用时域自相关匹配方法降低OFDM系统的PAPR

对时域自相关匹配方法降低 OFDM (正交频分复用)系统的PAPR (峰均功率比)进行了研究。该方法的基本思想是在时域加入一个随机序列发生器,随机序列与原始信号在时域叠加,以达到降低 OFDM系统 PAPR的目的,并可以在接收端实现信号的盲检测。该方法的信号处理过程是在时域,故仅需要一个 IFFT (快速傅里叶逆变换)操作,就能降低计算复杂度。仿真结果表明,该方法可以获得与传统 SLM (选择性映射)方法相似的PAPR和BER (误码率)性能,但计算复杂度比传统的SLM方法降低了很多,从而验证了该方法的有效性。     

减小OFDM信号出现大峰平比的方法研究

介绍OFDM系统的OFDM信号峰平功率比(PAPR)的概念,研究减小OFDM信号PAPR值方法的 Selected Mapping(SLM).     

降低OFDM系统峰均比的SLM和PTS技术研究

正交频分复用（OFDM）是一种多载波调制技术,它具有良好的抗多径干扰能力、频谱利用率高和数据传输率高等优点。但OFDM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,因此,有必要研究降低PAPR的方法。本文首先介绍了SLM和PTS技术的基本原理,然后与原始OFDM系统的CCDF、功率谱和系统误码率进行比较。仿真结果表明：采用SLM和PTS技术可以有效改善OFDM信号的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.     

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。     

限幅SLM算法降低DD-OFDM系统PAPR的研究

提出了限幅SLM(Selected Mapping)算法降低直接检测光正交频分复用系统(DD-OFDM)的峰均功率比(peak-to-average power ratio,PAPR).SLM算法降低了PAPR出现的概率,但并不能完全限制高PAPR.限幅SLM算法在传统SLM算法基础上对高PAPR信号进行限幅运算,进而将PAPR控制在所需要的范围内,相对限幅算法又改善了系统误码率性能.该算法可以控制高PAPR,进而降低光信号的功率,其有效性在DD-OFDM系统信道仿真中得到证实.     

一种降低OFDM系统峰均比的新方案

提出了一种降低OFDM系统峰均比(PAPR)的实现方案,该方案利用编码和选择性映射(SLM)方法相结合来降低OFDM系统的PAPR,可以认为是一种改进的SLM算法。给出了具体的编解码方案、边信息的传输方案,他通过将边信息嵌入到传输数据中,随数据码元一起发送,不会造成系统频谱利用率的下降。最后,对PAPR和误码率(BER)性能进行了仿真研究,结果表明改进SLM算法可以有效降低OFDM系统的PAPR,同时在瑞利衰落信道下可以降低系统的误码率。     

降低OFDM峰均比SLM算法比较

正交频分复用（OFDM）是未来无线通信关键的技术之一,但是高峰值平均功率比（PAPR）一直是将OFDM技术实用化的一大障碍。选择映射（SLM）算法是无失真降低OFDM信号峰平比的有效方法之一。但计算复杂度高和需要发送边带信息是传统SLM算法的主要缺点。通过分析比较了多种改进方法,发现如果能够将传统SLM算法这两方面的缺点综合考虑,就能更好地改善SLM算法的性能,这将是今后研究SLM算法的方向之一。     

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。     

基于星座映射降低OFDM系统峰均功率比的新方法

降低峰均功率比(PAPR)是正交频分复用(OFDM)技术所要解决的关键问题之一,为此,提出了一种新的降低PAPR的方法——星座映射法。在发送端,对经IFFT变换后的超过最大允许范围的数据样值进行软限幅,提高了发射系统的输出功率。在接收端,根据不同调制方式所具有的不同星座分布特性,恢复出被限幅的数据样值,从而减小了由于限幅而造成的信号畸变。理论分析和仿真结果表明,新方法能够有效降低OFDM系统的峰均功率比,同时使系统获得较好的误码性能。     

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.     

Control information transmission without resource consumption for PAPR reduction of OFDM signal

A peak-to-average power ratio (PAPR) reduction method for orthogonal frequency division multiplexing (OFDM) signals is proposed that requires no additional resources to transmit side information. The approach used to reduce PAPR is based on selected mapping (SLM). SLM produces several candidates of OFDM symbols, the subcarrier phases of which are rotated, and the OFDM symbol that yields the minimum PAPR is selected and transmitted to the receiver. To cancel the rotation used to generate the original signal at the receiver, transmission of side information using a time slot is usually required. This decreases the efficiency with which data can be transmitted. The proposal is to modify SLM so as to implant the side information into the OFDM data symbol. This results in no efficiency loss. Additionally, the error rate in estimating the side information is extremely low when enough subcarriers are used to carry the side information. The performance of the method is confirmed by numerical simulation. The PAPR improvement equals that of the original SLM. The implanted side information was transmitted with high reliability.     

SLM based PAPR reduction of OFDM signal using new phase sequence

One of the main issues of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the transmitted signal which adversely affects the complexity of power amplifiers. The selected mapping (SLM) technique is one of the promising PAPR reduction techniques for OFDM. In this reported work, rows of normalised Riemann matrices are selected as phase sequence vectors for the SLM technique. MATLAB simulations show PAPR reduction of around 2.3 dB using the proposed method compared with methods reported in the literature.     

A computationally efficient selected mapping technique for reducing PAPR of OFDM

In orthogonal frequency division multiplexing (OFDM) system, high value of peak-to-average power ratio (PAPR) is an operational problem that may cause non-linear distortion resulting in high bit error rate. Selected mapping (SLM) is a well known technique that shows good PAPR reduction capability but inflicts added computational overhead. In this paper, using Riemann sequence based SLM method, we applied reverse searching technique to find out low PAPR yielding phase sequences with significant reduction in computational complexity. Additionally, we explored side-information free transmission that achieves higher throughput but sacrifices PAPR reduction. Finally, to overcome this loss in PAPR reduction, we proposed application of Square-rooting companding technique over the output OFDM transmitted signal. Simulation results show that the proposed method is able to compensate the sacrifice in PAPR and achieved PAPR reduction of 8.9 dB with very low computational overhead.     

A novel search method to reduce PAPR of an OFDM signal using partial transmit sequences

One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak‐to‐average power ratio (PAPR) of the transmitted OFDM signal. Partial transmit sequence (PTS) technique can improve the PAPR statistics of an OFDM signal. As ordinary PTS technique requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of sub‐blocks. In this paper, we propose a novel PTS technique with reduced complexity that each level inverts twice of phase factor bits from previous level. Then we also use initial random phase sequence to find the better search way of PAPR reduction. Numerical results show that the proposed method can achieve significant reduction in search complexity with little performance degradation. Copyright © 2006 John Wiley & Sons, Ltd.     

SLM‐based PAPR reduction method using partial data circulation and side information insertion in OFDM systems

In this paper, two selected mapping (SLM)‐based schemes are proposed to reduce the peak‐to‐average power ratio (PAPR) in the orthogonal frequency division multiplexing (OFDM) systems. One is SLM‐based partial data circulation (PDC) scheme. The other is SLM‐based PDC with hamming coded side information (SI) scheme. In the PDC scheme, the partial samples within the data sequence are scrambled by circularly shifting to obtain a set of candidate sequences and, then, each sequence is combined with the corresponding SI to form the candidate OFDM symbol. With the selection of the candidate OFDM symbols with the lowest PAPR, the PAPR of the transmitted signal could be greatly reduced. In the other scheme, hamming code is used to protect the SI to improve the system performance. Simulation results show that the proposed method could reduce PAPR and it has a better bandwidth efficiency and less modules of inverse fast Fourier transform than that with the SLM‐based dummy sequence insertion scheme. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

VLM Precoded SLM Technique for PAPR Reduction in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is perhaps the most spectrally efficient, robust transmission technique discovered so far for communication systems, and it also mitigates the problem of multipath environment. High peak-to-average power ratio (PAPR) has always been a major drawback of the OFDM systems. In this article, a new precoding technique has been proposed based on Vandermonde-like matrix (VLM) and selective mapping (SLM) to reduce PAPR in OFDM systems. VLM precoding reduces the autocorrelation of the input sequences while SLM takes an advantage of the fact that the PAPR is very sensitive to phase shifts of the signal. The main advantage of this proposed scheme is to achieve a significant reduction in PAPR without increasing the system complexity. Computer simulations show that, the proposed method outperforms the existing precoding techniques without degrading the error performance of the system.     

Low-complexity selected mapping schemes for peak-to-average power ratio reduction in OFDM systems

Orthogonal frequency-division multiplexing (OFDM) is an attractive transmission technique for high-bit-rate communication systems. One major drawback of OFDM is the high peak-to-average power ratio (PAPR) of the transmitter's output signal. The selected mapping (SLM) approach provides good performance for PAPR reduction, but it requires a bank of inverse fast Fourier transforms (IFFTs) to generate a set of candidate transmission signals, and this requirement usually results in high computational complexity. In this paper, we propose a kind of low-complexity conversions to replace the IFFT blocks in the conventional SLM method. Based on the proposed conversions, we develop two novel SLM schemes with much lower complexity than the conventional one; the first method uses only one IFFT block to generate the set of candidate signals, while the second one uses two IFFT blocks. Computer simulation results show that, as compared to the conventional SLM scheme, the first proposed approach has slightly worse PAPR reduction performance and the second proposed one reaches almost the same PAPR reduction performance.     

A low complexity selected mapping scheme for peak to average power ratio reduction with digital predistortion in OFDM systems

One of the effective methods used for reducing peak‐to‐average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems is selected mapping (SLM). In this paper, a new SLM scheme called DSI‐SLM, which is a combination of dummy sequence insertion (DSI) and conventional selected mapping (C‐SLM) is proposed. Previous techniques have had some drawbacks. In DSI, increasing the number of dummy sequences to have better PAPR degrades transmission efficiency, and in C‐SLM, the complexity rises dramatically when the number of sub‐blocks increases. The proposed DSI‐SLM scheme significantly reduces the complexity because of the reduction in the number of sub‐blocks compared with the C‐SLM technique while its PAPR performance is even better. To enhance the efficiency of the OFDM system and suppress the out‐of‐band distortion from the power amplifier nonlinearity, a digital predistortion technique is applied to the DSI‐SLM scheme. Simulations are carried out with the actual power amplifier model and the OFDM signal based on the worldwide interoperability for microwave access standard and quadrature phase‐shift keying modulation. The simulation results show improvement in PAPR reduction and complexity, whereas the BER performance is slightly worse. Copyright © 2011 John Wiley & Sons, Ltd.