Sungsoo Choi

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

Capacity of OFDM Two-Hop Relaying Systems for Medium-Voltage Power-Line Access Networks

Orthogonal frequency-division multiplexing (OFDM) transmission is considered for a medium-voltage (MV) power-line access network (AN). In this paper, we analyze the channel capacity of OFDM-based two-hop relaying systems over MV power lines, where a single relay node is used between the source and destination nodes in an effort to enhance the channel capacity using either cooperative relaying (CR) or noncooperative relaying protocols. For each relaying protocol, the relay node operates in either the amplify-and-forward (AF) or the decode-and-forward (DF) mode. Numerical results show that the channel capacity of the CR protocol in the DF mode is superior to that in the AF mode, as well as to the NCR protocol in the AF and DF modes.

A simple asynchronous UWB position location algorithm based on single round-trip transmission

We propose a simple asynchronous UWB (ultra wide band) position location algorithm with low complexity, low power consumption and minimal processing delay. In the proposed algorithm, UWB pulses are only twice utilized for single RTT (round-trip transmission) based on ToA (time of arrival) principle. Hence, the proposed UWB position location algorithm can decrease power consumption as well as minimize processing delay compared with basic ToA algorithm based on triple RTTs. Moreover, unlike TDoA (time difference of arrival) algorithm, the proposed algorithm can perform the position location with low complexity since it does not require strict synchronization. Nevertheless, simulation results in IEEE 802.15.4a UWB channel model reveal that the proposed UWB position location algorithm based on single RTT can achieve closely comparable position location accuracy of basic ToA and TDoA algorithms.

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.

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.

Coupler with transformer for impedance matching on mv power distribution line for BPLC

In this paper, the couplers with transformers for the purpose of impedance matching at signal input terminal of Medium Voltage(MV) power distribution lines for Broadband Power Line Communication(BPLC) which used in the frequency range of 1 MHz to 35 MHz have been designed, and the performance of those has been verified experimentally. In fact, the input impedance values of MV power distribution lines have been obtained between 200Omega and 300Omega[6]. In the range of these values, we have designed the transformers with general specific values of impedance: 50Omega, 112Omega, 253Omega, 356Omega, and 450Omega by utilizing the Ruthroffs transmission line transformer method[7]. The most proper transformer, matching well is embedded in a coupler and is implemented to transfer a transmitting signal with maximum power into the MV distribution lines. The performance of the designed coupler with a transformer is verified through measuring the reflection characteristics and signal attenuation in given MV test field. The measured results have informed that the couplers with transformers with impedance values of 253Omega or 356Omega have represented the best performance of them.

A Novel Ranging Method using Energy Window Bank in Non-coherent UWB Systems

This paper proposes a novel UWB ranging scheme employing 1-bit ADCs and analog window bank for energy collection. For an appropriate 1-bit ADC process DC offset is exploited and removed via performing analog low pass filter. To improve ranging accuracy in presence of ambiguity, dual overlapped window banks designated as primary and auxiliary windows are utilized. Corresponding to the proposed ranging scheme, its performance is verified by conducting simulations in two types of channel conditions. The simulation results show that the proposed ranging scheme performs well even in condensed multipath environment and low SNR situation.

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.

Performance of RCPC codes with soft-decision decoding over Nakagami-m fading channels

The analytical upper bounds on the pairwise error probability of rate compatible punctured convolutional (RCPC) codes, using coherent BPSK signals over slow frequency nonselective Nakagami-m fading channels with AWGN, are evaluated. With perfect channel state information (CSI) assumption, we use a direct integral with the Nakagami-m probability density function to obtain a closed form upper bound. For the case without CSI, we find an approximated upper bound for the high SNR cases and the approximation can be justified for signal to noise ratio (SNR) E/sub s//N/sub 0/ /spl Gt/ 1.5 dB.

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.