• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -2
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• pp.1320-1323
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• 2002

This paper reviews the Korean government’s selection process of core wireless communications technologies, and presents technology trends, perspectives and strategies of 5 core technologies to develop in wireless communications areas based on the mid term IT technology development plan(2002∼2004). Delphi Panel Method and Analytic Hierarchy Process(AHP) Analysis were adapted to select 30 core technologies in 9 strategic areas. Especially, 5 core wireless communications technologies out of 24 required technologies are selected: 4 G Core Technology, Broadband Wireless Access Network Technology, IMT-2000 Plus STP Technology, OBP Based Multimedia Satellite Communications Technology, Stratosphere Communications System Technology. Strategic national IT R&D program has been essential to continue success story of CDMA technology, and acquiring technology independency from advanced nations. In long term perspectives, a strategy of intensive investment with prudent selection onto core technologies should be deployed in the IT R&D programs. Also, the national IT R&D programs should be limited in the high risk & high returen areas where only government can afford the failures as well as better spill over effects are expected for the technology development and national economy. Korean industry has some strength in wireless communications technology area. Therefore, more policy concerns should be given into this area not only to secure present strength but also to explore better technology competitiveness.

• Journal of Communications and Networks
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• 제5권3호
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• pp.187-196
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• 2003

We consider the use of error control coding in direct sequence-code-division multiple access (OS-COMA) systems that employ multiuser detection (MUO) and space diversity. The relative performance gain between Reed-Solomon (RS) code and convolutional code (CC) is well known in [1] for the single user, additive white Gaussian noise (AWGN) channel. In this case, RS codes outperform CC's at high signal-to-noise ratios. We find that this is not the case for the multiuser interference channel mentioned above. For useful error rates, we find that soft-decision CC's to be uniformly better than RS codes when used with DS-COMA modulation in multiuser space-time channels. In our development, we use the Gaussian approximation on the interference to determine performance error bounds for systems with low number of users. Then, we check their accuracy in error rate estimation via system's simulation. These performance bounds will in turn allow us to consider a large number of users where we can estimate the gain in user-capacity due to channel coding. Lastly, the use of turbo codes is considered where it is shown that they offer a coding gain of 2.5 dB relative to soft-decision CC.

• 한국통신학회논문지
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• 제22권7호
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• pp.1427-1436
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• 1997

Turbo codes, decoded through an iterative decoding algorithm, habe recently been shown to yidel remarkable coding gains close to theoretical limits in the Gaussian channel environment. This thesis presents the performance of Turbo code through the computer simulation. The performance of modified Turbo code is compared to that of the conventional Turbo codes. The modified Turbo code reduces the time delay in decoding with minimal effect to the performance for voice transmission sytems. To achieve the same performance, random interleaver the size of which is no less than the square root of the original one should be used. Also, the modified Turbo code is applied to MC-CDMA system, and its performance is analyzed under the Rayleigh Fading channel environment. In Rayleigh fading channel environment, due to the amplitude distortion caused by fading, the interleaver of the size twice no less than that in the Gaussian channel enironment was required. In overall, the modified Turbo code maintained the performance of the conventional Turbo code while the time delay in transmission and decoding was reduced at the rate of multiples of two times the squared root of the interleaver size.

• 한국통신학회논문지
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• 제33권11C호
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• pp.874-879
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• 2008

[1]에서 LCZ 수열군의 2배 확장을 제안하였다. 본 논문에서는 [1]에서의 2배 확장방법을 일반화하는 새로운 확장방법을 제안한다. 이 생성방법을 사용하면 인수가 (N,M,L,${\epsilon}$)인 q진 LCZ 수열군은 인수가 (pN,pM,p[(L+1)/p]-1,p${\epsilon}$)인 q진 LCZ 수열군이 된다. 이 때, p는 소수이고 p는 q의 약수다. 특히 L${\equiv}$p-1modp일 때, 확장된 q진 LCZ 수열군의 인수는 (pN,pM,L,p${\epsilon}$)이 된다.

• 한국전자파학회논문지
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• 제13권10호
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• pp.1061-1070
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• 2002

본 논문은 IS2000 환경에서 기지국의 수신 성능을 증대시키기 위한 스마트 안테나 Test-bed의 성능을 분석하였다. 따라서 본 논문에서는 IS2000 1x의 수신 신호 모델링, 빔형성 알고리즘, 빔형성 모듈 설계 및 테스트 베드를 이용한 성능 분석을 하였다. 수신 성능을 높이는 최적의 빔형성을 위해 빔형성 알고리즘은, Lagrange 공식을 이용한 Generalized Lagrange 알고리즘을 이용하였다. 이를 신호처리 칩을 이용한 보드로 직접 설계, 제작하였다. 빔형성 모듈에 대한 성능시험 결과 정상동작 확인 및 실시간 동작처리가 가능함을 보였다. 따라서 본 논문에서 제시한 스마트 안테나 Test-bed는 IS2000 이동통신 환경에서 우수한 성능을 나타낼 수 있음을 증명하였다.

• 산업공학
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• 제9권3호
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• pp.180-193
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• 1996

본 논문에서는 시뮬레이션 모델을 통해 호유형뿐만 아니라 개인통신서비스에서 필수적인 핸드오버 및 위치등록 등의 모든 트래픽 유형을 고래했을 때 개인통신교환기(PCX : Personal Commuincations Exchange)에서의 지연시간을 분석하며, 지연시간에 대한 결과와 프로세서의 이용율로부터 개인통신교환기의 호처리 및 이동성처리용량을 분석하고 그에 따른 가입자의 수용능력을 추정한다. IPC(Inter-Processor Communications) 메시지의 송수신시간 및 메시지의 처리시간등 교환기 제어계의 성능분석에 필요한 입력 파라미터 값은 기존 ISDN(Integrated Services Digital Network) 및 CMS-MX(CDMA Mobile System-Mobile Exchange) 교환기의 측정자료를 이용하였다. 시뮬레이션 분석결과 PCX 교환기의 호처리 성능은 주로 번호번역 기능을 담당하는 프로세서인 NTP(Number Translation Processor)의 용량에 의해 결정되며, 가입자 밀도가 1,500명$/km^2$인 경우 호처리용량은 약 42만 BHC(Busy Hour Call Completion)로 추정되었고, 이에 상응하는 핸드오버 및 위치등록 처리용량은 각각 시간당 약 2만 6천히 및 40만 6천회로 나타났다. 이것은 가입자당 호처리 부하가 1.6BHC일 경우, 약 15만 7천 가입자를 수용할 수 있는 용량에 해당한다.

• 한국통신학회논문지
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• 제25권8B호
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• pp.1333-1340
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• 2000

본 논문에서는 고속의 초기동기가 가능한 Kronecker 부호를 DS/CDMA 시스템의 확산부호로 하여 패킷 무선 데이터 통신에서의 사용을 위한 타당성을 보인다 먼저 Kronecker 부호의 생성방법 상관특성을 보여 대체적인 부호의 특성을 밝히고 부분 상관기를 이용할 수 있음을 보인다 더 나아가 PN 부호와 같은 평균 초기동기획득 시간을 가질 때의 Kronecker 부호의 오경보 확률과 실패 확률을 구하여 Kronecker 부호가 PN 부호보다 더 높은 동기 확률을 가짐을 보임으로써 패킷 통신에서 Kronecker 부호를 사용할 수 있는 가능성을 확인한다.

• Journal of Communications and Networks
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• 제6권1호
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• pp.9-18
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• 2004

Self-encoded multiple access (SEMA) is a unique realization of random spread spectrum. As the term implies, the spreading code is obtained from the random digital information source instead of the traditional pseudo noise (PN) code generators. The time-varying random codes can provide additional security in wireless communications. Multi-rate transmissions or multi-level grade of services are also easily implementable in SEMA. In this paper, we analyze the performance of SEMA in additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. Differential encoding eliminates the BER effect of error propagations due to receiver detection errors. The performance of SEMA approaches the random spread spectrum discussed in literature at high signal to noise ratios. For performance improvement, we employ multiuser detection and Turbo coding. We consider a downlink synchronous system such as base station to mobile communication though the analysis can be extended to uplink communications.

• Journal of Communications and Networks
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• 제6권1호
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• pp.26-34
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• 2004

A blind interference canceller in the presence of subchipspaced multipath channels for direct-sequence code division multiple access (DS-CDMA) down-link system is considered. This technique is based on combining the existing blind interference canceller with a technique that involves assigning subchip-tap spacing to the Rake receiver. The proposed receiver minimizes the receiver’s output energy subject to a constraint in order to mitigate the multiple access interference (MAI) along each multipath component, and then suboptimally combining all the multipath components. Moreover, it is able to mitigate the mismatch problem when subchip-spaced multipath components arrive at the blind interference canceller. It is known that optimal combining techniques perform a decorrelation operation before combining, which requires both knowledge and computational complexity. In the following, we have adopted a simpler but suboptimum approach in the combining of the suppressed signals at the output of our proposed receiver. Computer simulation results verify the effectiveness of the proposed receiver to handle subchip-spaced multipath components and still suppresses MAI significantly.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.237-241
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• 2008

Femtocells are cellular access points that connect to a mobile operator's network using residential DSL or cable broadband connections. They have been developed to work with a range of different cellular standards including CDMA, GSM and UMTS. Like legacy base station, the frequency accuracy and phase alignment is necessary for ensuring the quality of service (QoS) for applications such as voice, real-time video, wireless hand-off, and data over a converged access medium at the femtocell. But, the GPS has some problem to be used at the femtocell, because it is difficult to set-up, depends on the satellite condition, and very expensive. So, some techniques are discussed to alternate with the legacy GPS system. NTP, PTP, Synchronous Ethernet use the ethernet to synchronize distributed clocks in packet networks. AGPS support reliable position information than the legacy GPS in poor signal conditions. But, These method also have some problems. So, hybrid timing method like A-GPS+PTP and TV+GPS was developed to make up the weak point of GPS. This paper introduces the each method and compare each other and y propose much better solution for timing synchronization at the Femtocell