• Journal of Advanced Navigation Technology
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• v.6 no.4
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• pp.306-311
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• 2002

In this paper, we have proposed the Multi-Carrier (MC) CDMA system by adopting multi-interference cancellation techniques connecting an adaptive array antenna and a CCI canceller in cascade form. And, we have analyzed the BER performance of system in AWGN channel where MUI is a major interference degrading the performance of the proposed MC CDMA system. Also, we have evaluated the degree of performance improvement in the proposed MC CDMA system. As the result of analysis, a CCI canceller is better efficient than an adaptive array antenna in the performance improvement and that the performance improvement becomes large as the number of users increases when multi-interference cancellation techniques are used in cascade form. Also, we found that performance of $10^{-5}$ in a point of view BER could be achieved when $E_b/N_o$ is more than 10 dB.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.6
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• pp.42-47
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• 2008

In this article a novel constant amplitude precoding for impulse UWB system is proposed. According to IEEE 802.15.4a, impulse UWB can be used in indoor localization and sensor data transmission. Most USN(ubiquitous sensor networks) needs multiple access. However impulse UWB system has a limited capability to detect superpositioned signal induced by multiple access. To overcome this problem we have adopted the concept of CAMC(Constant Amplitude Multi-Code) deviced by Wada and Kim. The proposed system consists of systematic constant amplitude precoding and LDPC decoding. And this system shows a good BER performance in computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6A
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• pp.775-781
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• 1999

A multi-media variable processing gain DS/CDMA system are considered. Two types of information sources with different rates and transmitting powers are assumed to be stransmitted simultaneously in the same channel. Average signal-to-noise ratios at the correlation receiver outputs for each type of information sources are analytically derived as funtions of partial cross-correlations between spreading code sequences. As the difference of information rates between information sources increase, the difference between signal-to-noise ratio regarding random spreading code and that regarding pseudo random spreading code increases (maximum 1.3dB). The result can provide a analytical tools for use in multi-media DS/CDMA system design.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2000.12a
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• pp.5-8
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• 2000

In this paper, The new scheme for Demand Assigned Multiple Access(DAMA) system is proposed. To focus on the onboard processor's specific monitoring of output port of the downlink, we found the Throughput and Blocking probability by the request traffic(λ) and channel's departure probability(Ρ).

• Proceedings of the KAIS Fall Conference
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• 2010.05a
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• pp.218-220
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• 2010

최근에 멀티미디어 환경을 기반으로 한 온라인 회의 시스템은 큰 발전을 가져왔지만 회의 통제 불가 같은 단점과 정보 보안에 있어서의 취약점이 존재한다. 이에 본 논문에서는 비대칭키 암호 알고리즘과 OTP 및 티켓 시스템을 이용해 기밀성과 회의 통제 기능을 추가하여 이전에 제안한 것보다 개선된 다중 접속 도메인 시스템을 제안하고자 한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.11a
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• pp.703-704
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• 2009

멀티미디어 환경을 기반으로 한 온라인 회의 시스템은 큰 발전을 가져왔지만 회의 통제 불가 같은 단점과 정보 보안에 있어서의 취약점이 존재한다. 이에 본 논문에서는 비대칭키 암호 알고리즘과 OTP 및 티켓 시스템을 이용하여 기밀성과 회의 통제 기능을 추가한 다중 접속 도메인 시스템을 제안하고자 한다.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.5
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• pp.865-872
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• 2020

In the fifth generation (5G) mobile networks, non-orthogonal multiple access (: NOMA) has been considered as a promising technology, to increase the channel capacity. In NOMA, the multiple users share the channel resources and multiplex simultaneously. Recently, for the stronger channel user, it was reported that the bit-error rate (: BER) performance with interactive mobile users is degraded, compared to the BER of non-interactive users. In this paper, in order to improve such degraded BER performance, we propose the maximum-likelihood (: ML) receiver. First, the closed-form expression for the BER of the ML receiver is derived, and then it is shown that the BER of the ML receiver is improved, compared with the BER of the ideal perfect successive interference cancellation (: SIC) receiver. Additionally, based on the analytical expression, Monte Carlo simulations validates the above-mentioned results.

• Journal of Korea Game Society
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• v.15 no.6
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• pp.97-106
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• 2015

In an Unity engine for multi-player online games, the main thread processing game logic must be separated from the network thread that is responsible for network packet communication. Packet communication between the network threads needs to drop packets that overlap in order to improve the rendering speed. In this paper, the packet discard policy of network thread is proposed for an Unity engine for multi-player online games. The proposed method is the hybrid method of both Partial Packet Discard and Periodic Packet Discard methods to improve the rendering speed by periodically discarding overlapped network packets managed by the queue. The rendering speed of the proposed method is analyzed and its effectiveness is verified by various packet generating simulations of the Unity engine for multi-player online games.

• Journal of Convergence for Information Technology
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• v.10 no.10
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• pp.24-31
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• 2020

In non-orthogonal multiple access (NOMA), the degraded performance of the weaker channel gain user is a problem. In this paper, we propose the asymmetric binary pulse amplitude modulation (2PAM), to improve the bit-error rate (BER) performance of the weaker channel user in NOMA with the tolerable BER loss of the stronger channel user. First, we design the asymmetric 2PAM, calculate the total allocated power, and derive the closed-form expression for the BER of the proposed scheme. Then it is shown that the BER of the weaker channel user improves, with the small BER loss of the stronger channel user. The superiority of the proposed scheme is also validated by demonstating that the signal-to-noise ratio (SNR) gain of the weaker channel user is about 10 dB, with the SNR loss of 3 dB of the stronger channel user. In result, the asymmetric 2PAM could be considered in NOMA of 5G systems. As a direction of the future research, it would be meaningful to analyze the achievable data rate for the propsed scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.8A
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• pp.1298-1310
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• 2001

이 논문에서는 채널 상태가 천천히 변할 때, 직교 주파수 분할 다중화-부호분할 다중접속 시스템에 적합한 채널 추정 방법을 제안하고 성능을 분석한다. 제안한 채널 추정 방법은 시간과 주파수 영역 모두에 파일럿 심볼을 삽입하고, 이산 퓨리에 변환 후 영을 채워 넣는 방법을 이용한 내삽법으로 모든 부채널의 전달 함수를 얻는다. 또한 변환 영역에서 저대역 여파를 통해 받은 파일럿 신호에 존재하는 가산성 백색 정규 잡음의 영향을 상당히 줄일 수 있다. 이 때 저대역 여파기의 차단 주파수는 채널의 다중경로 수에 따라 정해진다. 같은 방법을 이용한 내삽법을 시간축으로 적용하여 시간에 따라 변하는 부채널의 채널 응답을 얻을 수 있다. 이 논문에서는 여러 가지 내삽법에 대한 평균 제곱 오차 성능을 수식적으로 제시한다. 제안한 저대역 여파를 결합한 내삽법을 쓰면 채널의 통계적 특성에 관한 정보 없이, 그리고 훨씬 적은 계산량으로 선형 최소 평균 제곱 오차 추정기와 비슷한 성능을 얻는다. 레일리 감쇄 채널에 대한 모의 실험을 통해 같은 비트 오류율에 대한 신호 대 잡음 비의 이득이 있음을 보인다.