• 한국정보통신학회논문지
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• 제13권11호
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• pp.2447-2458
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• 2009

Ad hoc 네트워크는 데이터 발신과 라우터 역할을 동시에 수행할 수 있는 노드들로 구성되며 특정한 네트워크 기반 구조의 지원 없이도 동작할 수 있는 장점을 지니고 있다. Ad hoc 네트워크에서는 무선 네트워크 상의 전체 전송영역에서 높은 처리율과 낮은 지연시간을 반드시 제공할 수 있어야 한다. 최근 들어 빔 생성(beam-forming) 방식이나 멀티플렉싱 방식의 다중안테나 (MIMO)를 이용하여 높은 처리율과 낮은 지연시간을 제공하기 위한 새로운 연구가 수행된 바 있으며, 이러한 연구 결과에 의해 송 수신자들이 서로간에 심각한 간섭을 일으키지 않는다면 다수의 송 수신자가 안테나의 지향성 빔을 이용하여 통신을 위한 공간 재사용 가능성을 높일 수 있음을 검증한바 있다. 그러나 Ad hoc 네트워크에서 노드 밀도가 증가하면 지향성 안테나의 성능은 무지향성 안테나의 성능과 유사하게 된다. 본 연구에서는 QualNet을 이용한 시뮬레이션을 통해 Ad hoc 네트워크 내의 노드 수가 크게 증가하면 지향성 안테나의 평균 처리량과 패킷 에러율이 무지향성 안테나의 성능에 점진적으로 근접한다는 사실을 증명하였으며, 무선네트워크에서 지향성 안테나 성능 개선을 위해 비중 있게 다루어야 할 중요 이슈들에 대해 자세히 기술하였다.

• 대한임베디드공학회논문지
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• 제1권2호
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• pp.64-72
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• 2006

The long propagation delay over satellite internet causes degradation of TCP performance in slow start phase. Especially, web traffic performance is greatly reduced by low throughput in slow start phase. To improve web traffic performance, we propose the Dynamic ACK Generation Scheme which generates ACKs and considers sender RTO in PEP (Performance Enhancing Proxy). The Normal ACK generation mechanism improves TCP throughput, and also decreases sender RTO. if PEP stops generating ACKs, TCP performance will be reduced by frequent RTO expiration. To solve this problem, our scheme adjusts RTO using ACK generation interval. And it supports retransmission mechanism for loss recovery in PEP. The results of the performance analysis provide a good evidence to demonstrate the efficiency of our mechanisms over satellite internet.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권1호
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• pp.79-95
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• 2016

In order to improve the Quality-of-Service (QoS) of latency sensitive applications in next-generation cellular networks, multi-path is adopted to transmit packet stream in real-time to achieve high-quality video transmission in heterogeneous wireless networks. However, multi-path also introduces two important challenges: out-of-order issue and reordering delay. In this paper, we propose a new architecture based on Software Defined Network (SDN) for flow aggregation and flow splitting, and then design a Multiple Access Radio Scheduling (MARS) scheme based on relative Round-Trip Time (RTT) measurement. The QoS metrics including end-to-end delay, throughput and the packet out-of-order problem at the receiver have been investigated using the extensive simulation experiments. The performance results show that this SDN architecture coupled with the proposed MARS scheme can reduce the end-to-end delay and the reordering delay time caused by packet out-of-order as well as achieve a better throughput than the existing SMOS and Round-Robin algorithms.

• East Asian mathematical journal
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• 제30권1호
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• pp.23-29
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• 2014

To solve inefficient spectrum usage problem under current static spectrum management policy, various kinds of dynamic spectrum access strategies have appeared. Myopic policy, which maximizes immediate throughput, is a simple and robust strategy with reduced complexity. In this paper, we present a simple mathematical model to evaluate the saturation throughput and medium access delay of a myopic policy in the presence of multiple channels.

• ETRI Journal
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• 제30권2호
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• pp.282-289
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• 2008

We propose a new mini-slot transmission scheme for a passive optical network (PON) in which each customer can be switched either to access mode or to internetworking mode dynamically. In this paper, we present the system implementation (called LAN-PON) as well as the performance of the proposed transmission scheme to illustrate its feasibility and benefits. A mini-slot scheme can rapidly reduce the queuing delay, which increases due to the flooding of the deflected packets in a deflection scheme. We evaluate the impact of mode switching time on the bandwidth gain (throughput) and delay of local area network (LAN) traffic in the LAN-PON with a mini-slot scheme. We also analyze a theoretical delay model of the proposed scheme. The simulation results demonstrate that switching time has an impact on LAN performance, and the average packet delay of the proposed scheme is significantly improved compared to that of the deflection scheme.

• 한국통신학회논문지
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• 제21권10호
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• pp.2620-2633
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• 1996

In this paper, a new high-speed local area network using a dual mode switching access (DMSA) protocol implemented on a dual unidirectional bus is described. By utilizing the implicit positionalordering of stations on a unidirectional bus, the proposed system switches between random access mode and the token access model withoug unnecessary delay. Therefore, unlike other hybrid systems such as Buzz-net and Z-net, DMSA does not show a rapid degradation in performance as the load increases. We obtain the average channel utilization and the average access delay by using a simplified analytic model. The numerical results obtained via analysis are compared to the simulation resuls for a partial validation of the approximate model. The performance characteristics of DMSA are superior delay-throughput characteristics at light and medium loads, compared to compared to other LAN systems, and the capability of providing a single active station with full capabity of the channel.

• 한국통신학회논문지
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• 제32권12A호
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• pp.1320-1328
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• 2007

최근 무선 LAN의 인기로 IEEE 802.11 프로토콜의 성능 분석과 개선에 많은 관심이 생겨났다. 본 논문에서는 도착하는 패킷의 크기가 일반 확률분포를 가질 때 MAC 계층 패킷 서비스 시간을 조사하여 IEEE 802.11 프로토콜의 두 가지 매체 접속 방식을 분석한다. 무선 LAN에서 IEEE 802.11 프로토콜의 수율 및 지연 성능을 분석하기 위해 M/G/1/K 큐잉 모델을 사용한다. 두 가지 접속 방법, 기본 접속과 RTS/CTS 접속 방식의 성능을 비교한다. 그리고 시스템의 수율 및 평균 패킷 지연과 패킷 블록킹 확률을 포함하여 큐의 동작 상태를 보기 위한 여러가지 수치예를 보여준다.

• 한국항공운항학회지
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• 제20권3호
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• pp.22-27
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• 2012

In oceanic flight routes, HF radio and satellite data links have been used for air-to-ground communication, but these systems have long propagation delay and low data throughput. In this paper, we propose a reliable system to overcome the weakness of current HF radio and satellite communication systems for oceanic aeronautical flight routes. The proposed scheme uses only one aeronautical VHF channel in multi-hop oceanic communication environments and supports a hybrid type of multiple access, which consists of random access and TDMA (Time Division Multiple Access) scheme. The proposed system improves performance on delay and throughput as an effective solution to communicate end-to-end on the oceanic flight routes and strengthens the reliability of oceanic aeronautical communication.

• 산업공학
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• 제4권1호
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• pp.63-69
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• 1991

In this paper, the Go-Back-N ARQ protocol with decoding in communication network is considered. The time delay and throughput are respectively analyzed as a function of window size and decoding time out. Packets arrive continuously at the decoder, and are stored in a buffer if the decoder is busy upon its arrival. The decoder devotes no more than a time-out period of predetermined length to the decoding of any single packet. If packet decoding is completed within that period, the packet leaves the system. Otherwise, it is retransimitted and its decoding starts anew. The time delay and throughput are obtained using recursive formula and difference equation. An appropriate time out and window size that satisfies the grade of service can be determined.

• ETRI Journal
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• 제42권1호
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• pp.36-45
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• 2020

A priority-based data communication approach, developed by employing cognitive radio capacity for sensor nodes in a wireless terrestrial sensor network (TSN), has been proposed. Data sensed by a sensor node-an unlicensed user-were prioritized, taking sensed data importance into account. For data of equal priority, a first come first serve algorithm was used. Non-preemptive priority scheduling was adopted, in order not to interrupt any ongoing transmissions. Licensed users used a nonpersistent, slotted, carrier sense multiple access (CSMA) technique, while unlicensed sensor nodes used a nonpersistent CSMA technique for lossless data transmission, in an energy-restricted, TSN environment. Depending on the analytical model, the proposed wireless TSN environment was simulated using Riverbed software, and to analyze sensor network performance, delay, energy, and throughput parameters were examined. Evaluating the proposed approach showed that the average delay for sensed, high priority data was significantly reduced, indicating that maximum throughput had been achieved using wireless sensor nodes with cognitive radio capacity.