• Journal of electromagnetic engineering and science
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• v.9 no.3
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• pp.124-129
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• 2009

Although the maximum sum-rate capacity of multiple-input multiple output(MIMO) broadcast channels(BCs) can be achieved by dirty-paper coding(DPC), the results were obtained without fairness considerations in uncorrelated MIMO channels. In this paper, we propose new multiuser scheduling algorithms, which find a best user set for approaching the maximum sum-rate capacity while maintaining fairness among users. We analyze the performance of the proposed algorithms using zero-forcing dirty paper coding(ZF-DPC) in the correlated MIMO BCs for throughput and delay fairness, respectively. Numerical results demonstrate that a large time window can reduce the average throughput difference between users, but it increases head-of-line(HOL) delay jitters in the case of delay fairness.

• Journal of electromagnetic engineering and science
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• v.12 no.1
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• pp.8-12
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• 2012

In this paper, we evaluate performances of dual-hop decode-and-forward relaying systems with the $N^{th}$ best-relay selection scheme. In some schemes, such as scheduling or load balancing schemes, the best relay is unavailable and hence the system must resort the second best, third best, or generally the $N^{th}$ best relay. We derive the expressions of the outage probability and symbol error rate (SER) for this scenario over Rayleigh fading channels. Monte-Carlo simulations are presented to verify the analytical results.

• IEIE Transactions on Smart Processing and Computing
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• v.1 no.1
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• pp.50-64
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• 2012

Quality of Service (QoS) and fairness considerations are undoubtedly essential parameters that need to be considered in the design of next generation scheduling algorithms. This work presents a novel game theoretic cross-layer design that offers optimal allocation of wireless resources to heterogeneous services in Orthogonal Frequency Division Multiple Access (OFDMA) networks. The method is based on the Axioms of the Symmetric Nash Bargaining Solution (S-NBS) concept used in cooperative game theory that provides Pareto optimality and symmetrically fair resource distribution. The proposed strategies are determined via convex optimization based on a new solution methodology and by the transformation of the subcarrier indexes by means of time-sharing. Simulation comparisons to relevant schemes in the literature show that the proposed design can be successfully employed to typify ideal resource allocation for next-generation broadband wireless systems by providing enhanced performance in terms of queuing delay, fairness provisions, QoS support, and power consumption, as well as a comparable total throughput.

• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.256-259
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• 2007

Multicast and Broadcast Service (MBS) provides flexible and efficient transmission of the same information to multiple users using shared radio resources on WiBro network. The advantage of this service is to achieve the most efficient use of radio and network resources as well as to lessen sender's processing load when sending the same information to multiple users. Though radio resources are saved since a multicast or broadcast transport connection is associated with a service flow, it is hard to change MBS service channel dynamically. In this paper, we propose a Radio Resource Management System (RRMS) for supporting dynamic scheduling of MBS service channels. Results show that our proposed scheme using Radio Resource Allocation Table (RRAT) can efficiently support MBS services by providing dynamic schedule for MBS service channels.

• Proceedings of the Korean Information Science Society Conference
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• 2007.10c
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• pp.163-168
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• 2007

무선 모바일 환경에서 통신 장비의 에너지와 전송 대역폭의 제한을 해결하기 위하여 방송기법을 사용한다. 기존의 방송 스케줄링 방법들은 고정된 데이터 요청 빈도를 바탕으로 방송 스트림을 구성하기 때문에 사용자의 요구가 동적으로 변화하는 모바일 환경에서 활용하는 것은 비효율적이다. 또한 사용자의 우선순위를 고려하지 않음으로써 요청빈도가 낮은 데이터를 원하는 중요한 사용자가 오랜 시간 대기하는 상황이 발생할 수 있다. 본 논문에서 제안한 DNPS와 FPDNPS 방법은 실제 방송 청취를 시작한 사용자들의 프로파일 정보를 바탕으로 방송 스트림을 구성함으로써 동적인 변화를 반영할 분만 아니라, 사용자의 우선순위를 함께 고려함으로써 중요한 사용자의 대기시간을 줄일 수 있다. 또한 동시에 여러 개의 데이터를 요청하는 사용자들의 대기시간을 단축시키는 FPDNPS 알고리즘을 다중 채널환경으로 확장한 M-FPDNPS를 제안하고 실험을 통해 성능을 평가한다.

• ETRI Journal
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• v.39 no.2
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• pp.255-263
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• 2017

This paper proposes a graph-theatrical approach to optimize spatial reuse by adopting a technique that quantizes the channel information into single bit sub-messages. First, we introduce an interference graph to model the network topology. Based on the interference graph, the computational requirements of the algorithm that computes the optimal spatial reuse factor of each user are reduced to quasilinear time complexity, ideal for practical implementation. We perform a resource allocation procedure that can maximize the efficiency of spatial reuse. The proposed spatial reuse scheme provides advantages in beamforming systems, where in the interference with neighbor nodes can be mitigated by using directional beams. Based on results of system level measurements performed to illustrate the physical interference from practical millimeter wave wireless links, we conclude that the potential of the proposed algorithm is both feasible and promising.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1348-1356
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• 2002

The present work concerns the optimal design for injection molding processes by using the design of experiments (DOE) and numerical analysis. The DOE approaches is planned to be able to consider two-way interaction, and have been applied progressively for both mold design and process design. Numerical analyses have been carried out as a design of experiments for mold parameters such as runner specifications and cooling channel configurations. In order to determine optimal process parameters, experiments have been performed for various process conditions with the DOE scheduling. As a result, the quality and productivity of the product have been improved, and the proposed approach can be successfully reflected on the industrial injection molding process of precision electronics parts.

• Journal of Communications and Networks
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• v.5 no.3
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• pp.222-229
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• 2003

In this paper, we propose a delayed multiple copy retransmission (DMCR) scheme for data communication in wireless networks, by which multiple copies of a lost link layer frame are retransmitted one-by-one with a retransmission delay in between. The number of the copies gradually increases with the number of retransmissions. Furthermore, for implementation of the DMCR scheme in practical mobile communication system, we also propose a dynamic retransmission scheme by interleaving and a new round-robin scheduling algorithm. We compare our scheme with the previous non-delayed retransmission schemes on the performance of frame loss probability, channel capacity and total transmission time. Numerical results show that the DMCR scheme can achieve higher performance. The effect of the delay time on endto-end TCP throughput is investigated as well.

• Proceedings of the Korean Information Science Society Conference
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• 2011.06d
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• pp.311-314
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• 2011

Wi-Fi 메쉬 네트워크는 IEEE 802.11 표준을 기반으로 노트북, 스마트폰 등의 무선 단말에 인터넷 연결을 제공하기 위한 무선 다중 홉 네트워크이다. Wi-Fi 메쉬 네트워크에서는 무선 채널의 방송 특징으로 인해 발생하는 간섭(Interference) 때문에 프레임 충돌 문제가 발생한다. 본 논문에서는 이러한 프레임 간섭을 미연에 방지하는 스케줄링 MAC 프로토콜을 제안한다. 제안하는 방법은 각각의 무선 채널에서 간섭 조건을 만족하는 링크 조합을 결정하고, 이를 통하여 Wi-Fi 메쉬 네트워크의 프레임 전달 수율(Throughput)을 극대화함을 목표로 한다. 시뮬레이션 결과를 통해 본 논문에서 제시하는 스케줄링 MAC 프로토콜이 기존에 알려진 CSMA/CA 기반의 MAC 프로토콜에 비해 수율을 50 % 이상 향상함을 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.5
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• pp.1587-1605
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• 2015

Mobile cloud computing (MCC) combines mobile Internet and cloud computing to improve the performance of applications. In MCC, the data processing and storage for mobile devices (MDs) is provided on the remote cloud. However, MCC faces the problem of energy efficiency caused by randomly varying channels. In this paper, by introducing the Lyapunov optimization method, we propose a combined service subscription and delivery (CSSD) algorithm that can guide the users to subscribe to services reasonably. This algorithm can also determine whether to deliver the data and to whom data is sent in the current time unit based on the queue backlog and the channel state. Numerical results validate the correctness and effectiveness of our proposed CSSD algorithm.