A Factor Graph Approach to Joint OFDM Channel Estimation and Decoding in Impulsive Noise Environments

A simple method of improving orthogonal frequency division multiplexing (OFDM) receiver performance in an impulsive noise environment is to precede a conventional OFDM demodulator with blanking nonlinearity. This method is widely used in practice since it is efficient and very simple to implement. However, performance analysis of this scheme has not yet appeared. In this paper, we study performance of the OFDM receiver with blanking nonlinearity in the presence of impulsive noise. Closed form analytical expressions for the signal-to-noise ratio (SNR) at the output of blanking nonlinearity and the optimal blanking threshold that maximizes SNR are derived. Simulation results are provided that show good agreement with theory if the number of OFDM subcarriers is sufficiently large.

Orthogonal frequency division multiplexing (OFDM) transmission technique is an effective method to mitigate frequency selective multipath characteristic of PLC channel. It is used for data communication in Power Line systems. However, OFDM is susceptible to lack of orthogonality between its subcarriers. Inter-carrier interference (ICI) cancellation technique was introduced in wireless communication to address that issue. Parallel Cancellation (PC) scheme is one method proposed for mitigating ICI in wireless systems. In this paper, Space-Time Parallel Cancellation (STPC) with OFDM is applied to PLC. Linear time variant (LTV) 15-path PLC channel model is employed to investigate BER performance of the 2x1 and 2x2 ST-OFDM versus 2x2 STPC-OFDM systems in Additive Impulsive Gaussian Noise (AIGN) via computer simulations.

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 this paper, an algorithm that estimates the parameters of impulse noise (IN) is proposed in power line communication. The Peak to Average Power Ratio (PAPR) of the Orthogonal Frequency Division Multiplexing (OFDM) symbol sent by the transmitter is reduced by the selective mapping (SLM) technology. In addition, the peak value of each OFDM symbol is sent with a separate control channel. At receiver, the frequency characteristics of IN is calculated using the received peak value and the OFDM symbol. The noise used for simulation comes from actual measurement. Results from simulations show that the proposed algorithm can estimate the IN well under different IN environments, and the obtained parameters are very valuable for mitigating IN in power line communication.

Broadband communications for indoor power-line networks with impulsive noise using orthogonal frequency division multiplexing (OFDM) is considered. From earlier investigations, it is known that this channel suffers from multipath fading and frequency selectivity along with man-made impulsive bursty noise. Nevertheless, the calculated channel capacity limit promises very high data rates over this channel. Enhancement techniques, such as coding can help an OFDM system to tackle impulsive noise burst. In this paper, the bit error rate (BER) performance of the OFDM system under impulsive noise and frequency fading is theoretically analyzed and closed form expression for the performance is derived. Two different impulsive noise environment models are studied and it is confirmed that both models represent the same environment. Furthermore, a theoretical upper bound on the performance of coded OFDM system is obtained, given perfect interleaving. The effect of the interleaver length on coding performance is also studied. Simulations show that the upper bound is quite tight for the case of employing a longer interleaver. The effect of interleaver size on the system performance is studied, as well

This paper reports on findings on the analysis of the fast Fourier transform (FFT) hybrid power line communication (PLC) - visible light communication (VLC) system (PLC- VLC) based on ACO-OFDM in impulsive noise, when the perfect nulling technique is utilized to combat noise in the system. In this work, we develop theoretical expressions that describe the error floors realized in the system due to perfect nulling. Perfect nulling refers to a noise mitigation technique that perfectly identifies impulsive noise locations in a string of data samples and clips them to zero, leading to an error floor at a high Signal to Noise (SNR) ratio. Thus, the principal contribution of this paper is to analyze and derive theoretical Bit Error Rate (BER) expressions for the error floor achieved by a BPSK OFDM signal in the FFT hybrid PLC-VLC system based on asymmetrically clipped optical - orthogonal frequency division multiplexing (ACO-OFDM), in a channel corrupted with Added White Gaussian Noise (AWGN) and impulsive noise. The derived theoretical BER results will be compared to the error floors obtained through simulations.

In this study, the authors presented discrete Fourier transform (DFT)-based channel estimation algorithms for a coherent optical orthogonal frequency division multiplexing (CO-OFDM) transmission system. Influence of the proposed algorithms to the performance and computational complexity of the CO-OFDM system was analysed and compared with other published algorithms. Their simulation results demonstrated that the improved DFT-based channel estimation algorithms are significantly efficient in our experimental conditions. Those algorithms can be considered as efficiently compromised systems in balance out the outcome of performance and the requirement on computational complexity. Such relatively economic and practical approaches have provided an optimistic prospect in studies of transmission systems for future optical communications.

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.

Although Power Line Communication (PLC) is not a new technology, its use to support data transmission over low voltage (LV) distribution networks is still the focus of ongoing research. This thesis focuses on the channel modelling and performance evaluation of narrowband (NB) PLC system. First, the channel modelling approaches of PLC are studied. Then, the proposed PLC channel modelling method based on the bottom-up approach for LV narrowband PLC in a frequency band between 9 kHz and 490 kHz is presented. This proposed model employs the transmission and scattering matrix methods to calculate the transfer function of a typical LV PLC network which comprises two common cable types (copper cables and aluminium conductor steel reinforced). Unlike the top-down approaches, this model is scalable as the network complexity increases and can better describe the network behaviour as a function of physical parameters.In addition, the noise characteristics and popular noise reduction techniques of PLC are studied. The major impairment to the PLC is the impulsive noise which is mainly generated by the switching transient in the network. Hence, a new technique is proposed to mitigate the impact of impulsive noise on data transmission over power lines. This proposed technique is an optimal Clipping/Blanking nonlinearity technique which is based on the minimum bit error rate (BER) search. Results obtained from the simulation of this technique demonstrate that performance has been enhanced in the NB-PLC system. The performance of the narrowband PLC system is also evaluated in both physical (PHY) and medium access control (MAC) layers. Since Orthogonal Frequency Division Multiplexing (OFDM) is a suitable modulation scheme for hostile environment of the power line, it is used to evaluate the PHY layer performance. As a result of the PHY layer performance analyses, it is found that the BER performance between neighbouring points in the typical LV PLC network is reasonable, but communication beyond one hop have to rely on upper layer protocols. In the MAC layer performance evaluation of the PLC system, the widely known random access MAC protocol that uses the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) will be utilised. The MAC performance evaluation of the PLC system demonstrates a significant packet loss in LV PLC network even with a light traffic condition due to the noisy channel. Furthermore, the goodput declines abruptly once the individual transmission rate is high enough to block the network. In addition, the simulation results show that the channel errors can be reduced by adjusting the MAC parameters to allow the re-transmissions mechanisms to recoup the lost packets.

In this paper, we propose a novel receiver design for orthogonal frequency division multiplexing (OFDM) transmission over doubly (time- and frequency-) spread channels, where the receiver employs a turbo message passing (TMP) algorithm for joint channel estimation and data detection. We show that the proposed TMP-based receiver is able to make more efficient use of the prior information about the channel and the data for inter-carrier interference (ICI) cancellation than the existing iterative receivers. The proposed TMP algorithm can be further combined with a soft-input soft-output (SISO) decoder for joint channel estimation, data detection and decoding. Numerical results are presented to demonstrate the performance superiority of our proposed TMP-based OFDM receiver.

A novel encryption scheme using chaotic Zadoff-Chu matrix transform (ZCMT) precoding is proposed to improve both of the data security and performances in orthogonal frequency-division multiplexing (OFDM) transmission, where the security is significantly enhanced with a huge key space of ∼10400 provided by hyper digital chaos. The chaotic ZCMT matrix is generated with the reconfigurable parameters and row permutation of ZCMT matrix, both of which are predetermined by a hyper digital chaos. The OFDM data encryption using the chaotic ZCMT precoding effectively reduces the peak-to-average power ratio (PAPR) and consequently improves the OFDM transmission performance, if compared with the traditional OFDM transmission. The significant PAPR reduction is numerically analysed via the autocorrelation and the complementary cumulative distribution function (CCDF).

OFDM (Orthogonal Frequency Division Multiplexing) is used in many applications that require high-speed communication. However, in the system using OFDM such as PLC (power line communication), there is a problem that reception characteristics are strongly deteriorated by the impulsive noise because impulsive noise has short time duration and very large magnitude. Therefore, many schemes such as clipping and nulling scheme and time sample replacement scheme have been proposed to reduce the influence of the impulsive noise in OFDM systems. In this paper, a combination of the conventional nulling scheme and time sample replacement scheme is proposed to improve the characteristics of the bit error rate.

Power-line Communications (PLC) effectively uses the pervasive power grid as a high data rate communication medium. Despite its advantages, the presence of severe multipath fading and susceptibility to impulsive noise make reliable communication in a PLC system challenging. In PLC systems, orthogonal frequency-division multiplexing (OFDM) is an attractive choice mainly due to its resilience to multipath fading. However, OFDM signals suffers from large peak-to-average power ratio (PAPR) thus resulting in non-linear signal distortions at the transmitter. Therefore, for an OFDM-based PLC system, the combined effect of large PAPR and the presence of impulsive noise results in high bit error rate (BER). This paper proposes the use of precoding at the transmitter to reduce PAPR, and blanking non-linearity at the receiver to mitigate impulsive noise. Precoding is a data-independent and robust PAPR reduction scheme that essentially distributes the power of the individual OFDM symbols over the entire OFDM block. Blanking is an effective impulsive noise mitigation technique that results in better BER performance at the receiver. Simulation results show that, with the combination of precoding and blanking, significant gains in BER performance for an OFDM based PLC system can be obtained with minimal increase of transceiver complexity.

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

This paper considers an adaptive orthogonal frequency-division multiplexing (OFDM) transmission scheme for narrowband (NB) power line communication (PLC). The NB PLC channel is found to show strong cyclostationary characteristics due to the periodic mains voltage. However, conventional systems do not use these time-varying channel features. An improvement of the performance is achieved by exploiting the cyclic properties of the channel. Therefore, adaptive bit and power loading methods are of great interest for PLC. In this work, we will evaluate a cyclic loading method for an OFDM system in the CENELEC A-band. Our analysis is based on noise measurements at three different locations over an observation time of 23 hours. Our contribution includes an OFDM system model comprising both additive noise and channel attenuation. Furthermore, we present a method for limiting the amplitude and power spectral density to comply with narrowband regulations. In conclusion, our proposed method achieves a lower bit error rate at all locations. The improvement reaches up to a 102 times lower bit error rate compared to non-adaptive carrier allocation at the same data rate.