• Journal of Communications and Networks
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• 제15권3호
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• pp.283-291
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• 2013

In this paper, we propose new multiuser detectors (MUDs) based on compressed sensing approaches for the large-scale multiple antenna systems equipped with dozens of low-power antennas. We consider the scenarios where the number of receiver antennas is smaller than the total number of users, but the number of active users is relatively small. This prior information motivates sparsity-embracing MUDs such as sparsity-embracing linear/nonlinear MUDs where the detection of active users and their symbol detection are employed. In addition, sparsity-embracing MUDs with maximum a posteriori probability criterion (MAP-MUDs) are presented. They jointly detect active users and their symbols by exploiting the probability of user activity, and it can be solved efficiently by introducing convex relaxing senses. Furthermore, it is shown that sparsity-embracing MUDs exploiting common users' activity across multiple symbols, i.e., frame-by-frame, can be considered to improve performance. Also, in multiple multiple-input and multiple-output networks with aggressive frequency reuse, we propose the interference cancellation strategy for the proposed sparsity-embracing MUDs. That first cancels out the interference induced by adjacent networks and then recovers the desired users' information by exploiting the low user activity. In simulation studies for binary phase shift keying modulation, numerical evidences establish the effectiveness of our proposed MUDs exploiting low user activity, as compared with the conventional MUD.

• 전자공학회논문지S
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• 제36S권9호
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• pp.18-26
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• 1999

여러쓰는이 검파는 간섭과 근원 효과 문제를 해결할 수 있기 때문에 널리 연구되고 있다. 이 논문에서는 유사동기 채널에서 안테나 배열을 쓰는 역방향 연결 시스템에서의 유사최대비슷함 검파기를 생각하였다. 제안한 시스템은 다른 쓰는이들의 정보를 모두 알지 않더라고 쓰는이 사이 간섭을 줄일 수 있음과 이제까지의 정합 여파기보다 성능이 더 뛰어남을 보였다.

• 대한전자공학회논문지TC
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• 제49권4호
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• pp.18-25
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• 2012

최근 들어, 스마트 기기의 수요가 급증하면서 기존의 3G 표준에 비해 향상된 품질을 제공하는 long-term evolution (LTE) 서비스가 전 세계적으로 활발히 보급되고 있다. 2010년에 발표된 릴리즈 10은 흔히 LTE-Advanced (LTE-A)로 불리는데, LTE-A의 여러 특징 중 다중사용자 MIMO (MU-MIMO) 기술은 정보 처리량을 향상시키기 위한 LTE-A의 핵심기술로 근래 많은 주목을 받고 있다. 본 논문에서는 LTE 및 LTE-A 시스템에서 도입된 MU-MIMO 기술의 이론적 배경 및 표준의 주요 특징을 소개한다.

• IEIE Transactions on Smart Processing and Computing
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• 제2권3호
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• pp.148-159
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• 2013

An analysis of the throughput and stability region of random access systems is currently of interest in research and industry. This study evaluated the performance of a multiuser random access channel with a retransmission gain. The channel was composed of a media access control (MAC) determined by the transmission probabilities and a multiuser communication channel characterized by the packet reception probabilities as functions of the number of packet transmissions and the collision status. The analysis began with an illustrative two-user channel, and was extended to a general multiuser channel. For the two-user channel, a sufficient condition was derived, under which the maximum throughput was achieved with a control-free MAC. For the channel with retransmission gain, the maximum steady throughput was obtained in a closed form. The condition under which the random access channel can acquire retransmission gain was also obtained. The stability region of the general random access channel was derived. These results include those of the well-known orthogonal channel, collision channel and slotted Aloha channel with packet reception as a special instance. The analytical and numerical results showed that exploiting the retransmission gain can increase the throughput significantly and expand the stability region of the random access channel. The analytical results predicted the performance in the simulations quite well.

• Journal of Communications and Networks
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• 제18권2호
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• pp.173-181
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• 2016

In this paper, we address a new robust optimization problem in a multiuser multiple-input single-output broadcasting system with simultaneous wireless information and power transmission, where a multi-antenna base station (BS) sends energy and information simultaneously to multiple users equipped with a single antenna. Assuming that perfect channel-state information (CSI) for all channels is not available at the BS, the uncertainty of the CSI is modeled by an Euclidean ball-shaped uncertainty set. To optimally design transmit beamforming weights and receive power splitting, an average total transmit power minimization problem is investigated subject to the individual harvested power constraint and the received signal-to-interference-plus-noise ratio constraint at each user. Due to the channel uncertainty, the original problem becomes a homogeneous quadratically constrained quadratic problem, which is NP-hard. The original design problem is reformulated to a relaxed semidefinite program, and then two different approaches based on convex programming are proposed, which can be solved efficiently by the interior point algorithm. Numerical results are provided to validate the robustness of the proposed algorithms.

• 한국정보통신학회논문지
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• 제19권2호
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• pp.293-300
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• 2015

우수한 성능의 OFDM 전송을 위하여, 각 사용자에게 유리한 채널을 할당하는 다중 사용자 다이버시티(MUD) 방식이 최근 사용되고 있다. 또한 시스템의 성능을 향상시키기 위하여 STBC 안테나 다이버시티 방식이 현재 사용되고 있다. 파일럿 심볼을 이용하여 전송 채널을 추정하는 현 시스템에서는 채널 추정 오차로 인하여 시스템의 성능이 열화 된다. 그러므로 본 논문에서 채널 추정 오차의 영향을 고려하여 MUD STBC OFDM 전송 시스템의 비트 오류율 성능을 분석한다. 분석 결과, MUD를 사용한 시스템에서는 같은 비트 오류율에 대하여 사용자 수가 32인 경우에 5 dB 정도의 다이버시티 전력 이득을 얻는다.

• ETRI Journal
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• 제41권5호
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• pp.637-647
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• 2019

Separating highly correlated users can reduce the loss caused by spatial correlation (SC) in multiuser multiple-input multiple-output (MU-MIMO) systems. However, few accurate analyses of the loss caused by SC have been conducted. In this study, we define signal-to-interference-plus-noise ratio (SINR) loss to characterize it in multiuser multiple-input single-output (MU-MISO) systems, and use coefficient of correlation (CoC) to describe the SC between users. A formula is deduced to show the accurate relation between SINR loss and CoC. Based on this relation, we propose a user selection method that utilizes CoC to minimize the average SINR loss of users in massive MU-MISO systems. Simulation results verify the correctness of the relation and show that the proposed user selection method is very effective at reducing the loss caused by SC in massive MU-MISO systems.

• ETRI Journal
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• 제46권2호
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• pp.184-193
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• 2024

This paper presents the performance evaluation of an amplify-and-forward (AF) relay-assisted multiuser multiple input-multiple output (MU-MIMO) downlink transmission system for correlated fading channels. The overall system performance was improved by incorporating a double-quadrature spatial modulation (DQSM) scheme. The bit error rate (BER) performance and detection complexity of the AF-MU-MIMO-DQSM system were analyzed and compared with those of a conventional AF-MU-MIMO system under the same conditions and parameters. The results showed that the correlated fading channel severely affected the performance of systems with higher spectral efficiency (SE). Considering an SE of 12 bpcu/user, the AF-MU-MIMO-DQSM system yielded a gain of up to 3 dB in BER performance compared with that of its conventional counterpart for the analyzed cases. In terms of detection complexity, the AF-MU-MIMO-DQSM system showed a reduction of up to 56 % compared with that of the conventional system for the optimal maximum likelihood detection criterion.

• 한국통신학회논문지
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• 제25권3A호
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• pp.352-361
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• 2000

본 논문에서는 주파수 다중경로 페이딩과 Near/Gar 영향을 받는 Multi-Carrier CDMA 시스템의 성능을 분석하였다. 성능 분석을 위해 사용한 파라미터들을 Multi-Carrier의 수, 다중사용자의 수, RAKE 수신기의 가지수, 주파수 선택성 다중경로 페이딩의 감쇄지수, 그리고 CDMA 다중사용자의 분포와 세기이다. Multi-Carrier CDMA 시스템에서 Near/Far 영향을 분석하기 위하여 3가지 간섭 분포 모델을 설정하였다. 첫 번째 모델은 다중사용자가 간섭파 대 반송파 비인 I/C를 -4dB에서 4dB 사이에서 2 dB씩의 차이를 가지며 20%씩 균일하게 분포하는 경우이다. 두 번째 모델은 다중사용자가 I/C 비를-2dB에서 2dB 사이에서 2dB씩의 차이를 가지며 33.3%씩 균일하게 분포하는 경우이다. 그리고 세 번재 모델은 모든 다중사용자가 I/C가 0dB로 신호 전력과 간섭전력이 동일하게 분포하여 전력이 완전하게 제어된 경우이다. 그리고 본 논문에서는 주파수 선택성 다중경로 페이딩의 영향을 감소시키기위하여 RAKE 수신기를 채용한 Multi-Carrier CDMA 시스템을 제안하였다. 이 시스템에서는 제시한 3가지 간섭 분포 모델중에서 세 번째 모델(완전 전력제어가 된 경우)이 가장 좋은 성능을 나타내었고, 간섭파의 전력과 신호파의 전력차이가 적을수록 희망 신호에 영향을 주는 간섭 신호의 전력량이 적어서 Multi-Carrier CDMA 시스템의 성능이 향상됨을 알 수 있었다.

• Journal of Communications and Networks
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• 제5권4호
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• pp.365-373
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• 2003

This paper investigates the performance of M-ary pulse position modulation (PPM) multiuser ultra-wideband (UWB) communication systems in terms of symbol error rate (SER) over fading and additive white Gaussian noise (AWGN) channel. Based on Gaussian approximation for the multiple access interference, an expression for the signal-to-noise ratio (SNR) is derived for the UWB system. This expression is used to derive exact SER expressions for coherent UWB receivers. The effect of pulse selection on the SER of multiuser UWB system is studied. In addition to rectangular pulse, the 2nd derivative Gaussian waveform and Rayleigh pulses were considered. We show that the system capacity and/or SER performance can be significantly increased by using the monocycle pulse in fading channels.