Impulsive Interference Research Articles

Kernel Affine Projection Sign Algorithms for Combating Impulse Interference

The kernel method has been successfully applied to nonlinear adaptive filtering. This brief presents a kernel affine projection sign algorithm (KAPSA), which is a nonlinear extension of the affine projection sign algorithm (APSA). The proposed KAPSA combines the benefits of the kernel method and the APSA, and is robust against non-Gaussian impulse interference. In order to further improve the filtering performance, a variable step-size adjustment is incorporated into the KAPSA, resulting in a new variable step-size kernel APSA (VSS-KAPSA) without increasing the computational burden. Simulations in the context of time-series prediction show that both the KAPSA and the VSS-KAPSA are robust against impulse interference and that both outperform other affine projection algorithms in terms of steady-state mean square errors.

Two variants of the sign subband adaptive filter with improved convergence rate

Sign algorithms (SAs) have attracted much attention because of their robustness against impulsive interference. To reduce the computational cost of SAs, a sign subband adaptive filter (SSAF) has recently been proposed. However, the SSAF converges slowly and the convergence rate of the SSAF does not increase with the number of subbands. In this paper, two variants of the SSAF, called the affine projection SSAF (AP-SSAF) and the proportionate SSAF (P-SSAF), are proposed to solve this problem. The AP-SSAF updates the tap-weight vector based on several previous input vectors, which can not only maintain robustness against impulsive interference, but also increase the convergence rate for both white and colored input signals; the P-SSAF incorporates a gain distribution matrix into the SSAF to proportionately adapt the tap-weight vector of the adaptive filter, which can both maintain robustness against impulsive interference and increase the convergence rate of the SSAF for sparse system identification. Simulation results are presented to demonstrate the improved performance of the AP-SSAF and the P-SSAF.

Sign subband adaptive filter with ℓ 1 ‐norm minimisation‐based variable step‐size

A new variable step-size sign subband adaptive filter (VSS-SSAF), not requiring any a priori information, is proposed by minimising the l1-norm of the subband a posteriori error under a box-constraint on the step-size. In addition, an efficient numerical procedure for updating its VSS is introduced to solve the non-differentiable convex problem. The proposed algorithm provides comparable or better convergence performance, when compared with the recent VSS-SSAF (minimising the mean-squares deviation with a priori knowledge of noise variance) or other conventional algorithms aimed at robustness against impulsive interferences.

Interference of Impulses, Scattered and Radiated by Bodies of Spheroidal Form

With the help of the Fourier transform and characteristics of the scattering of the stationary (continuous) sound signal are calculated the interference of the impulses, scattered and radiated by bodies of the prolate spheroidal form (ideal and elastic), with the harmonic and the frequency-modulated filling.

A Novel Mitigation Scheme for JTIDS Impulsive Interference on LDACS System Based on Sensing and Symbol Retransmission

Future digital air/ground communication systems (LDACS) will operate on the L-Band where the coexistence with existing legacy systems shall be guaranteed. This paper proposes a scheme to detect and...

Clipping Demapper for LDPC Decoding in Impulsive Channel

This paper deals with the performance of Low-Density Parity-Check codes in impulsive interference modeled by α-stable random variables. In case of α-stable noise, the optimal inputs of the belief propagation decoder are complex to obtain. We propose to use the simple clipping approach that reduces the impact of large noise values. Our main contribution is to give three different approaches to obtain the parameters of the clipping function and to assess the performance of the decoder. We show that a look-up table whose values are pre-determined, thanks to the Density Evolution tool, is the most efficient approach.

Sub-Optimum Receiver Architecture for AWGN Channel with Symmetric Alpha-Stable Interference

In many scenarios, the undesirable disturbance at a communication receiver has to be modeled as the sum of Gaussian noise and impulsive interference for which closed form probability density function (pdf) generally does not exist. This makes optimum receiver implementation difficult. In this paper, motivated by the heavy tail nature of the resultant pdf, an alternate parametric solution is proposed. After estimation of the appropriate parameters, the alternate solution may then be written in closed form, leading to a relatively simple architecture. Simulation results show that the proposed receiver performance, in terms of bit error rate (BER), is almost indistinguishable from the optimum receiver while outperforming other sub-optimum receivers. Noise parameter estimation using empirical characteristic functions is also discussed.

CLOSED-FORM PDF FOR MULTIUSER TR-UWB SYSTEMS UNDER GAUSSIAN NOISE AND IMPULSIVE INTERFERENCE

In most existing transmitted-reference ultra-wideband (TR-UWB) communication systems, receivers use the standard Gaussian approximation (SGA) for multiuser interference (MUI). It is an assumption used in most conventional multiuser systems, where the MUI tends to a Gaussian process by the central limit theorem, and convergence is relatively fast with respect to the number of users. However, for TR-UWB systems which are developed for short-range applications, we have a small number of active users. In this case, significant performance degradation is found in TR-UWB receivers due to the impreciseness of SGA. In this paper, we show that the Middleton class-A model is a more appropriate statistical model for MUI modeling in TR-UWB systems than the often used SGA. A closed-form expression for the probability density function (PDF) of the TR-UWB system under MUI, Gaussian noise and impulsive alpha-stable interference is developed. All these analytical results are confirmed by numerical simulations. (17 References).

Decision Boundary Evaluation of Optimum and Suboptimum Detectors in Class-A Interference

The Middleton Class-A (MCA) model is one of the most accepted models for narrow-band impulsive interference superimposed to additive white Gaussian noise (AWGN). The MCA density consists of a weighted linear combination of infinite Gaussian densities, which leads to a non-tractable form of the optimum detector. To reduce the receiver complexity, one can start with a two-term approximation of the MCA model, which has only two noise states (Gaussian and impulsive state). Our objective is to introduce a simple method to estimate the noise state at the receiver and accordingly, reduce the complexity of the optimum detector. Furthermore, we show for the first time how the decision boundaries of binary signals in MCA noise should look like. In this context, we provide a new analysis of the behavior of many suboptimum detectors such as a linear detector, a locally optimum detector (LOD), and a clipping detector. Based on this analysis, we insert a new clipping threshold for the clipping detector, which significantly improves the bit-error rate performance.

Joint Estimation with Time Delay and Doppler Frequency Shift in the Multi-Carrier Acoustic Communication

Timing synchronization is very important in the multi-carrier acoustic communication system. With regard to the transmitted signal of the baseband OFDM in the acoustic communication system, which is in the complex environment over the acoustic channel gauss noisy and SαS impulse noisy interference,this paper proposes a joint time delay and Doppler frequency shift estimation algorithm based on the fractional lower order cyclic cross ambiguity function with multi-cycle frequency(FCCAF). This method combines the fractional lower order moment with the feature of cycle stationary, and can detect the signal characteristic of cyclo-stationarity under the SaS impulse noisy. The algorithm takes full advantage of the cycle frequency information of the signal, and can be equipped with the capacity of suppression interference. The simulation results show that the algorithm proposed in this paper can work very well in the presence of the impulse noise and interference, the superior to that algorithm based on the second order cycle fuzzy function, and is a robust joint estimation algorithm with time delay and Doppler shift.

STABILITY OF THE ESTIMITATION OF FREQUENCY OF THE HARMONIOUS SIGNAL WITH THE CONSTANT COMPONENT TO PULSE HINDRANCES

The impulse interference impact on robustness of quazioptimal frequency estimation of harmonic signal with additive constant component and Gaussian noise are researched. The critical conditions for instability are defined. The dependencies of frequency estimation precision on parameters chaotic impulse interferences are obtained by statistic modeling.

A Cyclic Correlation-Based Blind SINR Estimation for OFDM Systems

A blind signal-to-interference-plus-noise ratio (SINR) estimation method is proposed for orthogonal frequency division multiplexing (OFDM) systems in the presence of impulsive noise over multi-path fading channels. By exploiting the cyclostationarity of the OFDM signal, the received signal power is decomposed into the transmitted signal power and the impulsive interference plus the Gaussian noise power, which are estimated respectively using the cyclic correlations of the received signal. Simulation results are provided to examine the performance of the proposed estimation method and show that the estimated results approach the true values of SINR.

Mitigation of Impulsive Frequency-Selective Interference in OFDM Based Systems

In this paper, an algorithm for mitigating impulsive interference in OFDM based systems is presented. It improves the conventional blanking nonlinearity approach for interference mitigation, which typically distorts the entire received signal, by combining the blanked and the original signal. The algorithm uses a Neyman-Pearson like testing procedure to detect interference at individual sub-carriers. Provided interference is detected, the blanked and the original received signals are then optimally combined such as to maximize the signal-to-interference-and-noise ratio. The algorithm does not require any prior knowledge about the impulsive interference and only marginally increases computational complexity as compared to the conventional blanking nonlinearity approach. Numerical results demonstrate the superior performance of the proposed scheme.

Research of influence of pulse interference on the tone rail circuits

The work is devoted to the influence of pulse interference on the tone rail circuits. As a result of simulations, the mechanism of influence on the track receiver of tone rail circuit single impulse interference, periodic and random sequence of pulses has been investigated; «dangerous» levels of noise have been defined.

Impulsive interference in communication channels and its mitigation by SPART and other nonlinear filters

A strong digital communication transmitter in close physical proximity to a receiver of a weak signal can noticeably interfere with the latter even when the respective channels are tens or hundreds of megahertz apart. When time domain observations are made in the signal chain of the receiver between the first mixer and the baseband, this interference is likely to appear impulsive. The impulsive nature of this interference provides an opportunity to reduce its power by nonlinear filtering, improving the quality of the receiver channel. This article describes the mitigation, by a particular nonlinear filter, of the impulsive out-of-band (OOB) interference induced in High Speed Downlink Packet Access (HSDPA) by WiFi transmissions, protocols which coexist in many 3G smartphones and mobile hotspots. Our measurements show a decrease in the maximum error-free bit rate of a 1.95 GHz HSDPA receiver caused by the impulsive interference from an OOB 2.4 GHz WiFi transmission, sometimes down to a small fraction of the rate observed in the absence of the interference. We apply a nonlinear SPART filter to recover a noticeable portion of the lost rate and maintain an error-free connection under much higher levels of the WiFi interference than a receiver that does not contain such a filter. These measurements support our wider investigation of OOB interference resulting from digital modulation, which appears impulsive in a receiver, and its mitigation by nonlinear filters.

CRLB for DOA Estimation in Gaussian and Non-Gaussian Mixed Environments

The determination of Cramer-Rao lower bound (CRLB) as an optimality criterion for the problem of Direction-of-arrival (DOA) estimation is a very important issue. Several CRLBs on DOA estimation have been derived for Gaussian noise. However, a practical channel is affected by not only Gaussian background noise but also non-Gaussian noise such as impulsive interference. This paper derives the deterministic CRLB for Gaussian and non-Gaussian mixed environments. Since non-parametric kernel method is used to build the probability density function (PDF) of non-Gaussian noise, the CRLB derived is suitable for various noise distributions with or without symmetric PDF. The relationship between the CRLB for Gaussian noise and the proposed CRLB is also investigated. Theoretical analysis shows that the proposed CRLB provides a unified representation for both the cases of Gaussian and mixed environments. Computer simulations are included to verify the derived CRLB in different noise environments.

Robust Tracking Time-Varying High-Frequency CW Telegraph Signal

Continuous wave (CW) telegraph is a crucial communication means for high-frequency tactical communication. But there is serious frequency deviation and impulsive noise in High-frequency channel, thus the conventional tracking method based on Gaussian noise assumption may lose the track of time-varying CW signal. A new robust kalman filter-based tracker is proposed in this paper to extract the time-varying CW signal in presence of impulsive interference, which uses a nonlinear statistical model. Simulation studies show this method can dynamically track nonstationary CW signal and effectively suppress burst impulse noise.

Memory improved proportionate affine projection sign algorithm

A new proportionate affine projection sign algorithm is proposed for network echo cancellation. It uses a recursive procedure and takes into account the previously computed proportionate coefficients. It is shown that the proposed algorithm can obtain a lower steady-state misalignment than other affine projection sign algorithms for different echo paths, impulsive interferences and step sizes.

Efficient Implementation of the Affine Projection Sign Algorithm

-norm optimization-based sign algorithms (SAs) are more robust against impulsive interference than -norm optimization-based adaptive filtering algorithms. However, most SAs suffer from slow convergence rate, especially for highly correlated input signals. In order to overcome this problem, recently, an affine projection SA (APSA) has been proposed , which exhibits fast convergence rate. In this letter, we first analyze the computational complexity of the APSA in detail and then apply a recursive approach proposed for the affine projection algorithm (APA) to the APSA to reduce its computational complexity. Analysis results show that the computational complexity of the APSA with the efficient implementation method is even lower than that of the classical fast affine projection (FAP) algorithm.

Relation between impulsiveness correction factor and amplitude probability distribution of impulsive interference for estimating its impact on communication systems

Relation between impulsiveness correction factor and amplitude probability distribution of impulsive interference for estimating its impact on communication systems