• Journal of Korea Multimedia Society
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• v.18 no.12
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• pp.1475-1482
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• 2015

In network routers, buffers are used to resolve congestion and reduce packet loss rate whenever congestion occurs at bottleneck link. Most of the existing methods to manage such buffers focus only on queue-length-based control as one loop which have some issues of low link utilization and system stability. In this paper, we propose a novel framework which exploits two-loop control method, e.g. queue-length and congestion window size, combined with optimal margin method to facilitate parameter choices. Simulation results in ns-2 demonstrate that bottleneck link performance can be improved with higher link utilization (85%) and shorter queue length (22%) than the current deployed scheme in commercial routers (RED and DropTail).

• Aerospace Engineering and Technology
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• v.8 no.2
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• pp.105-112
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• 2009

Telemetry data is very important for the Launch Mission and Flight Safety Control during the Space Launch. In Naro Space Center, several telemetry stations such as a small station in the NARO space center, two stations in Jeju and a downrange station on a ship are deployed for the stable acquisition/receiving of the telemetry signals. In this paper, the Link Margin and Reliability for the telemetry are analyzed to evaluate the probability of the signal receiving of each station. Even though the proper analysis is to using the on-board EIRP(Effective Isotropic Radiation Power) values in the direction of the ground station considering the predicted flight trajectory and the locations of the stations, the global EIRP of 95% spatial coverage has been used for the analysis, due to the limitation of the available data.

• Journal of Communications and Networks
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• v.10 no.3
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• pp.351-361
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• 2008

This paper presents a delay-margin based traffic engineering (TE) approach to provide end-to-end quality of service (QoS) in multi-protocol label switching (MPLS) networks using differentiated services (DiffServ) at the link level. The TE, including delay, class, and route assignments, is formulated as a nonlinear optimization problem reflecting the inter-class and inter-link dependency introduced by DiffServ and end-to-end QoS requirements. Three algorithms are used to provide a solution to the problem: The first two, centralized offline route configuration and link-class delay assignment, operate in the convex areas of the feasible region to consecutively reduce the objective function using a per-link per-class decomposition of the objective function gradient. The third one is a heuristic that promotes/demotes connections at different links in order to deal with concave areas that may be produced by a trunk route usage of more than one class on a given link. Approximations of the three algorithms suitable for on-line distributed TE operation are also derived. Simulation is used to show that proposed approach can increase the number of users while maintaining end-to-end QoS requirements.

• The KIPS Transactions:PartC
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• v.13C no.6 s.109
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• pp.677-684
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• 2006

This paper investigates the link margin of MB-OFDM UWB system quantitatively. Various simulations are performed considering the implementation loss by imperfect synchronization unit and the effect of multi-path fading channels. MB-OFDM UWB system uses ZP(Zero Padding) instead of CP(Cyclic Prefix) and supports two transmission modes; one is TFI(Time Frequency Interleaving) mode that transmits OFDM symbols using different carrier frequency from symbol to symbol according to Time Frequency(TF) codes, the other is FFI(Fixed Frequency Interleaving) mode that transmits OFDM symbols using a specific carrier frequency. The advantage of if and TFI is to be able to increase the transmitting power effectively compared to the existed OFDM systems that transmit the signal continuously at the same average transmitting power. From the analysis results of Ink margin, to guarantee the service range of 4m in 200Mbps mode, TFI mode must necessarily be implemented and the service range of 480Mbps mode is estimated about 1-2m in the line-of-sight multi-path channel (CMI).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.12A
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• pp.951-957
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• 2003

The analysis of RF performance requirement conditions on communication system is critical indicator to predict the performance of system. UWB(Ultra Wide Band) system which the standard is not established yet is difficult to derive the precise system performance requirement condition. Also, there are differences between conventional UWB system and multi-band system about RF performance requirement condition. In this thesis, the differences are analyzed and performance requirement conditions of multi-band UWB system are described on the basis of the differences. Throughput, maximum transmit power, and sensitivity of multi-band UWB system is varied with respect to the number of Sub-Bands. In addition, because of Multi-path effect, if PRF(Pulse Repetition Frequency) is changed, the Multi-path link margin is happened to compensate for Multi-path Energy Loss which is contributed by increasing of the Link Margin. According to Multi-path Margin, the variation of the resistance with respect to sensitivity and interference signal is observed and analyzed through the simulation.

• Journal of Astronomy and Space Sciences
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• v.37 no.1
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• pp.11-18
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• 2020

Satellite optical communication has gained significant attention owing to its many quality features (e.g., a larger bandwidth, license free spectrum, higher data rate, and better security) compared to satellite microwave communication. Various experiments have been performed during many space missions to demonstrate and characterize inter-satellite links, downlinks, and uplinks. Korea has also planned to establish an experimental communication system using a geostationary earth orbit (GEO) satellite and the Geochang station as an optical ground station for low Earth orbit (LEO)-to-ground optical relay links. In this study, the performance of inter-satellite communication links and downlinks was investigated for the new Korean experimental communication system in terms of link margin, bit error rate (BER), and channel capacity. In particular, the performance of the inter-satellite links was analyzed based on the receiving apertures and the transmitting power, while that of the downlink was analyzed in terms of atmospheric turbulence conditions and transmitting power. Finally, we discussed two system parameters of receiving aperture and transmitting power to meet the three criteria of link margin, BER, and channel capacity.

• Journal of Broadcast Engineering
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• v.15 no.1
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• pp.99-111
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• 2010

In this paper as a follow-up to Paper I, the required fade margin derived in Paper I to preserve the same service quality has been examined by analyzing system and propagation characteristics as well as measured data. The comparison of the fade margin between simulated and measured results is also performed for the actual operating line-of-sight(LOS) and non-LOS links, and practical usefulness as an analysis tool is revealed by checking service quality of M/W system relevant to frequency reallocation. According to simulated and measured results, there was a little difference for LOS link between Mt. Moodung and Mt. Mangun, but a fairly good agreement was reached for non-LOS link between Andong KBS and transmitter site.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.11
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• pp.1528-1538
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• 2016

Common data link systems are designed to transmit the imaginary and signal intelligence data at long distance air-ground line of sight(LOS) link. In this paper, we analyze the received power variation according to the communication distance of the common data link using curved earth 2-Ray model suitable for received signal power analysis of long distance air-ground wireless channel. We propose optimal elevation angle control method of the receiving antenna to reduce a power variation caused by ground-reflected wave. Proposed method can get additional link margin compared to the conventional method without any additional hardware performance enhancement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.10
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• pp.965-976
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• 2012

Multi-Platform Image and Intelligence Common data link(MPI-CDL) systems are designed to transmit the imaginary and signal intelligence data at an aeronautical to ground line of sight(LOS) link. This paper proposes a method to predict a link availability and analyzes the required link margin to satisfy a given link availability for MPI-CDL systems. To estimate a link availability the proposed method applies the conditional probability so that both a rain attenuation and a multipath fading are considered simultaneously. Link margins to meet the link availability for MPI-CDL systems are calculated according to an operating environment including frequencies, flight altitudes and transmission ranges. The required link margins for actual unmanned air vehicle systems are also given by simulation results.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.98-100
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• 2005

This paper describes link analysis on the processed data, HRIT (High Rate Information Transmission) and LRIT (Low Rate Information Transmission), for the preliminary design of interface between COMS (Communication, Ocean and Meteorological Satellite) and ground station. At the MODAC (MeteorologicaVOcean Data Application Center), the processed data are transmitted to user station via COMS with normalization and calibration by pre-processing of MI (Meteorological Imager) data. Due to consider satellite as radio relay, overall analysis containing uplink and downlink is needed. Specific link parameters can be obtained with using the outcomes of SRR (System Requirement Review) which was held on 13-14 June 2005, in Toulouse. From the relation between overall link margin and output power of HPA (High Power Amplifier) of MODAC, it is shown that even though the minimum power related with COMS receiving power range is transmitted at MODAC, the obtained link margin of HRIT could be above 3 dB at user station which antenna elevation angle is 10 degree.