Companding schemes based on transforming signal statistics into trigonal distributions for PAPR reduction in OFDM systems

This paper proposes four companding transforms to reduce the peak‐to‐average power ratio in orthogonal frequency division multiplexing systems. The four companding transforms are obtained by transforming signal statistics into four trigonal distributions. Computer simulations show that the proposed schemes can effectively improve the PAPR performance and bit error rate performance of OFDM systems. Copyright © 2010 John Wiley & Sons, Ltd.     

A novel constellation amplitude modification method for PAPR reduction in OFDM systems

In this paper, we propose a constellation amplitude modification (CAM) method to reduce the peak‐to‐average power ratio (PAPR) in orthogonal frequency division multiplexing systems. The key idea of the proposed CAM method is to modify the original constellation amplitude and choose the constellation points with the minimum PAPR as the transmitted constellation points. The CAM method formulates the PAPR reduction as a convex optimization problem, and then, it applies the customized interior‐point method to solve the optimization problem. Compared with the traditional methods, the CAM method does not increase the transmit power, and the receiver has no additional operations. Simulation results show that the CAM method converges fast and offers significant PAPR reduction. Copyright © 2016 John Wiley & Sons, Ltd.     

Nonlinear effect mitigation based on PAPR reduction using electronic pre-distortion technique in direct-detection optical OFDM system

The nonlinear effect induced by the Mach–Zehnder modulator (MZM) and optical self-phase modulation (SPM) in the presence of high peak-to-average power ratio (PAPR) is investigated theoretically. We theoretically and experimentally investigate the direct-detection optical orthogonal frequency-division multiplexing (DD-OOFDM) system with an electronic pre-distortion technique of companding transform (CT) to reduce the peak-to-average power ratio (PAPR) of OFDM signals and improve the receiver sensitivity. Experimental results show that the PAPR reduction can reach about 3 dB when the complementary cumulative distribution function is 1 × 10⁻⁴, which means the number of random OFDM signals is 1 × 10⁴, and the receiver sensitivity is improved by 0.7, 1.7, and 2.4 dB for the launch power of 2, 6 and 10 dB m, respectively, at the BER of 1 × 10⁻⁴ after transmission over 100-km single-mode fiber with the μ of 2. It shows that the PAPR reduction can mitigate not only the nonlinearity of MZM, but also the nonlinear phase noise in the fiber link when the optical power into fiber is high.     

降低LWT-OFDM系统PAPR的联合算法

针对小波提升变换的正交频分复用( LWT-OFDM)系统峰均功率比( PAPR)过高的问 题,采用了部分传输序列( PTS)与指数压扩变换的联合算法?首先由PTS算法选出 系统中峰值最小的一组信号,再通过指数压扩变换来降低峰均功率比?仿真结果表明,相对于其它的限幅类技术,本文所提联合算法在该系统中能更有效的降低峰均功率比,并且误码率相对较低?     

Low-complexity PAPR reduction technique for OFDM systems using modified widely linear SLM scheme

In this paper, a modified widely linear selective mapping (MWL-SLM) scheme is proposed to reduce the peak-to-average power ratio (PAPR) of the orthogonal frequency-division multiplexing (OFDM) systems. In the proposed MWL-SLM scheme, through partition one complex signals into two real signals and combining the linear properties of the Fourier Transform, at most 4M² candidate signals can be obtained but only require M inverse fast Fourier transform (IFFT) operations. As a result, the proposed SLM scheme has the ability to generate more candidates when compared with conventional SLM (C-SLM) and widely linear SLM (WL-SLM). Therefore, MWL-SLM outperforms C-SLM and WL-SLM for the same computational cost of IFFT operations. Alternatively, for a given number of candidates, MWL-SLM has slightly inferior PAPR reduction performance to C-SLM and WL-SLM but requires less IFFT operations to be implemented, thus resulting in a lower computational complexity. Simulation results demonstrate the effectiveness of the proposed scheme.     

一种改进的低复杂度OFDM峰均比抑制PTS算法

针对正交频分复用系统中的信号峰值平均功率比问题,提出了一种基于时域采样点幅度筛选的低复杂度部分传输序列算法。算法通过设置信号经过逆向傅里叶变换后时域采样点的幅度之和为判别函数,并设置适当的幅度门限,筛选出幅度大于门限的信号采样点集合,利用该集合来搜索信号峰均比抑制相位因子,从而降低算法复杂度。仿真表明,与传统峰均比抑制算法相比,改进算法在保持峰均比抑制性能的同时降低了算法复杂度。     

降低光OFDM系统峰均比的TR-clipping算法

针对光正交频分复用(O-OFDM)系统中峰值平均功率比(PAPR)过高的问题,对传统的预留子载波(TR)方法进行了改进并引入到O-OFDM系统,提出将削波与TR法相结合,以减小削波噪声对信号的影响,同时有效降低信号的PAPR。研究结果表明:本文方法计算复杂度较低,易于实现;通过合理地选取门限A与预留子载波条数W的大小,可以有效抑制削波噪声在信号带内与带外引起的畸变;在误码率BER=10-6的条件下,当削波率γ由7dB降低至2dB时,所需的光信噪比(OSNR)相比削波法降低了0.2～7dB。     

Peak‐to‐average power ratio reduction of a hidden training sequence‐aided precoding scheme for MIMO‐OFDM

We analyze a peak‐to‐average power ratio (PAPR) reduction property based on a hidden training sequence‐aided precoding scheme for MIMO‐OFDM systems. In addition to the benefits of a hidden training sequence‐aided precoding scheme such as improvement in bandwidth efficiency and frequency diversity gain, we address that power amplifier efficiency can be improved without any additional complexity burden. By mathematically analyzing PAPR of the precoded MIMO‐OFDM signal with a hidden training sequence, we demonstrate that PAPR reduction can be obtained by varying the allocated power to the hidden training sequence. Because of the low PAPR property of this scheme, it is possible to utilize a low‐cost power amplifier, resulting in the reduction in the total cost for hardware implementation. Copyright © 2014 John Wiley & Sons, Ltd.     

Partial Transmit Sequence Optimization Using Improved Harmony Search Algorithm for PAPR Reduction in OFDM

This paper considers the use of the Partial Transmit Sequence (PTS) technique to reduce the Peak‐to‐Average Power Ratio (PAPR) of an Orthogonal Frequency Division Multiplexing signal in wireless communication systems. Search complexity is very high in the traditional PTS scheme because it involves an extensive random search over all combinations of allowed phase vectors, and it increases exponentially with the number of phase vectors. In this paper, a suboptimal metaheuristic algorithm for phase optimization based on an improved harmony search (IHS) is applied to explore the optimal combination of phase vectors that provides improved performance compared with existing evolutionary algorithms such as the harmony search algorithm and firefly algorithm. IHS enhances the accuracy and convergence rate of the conventional algorithms with very few parameters to adjust. Simulation results show that an improved harmony search‐based PTS algorithm can achieve a significant reduction in PAPR using a simple network structure compared with conventional algorithms.     

光OFDM系统中削波噪声的建模与研究

针对光正交频分复用(OFDM)系统中峰值平均功率比(PAPR)较高的缺点,研究了削波法降低PAPR的原理;根据这一原理,通过大量数据分析计算,建立了基于MQAM调制下光OFDM系统中的削波噪声模型;由所建立的模型,直接计算得出不同调制下光OFDM系统削波后的误符率。仿真结果表明,每种进制调制下,根据本文建立的削波噪声模型与OFDM具体系统模型仿真所得到的两条曲线基本吻合,并且这两条曲线在不同削波比下的最大均方误差(MSE)不超过1.26×10-2。这充分论证了所建立的削波噪声模型的可行性与适用性。     

A PAPR reduction technique using Hadamard transform combined with clipping and filtering based on DCT/IDCT for IM/DD optical OFDM systems

In Intensity Modulator/Direct Detection (IM/DD) optical OFDM systems, the high peak-to-power average ratio (PAPR) will cause signal impairments through the nonlinearity of modulator and fiber. In this paper, a joint PAPR reduction technique based on Hadamard transformation and clipping and filtering using DCT/IDCT transform has been proposed for mitigating the impairments in IM/DD optical OFDM system. We then experimentally evaluated the effect of PAPR reduction on the bit error rate (BER) performance and the results show the effectiveness of the proposed technique. At a bit error rate (BER) of 1 × 10⁻³, the receiver sensitivity of the proposed 2.5 Gb/s IM/DD optical OFDM system after 100-km standard single-mode fiber transmission has been improved by 0.8 dB, 1.3 dB and 3.1 dB for a launch power of 6.4 dBm, 8 dBm and 10 dBm respectively when compared with the classical system.     

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.     

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.     

CO-OFDM系统中基于维纳滤波的相位噪声ICI抑制算法

针对相干光正交频分复用(CO-OFDM)通信系统中相位噪声引起的载波间干扰(ICI)问题,提出一种基于维纳滤波的相位噪声ICI抑制算法。算法不需要改变OFDM符号原有的结构,只需要利用相位噪声预先得到的统计数据,通过相关计算,得到ICI的修正项。由于没有在OFDM符号中添加额外的辅助数据,所以与ICI自消除算法相比,所提出的ICI抑制算法具有较高的频谱利用率。仿真结果表明,在相位噪声比率为10-4级别时,基于迭代检测的ICI消除算法的误码率(BER)趋于10-4,出现错误平层;而本文所提出的ICI抑制算法能够有效地降低错误平层,改善BER性能。     

A partial transmit sequence technique with error correction capability and low computation

Orthogonal frequency division multiplexing (OFDM) is a popular transmission technique in wireless communication. Although already widely addressed in many studies, OFDM still has flaws, one of which is the occurrence of high peak‐to‐average power ratio (PAPR) in the transmission signal. The partial transmit sequence (PTS) technique is one method adopted to reduce high PAPR in OFDM systems. However, as PTS utilizes phase factors to generate multiple candidate signals, large amounts of calculation and time are required to search the candidate signal with the minimal PAPR, which will then be adopted as the final transmission signal. This paper proposes a novel PAPR reduction method, which can be applied in OFDM systems with M‐ary phase‐shift keying modulation. It not only requires less computation but also possesses error correction capabilities. More precisely, the proposed method is to divide a block‐coded modulation code into the direct sum of a correcting subcode for encoding information bits and a scrambling subcode for generating phase factors. Our proposed method is a suboptimal technique with low computation, because it uses a genetic algorithm with a partheno‐crossover operator as the transmitted signal selection mechanism. Simulation results show our proposed method has better PAPR performance than the GA‐PTS scheme. Based on the simulation results in Figures 5 and 6, it is evident that our proposed method can be employed in any OFDM system by using M‐PSK modulation.Copyright © 2013 John Wiley & Sons, Ltd.     

Frequency shift filter‐based multi‐carrier transceiver

It is well known that orthogonal frequency division multiplexing (OFDM) is sensitive to carrier frequency offset (CFO) and suffers from a high peak‐to‐average ratio. In addition, the performance of OFDM is severely affected by strong co‐channel interference and strong narrowband interference. To mitigate the limitations of OFDM, we propose a new multi‐carrier transceiver based on frequency‐shift filter. A frequency‐shift filter can separate spectrally overlapping sub‐carrier signals by exploiting the spectral correlation inherent in the cyclostationary modulated signals. To increase spectral efficiency, we increase the percentage of spectral overlap between two adjacent sub‐channels. We derive an upper bound and a lower bound on the bit error rate performance of the proposed multi‐carrier transceiver in additive white Gaussian noise channel and frequency‐nonselective Rayleigh fading channel, respectively. Compared with OFDM, our simulation results show that the proposed multi‐carrier transceiver is much less sensitive to CFO and has a lower peak‐to‐average ratio; moreover, without any additional interference suppression technique, the proposed transceiver has the advantage of being able to mitigate strong co‐channel interference with CFO from the intended multi‐carrier signal and mitigate strong narrowband interference in additive white Gaussian noise channel and in Rayleigh fading channel in which a large CFO between the transmitted signal and the received signal often occurs. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of minimum transmit sum power and scheduling power gain for multi‐user MIMO‐OFDM networks with rate constraints

Minimum transmit sum power (MTSP) is of high theoretical and practical value in multi‐user rate‐constrained systems; it is, however, quite difficult to be numerically characterized in complex channels for the prohibitively high computational power required. In this paper, we present a computationally efficient method to approximate the MTSP in multi‐user multiple‐input multiple‐output orthogonal frequency division multiplexing (MU‐MIMO‐OFDM) wireless networks. Specifically, we propose both lower and upper bounds of the MTSP, which are asymptotically accurate in the limit of large K, the number of users. Then, we develop two iterative water‐filling algorithms to numerically solve the proposed bounds. These algorithms are with low complexity, that is, linear in K, and therefore enable the analysis of MTSP in complex channels even if K is large. Numerical results demonstrate the effectiveness of the bounds in approximating the MTSP and the high computational efficiency of the proposed iterative water‐filling algorithms. With the proposed bounds, we further numerically study scheduling power gain (SPG), which is defined as MTSP reduction achieved by scheduling resources over multiple channel blocks in time domain. We simulate the SPG in different wireless environments defined in Third Generation Partnership Project spatial channel extended model and find insignificant SPG in some cases, indicating that the benefit from scheduling over multiple channel blocks is limited and simply allocating resources within the present channel is sufficient. Our analysis on the MTSP and SPG provides guidelines on the design of resource schedulers in MU‐MIMO‐OFDM networks. Copyright © 2014 John Wiley & Sons, Ltd.     

Peak‐to‐average power ratio reduction in space frequency block coding multi‐input multi‐output orthogonal frequency division multiplexing systems by tone reservation

In this paper, a tone reservation (TR) method is employed to reduce the peak‐to‐average power ratio (PAPR) in multi‐input multi‐output orthogonal frequency division multiplexing systems with space frequency block coding (SFBC). The key idea of the employed TR method is taking signals on multiple transmit antennas into account to design appropriate peak reduction symbols, which can significantly reduce the PAPR of SFBC multi‐input multi‐output orthogonal frequency division multiplexing signals. With the employed TR scheme, the SFBC structure can be maintained, whereas the traditional TR method would destroy it, resulting in the degradation of bit error rate (BER) performance. Simulation results demonstrate that the employed TR scheme can provide significantly better BER performance than the traditional TR method with slight PAPR reduction degradation. Copyright © 2013 John Wiley & Sons, Ltd.     

Adaptive subcarrier bandwidth and power in OFDM‐based cognitive radio systems for high mobility applications

OFDM‐based cognitive radio systems are spectrally flexible and efficient, but they are vulnerable to intercarrier interference (ICI), especially in high mobility environments. High mobility of the terminal causes large Doppler frequency spread resulting in serious ICI. Such ICI severely degrades the system performance, which is ignored in the existing resource allocation of OFDM‐based cognitive radio systems. In this paper, an adaptive subcarrier bandwidth along with power allocation problem in OFDM‐based cognitive radio systems for high mobility applications is investigated. This adaptive subcarrier bandwidth method should choose the suitable subcarrier bandwidth not only to balance the tradeoff between ICI and intersymbol interference but also to be large enough to tolerate an amount of Doppler frequency spread but less than the coherence bandwidth. The power budget and interference to primary users caused by cognitive radio users are imposed for primary users' protection. With these constraints, a joint optimization algorithm of subcarrier bandwidth and power allocation is proposed to maximize the bandwidth efficiency of OFDM‐based cognitive radio systems in such conditions. Numerical simulation results show that the proposed algorithm could maximize the system bandwidth efficiency and balance this tradeoff while satisfying the constraints. Copyright © 2012 John Wiley & Sons, Ltd.     

Performance analysis of switch‐and‐stay combining in two‐way relay systems with analog network coding and time‐division broadcast protocols

In this paper, we consider switch‐and‐stay combining (SSC) in two‐way relay systems with two amplify‐and‐forward relays, one of which is activated to assist the information exchange between the two sources. The system operates in either analog network coding (ANC) protocol where the communication is only achieved with the help of the active relay or time‐division broadcast (TDBC) protocol where the direct link between two sources can be utilized to exploit more diversity gain. In both cases, we study the outage probability and bit error rate (BER) for Rayleigh fading channels. In particular, we derive closed‐form lower bounds for the outage probability and the average BER, which remain tight for different fading conditions. We also present asymptotic analysis for both the outage probability and the average BER at high signal‐to‐noise ratio. It is shown that SSC can achieve the full diversity order in two‐way relay systems for both ANC and TDBC protocols with proper switching thresholds. Copyright © 2014 John Wiley & Sons, Ltd.