OFDM削波噪声迭代消除算法

高峰均功率比(PAPR)的OFDM信号通过功率放大器的时候会产生非线性干扰,同时降低了放大器的工作效率。传统削波算法可以降低信号的PAPR,但是会带来较大的频谱扩展。作为一种新的削波算法,误差削波可以在降低OFDM信号PAPR值的同时不带来任何频谱扩展。但是这种削波会给信号带来更大的带内干扰噪声。提出了一种OFDM削波噪声迭代估计和消除算法,它能有效的消除由于误差削波带来的噪声。新方法通过建立削波噪声模型,在接收端根据该噪声模型用迭代的方法重新产生削波噪声。仿真结果表明,使用削波噪声消除算法后,使得系统的误码率性能接近未削波信号的水平。     

Wireless mesh networks channel reservation: modelling and delay analysis

In order to overcome the negotiation procedure bottleneck of the standard DCF in wireless mesh networks, the authors propose a new channel reservation function (CRF) that reduces the negotiation overhead of the DCF, which as a result reduces the overall transmission delay effectively without of any extra bandwidth consumption. Furthermore, the authors provide an analytical model for the proposed scheme for which the simulation results measure the amount that the new method can reduce the average total delay for both regular and fragmented mesh topologies demonstrating superiority of the new method over the classic 802.11 solution. Additionally, the authors extend the scheme to multichannel CRF upon which the proposed method can be used for multichannel applications.     

Transceiver scheme for single-carrier frequency division multiple access implementing the wavelet transform and peak-to-average-power ratio reduction methods

Single-carrier frequency division multiple access (SC-FDMA) has been adopted as a possible air interface for future wireless networks. It combines most of the advantages of orthogonal frequency division multiple access (OFDMA) and the low peak-to-average-power ratio (PAPR) of single-carrier transmission. This study proposes a new transceiver scheme for SC-FDMA systems implementing the wavelet transform to decompose the transmitted signal into approximation and detail components. The approximation component can be clipped or companded whereas the detail component is left unchanged because of its sensitivity to noise. Wavelet filter banks at the transmitter and the receiver demonstrate the ability to reduce the distortion in the reconstructed signal while retaining all the significant features present in the signal. The performance of the proposed scheme is investigated with different PAPR reduction methods. Simulation results show that the proposed scheme with the hybrid clipping and companding method provides a significant performance enhancement when compared with the conventional SC-FDMA system, while the complexity of the system is slightly increased.     

Precoded orthogonal frequency division multiplexing with hidden pilots for ultrawideband wireless communications

The authors propose a new hidden pilot scheme equipped with precoding and its application to orthogonal frequency division multiplexing-ultra-wideband (OFDM-UWB) systems. The proposed scheme can be thought of as an improvement over conventional hidden pilot schemes. By carefully designing precoder and hidden pilot from the view point of frequency diversity, channel estimation and the peak-to-average power ratio (PAPR), more frequency diversity gain and reduced PAPR can be achieved. In addition, the authors can support more pilots to estimate a channel providing mitigated self-interference between data symbol and hidden pilot with almost no loss of bandwidth efficiency in OFDM-based UWB communication systems. The authors show improved performance of the proposed scheme over the multiband OFDM scheme through simulations in a realistic UWB channel environment.     

Reducing the PAPR by utilisation of the LDPC code

Peak-to-average power ratio (PAPR) is a major drawback in most multi-carrier communication techniques such as orthogonal frequency division multiplex system (OFDM). OFDM consists of lots of independent modulated subcarriers, as a result the amplitude of such a signal can have very large values. These large peaks increase the amount of intermodulation distortion resulting in an increase in the error rate. The PAPR of an OFDM signal can be reduced in several ways: selective mapping, Golay sequences, cyclic coding, clipping and filtering, and multiple signal representation techniques. The authors have improved the performance of the OFDM system by using low-density parity-check (LDPC) codes as an alternative to turbo coding in mitigating the PAPR problem which has been used in the pervious works of the authors. The authors present the design for the proposed (LDPC) code technique that achieves good error correction performance and is used to lower the PAPR in a multiple-input multiple-output OFDM system. The simulation results show that 6-60- reduction in PAPR over current values in the literature can be achieved depending on the system type.     

NUMERICAL ALGORITHMS FOR SOLUTIONS OF LARGE EIGENVALUE PROBLEMS IN PIEZOELECTRIC RESONATORS

Two algorithms for eigenvalue problems in piezoelectric finite element analyses are introduced. The first algorithm involves the use of Lanczos method with a new matrix storage scheme, while the second algorithm uses a Rayleigh quotient iteration scheme. In both solution methods, schemes are implemented to reduce storage requirements and solution time. Both solution methods also seek to preserve the sparsity structure of the stiffness matrix to realize major savings in memory. In the Lanczos method with the new storage scheme, the bandwidth of the stiffness matrix is optimized by mixing the electrical degree of freedom with the mechanical degrees of freedom. The unique structural pattern of the consistent mass matrix is exploited to reduce storage requirements. These major reductions in memory requirements for both the stiffness and mass matrices also provided large savings in computational time. In the Rayleigh quotient iteration method, an algorithm for generating good initial eigenpairs is employed to improve its overall convergence rate, and its convergence stability in the regions of closely spaced eigenvalues and repeated eigenvalues. The initial eigenvectors are obtained by interpolation from a coarse mesh. In order for this multi-mesh iterative method to be effective, an eigenvector of interest in the fine mesh must resemble an eigenvector in the coarse mesh. Hence, the method is effective for finding the set of eigenpairs in the low-frequency range, while the Lanczos method with a mixed electromechanical matrix can be used for any frequency range. Results of example problems are presented to show the savings in solution time and storage requirements of the proposed algorithms when compared with the existing algorithms in the literature.     

Postbuckling analysis stabilized by penalty springs and intermediate corrections

Whenever a critical point in a non-linear finite element analysis is reached, an implicit Newton procedure is prevented from proceeding until the stiffness matrix is stabilized. Most stabilization procedures result in a damped Newton scheme. This can cause a reduced convergence rate. Based on documented stabilization strategies, an iterative procedure to reduce negative impact on the convergence rate resulting from the damping is to be proposed here. This will be done by a corrector iteration carried out between two successive equilibrium iterative steps. The equilibrium iteration is a Newton–Raphson scheme. Since the stiffness matrix has already been factorized within the preceding standard equilibrium iterative step, the stiffness matrix will be held constant during the corrector iteration, which in turn allows for a computational efficient treatment of the additional iterations. The proposed procedure has been strongly driven by Wright and Gaylord’s (ASCE J. Struct. Div., 94, 1143–1163, 1968) investigation.     

AN ADAPTIVE SUCCESSIVE OVER RELAXATION DOMAIN DECOMPOSITION BY THE BOUNDARY SPECTRAL STRIP METHOD

In the present paper a new adaptive successive over relaxation domain decomposition technique is developed for the boundary spectral strip method. The proposed scheme is based on dividing the overall domain of the problem into several subdomains. First each of the subdomains in the BIEM matrices is analysed independently. These matrices together with an arbitrary initial guess of displacements on the interface of each two neighbouring subdomains, enable an iterative and a very efficient solution of the whole problem. An adaptive procedure, based on comparing two norms along the interface of subregions, is carried out to impose successive over relaxation convergence. Numerical results comparing the present scheme with single domain solutions emphasize the capability of the proposed technique regarding accuracy and computational efforts. © 1997 by John Wiley & Sons, Ltd.     

改进迭代过程的车轨耦合振动数值解法及应用

针对列车-轨道耦合振动迭代求解过程,结合Newmark-β 积分格式,提出一种基于有限元法与非线性接触理论的改进迭代过程数值解法。考虑分别建立车辆系统和轨道系统振动方程,在耦合和解耦迭代过程中,构造松弛因子函数和收敛准则函数,简化轮轨界面协调适应条件,利用轮轨相互作用力在两子系统之间的快速迭代实现动态耦合关系的高效求解。此算法增强了对迭代收敛精度、迭代过程稳定性的控制,同时也减小了程序设计的难度。应用此算法分别对竖错和路基沉降两类典型线路缺陷引起的车轨振动响应进行了算例对比和分析,计算结果表明,改进解法在迭代速度和迭代稳定性上具有优势,可广泛应用于高速铁路车辆运行和轨道结构动力学问题的分析中。     

Internally coded multicarrier frequency-hopping CDMA communication system and its performance analysis

A new internally coded scheme that combines frequency hopping (FH) and multicarrier (MC) code division multiple access (CDMA) techniques using a super-orthogonal encoder is proposed. In this method, the total bandwidth is partitioned into Ns₂ disjoint bands and each band is also segmented into Ns₁ subbands. On the basis of a super-orthogonal encoder output and a pseudorandom sequence, one of the Ns₁ bands is selected. The data bit is then transmitted in the band in the form of the multicarrier FH (MC-FH) CDMA scheme, that is, Ns₂ carriers are transmitted in the Ns₂ subbands of the selected band. At the receiver, both hard and soft detectors are used. The performance of the proposed method in the additive white Gaussian noise (AWGN) and fading channels is evaluated. The results indicate that the proposed method outperforms the previously presented uncoded and coded MC-FH-CDMA systems, where the data are transmitted over the whole bandwidth, keeping the same bandwidth (spectral efficiency). Further, in the new method, the carriers hop in part of the total bandwidth, and hence coherent detection is more feasible.     

极坐标-直角坐标下水下目标跟踪算法及试验研究

在实际水下目标跟踪系统中,由声纳获得的速度量测是一个相对径向速度,并且量测噪声是非白的,为此提出了基于扩展量测和扩展状态的混合坐标系下水下目标跟踪算法。该方法把径向速度量测引入观测模型,提高了目标的状态估计精度和收敛时间;引入了扩充向量,克服了实际水下目标观测噪声非白的影响。提出了水下多目标跟踪水池试验方法。该方法应用静态长线阵和多目标信号源在水池实现了多目标和跟踪体之间的相对运动的模拟。水池试验结果表明所提出的方法性能明显优于基于量测转换跟踪方法(如MC方法),具有重大工程应用价值。     

A cooperative turbo coding scheme for wireless fading channels

A coded cooperative transmission scheme based on turbo encoding/decoding, in which only newly generated parity bits of the partner are sent if the user successfully decodes its partner's information in order to improve bandwidth efficiency is proposed. The proposed encoding structure introduces correlation between users' data over multiple frames, which offers effectively longer codes and facilitates high-performance iterative multi-user decoding at the destination. Additionally, the iterative decoding over multiple frames can provide time diversity besides spatial diversity inherent in user cooperation even for flat block fading channels. Simulation results show that the proposed scheme significantly outperforms direct transmission for the same transmitted power and bandwidth efficiency.     

特征扰动频率辨识的自适应倾斜扰动抑制技术

为了抑制倾斜校正系统中的时变扰动,提出了一种基于特征扰动频率辨识的自适应扰动抑制方法。采用最小均方误差准则对闭环系统误差进行特征扰动频率辨识,以实现自适应控制器参数的在线调整,且将辨识的滤波参数与控制器调整并行化设计。同时提出频率分割的方法,将低频扰动以及高频扰动的抑制相结合,进一步提高了特征频率辨识速度以及简化设计流程,实现对闭环带宽内的扰动自适应抑制。所提出的方法在倾斜校正装置中进行了闭环验证,实验结果表明该方法能快速辨识特征扰动并自适应调节控制器,可以在单频或多频时变扰动下提升系统的闭环性能。

     

Multiframe blind deconvolution of heavily blurred astronomical images

A multichannel blind deconvolution algorithm that incorporates the maximum-likelihood image restoration by several estimates of the differently blurred point-spread function (PSF) into the Ayers-Dainty iterative algorithm is proposed. The algorithm uses no restrictions on the image and the PSFs except for the assumption that they are positive. The algorithm employs no cost functions, input parameters, a priori probability distributions, or the analytically specified transfer functions. The iterative algorithm permits its application in the presence of different kinds of distortion. The work presents results of digital modeling and the results of processing real telescope data from several satellites. The proof of convergence of the algorithm to the positive estimates of object and the PSFs is given. The convergence of the Ayers-Dainty algorithm with a single processed frame is not obvious in the general case; therefore it is useful to have confidence in its convergence in a multiframe case. The dependence of convergence on the number of processed frames is discussed. Formulas for evaluating the quality of the algorithm performance on each iteration and the rule of stopping its work in accordance with this quality are proposed. A method of building the monotonically converging subsequence of the image estimates of all the images obtained in the iterative process is also proposed.     

具有内衬的缠绕容器缠绕层等张力设计的迭代搜索

基于本文作者已提出的模拟具有金属内衬缠绕容器缠绕过程的有限元策略或者其它一些简化的解析公式,发展了一种确定具有内衬缠绕容器实现等张力状态的预拉张力过程的迭代方法。以典型钢带或碳纤维缠绕的圆筒压力容器为例进行了数值分析。结果表明:采用本文中的方法可以通过可控的缠绕预拉张力工艺过程达到在缠绕工艺结束后实现压力容器等张力状态。      

Assessment of harmonic distortion level considering the interaction between distributed three-phase harmonic sources and power grid

An iterative frequency domain-based harmonic analysis method for harmonic distortion assessment for systems with distributed harmonic sources has been proposed. The proposed method, unlike the traditional method, is able to consider harmonic attenuation and diversity due to the interaction between the harmonic sources and power grid. Time domain simulation for systems with distributed adjustable speed drives is used to validate the proposed method. Case studies are conducted to show the merits of the proposed method especially with a large number of distributed harmonic sources     

Hybrid detectors for wireless orthogonal frequency division multiplexing with code division multiplexing systems based on reliability information

Orthogonal frequency division multiplexing with code division multiplexing (OFDM-CDM) is attractive for the next generation high-speed wireless systems due to the fact that the performance of OFDM-CDM systems can be considerably improved by employing a joint detection scheme such as the maximum likelihood (ML) detector. However, the complexity of the ML detector increases rapidly as the number of orthogonal spreading codes and/or the number of bits per modulation symbol increase. In this study, the authors introduce a unified detection model and propose two hybrid detectors, which combine zero forcing (ZF) with successive interference cancellation (SIC) and sphere detection (SD) algorithms, respectively. After obtaining the initial solution from the front-end ZF receiver, the proposed back-end algorithms are adopted to extend the potential solution list and search for the final result. The objective is to utilise the combination of a simplified linear equaliser and a comprehensive detection scheme to achieve enhanced performance and offer alternatives to the more complex and channel-estimation-sensitive minimum mean squared error (MMSE) scheme. The results show that the proposed hybrid detectors are able to achieve superior performance compared to the MMSE scheme and provides a significant performance improvement compared to the conventional OFDM counterpart.     

An augmented Lagrangian algorithm for contact mechanics based on linear regression

The penalty method for the solution of contact problems yields an approximate satisfaction of the contact constraints. Augmentation schemes, which can be adopted to improve the solution, either include the contact forces as additional unknowns or are strongly affected by the penalty parameter and display a poor convergence rate. In a previous investigation, an unconventional augmentation scheme was proposed, on the basis of estimating the ‘exact’ values of the contact forces through linear interpolation of a database extracted by the previous converged states. An enhanced version of this method is proposed herein. With respect to the original method, the enhanced one eliminates some numerical problems and improves the regularity of the convergence path by carrying out the estimate through linear regression methods. The resulting convergence rate is superlinear, and the method is quite insensitive to the penalty parameter. The main underlying concept is that, within the iterative solution of a non‐linear problem, linear regression techniques may be used as a tool to ‘shoot’ faster to the final solution, on the basis of a set of intermediate data. The generality of this concept makes it potentially applicable to contact problems in more general settings, as well as to other categories of non‐linear problems. Copyright © 2012 John Wiley & Sons, Ltd.     

四参数正弦波组合式拟合算法

提出了一种组合式四参数正弦曲线拟合方法。首先,使用已知频率的三参数正弦拟合算法进行频率搜索,构造出一维搜索迭代正弦拟合算法,获得幅度、频率、相位、直流分量4个参数。然后,以其作为初始值,使用四参数搜索迭代方式,获得最终的正弦拟合结果。该方法可以适用于多周期和残周期序列情况,具有明确的收敛域,可以保证在任何情况下获得总体最优的收敛拟合结果。仿真和实测实验,均验证了所述方法的有效性与可行性。     

Joint maximum-likelihood frequency offset and channel estimation for multiple-input multiple-output?orthogonal frequencydivision multiplexing systems

The problem of joint maximum-likelihood estimation of the carrier-frequency offset (CFO) and channel coefficients in multiple-input multiple-output orthogonal frequency-division multiplexing systems is investigated, assuming that a training sequence is available. The exact solution to this problem turns out to be too complex for practical purposes. To overcome this difficulty, the authors resort to the expectation?maximisation (EM) algorithm and propose an iterative scheme which iterates between estimating the channel parameters and the frequency offset. This results in an estimation algorithm of a reasonable complexity which is suitable for practical applications. Moreover, the Cramer?Rao bounds (CRB) for both CFO and channel estimators are developed to evaluate the performance of the proposed scheme. Simulation results show that the proposed algorithm achieves almost ideal performance compared with the CRBs in all ranges of signal-to-noise ratio for both channel and frequency offset estimates.