• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10B
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• pp.866-871
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• 2006

This paper presents the design of a reservation-based MAC protocol to support multimedia traffic over mobile ad-hoc networks and evaluates its performance. Our MAC protocol is based on a hierarchical approach consisting of two sub-layers. The lower sub-layer of the MAC protocol with reservation provides a fundamental access method using CSMA/CA in order to support asynchronous data traffic over mobile ad-hoc networks. The upper sub-layer supports real-time periodic data by making a slot reservation before transmitting actual data. The proposed protocol has been validated through simulations using ns-2. The results show that the proposed MAC protocol can offer higher throughput and lower delay than standard implementations of the IEEE 802.11.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.8B
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• pp.757-763
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• 2006

In this paper, a novel multiple access scheme using SMA(Split and Merge Algorithm) is proposed to reduce the accessdelay of wireless MAC protocols. The key idea of the SMA is to dynamically split and merge the contending terminals depending on their traffic loads for effective control of access to the channels. The SMA divides the collided terminals into several sub-groups if a collision occurs and merges the idle terminals of the split sub-groups into their original group. The merge algorithm can be used to resolve collision and split operation can be used to dynamic group management. The simulation results indicate that our algorithm may provide a higher throughput and a lower collision rate than the existing algorithms, especially under heavy traffic loads.

• Journal of KIISE:Computing Practices and Letters
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• v.8 no.4
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• pp.468-478
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• 2002

In this paper, we designed a B-WLL MAC(Media Access Control) protocol and validated its operation for implementation of high-speed subscriber networks. Our MAC protocol was designed by SDL using the DAVIC specifications based upon the variable contention/reserved time slot allocation algorithm. For validation of our MAC protocol, Syntax and semantic error check were performed by the Simulation Builder of ObjectGeode and the MAC(Message Sequence Chart) respectively. The validation results showed that our B-WLL MAC protocol is working correctly and may successfully support B-WLL services.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.5
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• pp.906-914
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• 2007

In the upstream link of EPON, numerous ONUs In the reverse link of the EPON network, numerous ONUs receive the privileges to use the optical medium from the scheduler of the LOT, but not through the competition with others. Therefore, it is very important to select a proper DBA algorithm to allocatethe frequency band to each ONU in an effectively and fair manner. In our preceding study, we proposed the RC-DBA algorithm that complements many problems in existing DBA algorithms. In this paper, we designed the MAC scheduler for the OLT, which the proposed algorithmwas applied to and implement it in the FPGA. In addition, in order to verify the operation of the scheduler, we developed the embedded Linux based testbed.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.2
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• pp.70-76
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• 2000

A numerical study on the viscous flow around a 2-dimensional circulation control foil is carried out for application on the field of naval architecture and ocean engineering. The governing equations are the RANS and the continuity equations. The equations are discretized by finite difference method and MAC method and the pressure poisson equation is calculate by a SOR method and an O-type non-staggered boundary fitted coordinate system which is overlapped near the slot is used to improve the numerical accuracy. Turbulence is approximated by a modified Baldwin-Lomax turbulence model. In the present paper, the Coanda effect on a 2-dimensional foil of a 20% thickness ellipse with modified rounded trailing edge has been numerically studied. The change in drag and lift of the foil with various jet momentums are calculated and compared to the experimental results to show good agreements.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.6
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• pp.124-131
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• 2014

This paper describes a design of an adaptive baseband modem based on TDMA(time division multiple access) with a relay protocol function for wireless personal area networks. The designed baseband modem is controlled by a master synchronization signal and can be configured a relay network up to 14 hops. For efficient data relay communications, the internal buffer design is optimized by implementing a priority memory bus controller to a single port memory. And the priority memory bus controller is also designed to minimize the number of synthesized logic gates. To implement the synchronization function of the narrowband TDMA relay communication, the number of gates has been reduced by dividing the frame synchronization circuits and the network slot synchronization circuits. By using these methods, the number of gates are used about 37%(34,000 gates) on Xilinx FPGA XC6SLX9 which has 90,000 gates. For the 1024-bit frame size with a 32-bit synchronization word, the communication reception rate is 96.4%. The measured maximum transmission delay of the designed baseband modem is 230.4 msec for the 14-hop relay communication.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.6
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• pp.151-158
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• 2010

In line with the requirement of appropriate protocol support for such mission-critical wireless sensor network (WSN) applications as patient monitoring, we investigate the framework for designing medium access control (MAC) schemes. The data traffic in medical systems comes with inherent traffic heterogeneity as well as strict requirement of reliability according to the varied extents of devise-wise criticality in separate cases. This implies that the quality-of-Service (QoS) issues are very distinctly delicate requiring specialized consideration. Besides, there are features in such systems that can be exploited during the design of a MAC scheme. In a monitoring or routine surveillance application, there are degrees of regularity or predictability in traffic as coordinated from a node of central control. The coordinator thus takes on the role of marshaling the resources in a neighborhood of nodes deployed mostly for upstream traffic; in a collision-free scheme, it schedules the time slots for each superframe based on the QoS specifications. In this preliminary study, we identify the key artifacts of such a MAC scheme. We also present basic performance issues like the impact of superframe length on delay incurred, energy efficiency achieved in the network operation as obtained in a typical simulation setup based on this framework.

• The Transactions of the Korea Information Processing Society
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• v.7 no.11
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• pp.3479-3489
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• 2000

Most of the study on fairness control method for Distributed-Queue Dual-Bus(DQDB) have been performed under specific load types such as equal probability load types or symmetric load types. On Web-based internet enviroments client-server load types are more practical traffic patlerns than specrfic load types. In this paper, an effiective fairness control method to distribute DQDR network bandwidth fairly to all stations under a client-server load is proposed. In order to implement a dynamic bandwidth timing capabihty needed to distribute the bandwidth fairty at heavy loads, the proposed method uses two pararnetexs, one is an access hrnit to legulate each station's packet transmission and the other is the number of extra emply slots that are yielded to downstream stations. In point of implementation this mechanism is simpler and easier than Bandwidth Tuning Mechanism(BTM) that uses an intermediate pattern and an adptation function. Simulation results show that it outperforms othen mecharusms.

• Journal of IKEEE
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• v.5 no.1 s.8
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• pp.111-120
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• 2001

VC merging involves distinguishing cells from an identical merged VC label. Various approaches have been proposed to help this identification process. However, most of them incur additional buffering, protocol overhead and/or variable delay. They make the provision of QoS difficult to achieve. So it was proposed a merge capable scheduler to support VC-merging (VCMS). However, in situations where all VCs are to be merged or the incoming traffic load is very low, it could happen that there are not enough non-merging cells to snoop. In this situation the scheduler uses special control cells to fill the empty time slots out. Too many control cells can cause high cell loss ratio and an additional packet transfer delay. To overcome the drawbacks, we propose a Sequence Skipping(SS) method where the sequencers skip the empty queues and insert SS cells. We show SS method is suitable for VC-merging and can reduce the cell loss ratio and the mean packet transfer delay through simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.4B
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• pp.270-281
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• 2003

E-PON supports efficiently the increased Internet data traffic and efficient bandwidth assignment function by which the shared upstream bandwidth in the broadband access networks. In this paper, when different types of incoming sources are mapped into QoS-aware source and Best-Effort(BE) source, we propose the Dual-GPS schedulaer in E-PON that has the characteristics to provide delay and delay-constraint application, and maximizes the bandwidth to best-effort service. When transmit upstream data in E-PON, The proposed scheme supports the control capabilities of delay and delay-variation for required QoS flow through the novel bandwidth assignment scheme. Simulation results show our scheme outperforms the conventional bandwidth allocation scheme in controlling the delay and delay-variation of E-PON system.