Matching pursuit-based region-of-interest image coding.

Matching pursuit (MP) is a multiresolution signal analysis method and can be used to render a selected region of an image with a specific quality. A novel, scalable, and progressive MP-based region-of-interest image-coding scheme is presented. The method is capable of providing a trade off between rate, distortion, and complexity. The method also provides an interactive way of information refinement for regions of an image with higher receiver's priority. By selecting a proper subset of the huge initial MP dictionary, using the method described in this paper, the complexity burden of MP analysis can be adapted to the computational power of the image encoder.     

一种较低复杂度的UWB信道自适应均衡技术

针对多用户UWB信道存在的符号间干扰和用户间干扰问题,提出了一种用于DS-UWB/TH-UWB接收机的较少复杂度的自适应均衡技术及相应算法,并与传统算法在复杂性和性能方面进行了比较。研究结果表明所提出的算法在运算量上远小于单独使用RLS算法,在输出误差的收敛上远快于单独使用LMS算法。     

基于Turbo迭代技术的信道均衡算法研究

针对中国国家广播电影电视总局颁布的CMMB系统数据传输模型,研究了Turbo迭代技术对CMMB系统信道解码性能的影响.对比了基于软判决反馈值的MMSE信道估计和BE模型信道估计算法,提出了利用软判决消除ICI干扰的Turbo迭代均衡方法.借助MATLAB对上述三种方法进行了仿真实验.仿真结果证实了提出的方法有较低的计算复杂度和更好的误码性能.     

Automatic channel equalization algorithm

Results are reported which are of interest in the automatic equalization of telephone lines or other narrow bandwidth channels where data transmission is limited primarily by intersymbol interference. We describe an algorithm for adjusting the tap gains of a tapped delay line equalizer which converges for all channels. The algorithm also adjusts the tap gains to match a changing channel.     

联合信道均衡与时间反演的室内保密通信方法

针对物理层无线通信的窃听信道问题,提出了一种适用于室内频率选择性衰落信道的均衡时间反演(Equalized Time Reversal,ETR)保密通信方法。首先,建立了均衡时间反演窃听模型,在信号发送端将均衡器级联配置,利用信道均衡技术提高信息传输的保密性能;其次,通过传统时间反演(Time Reversal,TR)技术的等效信道分析对均衡器进行了设计,根据均衡后的信道推导了系统保密信干噪比、系统保密容量、误码率的闭合表达式。理论分析和仿真结果表明,与传统的TR技术相比,ETR的保密信干噪比、系统保密容量更高,合法接收用户的误码率更低。     

Turbo equalization: adaptive equalization and channel decodingjointly optimized

This paper deals with a receiver scheme where adaptive equalization and channel decoding are jointly optimized in an iterative process. This receiver scheme is well suited for transmissions over a frequency-selective channel with large delay spread and for high spectral efficiency modulations. A low-complexity soft-input soft-output M-ary channel decoder is proposed. Turbo equalization allows intersymbol interference to be reduced drastically. For most time-invariant discrete channels, the turbo-equalizer performance is close to the coded Gaussian channel performance, even for low signal-to-noise ratios. Finally, results over a time-varying frequency-selective channel proves the excellent behavior of the turbo equalizer     

复合导频UWB系统信道估计方法

隐藏系统具有估计精度差的缺陷,辅助导频具有占用带宽多的缺陷,针对这种情况提出了复合导频信道估计方法,在隐藏导频中插入极少量的辅助导频,由于UWB信道是慢变信道,所以隐藏导频可以借鉴辅助导频的信道估计。把辅助导频和隐藏导频的信道估计叠加成新的信道估计。仿真结果表明复合导频信道估计继承了两种导频信道估计的优点,提高了信道估计精度,减少了带宽占用率。     

Single-user channel estimation and equalization

There has been much interest in blind (self-recovering) channel estimation and blind equalization where no training sequences are available or used. In multipoint networks, whenever a link from the server to one of the tributary stations is interrupted, it is clearly not feasible (or desirable) for the server to start sending a training sequence to re-establish a particular link. In digital communications over fading/multipath channels, a restart is required following a temporary path interruption due to severe fading. During on-line transmission impairment monitoring, the training sequences are obviously not supplied by the transmitter. Consequently, the importance of blind channel compensation research is also strongly supported by practical needs. We present a comprehensive summary of research development on single-user channel estimation and equalization, focusing on both training-based and blind approaches. Our emphasis is on linear time-invariant channels.     

Adaptive algorithms for channel equalization with soft decisionfeedback

A new approach based on joint entropy maximization (JEM) is taken and adaptive algorithms are developed for channel equalization with a decision feedback equalizer (DFE). The proposed work generalizes the existing algorithms for DFE with a hard decision device. Previous research has shown that when the hard decisions in a DFE are replaced with soft decisions, the performance of the adaptive algorithms [e.g., minimum mean square error (MMSE)] improves dramatically. The soft decisions can be introduced naturally via the viewpoint taken here. Additionally, constant modulus and other (blind) algorithms for DFE with soft decisions can be derived from this JEM approach     

一种适用于稀疏多径信道的自适应均衡算法

针对传统的自适应均衡算法在稀疏多径信道下性能表现不佳的问题,提出了一种基于基追踪降噪的自适应均衡算法。该算法利用稀疏多径信道下均衡器权值的稀疏性,将自适应均衡器的训练过程看作压缩感知理论中稀疏信号对字典的加权求和,并利用重构算法直接对稀疏权值进行求解,解决了迭代参数设置和收敛慢的问题。采用基追踪降噪作为重构算法并选用变量分离近似稀疏重构对该最优化问题进行求解,既提高了权值的重构精度又降低了计算的复杂度。仿真结果表明,所提算法能够以较低的计算量和较少的训练序列达到更优性能,这对提升系统的通信性能具有参考价值。     

一种遥感卫星高码速VCM数传信道的均衡技术

在基于第二代数字卫星视频广播协议（DVB-S2）标准的遥感卫星可变编码调制（VCM）高码速数传信道中,宽带信号的大失真、大频偏和低信噪比会导致解调器载波环路不锁定。传统的DVB-S2解调器并不能解决这个问题。在载波环路前增加一个均衡器补偿失真,可以让载波环路稳定锁定。为了克服载波环路前信号的频偏和相偏对均衡器的影响,提出了一种均衡技术,利用起始序列（SOF）和导频的先验信息进行双重自相关变换,设计了一种新的误差函数和迭代过程。仿真结果表明,该均衡技术可在该应用条件下支持解调稳定工作。     

面向ASIC设计的单载波超宽带信道均衡研究

单载波超宽带通信系统的均衡在芯片实现中面临高吞吐率、高性能和低复杂度三方面问题。该文首先比较了最大似然均衡（MLSE）、线性均衡（LE）、判决反馈均衡（DFE）及单载波频域均衡（SC-FDE）在性能、复杂度及高速化实现上的优缺点,并综合考虑SC-UWB系统这一特殊的应用场景最终选择了DFE。然后针对DFE算法中的三个关键参数——前馈阶数Nf,反馈阶数Nb及判决延迟D,提出了一种实际系统中有效且实用的参数优化设计策略,最后仿真证明了优化策略的实用性和有效性。     

A fully pipelined RLS-based array for channel equalization

It is shown that several recursive least squares (RLS) type equalization algorithms such as, e.g., decisiondirected schemes and orthogonalized constant modulus algorithms, possess a common algorithmic structure and are therefore rather straightforwardly implemented on an triangular array (filter structure) for RLS estimation with inverse updating. While the computational complexity for such algorithms isO(N ²), whereN is the problem size, the throughput rate for the array implementation isO(1), i.e., independent of the problem size. Such a throughput rate cannot be achieved with standard (Gentleman-Kung-type) RLS/QR-updating arrays because of feedback loops in the computational schemes.     

Rake接收机在超宽带系统中的均衡性能分析

从缩短信道时延扩展的角度出发,研究了Rake接收机的部分信道均衡能力,并推导出了Rake接收机均衡性能与Rake接收机的复杂度和信道衰减系数之间的关系;分析了信道估计误差对Rake接收机合并前后多径信道变化的影响。研究表明当存在估计误差时,Rake接收机仍然能实现均衡的作用,但是性能有所下降;由于低复杂度Rake接收机引入的估计误差较少,在低信噪比条件下其均衡性能甚至会优于高复杂度的Rake接收机。     

A new channel estimator for fast start-up equalization

A novel noniterative algorithm is proposed for estimating the sampled impulse response of unknown channels. With the proper choice of the training sequence, implementation of the proposed channel estimator requires only additions and subtractions, i.e. no multiplications of the estimator is so simple that it can be easily implemented using an ordinary microprocessor with minimal storage. The channel estimate can serve to reduce the effects of intersymbol interference either by the maximum likelihood sequence estimator using the Viterbi algorithm or by channel equalization with a direct solution to obtain the optimum equalizer taps. A new procedure for the latter case is proposed using the Levinson-Trench algorithm for fast start-up of adaptive equalizers in noisy environments. The performance of the proposed algorithm is evaluated through simulation, and it is compared to some previous techniques. Computational efficiency is also taken into account. The results of the simulation show the superiority of the proposed scheme     

超宽带室内多径信道随机分析模型

使用随机分析方法研究超宽带(UWB)室内多径信道.从UWB信号的基本传播特性出发构建随机分析模型的物理基础.假设UWB信号的多径分量在信道中的传播轨迹是某个随机过程的样本,把UWB信号在信道中传播时发生的传播损耗,和与散射体发生碰撞产生的损耗分开,建立UWB室内多径信道的随机分析模型,包括完全随机的布朗桥模型和有约束的布朗桥模型.使用有约束的布朗桥模型对假设的有8个散射体的不完全随机分布室内环境,以及有金属网格玻璃门反射的走廊环境进行仿真,得到了具有明显成簇现象的UWB信道的功率延迟分布.仿真结果与已公布的UWB信道实测结果具有很好的相似性.     

Novel sampling technique for digital video demultiplexing,descrambling and channel selection

Describes a novel method of distributing a large number of digital video channels over a passive optical fibre network, while allowing the use of baseband binary receive equipment. The synchronous TDM is sampled, and receive channels are descrambled using a programmable delay-lock loop     

Performance of maximum-likelihood channel estimator for UWB communications

Data-aided channel estimation based on maximum-likelihood criterion has recently been proposed for ultra-wideband communications. However, its performances was evaluated by using only numerical simulation. This letter derives the Cramer-Rao lower bound for the method and verifies the analytical results via a numerical example.     

Spatial correlation technique for UWB antenna arrays

A computation technique for predicting the spatial correlation coefficients, based on data captured by an ultra-wideband antenna array, is presented. Signal correlation coefficients obtained from adjacent array positions were calculated at each time bin. In addition, the application of this technique can lead to ultra-wideband multipath cluster identification. Time bins associated with high correlation values were selected as cluster arrival times and were compared with results estimated by the Sensor-CLEAN algorithm.     

Hybrid digital-analog technique for UWB direction finding

In this letter, we propose an alternative approach for UWB direction finding using hybrid digital-analog technique. The proposed system uses an array of leading-edge pulse detection scheme in analog domain. The detection scheme is realized using tunnel diode with envelope detector and comparator latch, whose output is digital binary signal. The outputs or all array branches are then summed up to form a staircase-shaped waveform, whereby the slope of the waveform indicates the direction of impinging UWB signal. In order to detect the slope and produce the estimation of the direction, an analog differentiator joint with a peak detector is utilized. The proposed system is relatively simple and does not require high sampling rate or high speed DAC.