Hui-Myoung Oh

Mitigation of Performance Degradation by Impulsive Noise in LDPC Coded OFDM System

In the paper, LDPC (low-density parity-check) coded OFDM system applicable for impulsive noise channel, such as powerline channel (PLC) will be presented. Performance degradation in the proposed system over impulsive noise channel is mitigated using a simple estimator based on the Gaussian approximation with estimated channel information (ECI) and a signal level limiter. At first, it will be shown that the performance of a conventional LDPC coded OFDM system is seriously degraded due to the imperfection of estimating the initial LLRs (log likelihood ratios) of sum-product decoder over impulsive noise channels and hard evaluation of the initial LLRs from the decentralized noise samples by OFDM demodulator. Thereafter, to overcome the problems, the system using the simple estimator and the received signal level limiter is proposed. Simulation results show that the proposed system has much better performance than that of conventional systems. For the verification, Monte Carlo simulation is applied

Closed-Form Expression of Nakagami-Like Background Noise in Power-Line Channel

A closed-form expression for the real part of background noise is derived for the power-line channel modeled by Nakagami probability density function. Simulation with various parameters shows the derived expressions validity. The closed-form expression can be of benefit to communication system designers in that it facilitates the design of optimum receiver and its performance evaluation.

Mitigation of effect of impulsive noise for OFDM systems over power line channels

Impulsive noise introduces significant time variance into the power line channel and causes performance degradation of orthogonal frequency division multiplexing (OFDM) systems. In this paper, we provide a performance analysis for OFDM-based power line communications in the presence of impulsive noise. Performance degradation of coherent M-ary PSK and differential MPSK can be mitigated by a signal level limiter. Simulation results present that the optimum signal level can significantly improve the performance of OFDM systems over power line channels with impulsive noise.

A Systematic Approach to Analyzing Multipath Parameters From PLC Channel Response

The reliable analysis of the power-line communication (PLC) channels is necessary to model, design, and implement a well-matched PLC transceiver. However, a typical power-line channel has not yet been properly described since it is difficult to analyze the time- and space-varying characteristics. Consequently, it is still very important to measure, analyze, and model the power-line channel well. In this paper, focusing on the analysis of the channel response, we suggest a novel systematic approach to analyzing the multipath parameters. The proposed approach is convenient in that we can systematically find the multipath parameters like time delays and attenuation factors including magnitudes and phases from the measured complex impulse response. The simulation and experimental results show that the proposed approach is valid and appropriate for a typical power-line channel.

A Systematic Technique for Estimating Multipath Parameters of Power-Line Communication Channel

In recent years, the channel measurement method using PN sequence have been suggested as the best choice for power-line communication (PLC) channel with respect not only that it can give the complex impulse response which can be converted to the frequency response but also that it can be effectively adopted even over noisy and long-length power line channel. However, finding each multipath from the measured impulse response is still challengeable. In this paper, we introduce the noble technique systematically finding each multipath from the measured complex impulse response using matrix operation. This technique is more applicable to estimating the excess delay of each multipath for power-line channel because the impulse response of power line channel has the first path with the smallest attenuation. The simulation results show that we can get the high resolution time delay and the attenuation factors corresponding to the multipaths. The estimated time delays and attenuation factors will facilitate the analysis of the PLC channel with multipaths.

Study on Very High-Rate Power Line Communications for Smart Grid

In this paper, we study on the reliability of Very High-rate Power Line Communication (VH-PLC) for Smart Grid, so that the resultant data rate is over 400Mbps at a physical layer. Firstly, reviewing the research trend of the PLC, we discuss the required techniques for supporting the Smart Grid. Considering a pre-specification with the value of several parameters, we investigate a multi-carrier modulation technique to overcome limitations of higher rate transmission under power line channel environments. Then, we propose a system specification of the VH-PLC in the sense of enhancing two features. One is resolving the problem of the co-existence of the deployed high-speed PLC according to the published standardization of KS X 4600-1 in Korea. The other is getting better performance on the grid adopting the diverse element techniques, such as multi-carrier modulation, a subcarrier utilization mode, a variable rate LDPC (Low Density Parity Check) code, and a time and frequency diversity technique. Further, a simulation tool, composed of an Event-Driven simulator and a Time-Driven simulator, is developed for the purpose of verifying the system performance and continuously cross-checking the test bench signal of the proposed VH-PLC system.

Performance of scaled SLM for PAPR reduction of OFDM signal in PLC channels

Orthogonal frequency division multiplexing (OFDM) modulation using orthogonal subcarriers reduces the delay spread by increasing robustness to multipath fading and can use overlapped bandwidth due to orthogonality on frequency domain. Thus, OFDM has been adopted for high speed data transmission of multimedia traffic such as HomePlug A/V and Mobile WiMax. However, OFDM also has a drawback of a high PAPR (peak-to-average-power-ratio). This high PAPR takes place due to parallel processing of a number of data at once using a fast Fourier transform (FFT) processor. Due to this high PAPR amplifier usually does not act in dynamic range. In this paper, we propose an algorithm that can reduce PAPR using selective mapping (SLM) in power line communication (PLC) channel. In order to utilize SLM technique, side information needs to be transmitted for demodulation while degrading transmission efficiency. We propose and analyze scaled SLM technique which removes necessity of the side information.

Performance of polar codes with successive cancellation decoding over PLC channels

Polar codes are the first proven capacity achieving codes for a wide array of channels with low complexity. It is considered a next generation candidate for error-correcting codes (ECC) with turbo codes and low-density parity check (LDPC) codes. The aim of this paper is to analyze the bit error rate (BER) performance of polar codes with successive cancellation (SC) decoding over power line communication (PLC) channels. First, the performance of polar codes in additive white Gaussian noise (AWGN) and impulsive noise channels will be shown. In addition, a signal level limiter is used to mitigate the degradation of the performance over the impulse noise channels. Thereafter, the performance over real PLC channels is investigated. Simulation results show that polar codes are applicable to PLC channels with lower complexity than a turbo or a LDPC code.

Neutral inductive coupling for improved underground medium voltage BPLC

In the underground MV BPLC systems, the inductive coupler has been mainly used being clamped around the MV power cable. But the high current on the MV power line causes the magnetic saturation of the inductive coupler, so the quality of coupling could be gone down. To solve this problem, we suggest that the neutral line of the underground MV power line can be used for the coupling as a communication medium, and we have newly developed a inductive coupler with loss less than 5dB for the underground MV neutral line and experimentally assessed it. For the purpose of evaluating the coupler, we had constructed the underground MV BPLC test bed that has the 9 repeating points with the 200Mbps class BPLC repeaters. The length of the test bed is about 836 m. It is located in Ansan-city, Korea. We have measured the transmitted signal attenuation and TCP data rate as the factors of the performance evaluation where the TCP data rate means the data rate over TCP layer. The results measured about the existing inductive coupler and the new one have been compared, and the results measured according to the inductive coupling methods included the neutral line coupling method have also compared. As a result, the suggested coupling method and the newly developed inductive coupler have not only the good performance, but also the cost effectiveness because of the fact that there is no magnetic saturation problem and its small size. Therefore, when we consider the cost effective communication infrastructure for Smart Grid, we can say that the underground MV BPLC system is still attractive.

A Common Signaling Mechanism for Coexistence between High-speed Power Line Communication

AbstractIn the field of high-speed power line communications, there are three major standards; ISO/IEC 12139–1, IEEE 1901–2010, and ITU-T G.99xx. However, they are not interoperable because of having their own physical and MAC layer specification. Actually, they cannot even avoid interfering with each other because they are using the same frequency band of 1 ∼ 30 MHz. In this paper, a common signaling mechanism is suggested which uses multi-carrier partitioning and carrier sensing, so that all standards can be coexisted by sharing time resource. The suggested mechanism has been compared with the ISP protocol which is included in IEEE and ITU-T standard for coexistence.