Bayesian blind turbo receiver for coded OFDM systems with frequencyoffset and frequency-selective fading

The design of a blind receiver for coded orthogonal frequency-division multiplexing communication systems in the presence of frequency offset and frequency-selective fading is investigated. The proposed blind receiver iterates between a Bayesian demodulation stage and a maximum a posteriori channel decoding stage. The extrinsic a posteriori probabilities of data symbols are iteratively exchanged between these two stages to achieve successively improved performance. The Bayesian demodulator computes the a posteriori data symbol probabilities, based on the received signals (without knowing or explicitly estimating the frequency offset and the fading channel states), by using Markov chain Monte Carlo (MCMC) techniques. In particular, two MCMC methods-the Metropolis-Hastings algorithm and the Gibbs sampler-are studied for this purpose. Computer simulation results show that the proposed Bayesian blind turbo receiver can achieve good performance and is robust against modeling mismatch     

一种基于混合MCMC的时域波达方向估计算法

基于马尔科夫链蒙特卡洛（Markov Chain Monte Carlo,MCMC）方法的时域波达方向估计算法通过构造马尔科夫链的方式来对波达方向进行估计,但是现有的算法在马尔科夫链的收敛速度和结果上并没有表现出很好的鲁棒性。为了优化算法的性能,采用多(短)链并行的方式代替原来的长链生成方式,提高了算法收敛的稳定性;并对特定模型下的构造过程进行分析,优化了状态空间,提高了算法的搜索效率;同时结合多混合的MCMC方法,进一步提高了算法估计的精确度和收敛速度。仿真结果表明,改进后的算法对波达方向估计的准确性和实时性都有很大提升。     

基于LDPC编码的MIM0系统迭代接收机研究

研究了基于LDPC编码无线MIMO通信系统中的软输出最小均方误差干扰抵消迭代(MMSE PIC)检测算法.针对初次迭代检测时PIC输出的后验比特对数似然比(LLR)不可靠的问题,利用MMSE滤波器输出的高斯近似表示,给出了基于后验概率估计的迭代干扰抵消检测算法,以提高检测器输出的编码比特对数似然比的可靠性.仿真结果表明...     

一种基于16QAM调制系统的LDPC改进算法

对QAM调制系统进行分析,提出了一种简化状态软输入软输出APP算法。它基于LDPC和积算法思想,与其他简化状态SISO算法相比,具有更为一般的形式。该算法在解调输出时有效利用映射点之间的欧氏距离,计算出每一个编码比特的似然值,从而简化运算复杂度,并且利用判决反馈减小简化状态网格的Euclid距离损失。仿真表明,该方案能够有效利用QAM解调中的软输出,在高斯信道下,简化的译码算法比原有LDPC方案提高了0.25 dB增益。     

Bayesian Monte Carlo multiuser receiver for space-time codedmulticarrier CDMA systems

We consider the design of optimal multiuser receivers for space-time block coded (STBC) multicarrier code-division multiple-access (MC-CDMA) systems in unknown frequency-selective fading channels. Under a Bayesian framework, the proposed multiuser receiver is based on the Gibbs sampler, a Markov chain Monte Carlo (MCMC) method for numerically computing the marginal a posteriori probabilities of different users' data symbols. By exploiting the orthogonality property of the STBC and the multicarrier modulation, the computational complexity of the receiver is significantly reduced. Furthermore, being a soft-input soft-output algorithm, the Bayesian Monte Carlo multiuser detector is capable of exchanging the so-called extrinsic information with the maximum a posteriori (MAP) outer channel code decoders of all users, and successively improving the overall receiver performance. Several practical issues, such as testing the convergence of the Gibbs sampler in fading channel applications, resolving the phase ambiguity as well as the antenna ambiguity, and adapting the proposed receiver to multirate MC-CDMA systems, are also discussed. Finally, the performance of the Bayesian Monte Carlo multiuser receiver is demonstrated through computer simulations     

Perfect sampling for the wavelet reconstruction of signals

The coupling from the past (CFTP) procedure is a protocol for finite-state Markov chain Monte Carlo (MCMC) methods whereby the algorithm itself can determine the necessary runtime to convergence. In this paper, we demonstrate how this protocol can be applied to the problem of signal reconstruction using Bayesian wavelet analysis where the dimensionality of the wavelet basis set is unknown, and the observations are distorted by Gaussian white noise of unknown variance. MCMC simulation is used to account for model uncertainty by drawing samples of wavelet bases for approximating integrals (or summations) on the model space that are either too complex or too computationally demanding to perform analytically. We extend the CFTP protocol by making use of the central limit theorem to show how the algorithm can also monitor its own approximation error induced by MCMC. In this way, we can assess the number of MCMC samples needed to approximate the integral to within a user specified tolerance level. Hence, the method automatically ensures convergence and determines the necessary number of iterations needed to meet the error criteria     

基于阵列单通道的机动目标DOA跟踪方法

针对现有利用阵列单通道系统对机动目标跟踪精度不高,实时性差等不足,提出了一种新的基于改进粒子滤波算法的阵列单通道机动目标波达方向(direction of arrival, DOA)跟踪方法。该方法首先在利用接收机轮流采样建立数学模型的基础上,建立跟踪模型。然后,利用粒子群优化算法对马尔科夫链蒙特卡罗(Markov Chain Monte Carlo, MCMC)粒子滤波算法的重采样环节进行优化处理,给出了一种交互MCMC粒子滤波算法,该算法克服了传统粒子滤波算法粒子退化及样本贫化的固有缺陷。最后利用该算法求解跟踪方程,实现了实时DOA估计。理论分析与仿真结果表明,本文方法可实现基于阵列单通道的DOA跟踪与波束形成一体化,且能够处理相干信号,与标准粒子滤波和子空间类算法相比,收敛速度快,跟踪精度高。      

Modification of the MAP algorithm for memory savings

It is usually assumed that all state metric values are necessary in the maximum a posteriori (MAP) algorithm in order to compute the a posteriori probability (APP) values. This work extends the mathematical derivation of the original MAP algorithm and shows that the log likelihood values can be computed using only partial state metric values. By processing N stages in a trellis concurrently, the proposed algorithm results in savings in the required memory size and leads to a power efficient implementation of the MAP algorithm in channel decoding. The computational complexity analysis for the proposed algorithm is presented. Especially for the N=2 case, we show that the proposed algorithm halves the memory requirement without increasing the computational complexity.     

Distributed localization using mobile beacons in wireless sensor networks

A new distributed node localization algorithm named mobile beacons-improved particle filter (MB-IPF) was proposed. In the algorithm, the mobile nodes equipped with globe position system (GPS) move around in the wireless sensor network (WSN) field based on the Gauss-Markov mobility model, and periodically broadcast the beacon messages. Each unknown node estimates its location in a fully distributed mode based on the received mobile beacons. The localization algorithm is based on the IPF and several refinements, including the proposed weighted centroid algorithm, the residual resampling algorithm, and the markov chain monte carlo (MCMC) method etc., which were also introduced for performance improvement. The simulation results show that our proposed algorithm is efficient for most applications.     

双向中继信道中物理层网络编码的检测

对双向中继信道中物理层网络编码的检测进行了研究,最大似然检测性能好但是实现复杂度高。因此,在信源节点未知信道状态信息情况下,提出了2种检测方案:基于似然比函数的似然比检测和基于最大后验概率准则的最大后验概率检测。同时,针对信源节点已知信道状态信息的特殊情形,进行了同样的推导。分析和仿真结果表明,相比于分别检测出2个信源信息的最大似然检测,似然比检测的BER性能更优,但似然比检测需要知道额外的噪声方差信息,最大后验概率检测与最大似然检测等价,而且最大后验概率检测在实现复杂度上相对较低。     

混沌粒子群优化粒子滤波算法

针对基于粒子群优化算法的粒子滤波计算复杂度大,并且容易陷入局部最优,提出了一种新的基于混沌的粒子群优化粒子滤波算法。该算法在粒子群优化的基础上,引入混沌序列,利用混沌运动的遍历性、随机性等特点改善了初始样本的质量,同时利用混沌扰动避免搜索过程陷入局部最优,使算法具有更快的收敛速度和更好的全局搜索能力。最后利用UNGM模型将该算法与标准粒子滤波和粒子群粒子滤波进行仿真对比,并利用纯角度目标跟踪模型验证了算法的有效性。实验结果表明,该算法改善了粒子群优化算法的粒子滤波易陷入局部最优的现象,提高了粒子滤波的精度和速度,具有较高的应用价值。     

Modified higher order spectral analysis based TDE algorithm for CFAR signal detection problem

With the conditions of small data size and low Signal-to-Noise Ratio (SNR), the application of Higher Order Statistics (HOS) is restrained not only by its high estimation variance, but also by its low estimation precision. Therefore, a modified HOS based Time Delay Estimation (TDE) algorithm is proposed to overcome these problems. Comparing with the conventional TDE algorithms, the estimation variance is improved greatly. A typical simulation example is completed in order to test the performance of the algorithm proposed, which shows that the proposed algorithm has advantages over the traditional ones in both detection performance and computation efficiency.     

HMM-WC-FNM模型在触头表面形貌去噪中的应用

本文提出了一种可靠的图像去噪算法,基于观察图像是期望图像叠加了不规则噪声的假设,用有限高斯混合分布(FNM)描述期望图像分解小波系数(WC)的先验分布,用隐马尔可夫模型(HMM)描述同一方向不同分解级之间的小波系数的依赖关系,采用Bayes准则,根据期望图像的后验分布(以观测图像为条件)所对应的HMM模型的条件概率,用EM(expectation maximization)优化算法,获得MAP(maximization a posteriori)准则下的去噪图像。针对银基触头材料表面形貌去噪对几种算法作定性比较,并对去噪性能给出定量分析,仿真结果表明,此方法有效去除噪声的同时,能保留原始图像的细节信息。     

一种水声通信中的多阵元Turbo均衡算法

Turbo均衡应用在水声通信中的问题主要在于水声信道时间扩展长,多接收阵元处理复杂度较高。该文研究了将时间反转与马尔可夫链蒙特卡罗(MCMC)均衡联合优化算法用于实现Turbo均衡。首先进行时间反转实现多接收阵元较长多径时延的压缩,再利用白化滤波器解决时间反转造成的噪声模型失配问题,最后利用复杂度较低的MCMC均衡器结合软迭代信道估计对时间反转合并后得到的信号进行均衡。结合真实实验信道条件对信道响应估计的误差建立模型,通过仿真比较得出, 该算法在相同条件下相对于多阵元直接自适应Turbo均衡算法复杂度降低67%,且有1.6 dB的误码率性能增益。通过对湖上试验数据进行处理,进一步验证了该算法的优势。     

基于奇异值分解的MIMO-OFDM系统角域MAP信道估计算法

最大后验概率信道估计算法应用于多输入多输出-正交频分复用(MIMOOFDM)系统时需要大规模的矩阵求逆和乘积运算,且系统数据传输效率随发送天线数的增加明显降低.为克服这些问题,提出了一种基于奇异值分解的角域最大后验概率信道估计算法.该算法通过期望最大化把(MIMO)信道估计问题简化为一系列独立的单输入单输出(SISO)问题,并使用奇异值分解避免了大规模矩阵求逆和乘积运算;通过多个OFDM符号联合估计信道提高了系统数据传输效率及算法的估计性能.仿真实验验证了此算法的有效性.     

并行MCMC算法的SAR影像分割

MCMC(Markov Chain Monte Carlo, MCMC)方法采用顺序改变表征像素类属性的标号变量值会导致算法运算时间长、收敛速度慢等问题。为此,本文提出并行化改变像素标号值的MCMC方案,在贝叶斯推理框架下,依据高斯分布及MRF(Markov Random Field, MRF)模型建立SAR(Synthetic Aperture Radar, SAR)影像分割模型,设计实现基于多线程的并行采样方案;为了解决MRF标号场中邻域像素标号相关性问题,提出独立的像素并行采样的准则;同时,限制并行线程的数量,以保证采样的随机性。运用传统的串行算法和提出的并行算法对模拟和真实SAR影像进行影像分割实验;定性和定量的时间和精度评价结果表明:该方案在不影响分割精度的前提下大幅缩短影像分割时间,提高了效率。      

Implementation of a Markov Chain Monte Carlo Based Multiuser/MIMO Detector

Multiuser/multiple-input–multiple-output detectors that use Markov chain Monte Carlo (MCMC) simulation techniques to obtain likelihood of information bits have been developed recently. In this paper, we explore the implementation details of one such detector and present an efficient hardware architecture of it. The first step in development of this architecture is to derive a log-domain version of the Gibbs sampler, an efficient method of obtaining samples of MCMC simulator. This formulation is numerically stable and can operate with low precision. The log- domain formulation also lends itself to a hardware architecture that involves only addition, subtraction, and compare operations. Moreover, pipelining is introduced in the proposed architecture straightforwardly. We also explore the word-length requirement of the developed architecture through computer simulations.      

Parallel sequence fault simulation for synchronous sequential circuits

A novel parallel sequence fault simulation (PSF) algorithm for synchronous sequential circuits is presented. The algorithm successfully extend the parallel pattern method for combinational circuits to sequential circuits by proposing a multiple-pass mechanism to overcome the state dependency in sequential circuits. The fault simulation is performed in parallel by partitioning the entire sequence into subsequences of equal length. Furthermore, techniques are developed to minimize the number of simulation passes. Notably, two compact counters, C _x and C _d , are proposed to faciliate the early stabilization detection of faulty circuit simulation with minimum space overhead. The experimental results on the benchmark circuits show that the speedup ratio over a serial sequence fault simulator based on ROOFS is 9.16 on average for pseudo random vectors. The parallel sequence algorithm of PSF is especially adaptable to parallel and distributed simulation which exploits sequence partition.     

一种无线传感器网络中目标跟踪的自适应节点调度算法

在无线传感器网络目标跟踪的过程中进行节点调度,可以综合考虑跟踪误差和能量消耗,延长传感器网络的使用寿命。为了综合考虑节点调度的短期和长远损失,该文将问题建模为部分可观测马尔科夫决策过程(POMDP)以得到更优的调度策略,并提出一种近似求解算法C-QMDP。该算法利用马尔科夫链蒙特卡洛方法(MCMC)推导连续状态空间的置信状态的转移,并计算瞬时代价。使用状态离散化方法,基于马尔科夫决策过程(MDP)值迭代求解未来代价的近似值。仿真结果表明,相比现有POMDP近似算法,该文算法既可以降低跟踪过程中的累积损失,又可以将大量运算进行离线计算,减小了在线决策时的计算量。     

Comparative analysis of maximum power point tracking controller for wind energy system

This paper proposes an adaptive maximum power point tracking (MPPT) control method to achieve the maximum power from the wind turbine (WT) power generation system. The MPPT control method has a vital role to find the maximum power point, and also compute the simulation results in both analysis such as offline using MATLAB/SIMULINK? and online using OPAL-RT simulator. The proposed adaptive perturb and observe (P&;O) algorithm provides better results using the OPAL-RT simulator compared to the P&;O method using MATLAB/SIMULINK?. The power generation through doubly fed induction generator (DFIG) WT system is becoming important day by day throughout the world. The simulation result by OPAL-RT simulator showed that the efficiency of WT-DFIG has been enhanced.