三维LMS运动估计的迭代算法和线性算法

本文阐述了引入特征点集误差分布的最小均方（ＬＭＳ）运动估计问题，最优运动 估计本质是上６自由度的非线性问题，本文提出推广的主重合定理和运动参数分解定量，将其简化成３自由度的纯旋转问题，我们给出最优运动参数估计的线性算法，兼有运动 估计的最优性质和能够实时实现的优点；同时给出一个迭代算法，其性能也是最优的，并且收敛性能更好。     

一种数据辅助的前向位定时估计算法

以平方法为代表的非数据辅助(NDA)类前向位定时估计算法在低信噪比和小成性系数场合估计性能严重恶化,而采用数据辅助(DA)类估计是值得考虑的选择。但传统的数据辅助类算法需要大量的搜索以获取位定时的精确估计,运算量大实现困难。本文将三角内插技术应用于位定时估计,提出了一种新的数据辅助前向位定时估计算法,该算法简单、便于实现。仿真结果表明,本文算法估计性能逼近修正卡美罗界(MCRB),且对成形滚降系数不敏感,适合于低信噪比突发通信。最后,本文针对突发信号给出了前导码捕获与位定时估计一体化的实现结构。      

一种H.264运动估计器的VLSI设计

MPEG4AVC／ITU—T H．264视频编码标准中所采用的多模式运动估计算法与传统的MPEG4、H．263 高级预测模式相比较而言，编码效率和性能都大大提高。但其诸如模式决策等问题却给运动估计器，特别是硬件运动估计器带来非常大的运算复杂度。本文提出一种H．264运动估计器硬件结构，它采用了新的模式决策算法和快速运动估计算法。仿真结果证明，这两种算法不但能使运动估计器降低其硬件实现成本，而且能减少模式决策和运动估计的时间。     

载波频率估计的编码辅助算法

本文讨论了载波频率估计的编码辅助(code-aided)算法。因为难以直接计算频率的最大似然估计值,我们转而利用EM算法迭代逼近这一结果,而且将EM迭代与MAP译码器结合起来,在频率估计中利用了译码输出的信息,从而在低信噪比下获得了非常理想的性能。仿真结果表明,文中所给算法的性能远优于传统的NDA算法。     

一种适合突发数字通信的快速载波频偏估计算法

给出了一种适用于MPSK解调的非数据辅助(NDA)载波频偏估计算法,该算法采用前向开环载波同步方式,与传统的Costas环相比,这种方式具有同步速度快、载波频偏估计范围大的优点,尤其适用于高速突发数字通信系统。理论和实验结果表明,该算法计算量小,复杂度低,抗噪声性能好,适合于工程实现。     

基于粒子群优化的MPSK信号频偏估计算法

针对传统多进制数字相位调制(MPSK)信号非数据辅助(NDA)频偏估计算法存在估计范围有限、估计方差较大、符号个数少时估计性能受限等问题,提出了基于粒子群优化的频偏估计方法。该算法以频偏估计的似然函数为目标函数,模拟群体智能搜索最优解。仿真结果表明,本算法无偏估计范围大,在符号数较少、信噪比较低时,估计方差接近克拉美罗下限(CRLB),性能优于经典的离散傅里叶变换(DFT)算法和Kay算法。     

基于循环互相关的宽带信号时差估计

研究了定位中的宽带信号时差估计问题，给出了时差估计信号模型，分析了信号的循环相关特性，提出了基于宽带信号循环互相关的时差估计算法。最后采用计算机进行了仿真实验，给出了估计性能的曲线，并和广义相关算法进行比较，仿真实验表明本文所提算法具有较好的估计性能。     

视频压缩中运动估计块匹配算法研究

首先介绍了视频压缩系统，并在此基础上阐述了运动估计块匹配算法，分别介绍了块匹配的基本原理、提高运动估计效率的几个关键技术，分析了传统的基于块的运动估计块匹配算法和后来改进的匹配算法的性能，同时在分析MPEG-4特性的基础上，阐述了未来的运动估计匹配算法的发展趋势。     

一种自适应的六边形一方形运动估计搜索算法

运动估计在视频压缩中占有相当重要的地位。本文设计了一种自适应的六边形一方形运动估计搜索算法,该算法根据实际视频序列的统计特性,充分利用搜索起始点预测技术,中止判别技术,以及零运动向量的判决技术,有效提高了运动估计的搜索精度。最后给出了仿真比较结果,以证明本文算法的有效性。     

H.264中块匹配的快速搜索算法研究

在新一代视频压缩编码标准H．264中，块匹配运动估计有着举足轻重的地位，它的性能影响着输出码流的质量。在块匹配中运动估计耗时最多，为了减少运动估计的时间和搜索的次数，常采用快速搜索算法。介绍块匹配运动表示法，详细研究块匹配中的3种快速搜索算法的搜索过程，并对3种算法的性能作比较分析。     

A performance lower bound for quadratic timing recovery accounting for the symbol transition density

The symbol transition density in a digitally modulated signal affects the performance of practical synchronization schemes designed for timing recovery. This paper focuses on the derivation of simple performance limits for the estimation of the time delay of a noisy linearly modulated signal in the presence of various degrees of symbol correlation produced by the various transition densities in the symbol streams. The paper develops high- and low-signal-to-noise ratio (SNR) approximations of the so-called (Gaussian) unconditional Crame/spl acute/r-Rao bound (UCRB), as well as general expressions that are applicable in all ranges of SNR. The derived bounds are valid only for the class of quadratic, non-data-aided (NDA) timing recovery schemes. To illustrate the validity of the derived bounds, they are compared with the actual performance achieved by some well-known quadratic NDA timing recovery schemes. The impact of the symbol transition density on the classical threshold effect present in NDA timing recovery schemes is also analyzed. Previous work on performance bounds for timing recovery from various authors is generalized and unified in this contribution.     

Cramer–Rao lower bounds and maximum likelihood timing synchronization for dirty template UWB communications

Timing acquisition constitutes a major challenge in realizing ultra-wideband communications. In this paper, we propose the timing with dirty template (TDT) approach as a promising candidate for achieving rapid, accurate and low-complexity acquisition. We describe the dirty template (DT) technique, in order to develop and test timing algorithms in both modes: data-aided (DA) and non-data- aided (NDA) modes. First, we derive the Cramer–Rao lower bound, which is used as a fundamental performance limit for any timing estimator. Next, the TDT acquisition estimator is achieved by using the Maximum Likelihood concept. Then we propose a new method, based on Time-Hoping codes, to improve the performance estimation of the original dirty template algorithms. Simulation shows the estimation error results of the modified method in the DA and NDA modes. It confirms the high performance and fast timing acquisition of DA mode, compared with NDA mode, but with less bandwidth efficiency.     

莱斯正弦和法的色高斯过程仿真分析

在无线移动通信中,深刻理解和精确模拟传播信道对于通信系统的设计和性能分析是至关重要的。对基于莱斯正弦和法仿真色高斯随机过程的5种方法即等距离法、等面积法、蒙特卡洛法、最小均方误差法和精确多普勒扩展法进行了性能分析。通过分析得出,精确多普勒扩展法性能最好,最小均方误差法次之,然后是等面积法和等距离法,性能最差的是蒙特卡洛法。通过与理论值进行比较,证明了当正弦函数的数目越大逼近程度越好这一结论。     

A new detection algorithm (NDA) based on fuzzy cellular neural networks for white blood cell detection.

White blood cell detection is one of the most basic and key steps in the automatic recognition system of white blood cells in microscopic blood images. Its accuracy and stability greatly affect the operating speed and recognition accuracy of the whole system. But there are only a few methods available for cell detection or segmentation due to the complexity of the microscopic images. This paper focuses on this issue. Based on the detailed analysis of the existing two methods--threshold segmentation followed by mathematical morphology (TSMM), and the fuzzy logic method--a new detection algorithm (NDA) based on fuzzy cellular neural networks is proposed. NDA combines the advantages of TSMM and the fuzzy logic method, and overcomes their drawbacks. With NDA, we can detect almost all white blood cells, and the contour of each detected cell is nearly complete. Its adaptability is strong and the running speed is expected to be comparatively high due to the easy hardware implementation of FCN. Experimental results show good performance.     

Non‐Data‐Aided Weighted Non‐Coherent Receiver for IR‐UWB PPM Signals

This letter proposes an energy‐detection‐based non‐data‐aided weighted non‐coherent receiver (NDA‐WNCR) scheme for impulse radio ultra‐wideband (IR‐UWB) pulse‐position modulated signals. Compared to the conventional WNCR, the optimal weights of the proposed NDA‐WNCR are tremendously simplified as the maximum eigenvector of the IR‐UWB signal energy sample autocorrelation matrix. The NDA‐WNCR serves to blindly obtain the optimal weights and entirely circumvent the transmission of training symbols or channel estimation in practice. Analysis and simulation results verify that the bit error rate (BER) performance of the NDA‐WNCR closely approaches the ideal BER of the conventional WNCRs.     

低信噪比下非数据辅助的OFDM系统信道阶数和噪声方差的估计

在低信噪比情况下,该文提出一种新的针对正交频分复用(OFDM)系统信道阶数和噪声方差的非数据辅助(NDA)估计算法。算法中应用了一种新的基于联合极大几何均值(MGM)的代价函数。新的代价函数不仅利用了循环前缀(CP)冗余性,同时也利用了信道记忆性。对比只利用了CP的方法,该算法可以在低信噪比情况下更准确地估计信道阶数和噪声方差。仿真结果表明,在低信噪比情况下,该算法针对信道阶数的估计得到约10 dB的信噪比增益;同时,对噪声方差的估计,该算法显著提高了估计精度,抑制了信噪比20 dB以下估计性能恶化的现象。     

Channel estimation for ultra-wideband communications

This paper deals with channel estimation in ultra-wideband communications operating in a multipath environment and in the presence of multiaccess interference. The channel parameters are the attenuations and delays incurred by the signal echoes along the propagation paths. Time-hopping modulation with binary symbols is assumed. The estimation method is based on the maximum-likelihood criterion and is applied to two different scenarios: either with known symbols (DA estimation) or with unknown symbols (NDA estimation). The effects of the estimation errors on the performance of a RAKE receiver are assessed by simulation by comparing the receiver bit-error rate with either perfect channel estimates or imperfect estimates as obtained from the proposed algorithms. The results show that the degradations are tolerable as long as the number of users is limited. They also show that the DA method has an edge over the NDA in that it can handle a larger number of users for a fixed degradation. The number of users that can be accommodated in practice is found for some values of the system parameters.     

The generalized method of equal areas for the design of sum‐of‐cisoids simulators for mobile Rayleigh fading channels with arbitrary Doppler spectra

We present in this paper a generalized version of the method of equal areas (MEA) that is well suited for the design of sum‐of‐cisoids (SOC) simulators for narrowband mobile Rayleigh fading channels characterized by any type of Doppler power spectral densities (DPSDs). Unlike the original MEA, the generalized MEA (GMEA) can be applied to the simulation of fading channels with asymmetrical DPSDs. This is an important feature because the simulation of such channels is of great interest for the laboratory analysis of mobile communication systems under non‐isotropic scattering conditions. We show that irrespective of the underlying DPSD, the GMEA results in a very good approximation to the autocorrelation function, average Doppler shift, Doppler spread, and envelope distribution of the channel. We compare the performance of the GMEA with that of the L_p‐norm method (LPNM), which is the method that has been most widely used for designing SOC simulators for fading channels with arbitrary DPSDs. The obtained results demonstrate that the performance of the GMEA measures up to that of the LPNM. In addition, the results show that the determination of the model parameters is easier and less time‐consuming when applying the GMEA. Copyright © 2011 John Wiley & Sons, Ltd.     

非数据辅助的OFDM系统符号同步算法

该文中研究了OFDM系统中的非数据辅助符号同步问题。首先,假设OFDM相邻子载波信道的频域响应相同,建立了一种基于OFDM系统相邻子载波间功率差值平方的代价函数,通过对代价函数最小化得到了一种适用于基带调制为恒幅调制的OFDM系统的非数据辅助符号同步算法。然后,通过对信道进一步假设,得到了其它两种类似的代价函数,并对载波频偏及信道噪声对算法的影响和算法的运算量进行了分析和讨论。最后,通过计算机仿真对所得同步算法在不同代价函数及不同载波频偏时的性能进行了分析,并同其它两种已有同类算法进行了比较。仿真结果表明,所得算法的性能总体上优于其它两种已有同类算法。     

Two-stage nondata-aided adaptive linear receivers for DS/CDMA

Closed-form steady-state performance analysis of the signal-to-interference plus noise ratio (SINR) at the output of well-known adaptive implementations of the linear minimum mean-square error (MSE) receiver for direct-sequence code-division multiple access show that nondata-aided (NDA) schemes may suffer from a considerable performance degradation with respect to their data-aided counterparts. Motivated by this fact, we propose a new two-stage NDA scheme where symbol-by-symbol predecisions at the output of a first adaptive stage are used to train a second stage. We derive closed-form steady-state performance analysis for both the two-stage and classical decision-directed schemes, taking into account detection errors in decision-directed adaptation. Our analysis shows that the SINR of the two-stage algorithm is close to optimal over a large range of values, while the SINR of the decision-directed scheme is far from optimal when the optimal SINR is small. Finally, we consider the case of time-varying fading channels. We derive modified recursive least square and least mean square adaptation schemes by considering SINR maximization rather than MSE minimization (that is useless under the assumption of zero-mean random channels). The resulting two-stage receiver shows good tracking properties in heavy near-far conditions (at least for moderate normalized Doppler bandwidth), while the decision-directed receiver may easily loose tracking after deep fades.