基于多用户反馈的判决反馈均衡器的研究

本文提出的一种新颖的基于多用户反馈的判决反馈均衡器,解决了在CDMA多用户检测中传统自适应判决反馈均衡器误码率高、系统容量小的缺点.它由具有误差反馈滤波器的判决反馈均衡器(Decision Feedback Equalizer with Error Feedback Filter,DFE-EFF)构成,并在判决后反馈多用户数据抵消多址干扰(多用户反馈干扰抵消).文中给出其结构图,分析各种判决反馈均衡算法.理论证明,具有误差反馈滤波器的多用户反馈干扰抵消判决反馈均衡器(多用户反馈干扰抵消DFE-EFF)较各种判决反馈均衡器为最优,它能同时有效处理ISI,MAI和噪声的干扰.仿真结果表明,在误码率性能和系统容量两方面,多用户反馈干扰抵消DFE-EFF比DFE、DFE-EFF均有较大改善.     

改善判决反馈均衡器性能的一种新方法

判决反馈均衡器是一种算法复杂度较低、性能也较好、并在实际中得到广泛应用的均衡器。它的一个内在的缺陷是错误判决结果反馈所引起的性能损失。利用判决反馈均衡器中前向滤波器输出中的信息,提出了一种改善判决反馈均衡器性能的方法,并给出改进后判决反馈均衡器的结构和实现方法。仿真结果证明了该方法的有效性。     

数字微波自适应判决反馈均衡器

本文在分析判决反馈均衡器(DEF)和分数间隔均衡器(FSE)的基础上,提出了一种新型实用的判决反馈均衡器方案,设计出了实用的DFE硬件电路并给出了实验结果。     

数字电路倍增设备传真解调中自适应均衡器的设计与仿真

介绍了在DCME (数字电路倍增设备 )传真解调 /再调制模块中所采用的符号间隔判决反馈自适应均衡器的设计方法。在均衡器的设计中采用了最小均方准则的随机梯度算法 (LMS SG)。文中说明了系统模型的建立、算法仿真的过程 ,并给出了仿真结果。     

用于PMD补偿的判决反馈均衡器的结构研究

文章采用自适应均衡技术对偏振模色散(PMD)进行补偿,给出了判决反馈均衡器(DFE)结构,通过对前向均衡器(FFE)部分的改进,得到了适用于高速光纤通信系统的行波滤波器(TWF)及折叠级联的TWF结构,最后通过ADS仿真软件,得到了系统S参数仿真结果.     

基于多模算法的判决反馈均衡器

研究了基于MMA/GMMA(多模算法/通用多模算法)全数字QAM接收机中DFE(判决反馈均衡器)的设计.此均衡器首先工作于MMMGMMA模式,当均衡器输出的误差足够小时,切换到判决反馈模式.通过大量仿真可以看出,该均衡器能够达到较好的性能.     

一种T/4分数间隔预测判决反馈盲均衡算法

为了消除由深衰落信道引起的严重码间干扰,本文给出一种基于改进双模式多模算法的 T/4 分数间隔预测判决反馈均衡器.该均衡器采用改进的双模式多模算法独立优化前向、反馈滤波器,前向滤波器采用 T/4 分数间隔,反馈滤波器采用预测结构,仍为符号速率.在两种深衰落信道条件下仿真实验表明,本文给出的均衡器能够避免传统判决反馈均衡器的误收敛情况;同时其稳态均方误差小于基于常模算法的 T/4 分数间隔均衡器、基于常模算法的 T/4 分数间隔判决反馈均衡器,以及基于双模式多模算法的 T/4 分数间隔预测判决反馈均衡器,更适合处理 QAM 信号.     

10Gb/s光通信系统中EDC均衡器的性能研究

采用数值仿真的方法对几种使用在10Gb/s光通信系统中的电色散补偿(EDC)均衡器的性能进行了研究,包括判决反馈均衡器、线性均衡器、最大似然序列估计器(MLSE).仿真结果表明MLSE的性能最好,但由于它不易实现,可以采用判决反馈均衡器替代,这对实际系统的设计具有参考价值.     

基于稀疏多径信道的均衡技术分析

为了解决宽带通信稀疏多径信道下均衡器结构复杂和收敛速度慢的问题,介绍了稀疏多径信道和基于伪随机序列的多径搜索。针对稀疏多径信道的特点,对判决反馈均衡器进行改进,提出了一种基于正交匹配追踪信道估计的完全判决反馈均衡器。利用正交匹配追踪估计结果在前馈均衡器前消除已判决码元对当前判决码元的码间串扰,降低了均衡器的复杂度,提高了收敛速度。通过仿真分析表明完全判决反馈均衡器能取得良好的性能。     

MIMO通信系统中一种新的自适应均衡方法

该文提出了时变频率选择性衰落环境下多输入多输出(MIMO)通信系统中一种新的基于递归最小二乘(RLS)的自适应干扰对消的判决反馈均衡方法(RLS-IC-DFE)。该方法将每个数据子流上的自适应判决反馈均衡器等效为一个加长的新的均衡器,并把已解出的子流数据作为新的输入参数,应用RLS算法自适应调整新的均衡器参数。仿真结果表明,该文提出的自适应干扰对消的判决反馈均衡器可以自适应跟踪信道变化,同时比已有的判决反馈均衡器(RLS-DFE)能提供更好的误符号率(SER)性能。     

Adaptive Lattice Decision-Feedback Equalizers--Their Performance and Application to Time-Variant Multipath Channels

This paper presents two types of adaptive lattice decisionfeedback equalizers (DFE), the least squares (LS) lattice DFE and the gradient lattice DFE. Their performance has been investigated on both time-invariant and time-variant channels through computer simulations and compared to other kinds of equalizers. An analysis of the self-noise and tracking characteristics of the LS DFE and the DFE employing the Widrow-Hoff least mean square adaptive algorithm (LMS DFE) are also given. The analysis and simulation results show that the LS lattice DFE has the faster initial convergence rate, while the gradient lattice DFE is computationally more efficient. The main advantages of the lattice DFE's are their numerical stability, their computational efficiency, the flexibility to change their length, and their excellent capabilities for tracking rapidly time-variant channels.     

一种单载波频域均衡方案及性能仿真

参考IEEE802.16标准建议的单载波频域均衡的方法,提出了一种适合时变深衰落信道的单载波均衡方案。该方案采用了基于分集合并的判决反馈均衡结构,不但具有较好的抗符号间干扰能力,而且可以显著改善无线通信系统的抗衰落性能。对该方案的抗符号间干扰能力进行了软件仿真。     

Decision Feedback Equalization of Dispersive Radio Channels

The performance of adaptive decision feedback equalization applied to high bit rate digital radio systems in the presence of multipath propagation is analytically investigated. Minimum phase (MP) and nonminimum phase (NMP) type fades as well as the transition periods between these two states are considered. Insight is given into the IF recovered timing epoch and its consequences on the decision feedback equalizer (DFE) behavior, especially during transition periods. Required conditions on the DFE structure for ensuring its maximum efficiency are derived and a modified updating algorithm is presented. Finally, dynamic simulation results are reported and compared to theoretical results. They show that the proposed structure is capable of coping with most propagation conditions.     

面向云计算环境的动态公平性度量方法

针对云计算环境资源动态性特点,给出了一种资源分配算法公平性动态度量模型——DFE (dynamic fairness evaluation)。模型引入了公平、效率和时间参数,通过将资源分配结果进行量化处理,定量地描述不同分配算法的公平性。首先考虑了云环境下的2种典型动态因素：1）节点资源需求动态变化;2）虚拟节点动态变化,并分别对这2种场景建立子模型,通过这2种模型导出了公平性动态度量模型DFE。分析了2种子模型以及DFE,通过DFE对几种典型资源分配算法进行度量,验证了在资源需求以及虚拟节点动态变化的情况下,DFE能够有效度量分配算法公平性,为云计算平台资源分配算法的选择提供了重要的参考。     

Realizable linear and decision feedback equalizers: properties and connections

Recently, there has been renewed interest in the use of infinite impulse response (IIR) linear equalizers (LEs) for digital communication channels as a means for both improving performance and blindly initializing decision feedback structures (DFEs). Theoretical justification for such an approach is usually given assuming unconstrained filters, which are not causal and therefore not implementable in practice. We present an analysis of realizable (i.e., causal, stable, and of finite degree) minimum mean square error (MMSE) equalizers for single-input multiple-output channels, both in the LE and DFE cases, focusing on their structures and filter orders, as well as the connections between them. The DFE resulting from rearranging the MMSE LE within a decision feedback loop is given special attention. It is shown that although this DFE does not in general coincide with the MMSE DFE, it still enjoys certain optimality conditions. The main tools employed are the Wiener theory of minimum variance estimation and Kalman filtering theory, which show interesting properties of the MMSE equalizers not revealed by previous polynomial approaches.     

A study of analog decision feedback equalization for ADC-Based serial link receivers

High-speed serial link receivers based on analog-to-digital converters (ADCs) provide better programmability with different channel characteristics and the possibility of employing powerful signal equalization techniques in the digital domain. However, complexity and power consumption are still major issues in adopting such receivers in high-speed applications when compared to traditional binary or mixed-signal approaches. Embedded decision feedback equalization (DFE) before ADC quantization can relax the design requirements of both the ADC and post-ADC digital processing. This paper studies the impact of embedded analog DFE on voltage margin improvement of an ADC-based receiver through worst-case analysis. An analytical expression for the link bit-error-rate (BER) with analog DFE is derived and validated through simulations. An empirical study is conducted that evaluates the achievable BER of embedded analog DFE as a function of the channel inter-symbol interference (ISI) and ADC resolution. A channel-dependent parameter is introduced and employed to quantify the BER improvement achieved by embedding analog DFE in a receiver. A prototype receiver with embedded DFE is designed and laid out in a 130 nm CMOS process and achieves 4.64-bits peak ENOB and 4.08 pJ/conv.-step FOM at a 1.6-GS/s sampling rate. The BER performance of the receiver over high-loss FR4 channels at 1.6 Gb/s is evaluated and used to validate the simulation results.     

Parallel adaptive decision feedback equalizers

Several algorithms for parallel implementation of adaptive decision feedback equalizers (DFEs) are proposed. The first is a double-row DFE algorithm that outperforms previous approaches. Under the no-error-propagation assumption, the algorithm will perform exactly like a serially adapting DFE. The multiplication complexity of the double-row DFE algorithm is of the same order as that of the parallel DFE algorithm and the extended least-mean-square (LMS) method. The previous algorithms and the double-row DFE algorithm may become impractical to implement due to their large computational complexity, so three additional parallel implementations of the DFE, which lead to considerable hardware savings and avoid the coding loss of the former approaches, are presented. The different algorithms are compared on the basis of convergence analysis and simulation results     

Square root Kalman filtering for high-speed data received over fading dispersive HF channels

This paper shows how to apply square root Kalman filtering to high speed data transmission on fading dispersive high-frequency (HF) channels. High data-rate HF transmission can be achieved by use of a single carrier bandwidth efficiency modulation that is demodulated with decision-feedback equalization (DFE). The DFE coefficients are updated adaptively by square root Kalman algorithms. Theoretical formulation and mechanization procedures for the square root Kalman algorithms are given. Computer simulation indicates that good error-rate performance can be achieved with these algorithms for rapid fading HF radio channels.     

Decision Feedback Equalization for Multipath Induced Interference in Digital Microwave LOS Links

The performance of a 49-QPRS, 90 Mbit/s digital radio receiver equipped with a decision feedback equalizer (DFE) to counter multipath fading is investigated via computer simulation. The simulation includes the transmitted data, multipath fade model, receiver model, and DFE. The results indicate that a DFE equipped with five forward and five feedback taps can adequately compensate a 40 dB minimum-phase fade anywhere in the receiver passband. The study is extended to other receiver configurations including the use of space diversity and/or slope equalizers and the use of a transversal equalizer (TE) with the same delay-span in place of the DFE. The results indicate that the DFE equipped receiver outperforms the TE receiver and that still better performance may be achieved using a combination of space diversity and DFE.     

Minimum mean-squared error decision-feedback equalization fordigital subscriber line transmission with possibly correlated line codes

The author presents a theory on MMSE (minimum mean-squared error) decision-feedback equalization which augments previously published results by allowing both a correlated symbol sequence and a fractionally spaced DFE (decision-feedback equalizer) forward filter. This theory facilitates calculating the potential DSL (digital subscriber line) transmission performance in cases of correlated line codes, especially for situations where one or both of the DFE filters are infinite in length. The situation of an infinite-length DFE is of interest because it provides information on the limit of MMSE equalization and can thus serve as a benchmark against which the performance of a finite-length DFE may be compared. The author also presents a few numerical examples of the performance of MMSE decision-feedback equalization in DSL transmission at ISDN (integrated services digital network) basic access rates with several well-known line codes