• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.2
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• pp.374-384
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• 2007

In this paper, we propose and observe a system that adopts Independent-MCS (Modulation and Coding Scheme) level for each layer in the combined AMC-V-BLAST (Adaptive Modulation and Coding-Vertical-Bell-lab Layered Space-Time) system. In addition, we consider the throughput performance of combined AMC-V-BLAST system using STD (Selection Transmit Diversity) and Independent-MCS level. Also, comparing with the combined system using Common-MCS level, we observe throughput performance improvement. As a result of simulation Independent-MCS level case adapts modulation and coding scheme for maximum throughput to each channel condition in separate layer, resulting in improved throughput compared to Common-MCS level case. Especially, the results show that the combined AMC-V-BLAST system with Independent-MCS level achieves a gain of 700kbps in $7{\sim}9dB$ SNR (Signal-to-Noise Ratio) range and the combined AMC-V-BLAST system with STD and Independent-MCS level achieves a gain of 350kbps in the same SNR range.

• Journal of KIISE:Databases
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• v.32 no.4
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• pp.405-415
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• 2005

Indexing techniques are used to implement selective tuning in wireless environments Indices are broadcast together with data to help mobile clients locate the required information. As a result, clients stay in doze mode most of the time. The drawback of this solution is that broadcast cycles are lengthened due to additional index information. In location-aware mobile services(LAMSs), it is important to reduce the query response time, since a late query response nay contain out-of-date information. In this paper, we present a broadcast-based spatial query processing method (BBS) designed to support k-NN query processing. In the BBS, broadcasted data objects are sorted sequentially based on their locations, and the server broadcasts the location dependent data along with an index segment. The performance of this scheme is investigated in relation to various environmental variables, such as the distributions of the data objects, the average speed of the clients and the size of the service area.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.11
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• pp.1410-1413
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• 2016

Array beamforming for anti-jamming means that jamming signals are superposed destructively, while superposing information signals constructively at a receiver. However, according to channel state variation, the anti-jamming performance of the beamforming can be degraded because of large beamwidth of the sidelobe and lower selectivity of the mainlobe. To mitigate this problem, we introduce a beamformed decoy signal which uses frequency band distinguished from the information signal to make the jammer concentrate its jamming power to a wrong target under limited feedback. In this paper, we show that the performance of the proposed scheme can approach that of optimal one with perfect feedback.

• Journal of KIISE:Computing Practices and Letters
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• v.10 no.1
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• pp.66-74
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• 2004

To get changing data or retrieved information in a web service environment, we need the CGI method in which we designate an executable file and receive the output of the executable file as a document. But the original CGI method has some performance pitfalls caused by the native condition that a process for the requested executable file should be created every time it is requested. Several approaches that make the process as a daemon wholly or partly have been made to solve those problems and they have exclusive strength and weakness. So, many developers are confused when they have to choose which of the CGI methods. We proposed an efficient CGI gateway design called SendFD that the main part of CGI gateway was separated as a daemon and taken over the communication channel by the other small part forked whenever it was requested. Then we testified the efficiency of SendFD styled CGI gateway in real web service environment and it showed about 3% performance improvement compared to the conventional socket pipe method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.3
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• pp.537-542
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• 2017

In this paper, we propose a new scheduling scheme to reduce the complexity and overhead in TDD uplink cellular networks. In a TDD network, users can estimate the interference causing to neighboring BSs by measuring the signals transmitted from them. In the existing max SGIR scheduling scheme, each user calculates SGIR and feeds back to BS. Then, the BS selects a user having the largest SGIR value to transmit data. This scheme has a problem that as the number of BSs increases, the number of interference channels to be measured by the users increases, and thus the hardware and algorithm complexity of the user increases. We propose a max SmGIR (Signal-to-max generating interference ratio) scheduling scheme that can reduce the user complexity by predicting the SGIR value based on only the largest interference information. According to computer simulations, the proposed scheme has similar performance to the existing max SGIR scheme despite this low complexity.

• Proceedings of the KIEE Conference
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• 2008.10b
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• pp.480-481
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• 2008

본 논문은 U-Health 장치 인터페이싱을 위하여 표면 근전도를 이용한 손동작 특징들의 모델링 알고리즘에 대하여 제안하였다. 지금까지 연구에서는 표면 근전도를 측정하기 위하여 전완의 여러 부위에서 신호를 측정하였지만 휴대용 U-Health 장치들의 특성상 센서를 부착 할 수 있는 공간이 한정 되어있기 때문에 한 채널당 손동작의 인식률이 높아야하고 착용하기 편한 위치예서 신호를 측정해야 한다. 따라서 본 논문에서는 손목 근처의 수지신근(finger extensor)과 소지신근(extensor digiti minimi) 사이에 생체신호 센서를 부착하는 것을 제안했으며, 적은 수의 센서에서도 손동작에 따른 충분한 근전도 패턴을 구분해 내기 위하여 3차원 공간상에서 시간과 스케일 정보를 분석할 수 있는 다해상도 웨이블릿을 이용하였다. 정밀한 근전도 분석을 위하여 모 웨이블릿을 신경 신호의 활동전위(action potential)와 가장 유사한 형태를 가지고 있는 Daubechies 4 (db4)로 선택하였고, 이렇게 웨이블릿 분석을 통하여 1차원 신호를 16레벨로 나누어 각 신호에 대하여 에너지를 200 ms 간격으로 평가함으로서 7가지 손동작 인식을 위한 패턴 모델을 구하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7C
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• pp.907-914
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• 2004

In this paper, we propose an application of the receiver antenna switching to an conventional adaptive modulation system and derived the optimal antenna switching threshold of the system to maximize the average transmission bit rate and analyzed its performance. Also, we compare the performances of the presented scheme with those of an adaptive modulation using the antenna selection diversity and the one with a single antenna in terms of the average number of bits per symbol and the probability of no transmission. Performance comparison results show that the proposed system has an SNR gain of 1.4 dB over the adaptive modulation using a single antenna when the average number of bits per a symbol is two and yields an SNR gain of 6 dB for maintaining the probability of no transmission at the level of 0.1.

• Journal of IKEEE
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• v.4 no.2 s.7
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• pp.249-256
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• 2000

In EIT(electrical impedance tomography), the internal resistivity(or conductivity) distribution of the unknown object is estimated using the boundary voltage data induced by different current patterns using various reconstruction algorithms. In this paper, we present a regularized modified Newton-Raphson(mNR) scheme which employs additional a priori information in the cost functional as soft constraint and the weighting matrices in the cost functional are selected based on the exponentially weighted least square criterion. The computer simulation for the 32 channels synthetic data shows that the reconstruction performance of the proposed scheme is improved compared to that of the conventional regularized mNR at the expense of slightly increased computational burden.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5A
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• pp.474-481
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• 2010

In this paper, we present an effective cross layer-based video transmission algorithm over multi-hop mobile ad hoc networks. The proposed algorithm selects the most efficient PHY mode of wireless LAN multi-rate service at each node in a distributed way based on the available information at application, MAC, and physical layers in order to minimize end-to-end delay and maintain packet loss rate in tolerable range at the receiver. Finally, experimental results are provided to show superior performance of the proposed algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5B
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• pp.466-474
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• 2003

In this paper, we develope the simulation model for Ethernet passive optical networks (Ethernet-PON) by using OPNET. Ethernet-PON is an emerging access network technology that provides a low-cost method of deploying optical access lines. The simulator uses a Request/Grant TDMA MAC protocol based on IEEE 802.3ah EFM. It also executes registration, ranging and dynamic bandwidth allocation algorithm by exchanging control packets between OLT and ONUs. We have evaluated for success ratio of initial registration process and delay of late registration process. We also have simulated for dynamic TDMA protocol and static TDMA protocol in terms of channel utilization and queueing delay. We expect that this simulator can help to determine various parameters which are considered for designing Ethernet-PON system.