Seungyoup Han

Effect of Channel-Estimation Error on BER Performance in Cooperative Transmission

In this paper, a framework for evaluating the bit-error-rate (BER) performance of amplify-and-forward (AF) relay-assisted cooperative transmission is provided in the presence of imperfect channel estimation. First, the AF relaying is classified into two cases - a variable gain and a fixed gain. For each case, the closed-form average BER is derived by using the moment-generating function (MGF) of the effective output SNR, which quantifies the SNR penalty due to the noisy channel estimate. Moreover, the asymptotic BER bound is also provided at a high SNR regime for the insight of our approach. In particular, the effect of the feedforward delay on informing the source-relay channel estimate as to the destination is presented in the variable-gain relay. Numerical investigation shows that the analytic result makes an exact match with the simulation, and the comparative superiority between the fixed- and variable-gain relay is discussed.

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.

Performance Analysis of Reuse-Partitioning-Based Subchannelized OFDMA Uplink Systems in Multicell Environments

This paper presents a performance analysis of reuse partitioning (RUP)-based subchannelized orthogonal frequency-division multiple-access (OFDMA) uplink systems in multicell environments. The cochannel interference (CCI) statistic is calculated for OFDMA uplink systems. The derived statistic is then used to analyze the performance of subchannelized OFDMA systems based on RUP. Analysis and simulation results show that the performance of a subchannelized OFDMA system in multicell environments is noticeably dependent on the CCI, and the effect of CCI can be reduced by the RUP scheme. Finally, the results of the analysis yield the optimum RUP area for achieving the maximum system throughput.

Call admission control strategy for system throughput maximization considering both call- and packet-level QoSs

This letter presents a call admission control (CAC) strategy for system throughput maximization in wireless uplink systems. This strategy considers not only the call-level quality of service (QoS) (i.e., blocking probability) but also the packet-level QoS (i.e., outage probability). Using the statistical co-channel interference (CCI) model and state diagram, the outage probability and the blocking probability are investigated as a function of the relative traffic load. We formulate the CAC strategy problem based on relative traffic load, and suggest a solution. The numerical results show that maximum system throughput can be achieved by controlling the relative traffic load. In addition, we illustrate the region where system throughput is constrained by call- and packet-level QoSs. This examination shows that the call and packet-level QoSs must be considered together to achieve maximum system throughput.

Performance Analysis of Dynamic Channel Allocation Based on Reuse Partitioning in Multi-Cell OFDMA Uplink Systems*This paper was presented on Poster 3: Communications (1) section at the ITC-CSCC 2005.

Our investigation is presented into analysis of the co-channel interference (CCI) statistic in orthogonal frequency-division multiple access (OFDMA) uplink systems. The derived statistic is then used to analyze the performance of reuse partitioning (RP)-based dynamic channel allocation (DCA). Analysis and simulation results show that the performance of DCA in multi-cell environments is noticeably dependent on the CCI. Finally, the results of the analysis yield the optimum RP area for achieving the maximum spectral efficiency.

The Effect of Multiplexing Users in QoS Provisioning Scheduling

In this paper, we consider the effect of multiplexing users in a frame (more specifically, coherent time) on providing quality of service (QoS) in multiuser wireless networks. For this purpose, we propose simple and efficient scheduling schemes that can yield substantial capacity gain. Our approach involves maximizing the throughput subject to a given delay QoS constraint by choosing the appropriate number of users to be served in a frame. We call this number the degree of multiplexing. We investigate the effect of the degree of multiplexing on QoS performance in wireless multiuser scheduling by analyzing the effective capacity and then develop an approach to finding the optimal degree of multiplexing by asymptotic approximation.

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.

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.

UWB interference cancellation receiver in dense multipath fading channel

Interference cancellation (IC) scheme using partial RAKE combining is proposed in multiuser ultra-wideband (UWB) fading channels. The UWB system under consideration employs a time-hopping impulse radio multiple access (TH-IRMA) format. The proposed IC scheme includes a design for a modified impulse radio transmitter model, and uses a partial RAKE combining technique to estimate the tentative decisions for reconstructing multiple access interference (MAI). In addition, partial user interference cancellation is considered in order to reduce the complexity of the receiver. Unlike conventional UWB systems, the proposed IC scheme exhibits little degradation in BER performance as the number of users increases. Moreover, the partial user IC scheme achieves considerable improvement in performance with reduced IC receiver complexity.

Group-Wise Distributed Space-Time-Frequency Coded OFDM over Asymmetric Frequency-Selective AF Relay Channels

Distributed space-time-frequency coding (DSTFC) is a method to achieve diversity from both multipaths and user cooperations. The DSTFC has been researched by assuming that the multipath profiles of relays are the same (symmetric). However, the symmetric frequency- selective channel is limited in the wireless relay communications. Thus, in this paper, we propose a new DSTFC for relay-based amplify-and-forward (AF) cooperative scheme over the asymmetric frequency selective channels. The proposed scheme is based on the sub-carrier grouping in OFDM transmission. By analyzing pairwise error probability (PEP), diversity order of the proposed DSTFC is derived. In addition, a necessary condition of sub-carrier grouping to achieve the maximum diversity and minimize the decoding complexity is investigated. Simulation results verify that the proposed scheme can achieve the maximum diversity gain for a given asymmetric multipath profile.