Myeongsu Han

Average SNR and ergodic capacity analysis for opportunistic DFrelaying with outage over rayleigh fading channels

In the paper, we deal with a single-selection opportunistic relaying with the decode-and-forward (DF) protocol over Rayleigh fading channels. The exact end-to-end average signal-to-noise ratios (SNR) and ergodic capacities of both proactive and reactive opportunistic relaying are derived as a closed-form for arbitrary link SNR. In addition, the effective ergodic capacity satisfying the minimum required data rate without outage is also identified for both relaying schemes. The analysis results are used to demonstrate which relaying scheme outperforms the other for given system parameters.

OFDM Channel Estimation With Jammed Pilot Detector Under Narrow-Band Jamming

This paper presents a channel estimation scheme using a new jammed pilot detection algorithm for orthogonal frequency-division multiplexing (OFDM) systems under narrow-band jamming (NBJ).signal-to-jamming ratio The jammed pilot subcarrier can be detected and excised by using the proposed algorithm after least squares estimation. The average mean square error (mse) on one OFDM symbol both under a jammed and a removed pilot subcarrier are derived analytically. Moreover, the symbol error rate (SER) performance for the channel estimation scheme using the proposed algorithm is evaluated by simulation. From the results, we can show that the channel estimator with the proposed algorithm improves the mse and SER performances at a low signal-to-jamming ratio.

Average SNR and Ergodic Capacity Analysis for Proactive and Reactive DF Relaying over Rayleigh Fading Channels

In this paper, we focus on single-selection oppor- tunistic relaying with the decode-and-forward protocol over Rayleigh fading channels. The end-to-end average signal-to-noise ratios (SNR) and ergodic capacities of both proactive and reactive opportunistic relaying are analyzed as a closed form in a high source-to-relay SNR regime where all link qualities satisfy the required SNR. The derived results are then used to prove that the end-to-end average SNR for the proactive scheme is greater than or equal to that of the reactive scheme. In addition, it is proven that the SNR and ergodic capacity differences of these schemes are broaden as the number of relays increases. The end-to-end ergodic capacities of the two methods are investigated both with and without the threshold using simulations. In this paper, we analyze the end-to-end average signal-to- noise ratios (SNR) and the ergodic capacities of two oppor- tunistic DF relaying schemes over dual-hop Rayleigh fading channels based on the assumption of a high source-to-relay SNR regime such that all link qualities attain the required SNR threshold. In addition, we use the results to verify that the end- to-end average SNR of the proactive scheme is greater than or equal to that of the reactive scheme. Moreover, it is derived how much the proactive scheme is better than the reactive one for given environment. In company with the SNR analysis, the end-to-end ergodic capacities of the two methods are also analyzed, and their performances are examined via simulations when a threshold is present. This paper is organized as follows: Section II presents the characteristics of the two opportunistic DF relaying schemes. Section III derives the end-to-end average SNRs of the two methods and proves the average SNR of P-DF outperforms that of R-DF. In addition, the SNR difference between two schemes are inspected according to the number of relays and link qualities of source-to-relay and relay-to-destination. Section IV analyzes the end-to-end ergodic capacities of the two types, and Section V provides the simulation results and discussion. Finally, our conclusions are presented in Section VI.

A New Power Allocation Scheme with Relay Selection in Multinode AF Relay Networks

In this paper, we present an improved power allocation scheme to minimize the outage probability subject to the total power constraint. For the proposed approach, the source power is determined by simplified optimization approach. The remaining power is then allocated equally to the set of selected relays by two proposed relay selection methods, optimal and simplified. Simulation results show that the power allocation with the proposed relay selection method improves the outage performance by both optimal and the simplified techniques. Moreover, the proposed method improves the performance even in the case of small number of relays.

A New Adaptive Code-Acquisition Algorithm Using Parallel Subfilter Structure

This paper presents a new adaptation algorithm using parallel subfilter structure, which enables fast-code acquisition for direct-sequence spread-spectrum systems. The proposed algorithm adapts the filter, based on a concept of dividing it into several subfilters, thus reducing the adaptation time. The detection and false-alarm probabilities are derived analytically. Simulation results show that the adaptive code-acquisition scheme, using the proposed algorithm, improves the mean-acquisition-time performance by 4-5 and 3-4 dB on additive white Gaussian noise and multipath Rayleigh fading channels for 64 taps, respectively

Improved adaptive code acquisition scheme for practical DS/SS systems

This paper presents our proposals to overcome two problems in applying the adaptive code acquisition scheme to practical systems. At first, a system parameter setting method based on SNR estimation is proposed to obtain near-optimum performance in real environments. Secondly, we propose a novel adaptation algorithm using a sub-filter structure, which enables the fast acquisition required in the practical systems. Simulation results show that the first proposal gives reliable acquisition performance in real situations without severe degradation, and the proposed adaptation algorithm offers 5-6 dB gain compared to the conventional adaptation algorithm for a number of taps of 64.

Performance Analysis of Multistage Interference Cancellation for Asynchronous TH-UWB Systems in Multipath Fading Channels

In this paper, we present an accurate analytical method for an asynchronous time-hopping (TH) ultrawideband (UWB) system using multistage interference cancellation (MIC) in multipath fading channels. To model the asynchronous transmission, we first investigate the chip-asynchronous case and extend the results of chip-asynchronous transmission into completely asynchronous transmission as a more general environment. Specifically, the approximate closed-form expression is derived for numerically calculating the average bit-error probability (BEP) of the MIC receivers, which are based on the hard-decision (HD) and soft-decision (SD) detections, respectively. In performing the analysis, the effect of multiple-access interference (MAI) is modeled as a Gaussian process. The results of an interference cancellation (IC) receiver as a function of the ratio between the two types of processing gain-1) pulse combining gain N s and 2) pulse spreading gain N c-are analyzed and compared under the constraint that the total processing gain of the system is large and fixed. To build up intuitive knowledge, some remarks on the analytic results are presented to describe the design criterion for the interference suppression. In numerical results, the theoretical analysis is verified via comparison with simulation results in terms of the number of IC stages, the set of cancellation parameters, and the number of users.

An Efficient Channel Estimation Algorithm under Narrow-Band Jamming for OFDM Systems

This paper presents a channel estimation scheme using a new jammed pilot detection algorithm for orthogonal frequency division multiplexing (OFDM) systems under narrow-band jamming (NBJ). The jammed pilot subcarrier can be detected and excised by using the proposed algorithm after least-squares estimation. The average mean-squared error (MSE) on one OFDM symbol both under a jammed and a removed pilot sub-carrier are derived analytically. Simulation results show that the channel estimator with the proposed algorithm significantly improves the MSE performance at a low signal-to-jamming ratio