• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1206-1210
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• 2005

This paper presents performance improvement in optical CDMA system under the presence of beat noise using a cancellation technique. Optical fibers and atmospheric optical communications have been proposed the connection between base stations and central station. The optical signal beat noise is due to interference between lightwave, many optical waves are simultaneously incident on each receiver photodiode. Since the photodiode acts as a square-law detector, beat noise can occur in the receiver. While A two-stage cancellation technique is analyzed and verified via simulation employed here because of its system simplicity. By using the random ingredients of all user signals are estimated, the beat noise is rebuilt and removed from the intended signal. In addition to cancellation technique cancel the inherent multiuser interference (MUI) in CDMA system and nonlinear distortion (NLD) in optical system. It is performed at the receiver of the central station where the random ingredients of all user signals are estimated and the MUI and the NLD are rebuilt and removed from the received signal. The validity of the cancellation technique is theoretically analyzed and shown by numerical results. The increasing of capacity in two stage cancellation are obtained.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.11
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• pp.1311-1317
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• 2010

In this paper, for a uplink space division multiple access system named cooperative spatial multiplexing(CSM), radio resource management(RRM) algorithms are proposed based on sharing uplink channel information among a serving base station(BS) and interfering BSs in a uplink coordinated wireless communication system. A constrained maximum transmit power algorithm is proposed for mobile station(MS) to limit uplink inter-cell interference(ICI). And joint scheduling algorithm among coordinated BSs is proposed to enhance uplink capacity through ICI mitigation by using channel information from interfering BSs. It is shown that the proposed RRM algorithm provides a considerable uplink capacity enhancement by effective ICI mitigation only with moderate complexity.

• Journal of Advanced Navigation Technology
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• v.14 no.6
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• pp.865-873
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• 2010

In this paper, a novel schedulability criteria is developed to provide handover calls with Quality of Service (QoS) guarantees in terms of both minimum available bandwidth, maximum tolerated packet delay, and other additive QoS constraints as required by the real-time mobile traffic. This requires prediction of the handover time using mobility trends on the mobile station, which is used as input to this work. After the handover time and the QoS are negotiated, the destination base station makes attempts to give priority to handover calls over new calls, and pre-reserves resources that will have more chance of being available during the actual handover.

• Journal of Korean Society for Geospatial Information Science
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• v.19 no.4
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• pp.65-70
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• 2011

National Geographic Information Institute provides VRS service using permanent GPS networks. VRS-RTK(Virtual Reference System-Real Time Kinematic)GPS surveying which enable to accomplish the real time-based GPS surveying has been increasingly popular. However the positioning accuracy tends to deteriorate as the distance between the rover and base station increases in the VRS-RTK GPS surveying. To analysis this problem in this study, the accuracy of VRS-RTK data was analyzed with 2 different test sites of Geoje city, Gyeongnam province within and without the permanent GPS networks in order to accomplish the cadastral supplementary control surveying. As a result of surveying accuracy analysis at two test sites, positioning errors were ${\pm}0.03m$(RMSE) in both sites. The result was that within the tolerance specified in cadastral surveying law, and indicated the possibility of VRS-RTK GPS surveying in cadastral surveying.

• Journal of Information Processing Systems
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• v.2 no.2
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• pp.107-113
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• 2006

It is essential to guarantee a handoff dropping probability below a predetermined threshold for wireless mobile networks. Previous studies have proposed admission control policies for integrated voice/data traffic in wireless mobile networks. However, since QoS has been considered only in terms of CDP (Call Dropping Probability), the result has been a serious CBP (Call Blocking Probability) unfairness problem between voice and data traffic. In this paper, we suggest a new admission control policy that treats integrated voice and data traffic fairly while maintaining the CDP constraint. For underprivileged data traffic, which requires more bandwidth units than voice traffic, the packet is placed in a queue when there are no available resources in the base station, instead of being immediately rejected. Furthermore, we have adapted the biased coin method concept to adjust unfairness in terms of CBP. We analyzed the system model of a cell using both a two-dimensional continuous-time Markov chain and the Gauss-Seidel method. Numerical results demonstrate that our CAC (Call Admission Control) scheme successfully achieves CBP fairness for voice and data traffic.

• Proceedings of the KIEE Conference
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• 2006.07d
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• pp.2122-2123
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• 2006

본 논문에서는 멀티 홈 패킷 무선통신 네트워크를 위한 An Energy-efficient Topology Control 을 제안한다. 센서 네트워크의 기본적인 형태에 따라 네트워크 망의 구성 방식은 큰 차이를 가져온다. 현재 센서 네트워크의 topology control 의 많은 부분에서는 clustering을 이용하여 센서 네트워크의 lifetime 을 연장시키는 연구가 진행 되고 있다. 그러나 cluster 로의 노드의 연합과 분리는 네트워크 topology 의 안정성을 혼란시킬 뿐만 아니라, BS(Base Station)가 시스템의 외부에 존재하는 경우 더 적합한 방식이라고 볼 수 있다. 본 논문에서는 BS 가 시스템의 내부에 존재하는 경우에 대한 sensor network의 lifetime 을 연장시키는 방안에 대해 제안 하고 있다. 이러한 시스템의 경우 BS에 가까운 지역일수록 Black-hole effect 가 발생할 가능성이 증가하게 되고 이는 네트워크의 수명을 단축시키게 된다. 따라서 노드의 energy를 균등하게 사용 함 으로서 lifetime을 연장 하는 on-demand 방식의 topology control을 제시하고 이를 시뮬레이션으로 확인하였다.

• 전자공학회논문지 IE
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• v.47 no.4
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• pp.34-38
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• 2010

In this paper, we suggest DCU(Digital Control Unit) for performance improvement and stability security of base station power amplifier. The designed DCU controls electric power that is supplied to power amplifier. When the regular input is 10dBm, the regular output is measured 47.8dBm and the results are compared between the case of the applying and the non-applying the DCU. We got the result that PA system is very stable as DCU are very well operating in the boundary degradation of IMD by the over-power level input.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.1
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• pp.183-189
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• 2018

This paper proposes distributed file placement and coverage expansion techniques for mitigating the traffic bottleneck in backhaul for small-cell networks. In order to minimize the backhaul load with limited memory space, the proposed scheme controls the coverage and file placement of base station according to file popularity distribution and memory space of base stations. In other words, since the cache hit ratio is low when there is small memory capacity or widespread file popularity distribution, the base stations expand its coverage and cache different set of files for the user located in overlapped area to exploit multiple cached file sets of base stations. Our simulation results show that the proposed scheme outperforms the conventional cache strategy in terms of network throughput when there is small memory capacity or widespread file popularity distribution.

• Journal of information and communication convergence engineering
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• v.9 no.5
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• pp.530-538
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• 2011

Performance of TCP can be severely degraded in Mobile IP-based wireless networks where packet losses not related to network congestion occur frequently during inter-subnetwork handoffs by user mobility. To solve such a problem in the networks using Mobile IP, the packet buffering method at a base station(BS) recovers those packets dropped during handoff by forwarding the buffered packets at the old BS to the mobile users. But, when the mobile user moves to a congested BS in a new foreign subnetwork, those buffered packets forwarded by the old BS are dropped and TCP transmission performance of a mobile user degrades severely. In this paper, we propose a Modified BLUE(MBLUE) buffer required at a BS to increase TCP throughput in Mobile IP-based networks. When a queue length exceed a threshold and congestion grows, MBLUE increases its packet drop probability. But, when a TCP connection is added at new BS by a handoff, the old BS marks the buffered packets. And new BS receives the marked packets without dropping. Simulation results show that MBLUE buffer reduces congestion during handoffs and increases TCP throughputs.

• Journal of the Korea Computer Industry Society
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• v.2 no.11
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• pp.1373-1382
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• 2001

Traditionally, Mobile Teletraffic model consists of two sub-models, i.e. the network traffic model and the traffic source model. In this paper, we present the traffic source model by developing MobCall(Mobile Call Simulator) which analyses various mobile wireless environments based on regional characteristics that the base stations are located. User mobility is presented by regional average vehicle speeds and the transportation share rate. Moreover, the user mobility on subway, which is increasing in urban area, is considered in MobCall. Using MobCall, the accumulated number of calls in residential and commercial regions, the handoff rate with respect to traffic sources of Seoul, the handoff rate on highway, and the handoff rate according to the call duration are presented. MobCall enables the simulation of dynamic handoff buffering and functional entity control of one base station according to the changes in user's calling pattern at the design phase.