• ETRI Journal
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• v.37 no.5
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• pp.845-855
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• 2015

To enable the coexistence of Licensed Assisted Access (LAA) and Wi-Fi in 5 GHz unlicensed bands, a new channel access mechanism is proposed. Accounting for the fairness between LAA and Wi-Fi, the proposed mechanism finds the optimal transmission time ratio by adaptively adjusting the transmission durations for LAA and Wi-Fi. In addition, we propose a new analytical model for the distributed coordination function of IEEE 802.11 through some modifications of conventional analytical models for saturation and non-saturation loads. By computing the activity ratio of Wi-Fi, the proposed analytical model is able to control the time ratio between LAA and Wi-Fi, which is required for practical implementation of the proposed access mechanism. Through numerical simulations, the proposed channel access mechanism is compared with conventional methods in terms of throughput and utility.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7A
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• pp.727-734
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• 2004

Collision Management Protocol (CMP) efficiently resolves collisions when data frames are transmitted in networks consisting of HomPNA 3.0 asynchronous MAC mode device with random access. Unlike Distributed Fair Priority Queueing (DFPQ) algorithm in HomePNA 2.0 or Binary Exponential Backoff (BEB) algorithm in IEEE 802.11, order of retransmission is decided according to Collision Signaling Sequence (CSS) values allocated to each device. Thus, CMP can minimize the number of mean collisions because order of retransmission is decided in a deterministic way. In this paper. we evaluate the saturation performance of CMP in HomePNA 3.0 using an analytic method.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.8
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• pp.3862-3888
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• 2017

In high diversity node situation, single-channel MAC protocols suffer from many collisions. To solve this problem, the research of multichannel MAC protocol has become a hotspot. And the cyclic quorum-based multichannel (CQM) MAC protocol outperformed others owing to its high frequency utilization. In addition, it can avoid the bottleneck that others suffered from and can be easily realized with only one transceiver. To obtain the accurate performance of CQM MAC protocol, a Markov chain model, which combines the channel hopping strategy of CQM protocol and IEEE 802.11 distributed coordination function (DCF), is proposed. The metrics (throughput and average packet transmission delay) are calculated in performance analysis, with respect to node number, packet rate, channel slot length and channel number. The results of numerical analysis show that the optimal performance of CQM protocol can be obtained in saturation bound situation. And then we obtain the saturation bound of CQM system by bird swarm algorithm (BSA). Finally, the Markov chain model and saturation bound are verified by Qualnet platform. And the simulation results show that the analytic and simulation results match very well.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.3
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• pp.86-94
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• 1990

This paper suggests a unified packet telecommunication network, which is designed by applying network design algorithm and distribution network design algorithm, Proposed local network design algorithm is based on MST topology, and it can satisfy the limited capacity and get a distribution effect of communication flow, With the result of the comparison with Kruskal and Esau-Willams algorithm, an increase of 2.7% in cost and a decrease of 44.8% in average delay time are shown. Starting with MST topology, proposed distribution network design algorithm gradually increases its reliability, and proposes a conclusive algorithm to determine a topology with minimum cost. In compared with Cut-Saturation algorithm in the aspect of end-to-end delay time and communication flow restricted condition, this proposed algorithm results in 1/7 cost down and about 2.5 times increases in Throughput.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.11C
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• pp.1139-1151
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• 2002

In this paper, we propose the novel module-type optical space switch, employing time division multiplexing (TDM) method and multihop structure, in order to enlarge the capacity of the switching system. And we show that the proposed structure is superior over conventional ones, in terms of power loss, the number of the devices used, and signal to crosstalk (SXR). We also analyze the saturation throughput with the number of module M. As a result, the saturation throughput of the switching system with M modules is M+ 1-√(M$^2$+1), when the number of input port in a module (N) is large. Finally, we confirmed the cell loss rate (CLR) performance with the proposed switch through simulation. For example, when p=0.9, M=8 and N=32, to get the CLR that is less than or equal to 10$\^$-6/, the number of input buffers storage unit is greater than or equal to 6 and output buffers storage unit is greater than or equal to 52.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.7
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• pp.3446-3464
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• 2017

Backoff mechanism serves as one of the key technologies in the MAC-layer of wireless mobile networks. The traditional Binary Exponential Backoff (BEB) mechanism in IEEE 802.11 Distributed Coordination Function (DCF) and other existing backoff mechanisms poses several performance issues. For instance, the Contention Window (CW) oscillations occur frequently; a low delay QoS guarantee cannot be provided for real-time transmission, and services with different priorities are not differentiated. For these problems, we present a novel Multi-Priority service differentiated and Adaptive Backoff (MPAB) algorithm over IEEE 802.11 DCF for wireless mobile networks in this paper. In this algorithm, the backoff stage is chosen adaptively according to the channel status and traffic priority, and the forwarding and receding transition probability between the adjacent backoff stages for different priority traffic can be controlled and adjusted for demands at any time. We further employ the 2-dimensional Markov chain model to analyze the algorithm, and derive the analytical expressions of the saturation throughput and average medium access delay. Both the accuracy of the expressions and the algorithm performance are verified through simulations. The results show that the performance of the MPAB algorithm can offer a higher throughput and lower delay than the BEB algorithm.

• Journal of Digital Contents Society
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• v.12 no.3
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• pp.299-307
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• 2011

The MAC of IEEE 802.11 WLAN to control data transmission uses two control methods called DCF and PCF. The DCF controls the transmission based on CSMA/CA The BEB backoff algorithm of DCF shows relatively excellent performance in situation that the number of competing station is less, but has a problem that performance of throughput and delay is degraded in situation that the number of competing station is increased. This paper mathematically analyzes an MIMD backoff algorithm considering retry limit that increases the CW to doubled after collision and decreases smoothly the CW to halves after successful transmission in order to reduce the collision probability. To prove efficiency of the MIMD backoff algorithm, lots of simulations are conducted and analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1613-1621
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• 2015

This paper analyzes the rate adaptation scheme and suggests applicable strategy of the MCS(Modulation and Coding Scheme) for improving DCF throughput in the IEEE 802.11ad and 802.11ad wireless LAN. IEEE 802.11ac and 802.11ad wireless LAN provide MCS technique that dynamically adjusts modulation level and code rate to the time-varying channel conditions in order to obtain considerably high data rates. But these standards did not provide rate adaptation algorithm, so this paper surveyes rate adaptation algorithm and suggests MCS scheme applied to IEEE 802.11ac and 802.11ad wireless LAN. Specially A MAC(Medium Access Control) layer throughput is evaluated over error-prone channel in the IEEE 802.11ac-based wireless LAN. In this evaluation, DCF (Distributed Coordination Function) protocol and A-MPDU (MAC Protocol Data Unit Aggregation) scheme are used. Using theoretical analysis method, the MAC saturation throughput is evaluated with the PER (Packet Error Rate) on the condition that the number of station, transmission probability, the number of parallel beams and the number of frames in each A-MPDU are variables.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.11
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• pp.1726-1734
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• 1993

This paper propose a survivable communication network design process using node degree that augments the usual traffic flow and cost analyses with previously ignored topological survivability and computing time considerations. At first, decide a initial topology, and then measure a throughput of network. If the throughput is smaller than the required traffic, add edge to the optimum place by using minimum node degree and link distance. Otherwise, drop useless edge by using maximum node degree, link distance and link utilization. This process is repeated until throughput equals to the required traffics. This Process designs a survivable communication network with the minimized cost and computing time and usual traffic flow. The design proceses that minimized computing time are freely select initial topology and easily design a large network. And these results of algorithm are compared with the Kris and Pramod's in order to analyses the perfmance of the designed network.

• ETRI Journal
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• v.22 no.4
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• pp.40-50
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• 2000

We apply a "sliding-window" Maximum Likelihood(ML) estimator to estimate traffic parameters On-Off source and develop a method for estimating stochastic predicted individual cell arrival rates. Based on these results, we propose a simple Connection Admission Control(CAC)scheme for delay sensitive services in broadband onboard packet switching satellite systems. The algorithms are motivated by the limited onboard satellite buffer, the large propagation delay, and low computational capabilities inherent in satellite communication systems. We develop an algorithm using the predicted individual cell loss ratio instead of using steady state cell loss ratios. We demonstrate the CAC benefits of this approach over using steady state cell loss ratios as well as predicted total cell loss ratios. We also derive the predictive saturation probability and the predictive cell loss ratio and use them to control the total number of connections. Predictive congestion control mechanisms allow a satellite network to operate in the optimum region of low delay and high throughput. This is different from the traditional reactive congestion control mechanism that allows the network to recover from the congested state. Numerical and simulation results obtained suggest that the proposed predictive scheme is a promising approach for real time CAC.