• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.07a
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• pp.174-176
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• 2010

이 논문에서는 직교 주파수 분할 다중 접속방식(orthogonal frequency division multiple access : OFDMA)을 이용한 상향 링크 시스템에서 수신된 신호에 주파수 옵셋이 존재할 때 나타나는 영향을 보상하는 방법을 제안한다. OFDMA에서 각 사용자가 전송한 신호에서 발생하는 주파수 옵셋은 다중 접속 간섭(multi-user interference : MUI)을 발생시킨다. 이러한 다중접속 간섭은 OFDMA 시스템의 성능을 저하시키는 주요한 원인 중에 하나이다. 이 논문에서는 시간영역에서 특정 사용자의 신호에 대한 주파수 옵셋의 보상을 한 뒤, 주파수 영역에서 일반적인 채널간간섭 제거 방법을 적용하여 다중 접속 간섭에 의한 영향을 효과적으로 제거하는 방법을 제안한다. 또한 부반송파에 위치에 따라 달리 나타나는 다중 접속 간섭의 크기에 따라 간섭 제거 방법을 달리하여 보다 적은 계산량으로 간섭을 제거하는 방법을 제안한다.

• Journal of Satellite, Information and Communications
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• v.6 no.1
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• pp.32-36
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• 2011

In this paper, we propose a cancellation scheme of multiple access interference (MAI), which is caused by carrier frequency offset, for the receiver of an interleaved orthogonal frequency division multiple access (IFDMA) uplink system. In the IFDMA systems, carrier frequency offsets introduce adjacent channel interference from other users' subcarriers, which results in performance degradation. In the proposed method, we compensate the carrier frequency offset in time domain and then eliminate MAI by using parallel interference cancellation in frequency domain. Simulation results show that the proposed method is effective in removing the MAI especially when the number of users are large and the MAI severely degrades the system performance.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.686-690
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• 2003

직접 확산 부호 분할 다원 접속 (Direct Sequence Code Division Multiple Access : DS-CDMA) 시스템과 시분할 다원 접속 (Time Division Multiple Access : TDMA) 시스템을 동일 주파수 대역에서 중첩되어 전송할 때 DS-CDMA 신호에서의 TDMA 신호의 협대역 간섭이 문제된다. 본 논문에서는 DS-CDMA 신호의 협대역 간섭(narrowband interference : NI)를 제거하는 방법으로서 노치필터를 이용해서 협대역 간섭파 제거법을 제안하고, 간섭제거기(CCI canceller)를 이용해서 다중접속간섭을 제거하여 DS-CDMA 신호의 성능을 개선한다. 본 논문은 잡음, 다중접속 간섭 및 협대역 간섭환경에서 DS-CDMA 신호와 TDMA 신호의 주파수 공용 시스템에 적용할 때의 성능을 분석하였다.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.33-36
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• 2000

DS-CDMA (direct sequence-code division multiple access) 시스템에서 여러 사용자가 동일 주파수 대역을 공유함으로써 다중 접속 간섭 (multiple access interference; MAI)이 발생하고 시스템의 성능을 크게 제한한다. 이러한 다중 접속 간섭을 제거하여 전송 신호의 질을 높이고 용량을 증대시키는 중요한 신호 처리 기술 가운데 하나가 적응 간섭 억제 기술이다. 적응 간섭 억제 기술 가운데 CMA (constant modulus algorithm) 기반의 블라인드 적응 간섭 억제기는 훈련수열을 필요로 하지 않고 빠른 수렴을 통하여 간섭을 효과적으로 제거할 수 있으나, 다중 경로 환경에서 심벌간 간섭 (intersymbol interference; ISI)이 증대되어 기존의 적응 수신기보다 악화된 성능을 보인다. 본 논문에서는 CMA를 기반으로 훈련 수열 없이 빠른 수렴을 하며 MAI와 ISI를 효과적으로 제거하기 위한 다이버시티 결합기 구조의 적응 간섭 억제기를 제한한다. 다중 경로 페이딩 채널 환경에서 기존의 블라인드 적응간섭 억제기와의 성능 비교 결과, 제안된 방식이 다중경로에 의한 ISI의 영향을 효과적으로 제거하여 우수한 성능을 얻을 수 있음을 확인하였다.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.4
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• pp.585-590
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• 2021

This paper proposes a 3-user non-interfering binary pulse amplitude modulation(2PAM) and non-orthogonal multiple access(NOMA) scheme, to improve the bit-error rate(BER) performance of the weakest channel user with the tolerable BER loss of the stronger channel users. First, we design the 3-user non-interfering 2PAM NOMA, and then derive the closed-form expressions for the BERs of the proposed scheme. Numerical results are also presented to demonstrate that the BER of the weakest channel user improves greatly, with the small BER losses of the stronger channel users. As a result, the non-interfering 2PAM could be considered in NOMA of 5G systems.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.11
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• pp.2457-2462
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• 2010

In this paper, We applied CCI canceller to remove multiple access interference in co-channel environment and improved performance of Impulse Radio UWB system. Also, we have evaluated the performance of UWB system with Truncated Type-II Hybrid ARQ scheme for achieving high quality data transmission.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.11-19
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• 2021

In this paper, we propose a non-orthogonal multiple access (NOMA) method based on channel alignment to simultaneously transmit multiple unicast and multicast streams in frequency-efficient manner. In this method, all receivers in a multicast cluster use the receive beamforming vectors that align their channels, and the base station uses the aligned channel information to design the transmit beamforming vectors that eliminate interference between multicast clusters. Using the effective receive channel information combined with the transmit beamforming vectors, unicast receivers design their own receive beamforming vectors that eliminate interference between unicast receivers. Since the proposed method effectively eliminates the interference, it achieves a higher sum rate than the existing orthogonal multiple access (OMA) method in high SNR regions. In addition, we present a hybrid method that exploits the benefits of the proposed NOMA method and the existing OMA method. Depending on the channel state, the hybrid method adaptively employs the existing OMA method, which improves the received signal power, in low SNR regions and the proposed NOMA method, which effectively eliminates the interference, in high SNR regions, thereby achieving a good sum rate over the entire SNR region.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.1
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• pp.96-107
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• 2013

In this study, we examine the effect of spreading sequence matched filtering on the power parameters of ultrawideband (UWB) multiuser interference (MUI) under different multiple access (MA) scenarios. More specifically, we investigate the manner in which the length of the sequence MF affects the average power, peak power, and the peak-to-average ratio (PAR) of the matched filtered version of an MUI signal. The results of the analysis performed for a simplified scenario are supported by the simulation results obtained for a realistic multipath environment.

• Journal of the Institute of Convergence Signal Processing
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• v.2 no.3
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• pp.45-49
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• 2001

Wideband code division multiple access (WCDMA) is the most widely adopted third generation air interface. The physical layer of the air interface is the main discussion topic during standardization processes. This paper aims to investigate the performance of uplink WCDMA over many conceivable transmission scenarios in realistic operating conditions. The focus of the study is placed on the performance under frequency selective fading channel conditions with multiple access interference (MAI) in mixed services environments. For the investigation, a simulator has been developed and it encompasses a variety of WCDMA air interface features. The results show that the performance is greatly affected by MAI and is further aggravated with the presence of frequency selective fading, thereby necessitating a suitable compensation measure.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2001.06a
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• pp.5-8
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• 2001

Wideband code division multiple access (WCDMA) is the most widely adopted third generation air interface. The physical layer of the air interrace is the main discussion topic during standardization processes. This paper aims to investigate the performance of uplink WCDMA over many conceivable transmission scenarios in realistic operating conditions. The focus of the study is placed on the performance under frequency selective fading channel conditions with multiple access interference (MAI) in mixed services environments. For the investigation, a simulator has been developed and it encompasses a variety of WCDMA air interface features. The results show that the performance is greatly affected by MAI and is further aggravated with the presence of frequency selective fading, thereby necessitating a suitable compensation measure.