REDUCING THE PEAK-TO-AVERAGE POWER RATIO OF OFDM SYSTEM WITH LOW COMPLEXITY

This paper proposes a companding scheme, where small signals are enlarged and large signals are reduced, to reduce the Peak-to-Average Power Ratio(PAPR). Computer simulation results show that the proposed technique has two advantages at least when compared with the conventional methods such as partial transmit sequence, selective mapping and the previous companding. First, it gets better PAPR performances with a lower complexity. Second, the scheme achieves greater performances gain with hardly any damnification of OFDM signals in some degree.

Peak-to-average power ratio reduction using selective mapping with unequal power distribution

A new approach for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems was proposed.This approach is based on assigning powers to the different subcarriers of OFDM using an unequal power distribution strategy.In addition,a reduced complexity selective mapping (RC-SLM) scheme was proposed.The proposed scheme is based on partitioning the frequency domain symbol sequence into several sub-blocks,and then each sub-block is multiplied by different phase sequences whose length is shorter than that used in the conventional SLM scheme.Then,a kind of low complexity conversions is used to replace the IFFT blocks.The performance of the proposed RC-SLM scheme along with the new approach was studied with computer simulation.The obtained results show that the proposed RC-SLM scheme is able to achieve the lowest computational complexity when compared with other low complexity schemes proposed in the literature while at the same time improves the PAPR reduction performance by about 0.3 dB.

COMPLEMENT BLOCK CODING SCHEME FOR REDUCING PEAK-TO-AVERAGE POWER RATIO OF OFDM SYSTEMS

A new scheme termed as Complement Block Coding (CBC) technique is proposed to reduce the Peak-to-Average Power Ratio (PAPR) of OFDM signals. Utilizing the complement bits which are added to the original information bits,this method can effectively reduce the PAPR of OFDM systems with random frame size N and the coding rate R ≤ (N - k)/N, where kis a positive integer and k ≤ N/2. The performance results obtained with CBC are given and compared with that of some well known schemes, such as Simple Block Coding (SBC), Modified Simple Block Coding (MSBC) and Simple Odd Parity Code (SOPC) for the same purpose. The results show that, at the same coding rate 3/4, the CBC can achieve almost the same performance as SBC, MSBC, but with lower complexity, and that the same performance can be obtained with higher coding rate by using CBC. At the same coding rate (N - 1)/N, the PAPR reduction of CBC is almost the twice as that of SOPC when N ≥ 16. Further more, the PAPR reductions with coding rate (N - 1)/N are almost the same as that with coding rate less than (N - 1)/N,so the proposed scheme CBC is more suitable for the large frame size with high coding rate and can provide error detection.

不同叠加训练序列PTS降低PAPR性能比较

部分传输序列(PTS)能有效降低正交频分复用(OFDM)系统的峰均功率比(PAPR),但是其存在降低性能有限和边带信息占用频谱资源的问题。文中在传统PTS方法的基础上,基于叠加训练序列PTS降低PAPR的方法,分析了叠加不同训练序列、不同训练序列作相位旋转因子及功率分配因子对降低PAPR性能的影响。仿真结果表明:叠加自相关性较好的训练序列,降低PAPR的能力更强;不同训练序列作相位旋转因子时,对降低PAPR的效果影响不大;采用Hadama码、功率分配因子大于0.15时,降低PAPR的能力增强。该方法中的训练序列,不仅可以用于同步﹑信道估计,而且可以降低PAPR,并提高系统频谱利用率。

OFDM系统梳状导频的PAPR问题及解决方案

分析了梳状导频对OFDM信号PAPR的影响。特别指出,取值不当的导频符号,例如等值导频,会加剧OFDM信号的PAPR。OFDM系统发送端通常采用降低PAPR的技术。带有等值梳状导频的OFDM信号会发生更大的失真,从而降低系统性能。经过分析,提出应用Newmann相位旋转方案优化等值导频。优化后的导频既不会降低信道估计的精度也不会恶化PAPR。优化方法能够与具体的信道估计方法相结合,并且不会增加信道估计的复杂度。

Novel PAPR Reduction Scheme Based on Continuous Nonlinear Piecewise Companding Transform for OFDM Systems

In this paper,a novel efficient continuous piecewise nonlinear companding scheme is proposed for reducing the peak-to-average power ratio(PAPR)of orthogonal frequency division multiplexing(OFDM)systems.In the proposed companding transform,signal samples with large amplitudes is clipped for peak power reduction,and the signal samples with medium amplitudes is nonlinear transformed with power compensation.While the signal samples with small amplitudes remain unchanged.The whole companding function is continuous and smooth in the range of positive numbers,which is beneficial for guaranteeing the bit error rate(BER)and power spectral density(PSD)performance.This scheme can achieve a significant reduction in PAPR.And at the same time,it cause little increment in BER and PSD performance.Simulation results indicate the superiority of the proposed scheme over existing companding schemes.

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.

OFDM Wireless Downhole Transmission Systems and Proposed SLM Method for PAPR Reduction

At present, mud pulse transmission systems are widely used in downhole data transmission. But the systems are very low in transmission efficiency, only 5-10 bits/s, with very large anti-inter-symbol-interference (ISI). It cannot meet high requirements for high-speed transmission of modern logging system. The development of communication technology has laid some foundation for this requirement. For this purpose, the Orthogonal Frequency Division Multiplexing (OFDM) Wireless Downhole Transmission Systems are proposed for the first time because of their high transmission rate, anti-inter-symbol-interference (ISI), and high spectral efficiency, etc. Due to non-linear power amplifier (PA) of logging systems with limited dynamic range, the drawbacks of high peak-average power ratio (PAPR) may outweigh all the potential benefits of OFDM wireless downhole transmission systems. Selective mapping (SLM) method can reduce the PAPR of OFDM logging signals without distortion. But at the receiver, the conventional SLM method needs exact bits of side information (SI) to recover the data signal. The probability of erroneous SI detection has a significant influence on the error performance of the system. And individual transmissions of SI result in the reduction of bandwidth efficiency. To restore the exact data signal, our scheme codes the SI bits by linear block codes (LBC), and is easily decoded by syndrome decoding. And then the coding SI bits are superimposed onto the logging signals to omit SI bits transmission. The theory and simulation results show that the proposed method has better performance than the conventional one. Accordingly, the OFDM wireless downhole transmission systems can tackle the high PAPR problem, and highten the transmission rate of logging signals.

A NOVEL PAPR REDUCTION WITH TRELLIS SHAPING FOR NC-OFDM IN COGNITIVE RADIO

In this paper, trellis shaping is applied to reducing the Peak-to-Average Power Ratio(PAPR) of NC-OFDM signals due to the fact that the total number of active subcarriers and their locations might change continuously in a dynamic spectrum access network.A new branch metric of trellis shaping is proposed which reduces the PAPR of OFDM signals through minimizing the variance of the power by VA decoder.The overall performance considerably depends on the type of signal mapping, and therefore a new type of 64QAM mapping method is designed.Simulation results show that this scheme significantly reduces the PAPR.Finally, a significant phenomenon is demonstrated that the PAPR of NC-OFDM signals in which the deactivated carriers is distributed in the Bernoulli distribution has better performance than that of OFDM signals.

Exhaustive entropy based SLM method for PAPR reduction of OFDM system

Orthogonal frequency division multiplexing(OFDM) is an attractive technology to provide immense improvement in wireless transmission capacity but high peak-to-average power ratio(PAPR) is a major drawback of OFDM system.Selected mapping(SLM) scheme has good performance for PAPR reduction.It requires the transmitting data to be multiplied by random phase sequences.However,the sequences are pseudo-random which will decrease the method effectiveness.Exhaustive entropy is introduced in this paper which can identify the strength of random phase sequences property.Then an exhaustive entropy based on SLM method is proposed.The scheme improves the effectiveness of random phase sequences by selecting the larger exhaustive entropy of them.The simulation results show that the PAPR reduction performance is better than that of conventional SLM through this method.

Reduction PAPR of OFDM Signals by Combining Grouped DCT Precoding with PTS

The high peak-to-average power ratio (PAPR) is one of the serious problems in the application of OFDM technology. In this paper, an improved partial transmit sequence (PTS) scheme based on combining the grouped discrete cosine transform (DCT) with PTS technique is proposed. In the proposed scheme, the adjacent partitioned data are firstly transformed by a DCT into new modified data. After that the proposed scheme utilizes the conventional PTS technique to further reduce the PAPR of the OFDM signal. The performance of the PAPR is evaluated using a computer simulation. The simulation results indicate that the proposed scheme may improve the PAPR performance compared with the conventional PTS scheme, the grouped DCT scheme, and original OFDM respectively.

Science Letters:Peak-power reduction by the lattice-reduction-aided closest point search for MIMO broadcast channels

In this letter, we present a modified vector-perturbation precoding scheme for the multiple-input multiple-output broadcast channel, where a perturbation vector is chosen to take into account both the instantaneous power and the instantaneous peak power of the transmitted signal. This perturbation vector is obtained by using the closest point search, with the aid of the lattice-reduction algorithm. Simulation results show that the proposed scheme yields a tradeoff among power efficiency, peak-to-average power ratio reduction, and complexity.

Efficient nonlinear companding scheme for substantial reduction in peak-to-average power ratio of OFDM

Orthogonal frequency division multiplexing(OFDM)produces a high peak-to-average power ratio(PAPR) that adversely affects high-speed OFDM data transmission. In order to reduce the high PAPR, an efficient nonlinear companding transform(NCT) function is proposed. With the proposed NCT function,the compression and expansion weights can be applied independently with suitably chosen function parameter values. As a result, the proposed function can easily maintain the average signal power approximately unchanged during the companding process.In this regard, the proposed function is superior to previously proposed schemes. Also, the simulations show the outstanding PAPR reduction performance of the proposed function. It is demonstrated that the proposed scheme performs well with nonlinear transmitter amplifiers and delivers superior error performance, compared with error function and exponential function based schemes.

A novel Haar wavelet-based precoded BPSK-OFDM system with reduced PAPR

The performance of OFDM systems may be degraded when intersymbol interference （ISI） channels have spectral nulls. Recently, the precoded OFDM was proposed to combat this problem. However, due to inserting （M- K） zeros between each two sets of K consecutive information symbols, the average transmitting power of the precoded OFDM system reduces by 10log10（M/K） dB compared with the conventional OFDM system. Under the same points inverse fast Fourier transformation （IFFF）, the precoded OFDM system has a higher peak-to-average power ratio （PAPR） compared with the conventional OFDM system. This paper proposes a novel precoded BPSK-OFDM system based on Haar wavelet transformation. The Haar wavelet transformation operating decomposition over the vector information symbols produced by a precoder shows that half of the information symbols are zeros and the rest are either √2- or √2. Then, we have the peak power and PAPR reduced by 10log1002=3dB at most compared with the precoded OFDM system. Finally, we compare PAPR of the proposed OFDM system with the precoded OFDM and the conventional OFDM system.

A PTS Optimization Scheme with Superimposed Training for PAPR Reduction in OFDM System

Partial Transmit Sequences (PTS) is an efficient scheme for Peak-to-Average Power Ratio (PAPR) reduction in Orthogonal Frequency Division Multiplexing (OFDM) system. It does not bring any signal distortion. However, its remarkable drawback is the high computational complexity. In order to reduce the computational complexity, currently many PTS methods have been proposed but with the cost of the loss of PAPR performance of the system. In this paper, we introduce an improved PTS optimization method with superimposed training. Simulation results show that, compared with conventional PTS, improved PTS scheme can achieve better PAPR performance while be implemented with lower computation complexity of the system.

PAPR Distribution Analysis at the Output of Nonlinear PAPR Reducers

Nonlinear PAPR reducers, such as clipping and companding techniques, are some simple methods used to reduce the Peak-to-Average Power Ratio (PAPR). In this paper, assuming that the baseband OFDM signal is characterized as a band-limited complex Gaussian process, we investigate the PAPR distribution of an OFDM signal when it is passed through a nonlinear PAPR reducer. The obtained PAPR distribution depends on the nonlinear function which characterizes the PAPR reducer. Later in this paper, we apply the obtained PAPR distribution in the clipping case. The comparisons made between the proposed distribution and that obtained thanks to computer simulations show good agreement.

一种基于小数倍多普勒信道的OTFS信道估计方法

针对现有正交时频空(OTFS)调制系统的信道估计中存在的高峰均比和小数倍多普勒信道下估计困难及复杂度高的问题,提出了一种基于序列导频的匹配滤波(SMF)信道估计方法。该算法首先将序列导频与数据联合成帧,依靠序列的自相关性获取路径数、时延和整数倍多普勒;然后通过互相关匹配滤波估计小数倍的多普勒抽头和信道增益,从而得到信道状态信息;最后根据小数倍信道整数采样的特征,更新信道增益和信道初始相位。仿真结果表明,该方法相比基于嵌入式脉冲导频的信道估计,改善了峰均比,并提高了信道估计性能。相比于传统的序列导频,该方法可以估计得到小数倍多普勒抽头,估计的信道状态信息更准确。该信道估计方法更具有普遍性。

OFDM系统中限幅非线性失真迭代对消法性能分析

限幅技术常用于正交频分复用系统中以抑制高峰值平均功率比,为抑制限幅造成的带内失真和带外辐射,可以在接收端进行限幅噪声的迭代估计和对消。该文提出对限幅带来的非线性失真进行迭代估计和对消的效果要比仅对限幅噪声进行估计对消好。前者在理想情况下能完全恢复出发端未限幅前的信号,但后者将始终受到由限幅带来的信号衰减的影响。理论分析和仿真结果验证了该结论及性能,同时数字结果表明,该算法能有效改进系统性能。在归一化限幅门限为1.2时,只通过一次迭代就能提高2dB。

Partial transmitting sequence method based on trellis factor search

To obtain good trade-offs between complexity and performance onpeak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM)using partial transmitting sequence (PTS) schemes, a trellis structure based PTS factor searchmethod is proposed. The trellis search is with a variant constraint length L_C, 1 ≤ L_C ≤ V-1,where V is the number of PTS subblocks. The method is to decide a PTS factor by searching all thepossible paths obtained by varying L_C consecutive factors. The trellis search can be viewed as ageneral PTS factor search model. If L_C = V-1, it is a full search, and if L_C = 1, it is aniterative search. Using different constraint lengths, trellis factor search PTS exhibits differentPAPR reduction performances. A larger L_C results in a better performance and L_C = V-1 results inthe optimum. However, a larger L_C requires more computation. This helps to choose a good trade-offbetween complexity and performance.

LTE系统中采用SGA-PTS技术降低OFDM峰均比的研究与仿真

LTE系统以OFDM技术为核心,但OFDM技术自身存在高峰均比的问题。随着硬件技术的迅速发展,概率类技术被认为是最有希望解决OFDM系统峰均比PAPR问题的一类方法。部分传输序列PTS(Partial Transmit Sequence)技术作为概率类技术中的代表技术一直广受关注,其关键问题在于搜索到合适的相位因子序列,使OFDM信号的峰均比性能最好。本文将混合的模拟退火遗传算法SGA(Simulated Annealing Genetic Algorithm)应用于PTS技术中相位因子序列的搜索,并通过仿真验证其有效性及优越性。对于相同的峰均比阈值要求,SGA算法能更好地改善PTS技术搜索最优相位因子序列的复杂度问题,使其更易于实现。