Khaled M. Rabie

Dynamic Peak-Based Threshold Estimation Method for Mitigating Impulsive Noise in Power-Line Communication Systems

Impulsive noise (IN) is one of the most dominant factors responsible for degrading the performance of power-line communication systems. One of the common techniques for mitigating IN is blanking which is applied at the front end of the receiver to zero the incoming signal when it exceeds a certain threshold. Determining the optimal blanking threshold (OBT) is, however, key for achieving the best performance. Most reported work to find the OBT is based on the availability of the long-term characteristics of IN at the receiver. In this paper, we consider orthogonal frequency-division multiplexing (OFDM)-based power-line communications and propose a method for finding the OBT without requiring any knowledge about the IN. We show that there is a direct relationship between the OBT and the peak-to-average power value of the OFDM symbol and utilize it to identify the OBT. The results reveal that the proposed technique not only eliminates the need to prior knowledge about the characteristics of IN but also achieves a gain between 0.5-2.5 dB depending on the accuracy of the signal peak-to-average estimate. It will also be shown how the performance of the proposed method can be further enhanced by employing some basic signal per processing at the transmitter.

Physical Layer Security With RF Energy Harvesting in AF Multi-Antenna Relaying Networks

In this paper, we analyze the secrecy capacity of a half-duplex energy harvesting (EH)-based multi-antenna amplify-and-forward relay network in the presence of a passive eavesdropper. During the first phase, while the source is in the transmission mode, the legitimate destination transmits an auxiliary artificial noise (AN) signal which has two distinct purposes: 1) to transfer power to the relay and 2) to improve system security. Since the AN is known at the legitimate destination, it is easily cancelled at the intended destination, which is not the case at the eavesdropper. In this respect, we derive new exact analytical expressions for the ergodic secrecy capacity for various well-known EH relaying protocols, namely, time switching relaying (TSR), power splitting relaying (PSR), and ideal relaying receiver (IRR). Monte Carlo simulations are also provided throughout our investigations to validate the analysis. The impacts of some important system parameters, such as EH time, power splitting ratio, relay location, AN power, EH efficiency, and the number of relay antennas, on the system performance are investigated. The results reveal that the PSR protocol generally outperforms the TSR approach in terms of the secrecy capacity.

Preprocessing-Based Impulsive Noise Reduction for Power-Line Communications

Signal blanking is a common technique for mitigating impulsive noise (IN) in power-line communications. When signal samples unaffected by IN are erroneously blanked, part of the useful signal will be lost and performance will degrade. In this paper, we show that the performance of this technique is sensitive not only to the blanking threshold but also to the signals peak-to-average power ratio (PAPR). We thus propose enhancing the capability of the conventional blanking technique by preprocessing the signal at the transmitter. With this in mind, a closed-form analytical expression for the probability of blanking error is then derived and the problem of blanking threshold optimization is addressed. The results reveal that the proposed technique is able to minimize the probability of blanking error dramatically and can provide up to 3.5-dB signal-to-noise ratio (SNR) improvement relative to the conventional technique. Furthermore, it will be shown that if the transmitted signals PAPR is maintained below a certain threshold, then not only can a considerable SNR enhancement be achieved but it is also possible to completely alleviate the need for any prior knowledge about the IN characteristics in order to optimally blank it.

Channel characterisation of cooperative relaying power line communication systems

Power line communication (PLC) technology offers a promising platform for numerous communication applications. The power lines however can significantly attenuate communication signals operating in high frequency band. For this reason, multi-hop PLC systems become desirable. In this paper, we investigates the effect of multi-hop relaying on the power line channel transfer function. Measured results are compared with results obtained from sumulations in Matlab. Results show that the presence of relays between a transmitting and a receiving PLC nodes can intensify the attenuation and frequency selectivity. Measurements show that maximum attenuation increases with number of relays.

Constant envelope OFDM transmission over impulsive noise power-line communication channels

Signal blanking is a simple and efficient method to reduce the effect of impulsive noise over power-line channels. The efficiency of this method, however, is found to be not only impacted by the threshold selection but also by the average peak-to-average ratio (PAPR) value of the orthogonal frequency division multiplexing (OFDM) signals. As such, the blanking capability can be further enhanced by reducing the PAPR value. With this in mind, in this paper we evaluate the performance of constant envelope OFDM (CE-OFDM) which has inherently the lowest achievable PAPR of 0 dB; therefore, the proposed system is expected to provide the lower bound performance of the blanking-based method. In order to characterize system performance, we consider the probability of blanking error and signal-to-noise ratio (SNR) at the output of the blanking device. The results reveal that the proposed system can achieve significant improvements over the conventional OFDM blanking-based scheme in terms of minimized probability of blanking error. It will also be shown that output SNR gains of up to 6 dB can be attained over the conventional OFDM blanking-based systems.

On Improving Communication Robustness in PLC Systems for More Reliable Smart Grid Applications

Power-line communication (PLC) has been the main enabler for modernizing the aging electrical power grid. As such, PLC systems have been the subject of intensive research in the community. One of the major aspects of PLC is the link interface, for which orthogonal frequency-division multiplexing (OFDM) has been widely adopted. In this paper, we propose the application of orthogonal poly-phase-based multicarrier code division multiple access (OPP-MC-CDMA) due to its inherent better flexibility and signal-envelope properties which can be utilized to further enhance the reliability of PLC signals. The proposed OPP-MC-CDMA system is implemented with a minimum mean square error equalizer and nonlinear preprocessing to overcome the effects of bursty noise and multipath frequency-selective fading commonly experienced in PLC channels. We study the performance of this system in terms of the output signal-to-noise ratio (SNR) and symbol error rate with various constellation sizes of OPP codes under different noise scenarios and nonlinear processors thresholds. For comparison-sake, the performance of the OFDM scheme is included. The results reveal that the proposed approach always provides superior performance over the OFDM one with a maximum output SNR gain of up to 5.25 dB. It is also shown that the performance of the OPP-MC-CDMA technique improves when increasing the constellation size of the OPP codes, which consequently enhances the reliability of PLC.

Performance analysis of adaptive hybrid nonlinear preprocessors for impulsive noise mitigation over power-line channels

Impulsive noise (IN) over power-lines can significantly corrupt communication signals. To diminish its effect, a nonlinear preprocessor is usually applied at the receivers frond-end to blank or clip the incoming signal when it exceeds a certain threshold. Applying a combination of blanking and clipping in a hybrid fashion is characterized by two thresholds T1 and T2 (T2 = αT1), where α is a scaling factor. Previous studies assumed a fixed value for the scaling factor and found that optimizing the threshold T1 is the key to improve performance. In contrast to the existing work, in this paper we show that the performance of the hybrid technique is sensitive not only to the threshold but also to the scaling factor, and in light of this we propose to enhance the capability of this technique by optimizing the two parameters. System Performance is evaluated mathematically in terms of the probability of missed blanking/clipping (Pm), probability of IN identification (Pi) and the symbol error rate (SER) performance. In all our investigations, simulation results are provided to validate the analysis. Results reveal that the proposed scheme is superior in terms of minimizing Pm and maximizing Pi which consequently results in improving SER performance.

Quantized peak based impulsive noise blanking in powerline communications

Many IN mitigation techniques have been proposed to mitigate impulsive noise (IN) over powerlines, the most common of which is the blanking technique. The conventional way to implement this technique however requires prior knowledge about the IN characteristics to identify the optimal blanking threshold (OBT). When such knowledge cannot be obtained the performance deteriorates rapidly. To alleviate this, a look-up table (LUT) based algorithm with uniform quantization is deployed to utilize estimates of the peak to average power ratio at the receiver to determine the OBT. In this paper, we investigate the impact of quantization bits on the system performance as well as the performance loss due to the impact of IN on the side information. Two aspects of the achievable performance are considered namely, output signal-to-noise ratio (SNR) and symbol error rate under various IN scenarios. The results reveal that a 5 bit LUT is sufficient to achieve a gain of up to 3dB SNR improvement relative to the conventional blanking method. Furthermore, it will be shown that the loss due to the practical impact of IN on the side information is insignificant.

Vector OFDM Transmission Over Non-Gaussian Power Line Communication Channels

Most of the recent power line communication (PLC) systems and standards, both narrow-band and broadband, are based on orthogonal frequency-division multiplexing (OFDM). This multiplexing scheme, however, suffers from the high peak-to-average power ratio (PAPR), which can considerably impact the energy efficiency, size, and cost of PLC modems as well as cause electromagnetic compatibility (EMC) issues. This paper investigates the performance of vector OFDM (VOFDM), which has inherently better PAPR properties, over non-Gaussian broadband PLC channels equipped with two nonlinear preprocessors at the receiver. In addition, the low PAPR property of the VOFDM system is exploited to further enhance the efficiency of the nonlinear preprocessors. The achievable gains are studied in terms of the complementary cumulative distribution function of the PAPR, probability of noise detection error, and the signal-to-noise ratio at the output of the nonlinear preprocessors. For comparisons sake, the performance of conventional OFDM systems is also presented throughout this paper. Results reveal that the proposed system is able to provide up to 2-dB saving in the transmit power relative to the conventional OFDM under same system conditions, which eventually also translates into a system that is more resilient to EMC limits, reduced cost, and size of PLC modems. It is also shown that the achievable gains become more significant as the vector block size of the VOFDM system is increased.

Improving energy efficiency in dual-hop cooperative PLC relaying systems

Energy efficiency (EE) in multi-hop cooperative communication systems, both wireless and wired, is increasingly becoming more and more critical. This has recently been extended to include power line communications (PLC). In this respect, we propose in this paper to enhance the EE of a dual-hop amplify-and-forward (AF) cooperative relaying PLC system by considering energy-harvesting (EH) at the relay node. The energy harvester exploits the high noisy PLC channel feature as well as the transmitted signal power to forward the source information. In light of this, we derive an analytical expression for the EE and verify it with Monte Carlo simulations. The performance of the conventional relaying system, i.e. without any EH, is also considered to clearly quantify the achievable gains. The results show that the proposed system can considerably improve the EE of PLC systems and that increasing the channel variance will always make the proposed system more energy-efficient.