Interference Cancellation Using Partial Rake Combining for UWB Communication Systems

Seungyoup Han,ChoongChae Woo,Kyunbyoung Ko,Daesik Hong 한국통신학회 2004 한국통신학회 학술대회 및 강연회 Vol.2004 No.4

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

Seungyoup Han,Eunsung Oh,Myeongsu Han,Choongchae Woo,Daesik Hong IEEE 2009 IEEE Transactions on Vehicular Technology VT Vol.58 No.3

<P>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 <I>N</I> <SUB>s</SUB> and 2) pulse spreading gain <I>N</I> <SUB>c</SUB>-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.</P>

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

Seungyoup Han,Seongwoo Ahn,Eunsung Oh,Daesik Hong IEEE 2009 IEEE Transactions on Vehicular Technology VT Vol.58 No.4

<P>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.</P>

OFDMA 시스템에서 비율적 전송률 분배를 위한 자원 할당

한승엽(Seungyoup Han),오은성(Eunsung Oh),한명수(Myeongsu Han),홍대식(Daesik Hong) 대한전자공학회 2008 電子工學會論文誌-TC (Telecommunications) Vol.45 No.1

본 논문에서는 직교 주파수 분할 다중 접속 방식 (OFDMA, Orthogonal Frequency Division Multiple Access)에서 전송률의 비율적 제한 조건 (Constraint)이 고려된 자원 할당 방식에 대해 논의한다. 제안된 자원 할당 방식은 비트 오율, 전송 전력 및 전송 비율 등에 관한 제한 조건 하에서 사용자들이 요구하는 다양한 서비스를 만족하면서 최대의 시스템 전송률을 얻기 위한 최적화 문제를 다룬다. 본 문제에 관한 최적의 해 (optimal solution)는 상당히 복잡하므로 부 채널 할당과 전력 할당을 나누어 복잡도를 낮춘 부 최적 해 (Suboptimal solution)를 제안한다. 먼저, 각 사용자에게 할당될 부 채널의 수를 사용자들의 평균 신호 대 잡음비와 전송률 비율을 기반으로 결정한다. 이어서 사용자에게 할당될 부 채널은 변형된 max-min 알고리즘에 따라 결정되고 이를 기반으로 최적화 문제에 대한 Lagrange dual 문제의 해를 구하는 최적의 전력 할당 방식을 제안한다. 또한 보다낮은 복잡도를 갖는 전력 할당을 위해 반복적 전송 비율 검출 알고리즘을 제안한다. 마지막으로 모의실험을 통해 본 논문에서는 제안하는 알고리즘이 사용자 간의 전송률에 관한 공평성 (fairness)을 정확히 만족하면서 시스템의 전송률을 극대화할 수 있음을 분석한다. In this paper, a new adaptive resource allocation scheme is proposed in orthogonal frequency-division multiple access (OFDMA) systems with rate proportionality constraints. The problem of maximizing the overall system capacity with constraints on bit error rate, total transmission power and rate-proportionality for user requiring different classes of service is formulated. Since the optimal solution to the constrained fairness problem is extremely complex to obtain, a low-complexity suboptimal algorithm that separates subchannel allocation and power allocation is proposed. Firstly, the number of subchannels to be assigned to each user is determined based on the users’ average signal-to-noise ratio and rate-proportion. Subchannels are subsequently distributed according to the modified max-min criterion. Lastly, based on the subchannel allocation, the optimal power allocation by solving the Language dual problem is proposed. Additionally, in order to reduce the computational complexity, iterative rate proportionality tracking algorithm is proposed for maximizing the capacity together with maintaining the rate proportionality constraint.

주파수 가간섭성을 이용한 피드백을 사용하는 하향 링크 OFDMA 시스템에서의 동적 자원 할당 방법

한재민(Jaemin Han),오은성(Eunsung Oh),한승엽(Seungyoup Han),주형식(Hyungsik Ju),홍대식(Daesik Hong) 대한전자공학회 2007 대한전자공학회 학술대회 Vol.2007 No.11

In this paper, we propose a new DCA (Dynamic Channel Allocation) in DL (Downlink) OFDMA (Orthogonal Frequency Division Multiple Access). The proposed DCA scheme exploits each user"s coherence bandwidth in a multi-path environment, resulting in the better multi-user diversity performance than the amplitude craving greedy (ACG) method and Modified ACG (M-ACG) with the reduced feedback overhead.

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

Eunsung Oh,Seungyoup Han,Choongchae Woo,Daesik Hong IEEE 2008 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.56 No.10

<P>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.</P>

Performance Analysis of Dynamic Channel Allocation based on Reuse Partitioning in Multi-cell OFDMA Uplink Systems

Eunsung Oh,Seungyoup Han,Choonchae Woo,Daesik Hong 대한전자공학회 2005 ITC-CSCC :International Technical Conference on Ci Vol.2005 No.2

OFDMA 시스템에서 그리디 방법을 기반으로 한 동적 채널 할당 알고리즘의 성능분석

오은성(Eunsung Oh),한승엽(Seungyoup Han),홍대식(Daesik Hong) 대한전자공학회 2007 電子工學會論文誌-TC (Telecommunications) Vol.44 No.11

본 논문은 직교 분할 다중 반송파 다중 접속 방식(OFDMA, Orthogonal Frequency Division Multiple Access)에서 그리디 방법(GA, Greedy Approach)을 사용한 동적 채널 할당 알고리즘의 성능분석에 관한 것이다. GA를 기반으로 한 동적 채널 할당의 경우 사용자간의 다이버시티 효과를 통하여 성능 이득을 얻을 수 있다. 본 논문에서는 동적 채널 할당 알고리즘에서 다중 사용자 다이버시티 계수인 할당 가능한 사용자 수(NAU, Number of Allocable Users)를 모델링하고, 이를 통하여 GA를 기반으로 한 동적 채널 할당 알고리즘의 성능(실패 확률 및 데이터 전송량)을 분석한다. 분석된 결과를 기반으로 GA를 기반으로 한 동적 채널 할당 알고리즘의 성능을 최대화 할 수 있는 조건을 제시할 수 있다. This paper presents a performance analysis of dynamic channel allocation (DCA) based on the greedy approach (GA) for orthogonal frequency division multiple access (OFDMA) systems over Rayleigh fading channels. The GA-based DCA achieves its performance improvement using multi-user diversity. We analyze the statistics of the number of allocable users (NAU), which represents the multi-user diversity order at each allocation process. The derived statistics are then used to analyze the performance of GA-based DCA. The analysis results show that the number of subcarriers allocated to each user must be equal to achieve the maximum system performance (i.e., based on outage probability and data throughput).

릴레이 기반의 OFDMA 시스템에서 전송량 증대를 위한 간략화 된 자원 할당 방법

오은성(Eunsung Oh),주형식(Hyungsik Ju),한승엽(Seungyoup Han),홍대식(Daesik Hong) 大韓電子工學會 2009 電子工學會論文誌-TC (Telecommunications) Vol.46 No.9

본 논문은 릴레이 시스템을 기반으로 한 직교 분할 다중 반송파 다중 접속 방식(OFDMA, Orthogonal Frequency Division Multiple Access)에서 전송량을 증대를 위한 자원 할당 방법에 관한 것이다. 최적화 문제를 기반으로 하는 자원 할당 방법은 할당 가능한 자원에 대한 검색 과정을 수반하기 때문에 높은 복잡도를 갖는다. 본 논문에서는 복잡도를 줄이기 위하여 세 단계의 자원 할당 방법을 제안한다. 각각의 단계에서 릴레이, 주파수, 시간 자원이 독립적으로 할당되며, 자원을 분리하여 할당함에 따라 복잡도를 줄일 수 있다. 실험 결과를 통하여 제안하는 방법이 복잡도를 줄이면서 최적화 성능에 근접할 수 있음을 보인다. This paper presents a simple resource allocation scheme for throughput enhancement in relay based orthogonal frequency division multiple access (OFDMA) cellular systems. The resource allocation schemes, which are based on the optimization problem, have high computational complexity. That is why a searching process is required on the overall allocable resources. Since these schemes should be performed in real time, we propose a simple resource allocation scheme which has very low computational complexity. Firstly, we formulate the optimization problem and draw observations for throughput maximization. Based on observations, we propose a three step allocation scheme that separates the allocable resources into three (i.e. relay, frequency and time). By doing so, the computational complexity can be reduced. Simulation results show that the proposed scheme has near-optimum performance in spite of its low computational complexity.

The Effect of Multiplexing Users in QoS Provisioning Scheduling

Seong-woo Ahn,Hano Wang,Seungyoup Han,Daesik Hong IEEE 2010 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY Vol.59 No.5

<P>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 <I>degree of multiplexing</I>. 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.</P>