A Practical Approach Toward Maximum Likelihood Sequence Estimation for Band-Limited Nonlinear Channels

A receiver structure, called a "pseudo maximum likelihood sequence estimation" (pseudo MLSE), which approximates MLSE with a simple hardware configuration, was derived. By introducting a tentatively estimated sequence, the pseudo MLSE detects the received sequence symbol by symbol, retaining the MLSE optimum decision property. The number of arithmetic operations required in one symbol duration is reduced fromM^{L + 1}to(L + 1)Min anM-ary signaling case with channel memory lengthL. An adaptation algorithm for the variation in the channel characteristics was also developed. Pseudo MLSE application to quadrature phase shift keying (QPSK) for a band-limited nonlinear channel is described. The most practical application of pseudo MSLE, named the "adaptive threshold detector with estimated sequence" (ATDES), detects symbols with threshold detection and is suitable for high bit rate operation. For both the pseudo MLSE processor and ATDES, most of the hardware is occupied by a replica memory stored in the receiver. Performance in a typical nonlinear satellite channel model is evaluated by computer simulation. Simulation results show a 0.8 dB improvement by ATDES with 64 replica memories and 1.3 dB improvement by the pseudo MLSE processor with 3072 replica memories. The tentative estimation error effect is estimated to be less than 0.1 dB in the simulated satellite channel.     

Maximum Likelihood Sequence Estimation for Randomly Dispersive Channels

Receiver designs for maximum likelihood sequence estimation of digital data transmission through randomly dispersive channels are developed. The random channels are constrained to have finite memory of durationLin the sense that the casual minimum mean square error estimate of the channel output at any given time is a function of only the most recentLTseconds of observations. Examples of the channels included are the time varying Rayleigh, Rician and lognormal fading channels whose covariance functions have finite support, phase unsynchronized channels which satisfy the finite-memory constraint and point process channels. The information sequence may be either a stream of independent, equally-likely symbols of binary orM-ary alphabets or the output sequence of a trellis or convolutional encoder.     

Maximum Likelihood Sequence Detection for QPSK on Nonlinear, Band-Limited Channels

A receiver structure based on maximum likelihood sequence estimation (MLSE) for receiving quaternary phase shift keyed signals over band-limited, nonlinear satellite channels, in the presence of additive downlink Gaussian noise, is derived. This work is an extension of work done by Mesiya et al. [2] for binary PSK transmission. Error performance of the receiver at low to moderate signal-to-noise ratios is estimated using computer simulation. For moderate to high signal-to-noise ratios, an upper bound on the probability of symbol error is obtained. A suboptimum receiver structure is then developed and its performance evaluated using computer simulation. It is shown that the performance of the suboptimum receiver is very close to that of the MLSE receiver.     

自适应减少复杂度的盲最大似然序列估计

 基于逐幸存路径处理原理和自适应选择幸存路径的思想,本文提出了一种自适应减少计算复杂度的盲最大似然序列估计新算法.通过分析和推导,给出了一种近似估计网格图最小欧式距离的方法,并利用该估计值对幸存路径进行取舍,在网格搜索中仅保留少数幸存路径来进行信道参数和发送符号序列的联合盲估计.理论分析和计算机仿真结果表明,对严重符号干扰信道,在较高信噪比条件下,本文提出的新算法具有较理想的误符号率性能和较低的计算复杂度.     

Optimal Short Desired Impulse Response for Maximum Likelihood Sequence Estimation

In Maximum Likelihood Sequence Estimation, the number of operations per symbol depends critically on the length of the Desired Impulse Response (DIR). In this paper it is shown that a short but complex DIR of length 2 may be sufficient to cope with most severe distortion impairments found in quadrature modulation systems, thus permitting MLSE data decoding at still manageable complexity.     

A Decision Feedback Receiver Structure for Bandlimited Nonlinear Channels

A decision feedback receiver structure for receiving binary phase-shift keyed signals over bandlimited, nonlinear satellite channels, in the presence of both uplink and downlink additive Gaussian noise, is derived. As an illustrative example of the receiver, a hard-limiting channel model is considered in detail, and two special cases are examined. Based on the analysis, an alternative receiver structure which is more suitable for implementation is derived. The performance of the receiver is evaluated by computer simulation techniques, and it is shown that significant performance improvement over the single sample sign detector can be obtained.     

基于ML的多径信道下直扩信号PN码和信道的联合盲估计

针对非协作通信下多径信道直接序列扩频信号伪随机(PN,Pseudorandom)码的估计难题,本文在分析信号二阶统计特性的基础上,提出了一种基于最大似然(ML,Maximum Likelihood)的PN码和多径信道联合盲估计的方法.该方法首先建立PN码和信道序列的最大似然数学模型,然后通过交替转换数学模型和使用迭代最...     

最大似然估计的独立分量分析法

独立分量分析(ICA)在国内尚属一门新型的方法,它的主要应用是盲信号分离(BSS)。该文首先给出了ICA中一种有效的方法--最大似然估计法(ML),其次分析了ML方法和信息最大化方法(infomax)的等价性,最后给出了相应的计算机仿真结果。     

Joint Maximum Likelihood Sequence Estimation for Chromatic-Dispersion Compensation in ASK-DPSK Modulation Format

We determine the fundamental impairment mechanism in the chromatic-dispersion (CD)-limited hybrid amplitude shift keying (ASK)-differential phase-shift keying (DPSK) modulation format and propose the employment of joint maximum likelihood sequence estimation (J-MLSE) for CD compensation to extend the transmission reach of such format. We find that it is not the intrasubchannel interference of the ASK or DPSK subchannel but the interaction between these two subchannels that limits the transmission distance. Therefore, electronic equalization of the two subchannels separately cannot improve the overall CD tolerance of the ASK-DPSK signal. J-MLSE, however, exploits the correlation information between the detected ASK and DPSK signals and is numerically shown to improve the CD tolerance of the ASK-DPSK signal significantly     

Maximum Likelihood Phase Demodulation for Spatially Turbulent Channels

The likelihood equation for the maximum likelihood estimate (MLE) of a temporal phase modulation (a sample function of a wide-sense stationary zero-mean Gaussian random process) received in a spatial aperture after transmission through a spatially turbulent channel and addition to a white Gaussian noise field is derived for unknown, Gaussian, and limiting cases of log-normal received signal fields. The received signal field estimation performed by the demodulator structure is explicitly exhibited and other clarifications made. The likelihood equation is linearized and solved and the resulting mean-square estimation error calculated. The Cramer-Rao lower bound is given. In an example it is shown that the linear estimate is efficient and has variance inversely proportional toM, the number of coherence areas required to disjunctly cover the receiver spatial aperture. A heterodyne receiver with an optimized aperture weighting is shown to use essentially only one coherence area; its asymptotic mean-square error is also calculated.     

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.     

基于极大似然估计的奇异点检测

信号的奇异点往往包含信号比较重要的信息,对其进行检测和定位在许多实际问题中都有重要的意义。根据脉冲型奇异点的特点,提出了一个基于极大似然估计的脉冲奇异点检测方法。该方法利用Bernoulli概型来建模,用于对脉冲奇异点的检测,将脉冲奇异点的检测问题转化为一个参数估计问题,并利用极大似然估计方法给出了参数的估计。通过对大量的仿真信号及真实信号脉冲奇异点的检测证明,该检测方法计算简单,行之有效。     

一种新的时频极大似然DOA估计方法

针对非平稳信号,提出一种新的时频域极大似然DOA估计方法,利用参考阵元与阵列中其它阵元输出之间的互伪Wigner-Ville分布建立起时频域的阵列信号模型,通过时频域极大似然方法获得入射方向估计。与基于空间时频分布矩阵的阵列测向方法相比,该方法具有计算量小、交叉项时频分布利用充分的优点。仿真实验证实了该方法的有效性。     

一种码片内多径参数的最大似然估计算法

针对码分多址卫星移动通信中码片内两径参数估计问题,该文提出了基于最大似然的2维搜索算法。算法对两径时延进行2维搜索,同时对多径复振幅分别采用解相关和线性最小均方误差(LMMSE)算法进行估计,最后通过使似然函数最大化而找出最优的一组时延、复振幅估计值。仿真证明两径时延2维搜索结合采用近似的LMMSE算法进行多径复振幅估计具有良好的性能。     

叠加分数布朗运动的极大似然估计

本文提出了一种对叠加分数布朗运动两分量分别进行极大似然估计的算法．首先推导了重抽样情况下分数高斯噪声的小波系数方整公式,并讨论得知不同Ｈ值时方差随尺度变化存在两种截然不同的变化趋势。利用这一特点,可以对叠加的分数布朗运动的参数分别进行极大似然估计,仿真结果表明了该算法的有效性。     

基于FFT滑动平均极大似然法的正弦信号频率估计

该文基于正弦信号采样序列的FFT频谱,利用谱图上多条显著谱线与峰值谱线实部之间的关系,推导建立了一用于信号频率估计的滑动平均模型,基于此模型得出的极大似然频率估计器结合传统的Quinn方法后得到一种新的基于FFT谱滑动平均极大似然估计算法。仿真实验表明该算法精确有效,估计性能优于Rife,Quinn法,十分接近CRLB下限,计算量不大且信噪比门限要求可降至-9dB左右。     

Performance of Partial Response Digital Radio Systems in Linear and Nonlinear Bandlimited Channels

Lender's partial response baseband system model is analyzed, extended and compared with two other partial response models. The feasibility of each system model in practical implementation is assessed. The effects of filter imperfections and of channel nonlinearities on the performance of QPRS digital radio systems is analyzed by means of computer simulation.     

基于CORDIC算法的最大似然频差估计

针对频率偏移对低速散射通信中相干检测性能的影响,提出了基于CORDIC算法的最大似然频差估计;详细推导了最大似然频差估计的原理和CORDIC算法的基本原理;提出了具体的设计过程以及试验结果。     

利用多普勒信息的波达方向最大似然估计方法

为了充分利用信号的时域特性来改善信号波达方向（ＤＯＡ）的估计性能，本文从最大似然估计出发，推导出了有限快拍，低信噪比情况下多普勒信号波达方向的迭代估计计算法，为进一步减小运算量，本文还推导了一种简化算法，本文提出的两种算法对低信噪比，少快拍数下多普勒信号的ＤＯＡ估计性能比不利用时域特性的ＭＬ方法有明显改善，Ｍｏｎｔｅ－Ｃａｒｌｏ实验验证了本文方法的有效性。