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。     

TH-UWB系统中ML信道估计算法研究

跳时超宽带无线通信系统中信道估计的准确度对系统接收性能具有重要影响,首先对超宽带系统收发模型进行介绍,然后对TH-UWB系统中基于训练序列的非结构化最大似然信道估计算法进行分析,最后在超宽带信道模型下对估计算法性能进行仿真.仿真结果表明基于训练序列的非结构化最大似然信道估计算法能够有效估计出信道参数.     

Soft-Output MMSE V-BLAST Detector under ML Channel Estimation and Channel Correlation

Channel estimation errors have not been taken into account by existing soft-output minimum mean square error (MMSE) vertical Bell Lab Space Time (V-BLAST) detectors. As a result, the system performance will be degraded under practical channel estimation. In this letter, we propose a novel soft-output MMSE V-BLAST detector, which takes the estimation error of maximum likelihood (ML) multiple-input multiple-output (MIMO) channel estimation and receiver spatially correlation into account in the computation of the MMSE filter and loglikelihood ratio (LLR) of each coded bit. When compared with existing MMSE V-BLAST detectors, simulation results show that the proposed novel detector can obtain sizable performance gain.     

Cramer-Rao Lower Bounds for Semi-Blind ML Channel Estimation in UWB Systems

This paper derives a unified representation of the Cramer-Rao lower bounds (CRLBs) for semi-blind maximum-likelihood (ML) channel estimation in time-hopping (TH) ultra-wideband systems with pulse amplitude and position modulation, pulse amplitude modulation and pulse position modulation (PPM). These bounds subsume the existing results for both pilot-based and blind ML channel estimation in TH-PPM as special cases. A numerical example is used to illustrate the effects of different data modulation formats and system parameters on the CRLBs derived     

基于随机编码变换压缩感知超宽带信道估计

提出了一种产生简便的基于随机编码变换的压缩感知的超宽带信道估计方法,给出了基于压缩感知方法的UWB信道估计模型,研究了子空间追踪的压缩感知UWB系统的信道估计方法。对系统在IEEE 802.15.3a CM1信道下的信道响应进行了估计,仿真结果表明该方法是有效的。     

Improved ML Channel Estimation for Uplink MC-CDMA Systems in Closely Spaced Multipath Channels

In order to attain near-single user performance in uplink multicarrier code- division multiple-access (MC-CDMA) systems, multiuser detection (MUD) methods may be employed which rely on simultaneous estimation of the channel frequency responses of multiple users. Pilot symbol assisted (PSA) channel estimation is needed in fast fading channels and it can be performed either by applying maximum likelihood (ML) criterion or minimum mean-squared error (MMSE) criterion. The performance of ML estimation technique degrades significantly in the case of fractionally spaced (FS) multipath channels where dominant paths are closely spaced with respect to the time resolution of the system. In such situation, the number of effective paths (which contribute more towards signal power) becomes considerably less than the actual number of multipaths at low and moderate SNR values. We propose an improved ML estimation method which considers only effective paths during the estimation process. The proposed method performs nearly identical to the MMSE estimation method and it can also provide significant reduction in the computational complexity when a large number of users are accommodated in the system.     

基于正交训练序列的MIMO系统联合最大似然时频同步和信道估计

该文推导了多输入多输出(MIMO)系统中的符号定时、频偏和信道参数的联合最大似然(ML)估计。针对联合ML估计没有闭合的表达式、数值计算复杂度高的问题,该文提出了一种基于重复结构的正交训练序列的简化估计算法。该估计算法形式简单、复杂度低,且仍为最大似然估计。最后仿真分析了最大似然参数估计的均方误差与接收信噪比和天线数目的关系,并与Cramer-Rao界作了比较,表明了该算法的有效性。     

Rapid Hybrid Acquisition of Ultra-Wideband Signals

Impulsive ultra-wideband (UWB) radio provides many promising features for wireless communications in a dense multipath environment. However, these features are largely the result of the enormous effective processing gain, which can make acquisition difficult at the receiver. In this paper, a recently developed theory of minimum complexity sequential detection is applied to the hybrid acquisition problem. As in previous hybrid schemes, a number of potential timing phases are checked as a group; however, a phase is disregarded as soon as it appears unlikely rather than waiting for a “winner” to be chosen from the group. Another phase then replaces the disregarded one. Analysis and simulation results indicate that the proposed scheme can improve average acquisition times for highly spread systems operating over either additive white Gaussian noise (AWGN) or multipath fading channels. This paper is based in part upon work supported by the Army Research Office under Contract DAAD10-01-1-0477 and employed equipment obtained under National Science Foundation Grant EIA-0080119.     

Efficient Recursive IDFT Scheme for Complex-valued Signals in Tap-selective Maximum-likelihood Channel Estimation

This paper presents several efficient, recursive inverse discrete Fourier transform (IDFT) schemes for complex-valued input data in tap-selective maximum-likelihood channel estimation; the results of their implementation are also presented. The proposed schemes employ only real-valued arithmetic, which reduces the number of required real multiplication operations in comparison with conventional IDFT approaches; however, the number of real additions increases significantly due to the sliding window scheme. The results show that the schemes can reduce the computational complexity and enhance flexibility when only several subsets of the IDFT output bins are required.     

EM/SAGE Based ML Channel Estimation for Uplink DS-CDMA Systems over Time-Varying Fading Channels

The matrix inversion for the maximum likelihood (ML) channel estimation requires high complexity for the direct-sequence code-division multiple-access (DS-CDMA) systems. The prime motivation of the paper is to propose channel estimators that achieve mean square error (MSE) performance of ML channel estimator in an iterative manner without any matrix inversion. Therefore, two computationally efficient solutions to the problem of ML channel estimation are proposed.We compare the both algorithms in terms of the number of used iteration and show that the proposed algorithms converge the same MSE performance of the ML estimator as the increasing number of iterations.     

Ultra-Wideband Radio Signals Distribution in FTTH Networks

The use of an ultra-wideband (UWB) radio technique is proposed as a viable solution for the distribution of high-definition audio/video content in fiber-to-the-home (FTTH) networks. The approach suitability is demonstrated by the transmission of standards-based UWB signals at 1.25 Gb/s along different FTTH fiber links with 25 km up to 60 km of standard single-mode fiber length in a laboratory experiment. Experimental results suggest that orthogonal frequency-division-multiplexed UWB signals exhibit better transmission performance in FFTH networks than impulse radio UWB signals.     

时变信道中CDMA信号的波达方向和直接扩频序列盲估计

本文研究CDMA信号的波达方向和直接扩频序列同时估计问题，在无任期任何波达方向信息的条件下，提出了利用用户特征序列定义一种新的目标函数，通过对目标函数寻优得到最佳权矢量，从而实现对波达方向和直接扩频序列进行估计，并利用改进的递归算法对权矢量进行实时更新，以适应移动通信无线环境的时变而导致信号的非平稳变化。该方法既适用于平稳信号，也适用于非平稳信号，仿真结果证实了该方法的有效性。     

一种基于贪婪基追踪算法的压缩感知超宽带信道估计方法

超宽带系统信道在特定的场景下,可表现出较强的稀疏特性。考虑IEEE802.15.4a提供的UWB信道参考模型,选取其中稀疏特性较强的信道场景作为背景,结合压缩感知理论对信道估计进行了研究。研究中着重考虑了压缩感知过程的信号重构算法,将一种贪婪的基追踪算法应用到信道模型的重构过程,计算机仿真结果表明信道的稀疏性能够得到准确表达,且稳定性和计算效率均比较理想。     

Channel Uncertainty in Ultra-Wideband Communication Systems

Channel uncertainty limits the achievable data rates of certain ultra-wideband systems due to the need to estimate the channel. The use of bursty duty-cycled transmission reduces the channel uncertainty because the receiver has to estimate the channel only when transmission takes place, but the maximum amount of burstiness and hence the possible reduction of channel uncertainty both depend on the spectral efficiency of the modulation scheme used. This general principle is demonstrated by comparing the channel conditions that allow duty-cycled direct-sequence spread spectrum (DSSS) and pulse position modulation (PPM) to achieve the additive white Gaussian noise (AWGN) channel capacity in the wideband limit. We show that duty-cycled DSSS systems achieve the wideband capacity as long as the number of independently faded resolvable paths increases sublinearly with the bandwidth, while duty-cycled PPM systems can achieve the wideband capacity only if the number of paths increases sublogarithmically. The difference is due to the fact that DSSS is spectrally more efficient than PPM and hence allows more bursty transmission     

基于ML和相关器的超宽带系统同步捕获的实现

超宽带(UWB)以其传榆速率高、抗多径和抗干扰能力强等优点,在短距多址无线通信中良好的应用前景而引起广泛研究.文章提出了一种基于ML的UWB同步接收方案,采用相关器与ML估计准则结合在一起实现同步.仿真结果表明:捕获的导频序列M越长和估计的支路数越多,误码率就越低.     

超宽带室内信道仿真分析

对超宽带通信室内修正S-V信道模型的进行仿真,在分析S-V信道模型的参数特点的基础上,探讨修正S-V信道模型的数学模型的建立方法,在CM4的非视距(NLOS)信道环境下,用Matlab进行仿真实验,结果表明修正S-V信道模型更接近实际,比S-V信道模型具有更好的信道冲激响应特性,能够更好地应用于超宽带通信系统性能的信道传输特性研究。     

基于整体最小二乘的联合信道估计及OFDM信号检测算法

针对现有的联合信道估计及OFDM信号检测算法性能不高的问题,该文提出一种基于整体最小二乘的联合信道估计及OFDM信号检测算法。该算法首先通过导频估计初始的信道信息,在此基础上不断地采用整体最小二乘进行OFDM信号检测及信道估计,有效缓解迭代模型误差的影响,加快了算法迭代的收敛速度,提高了信道估计的精度,从而降低了OFDM系统的误码率。该文推导的信道估计克拉美罗界及仿真结果均表明所提出的算法在时变信道环境下优于现有的联合信道估计及OFDM信号检测算法。     

多带OFDM超宽带系统信道估计的研究

超宽带(UWB)以其隐蔽性好、传输速率高,抗多径和窄带干扰能力强等优点,在短距多址无线通信中良好的应用前景而引起广泛研究.以多带OFDM超宽带通信系统为背景,主要研究UWB系统室内密集多径信道的估计,提出两种基于训练比特的UWB信道估计算法--ML算法和IML算法.仿真结果表明:两种信道估计算法都能够有效估计信道参数,而IML算法在消除多径成分之间相互干扰方面更优越.     

Characterization of a Computer Board-to-Board Ultra-Wideband Channel

In this paper we present the results of an extensive ultra-wideband (UWB) measurement campaign performed inside the chassis of two desktop computers. The purpose of the campaign is to analyze the possibility of board-to-board communications, replacing cable connections. Measurements of the propagation channel are performed over a frequency range of 3.1 - 10.6 GHz using a vector network analyzer and antennas small enough to enable integration on a circuit board. The results show that the propagation environment is very uniform, with small variations in the path gain between different positions within a computer. We also performed interference measurements, showing that the interference is restricted to certain subbands.     

一种多卫星信号参数的快速盲估计方法

针对电子侦察领域中单通道多卫星信号处理这一新兴课题,提出了一种多信号盲多参数快速估计算法.该算法在检测到卫星信号的前提下,先进行信号个数的盲估计.在对目前存在的各种信号参数估计方法进行充分分析、研究的基础上,进而提出了一种通用的盲多参数快速估计方法,并对其中的滤波器群延迟等关键问题进行了深入分析.计算机仿真表明,与其它算法相比,该算法具有较好的多参数盲估计能力,且通用性和实时性强,能适应单通道多卫星信号的情况.