• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.3
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• pp.291-303
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• 2016

Recently, various forms of diverging sections in tunnels have been designed as the demand for underground passageway in urban areas increases. Therefore, the complexity of the ventilation system in tunnels with diverging sections requires a ventilation analysis method different from the conventional method for the straight tunnels. None of the domestic and foreign tunnel ventilation design standards specifies the method for the ventilation network analysis, and the numerical analysis methods have been most widely used. This paper aims at reviewing the ventilation network analytical method applicable as the design standard. The proposed method is based on the characteristic equations rather than the numerical analysis. Thanks to the advantages of easy application, the Hardy-Cross method has been widely applied in the fields of mine ventilation and tunnel ventilation. However, limitations with the cutting errors in the Taylor series expansion and the convergence problem mainly caused by the mesh selection algorithm have been reported. Therefore, this paper examines the applicability of the ventilation analysis method for network-type tunnels with the gradient method that can analyze flow rate and pressure simultaneously without the configuration of mesh. A simple ventilation analysis method for network-type tunnels is proposed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11B
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• pp.1305-1314
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• 2011

Initial entry section has vulnerability which exposes plain text parameter in Mobile WIMAX environment which is the 4th generation technology. Each node message need to be encrypted to prevent the third party attack or message leakage. In this paper, we propose Mobile WIMAX initial entry section encryption using Elliptic Curve Cryptosystem. We have compared proposed model with existing model using OPNET simulator tool. He delay rate has increased little bit in initial entry section than before after the comparison, but it has shown more effective in average delay and throughput than encryption applied other existing model.

• Journal of Convergence for Information Technology
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• v.10 no.10
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• pp.24-31
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• 2020

In non-orthogonal multiple access (NOMA), the degraded performance of the weaker channel gain user is a problem. In this paper, we propose the asymmetric binary pulse amplitude modulation (2PAM), to improve the bit-error rate (BER) performance of the weaker channel user in NOMA with the tolerable BER loss of the stronger channel user. First, we design the asymmetric 2PAM, calculate the total allocated power, and derive the closed-form expression for the BER of the proposed scheme. Then it is shown that the BER of the weaker channel user improves, with the small BER loss of the stronger channel user. The superiority of the proposed scheme is also validated by demonstating that the signal-to-noise ratio (SNR) gain of the weaker channel user is about 10 dB, with the SNR loss of 3 dB of the stronger channel user. In result, the asymmetric 2PAM could be considered in NOMA of 5G systems. As a direction of the future research, it would be meaningful to analyze the achievable data rate for the propsed scheme.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.10a
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• pp.681-682
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• 2012

The PDP using three functions provides active network control on policy based networks so that it processes the mobile terminal session control, mobility and QoS of network service. In this paper we consider PDP implementation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.11
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• pp.993-1003
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• 2012

In this paper, we propose a method that wireless mobile nodes can obtain high throughput in heterogeneous wireless networks using multiple connections and it has low packet loses under handover situation. Currently, a mobile node exchanges data with server for one network connection. The proposed method can use high throughput because it doesn't only use one network(WLAN, 3G, etc.) but also use multiple wireless networks. When mobile nodes move to area to use multiple connection, mobile nodes request heterogeneous wireless networks using multiple connections message from the server and the server transmit packets using multiple connections. Also, this method doesn't disconnect previous networks, so packets losses are decreased. Using the NS-2 simulation, we verify that the propose method enhances throughput.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.2B
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• pp.97-109
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• 2012

In this paper, we propose a modulation scheme for a network-coded bi-directional relaying (NBR) system over an asymmetric channel, which means that the qualities of the relay channel (the link between the BS and RS) and access channel (the link between the RS and MS) are not identical. The proposed scheme employs a dual constellation in such a way that the RS broadcasts the network-coded symbols modulated by two different constellations to the MS and BS over two consecutive transmission intervals. We derive an upper bound on the average bit error rate (BER) of the proposed scheme, and compare it with the hybrid constellation-based modulation scheme proposed for the asymmetric bi-directional link. Furthermore, we investigate the channel utilization of the existing bi-directional relaying schemes as well as the NBR system with the proposed dual constellation diversity-based modulation (DCD). From our simulation results, we show that the DCD gives better average BER performance about 3.5~4dB when $E_b/N_0$ is equal to $10^{-2}$, while maintaining the same spectral efficiency as the existing NBR schemes over the asymmetric bi-directional relaying channel.

• Journal of IKEEE
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• v.25 no.1
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• pp.156-167
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• 2021

In this paper, we propose a digital transceiver unit design for in-building of 5G optical repeaters that extends the coverage of 5G mobile communication network services and connects to a stable wireless network in a building. The digital transceiver unit for driving the proposed 5G optical repeater is composed of 4 blocks: a signal processing unit, an RF transceiver unit, an optical input/output unit, and a clock generation unit. The signal processing unit plays an important role, such as a combination of a basic operation of the CPRI interface, a 4-channel antenna signal, and response to external control commands. It also transmits and receives high-quality IQ data through the JESD204B interface. CFR and DPD blocks operate to protect the power amplifier. The RF transmitter/receiver converts the RF signal received from the antenna to AD, is transmitted to the signal processing unit through the JESD204B interface, and DA converts the digital signal transmitted from the signal processing unit to the JESD204B interface and transmits the RF signal to the antenna. The optical input/output unit converts an electric signal into an optical signal and transmits it, and converts the optical signal into an electric signal and receives it. The clock generator suppresses jitter of the synchronous clock supplied from the CPRI interface of the optical input/output unit, and supplies a stable synchronous clock to the signal processing unit and the RF transceiver. Before CPRI connection, a local clock is supplied to operate in a CPRI connection ready state. XCZU9CG-2FFVC900I of Xilinx's MPSoC series was used to evaluate the accuracy of the digital transceiver unit for driving the 5G optical repeater proposed in this paper, and Vivado 2018.3 was used as the design tool. The 5G optical repeater digital transceiver unit proposed in this paper converts the 5G RF signal input to the ADC into digital and transmits it to the JIG through CPRI and outputs the downlink data signal received from the JIG through the CPRI to the DAC. And evaluated the performance. The experimental results showed that flatness, Return Loss, Channel Power, ACLR, EVM, Frequency Error, etc. exceeded the target set value.

• Proceedings of the KAIS Fall Conference
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• 2009.12a
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• pp.287-289
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• 2009

무선 메쉬 네트워크(WMN, Wireless Mesh Network)에서의 전체적인 성능은 채널의 간섭을 최소화함으로써 개선될 수 있다. 본 논문은 3개의 멀티 채널을 지원하는 IEEE 802.11b/g 기반 WMNs를 위해 제안된 클러스터 기반 채널 할당 기법인 CB-CA(Cluster-Based Channel Assignment)[3] 알고리즘을 멀티 라디오 멀티 채널 WMN 환경에 적합하게 개선시키고자 한다. CB-CA 알고리즘에서는 메쉬 라우터들중에 선택된 클러스터 헤드(CH, Cluster Head) 노드들과 클러스터들 간의 에지 게이트웨이(EG, Edge Gateway) 노드들 간에는 모두 동일 채널을 사용함으로써 채널 스캐닝과 채널 스위칭을 수행하지 않는다. 그러나 이러한 모든 CH들과 EG들 간의 동일 채널의 사용은 많은 노드들에서 채널 간섭을 발생 시키는 문제점이 발생한다. 본 논문에서는 이를 해결하기 위하여 송수신 인터페이스를 구분하고 각 인터페이스에서의 채널을 랜덤하게 설정하고 이를 통신 범위 내에 인접한 이웃 클러스터들에게 알림으로써 서로 간섭이 발생하지 않는 채널들이 설정되도록 한다. 이로써 각 클러스터 간의 채널 간섭을 최소화 할 수 있음과 동시에 다중 인터페이스와 다중 채널을 모두 활용할 수 있어서 QoS를 향상시킬 수있다.

• Journal of KIISE
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• v.42 no.6
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• pp.723-733
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• 2015

The OTT service that provides multimedia video has spread over the Internet for terminals with a variety of resolutions. The terminals are in communication via a networks such as 3G, LTE, VDSL, ADSL. The service of the network has been increased for a variety of terminals giving rise to the need for a new way of encoding multimedia is increasing. SVC is an encoding technique optimized for OTT services. We proposed an efficient multimedia management system for the SVC encoded multimedia data. The I/O trace was generated using a zipf distribution, and were comparatively evaluated for performance with the existing system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.7
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• pp.1032-1039
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• 2022

In this paper, we designed and implemented a cavity bandpass filter combined with a cross-coupling equalizer structure to enhance Group delay for 5G mobile network repeater, which can replace the SAW (Surface Acoustic Wave) type bandwidth filter used in the existing mobile communication system. Using the 3D EM simulation tool (HFSS), the resonance frequency, the coupling coefficient between resonators, and external quality coefficient between resonators were calculated. Based on this, a 12th bandpass filter was constructed to have attenuation characteristics of more than 20dB at the edge end of both sides of the band with a metal cavity structure with a frequency band of 3500MHz to 3600MHz and bandwidth of 97.85MHz. The designed bandpass filter satisfies the group delay time requirement for the 5G mobile communication standard and the in-band and out-band frequency responses.