• Journal of the Korean Operations Research and Management Science Society
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• 제28권4호
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• pp.1-19
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• 2003

This paper studies power and rate control for data users on the forward link of CDMA system with two cells. The QoS for data users is specified by delay and error rate constraints as well as a family of utility functions representing system throughput and fairness among data users. Optimal power and rate allocation problem is mathematically formulated as a nonlinear programming problem, which is to maximize total utility under delay and error rate constraints, and optimal power and rate allocation scheme (OPRAS) is proposed to obtain a good solution in a fast time. Computational experiments show that the proposed scheme OPRAS works very well and increases total utility compared to the separate power and rate allocation scheme (SPARS) which considers each cell individually.

• Journal of the Korean Institute of Telematics and Electronics A
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• 제31A권1호
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• pp.1-8
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• 1994

In this paper, we have analyzed the performance of a BRAM (The Broadcasting Recognizing Access Method) protocol, as a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) scheme, which is widely used in wireles LAN systems. We have selected a Fair BRAM protocol among CSMA/CA schemes, considering the fairness of channel usage and the simplicity of the protocol. We have compared the performance of BRAM protocol to that of CSMA/CD. to research the characteristics of BRAM in wireless LAN system. In order to analyze the performance of this system, we have set up an imbedded Markov chain and calculated state transition probabilities. Then we have calculated steady state probabilities and finally derived the throughput of a Fair BRAM moder. To verify our analysis, we have simulated practical models. Then, we have found that analytic results are very close to simulation ones. Our analysis of the BRAM protocol will be expected to be very helpful to design and evaluate a MAC (Media Access Control) protocol in wireless LAN systems.

• Journal of information and communication convergence engineering
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• 제6권1호
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• pp.19-23
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• 2008

The AQM (Active Queue Management) starts dropping packets earlier to notify traffic sources about the incipient stage of congestion. The AQM improves fairness between response flow (like TCP) and non-response flow (like UDP), and it can provide high throughput and link efficiency. In this paper, we suggest the QVARED (Queue Variation Adaptive RED) algorithm to respond to bursty traffic more actively. It is possible to provide more smoothness of average queue length and the maximum packet drop probability compared to RED and ARED (Adaptive RED). Therefore, it is highly adaptable to new congestion condition. Our simulation results show that the drop rate of QVARED is decreased by 80% and 40% compare to those of RED and ARED, respectively. This results in shorter end-to-end delay by decreasing the number of retransmitted packets. Also, the QVARED reduces a bias effect over 18% than that of drop-tail method; therefore packets are transmitted stably in the bursty traffic condition.

• Proceedings of the IEEK Conference
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• 대한전자공학회 2002년도 ITC-CSCC -2
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• pp.892-895
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• 2002

We propose new buffer management scheme for GFR service through FIFO queuing discipline. Proposed scheme can provide minimum bandwidth guarantees for GFR VCs as well as improve the fairness among the competing GFR VCs on a single FIFO queue. From simulation results, we demonstrate the proposed scheme fulfills the requirements of GFR service as well as improves the TCP throughput.

• Journal of IKEEE
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• 제11권4호
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• pp.171-177
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• 2007

Although the Distributed Coordination Function is the fundamental access protocol of IEEE 802.11, it cannot meet the Quality of Service (QoS) requirements in general. So, the Point Coordinate Function is provided to support QoS related services. However, it has inherent problems. Access point (AP) has no knowledge of the queue status and instantaneous channel condition of stations in the system. In this paper we propose an efficient and versatile polling scheduler that shows excellent throughput and fairness performance. Comparison with well known polling schemes is provided through computer simulation under various channel situations including error prone environments.

• The Journal of the Korea Contents Association
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• 제6권2호
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• pp.9-16
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• 2006

This paper proposes a scheduling algorithm for efficiently processing multimedia pakcet services in OFDMA physical system of the future broadband wireless access networks. The scheduling algorithm uses wireless channel state estimation, and allocates transmission rates after deciding transmission ordering based on class and priority policy. As the result, the proposed scheduling algorithm offers maximum throughput and minimum jitter for realtime services, and fairness for non-realtime services. In simulation study, the proposed algorithm proves superior performances than traditional round robin method.

• Annual Conference of KIPS
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• 한국정보처리학회 2003년도 추계학술발표논문집 (중)
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• pp.1121-1124
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• 2003

스케줄링은 네트워크상의 공유된 자원을 보다 효과적으로 이용하기 위한 것으로서 delay, delay jitter, packet loss rate, throughput과 같은 서비스 값들의 QoA(Quality of Service)를 보장하기 위한 핵심 요소이다. 유선망에서의 스케줄링은 이미 익숙한 영역으로 많은 발전이 되어왔지만, 무선채널의 불안정성이나 사용자의 움직임으로 인해 발생하는 다양한 링크 에러율과 용량 때문에 무선망에서의 직접적용은 많은 문제를 일으키게 된다. 이 논문에서는 기존에 나와 있는 여러 무선 스케줄링 기법중 채널 보상 모델을 이용하여 서비스 차별화(Service Differentiation)와 공평성(Fairness)에 초점을 맞춘 QoS제공 성능향상 스케줄링 알고리즘을 제안하였다.

• Annual Conference of KIPS
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• 한국정보처리학회 2005년도 추계학술발표대회 및 정기총회
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• pp.1371-1374
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• 2005

지금까지 IEEE 802.11 WLAN 에서 많이 연구되어진 주제는 노드들 간의 공평성(fairness)과 처리량(throughput)을 높이는데 중점이 맞추어진 것들이 대부분이었다. 성능을 높이기 위한 AP의 CW값에 관한 연구는 노드들 간에 관한 연구에 비하여 비교적 적은 편이다. 지금은 노드들과 AP가 충돌하게 되면 BEB(Binary Exponential backoff)방식으로 셋팅되어 사용하게 있기 때문에 1:N의 불공평한(unfairness) 상황이 발생한다. AP에서 노드들로 가는 하향링크(downlink) 전송이 많은 상황에서 AP가 다른 노드들과 똑같은 채널 접근확률을 가지는 것은 바람직하지 않기 때문에 AP에게 우선권(priority)을 주어 전체 성능을 높이는 것이 필요하다. 따라서 본 논문에서는 AP의 CW(Contention Window)값이 변화함에 따라 전체 성능에 끼치는 영향과 노드 수의 변화에 따른 AP의 적절한 백오프 CW값을 분석해 보고자 한다.

• Management Science and Financial Engineering
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• 제16권1호
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• pp.59-79
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• 2010

This paper considers bandwidth allocation and scheduling problems on Ethernet Passive Optical Networks (EPON). EPON is one of the good candidates for the optical access network. This paper formulates the bandwidth allocation problem as a nonlinear mathematical one and characterizes the optimal bandwidth allocation which maximizes weighted sum of throughput and fairness. Based upon the characterization, two heuristic algorithms are suggested with various numerical tests. The test results show that our algorithms can be used for efficient bandwidth allocation on the EPON. This paper also shows that the WSPT (Weighted Shortest Processing Time) rule is optimal for minimization the total delay time in transmitting the traffic of the given allocated bandwidth.

• Proceedings of the IEEK Conference
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• 대한전자공학회 2000년도 ITC-CSCC -1
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• pp.77-79
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• 2000

Industrial communication networks have attracted much attention in the area of decentralized control systems for factory automation and computer integrated manufacturing. In this paper, we investigate the rate-based traffic control of industrial communication networks employing LonWorks to improve the performance measures of throughput, fairness, and error rates. To this end, we utilize the Feedback channel information through the additional network monitoring node and make the overall system closed-loop. We demonstrate the improved performance of the controlled network system by the experimentation upon an implemented lab-scale network system.