OFDM系统最大值抵消峰均比抑制算法

正交频分复用(OFDM)系统应用中的一个关键问题是如何降低信号的峰值平均功率比(PAPR).针对这一问题,本文提出一种新的峰均比抑制算法--最大值抵消算法.新算法利用OFDM系统的预留子载波,在子载波上注入冗余数据,形成新的信号,以改变原信号的PAPR值.在处理上,将新信号的PAPR值与原信号PAPR值进行比较,选取PAPR值较小的信号发送,从而降低信号的PAPR.仿真结果表明,由于新的算法不需要发送边带信息,不改变原信号的顺序和相位关系,故而在较好地抑制信号PAPR值的同时,该算法对误码率的影响非常小.这是本方法的主要特点和价值所在.     

OFDM系统中的迭代并行子载波间干扰消除技术

由于实际信道的时变性，OFDM系统中每一子载波上的接收信号受到其它子载波上所传输信号的影响，形成载波间干扰(ICI)并造成误码性能降低。本文提出了适用于OFDM系统的迭代并行子载波间干扰消除接收技术，分析和仿真结果表明此方法可以有效地消除载波间干扰，在归一化多普勒频移为0．1和0．001时，分别提高接收机的性能0.8dB和0．5dB。     

Selected Mapping Technique for PAPR Reduction Without Side Information Based on m-Sequence

Selected mapping (SLM) is a technique for reducing the high peak-to-average power ratio (PAPR) in which a suitable signal is selected among a set of alternative signals which all indicate alike information. The chief drawback existing in this method is that transmitter is compelled to send several additional bits called side information (SI) for each data block in order that recovering at the receiver side can be possible. In this paper, we present a novel SLM scheme by using the linear feedback shift register circuit and m-sequence named MSLM technique by which any side information bit is not explicitly sent. In MSLM, The basic idea is to fit the side information into transmitted symbols based upon which some special locations in the transmitted data block are expanded, i.e. some transmitted symbols are extended. In the receiver side, by using some properties of m-sequence the SI bits can be detected. We present the example of our method for an OFDM system through the use of 16-QAM modulation and different m-sequences and finally, concerned results are illustrated from the view point of bit error rate, probability of detection failure and PAPR reduction.     

Joint Optimization for PAPR Reduction and Opportunistic Beamforming (OBF) in OFDM Systems

Opportunistic beamforming (OBF) is an effective way to increase the multiuser diversity (MUD) of the communication systems; with employing OBF in OFDM system, in addition to the MUD gain, frequency diversity gain is also obtainable. However, the complexity of the OBF-OFDM system is increased and the peak-to-average power-ratio (PAPR) of the OFDM signals must be reduced. The reduction of signals’ PAPR and complexity of the system is modeled as the design of phase sequences in this paper. Hence, periodic phase sequences are designed and employed to reduce the OFDM signals’ PAPR and the complexity of the normal OBF-OFDM system simultaneously, where the transmit data at all antennas can be generated in time domain directly via one N-point IFFT. The simulation results show that, after the proposed schemes are adopted, complexity of the OBF-OFDM system is reduced and the system throughput, both in the maximum throughput scheduling scheme and the proportional fairness scheduling scheme, is almost same as that of the normal OBF-OFDM system and greater than that of non-OBF OFDM.     

OFDM系统中峰平比降低算法研究

提出了一种基于升余弦脉冲峰值抵消的改进方案,在降低系统峰平比的同时避免削波引入的频谱恶化,给出了理论分析及相应的仿真结果与结论。     

A Joint OFDM Channel Estimation and ICI Cancellation for Double Selective Channels

Orthogonal frequency division multiplexing (OFDM) systems suffer significantly from inter-carrier interference (ICI) caused by double selective channels. In this paper, we develop a two-stage hybrid channel estimation and ICI cancellation structure for OFDM. The double selective channels are approximated by an improved Basis Expansion Model (BEM), which is more accurate than the conventional BEM when the normalized Doppler frequency is smaller than one. Based on this improved model, a new ICI cancellation scheme is proposed to reduce ICI impact. Simulation results show that the framework performs well.

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.     

基于Hadamard矩阵变换降低OFDM系统PAPR的新算法

本文研究了一种基于Hadamard变换降低OFDM系统PAPR的新算法,该算法扩展了传统系统的星座点,减小了频域符号间的相关性,其编解码算法简便,易于实现。文中分析了该算法的基本原理,同时仿真结果表明,采用该算法其PAPR可以比传统方法降低3-4dB;并且可以与其它方法联合使用,从而进一步降低PAPR。     

A Low-Complexity PTS-based PAPR Reduction Technique for OFDM Signals without Transmission of Side Information

Increased peak-to-average power ratio (PAPR) imposes a design challenge for orthogonal frequency division multiplexing-based signals. An efficient technique to address the increased PAPR problem is the partial transmit sequences (PTS) approach. A significant drawback of PTS is the fact that it multiplies the transmitted symbol with weighting factors selected by the transmitter. Since the weighting factors are required for decoding, they are explicitly transmitted, in most cases. This paper proposes a new low-complexity technique for retrieving the weighting factors in the receiver. The proposed decoder uses the predefined values of pilot tones and explores all the permissible combinations of weighting factors in order to identify the factor combination employed by the transmitter. The proposed decoder requires no additional pilot tones or explicit transmission of side information, therefore no data rate loss is implied. Furthermore this paper presents a digital very large scale integration implementation of the proposed PTS decoder and demonstrates its low-power properties.     

降低OFDM峰均比的无边信息传输低复杂度PTS算法

部分传输序列(PTS)技术是正交频分复用(OFDM)系统中一种非常有效的降低峰均功率比方法.其缺点是在发送端需要选择权重因子与发送符号相乘来进行发送,而权重因子通常会作为边信息被额外地传输.本文首先讨论了一种基于导频音来恢复权重因子的PTS算法,它在接收端通过收到的导频音进行判决恢复.采用这种算法,能有效抑制系统的PA...     

移动WIMAX下OFDM载波间干扰消除

高速移动WIMAX下的信道变化使得OFDM的正交性遭到破坏，从而产生载波间干扰，导致系统估计性能明显降低，为了降低ICI的影响，文中提出了一种基于泰勒级数逼近的ICI消除算法，并以此进行了时域迭代消除信道估计，仿真结果表面估计算法在高速移动环境具有良好的估计性能，ICI消除效果好，计算复杂度低。     

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.     

PAPR Reduction in OFDM Systems: Polynomial-Based Compressing and Iterative Expanding

In this paper a companding-based scheme is proposed to reduce the Peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing system. At the transmitter side, a compressing polynomial function is appended to the inverse discrete Fourier transform block; and at the receiver the transmitted signal is retrieved iteratively through combining the discrete Fourier transform block with a reverse expanding function. In the iterative algorithm the Jacobi’s method is used for solving the equations. Also, the general form of the compressing polynomial functions is attained through the use of Daubechies wavelet functions. As an advantage, the proposed method involves less complexity at the transmitter compared to other PAPR reduction methods. Furthermore, it requires less increasing to signal-to-noise ratio for the same bit error rate in comparison with other companding methods. The order of compressing polynomial and the number of iterations for the proposed algorithm at the receiver can be set in accordance with the performance-complexity trade off.     

Simple Amplitude and Phase Predistortion for PAPR Reduction in OFDM Systems

One of the drawbacks in an OFDM system is the high peak‐to‐average power ratio (PAPR). Among a number of techniques to reduce the high PAPR, simple amplitude predistortion (SAP), a form of active constellation extension, has been proposed to effectively achieve the desired PAPR. In this letter, a novel scheme, simple amplitude and phase predistortion (SAPP), is proposed. In SAP the carriers' amplitude is utilized to combat the peak signal. Each amplitude is amplified according to its degree of contribution as a metric. In addition to amplitude, SAPP also utilizes the phase. Simulation results indicate that the proposed scheme provides better PAPR reduction than SAP.     

Transmitter Precoding for ICI Reduction in Closed-Loop MIMO OFDM Systems

The mitigation of intercarrier interference (ICI) in closed-loop single-input-single-output (SISO) and multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) is considered. The authors show that the ICI coefficient matrix is approximately unitary and exploit this property to design a nonlinear Tomlinson-Harashima precoder for the reduction of ICI in closed-loop SISO OFDM and orthogonal space-time block-coded (OSTBC) MIMO OFDM. With the proposed design, the transmitter does not need to know the frequency offsets, and hence, their impact on the bit error rate (BER) is significantly reduced. Moreover, for spatially correlated MIMO channels, the precoder and OSTBC OFDM perform with a negligible BER-performance loss     

ICI Reduction in OFDM Systems Using Phase Modified Sinc Pulse

This paper is focused on the problem of reducing the intercarrier-interference (ICI) power in the transmission over Orthogonal Frequency Division Multiplexing Systems (OFDM) using pulse shaping methods. A new pulse was proposed here and it was investigated in terms of ICI interference. It appears to be suitable for transmission in OFDM systems with carrier frequency offset. The results obtained by calculations show that the performance improvements are significant for reducing average intercarrier-interference (ICI) power and increasing the ratio of average signal power to average ICI power (SIR).     

A Novel Multi-Points Square Mapping Combined With PTS to Reduce PAPR of OFDM Signals Without Side Information

In this paper, we first propose a novel multi-points square mapping (MSM) scheme. Then, we describe in detail how to combine the proposed MSM scheme with conventional partial transmit sequence (C-PTS) scheme, named as M-PTS, to reduce the PAPR of OFDM signals. Compared with C-PTS, the proposed M-PTS scheme needs not to submit side information while keeping almost the same performance of PAPR reduction as the C-PTS scheme. Extensive simulations are conducted to validate analytical results, showing that the proposed M-PTS scheme has better bandwidth efficiency and bit error ratio (BER) performance compared with the C-PTS scheme.      

PTS with Non-Uniform Phase Factors for PAPR Reduction in OFDM Systems

Partial transmit sequence (PTS) is one of the effective and uncomplicated PAPR reduction methods for OFDM systems. The phase factors applied in the weighting sequences are assumed to be uniformly distributed within [0, 2pi). By carefully investigating the phase distribution of OFDM signals, we proposed a modified PTS scheme outperforming the conventional PTS scheme in PAPR reduction performance. The process of the proposed scheme is the same as the conventional PTS, except for applying the new non-uniform phase factors. The required side information is the same as the conventional PTS applying uniform phase factors.     

Iterative Channel Estimation and Successive ICI Cancellation for OFDM Systems over Doubly Selective Channels

In orthogonal frequency division multiplexing systems, significant inter-carrier interference (ICI) caused by doubly selective channels make challenge for reliable reception. In this paper, channel estimation and ICI cancellation are considered jointly. Relying on the basis expansion model (BEM) of time-varying channel, the linear system model of transceiver is established, and the corresponding joint optimization of the transmitted data and BEM coefficients is formulated. Due to the separability of the data and BEM coefficients, we use cyclic minimizing technique to perform channel estimation and equalization alternately. This yields a linear minimum mean square-error (LMMSE) channel estimator and a block MMSE equalizer respectively. The block MMSE equalizer has complexity O(N ³), where N is the number of data subcarriers. To reduce the complexity, instead of equalizing all the data simultaneously, we consider estimating each data symbol successively. This idea results in the per subcarrier interference canceller with lower complexity O(N ²). Finally, an iterative receiver consisting of the data-aided LMMSE channel estimator and the successive interference canceller is developed. Simulation results show the scheme is effective over the channel with relatively large Doppler spread.