中压配电线通信系统脉冲噪声处理的阈值优化算法

OFDM用于实现高速电力线通信越来越受关注。脉冲噪声是电力线信道的主要干扰之一。该文在消隐非线性输出SNR分析的基础上,提出了OFDM系统脉冲噪声处理的阈值优化算法。仿真结果显示,如果OFDM系统的子载波数足够大,则实际系统输出SNR与理论表达式可以很好吻合。对于给定的脉冲指数,存在一个最低最优阈值;不同的脉冲指数A,其最低最优阈值不同,A越小,最低最优阈值反而越大;消隐器输出SNR及其性能增益是信号脉冲噪声比(SINR)的函数:在低SINR和高SINR下,输出SNR呈线性变化,性能增益分别趋近于定值;在中间SINR下,消隐器输出SNR及其性能增益是SINR的非线性函数。本消隐非线性阈值的优化算法可以改进脉冲噪声检测算法的性能,进而大大改善OFDM系统在中压配电线脉冲噪声环境中的总体性能。     

水声通信系统中基于迭代自适应的脉冲噪声抑制方法

针对水声通信系统中脉冲噪声抑制问题,提出了一种迭代自适应的脉冲噪声抑制方法。基于 OFDM子载波之间的正交性,该方法首先利用空子载波矩阵从接收信号中提取出背景噪声和脉冲噪声。然后,利用空子载波矩阵构造导频矩阵,得到脉冲噪声的干扰协方差矩阵,并在加权最小二乘准则下通过对代价函数的求解得到脉冲噪声的闭式解。最后,在接收信号中减去脉冲噪声的估计值,完成对脉冲噪声的抑制。仿真结果表明,本文方法有效降低了水声通信系统的误码率,且在高信干噪比下性能提升更加明显。     

一种改进的电力线通信系统脉冲噪声抑制方法

为了抑制脉冲噪声对电力线正交频分复用（OFDM）通信系统的影响,最常用的方法之一是在接收端OFDM解调器之前前置一个置零非线性单元,即传统置零法。然而,由于引入了非线性失真,其性能并不理想。针对传统置零法引起的非线性失真问题,提出了一种基于迭代消除非线性失真的改进置零法。首先,对接收到的时域OFDM信号进行脉冲噪声检测和置零处理;然后,在频域利用已检测的符号来重构时域置零处理引入的非线性失真,并通过迭代提高重构的准确性;最后,从频域接收信号中减去重构的非线性失真。仿真结果表明,所提改进算法与传统置零法相比,有非常大的性能提升,增强了电力线OFDM通信系统对脉冲噪声的抵抗能力。     

Joint channel and impulsive noise estimation method for OFDM systems

Aiming at the impulsive noise occurring in OFDM systems,an impulsive noise mitigation algorithm based on compressed sensing theory was proposed.The proposed algorithm firstly treated the channel impulse response and the impulsive noise as a joint sparse vector by exploiting the sparsity of both them.Then the sparse Bayesian learning framework was adopted to jointly estimate the channel impulse response,the impulsive noise and the data symbols,in which the data symbols were regarded as unknown parameters.Compared with the existing impulsive noise mitigation methods,the proposed algorithm not only utilized all subcarriers but also did not use any a priori information of the channel and impulsive noise.The simulation results show that the proposed algorithm achieves significant improvement on the channel estimation and bit error rate performance.     

On the use of cascade structure to correct impulsive noise in multicarrier systems

We propose a new decoding algorithm based on a cascade structure for impulsive noise correction in multicarrier systems such as Orthogonal Frequency Division Multiplexing (OFDM) based systems. This new cascade structure based algorithm has the advantage to lead on one hand to a reducedcomplexity implementation in an OFDM demodulator and on the other hand to overcome the lacks of other algorithms dedicated for impulsive noise correction. To do so, we start the derivation by investigating closed-form analytical expressions of the a priori probabilities used in hypotheses tests that are necessary for the different steps needed for the execution of the cascade structure based decoding algorithm. Such closed-form expressions for the a priori probabilities, result in efficient setups of the threshold values used for the execution of the decoding algorithm. Furthermore, we show that this cascade structure can be applied to efficiently cancel the impulsive noise in OFDM systems. As the clipping event, present in OFDM systems, can be seen as an additive impulsive noise, we prove that after introducing some minor modifications, we can apply the proposed cascade structure to significantly reduce the Peak to Average Power Ratio (PAPR) level in such systems. Simulation results are given to illustrate the usefulness of the proposed algorithm results in practical OFDM based communication systems such as Hiperlan 2.     

An interconnected type-1 fuzzy algorithm for impulsive noise cancellation in multicarrier-based power line communication systems

This paper introduces an interconnected type-1 fuzzy algorithm which is trained by a modified version of the Scaled Conjugated Gradient method for impulsive noise cancellation in discrete multitone/orthogonal frequency-division multiplexing (DMT/OFDM)-based systems for broadband power line communications. The advanced algorithm makes use of the fuzzy systems capacity of dealing with uncertainties to reduce the presence of high-power impulsive noises while the DMT/OFDM technique copes with the severe intersymbol interference observed in power line channels. As a result, for a given error probability, a high number of bits can be allotted to each subchannel due to the signal-to-noise ratio enhancements achieved by the proposed fuzzy algorithm. The simulation results show that the novel fuzzy algorithm not only achieve a high data rate, but it also outperforms the standard impulsive noises techniques and other computational intelligence-based techniques, especially in the presence of additive and high-power impulsive noises.     

Adaptive noise mitigation based on peak estimate and feedback compensation in power line communication

According to the problem that the threshold for traditional blanking depends on the characteristic parameters of noise and exist large deviation,an adaptive noise mitigation algorithm based on peak estimate and feedback compensation(ANMPEFC)in power line communication was proposed.First,SLM mapping preprocessing method was employed to reduce the PAPR of emission signal,peak information was used to estimate the frequency of the received signal and the relationship between peak frequency and impulse characteristics was established.Next,received signal was processed by blanking block and feedback compensation block adaptively according to estimated pulse frequency.Finally, performance of proposed algorithm and existing algorithms were analyzed based on threshold deviation.According to the results from simulation,it is clearly demonstrated that the proposed ANMPEFC can work in power line impulse noise environment without knowing the noise characteristics and has better performance in contrast to existing impulse noise suppression algorithm.     

Theoretical analysis of iterative signal reconstruction for impulsive noise mitigation in OFDM systems

In this paper a theoretical analysis of the iterative signal reconstruction algorithm for impulsive noise mitigation in orthogonal frequency‐division multiplexing (OFDM) systems is developed. The following main results are developed: first, analytical model for the total noise in the frequency domain, and second the model for the total noise probability density function (pdf) in the frequency domain, both defined for each step of the iterative reconstruction process. Finally, based on the pdf of the total noise, explicit expressions for BER in kth iteration are defined as well. The main intention of the paper is to present the approach to theoretical analysis of the iterative impulsive noise mitigation algorithm that has not yet been appeared in the literature, because the theoretical analysis of the noise pdf during iterations has been considered as too complex a problem. Analyses and analytical results presented in the paper are given for scenario with a fixed number of noise impulses per frame. However, this is not a handicap of the proposed approach, since all presented models can be used as building blocks for scenarios with other impulsive noise distributions including Bernoulli–Gaussian and Middleton's Class A. Copyright © 2009 John Wiley & Sons, Ltd.     

基于OFDM技术的电力线通信系统的相位噪声估计与补偿

OFDM电力线通信系统对相位噪声非常敏感。由于电力线信道噪声大、衰减强,OFDM信号通过后发生严重失真,基于导频的公共相位误差估计效果变差。提出一种更可靠的相位噪声估计和补偿算法,能够更准确地估计公共相位误差。仿真表明该方法能够有效地抑制相位噪声。     

Equalization attacks against OFDM: analysis and countermeasures

This paper introduces, investigates, and proposes power‐efficient equalization jamming attacks against the orthogonal frequency division multiplexing (OFDM) and possible countermeasures. Signals known a priori, called pilot tones, are employed in the conventional OFDM‐based systems to estimate the channel response and perform equalization. Attacks against these pilot tones can hamper equalization and degrade target's performance. This paper begins with noise‐based pilot tone jamming and moves onto pilot nulling attack. The paper embraces two mitigation strategies of randomizing the pilot tones. The paper presents mathematical model of effective noise per symbol and simulation results for OFDM systems with conventional and randomized pilot‐tones under such attacks. The paper concludes that the noise‐based pilot tone attacks are power efficient than conventional attacks, and the pilot nulling is capable of doing the most damage, but in the expense of additional channel state information. The paper also claims that the mitigation strategies offer a remedy, but works relatively poorly when no jammer is present. Copyright © 2015 John Wiley & Sons, Ltd.     

A robust adaptive weighted constant modulus algorithm for blind equalization of wireless communications systems under impulsive noise environment

A robust adaptive weighted constant modulus algorithm is proposed for blind equalization of wireless communication systems under impulsive noise environment. The influence of the impulsive noise is analyzed based on numerical analysis method. Then an adaptive weighted constant modulus algorithm is constructed to adaptively suppress impulsive noise. Theoretical analysis is provided to illustrate that the proposed algorithm has a robust equalization performance since the impulsive noise is adaptively suppressed. Moreover, the proposed algorithm has stable and quick convergence due to avoidance of large misadjuntment and adoption of large step size. Simulation results are presented to show the robust equalization performance and the fast convergence speed of the proposed algorithm under both impulsive noise and Gaussian noise environments.     

Combined ML and QR Detection Algorithm for MIMO‐OFDM Systems with Perfect ChanneI State Information

An effective signal detection algorithm with low complexity is presented for multiple‐input multiple‐output orthogonal frequency division multiplexing systems. The proposed technique, QR‐MLD, combines the conventional maximum likelihood detection (MLD) algorithm and the QR algorithm, resulting in much lower complexity compared to MLD. The proposed technique is compared with a similar algorithm, showing that the complexity of the proposed technique with T=1 is a 95% improvement over that of MLD, at the expense of about a 2‐dB signal‐to‐noise‐ratio (SNR) degradation for a bit error rate (BER) of 10⁻³. Additionally, with T=2, the proposed technique reduces the complexity by 73% for multiplications and 80% for additions and enhances the SNR performance about 1 dB for a BER of 10⁻³.     

Adaptive subcarrier bandwidth and power in OFDM‐based cognitive radio systems for high mobility applications

OFDM‐based cognitive radio systems are spectrally flexible and efficient, but they are vulnerable to intercarrier interference (ICI), especially in high mobility environments. High mobility of the terminal causes large Doppler frequency spread resulting in serious ICI. Such ICI severely degrades the system performance, which is ignored in the existing resource allocation of OFDM‐based cognitive radio systems. In this paper, an adaptive subcarrier bandwidth along with power allocation problem in OFDM‐based cognitive radio systems for high mobility applications is investigated. This adaptive subcarrier bandwidth method should choose the suitable subcarrier bandwidth not only to balance the tradeoff between ICI and intersymbol interference but also to be large enough to tolerate an amount of Doppler frequency spread but less than the coherence bandwidth. The power budget and interference to primary users caused by cognitive radio users are imposed for primary users' protection. With these constraints, a joint optimization algorithm of subcarrier bandwidth and power allocation is proposed to maximize the bandwidth efficiency of OFDM‐based cognitive radio systems in such conditions. Numerical simulation results show that the proposed algorithm could maximize the system bandwidth efficiency and balance this tradeoff while satisfying the constraints. Copyright © 2012 John Wiley & Sons, Ltd.     

某对空情报雷达同频异步冲击干扰抑制方法研究

 多部雷达同时同地工作面临电磁兼容问题,某对空情报雷达因对方同频段雷达发射机产生的冲击干扰严重影响了探测性能.本文根据干扰特性提出一种基于恒虚警检测的冲击干扰时域抑制新算法.该算法应用恒虚警方式自适应设置干扰检测门限,利用逻辑判断进行干扰定位,增强了干扰检测的鲁棒性;运用时域相消在滤除干扰的同时保留了地杂波,防止因杂波泄漏而降低雷达探测性能.实测数据处理验证了算法的有效性.     

Stable adaptive channel estimation method under impulsive noise environments

Channel estimation is one of the key technologies for ensuring reliable wireless communications under impulsive noise environments. This paper studies robust adaptive channel estimation methods for mitigating harmful impulsive noises, which are described as alpha‐stable (α ‐stable) distribution models. Traditional adaptive channel estimation using the second‐order statistics based least mean square (SOS‐LMS) algorithm does not perform well under α ‐stable noise environments, even though it was considered one of attractive approaches for estimating channels in the case of Gaussian noises. Unlike the traditional SOS‐LMS algorithm, in this research, we propose a stable sign‐function‐based LMS algorithm, which can mitigate the impulsive noises. Specifically, we first construct the cost function with minimum ℓ ₁‐norm error criterion and then derive the updating equation of the proposed algorithm. Compared with the traditional SOS‐LMS, the effectiveness of the proposed algorithm is validated via Monte Carlo simulations in various α ‐stable noise scenarios. Copyright © 2015 John Wiley & Sons, Ltd.     

A robust auto‐adaptive approach for serial acquisition of generalized multi‐carrier spread spectrum in multipath fading mobile channels

In this paper, a new robust auto‐adaptive approach for pseudo‐noise (PN) code acquisition is proposed. It is applied to the generalized multi‐carrier direct‐sequence code‐division multiple‐access (MC DS‐CDMA) systems communicating over frequency‐selective multipath Rayleigh fading channels. This new approach is based on the constant false alarm rate (CFAR) detection algorithm, referred here as automatic selection partial sum ordered statistics (ASPSOS)‐CFAR. The proposed approach does not require any prior information about the background environment and uses maximum likelihood estimation (MLE) method to detect the interfering signals group in the ranked cells for the full reference window. Once this group is identified and censored, the remaining smaller ranked cells are combined to form an estimate of the background noise level to compute the adaptive threshold. Through simulations, the performance of the proposed detector is analyzed and compared with traditional CFAR detectors based on fixed or automatic censoring algorithms. The obtained results show that the proposed detector eliminates the drawbacks of the previously related detectors and offers a robust detection performance to enhance the acquisition process in heterogeneous background environments.     

应用形态学的自适应门限干扰检测算法

该文针对通信信号中背景噪声复杂的问题,应用数字形态学的信号预处理方法,能较好地滤除背景噪声;又由于单一门限值难以实现对不同宽度干扰的检测,提出一种应用形态学自适应门限的干扰检测算法。此算法首先对信号谱线进行功率谱估计,然后利用形态学的方法进行预处理,再根据信号功率谱的分布情况,选取不同的门限值,实现门限的自适应,为检测不同占有用信号带宽大小的窄带干扰提供了有效的方法。该文提出的方法不会受噪底变化的影响,计算量小,复杂度较低,适用于星上卫星通信的实时频谱监测。经过Matlab仿真实验得出,当采用结构元素长度为25的扁平型结构元素时,通过形态学中的膨胀预处理方法以及自适应门限可以得到检测效果比传统的连续均值去除算法(CME)算法有6dB以上的提升。      

Comparison of coded orthogonal frequency division multiplexing and multicarrier code division multiple access systems for power line communications

Orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC‐CDMA) systems are comparatively evaluated for power line communications (PLC) in a frequency‐selective fading environment with additive coloured Gaussian noise which is used to model the actual in‐home power line channel. OFDM serves as a benchmark in order to measure the performance of various MC‐CDMA systems, since multicarrier modulation systems are considered the best candidate for this kind of channel. Both single‐user and multi‐user cases are taken into account, making use of the appropriate combiner schemes to take full advantage of each case. System efficiency is enhanced by the application of different coding techniques, a fact which shows that powerful coding can make the difference under such a hostile medium. The impact of block interleaving is investigated, while the simulation examines how different modulation schemes fair under the imposed channel conditions as well. The performance of the system is assessed by the commonly used bit error rate vs signal‐to‐noise ratio diagrams and there is also a comparison regarding throughput efficiency among all the tested systems. As stated in Section 4, a promising PLC application is attained. Copyright © 2004 John Wiley & Sons, Ltd.     

抑制脉冲型噪声的限幅器自适应设计

针对脉冲型噪声的抑制问题,该文提出一种自适应的限幅器设计方法。该方法以效能函数为指标,采用自适应搜索算法,自动寻找削波器和置零器的最佳门限,且能适用于未知噪声分布的情形。首先分析了效能与非线性函数的关系,给出关键的优化问题。然后考虑到效能函数计算复杂,提出基于线搜索的自适应设计算法。其次针对未知分布情况,考虑非参数化的概率密度估计,该算法能够稳健运行且基本取得最优设计效果。最后,结合两种非高斯噪声和实测大气噪声数据仿真,结果表明：该文方法可自适应寻找最佳门限,使削波器和置零器效能达到最佳;当噪声分布未知时,该文方法无需假设噪声模型,可与非参数化概率密度估计方法结合,取得最优检测效果。

     

Adaptive robust impulse noise filtering

It is well known that when data is contaminated by non-Gaussian noise, conventional linear systems may perform poorly. The paper presents an adaptive robust filter (adaptive preprocessor) for canceling impulsive components when the nominal process (or background noise) is a correlated, possibly nonstationary, Gaussian process. The proposed preprocessor does not require iterative and/or batch processing or prior knowledge about the nominal Gaussian process; consequently, it can be implemented in real time and adapt to changes in the environment. Based on simulation results, the proposed adaptive preprocessor shows superior performances over presently available techniques for cleaning impulse noise. Using the proposed adaptive preprocessor to clean the impulsive components in received data samples, conventional linear systems based on the Gaussian assumption can work in an impulsive environment with little if any modification. The technique is applicable to a wide range of problems, such as detection, power spectral estimation, and jamming or clutter suppression in impulsive environments