A modified time-domain channel estimation method for OFDM systems in impulsive noise environment

Channel estimation in Underwater Acoustic Communication (UAC) faces significant challenges due to the non-Gaussian, impulsive noise in ocean environments and the inherent high dimensionality of the estimation task. This paper introduces a robust channel estimation algorithm by solving an l1−l1 optimization problem via the Alternating Direction Method of Multipliers (ADMM), effectively exploiting channel sparsity and addressing impulsive noise outliers. A non-monotone backtracking line search strategy is also developed to improve the convergence behavior. The proposed algorithm is low in complexity and has robust performance. Simulation results show that it exhibits a small performance deterioration of less than 1 dB for Channel Impulse Response (CIR) estimation in impulsive noise environments, nearly matching its performance under Additive White Gaussian Noise (AWGN) conditions. For Delay-Doppler (DD) doubly spread channel estimation, it maintains Bit Error Rate (BER) performance comparable to using ground truth channel information in both AWGN and impulsive noise environments. At-sea experimental validations for channel estimation in Orthogonal Frequency Division Multiplexing (OFDM) systems further underscore the fast convergence speed and high estimation accuracy of the proposed method.

In order to realize the high-resolution multipath Time Difference Of Arrival (TDOA) estimation which is not limited by the resolution limit of correlation method under impulsive noise environment, a Correntropy Expectation-Maximum (CEM) high resolution multipath TDOA estimation algorithm is proposed based on the Maximum Correntropy Criterion (MCC). The multipath TDOA is estimated by transforming multi-dimensional optimization problems into multiple one-dimensional optimization problems. The simulation results show that the CEM algorithm has good estimation performance under strong impulsive noise and low SNR environment, and the selection of kernel size in CEM algorithm is not depend on the prior information of the impulsive noise.

This paper studies the estimation of fast fading channel in the presence of impulse noise. The fast fading channel in a wireless communications system is typically modeled as an autoregressive (AR) process. The least-squares algorithm and Kalman filter have been previously proposed for estimating the AR parameters and the channel impulse response respectively using a training sequence. The performance of these algorithms, however, is very sensitive to impulse noise. In this paper, a robust Kalman filter and a robust recursive least M-estimate algorithm are employed to jointly estimate the channel impulse response and the AR parameters of fast fading channel under impulse noise. Simulation showed that the proposed algorithms are much less sensitive to impulse noise than the conventional algorithms.

This paper proposes a new algorithm for tracking time-varying channels in impulsive noise environment using a robust Kalman filter. It employs a simple dynamical model of the channel, where the changes in the impulse response coefficients are due entirely to the innovations of the Kalman filter. This reduces the arithmetic complexity, while offering reasonable good performance. The robust Kalman filter is used to restrain the adverse effect of impulsive noise and provide estimates of the covariance matrices of the state and measurement noises. The noisy channel estimates from the Kalman filter can be used to estimate the parameters of the channel coefficients when they are assumed to follow an AR model. Finally, the two processes can be coupled together to further improve the performance. Simulation results show that the new algorithm gives more stable performance than the conventional methods under impulsive noise environment.

A robust direction-of-arrival estimation method for impulsive noise environments

충격성 잡음 환경에서 최대 영확률 (MZEP) 알고리듬은 최소자승오차 (MSE) 기반의 알고리듬 보다 우수한 성능을 지닌다. 그리고 알고리듬 자체에 내재한 크기 조절 입력 (MCI)가 MZEP 알고리듬을 충격성 잡음으로부터 알고리듬을 안정되게 유지하는 역할을 하는 것으로 알려져 있다. 이 논문에서는 MCI 입력의 평균전력으로 MZEP 알고리듬의 스텝 사이즈를 정규화하는 방식을 제안하였다. 충격파 발생률이 0.03인 충격성 잡음하의 시뮬레이션에서 정상상태 MSE 성능 비교에서 기존 MZEP에 비해 제안한 방식이 약 2dB 정도 향상된 특성을 보인다. The maximum zero error probability (MZEP) algorithm outperforms MSE (mean squared error)-based algorithms in impulsive noise environment. The magnitude controlled input (MCI) which is inherent in that algorithm is known to plays the role in keeping the algorithm undisturbed from impulsive noise. In this paper, a new approach to normalize the step size of the MZEP with average power of the MCI is proposed. In the simulation under impulsive noise with the impulse incident rate of 0.03, the performance enhancement in steady state MSE of the proposed algorithm, compared to the MZEP, is shown to be by about 2 dB.

ABSTRACTWhile inter-symbol interference is not of concern, inter-carrier interference that is caused by carrier frequency offset (CFO) is more concerned in orthogonal frequency division multiplexing (OFDM) systems. The estimation of channel impulse response (CIR) is another important parameter of interest in the system. Recently, a number of approaches for the joint estimation of CFO and CIR in OFDM systems have been proposed in the literature, and most of them are traditional maximum-likelihood-based approaches. In this paper, we propose a number of mixture cost-reference particle filtering (CRPF) approaches for joint estimation of CIR and CFO, and a couple of them can be applied without the knowledge of both state and measurement noise statistics. Conventional least mean squares algorithm or recursive least squares algorithm is jointly employed with recently developed CRPF for nonlinear and multiple parameters estimation in OFDM systems. The computer simulation results show that mixture CRPFs are more robust against particle impoverishment (PI) problem than standard mixture particle filtering (PF) and mixture regularized PF (RPF) approaches although RPF was particularly developed to tackle the PI problem. In this paper, we investigate a number of mixture PF approaches including ones that do not need the information of noise statistics for the joint estimation of CFO and channel in OFDM systems.

In the context of two-dimensional (2-D) direction of arrival (DOA) estimation in impulsive noise environments, this paper extends the coprime array to a crossed V-shaped distributed structure and proposes a novel exponential weighted adaptive generalized covariance (EWAGC) based on the study of impulsive noise characteristics. Building on this, a redundant averaging dual-scale EWAGC-ESPRIT algorithm is introduced, which can adaptively adjust the suppression level of impulsive noise with varying intensities, enhancing the robustness of the estimation. Simulation results validate the superior performance of the proposed method in solving the 2-D DOA estimation problem in impulsive noise environments.

Under highly mobile environments, the bit error rate (BER) performance of DFT spreading-orthogonal frequency division multiplexing (DFTS-OFDM) signal with a frequency domain equalization method would be degraded relatively due to the loss of orthogonality among subcarriers. To solve this problem, this paper proposes an iterative based time domain equalization (TDE) technique with a time domain channel impulse response (CIR) estimation method for the DFTS-OFDM signal. The salient features of proposed method are to employ a time domain training sequence (TS) in the estimation of CIR instead of using the conventional pilot subcarriers method and to employ the TDE technique with a maximum likelihood (ML) estimation method instead of using the conventional minimum mean square error frequency domain equalization (MMSE-FDE) method. This paper also proposes a low-complexity iterative method for the TDE method by using the preconditioned conjugate gradient squared (PCGS) algorithm for solving the simultaneous equations instead of using a direct calculation of inverse matrix. This paper presents various simulation results under highly mobile environments to demonstrate the effectiveness of proposed iterative based TDE with the CIR estimation method for the DFTS-OFDM signal as comparing with the conventional MMSE-FDE method.

In this paper, we present a radio frequency (RF) front-end design for increasing robustness of non-coherent energy detection based impulse radio (IR) ultra-wideband (UWB) receivers in impulsive noise environment. Robustness against impulsive noise is achieved by on chip LNA-bandpass filter (BPF) circuit, which also works as a clipper for high energy impulsive noise bursts. The electrostatic discharge (ESD), wirebond, pad capacitance, and the chip package model are co-designed with wideband cascode LNA structure. These unwanted capacitive and inductive elements are designed as a part of input BPF. The LNA output stage includes an inductor that is coupling with the input capacitance of the VGA block results in additional filtering. In the post-layout simulations, 45 dB impulsive noise compression has been achieved. It has been shown that the RF front-end and LNA output stage reduces the impulsive noise and increases the noise performance of the IR-UWB receiver, hence becoming robust against the impulsive noise.

Impulse noise is a potential impairment of very-high speed digital subscriber line (VDSL) services. VDSL systems are protected from impulse noise using a combination of Reed-Solomon coding and interleaving. Since there are two competing proposals for VDSL, the first one based on the use of QAM line code and the second one using DMT modulation, it is interesting to compare their performance in terms of immunity to impulse noise. The paper presents a comparison of the behavior of QAM-VDSL and DMT-VDSL in the presence of impulse noise in real configurations. The required interleaving delay to correct all the generated errors for both systems is investigated. It is shown that when no notches are used in the radio-amateur bands, QAM and DMT systems require similar delays in order to achieve the same level of protection against impulse noise. However, when notches are implemented, DMT-VDSL achieves higher rates than QAM-VDSL. Therefore, larger error-correcting code redundancy can be used, which results in lower end-to-end delays for DMT-VDSL systems.

In this paper, we propose a channel estimation method for radio frequency multiple-input multiple-output orthogonal frequency division multiplexing (RF-MIMO-OFDM) systems. In RF-MIMO-OFDM systems, a receiver combines the received signals at the RF front-end. This implies that a receiver can estimate only one of MIMO channels during one OFDM symbol duration. Therefore, the conventional channel estimation method requires a number of pilot OFDM symbols in proportion to the numbers of transmit antennas and receive antennas. If the channels are varying during the pilot transmission, the accuracy of the conventional channel estimation is deteriorated. In this paper, we propose a channel estimation method which can estimate channels with a shorter time period considering the antenna switching time. Our proposed method uses time-domain maximum likelihood estimation and pilot symbols which have a repetitive waveform within one OFDM symbol duration. The proposed method estimates channel impulse responses (CIRs) of multiple channels during one OFDM symbol duration. From simulation results, we show that the proposed estimation method achieves a better estimation performance than the conventional estimation method. Furthermore, the error performance is also improved by the use of the proposed method.

SSP based underwater CIR estimation with S-BiFPN

The optimum detection and the design of trellis-coded modulation (TCM) signals under an impulsive noise environment are investigated. The optimum TCM receiver designed for impulsive noise is proposed, and it is shown that the TCM signals achieve better performance than the uncoded ones. Computer simulation shows that this optimum receiver, which is simple and easy to realize, gives a coding gain from several decibels up to several tens of decibels and that the performance improvement achieved by increasing the number of states of the convolutional codes is greater than that achieved under Gaussian noise. Moreover, from the capacity of the impulsive noise channel with phase modulated signals, it is shown that it is possible to achieve an improvement in performance by using the optimum TCM signal design methods, which are based on the statistical characteristics of the noise. >

We propose a novel receiver for orthogonal frequency division multiplexing (OFDM) transmissions in impulsive noise environments. Impulsive noise arises in many modern wireless and wireline communication systems, such as Wi-Fi and powerline communications, due to uncoordinated interference that is much stronger than thermal noise. We first show that the bit-error-rate optimal receiver jointly estimates the propagation channel coefficients, the noise impulses, the finite-alphabet symbols, and the unknown bits. We then propose a near-optimal yet computationally tractable approach to this joint estimation problem using loopy belief propagation. In particular, we merge the recently proposed “generalized approximate message passing” (GAMP) algorithm with the forward-backward algorithm and soft-input soft-output decoding using a “turbo” approach. Numerical results indicate that the proposed receiver drastically outperforms existing receivers under impulsive noise and comes within 1 dB of the matched-filter bound. Meanwhile, with N tones, the proposed factor-graph-based receiver has only O(NlogN) complexity, and it can be parallelized.