Impulsive Channels Research Articles

Constrained system identification in the presence of impulsive channel noise against noisy input

Constrained system identification in the presence of impulsive channel noise against noisy input

Robust time delay estimation based on non-Gaussian impulsive acoustic channel

Robust time delay estimation based on non-Gaussian impulsive acoustic channel

Spatially Coupled Generalized Low-Density Parity-Check Codes Over Class-A Impulsive Noise Channels

In this paper, a class of spatially coupled generalized low-density parity-check (SC-GLDPC) codes with minimum coupling width is introduced to mitigate the Class-A impulsive noise. Codes with minimum coupling width are beneficial to simple code structure, short window decoding delay, and small rate-loss. The SC-GLDPC code is constructed by coupling the multiple identical generalized low-density parity-check (GLDPC) codes. Decoding thresholds over impulsive channels are derived by a recursive extrinsic information transfer function approach and are further estimated by the fast prediction approach. An edge spreading optimization method is proposed to design SC-GLDPC codes with minimum coupling width. The simulation results show that the optimized SC-GLDPC codes with minimum coupling width can show capacity-approaching property over impulsive channels. Benefitting from spatial coupling and generalized check nodes the SC-GLDPC codes show better bit error rate performance over impulsive channels, compared with GLDPC codes and spatially coupled low-density parity-check (SC-LDPC) codes.

Upward negative leaders in positive triggered lightning: Stepping and branching in the initial stage

AbstractBy conducting comprehensive observation on the rarely triggered positive lightning flashes, two cases of upward negative leaders were quantitatively investigated with simultaneous data of current, optical, and electromagnetic field changes at fine time resolution. The impulsive channel current associated with the initial leader stepping involved pulse interval, peak, charge of 19.1 μs, 122.3 Å, 465.9 μC, and 20.3 μs, 58.4 Å, 267.2 μC, for the two cases, respectively. The negative charge of an individual step was nearly an order of magnitude larger than that of the positive leader step in triggered lightning. The upward negative stepped leader branches shortly after initiation, and consequently, the stepping‐caused current pulses became multipeaked, wider, and more frequent in waveforms. The main leader tip propagated at an average speed of 2.10 × 105 m/s, while its partial speed fluctuated a lot as was significantly influenced by the behaviors of subbranches development.

Neural networks applications for CDMA systems in non-Gaussian multi-path channels

Non-Gaussian noise is one of the most common noise models observed in wireless channels. This type of noise has severe impact on wireless systems with multiuser detection devices. In this paper, the issue of multiuser detection in non-Gaussian noise multipath channel is addressed. We also pay a close attention to the neural network applications, and propose a new robust neural network detector for multipath impulsive channels. The maximal ratio combining (MRC) technique is adopted to combine the multipath signals. Moreover, we discuss the performance of the proposed multiuser neural network decorrelating detector (NNDD), under class A Middleton model. Furthermore, the performance of the system under power imbalance scenario is shown. We show that the proposed NNDD has magnificent effect on the system performance. The system performance is measured through the bit error rate (BER). It is shown that the proposed robust receiver reduces the impact of the impulsive noise by processing the received signal and clipping the extreme amplitudes.

Robust Consensus in the Presence of Impulsive Channel Noise

A distributed average consensus algorithm robust to a wide range of impulsive channel noise distributions is proposed. This work is the first of its kind in the literature to propose a consensus algorithm which relaxes the requirement of finite moments on the communication noise. It is shown that the nodes reach consensus asymptotically to a finite random variable whose expectation is the desired sample average of the initial observations with a variance that depends on the step size of the algorithm and the receiver nonlinear function. The asymptotic performance is characterized by deriving the asymptotic covariance matrix using results from stochastic approximation theory. Simulations corroborate our analytical findings and highlight the robustness of the proposed algorithm.

Analytical bit error rate performance evaluation of an orthogonal frequency division multiplexing power line communication system impaired by impulsive and Gaussian channel noise

An analytical approach is presented to evaluate the bit error rate (BER) performance of a power line (PL) communication system considering the combined influence of impulsive noise and background PL Gaussian noise. Middleton class-A noise model is considered to evaluate the effect of impulsive noise. The analysis is carried out to find the expression of the signal-to-noise ratio and BER considering orthogonal frequency division multiplexing (OFDM) with binary phase shift keying modulation with coherent demodulation of OFDM sub-channels. The results are evaluated numerically considering the multipath transfer function model of PL with non-flat power spectral density of PL background noise over a bandwidth of 0.3–100 MHz. The results are plotted for several system and noise parameters and penalty because of impulsive noise is determined at a BER of 10−6. The computed results show that the system suffers significant power penalty because of impulsive noise which is higher at higher channel bandwidth and can be reduced by increasing the number of OFDM subcarriers to some extent. The analytical results conform well with the simulation results reported earlier.

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.

Robust Multiuser Detection in Chaotic Communication Systems over Non-gaussian Fading Channels

In this article, we deal with the problem of robust code division multiple access (CDMA) signal detection in a chaotic communication system transmitting across a Non-gaussian fading channel. Since the performance of robust multiuser detector depends on the selection of M-estimator and the spreading sequences, a new influence function is used to derive an improved robust detector for the problem of data detection in CDMA impulsive fading channels using chaotic spreading. Numerical results show that the proposed robustification offers improved performance over Huber’s minimax detector and outperforms the DPSK decorrelating detector, particularly when the channel is highly impulsive.

Channel Estimation for Powerline MC-CDMA System

Successful development of broadband over powerline is obviously a potential solution for wired communication systems with the existence of the powerline network. From past research, it is known that the powerline channel suffers from multipath fading, frequency selectivity and also impulsive noise. Multi Carrier Code Division Multiple Access (MC-CDMA) is a promising solution for an impulsive noise powerline channel. This paper starts with the MC-CDMA transmitter structure and focuses on powerline channel model, noise model and various types of available channel estimators. The main concern in Powerline Communication Systems is the existence of impulsive noise. The proposed pilot assisted channel estimation uses the modified least square estimator that reduces the effect of impulsive noise in the estimated channel impulse response.

Time-domain equalizer for multicarrier systems in impulsive noise

In multicarrier communication systems, a time-domain equalizer (TEQ) can be applied to shorten the channel impulse response and to eliminate inter-symbol interference (ISI). However, the presence of impulsive noise in the channel may paralyze the operation of TEQs and subsequently lead to poor error performance. In this paper, a multicarrier receiver that incorporates a constant false alarm rate algorithm and an iterative estimation technique (CFAR-IET) in conjunction with a TEQ is proposed to increase the robustness of the receiver against impulsive noise. Furthermore, an improved version of the CFAR-IET-TEQ scheme, which uses the buffering, sorting, removing and amplitude averaging (BSRA) processes, is presented. Performance comparisons of the proposed schemes with the existing Gaussian-optimized schemes are made. Simulation results show that the BSRA-IET-TEQ scheme is an effective approach to reduce symbol error rate (SER) in impulsive channels while performing satisfactorily in Gaussian channels. Copyright © 2011 John Wiley & Sons, Ltd.

Decoding of Turbo Codes in Symmetric Alpha-Stable Noise

This paper investigates the decoding of turbo codes in impulsive symmetric α-stable (SαS) noise. Due to the nonexistence of a closed-form expression for the probability density function (pdf) of α-stable processes, numerical-based SαS pdf is used to derive branch transition probability (btp) for the maximum a posteriori turbo decoder. Results show that in Gaussian noise, the turbo decoder achieves similar performance using both the conventional and the proposed btps, but in impulsive channels, the turbo decoder with the proposed btp substantially outperforms the turbo decoder utilizing the conventional btp. Results also confirm that the turbo decoder incorporating the proposed btp outperforms the existing Cauchy-based turbo decoder in non-Cauchy impulsive noise, while the two decoders accomplish similar performance in Cauchy noise.

PN Code Acquisition Based on the Locally Optimum Detector in Weakly Dependent Non-Gaussian Impulsive Channels

该文为解决弱相关非高斯噪声环境下的伪码捕获问题，提出了一种基于局部最佳检测算法的伪码捕获方法，将伪码捕获等价为假设检验问题，将弱相关非高斯噪声建模为一阶滑动平均SS噪声模型，利用局部最佳检测算法推导出弱相关非高斯噪声环境下的伪码捕获检测统计量，在此基础上对检测统计量进行了简化，给出了其实现结构，并与传统的伪码捕获方法进行了性能仿真对比，仿真结果表明该文所提出的捕获方法在弱相关非高斯噪声环境下检测性能有较大幅度的提高，且非高斯噪声脉冲特性越明显，所设计的检测器优势越明显。

On Reed–Solomon Coding for Data Communications Over Power-Line Channels

The problem of data communications through impulsive power-line channels using Reed-Solomon (RS) codes combined with M-ary modulation is treated. It is shown that under the influence of impulsive interference, the seemingly robust algebraic RS decoder can suffer drastic performance degradation even with the aid of an interleaver. We attempt to elucidate the mechanism that leads to the breakdown of such coding schemes. It is found that in impulse channels, excessive random and burst errors can occur prior to RS decoding mainly due to the deficiency of the Gaussian-based demodulator. An impulse mitigation strategy derived from the myriad filtering framework is incorporated into the demodulator for efficient baseband filtering and RS decoding. Even without an interleaver, the proposed solution leads to substantial performance improvements over the conventional interleaved scheme in impulsive channels. Consequently, the delay caused by interleaving can be avoided, which has significant benefits for future broadband power-line communication systems supporting interactive applications.

Robust multicarrier CDMA receiver for coded power-line communications

Existing indoor power-line grids are a potential solution to the last mile problem for broadband communication providers. However, power-line communication (PLC) channels suffer from deep frequency notches and severe impulsive noise making powerful signal processing essential if these channels are to be utilized. Broadband communications using Multicarrier Code Division Multiple Access(MC-CDMA) with channel coding is considered. Although resilient to frequency-selective fading, the coding gain from turbo signal processing is substantially compromised in the presence of impulsive noise. To overcome this, we propose a low complexity non-linear matched filter utilizing M-estimation technique. We will show that this matched M-estimate filter is indispensable in providing efficient baseband filtering in impulsive channels.

Space–time blind equalisation in impulsive noise

The presence of non-Gaussian impulsive noise in wireless system can degrade the performance of existing equalisers and signal detectors. The problem of blind source separation and equalisation for multiple-input/multiple-output (MIMO) channels under heavy-tailed impulsive noise environment is studied. A generalised multi-user constant modulus (CM) cost function is proposed by employing the fractional lower order CM property of the equaliser input signals as well as the fractional lower order cross-correlations between them. The associated adaptive blind equalisation algorithm based on a stochastic gradient descent method is defined as fractional lower order multi-user constant modulus algorithm (FMU_CMA), which is able to mitigate impulsive channel noise while recovering all input signals simultaneously. The steady-state mean-square error (MSE) performance of the FMU_CMA is studied in a noise-free environment; the approximate expression is derived based on the energy-preserving relation and the Taylor series expansion. Simulation studies are undertaken to support the analysis with CM and non-CM signal.

Approximate Conditional Mean Particle Filtering for Linear/Nonlinear Dynamic State Space Models

We consider linear systems whose state parameters are separable into linear and nonlinear sets, and evolve according to some known transition distribution, and whose measurement noise is distributed according to a mixture of Gaussians. In doing so, we propose a novel particle filter that addresses the optimal state estimation problem for the aforementioned class of systems. The proposed filter, referred to as the approximate conditional mean particle filter (ACM-PF), is a combination of the approximate conditional mean filter and the sequential importance sampling particle filter. The algorithm development depends on approximating a mixture of Gaussians distribution with a moment-matched Gaussian in the weight update recursion. A condition indicating when this approximation is valid is given. In order to evaluate the performance of the proposed algorithm, we address the blind signal detection problem for an impulsive flat fading channel and the tracking of a maneuvering target in the presence of glint noise. Extensive computer simulations were carried out. For computationally intensive implementations (large number of particles), the proposed algorithm offers performance that is comparable to other state-of-the-art particle filtering algorithms. In the scenario where computational horsepower is heavily constrained, it is shown that the proposed algorithm offers the best performance amongst the considered algorithms for these specific examples.

Robust chip-matched myriad filter-based multiuser receiver for impulsive channels

The problem of impulsive noise suppression for direct-sequence code-division multiple-access (DS-CDMA) systems employing multiuser detection in impulsive channels is treated. Prior to the detector, linear chip-matched filter is commonly used for continuous-to-discrete-time conversion. The effects of the non-Gaussian impulsive channel in an asynchronous system are studied by modeling the samples of noise before front-end filtering as a symmetric α -stable process. The error probability performance of the linear correlation receiver under these conditions is compared to that for additive white Gaussian noise (AWGN) channels. It is found that the approach performs poorly in the presence of impulsive noise. To overcome this problem, an impulse mitigation strategy derived from the myriad filtering framework is employed to produce reliable soft channel outputs over a wide range of noise characteristics. The asymptotic error probability performance of the chip-matched myriad filter (CMMyF)-based receivers is then computed and compared to the computer simulated expression. The results show that, in contrast to the linear filter, the CMMyF is effective in removing the impulsive noise and leads to a reliable recovery of the desired chips with low estimation error. The proposed method proves to be fruitful in that the subsequent k -opt multiuser detector is safe to process the chip samples obtained hereafter, thereby retaining all its optimality and advantages.

Adaptive Robust Turbo Equalization for Power-Line Communications

Data communication over power lines requires advanced signal-processing techniques to cope with time-varying intersymbol interference and severe impulsive noise. A further challenge comes from strict regulatory constraints that stipulate low transmission power. In this paper, we propose an adaptive robust turbo equalizer for single-carrier coded systems. The turbo equalizer has a component equalizer to deal with the deep frequency notches present in power-line channels. The component equalizer exchanges extrinsic information with a component decoder to perform iterative detection. To facilitate adaptive equalization in time-varying power-line channels, a simple system identification-based channel estimator is incorporated. Most important, a nonlinear-matched myriad filter (MMyF) is used for efficient baseband filtering in impulsive channels. The results show that the MMyF is indispensable for the turbo equalizer to achieve reliable channel estimation and data detection in impulsive power lines. Substantial performance improvements over the conventional scheme designed for Gaussian channels are observed.

Iterative Multiuser Detection/Decoding for Coded CDMA Systems in Non-Gaussian Noise

We propose a robust iterative multiuser receiver for decoding convolutional coded code-division multiple access (CDMA) signals in both Gaussian and non-Gaussian channel noise. The receiver is derived from a modified maximum a-posteriori (MAP) algorithm called the maxlog-MAP algorithm for robustness against erroneous channel variance estimation. Furthermore, the effect of destructive outliers arising from impulsive noise is mitigated in the proposed receiver by incorporating the robust Huber penalty function into the multiuser detector. The proposed receiver is shown to perform satisfactorily over Gaussian and non-Gaussian impulsive channels. In every iteration, cumulative improvement in the quality of the a-posteriori probabilities is also demonstrated.