO=0 dB, the system with predistorter is poorer than the one without predistorter. But this situation is inverted, if IBO is increased from 0 dB to 3 dB. So, we can find that there is a threshold value of IBO for the predistorter to effectively compensate for the nonlinear SSPA when the sub-carrier number and p value are changed. This threshold IBO value is proportional to the nonlinearity parameter p value but it is nearly independent of the sub-carrier number because amplitude and distribution are normalized. The OFDM system with predistorter can be improved only when thee IBO value is higher than the threshold value.     

The impact of impulse postfix length on the BER performance of IP‐OFDM systems

The impulse postfix OFDM (IP‐OFDM) system exploits the IP, which consists of a high power impulse sample and several zero samples at the end of a zero padded‐OFDM symbol block, to estimate channel impulse response (CIR) in time domain. In this paper, the impact of IP length on the BER performance of the IP‐OFDM system is analyzed. According to the analytic results, the BER performance can be significantly degraded with both a shorter length of IP as well as a longer length of IP than that of the CIR. Thus, an adaptive IP scheme, which adjusts the length of IP adaptively depending on the length of CIR, is proposed to enhance the BER performance of IP‐OFDM systems and its effectiveness is demonstrated by computer simulations. The BER performance of the IP‐OFDM systems with the proposed adaptive scheme is compared with that of the conventional IP‐OFDM system over various modulation schemes. Simulation results show that the IP‐OFDM with the proposed scheme can achieve about 2 dB performance enhancement compared with that of conventional systems at BER=10^?2. Copyright © 2010 John Wiley & Sons, Ltd.     

Block coding scheme for reducing PAPR in OFDM systems with large number of subcarriers

The major drawback in Orthogonal Frequency Division Multiplexing (OFDM) system is due to the high Peak-to-Average Power Ratio (PAPR), so the performance of the system is significantly degraded by the nonlinearity of a High Power Amplifier (HPA) in the transmitter. In order to mitigate distortion, a block coding scheme for reducing PAPR in OFDM systems with large number of subcarriers based on complementary sequences and predistortion is proposed, which is capable of both error correction and PAPR reduction. Computer simulation results show that the proposed scheme significantly improves Bit Error Rate(BER) performance as compared to an uncoded system when an HPA is employed or a coded system without predistortion.     

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.     

基于软限幅法降低峰均比的性能分析

在正交频分复用技术（OFDM）系统接收到的信号较弱的情况下,为了获得较好的系统误码率,OFDM系统峰均功率比的设定值应较小。此时,采用选择性映射和部分传输序列法虽然能够有效地降低OFDM系统的峰均功率比,但是,其效果并不理想,且算法较复杂。为此,提出了软限幅法来降低OFDM系统的峰均功率比。理论分析和仿真结果表明,在峰均功率比取值较小的情况下,采用软限幅法的OFDM系统具有较好地误码率性能,且易于实现。     

PAPR Reduction in OFDM Systems Based on Autoregressive Filtering

Orthogonal frequency division multiplexing (OFDM) has a very high peak-to-average power ratio (PAPR) that causes a severe nonlinear distortion in practical hardware implementation of high power amplifiers (HPA). In this article, a new PAPR reduction method is proposed based on autoregressive (AR) error filtering. This method proposes the use of signal whitening property of error filtering as a preprocessing step to remove the predictable content of stationary stochastic processes which can reduce the autocorrelation of input data sequences and is shown to be a very effective solution for the PAPR problem in OFDM systems. It is shown that the proposed method can achieve a significant reduction in PAPR without degrading the error performance or power spectral levels. It is also shown that the proposed method is applicable to any modulation scheme and can work for any number of subcarriers under both additive white Gaussian noise and wireless Rayleigh fading channel.     

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.     

Hartley变换OFDM调制的可见光通信研究

针对正交频分复用(OFDM)可见光通信系统中存在高峰均功率比的问题，将预编码与迭代限幅滤波技术相结合应用于Hartley变换OFDM调制的可见光通信系统中，并对传统的采用FFT/IFFT限幅滤波的OFDM系统进行改进。根据建立的FHT的可见光OFDM系统模型，分别比较了不同方案下系统的频谱利用率、PAPR和误码率等性能，并分析了离散余弦变换和Hadamard矩阵预编码对PAPR的抑制作用以及FFT/IFFT、DCT/IDCT和FHT/IFHT三种不同变换方案的滤波性能。结果表明:FHT的可见光OFDM系统比FFT的OFDM系统的计算复杂度低、频谱利用率高；DCT预编码技术在克服系统PAPR及提升系统误码性能上更具优势；FHT/IFHT迭代限幅滤波的误码性能优于FFT/IFFT和DCT/IDCT。      

A New PAPR Reduction Scheme for OFDM Systems Based on Gamma Correction

Orthogonal frequency division multiplexing (OFDM) is perhaps the most spectrally efficient method discovered so far for communication systems and yet have an excellent immunity against multipath fading and inter-symbol interference. One of the major drawbacks of OFDM systems is their high peak-to-average power ratio (PAPR), which degrades system performance when nonlinear high power amplifiers (HPA) are employed. In this article, a new companding technique based on gamma correction (GC) function is proposed and analyzed. Through extensive computer simulations, it is shown that the proposed technique outperforms the previously suggested A-law and μ-law companding methods for PAPR reduction. A thorough investigation of GCC companding is presented in terms of computational complexity (CC), complementary cumulative distribution function (CCDF), power spectral density (PSD), and bit-error-rate (BER). It is also shown that the proposed method is independent of modulation schemes and can be applied to any number of subcarriers.     

联合星座扩展的预留子载波OFDM信号峰均比抑制算法

针对现有预留子载波TR技术对无线OFDM信号峰均比（PAPR）抑制性能效率低,且难以同时兼顾峰均比抑制、误码率（BER）性能损失及带外频谱分量扩展的问题,提出一种联合智能梯度映射主动星座扩展ACE的预留子载波峰均比抑制ACE-TR算法,能以较低的复杂度同时对信号峰均比和接收端误码率性能进行联合优化,并在迭代过程中消除因限幅处理所导致的信号带外频谱分量再生;特别是,由于在优化迭代过程中可以对迭代参数进行自适应调整,能够有效提高算法的适用灵活性。对算法进行了全面深入的理论分析,推导了其可获得的PAPR抑制增益理论界和接收信号误码率性能理论值。理论分析与仿真表明,ACE-TR算法能以更快的收敛速度产生所需的削峰信号,并同时获得优异的峰均比抑制、误码率及带外功率谱性能。     

Selected mapping with symbol re‐mapping for OFDM/TDM using MMSE‐FDE

Orthogonal frequency division multiplexing (OFDM) signals have a problem with a high peak‐to‐average power ratio (PAPR). A distortionless selected mapping (SLM) has been proposed to reduce the PAPR, but a high computational complexity prohibits its application to an OFDM system with a large number of subcarriers. Recently, we proposed OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency‐domain equalization (MMSE‐FDE) to improve the bit error rate (BER) performance of conventional OFDM with a lower PAPR. The PAPR problem, however, cannot be completely eliminated. In this paper, we present an SLM combined with symbol re‐mapping for OFDM/TDM using MMSE‐FDE. Unlike the conventional OFDM, where SLM is applied over subcarriers in the frequency domain, we exploit both time and frequency dimensions of OFDM/TDM signal to improve the performance with respect to PAPR and BER. A mathematical model for PAPR distribution of OFDM/TDM with SLM is presented to complement the computer simulation results. It is shown that proposed SLM can further reduce the PAPR without sacrificing the BER performance with the same or reduced computational complexity. Copyright © 2010 John Wiley & Sons, Ltd.