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.     

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.     

一种基于频域的QPSK窄带干扰抑制算法

在QPSK系统中,当存在单频干扰或者窄带干扰时,会对系统的解调性能产生不利影响,导致误码率升高。提出了一种在变换域基于DFT变换的窄带干扰抑制技术,该方法将输入信号经FFT变换到频域,根据动态调整的门限找出认为存在干扰的频率谱线,将其置零,达到抑制窄带干扰的目的。仿真结果表明该抑制算法可以较好地抑制窄带干扰,同时又能对有用信号最大限度地保留,具有较高的工程使用价值。     

基于门限估计的直扩通信系统窄带干扰变换域抑制方法

该文提出一种基于门限估计的直接序列扩频(DS-SS)通信系统窄带干扰变换域抑制方法。该方法对直扩通信系统接收信号变换域数据的分布特点进行了分析,并采用高斯分布对其作了近似.由于高斯分布的方差即为直扩信号和高斯白噪声方差之和,因此估计出变换域数据的方差,将为频域抑制滤波器的门限设置提供参考。该文采用最大似然比(ML)准则对方差进行了估计,从而实现了频域抑制滤波器的自动门限设制。理论分析和计算机仿真结果均表明,该方法能够有效地抑制直扩通信系统中的窄带干扰。     

一种改进的双门限窄带干扰抑制算法

变换域双门限窄带干扰抑制算法是处理扩频信号中窄带强干扰的一种有效算法,但是当信号功率过强时双门限算法将会失效。基于传统的双门限算法,提出了一种改进型双门限窄带干扰抑制算法,研究了该算法的门限选取方法和干扰检测机制。实验结果表明,该算法能够解决传统双门限算法存在的问题,具有较好的性能。     

基于自适应多门限算法的变换域窄带干扰抑制

该文分析基于门限检测的直接序列扩频通信系统变换域窄带干扰抑制技术,提出一种基于自适应多门限窄带干扰抑制算法,并对其性能进行详细分析,理论分析和数字仿真结果表明,该算法可有效抑制直扩通信系统中的窄带干扰,并且相对于传统的门限检测算法,有自适应性强,门限设计简单等优点。     

一种直扩通信系统窄带干扰变换域抑制方法

本文提出一种基于AR模型谱估计和变换域处理相结合的直接序列扩频（DS-SS）通信系统窄带干扰抑制方法。该方法采用AR模型估计信号的频谱,并由此构造频域窄带干扰抑制滤波器。由于谱估计的同时也估计了最小误差功率,这为频域抑制滤波器的门限提供了参考,从而实现了自动门限设置。与时域AR预测型窄带干扰抑制方法相比,频域处理利用FFT实现了并行处理,提高了处理速度。     

自适应开环FIR滤波器抗窄带干扰方法研究

该文针对DSSS变换域抑制窄带干扰方法存在的不足,提出频域FFT干扰检测与时域自适应开环FIR陷波器相结合抑制窄带干扰的方法。给出了系统输出信噪比的解析表达式,并自适应地调整陷波器的零点位置和陷波幅度,使输出信噪比达到最优。仿真结果表明, 该方法在抗单音和多音干扰方面,性能均优于基于FFT加窗重叠处理的变换域抗干扰方法,并且结构简单、计算量小,是一种实用的抗干扰方法。     

变换域窄带干扰抑制算法的仿真与实现

本文主要针对变换域窄带干扰抑制算法进行了研究。文中详细介绍了窄带干扰抑制的关键性算法。通过对算法的 Matlab 仿真和在 FPGA 中的实现,证明了算法的有效性。     

短波宽带波形干扰抑制技术

短波宽带波形是现代短波通信的最新研究成果,采用带宽扩展方式实现短波高速通信。短波信道存在的各种各样强干扰信号使得干扰抑制成为现代短波宽带通信急待解决关键问题之一。针对这种现象,提出了一种基于变换域选择的双门限干扰抑制方法,该算法可以有效地选择最佳变换域去抑制干扰。仿真结果表明这种干扰抑制方法能够抑制不同类型干扰信号,在干扰环境下短波宽带波形具有较好传输性能。     

Analysis of the Narrowband Interference Effect on OFDM Timing Synchronization

In OFDM systems, the symbol timing synchronization is needed to find an estimate of where the symbol starts. The most popular of the pilot-aided timing estimators is the one proposed by Schmidl and Cox (S&C) ["Robust Frequency and Timing Synchronization for OFDM," IEEE Transactions on Communications, vol. 45, no. 12, pp. 1613-1621, Dec. 1997]. Generally, the proper action of the timing estimator may be strongly affected by the presence of disturbances, like narrowband interference (NBI) signals. This paper investigates the effect of NBI signals, which may arise in the OFDM band as the spectrum becomes more crowded, on the timing synchronization for OFDM systems. The performance of the S&C symbol timing synchronizer is evaluated in an analytical way in the presence of narrowband interferers. Also, the probabilities of both missing and false detection of a training sequence are addressed. Further, simulations have been carried out to verify the validity of the approximations in the analysis.     

Outage Analysis of OFDM‐Based Cognitive AF Relay Network in the Presence of Narrowband Interference

Orthogonal frequency‐division multiplexing (OFDM) is one of the most widely used technologies in current wireless communication systems and standards. Cognitive radio (CR) provides a robust solution to the problem of spectrum congestion as it offers opportunistic usage of frequency bands that are not occupied by primary users. Due to the underlying sensing, spectrum shaping, scaling, and interoperable capabilities of OFDM, it has been adapted as a best transmission technology for CR wireless systems. However, the performance of an OFDM‐based CR wireless system is affected by the existence of narrowband interference (NBI) from other users. Further, due to carrier frequency offset in NBI sources, NBI energy may spread over all subcarriers of an OFDM signal. In this paper, a fixed Amplify‐and‐Forward (AF) relay that operates at a frequency band that is different from that of direct mode is introduced to suppress the effect of NBI. Analytical expressions are derived for outage probability in direct, AF‐relay, and incremental relaying modes. The outage performance of the proposed AF relay–based CR network is proven to be better than that of direct mode.     

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.     

An EM-based frequency offset estimator for OFDM systems with unknown interference

We consider an orthogonal frequency-division multiplexing (OFDM) system and address the problem of carrier frequency estimation in the presence of narrowband interference (NBI) with unknown power. This scenario is encountered in emerging spectrum sharing systems, where coexistence of different wireless services over the same frequency band may result into a remarkable co-channel interference, and also in digital subscriber line transmissions as a consequence of the cross-talk phenomenon. A possible solution for frequency recovery in OFDM systems plagued by NBI has recently been derived using the maximum-likelihood criterion. Such scheme exhibits good accuracy, but involves a computationally demanding grid-search over the uncertainty frequency range. In the present work, we derive an alternative method that provides frequency estimates in closed-form by resorting to the expectation-maximization algorithm. This makes it possible to achieve some computational saving while maintaining a remarkable robustness against NBI.     

一种简易的正交频分多路系统的帧同步方法

提出了一个新的基于数据的帧同步方法.该方法基于接收到OFDM信号的同相部分和正交相部分的符号比特,导出最大似然的方法,而且,通过几个帧的求平均可以显著地提高产生的帧同步时钟的稳定性.仿真结果表明这种简单的求平均的帧同步方法可以用于OFDM系统.     

基于选择映射SLM降低OFDM信号峰平比的改进方案

本文针对OFDM系统中高峰均比问题,在基于正交映射降低峰平比的方法上提出了一种改进方案——随机分组正交映射（Random Group Design SLM）,即在SLM前加入了对信号随机分组处理,再选择峰均比最小的一路信号作为输出,本文并对这种方法进行了多种条件下的系统仿真,实验结果表明这种方法在改善OFDM传输信号峰平比上,比SLM方法有明显的改善。     

Non-cooperative signal modulation recognition algorithm based on joint feature parameter extraction

Aiming at the problem that in the current electromagnetic environment,the modulation method is complicated,the frequency-consuming equipment increases,the spectrum is congested,and the electromagnetic environment interference increases,the algorithm of OFDM signal detection and subcarrier identification in the background of non-cooperative communication were deeply studied.Using the different distribution states of OFDM signals and single carrier signals in the time domain,a joint characteristic parameter was proposed to solve the existence problem of OFDM in the received signal.For the phase shift and frequency offset problems caused by the channel transmission to the signal,by using the periodic stability the blind parameter estimation was performed to obtain the signal prior information.On the basis of the obtained signal prior information,a multi-level classification and recognition method for non-cooperative OFDM signal sub-carrier signals was proposed.Therefore,a model based on non-cooperative communication system OFDM signal detection and subcarrier modulation identification was designed,and finally modulation identification of unknown signals was completed.Simulation experiments show that in non-cooperative communication systems,OFDM signals and single-carrier signals can be accurately identified,and ideal modulation recognition effects can be achieved on empty subcarriers,QPSK,and 16QAM in the receiver OFDM signal subcarriers,overcoming the channel transmission band The problems of phase shift and frequency offset have improved the accuracy of modulation mode identification.     

基于CEEMD和排列熵的SAR窄带干扰抑制方法

为了有效抑制合成孔径雷达（SAR）系统中常见的窄带干扰（NBI）,本文提出一种基于互补集合经验模态分解（CEEMD）和排列熵（PE）的NBI抑制方法。矩峰度系数法用于检测原始回波中是否存在NBI,对包含NBI的回波使用CEEMD将其分解为一系列本征模态函数（IMF）。计算所有IMF排列熵得到全局阈值以区分NBI和有用信号,并使用去除NBI后的IMF分量重建信号以获得良好聚焦的SAR图像。结果表明：所提方法能有效克服经验模态分解（EMD）带来的模态混叠问题,且干扰抑制性能优于传统频域陷波法及基于EMD的NBI抑制方法。     

基于OFDM的POF通信PAPR抑制算法仿真与分析

OFDM技术能有效解决塑料光纤（POF）信道中频率选择性衰落及码间干扰等问题。这里在POF通信中引入OFDM技术,建立OOFDM通信模型,分析了高峰均比（PAPR）对POF系统的影响。提出采用脉冲整形技术改变原始数据相位和幅度的分布来抑制PAPR,通过仿真分析了不同基带调制方式对PAPR抑制性能影响,并与几种常见PAPR抑制方法进行比较,最后对模型的整体性能进行仿真。仿真结果表明该技术计算复杂度较小,效率比其他方法高很多,结合QPSK信号调制,降低峰均比效果明显,能有效降低BER值,提高信号质量。     

基于子空间分解的OFDM信道盲辨识

该文提出一种基于子空间分解的正交频分复用(OFDM)信道的盲辨识算法,将OFDM信号等效为单输入多输出的过采样信号,采用过采样信号的循环稳态特性和子空间分解方法估计信道参数,算法不需要任何训练序列和周期性的引导信号,实现了0FDM信道的盲辨识。对于宽带OFDM移动通信系统,通常子信道数较大,信道响应持续时间短于0FDM符号周期,因此,可以将整个系统分为若干个子系统,各子系统分别进行信道辨识,能有效地降低信道估算的复杂性。