• 한국통신학회논문지
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• 제24권7A호
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• pp.973-986
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• 1999

본 논문에서는 무선 패킷 데이터 서비스를 효율적으로 지원하기 위해 채널 액세스 메카니즘과 전송 매카니즘으로 구성되는 MAC 프로토콜을 제안하였다. 채널 액세스를 위해 방송채널은 랜덤 액세스 채널의 상태정보를 알려주고, 이동단말은 상태정보를 기반으로 랜덤액세스를 시도한다. 또한, 이동단말에 액세스 확률을 부여함으로서 랜덤 액세스 채널에서의 short 메시지 전송으로 인한 충돌증가를 방지하였다. 효율적인 전송을 위해 이동단말의 전송대기 큐의 상태에 따라 전송속도를 변경함으로서 버스트한 트래픽 특성에 적응할 수 있도록 하였다. 전송대역과 전송코드 수가 제한된 환경에서 제안한 MAC 프로토콜은 cdma2000 시스템 보다 효과적으로 전송을 지원함을 알 수 있었다.

• 한국정보통신학회논문지
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• 제10권9호
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• pp.1685-1690
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• 2006

미래의 이동통신 시스템은 제 한된 무선 자원 조전 하에 고품질의 멀티미디어 서비스를 제공하기 위해 계층 셀 시스템으로 동작해야한다. 본 논문에서는 매크로, 마이크로, 피코 셀이 공존하는 계층 CDMA 셀를라 시스템에 적용된 호 수락 제어 방식을 연구하였다. 제안된 호 수락 제어 알고리즘을 사용하였을 경우 호 수락 제어를 하지 않는 경우에 비해 시스템 용량이 20% 정도 향상됨을 알 수 있다.

• 전자공학회논문지A
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• 제31A권4호
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• pp.47-55
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• 1994

This paper presents the CDMA system using the RAKE receiver over a multipath fading channel and in multi-user environments. The interference between the propagation paths in a multipath fading causes a serious degradation in the mobile communication environment. In order to derive the path inteference and reduce the fading effect, the RAKE receiver is used. In a computer simulation, the path number of a fading channel and the branch number of the RAKE receiver are modified. As a result, the CDMA system using the RAKE receiver gives a better performance than the conventional CDMA system over a multipath fading channel and in multi-user environments.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2003년도 종합학술발표회 논문집 Vol.13 No.1
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• pp.576-580
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• 2003

In order to assess the spectrum usage efficiency in mobile radio services, we consider the capacity limits of a CDMA system. The maximum achievable capacity per $km^2$ is viewed as a meaningful figure of merit for a cellular system and a method is proposed here to estimate the minimum achievable distance between adjacent base stations in the case of CDMA. The probability for entering in soft handover state is used as a limit for densification in a CDMA system. From this criterion, conditions on the minimum possible cell radius are derived.

• 한국콘텐츠학회논문지
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• 제6권5호
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• pp.14-19
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• 2006

텔레매틱스는 자동차 등 최첨단 기계산업과 이동통신 등 IT산업의 집합체로서 향후 자동차 문화에 엄청난 변화를 몰고 올 전망이다. 본 논문에서는 GPS와 CDMA 이동통신망 및 인터넷을 이용하여 구현한 순환차량 도착시각 안내 시스템에 대하여 기술하였다. 본 시스템은 GPS수신기와 이동단말기(PDA)로 구성된 탑재장치를 실은 순환 차량의 위치정보를 CDMA망 및 인터넷을 이용하여 위치서버로 전송하고, 사용자는 웹, PDA 또는 휴대전화를 이용하여 순환 차량의 현재위치와 도착예정 시각을 확인할 수 있다.

• 한국통신학회논문지
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• 제22권8호
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• pp.1632-1642
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• 1997

In this paper, we studied the effects of the power control imperfection on the system performances of a microcellular DS/CDMA system. The maximum user capacity, defined as the maximum number of users can be serviced simultaneouly, meeting a given voice quality, is first considered. Then the performence degradation due to the control error is analyzed. The frequency selective Raician channel model is used to characterize a microcellular mobile communication environment. The DS/CDMA system under consideration uses BPSK modulation and convolutional coding/Viterbe decoding with soft decision for forward error correction. It is shown that the user capacity falls linearly down with the increase of the power control error(in terms of the standard deviation in dB) and the interference from users outside the third tier cells have a minor effect on the performance. And the performance of DS/CDMA with the imperfect power control model is made to be less than 50% of that with perfect power control moded.

• 한국통신학회논문지
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• 제25권9B호
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• pp.1579-1587
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• 2000

This paper presents the properties of the RF part in the receiving system based in IMT-2000 terminal technology. It mainly discuss the RF parameter performance of the receiving system for mobile telecommunication comparable to IS-98A and J-STD-018 specifications of commercially available CDMA and PCS, and is to anticipate the processing gain of the IMT-2000 receiving system, processing gain according to data processing rate, and terminal noise figure according to processing gain, relationship between noise figures according to Eb/Nt, Ioc. It is performed by such analysis method as CDMA and PCS receiving systems. Transmission bandwidth is n$\times$1.25 MHz(n=1, 3, 6, 9, 12) which is recommended by Qualcomm and NTT, the leading company in cdma 2000. Data transmission rate of IMT-2000 is classified into three cases as in moving vehicle environment of 144Kbps, outdoor pedestrian environment of 384Kbps, and indoor office environment of 2Mbps

• 한국컴퓨터정보학회논문지
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• 제11권3호
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• pp.213-219
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• 2006

이동통신시스템에서 사용자의 신호는 다른 방향에서 도래하는 신호로부터 간섭이 발생한다. 간섭을 제거하기위해서 다이버시티, 등화기 등 다양한 연구가 진행되었다. 본 논문에서는 배열안테나의 가중치을 구하여 신호대잡음비를 향상시키고자 한다. 가중치는 신호의 상관계수에 의해서 고유값과 고유벡터로부터 구한다. 구한 가중치를 CDMA시스템에 적용하여 시스템성능과 용량을 증가시켰다. 변조방식은 QPSK와 OQPSK를 시스템에 적용시켜 성능을 분석하였다.

• 한국IT서비스학회지
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• 제9권4호
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• pp.207-217
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• 2010

This paper is concerned with a protection system for the mentally handicapped, which is utilizing a GPS receiver and mobile communications. The protection system consists of a location notification equipment, a location identification and management server, and a cell phone of guardian. The location notification equipment is made up of a GPS receiver, a CDMA communication module and a microprocessor. The equipment transfers the location of the mentally impaired to the location identification and management server when the handicapped gets out of a certain bound of the designated facility. The server marks the handicapped's location on the map in the server and also notifies the guardian's cell phone of the locations. With applying the proposed protection system to social welfare organizations related to the mentally handicapped, it is expected to efficiently contribute to the promotion of the handicapped's welfare.

• 한국통신학회논문지
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• 제35권11A호
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• pp.1085-1090
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• 2010

Ultra wideband (UWB) technologies have been developed to exploit a new spectrum resource in substances and to realize ultra-high-speed communication, high precision geolocation, and other applications. The energy of UWB signal is extremely spread from near DC to a few GHz. This means that the interference between conventional narrowband systems and UWB systems is inevitable. However, the interference effects had not previously been studied from UWB wireless systems to conventional mobile wireless systems sharing the frequency bands such as Cellular CDMA and Korean PCS. This paper experimentally evaluates the interference from two kinds of UWB sources, namely a direct-sequence spread-spectrum UWB source and an impulse radio UWB source, to a Cellular CDMA and K-PCS digital transmission system. The average frame error rate degradation of each system arc presented. From these experimental results, we show that in all practical cases UWB system can coexist with Cellular CDMA and K-PCS terminal without causing any dangerous interference.