• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.5
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• pp.927-933
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• 2005

Multi carrier transmissions are digital modulation techniques where a single data symbol is transmitted at multiple subcarriers which are orthogonal to each other. With his technique, frequency diversity can be achieved. The performance of multi carrier transmission systems with various structure are analyzed, where data is transmitted over multi-path Rayleigh fading channel. The performance of this technique, gauged by the average bit error rate, is compared dependent upon the various structures.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.7
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• pp.747-756
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• 2014

In this paper, we propose a path loss model with the multiple antennas using diversity effect. Currently wireless communication systems use the multiple antennas in order to improve the channel capacity or diversity gain. However, until recently, many researches on path loss model only consider geographical environment between the transmitter and the receiver. There is no study about path loss model considering diversity effect. Nowaday wireless communication use the multiple antennas and we in common find examples using diversity scheme that is method in order to enhance a channel capacity. Moreover we anticipate that it work harder in future researches. But in this communication system, path loss model isn't established that predict strength of received signal. So, in order to predict strength of received signal, we take changing SNR by diversity gain. When exceeding the number of antennas of receiver are 7 in proposed model, diversity effect is saturated. Therefore we consider the number of antenna of receiver until 10. We find RMSE between proposed model and value of calculation is 1. We calculate the diversity gain by conventional BER curve. Proposed model can predict loss of received signal in system using multiple antennas.

• Journal of KIISE:Computing Practices and Letters
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• v.7 no.1
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• pp.12-23
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• 2001

Extended path expressions are used to denote multiple paths concisely by using '$\ast$' character. They are convenient for expressing OQL queries to retrieve XML data stored in OODBs. In this paper, we propose a multi-path index scheme as a new index scheme to efficiently process queries with extended path expressions. Our proposed index scheme allocates a unique path identifier for every possible single path in an extended path expression and provides functionalities of both a single path indexing and multiple path indexing through the composition of index key and path identifier while using only a index structure. The proposed index scheme provides better performance than single-path index schemes, and is practical since it can be implemented by little modification of leaf records of a B+-tree index.

• Journal of Korean Society of Transportation
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• v.19 no.6
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• pp.183-194
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• 2001

The centralized traffic information system is to gather and analyze real-time traffic information, to receive traffic information request from user, and to send user processed traffic information such as a path finding. Position information, result of destination search, and other information. In the centralized traffic information system, a server received path-finding requests from many clients and must process clients requests in time. The algorithm of multiple path-finding is needed for a server to process clients request, effectively in time. For this reason, this paper presents a heuristic algorithm that decreases time to compute path-finding requests. This heuristic algorithm uses results of the neighbor nodes shortest path-finding that are computed periodically. Path-finding results of this multiple path finding algorithm to use results of neighbor nodes shortest path-finding are the same as a real optimal path in many cases, and are a little different from results of a real optimal path in non-optimal path. This algorithm is efficiently applied to the general topology and the hierarchical topology such as traffic network. The computation time of a path-finding request that uses results of a neighbor nodes shortest path-finding is 50 times faster than other algorithms such as one-to-one label-setting and label-correcting algorithms. Especially in non-optimal path, the average error rate is under 0.1 percent.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1996.06a
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• pp.208-211
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• 1996

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9C
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• pp.871-879
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• 2009

The performance variations of a spatio temporal smart antenna which is equipped at the basestation of CDMA cellular communication network due to the parametric change of multipath fading environment are studied in this paper. The smart antenna of interest employs space diversity based adaptive array structure in conjunction with rake receiver that has fingers the number of which is the same as that of multipath links. The beamforming is achieved via LMS(Least Mean Square) algorithm in which a reference signal is generated using decision directed formula. It has been shown by computer simulation that the performance of our smart antenna of interest depends significantly upon not only the degree of desired signal's DOA(Direction of Arrival)spread but the number of fingers of the rake receiver. The relative insensitivity of the smart antenna's performance on desired signal's delay spread has also been observed. Computer simulation has shown that the increase of the number of fingers brings in a nonlinear enhancement of the performance of our smart antenna. The renewal of weight vector in the beamforming procedure is taken place at post PN despread stage.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2B
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• pp.176-183
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• 2011

In this paper, we propose the implementation and performance analysis of power line communication based on SISO/MIMO-OFDM which focuses on high speed data transmission in smart grid and future power line grid. We employ Zimmermann frequency model and Middleton Class A model as the multipath power line fading channel and impulse noise channel, respectively. In this paper, in order to improve the three-phase or single-phase PLC performance, we introduce a new MRC (called a&f-MRC) which effectively sums up multiple antenna diversity gain and multipath fading diversity gain. Via simulation, we prove the performance advantage over existing SISO/MIMO systems. In addition, we offer the tradeoff on system design through comparing with MRC, EGC and SC.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10a
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• pp.533-535
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• 1998

가상 다중 세그먼트 (Virtual Multi-Segment)란 하나의 LAN이 라우터나 방화벽을 사용하지 않고 가상적으로 여러 개의 세그먼트로 나뉘어진 것을 의미한다. 일반적으로 같은 LAN에 속한 호스트들일지라도 다양한 보안 정책을 가지게 되는데 그 결과로 우회 경로 공격(bypass path attack)이 가능해지고 (Hierarchical)방화벽 시스템을 구성하여 다른 보안 정책을 가진 세스먼트마다 방화벽을 구축하고 있는데 이 방식은 방화벽 시스템을 구성하여 다른 보안 정책을 가진 세그먼트마다 방화벽을 구축하고 있는데 이 방식은 방화벽을 여러 개 설치해야 하는 문제가 있다. 이런 문제를 해결하기 위해 본 논문에서 방화벽을 통해 지나오는 각 연결에 대해서 회선체인을 구성하는 기법을 이용하여 가상적인 다중 세그먼크를 구성한다. 회선체인구성을 효과적으로 수행하기 위해 Thumbpint기법을 사용하는데 이 기법은 동일한 시간대에 모든 회선이 갖는 내용에 대한 요약을 만들어 그 요약들을 가지고 어떤 회선들이 같은 내용을 가지고 있는지를 판단하여 회선체인을 구성하는 기법이다. 본 논문에서 가상 다중 세그먼트 방화벽을 설계와 구현하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.2
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• pp.250-257
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• 2004

MC-CDMA and OFDM are digital modulation techniques where a single data symbol is transmitted at multiple subcarriers which we orthogonal to each other. With this technique, frequency diversity can be achieved. The performance of multi currier systems is analyzed. when data is transmitted over multi-path Rayleigh fading channel. The performance of this technique, gauged by the average bit error rate, is numerically analyzed for the system with the application of antenna diversity.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.378-390
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• 2001

In this paper, it is analyzed that the error performance of a Multi-Carrier DS-CDMA system in a single cell with multipath Rician fading and multiple access interference (MAI) and the error performance of the system is compared with that of a Sing1e-Carrier DS-CDMA system. Moreover, the convolutional coding techniques with code rate of 1/2, 1/3, and 1/4 are adopted in order to improve the error performance degraded by the multipath fading and MAI and performance improvement through the coding techniques is analyzed. As a result, it is shown that the number of users in each system can be determined by the number of branches of the rake receiver in a Single-Carrier DS-CDMA system and the number of carriers in a Multi-Carrier DS-CDMA system. Furthermore, the convolutional coding should be chosen with considering the trade-off between coding gain and a power limitation in a Multi-Carrier DS-CDMA system. In case of increasing the number of carriers, the processing gain is decreased but the error performance is improved through the effect of frequency diversity and the system can be possibility implemented due to the low chip rate.