一种用于抑制直扩通信中窄带干扰的非线性自适应方法

在分析线性自适应滤波抑制单频干扰、自回归过程窄带干扰和窄带BPSK调制信号干扰的性能的基础上,提出了一种非线性自适应波抑制方法.在对窄带干扰进行预测前,通过对扩谱信号的估计,使得窄带干扰预测的背景噪声由非高斯转变为高斯,并消除扩谱信号对干扰估计的影响,再通过NLMS和RLS自适应算法进行干扰抑制.理论分析和仿真试验结果表明,这种改进方法对于系统性能的改善效果,明显优于常规自适应滤波抑制方法.     

Blind channel estimation for multicarrier systems with narrowband interference suppression

We present herein a novel blind channel estimator for multicarrier (MC) systems in the presence of unmodeled narrowband interference. A generalized multichannel minimum variance principle is invoked to design an equalizing filterbank that preserves desired signal components and suppresses the overall interference. While a channel estimate may be obtained by directly maximizing the filterbank output power through multidimensional nonlinear searches, such an approach is computationally prohibitive and suffers local convergence. To overcome this difficulty, we derive an asymptotically (in SNR) tight lower bound of the filterbank output power and use it for channel estimation, which reduces the problem to a quadratic minimization. Numerical examples show that the proposed scheme compares favorably with a subspace blind channel estimator in the presence of unknown narrowband interference.     

New nonlinear algorithms for narrowband interference suppression inCDMA spread-spectrum systems

The narrow-band interference suppression capability of spread-spectrum systems can be further enhanced by employing interference suppression filters. This paper proposes a number of new nonlinear algorithms for narrow-band interference suppression in code division multiple access spread-spectrum systems. Our research consists of two parts. (1) We propose a multiuser decision-directed Kalman (MDK) filter, which has the same performance as the nonlinear approximate conditional mean (ACM) filter but a much simpler algorithm. (2) We use the nonlinear function in the ACM and the MDK filters to develop nonlinear adaptive least mean square filters with significantly improved performance. Simulation results indicate that our nonlinear algorithms outperform conventional linear ones     

Polarization filtering for narrowband interference suppression in ultra‐wideband communications

To suppress narrowband interference (NBI) in an ultra‐wideband (UWB) communications environment, a null phase‐shift polarization (NPSP) filter is proposed. The proposed NPSP filter is a combination of a linear polarization‐vector transformer (PVT), a conventional single notch polarization (SNP) filter, and an amplitude and phase compensator (APC). The NBI, which has polarized states different from those of the UWB, can be suppressed completely and the UWB signal can be recovered without distortion if the polarized states can be estimated exactly. Analytical and simulation results indicate that the signal‐to‐interference ratio (SIR) can be improved effectively after NPSP filtering. The proposed NPSP filter can be implemented in a time‐hopping spread spectrum (TH‐SS) or a direct‐sequence spread spectrum (DS‐SS) UWB system. Copyright © 2007 John Wiley & Sons, Ltd.     

A rank-reduced LMMSE canceller for narrowband interference suppression in OFDM-based systems

We present a narrowband interference (NBI) canceller that suppresses spectral leakage in an orthogonal frequency-division multiplexing (OFDM)-based system caused by a narrowband (NB) signal. We assume that the spectrum of the NB signal is within the spectrum of the OFDM signal. This can be the case, e.g., on digital subscriber lines (DSL) and in new unlicensed frequency bands for radio transmission. The canceller makes linear minimum mean-square error estimates of the spectral leakage by measuring the NBI on a few modulated or unmodulated OFDM subcarriers. It uses a model of the NB signal's power spectral density as a priori information. Using a frequency invariant design, it is possible to cancel NBI from signals that are changing their frequency location with significantly reduced complexity overhead. The operational complexity of the canceller can be lowered by using the theory of optimal rank reduction and using the time-bandwidth product of the NB signal. Analytical performance evaluations, as well as Monte Carlo simulations, show that, without perfect a priori information, this canceller can suppress the spectral leakage from a strong NB signal (e.g., with equal power as the OFDM signal) to well below the background noise floor for typical applications where it causes negligible signal-to-noise ratio and symbol error rate degradation.     

面向IR-UWB基于直接序列设计抑制窄带干扰算法

针对窄带系统对超宽带冲激无线电系统(Impulse Radio Ultra-wideband,IR-UWB)的干扰问题,提出基于Rayleighritz理论的直接序列(Direct Sequence,DS)设计方案,记为RRDS。通过设计DS序列,使得IR-UWB频谱在窄带干扰频率点上产生陷波,从而实现抑制干扰的目的,同时,通过RRDS方案,提高IR-UWB系统的误码率。RRDS方案先建立目标矩阵,并求解最小特征值及对应的特征向量。如果特征向量里面的元素有非+1或-1的值,则通过符号函数将特征向量转变为全部由+1,-1组成。若最小特征值是多重,先将所有的特征向量通过符号函数转变为全部由+1或-1组成的向量,并在这些向量里找出使目标矩阵的值最小的特征向量,将此向量作为直接序列DS。仿真结果表明,提出的RRDS方案有效地抑制窄带干扰,并提高了IR-UWB系统的误码率。     

Performance analysis of transmitted‐reference UWB systems with narrowband interference suppression

In this paper, we propose a receiver structure for transmitted‐reference ultra‐wideband (TR‐‐UWB) systems with both narrowband interference (NBI) and inter‐pulse interference (IPI) mitigation capabilities. The effects of additive white Gaussian noise (AWGN) and the IEEE 802.15.4a fading channel are also taken into consideration. We adopt band‐stop filtering to suppress the NBI. For IPI, it is statistically removed by a sum‐and‐average process. Theoretical analysis is carried out to study the lower bound of the bit‐error rate (BER) performance of the proposed receiver. Numerical results show that the proposed receiver is able to provide satisfactory performance and is robust to variations in the system design parameters. It is also observed that the proposed receiver is able to deliver good performance even when there is zero delay between the reference and data pulses, which can effectively double the system throughput. Copyright © 2008 John Wiley & Sons, Ltd.     

SC-FDE UWB系统WMMDT抗窄带干扰信道估计

针对单载波频域均衡超宽带无线通信系统信道估计中存在的窄带干扰问题,提出了一种基于小波模极大值动态阈值的信道估计方法。该方法在信道最小二乘估计的基础之上进行小波模极大值动态阈值(WMMDT)计算,检测到窄带干扰的位置,然后通过插值法恢复干扰处信道频响。仿真结果表明,在极度频选室内CM4信道模型下,所提出方法较传统方法信道估计性能得到明显改善且复杂度增加不多。     

DS扩频系统抗多窄带干扰方法研究

针对AR过程的窄带干扰,本文构建了DS扩频系统多窄带干扰下的信号模型,给出了统一的观测模型,并用线性、非线性滤波方法对其进行干扰抑制。仿真结果表明,所建模型是有效的,而且滤波方法对多个窄带干扰仍有很好的抑制性能,且非线性滤波的性能要优于线性滤波。     

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.     

Subset Parallel Volterra Filter for narrowband interference suppression in DSSS communications

Subset Parallel Adaptive Volterra Filter （SPAVF） design algorithm is proposed in this letter. Contribution factor is introduced in SPAVF, and it can get rid of redundant elements efficiently in the extended input vector. Computational weight can be reduced largely, and BER performance of SPAVF can be improved by getting rid of the influence of redundant elements in the input vector. Simulation result proves its advantage compared to AVF and PSVF.     

卫星扩频通信中一种简化的窄带干扰抑制方法

针对卫星扩频通信中的强窄带干扰，提出了一种基于频域处理的窄带干扰抑制技术。该技术采用了简化的自适应方法估计接收信号中噪声的功率，确定窄带干扰与噪声之间的阂值。通过降低高于阈值的干扰谱线的幅度同时保持这些谱线的相位信息，降低了处理后信号中的干扰能量，使接收信号信噪比大大提高。该窄带干扰抑制算法的复杂度比较小，硬件实现占用的资源较少。     

Local polynomial Fourier transform: A review on recent developments and applications

The local polynomial Fourier transform (LPFT), as a high-order generalization of the short-time Fourier transform (STFT), has been developed and used for many different applications in recent years. This paper attempts to review previous research work on the following issues of the LPFT. Firstly, the definition, the properties of the LPFT and its relationships with other transforms are reviewed. The LPFT for multicomponent signal is then presented. The polynomial time frequency transform (PTFT), which is the maximum likelihood estimator to estimate the parameters in the LPFT, as well as its properties and fast algorithms are discussed. By comparing with the Fourier transform (FT), the STFT and the Wigner-Ville distribution (WVD), the LPFT has its superiority in obtaining improved SNRs, which can be supported by theoretical analysis and computer simulations. Furthermore, the reassignment method is combined with the LPFT and the robust LPFT to improve the concentration of the signal representation in the time-frequency domain. Performances obtained by using various LPP-related methods are compared for signals in different noise environments, such as the additive white Gaussian noise (AGWN), impulsive noise, and the mixture of AGWN and impulsive noise.     

Modified linear prediction algorithm for narrowband interference suppression in universal mobile telecommunication system

Narrow band interference (NBI) deteriorates the quality of the spectrum, leading to a poorer performance of modern universal mobile telecommunication system (UMTS) spread spectrum systems. The linear prediction algorithm is one of the most significant techniques to overcome NBI and enhance the performance of UMTS systems. In this paper, a modified linear prediction algorithm is proposed for NBI suppression in a conditionally stationary environment. This modification improves the error energy estimation in the auto‐regression model of the linear prediction. The convergence of the proposed algorithm is evaluated, and its robustness is verified using Kullback–Leibler metrics for conditionally stationary NBI signals. Computer simulations are carried out, and the obtained results demonstrate the performance of the proposed algorithm and its compliance with UMTS protocols. Copyright © 2012 John Wiley & Sons, Ltd.     

基于FPGA的窄带干扰抑制算法在GPS中的应用

针对GPS接收机有效信号弱,易受窄带干扰影响的不足,提出了一种基于FPGA的窄带干扰抑制算法的实现方案。该方案以Xilinx公司的Virtex5芯片为硬件平台,采用重叠加窗频域滤波算法和自适应多门限检测技术实现窄带干扰的实时检测和抑制,最后采用重叠相加的方法进行数据输出。测试结果表明,该设计能为GPS接收机提供至少60dB的抗窄带干扰能力。与其他窄带干扰抑制方法相比,收敛速度和信噪比损耗都得到了改善。     

一种具有窄带干扰抑制能力的改进型LSL插值算法

本文提出了一种基于QR分解技术的最小二乘格形插值算法-QRD-LSL插值算法来抑制直扩系统中的窄带干扰.该算法利用直扩信号、噪声信号和窄带干扰信号数据样值间相关特性的差异,通过对直扩系统接收端数据样值序列进行插值运算来估计窄带干扰信号成分,从而达到抑制直扩系统中窄带干扰的目的.由于该算法引入了QR分解过程避免了对数据矩阵求逆运算,并引用动态范围较小的新变量参与阶递推运算,极大程度上提升了算法在稳态特征、收敛速度和计算复杂度等方面的性能.仿真结果表明:QRD-LSL插值算法较LSL插值算法和LSL预测算法至少可获得4dB的处理增益,且计算量与滤波阶数呈线性关系.     

正交频分复用系统中抗线性调频干扰算法研究

针对基于离散傅立叶变换的正交频分复用系统（OFDM）,提出了一种新的线性调频（LFM）干扰抑制算法。该算法分为两部分：干扰估计和干扰重构抑制。干扰估计时,首先采用离散傅立叶变换进行粗略估计,然后采用离散匹配傅立叶变换进行精确估计,整个过程均可共用傅立叶变换单元,有效地节省了系统资源。实验结果表明：该算法的干扰抑制性能良好;与现有的抗线性调频干扰算法相比,其运算复杂度大为降低,具有很好的工程实用性。     

DSSS中抑制窄带干扰的实时频域滤波技术

针对直接序列扩频通信中大功率的窄带干扰,研究改进了基于频域的干扰抵消算法,对影响算法的几个因素:时窗函数、重叠算法及干扰信号带宽做了理论分析和仿真。仿真表明,该算法有效地提高了系统的抗干扰性能。     

Adaptive multiuser interference suppression for CDM satellite systems

This paper deals with the application of linear multiuser detectors in mobile terminals of code division multiplex (CDM) satellite systems. Generally, the interference caused by other users can dramatically reduce the performance of a CDM‐based satellite communication system. Since no spreading information of other users is given and since there are no trainings sequences, a blind adaptive interference detector with low complexity is needed. In order to implement a detector for suppressing the interference from other users, different adaptation algorithms can be applied. Comparing them in terms of complexity, adaptation speed and bit error rate, the LMS (least means squares) algorithm with adaptive step size shows the best performance. However, the implementation of this algorithm in a satellite system still leads to high processing times. For this reason, two new schemes with reduced complexity are presented. A very important point is, that the adaptive algorithms are basically restricted to short spreading codes (code period equals symbol period) whereas CDM‐based satellite systems use long codes (one‐code period spans over multiple symbols). In this paper, a new scheme is presented which can be applied to long codes. By cascading multiple separated interference detectors the adaptation is done every time when the same part of the spreading sequence appears. Copyright © 2005 John Wiley & Sons, Ltd.     

矢量正交频分复用系统的窄带干扰抑制

分析了窄带干扰对矢量正交频分复用(VOFDM)系统性能的影响,提出了一种VOFDM系统的窄带干扰抑制方法.该方法通过对接收矢量进行修正,把矢量子信道的接收转化为多载波码分多址(MC-CDMA)系统的接收检测问题,再采用最小均方误差合并技术实现窄带干扰抑制.性能分析及仿真结果表明,所建议的接收方法可有效提高系统对窄带干扰的顽健性,对于矢量长度为16的VOFDM,当信干比为15dB且误码率为10-2时,本方法相比于最小平方检测有约8dB的信噪比增益.