A Novel Interpolation Method for Maximum Likelihood Timing Recovery

An algorithm to recover bit timing is proposed which maximises a quadratic polynomial approximation to the log-likelihood function. The exact equation for the mean of the log-likelihood function derivative, i.e. the S-curve, is derived and shown to have a sine form. In each time interval the S-curve has two zeros. The zero corresponding to the maximum of the likelihood function is resolved using quadratic interpolation based on four samples per period. The resulting timing synchroniser has a simple open loop feedforward structure which has effectively no acquisition period. Receiver performances in terms of rms timing jitter and bit error rate (BER) are analysed and shown to agree closely with theoretical results.     

The Contributions of Intracerebral Currents to the EEG and Evoked Potentials

Scalp and cortical potentials due to implanted, dipole current sources were measured in the monkey. A four region spherical model of the head was developed and scalp potentials due to theoretical radial dipoles were computed and compared with experimental results. Dipole source locations were chosen to correspond to points along the somatosensory projection pathways to permit comparison of findings with clinical cortical and scalp evoked potential records. Data yielded by the theoretical head model compare well with those obtained experimentally. The results suggest that depth cerebral bioelectric sources can contribute to scalp recorded activity when averaging techniques are used.     

频率捷变相控阵雷达最大似然测角方法

频率捷变相控阵雷达的脉冲回波之间互不相关,且信噪比起伏严重,多次快拍数据不便积累,因此角度估计性能较差。鉴于此,分析研究了频率捷变相控阵雷达多次不相关快拍数据的积累方式,提出了频率捷变相控阵雷达最大似然测角方法。该方法通过对多次快拍的角度信息进行最优加权,将多次快拍数据有效积累起来,避免了频率捷变相控阵雷达因各快拍之间信噪比起伏而带来的性能损失,可明显提高测角精度,计算机仿真证明了该方法的正确性和有效性。     

A Maximum Likelihood Decoding Algorithm for Wireless Channels

A new maximum likelihood decoding (MLD) algorithm for linear block codes is proposed. The new algorithm uses the algebraic decoder in order to generate the set of candidate codewords. It uses the exact probability for each codeword as a new likelihood metric and a method to generate the appropriate set of codewords similar to Kaneko, et al., and Tanaka-Kakigahara algorithms. The performance of the proposed algorithm is the same as that of MLD as it is proved theoretically and verified by simulation results. The comparison with these similar algorithms shows that the new one always requires less average decoding complexity than those of the other algorithms. Finally, we compare the algorithms for terrestrial and satellite channels.     

A Graphic Method for Estimating Equivalent Dipole of Localized EEG Discharge

Location, orientation, and magnitude of a dipole in spherical conducting media are estimated by using a nomograph. No iterative numerical process on a computer is necessary for each dipole estimation. The estimation method was applied to computer generated dipoles. The difference between true and estimated locations was within 0.8 percent of the sphere radius, and the difference between true and estimated moments was within 3.3 percent of true dipole magnitude. It was also applied to pathological discharges from three patients. Estimated locations nearly agreed with abnormal regions observed in CT images.     

一种新的基于极大似然估计的系统辨识方法

进化计算是一种基于自然选择和自然变异机制的并行随机优化算法。由于递推极大似然估计法难以实现性能指标函数的全局寻优，所以本文提出了将改进的进化计算用于系统参数辨识的方法。计算机仿真结果表明，该算法能够实现似然函数的全局寻优。     

Maximum Amplitude Method for Estimating Compact Fractional Fourier Domain

A maximum-amplitude-based coarse-to-fine algorithm is proposed with two novel ideas highlighted: adopting the maximum value of the fractional Fourier amplitude spectrum to measure the compactness of a signal, and using a coarse-to-fine strategy to speed up the searching process. The simulation results on synthetic and real signals show the validity of the proposed method.      

Noise Cancellation for Brainstem Auditory Evoked Potentials

A technique for cancelling background noise in sensory evoked potential recordings is described. Since sensory evoked potentials are generally much smaller than the background noise, a large number of individual responses must be averaged. The proposed technique uses a second recording channel to estimate the background noise; a cancellation filter function is derived for each individual response in the average. The filter can vary from response to response; however, it does not attempt to adapt to long-term changes in the noise. The technique is intended for situations where the noise is intermittent or rapidly varying, as is often found in the operating room and intensive care unit. The technique was evaluated by a simulation using a known brainstem auditory evoked potential signal plus EEG samples obtained from a patient in the intensive care unit during an evoked potential test. The results showed that the technique could provide improvements in signal-to-noise ratio of 3-6 when the dominant noise component was external electrical interference. The effect was less when the background noise was muscle activity or spontaneous EEG, but there was still significant improvement. It was also found that the improvement obtained was approximately equal to the improvement that could be predicted from the formulation of the filter function.     

基于极大似然法的异类传感器配准方法研究

针对异类传感器数据融合空间配准问题,利用极大似然法对多传感器系统模型进行分析,推导出配准参数的估计值,以毫米波雷达/红外传感器复合制导为例,对空间配准算法进行了仿真,仿真结果具有较快的迭代收敛速度和较好的配准效果,满足了异类传感器融合实时性和精确度的要求.     

Some Improvements in the Measurement of Variable Latency Acoustically Evoked Potentials in Human EEG

Since averaging of acoustically evoked potentials of variable latency yields inconsistent estimates, we tried to improve the results by applying Woody's adaptive filter [8], a weli-known template-cross-correlation method. However, the results were worse and obviously less reliable than those reported by Woody. The following reasons for this behavior were found: 1) low signal-to-noise ratio and 2) large coincidences in the spectral components of EEG and of acoustically evoked potentials, enabling erroneous synchronizations of evoked potential-like EEG transients.     

波束域最大似然测高方法

针对雷达在低仰角搜索和跟踪目标时波束打地、受阵地反射多径影响严重的问题,提出了波束域最大似然雷达低仰角测高方法。该方法首先形成俯仰多波束覆盖目标,然后使用最大似然算法对多波束的目标数据进行处理,通过空间谱能量最大化的角度信息估计目标仰角和高度。与传统的和差波束及多波束比幅测角方法相比,该方法受多径影响小,具有较高的角度分辨率和高测量精度。计算机仿真和实测数据的处理结果验证了该算法可行有效。     

相控阵AEW雷达动目标检测的最大似然方法

非均匀环境对空时自适应处理(STAP)是一个挑战.对此,该文提出了一种基于最大似然估计的相控阵AEW雷达动目标检测方法.该方法具有计算量低、主杂波区性能好和孤立干扰抑制能力强等优点.其有效性得到计算机仿真数据和某实测数据的处理结果所证实.     

Adaptive Filterng of Evoked Potentials

We present an adaptive filtering (AF) technique for rapid processing of evoked potentials (EP). The AF algorithm minimizes the mean-square error (MSE) between successive ensembles. We demonstrate theoretically that the filter output converges to the least square estimate of the underlying signal. Computer simulations with known signal and added noise show that AF produces lower MSE than ensemble averaging. We also compare results of AF to those obtained by ensemble averaging for some EP recorded from animals and humans. For very noisy EP recordings, we propose techniques that combine AF and ensemble averaging. The AF technique shows promise for requiring fewer ensembles than averaging to attain adequate signal quality.     

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。     

A Maximum Likelihood Receiver for an Orthogonally Multiplexed QAM System

A maximum likelihood receiver for an orthogonally multiplexed QAM (OQAM) system has been derived based on the mathematical structure of an OQAM signal. The resulting receiver provides the minimum variance estimates of carrier and timing phases under the disturbance caused by not only Gaussian noise but also random data. It has also been proven that the carrier and timing joint control system is asymptotically stable almost everywhere in a state space. The equilibrium points are where the parallel synchronization over all subchannels in the OQAM system is established. Simulations have been carried out in order to verify the maximum likelihood receiver performances, where 9600 bit/s data are transmitted over 750-2450 Hz voiceband with 8×8 staggered QAM signal constellations. It has been shown that sufficient eye opening is obtained under 10 Hz carrier frequency offset and 10^-4timing frequency stability.     

基于网格爬山法的最大似然DOA估计算法

最大似然波达方向（DOA）估计具有最优的理论性能,但是存在计算量过大的问题。为了降低最大似然DOA估计的计算量,将参数估计转化为高维非线性函数的优化问题,并提出了一种新的优化算法。首先利用波束形成法对空间谱进行预估计并根据空间谱信息构造一组满足“预估分布”的初始解,这组初始解以较大概率落在全局最优解的局部吸引域中。然后将其中适应度最大的一个初始解作为局部搜索的起点。网格爬山法是一种以网格为单元的局部搜索方法,比传统爬山法更加高效和稳定,因此采用该方法获取全局最优解。新算法不仅能够得到精确的参数估计,同时具有较高的计算效率,计算机仿真显示新算法的计算效率高于基于粒子群优化的最大似然DOA估计算法。      

Adaptive Score Functions for Maximum Likelihood ICA

We propose Blind Source Separation (BSS) techniques that are applicable to a wide class of source distributions that may be skewed or symmetric and may even have zero kurtosis. Skewed distributions are encountered in many important application areas such as communications and biomedical signal processing. The methods stem from maximum likelihood approach. Powerful parametric models based on the Extended Generalized Lambda Distribution (EGLD) and the Pearson system are employed in finding the score function. Model parameters are adaptively estimated using conventional moments or linear combinations of order statistics (L-moments). The developed methods are compared with the existing methods quantitatively. Simulation examples demonstrate the good performance of the proposed methods in the cases where the standard Independent Component Analysis (ICA) methods perform poorly.