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.     

基于最大似然频率精细估计的载波捕获算法

深空通信中,星上对载波的主动捕获主要利用频率估计的方法。在实际载波捕获电路中,精确的频率估计值导入锁相环,使得锁相环捕获带余量充足。在锁相环带宽一定的情况下,估计精度的提高可以减少FFT实现点数。在FFT频率粗估计的基础上,通过频率精细估计算法可提高估计精度。为获得估计精度更高的频率精细估计算法,利用最大似然泛函不变性推导了频率精细估计的最大似然算法。载噪比在5 dB时,估计精度可以提高到FFT分辨率的10-4。仿真结果表明,该算法估计性能优于其他频率精细估计算法。     

MIMO-OFDM系统信道最大似然估计研究

在深入分析MIMO-OFDM系统信道模型的基础上,提出了一种新的导频符号设计方案和采用最大似然比估计算法估计MIMO-OFDM信道,并分析了该算法的性能;计算机仿真结果表明在信道统计特性未知的条件下,采用所提出的导频符号设计方案效率高,估计性能优于RRE和LE等其他方法.     

引入蝙蝠算法的最大似然DOA估计

DOA估计理论的传统算法中,最大似然DOA估计方法能准确地估计出目标方向角度,性能优良,并且具有很好的稳定性。与MUSIC及其他的子空间分解类算法相比,在信噪比较低、小快拍信号时,最大似然DOA估计算法优势更为突出。但是由于其自身算法复杂度较高的缺陷而碍于工程上的应用。针对这一问题,将蝙蝠算法与最大似然算法相结合,应用于信号的DOA估计,利用蝙蝠搜索算法搜索路径优、寻优能力强的优点,快速搜索到似然函数的全局最优值,优化多维非线性的估计谱函数。仿真结果表明,蝙蝠搜索算法有效地克服最大似然DOA估计中存在的运算量大,计算复杂度高等问题,通过与其他经典的仿生智能优化算法相比较,该方法体现出更好的收敛性。     

基于最大似然准则的超宽带分簇信道估计

在室内通信环境中,超宽带信号具有多径成簇到达的特性。利用此特性,文中提出了两种基于最大似然准则的分簇信道估计算法,仿真结果表明,与传统的最大似然信道估计算法相比,丈中的两种算法大大降低了系统的复杂度和误码率。     

空时网格码的联合迭代最大似然估计和译码

该文提出了一种适合空时网格码的联合迭代最大似然估计和译码的方法,利用较少的导频,能够获得比传统非迭代最大似然译码更好的系统性能,仿真结果显示经过4次迭代,其性能与接收机已知理想信道信息下的最大似然译码比较只有不到1dB的损失,最后根据仿真结果给出一个导频数目和迭代次数的合理选择。     

基于最大似然估计的16APSK载波捕获算法研究

针对在低信噪比情况下16APSK信号频偏捕获困难的问题,讨论了一种结合Kalman滤波和最大似然估计的非数据辅助频偏估计算法。该算法对包含载波频偏信息的相位序列进行最大似然频偏估计,通过Kalman滤波,降低了噪声对估计精度的影响。对结合Kalman滤波和最大似然估计的16APSK频偏估计算法进行了仿真。仿真结果表明,在低信噪比条件下,结合Kalman滤波的最大似然频偏估计算法可获得良好的性能。     

MSK信号的最大似然检测

最小频移键控(Minimum Shift Keying,MSK)是一种连续相位的频移键控。MSK信号包络恒定,相干检测时的误码率性能比一般的频移键控要好。MSK在引入倾斜相位的概念后,其相位格图类似于卷积码的时不变网格图,因此能用Viterbi算法实现最优解调。理论分析和数值模拟表明,在相位与时间严格同步的条件下,MSK基于Viterbi算法的最大似然检测法性能更好,是最优的解调方法。这里仅考虑在加性高斯白噪声信道下信号传输的相干检测。     

带判决反馈的盲最大似然序列估计

本文提出了一种新型的带有判决反馈的减小状态最大似然序列估计ＲＳＳＤＦＰＳＰ,新算法带有两个信道估值器并且可以工作在盲环境下．使用最大似然序列估计（ＭＬＳＥ）来处理信道冲激响应的前导干扰及主径,反馈滤波器处理后尾干扰,并且用ＰｅｒＳｕｒｖｉｖｉｎｇＰｒｏｃｅｓｉｎｇ（ＰＳＰ）算法来得到ＭＬＳＥ部分的信道冲激响应,信道估值器２得到后尾干扰．计算机模拟表明,这种ＲＳＳＤＦＰＳＰ方案在减小ＭＬＳＥ的计算复杂度的同时能最大限度地得到ＭＬＳＥ的性能,是ＭＬＳＥ在计算复杂度与性能之间的较好折中．     

基于最大似然估计的高动态GPS载波跟踪环

 基于最大似然估计提出了一种全新设计的GPS载波跟踪环结构,并将该环路应用于高动态、低信噪比条件下的GPS载波频率跟踪. 文中给出了环路的设计细节,并详细讨论了环路中各模块的功能及模块之间的参数传递. 利用具有典型高动态参数的GPS载波信号对环路的跟踪性能进行了测试. 测试结果表明,与普通GPS接收机的载波跟踪环相比,该环路对高动态环境下的失锁门限和门限附近的频率跟踪精度均有显著改善.     

Joint data and channel estimation for TDMA mobile channels

One of the main problems in time-division multiple-access (TDMA) digital mobile communications is the poor performance of the receiver for fast-fading channels. We propose to use a novel joint data and channel estimation (JDCE) technique to improve performance. The basic idea of this method originates from the so-called generalized likelihood ratio (GLR) test of classical detection theory. The technique was combined with the well-known Viterbi algorithm and applied to blind equalization by Seshadri [1]. In this paper, we introduce this technique to TDMA mobile communications. We find that the problems of delayed channel updating and divergence caused by error decision feedback in conventional maximum likelihood sequence estimation with decision delay (MLSE/DD) can be completely solved. An improvement of 4.5 dB can be obtained compared with the MLSE/DD method when it is applied to the Northern American Digital Cellular (NADC) system. The specified IS-54 requirement of 19 dB signal-to-noise ratio (SNR) at a bit error rate (BER) of 3% and a vehicle speed of 100 km/h can be met with a remarkable margin of 8 dB. When the intersymbol interference (ISI) of a channel is not severe, the required computation is moderate. For example, in the NADC system, the computational burden of the JDCE method is twice that of the MLSE/DD method if the least-mean-squares (LMS) algorithm is used for channel tracking.This work was presented in part in the Third International Symposium on Personal, Indoor and Mobile Radio Communications, Boston, MA, October 1992.     

Parallel structures for joint channel estimation and data detectionover fading channels

Joint data and channel estimation for mobile communication receivers can be realized by employing a Viterbi detector along with channel estimators which estimate the channel impulse response. The behavior of the channel estimator has a strong impact on the overall error rate performance of the receiver. Kalman filtering is an optimum channel estimation technique which can lead to significant improvement in the receiver bit error rate (BER) performance. However, a Kalman filter is a complex algorithm and is sensitive to roundoff errors. Square-root implementation methods are required for robustness against numerical errors. Real-time computation of the Kalman estimator in a mobile communication receiver calls for parallel and pipelined structures to take advantage of the inherent parallelism in the algorithm. In this paper different implementation methods are considered for measurement update and time update equations of the Kalman filter. The unit-lower-triangular-diagonal (LD) correction algorithm is used for the time update equations, and systolic array structures are proposed for its implementation. For the overall implementation of joint data and channel estimation, parallel structures are proposed to perform both the Viterbi algorithm and channel estimation. Simulation results show the numerical stability of different implementation techniques and the number of bits required in the digital computations with different estimators     

平坦慢衰落信道下基于HOS的PSK调制盲信道估计

提出一种基于符号高阶统计量（HOS, high-order statistics）的MPSK调制信道衰落系数盲估计算法。针对平坦慢衰落信道模型,首先分析了MPSK调制符号高阶统计量特征,证明了MPSK调制符号的M次方符号的值是唯一的,而当1≤M′相似文献   

OFDM channel estimation with dispersive fading channels

In this paper, we studied the channel estimation problem for the orthogonal frequency division multiplexing (OFDM) system when the statistics of the multi-path fading channel is not known or partial known. A channel estimation approach based on polynomial approximation of the channel response is proposed. The pilot symbols are periodically inserted the channel responses for entire OFDM data sequence for exploiting channel correlation in both time and frequency domain, which is obtained from a time-variant frequency-selective Rayleigh fading channel model. Simulation shows that the method is robust to different channel statistics. Moreover, a window dimension adaptation algorithm is proposed to adapt the channel estimator to the channel statistics which further improves the robustness of the system.     

Joint channel estimation and data demodulation algorithms for fast time varying band-limited frequency selective Rayleigh fading channels : a comparison study

In this paper, a comparison study is proposed between two recent algorithms which both perform joint channel and data estimation. The first one is the well known psp : per survivor processing algorithm and the second is called adaptive bloc sequence estimation (bse). Compared to the existing literature, we add, for our comparison study, the case of trellis coded transmissions combined with interleaving and deinterleaving techniques which are now currently employed for digital communications.     

Pilot-symbol aided channel estimation for OFDM with fast fading channels

In this paper, we address the problem of estimating a rapidly-varying channel in orthogonal frequency division multiplexing (OFDM) systems. To handle rapid variation within a transmission block, we propose a novel pilot-based estimation scheme which uses channel interpolation. In addition, we develop a simple Doppler frequency estimation scheme. We show that the proposed scheme has better performance in the high-Doppler frequency by simulations.     

Random coding error exponents for flat fading channels withrealistic channel estimation

There has been a considerable interest in determining the limits to communications over multipath fading channels. However, most studies have assumed that the channel is perfectly known at the receiver. In this paper, the random coding error exponent for flat fading channels with realistic channel state information (CSI) is studied. It is assumed that the CSI is obtained via some practical technique which utilizes a linear estimation scheme. Two commonly used techniques for channel estimation are considered in this paper, namely pilot tone extraction and pilot symbol transmission. The degradation in the achievable performance due to partial CSI is assessed and comparison of the different channel estimation methods is made. The focus of this paper is on the Jake's mobile Rayleigh flat fading model. Although Jake's model does not have a Markov property, such as that found in the commonly used exponential correlation model, which is usually attractive from the mathematical tractability point of view, Jake's model has a physical basis. Also, this model is considered herein from the standpoint of the random coding exponent. The results in this paper shed light on the amount of degradation in the achievable performance that is expected when the receiver has partial CSI. Finally, the sensitivity of the loss in achievable performance for the various channel estimation techniques with respect to channel parameters, such as Doppler spread and signal-to-noise ratio (SNR), is studied     

Joint iterative channel estimation and decoding in flat correlatedRayleigh fading

This paper addresses the design and performance evaluation with respect to capacity of M-PSK turbo-coded systems operating in frequency-flat time-selective Rayleigh fading. The receiver jointly performs channel estimation and turbo decoding, allowing the two processes to benefit from each other. To this end, we introduce a suitable Markov model with a finite number of states, designed to approximate both the values and the statistical properties of the correlated flat fading channel phase, which poses a more severe challenge to PSK transmission than amplitude hiding. Then, the forward-backward algorithm determines both the maximum a posteriori probability (MAP) value for each symbol in the data sequence and the MAP channel phase in each iteration. Simulations show good performance in standard correlated Rayleigh fading channels. A sequence of progressively tighter upper bounds to the capacity of a simplified Markov-phase channel is derived, and performance of a turbo code with joint iterative channel estimation and decoding is demonstrated to approach these capacity bounds     

CHANNEL ESTIMATION OF MULTI-RATE DS-CDMA SIGNALS IN SLOW FADING MULTIPATH CHANNELS

In Direct-Sequence Code Division Multiple Access(DS-CDMA) mobile communication systems, it is very important to obtain accurate estimation of the channel parameters,especially that of the propagation delay. But the near-far problem may make the estimation complicated and can degrade the estimation performance significantly. In this paper, an efficient Maximum Likelihood (ML) method is presented for channel parameter estimation of multi-rate DS-CDMA systems in slow fading multipath channels in a near-far scenario. The algorithm extended the ML approach to multi-rate DS-CDMA systems, and proposes decomposing a multidimensional optimization problem into a series of one-dimensional optimization and has improved computational efficiency. Theoretical analysis and numerical examples show that the estimator proposed is effective and near-far resistant.     

快衰落信道下OFDM系统的信道估计简化算法

在快衰落时变信道中，正交频分复用（OFDM：Orthogonal Frequency Division Multiplexing）系统子载波间的正交性会遭到破坏，由此引起的载波间干扰（ici：Inter-Carrier Interferellce）会对系统性能带来很大的影响。本文提出了一种利用时域线性模型的信道估计算法，利用随时间线性变化的模型描述信道。仿真结果表明，本算法能够有效地消除载波间干扰，降低系统的BER。与类似算法相比，当系统的BER性能相同时，算法复杂度大大的降低。