基于Viterbi-双向搜索的咬尾码最大似然译码算法

传统咬尾码最大似然(ML)译码算法在译码时存在两个问题:复杂度高和消耗存储空间大。针对这两个问题,该文提出了一种基于Viterbi算法和双向搜索算法的最大似然译码算法。新算法利用Viterbi算法得到的幸存路径度量值与最大似然咬尾路径度量值的关系,删除不可能的起始状态及其对应的咬尾格形子图,缩小搜索空间;然后利用双向搜索算法中门限值与最大似然咬尾路径度量值的关系来降低双向搜索算法的复杂度,从而得到一种在咬尾格形图上高效率的最大似然译码算法。新的最大似然译码算法不仅降低了译码复杂度,同时降低了译码器对存储空间的需求。     

基于最大似然交替投影算法的米波雷达测高工程实现

介绍了最大似然交替投影算法的基本原理,通过对单次快拍条件下最大似然交替投影算法的化简,提出了一种新的简化的最大似然交替投影算法,使运算量大大减少。最后结合某课题,采用新的简化后的最大似然交替投影算法实现了测高模块的设计,使用高性能的数字信号处理器（TS201）和FPGA完成算法的实现,并给出了工程实现的方法。     

数字通信前馈算法中的最大似然同步算法仿真

快速精确地实现传输时延的估计是突发数字通信中的研究重点和难点。研究了数字通信前馈算法中的最大似然同步算法,对最大似然同步算法的原理进行了分析,根据最大似然函数的不同,推导出4种不同的最大似然估计算法,并以QPSK调制方式为例,在Matlab环境下对4种算法进行了仿真,估计了各种因素对算法的影响。仿真结果表明,最大似然同步算法的估计精度高,估计范围广,满足突发通信的要求。     

一种修正最大似然调制分类算法

通过对观测样本进行非线形变换,对最大似然调制分类算法进行了修正,提出了一种最大似然数字调制分类算法。该算法有效消除了载波相位对最大似然算法性能的影响。理论分析和仿真结果均证明了算法的正确性和有效性。     

一种针对频率选择性MIMO信道的新型空时分层迭代检测算法

本文针对FS-BLAST算法中的误码扩散问题提出了一种新的分层迭代方法：部分最大似然分层迭代（MLIC）算法。FS-BLAST由于采用了干扰对消的方案,不可避免的产生了误码扩散问题。在本文中,提出了一种新的部分最大似然分层迭代方案,它在分层迭代算法中引入最大似然的概念,是最大似然检测和分层迭代算法的折衷。从实验仿真中,可以看出,这种改进的算法比传统的FS-BLAST和已有的迭代算法具有更好的系统性能。     

基于最大似然法的天波超视距雷达相位解污染算法

电离层解相位污染是天波超视距雷达信号处理的关键技术之一。由于模型的不准确性和电离层的复杂性,已有算法在污染较大时大多精度不高。该文提出一种基于最大似然法的相位解污染算法。该算法将信号建模为相位多项式,通过最大化似然函数来实现污染相位的估计。为了避免最大似然法中的矩阵求逆运算,该文进一步将最大似然问题转化为最小二乘问题,利用遗传算法求解相位系数。仿真结果表明,与传统算法比较,该文算法具有以下优点:相比HRR算法和CED算法,该文算法精度更高,校正后的信号频谱更加尖锐;在相位污染较大的情况下,该文算法仍具有较高的精度,有利于目标信息的提取;该文算法采用高阶多项式,避免分段处理和矩阵求逆,简化了运算。     

一种基于连续蚁群算法的快速最大似然DOA估计

针对传统最大似然估计计算量大的问题,将连续空间蚁群算法与最大似然估计算法相结合,在ACOML算法的基础上,提出了一种用混沌序列初始化状态空间的改进蚁群算法MACOML(Muddleheaded ACO)。该方法使用混沌映射产生的初始状态空间来代替ACOML算法中的随机序列产生的初始状态空间,增加了初始解的遍历性,同时在寻优过程中增加了局部搜索。仿真结果表明:MACOML能保持最大似然估计方法的高分辨性能,而计算复杂度只是最大似然方法的1/20。     

雷达低角跟踪环境下的最大似然波达方向估计方法

在时空级联最大似然算法的基础上,本文结合雷达低角跟踪的特点,提出一种新的目标仰角估计算法.该算法利用事先得到的目标距离信息和天线高度信息来得到目标直达波信号和多径信号之间的仰角关系,然后再对时空级联最大似然算法的似然函数进行一维搜索.与时空级联最大似然算法相比,新算法不仅运算量大大下降,而且还具有较好的性能.理论分析和计算机仿真结果都证实了新算法的优越性.     

相干信源波达方向估计的广义最大似然算法

论文基于广义导向矢量和广义阵列流形矩阵,建立了多相干源(组)情况下的阵列数据模型,然后提出了波达方向估计的广义最大似然算法。对于广义最大似然算法,入射信源可以是多相干源(组),阵列的几何结构也没有任何约束,而且它分辨的信源数还可以大于阵元数。随后,论文将广义最大似然算法与常规最大似然算法进行了理论比较,并给出了广义最大似然竹法方位估计一致性的证明和方位估计方差的计算公式。理论分析表明,在空间只存在非相干信源时,广义最大似然算法与常规的最大似然算法是等价的,而在空间存在多相干源(组)时,它的性能较常规最大似然算法有较大的改进,方位估计的方差更小。最后论文利用遗传算法实现了广义最大似然算法,并通过MonteCarlo仿真实验证明了广义最大似然算法的有效性。     

分布式空频编码协同通信系统分段ML迭代检测算法

该文针对频率选择性衰落下的多中继分布式空频编码协同通信系统,提出了一种分段最大似然迭代检测算法。目的节点将每一个分布式空频编码的频域向量划分成若干小段,分别对其进行最大似然迭代检测。理论分析和仿真结果表明,该迭代最大似然检测算法收敛速度快,且显著降低了分布式空频编码协同通信系统检测算法的复杂度,具有较高的实用价值。     

Active bearing estimation from a mobile two-dimensional array of sensors

A new approach for active-sonar target detection and bearing estimation from a mobile two-dimensional array of sensors operating in a predominantly noisy environment is presented. Sensor-level adaptive noise cancellation featuring an unconventional method for reference-noise estimation is the key preprocessing step in the proposed approach. A signal-subspace algorithm resulting from two-stage optimisation based on a generalised eigendecomposition of the signal plus (residual) noise covariance matrix is employed to estimate the bearing of the detected target. Simulation results conclusively demonstrate that the proposed scheme is capable of performing target detection and the subsequent two-dimensional bearing estimation with a high degree of reliability at signal-to-noise power ratios as low as -70 and -40-dB, respectively.     

Online identification of induction machine electrical parameters for vector control loop tuning

In a vector-controlled induction machine drive, accurate knowledge of the machine electrical parameters is required to ensure correct alignment of the stator current vector relative to the rotor flux vector, to decouple the fluxand torque-producing currents and to tune the current control loops. This paper presents a new method for online identification of the induction machine parameters required to tune a rotor-flux-oriented (RFO) vector control scheme. Accuracy of the slip frequency estimation required for RFO vector control is achieved by utilizing the parameter independent "flux pulse" rotor time constant estimation scheme, which utilizes short-duration pulses injected into the flux-producing current. The parameters required to tune the synchronous frame current control loops with a decoupling circuit are estimated using a recursive estimation scheme derived from the synchronous frame voltage equations. As the "flux pulse" scheme requires signal injection into the flux-producing current a new rotor time constant estimation scheme is presented, based on the sensitivity analysis of the recursive parameter estimation scheme. Simulation and experimental results are presented which demonstrate the effectiveness of the online parameter identification and control loop tuning technique.     

Robust adaptive multi-service transmission with hierarchical modulation for OFDM systems in high mobility scenarios

Wireless communications play a key role in intelligent transportation systems for bearing multiple application services with different quality of service (QoS) requirements. Hierarchical modulation (HM) is an effective technique to increase the spectral efficiency (SE) of differentiated services multiplexing transmissions. In high mobility scenario, due to the impact of the feedback delay and channel estimation error, only the imperfect channel state information is available at the transmitter. Thus, the performance of the existing HM schemes degrades severely. In this paper, we propose a robust adaptive HM scheme to increase the overall SE in the mobile orthogonal frequency division multiplexing system. The bit error rate of the HM symbol is derived for the reliable QoS-aware multi-service transmission, and the strategies of bit assignment and modulation parameters selection for different services are designed. Finally, comparing with the traditional uniform modulation scheme, the proposed robust adaptive HM scheme increases the overall SE of multiplexing transmissions by \(15\%\) at \(300\,\hbox { km}/\hbox {h}\).     

RLS-Based Joint Estimation and Tracking of Channel Response, Sampling, and Carrier Frequency Offsets for OFDM

This paper proposes a pilot-aided joint channel estimation and synchronization scheme for burst-mode orthogonal frequency division multiplexing (OFDM) systems. Based on the received signal samples containing pilot tones in the frequency domain, a cost function that includes the carrier frequency offset (CFO), sampling clock frequency offset (SFO) and channel impulse response (CIR) coefficients is formulated and used to develop an accompanying recursive least-squares (RLS) estimation and tracking algorithm. By estimating the channel CIR coefficients instead of the channel frequency response in the frequency domain, the proposed scheme eliminates the need for an IFFT block while reducing the number of parameters to be estimated, leading to lower complexity without sacrificing performance and convergence speed. Furthermore, a simple maximum-likelihood (ML) scheme based on the use of two long training symbols (in the preamble) is developed for the coarse estimation of the initial CFO and SFO to suppress dominant ICI effects introduced by CFO and SFO and to enhance the performance and convergence of the fine RLS estimation and tracking. Simulation results demonstrate that, over large ranges of CFO and SFO values, the proposed pilot-aided joint channel estimation and synchronization scheme provides a receiver performance that is remarkably close to the ideal case of perfect channel estimation and synchronization in both AWGN and Rayleigh multipath fading channels.      

Single tone jamming elimination scheme of multicarrier spread spectrum system

The proposed scheme is based on Discrete Fourier Transform (DFT) domain processing. The key technology of this scheme is jamming parameters‘ accurate estimation and jamming reconstruction. Compared with the “threshold exciser”scheme.the proposed scheme can eliminate more jamming energy on the whole frequency band with the minimum loss of useful signal energy. As shown in the research and simulation, the proposed scheme is much better than the “threshold exciser” scheme, especially in the case of high power jamming whereas the “threshold exciser” scheme might be invalid.     

A Signal Perturbation Free Whitening-Rotation-Based Semiblind Approach for MIMO Channel Estimation

It was shown in our previous work that, in the noise-free case, the whitening-rotation (WR)-based MIMO channel estimation algorithm is subject to a signal perturbation error, justifying that the WR-based method is efficient only in the low signal-to-noise ratio (SNR) case. In this paper, a very efficient signal-perturbation-free WR-based approach is proposed for semiblind channel estimation of MIMO systems. A novel transmit scheme is developed based on the eigenvalue decomposition of the correlation matrix of the transmitted signal. The new scheme is to send a small volume of data bearing the information of the correlation matrix to the receiver for the cancellation of the signal perturbation error so as to improve the performance of the WR-based method in the case of high SNRs. Then, a perturbation analysis of the proposed WR-based semiblind method with the new transmit scheme is conducted, leading to a closed-form expression for the mean square error (MSE) of the channel estimate. Computer simulations show that the proposed approach significantly outperforms the original WR-based method as well as some other channel estimation methods for all SNR levels.     

Two-dimensional angle-of-arrival estimation in the presence offinite distance sources

When sources are a finite distance away from an array system, most high-resolution bearing estimation techniques exhibit unsatisfactory performance due to the invalidity of the planar wavefront assumption. This problem has been addressed by a far-field approximation (FFA) method based on a preprocessing scheme. By exploiting favorable characteristics of a uniform linear array, the method constructs a FFA covariance matrix, which is Toeplitz and approximates to the far-field data covariance matrix, from the observed data covariance matrix. Then eigenstructure methods can be applied to perform bearing estimation without revising the planar wavefront assumption. This method is extended to the problem of two-dimensional angle-of-arrival (AOA) estimation using a uniform planar array in the presence of finite distance sources. A procedure is derived for reconstructing the 2-D FFA covariance matrix with block-Toeplitz structure. Using the 2-D FFA covariance matrix, eigenstructure methods can be applied in conjunction with a 2-D AOA search to solve the problem. Simulation results confirm the theoretical work     

On Achievable Data Rates and Optimal Power Allocation in Fading Channels with Imperfect Channel State Information

Achievable rates of wireless communication systems with pilot-based channel estimation are investigated for the case of time-selective fading. Novel analytical expressions for the maximum achievable rates of such systems are derived in terms of the system signal-to-noise ratio (SNR), fading rate and estimation scheme deployed. The frame size is optimized jointly based on the SNR and the fading rate. The maximum rate achieving coding scheme is suggested and shown to be a modified version of the classical water-filling algorithm that accounts for imperfect channel state information (CSI) at the transmitter. The impact of the estimation scheme and the angular spread of the received signal on the quality of estimation and achievable rates is evaluated. A number of numerical simulations are provided to illustrate the dependence of the optimal block length and achievable rates on SNR, fading rate, estimation scheme and angular spread of the channel.

A Built-in-Self-Test Scheme for Segmented and Binary Weighted DACs

This paper describes a new Built-In-Self-Test(BIST) scheme for estimation of static non-linearity errors in segmented and binary weighted digital to analog converters (DACs). The BIST scheme comprises of a hierarchy of tests including tests for non-monotonicity, checks to detect if the DNL/INL errors exceed ±0.5 LSB and actual estimation of the DNL/INL. The BIST scheme has been experimentally verified on 10-bit segmented current steering DAC. The DAC, along with the additional circuits required for testing, was designed and fabricated using a 0.35 m process. Both simulation and experimental results are included in this paper. Errors estimated using the BIST scheme match well with measurements done on the fabricated device.     

Robust multiple signal classification algorithm based on the myriad covariation matrix

A robust version of the multiple signal classification (MUSIC) bearing estimation algorithm based on robust statistics is developed for a direct sequence-code division multiple access impulsive noise channel. The proposed subspace algorithm is computed by using the antenna array covariance matrix, which is derived from the robust maximum likelihood estimator of location. Each element of the robust covariance matrix is computed as the sample myriad of a window of the received observations. The MUSIC antenna array scheme is jointly used to mitigate the effects of multipath and impulsive noise. Simulation results demonstrate that the proposed scheme significantly outperforms the other linear and nonlinear schemes