• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.235-237
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• 2002

본 논문에서는 전용 코드 방식의 CDMA 슬롯 ALOHA 시스템에서 패킷 전송 확률을 동적으로 제어하는 알고리즘을 제안한다. 전용 코드 방식의 CDMA 슬롯 ALOHA 시스템에서는 고유의 확산코드론 이용하여 패킷을 전송하므로 패킷 충돌로 인한 전송 실패는 없는 반면, 다원 접속 간섭에 의한 비트 오류가 패킷 전송의 실패 요인 된다. 제안한 알고리즘에서는 기지국이 망의 부하에 따라 단말기들의 패킷 전송 확률을 계산하여 방송하고, 단말기에서는 이를 기반으로 패킷 전송을 시도한다. 성능 분석의 결과, 제안한 알고리즘은 망의 부하에 따라 적응적으로 전송 확률을 제어함으로써 동시에 전송되는 패킷의 수를 일정하게 유지시킬 수 있었으며, 이로 인하여 시스템 성능이 향상됨을 알 수 있었다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.10a
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• pp.235-238
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• 2000

In this paper the MUD(Multi-User Detection) schemes and turbo codes are utilized in DS-CDMA mobile communication systems. Theses schemes effectively mitigate the effects of MAI(Multiple Access Interference) and Rayleigh fading. Using Monte Carlo simulation, the performance of the proposed schemes is analyzed for various channel conditions.

• Journal of Industrial Technology
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• v.24 no.B
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• pp.143-148
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• 2004

We present a fast algorithm for CDMA (code division multiple access) multiuser detection using the gradient guided search. The fast algorithm calculates the maximum likelihood (ML) metric so efficiently that it needs only O(K) additions in the presence of K users once some initialization is completed. The computational advantages of the fast algorithm over the conventional method are more noticeable as more iterations are required to obtain a suboptimal solution as in the initialization with matched filters.

• Proceedings of the IEEK Conference
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• 2003.11a
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• pp.283-286
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• 2003

This paper presents a novel signal processing method for optimal beamforming of smart antenna system in cdma2000 1X mobile communication environments. This method utilizes characteristics of the reverse pilot channel of cdma2000 1X mobile communication systems, and applies them to improve the performance of an adaptive algorithm, which is used to a smart antenna system for beamforming.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.05a
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• pp.1048-1054
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• 2006

본 연구에서는 3G CDMA 이동통신시스템의 소프트블록킹 확률을 구할 수 있는 새로운 해석적인 모형을 제안한다. 제안된 모형은 트래픽의 지리적 분포에 따른 신호감쇄특성을 매크로화 하여, 트래픽 양(volume)의 변동성을 반영한 CDMA 트래픽 엔지니어링 모델개발에 효과적으로 이용될 수 있다. 제안된 모형은 현실시스템 상황을 반영한 실험을 통해 그 유효성을 검증하였다.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.541-544
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• 2003

In this paper, we analyzed a physical layer of W-CDMA system and a performance of a downlink of W-CDMA system by using the space-time code by computer simulation over the ITU-R realistic channel model. From the results of the simulation, we note that the increase of multi-path components affects the improvement of the system performance because of the effect of the RAKE receiver.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.77-80
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• 2002

In this paper, we analyze a physical layer of W-CDMA .system and design a transmitter and receiver by using ADS (Advanced Design System). Also, we simulated a link level performance with different channel estimation algorithm in Jakes fading channel environment. For the channel estimator, we used the WMSA(Weighted Multi-Slot Averaging) algorithm, EGE(Equal Gain Estimation) algorithm and SSE(Symbol-to-Symbol Estimation) algorithm. This study will be useful in the analysis and design of W-CDMA system.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.230-233
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• 2003

In this paper, it is shown that, in DS/CDMA mobile systems, halving or doubling the spreading factor (HSF or DSE) when retransmission is requested possibly improves the throughput. Given transmit power, DSF essentially decreases probability of packet error (PPE) by increasing the signal energy per information bit. It, however, doubles the time duration needed for transmitting the original packet. On the other hand, HSF increases PPE. It, however halves the time duration required to carry the original packet. Thus, the efficiency of HSF or DSF as a retransmission strategy depends on the amount of increased or reduced PPE after HSF or DSF is selected. With achieving given residual error probability (REP) in CDMA systems, the effective throughput is evaluated in this paper to find conditions with which HSF or DSF achieves better performance than using the original one. Analytic results show that HSF or DSF performs better when relatively small or big changes in their PPE's are present, respectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.1
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• pp.53-58
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• 1998

Traffic nonuniformity degrades the performance of DCMA cellular systems. This paper presents a new algorithm called the Soft Handoff with Dynamic Thresholds (SHDT) which reduces the performance degeradation due traffic nonuniformity on CDMA systems. Unlike the conventional fixed handoff thresholds, algorithm allows the handoff thresholds (T_ADD and T_DROP) to vary dynamically according to the traffic density of each cell. This algerian has been implemented by means of computer simulation and the results show that SHDT improves the overall CDMA system performance in terms of outage probability. The SHDT algorithm can easily be applied to CDMA cellular systems without my modification.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.484-491
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• 2000

It is necessary to apply SSB modulation method with high bandwidth efficiency to the DS-CDMA mobile communication systems in order to accommodate the increasing number of voice users as well as the broad band and high data rate service in the future. Even though the bandwidth efficiency increases if SSB modulation is applied to BPSK-DS/CDMA, its performance gets degraded because of the increased multiple access interference. Therefore for eliminating the increased multiple access interference, the SSB/BPSK-DS/CDMA with successive interference canceller(SIC) is proposed and its performance and capacity are analyzed. With the limited system bandwidth, it is shown that the SSB/BPSK-DS/CDMA with SIC can accommodate more capacity than the conventional BPSK-DS/CDMA with SIC.