• 조명전기설비학회논문지
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• 제18권4호
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• pp.149-154
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• 2004

본 논문에서는, 구내용 저간섭 무선통신설비용 시스템으로서 이진 2m(zero-correlation duration) 확산코드를 이용한 저간섭 CDMA(code division multiple access)시스템을 제시하였다. 이진 ZCD확산코드는 확산코드의 주기가 N인 경우 그 값이 4부터 2의 배수로 계속 확장이 가능하기 때문에 코드발생기의 구현이 용이함과 동시에 ZCD 특성을 가짐으로 인해서, CDMA무선통신 시스템을 구내용 무선설비로 사용할 경우에 발생되는 다중접속 및 다중 경로로 인한 간섭문제를 확산코딩기법을 이용하여 근원적으로 해결해주는 역할을 한다. 본 논문에서는 제안한 이진 ZCD확산코드기반의 구내용 저간섭 CDMA시스템의 간섭완화 성능을 확인하기 위하여, AWGN(additive white gaussian noise) 및 MAI(multiple access interference), MPI(multi path interference)와 같은 잡음 및 다양한 간섭 환경 하에서의 BER(bit error rate)특성을 정량적으로 분석하고, 모의실험을 통해 제안시스템의 간섭완화 능력을 입증하였다.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 1995년도 추계학술대회발표논문집; 서울대학교, 서울; 30 Sep. 1995
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• pp.384-384
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• 1995

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 추계종합학술대회 논문집
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• pp.27-30
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• 1999

A spatio-temporal vector channel model is introduced for the position location (PL) estimation problem for CDMA cellular system environment. Two common ways for the PL make use of the AOA (Angle Of Arrival) and TDOA (Time Difference Of Arrival) from a subscriber to the multiple sensors (base stations). In this paper, we applied the derived vector channel to simulate the multipath channel for the angle of the signal arrival in CDMA systems. Cross-correlation method is a good candidate among other direction finding algorithms available in literature, especially in wideband modulation as in the CDMA system. The PL estimation errors are evaluated for different channels, which are obtained as a parameter of scattering radius of the suggested model. We noted that the number of sensors (base-stations) are related to the PL errors in favor of the available data.

• 한국통신학회논문지
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• 제25권12B호
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• pp.2109-2119
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• 2000

In this paper, the Packet CDMA Reservation ALOHA protocol is proposed to support the multi-traffic services such as voice and videophone services with handoff calls, high-rate data and low-rate data services efficiently on the multi-rate transmission in uplink cellular systems. The frame structure, composed of the access slot and the transmission slot, and the proposed access permission probability based on the estimated number of contending users for each service are presented to reduce MAI. The assured priority to the voice and the videophone handoff calls is given through higher access permission probability. And through the proposed code assignment scheme, the voice service can be provided without the voice packet dropping probability in the CDMA/PRMA protocols. The code reservation is allowed to the voice and the videophone services. The low-rate data service uses the available codes during the silent periods of voice calls and the remaining codes in the codes assigned to the voice service to utilize codes efficiently. The high-rate data service uses the assigned codes to the high-rate data service and the remaining codes in the codes assigned to the videophone service. Using the Markov-chain subsystem model for each service including the handoff calls in uplink cellular systems, the steady-state performances are simulated and analyzed. After a round of tests for the examples, through the proposed code assignment scheme and the access permission probability, the Packet CDMA Reservation ALOHA protocol can guarantee the priority and the constant QoS for the handoff calls even at large number of contending users. Also, the data services are integrated efficiently on the multi-rate transmission.

• 한국통신학회논문지
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• 제25권12A호
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• pp.1806-1814
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• 2000

본 논문에서는 CDMA 계층구조 셀룰러 시스템에서 매크로 셀 기지국과 통신을 하는 고속 이동국과 마이크로 셀 기지국과 통신을 하는 저속 이동국의 비 그리고 소프트 핸드오프 영역 비에 따른 기지국이 받는 간섭전력과 시스템 용량을 구하였다. 매크로 셀 기지국과 통신을 하는 고속 이동국이 마이크로 셀 기지국과 통신을 하는 저속 이동국보다 많을수록 기지국이 받는 간섭전력은 증가하며 따라서 시스템 용량은 감소한다. 그러나 소프트 핸드오프 영역의 증가로 기지국이 받는 간섭전력은 감소하명 시스템 용량은 상당히 증가한다.

• 한국통신학회논문지
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• 제24권8A호
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• pp.1107-1114
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• 1999

본 논문에서는 대수정규 쉐도잉(shadowing)과 나카가미(Nakagami) 페이딩을 함께 받은 타 시스템의 동일 채널 간섭파가 불완전 전력제어 된 DS/CDMA 셀룰러 시스템의 용량에 미치는 영향을 분석하였다. 분석에는 먼저 간섭을 고려하지 않고 불완전 전력제어만을 해석한 Prasad와 Jansen의 결과와 비교하였으며, 대수정규-나카가미 페이딩을 받은 다중 간섭은 Schwartz와 Yeh가 제시한 방법을 적용하여 DS/CDMA 시스템에 미치는 영향을 오수신확률로 유도하였다. 유도한 오수신확률에 대해 불완전 전력제어, 페이딩 지수, 처리이득, 전력비, 간섭수, 음성화율 등을 파라미터로 하여 각각의 상황에서 DS/CDMA 시스템의 가입자 용량 감소를 분석하였다. 결과로부터 DS/CDMA 시스템의 용량은 전력제어 오차와 간섭파의 증가에 매우 민감하여 전력제어 오차가 클수록, 무선채널 환경의 페이딩이 심할수록, 또한 간섭파의 수가 증가할수록 감소하였다.

• Journal of Communications and Networks
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• 제12권3호
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• pp.216-221
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• 2010

In this paper, we propose and develop a new algorithm for the principle subspace tracking by orthonormalizing the eigenvectors using an approximation of Gram-Schmidt procedure. We carry out a novel mathematical derivation to show that when this approximated version of Gram-Schmidt procedure is added to a modified form of projection approximation subspace tracking deflation (PASTd) algorithm, the eigenvectors can be orthonormalized within a linear computational complexity. While the PASTd algorithm tries to extracts orthonormalized eigenvectors, the new scheme orthonormalizes the eigenvectors after their extraction, yielding much more tacking efficiency. We apply the new tracking scheme for blind adaptive multiuser detection for non-stationary cellular CDMA environment and use extensive simulation results to demonstrate the performance improvement of the proposed scheme.

• Journal of Communications and Networks
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• 제2권1호
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• pp.46-57
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• 2000

Ongoing standardization effort on 3G cellular system in 3GPP (UNTS) is based on GPRS core network and promises a global standard for systems capable of offering ubiquitous access to internet for mobile users. Considered radio access systems(FDD CDMA, TDD CDMA, and EDGE) are optimized for robust mobile use. However, there are alternative relatively high-rate radio interfaces being standardized for WLAN (IEEE802.11 and HIPER-LAN/2) which are capable of delivering significantly higher data rates to static or semi-static terminals with much less overhead. Also WPANs(BLUETOOTH, IEEE802.15), which will be present in virtually every mobile handset in the near future, are offering low cast and considerable access data rate and thus are very attractive for interworking scenarios. The prospect of using these interfaces as alternative RANs inthe modular UMTS architecture is very promising. Additionally, the recent inclusion of M-IP in the UMTS R99 standard opens the way for IP-level interfacing to the core network. This article offers an overview into WLAN-Cellular interworking. A brief overview of GPRS, UMTS cellular architectures and relevant WLAN standards is given. Possible interworking architectures are presented.

• 전자공학회논문지S
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• 제35S권2호
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• pp.22-30
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• 1998

In this paper, we analyze CDMA systems using M-orthogonal spreading codes. We assume that each user one set of M-orthogonal spreading codes allocated randomaly. The effect of multiple access interference from the reference and adjacent cells is considered slowly frequency selective rayleigh fading channels. and the adjacent cells interference is considered toanalyze the system performance. We calculate bit error rate and the maximum number of users whoe can communicate simulaneously within a cell by suing Rake receiver. By comparing CDMA systemwhich transmits 1 bit/spreding code, our system shows bit error rate decreases as M increases under the same bandwidth and infromation rate.

• ETRI Journal
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• 제19권3호
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• pp.259-280
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• 1997

This paper briefly explains the configuration of CDMA Mobile System (CMS) test bed. The measured fading and delay results of CDMA signal in Taejon area are shown. In comparison to other cellular systems, there are more parameters in the CDMA systems that affect system performance and capacity. We performed the optimization test of the selected parameters and present the effect of each parameter on the performance. This paper presents the capacity and performance test results of CMS. The capacity test was performed on ETRI site of three sectors in Taejon area. The performance tests include call completion rate, busy hour call attempt, and the delay characteristics of voice.