DSSS中基于重叠变换的自适应干扰抑制算法及仿真分析

提出了一种基于重叠变换的自适应干扰抑制算法，利用调制重叠变换（MLT）把接收机信号映射到变换域进行抗干扰处理，它可以有效地把干扰能量集中在有限的变换域子带（Transform Bins）中，与基于DFT、DCT等块变换相比有更好的滤波效果。由于可以使用基于重叠变换的快速算法，因此它结构简单，节省计算量。仿真结果表明，基于MLT的变换域处理方案可以有效地改善系统性能。     

多分辨重叠变换在扩频通信系统抗干扰中的应用

 本文利用多分辨重叠变换(HLT)把接收机信号映射到变换域进行抗干扰处理.与重叠变换(LT)不同,HLT对信号频谱的非均匀划分可以有效地把干扰能量集中在有限的变换域子带(Transform Bins)中,因此对抑制随机脉冲干扰非常有效.与小波变换(WT)相比,HLT对信号频谱的划分更加灵活.由于可以使用基于重叠变换的快速算法,在滤波性能相当的情况下,HLT比小波变换节省计算量.仿真结果表明,其于HLT的变换域处理方案可以有效地抑制非时变窄带干扰和时变宽带干扰,明显地改善系统性能.     

利用基于滤波器组的重叠变换抑制扩频通信系统中的时变干扰

本文提出了基于滤波器的重叠变换方法,并对滤波器组结构进行了一些改进,使之在提供频率信息的同时保留了信号的时域信息,因此物品处理时变干扰,仿真结果证明,采用基于滤波器的重叠变换并结合本文所介绍的阈值处理算法可以有效地抑制扩频通信系统中的时变干扰。     

一种新的重叠变换域抗窄带干扰技术

本文采用改进的重叠变换域中值滤波算法进行变换域抗干扰处理.该算法既考虑到直接序列扩频信号的特点,同时又利用重叠变换的特性对变换域系数进行了二次滤波.该算法节省处理时间,并且不需要有关干扰的先验知识,系统性能不会随干扰频率变化而变化,因而是一种很稳健的处理方法.     

Extended lapped transforms: properties, applications, and fastalgorithms

The family of lapped orthogonal transforms is extended to include basis functions of arbitrary length. Within this new family, the extended lapped transform (ELT) is introduced, as a generalization of the previously reported modulated lapped transform (MLT). Design techniques and fast algorithms for the ELT are presented, as well as examples that demonstrate the good performance of the ELT in signal coding applications. Therefore, the ELT is a promising substitute for traditional block transforms in transform coding systems, and also a good substitute for less efficient filter banks in subband coding systems     

DSSS系统中自适应小波包干扰抵消器

本文提出了一种DSSS系统中基于小波包变换域的自适应干扰抵消算法（AWPT）,分析了小波包变抵抵消窄带干扰和脉冲干扰的机理,提出了优化准则和相应的自适应抵消算法,通过计算机仿真研究了其抗窄带和脉冲干扰的能力,并与传统的加窗DFT干扰抵消和子带变换干扰抵消作了比较。     

On lapped orthogonal transforms [signal coding applications]

The energy compaction performance of several lapped orthogonal transforms (LOTs) are presented. It is shown that the LOT outperforms the conventional block transforms for all the cases considered. The performance of the poorly performing block transforms for high correlation sources increased dramatically in their LOT versions. It is found that the energy compaction performance of the LOT versions of the different block transforms considered is about the same. Therefore, the choice of LOT is based on the efficiency of the transform algorithm. The LOT is an alternative to the block transforms for signal coding applications. Also, the blocking effect is reduced with the increase in the computational complexity of the transform algorithm     

基于Simulink的直扩系统频域窄带干扰抑制研究

直接序列扩频系统（Direct Sequence Spread Spectrum,DSSS）自身具有抗窄带干扰的能力,但当存在强窄带干扰时,需要有效的窄带干扰抑制技术来提高系统性能。研究了基于FFT的频域窄带干扰抑制算法,并对其中的加窗、重叠复用及门限生成等关键技术进行了分析。利用Matlab的可视化工具Simulink建立了仿真模型,并在给定的仿真条件下进行了仿真,验证了基于FFT重叠变换的频域陷波技术抑制干扰的有效性,为直接序列扩频系统在干扰环境下的应用提供了依据。     

Analysis of DFT-based frequency excision algorithms fordirect-sequence spread-spectrum communications

The capacity of direct-sequence spread-spectrum modulation to reject narrow-band interference can be significantly improved by eliminating narrow-band energy at the receiver in a process called frequency excision. This paper considers several algorithms that operate on the real-time discrete Fourier transform (DFT) of the received signal to perform frequency excision. The case in which only the signal and additive white Gaussian noise (AWGN) are present at the receiver is considered as a means of comparing the relative performance of different algorithms that operate without knowledge of the power spectral density of the interference. An approach for analysis, using the postcorrelation signal-to-noise ratio (SNR) as the figure of merit, is presented that is valid for a broad class of spreading modulations. First, the algorithm that sets a fixed fraction of the frequency domain record to zero is examined using rank-order statistics as an analytical tool. This result is then generalized to confirm previous estimates of SNR degradation for the algorithm that sets all values that exceed a threshold to zero. These results are again generalized to apply to the algorithm that sets a fixed fraction of the band to a fixed amplitude while retaining phase information in an algorithm called fraction clip. The relative performances of several clip algorithm options are derived as special cases. Finally, a performance measure of the algorithms in the presence of multiple narrow-band interference is provided and illustrated with an example     

A single-chip narrow-band frequency-domain excisor for a GlobalPositioning System (GPS) receiver

In recent gears, we have witnessed the rapid adoption of the Department of Defense's Global Positioning System (GPS) for navigation in a number of military and civilian applications. Unfortunately, the low-power GPS signal is susceptible to interference. This paper presents a novel VLSI architecture that removes narrow-band signals from the wide-bandwidth GPS spectrum. The interference suppression technique employed is frequency-domain excision. The single-chip frequency-domain excisor transforms the received signal (GPS signal+noise+interference) to the frequency domain, computes signal statistics to determine an excision threshold, removes all spectral energy exceeding that threshold, and restores the remaining signal (GPS signal+noise) to the temporal domain. The heart of this VLSI implementation is an on-chip 256-point fast Fourier transform processor that operates at 40 million complex samples per second. It processes 12-bit (for each I and Q) sampled complex data. The 1.57 million-transistor chip was fabricated in 0.5-μm CMOS triple metal technology and is fully functional     

一种基于重叠变换域的抗窄带干扰算法

为了增强扩频系统的窄带干扰抑制能力,针对重叠域中值滤波(MF)算法会给信号带来失真的缺点,提出一种基于重叠变换域窄带干扰抑制算法.该算法基于直接序列扩频信号在重叠变换域的特点,利用阈值滤波、中值滤波、估计门限进行综合判决.仿真表明:该算法能有效降低信号干扰能量,同时减少中值滤波算法对信号造成的失真,增强了系统性能和鲁棒性.     

直扩通信中窄带干扰抑制的边带相关置换算法

论文提出了一种新的窄带干扰抑制算法,基于信号边带相关性的边带相关置换算法,通过计算接收信号频谱的边带相关函数确定载频和干扰中心频率,然后利用直扩信号频谱的对称性,用相对于窄带干扰的边带对称值代替干扰值达到消除干扰的目的。该算法对频谱具有对称性的调制方式都适用。计算机仿真结果表明边带相关置换算法的性能要优于变换域干扰置零的常规算法。     

Fast downscaled inverses for images compressed with M-channellapped transforms

Compressed images may be decompressed and displayed or printed using different devices at different resolutions. Full decompression and rescaling in space domain is a very expensive method. We studied downscaled inverses where the image is decompressed partially, and a reduced inverse transform is used to recover the image. In this fashion, fewer transform coefficients are used and the synthesis process is simplified. We studied the design of fast inverses, for a given forward transform. General solutions are presented for M-channel finite impulse response (FIR) filterbanks, of which block and lapped transforms are a subset. Designs of faster inverses are presented for popular block and lapped transforms.     

基于重叠变换和时频分析的自适应抗干扰算法

将时频分析和重叠变换结合,提出了一种新的直接序列扩频通信窄带干扰抑制算法,通过重叠变换将多分量信号分解成为一系列单分量信号并通过维格纳分布法确定单分量干扰的频率。在此基础上设计了一自适应滤波器抑制掉干扰。这种方法对平稳信号和非平衡信号同样适用。给出相应的计算机仿真结果,并与其它变换域算法进行了比较。     

Wavelet and subband transforms: fundamentals and communicationapplications

Subband and wavelet transforms have been a subject of great interest, especially in the fields of signal processing and applied mathematics. This article presents a tutorial on this subject, emphasizing the fundamentals and the reason for its success, importance, and potential. Subband and wavelet transform applications in communications are also reviewed. These application areas include interference excision, spread spectrum codes based on subband transform bases, CDMA, and discrete multitone transceivers     

An orientation-selective orthogonal lapped transform

A novel critically sampled orientation-selective orthogonal lapped transform called the lapped Hartley transform (LHT) is derived. In a first step, overlapping basis functions are generated by modulating basis functions of a 2-D block Hartley transform by a cosine wave. To achieve invertibility and orthogonality, an iterative filter is applied as prefilter in the analysis and as postfilter in the synthesis operation, respectively. Alternatively, filtering can be restricted to analysis or synthesis, ending up with a biorthogonal transform (LHT-PR, LHT-PO). A statistical analysis based on a 4000-image data base shows that the LHT and LHT-PO have better redundancy removal properties than other block or lapped transforms. Finally, image compression and noise removal examples are given, showing the advantages of the LHT especially in images containing oriented textures.     

基于信息辅助块稀疏贝叶斯学习的直扩通信窄带干扰抑制

现有基于Nyquist-Shannon采样定理的窄带干扰(Narrowband Interference,NBI)抑制方法存在应用受限于采样率较高的问题。应用压缩感知(Compressive Sensing,CS)理论解决上述问题,利用NBI在频域表现出的块稀疏特性以及直接序列扩频(Direct Sequence Spread Spectrum,DSSS)信号的类噪声特性,提出了基于块稀疏贝叶斯学习(Block Sparse Bayesian Learning,BSBL)框架的DSSS通信NBI抑制模型。实现干扰抑制后,利用传统的CS重构算法实现DSSS信号的压缩域解调。为进一步提高算法性能,将NBI稀疏分块的块内自相关矩阵建模为单位矩阵,提出了信息辅助BSBL(Aid BSBL,ABSBL)算法,设计了基于ABSBL的DSSS通信NBI抑制算法。该算法在保持较好NBI抑制性能的条件下,提高了运算效率并且不依赖NBI的稀疏结构。仿真验证和对比分析结果表明,所提方法能够有效抑制DSSS通信中的NBI,在干扰强度相同的条件下,NBI带宽越小、压缩率越大,算法对NBI的抑制性能越好。     

直扩通信系统抗窄带干扰技术研究与仿真

针对直扩通信系统中的强窄带干扰问题,通过Matlab/Simulink搭建完整的直扩通信系统模型.在此基础上分析了一种改进型的重叠变换干扰抑制算法.该算法利用重叠加窗降低了因数据截断引起的频谱泄漏,同时也减少了因加窗引入的信噪比损耗.计算机仿真分析证明,该算法可有效抑制强窄带干扰,改善系统的误码性能,提高系统的抗干扰能力.     

Narrow-band interference excision in spread-spectrum systems usingself-orthogonalizing transform-domain adaptive filters

Among many transform-domain interference excision techniques, transform-domain adaptive filtering has many advantages. It is based on a true optimization of some particular performance parameters such as the bit-error rate (BER). Moreover, it is insensitive to jammer frequency. However, transform-domain adaptive filtering also has the drawback of being incapable of tracking a rapidly changing interference because most adaptive algorithms require time to converge to the optimal solution. In this paper, a self-orthogonalizing transform-domain least mean square (SO-TRLMS) algorithm is used to speed up the convergence. Compared to a traditional transform-domain least mean square (TRLMS) algorithm, the SO-TRLMS algorithm can significantly improve the convergence rate of the LMS algorithm, thus making the transform-domain adaptive filtering technique more suitable for real-time processing. In order to show how the system performance is affected by various factors such as interference power and the transform used, this paper presents an analytical result for the BER performance that is applicable for arbitrary orthogonal linear transforms. Simulation results are also presented to demonstrate the validity of the analysis     

Frequency-domain motion estimation using a complex lapped transform

A frequency-domain algorithm for motion estimation based on overlapped transforms of the image data is developed as an alternative to block matching methods. The complex lapped transform (CLT) is first defined by extending the lapped orthogonal transform (LOT) to have complex basis functions. The CLT basis functions decay smoothly to zero at their end points, and overlap by 2:1 when a data sequence is transformed. A method for estimating cross-correlation functions in the CLT domain is developed. This forms the basis of a motion estimation algorithm that calculates vectors for overlapping, windowed regions of data. The overlapping data window used has no block edge discontinuities and results in smoother motion fields. Furthermore, when motion compensation is performed using similar overlapping regions, the algorithm gives comparable or smaller prediction errors than standard models using exhaustive search block matching, and computational load is lower for larger displacement ranges and block sizes.