• 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.

• ETRI Journal
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• 제40권3호
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• pp.309-317
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• 2018

Single carrier-frequency-division multiple access (SC-FDMA) has been adopted as the uplink transmission standard in fourth-generation cellular networks to facilitate power efficiency transmission in mobile stations. Because multiuser multiple-input multiple-output (MU-MIMO) is a promising technology employed to fully exploit the channel capacity in mobile radio networks, this study investigates the uplink transmission of MU-MIMO SC-FDMA systems with orthogonal space-frequency block codes (SFBCs). It is preferable to minimize the length of the cyclic prefix (CP). In this study, the chained turbo equalization technique with chained turbo estimation is employed in the designed receiver. Chained turbo estimation employs a short training sequence to improve the spectrum efficiency without compromising the estimation accuracy. In this paper, we propose a novel and spectrally efficient iterative joint-channel estimation, multiuser detection, and turbo equalization for an MU-MIMO SC-FDMA system without CP-insertion and with short TR. Some simulation examples are presented for the uplink scenario to demonstrate the effectiveness of the proposed scheme.

• 대한전자공학회논문지TC
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• 제41권11호
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• pp.1-7
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• 2004

본 논문에서는 다중 안테나를 사용한 다중 반송파 대역확산 다중접속 (MIMO MC-CDMA) 시스템을 위한 다단계 병렬 널링 및 병렬 부분 간섭 제거 수신기 (MPN-PPIC)를 제안한다. 기존의 V-BLAST 수신기는 널리 알려져 있는 다중 안테나 시스템에 대한 수신 방법으로, 단일 사용자 하향 링크 다중 안테나 MC-CDMA 시스템에 대해서는 어느 정도 좋은 성능을 보이지만, 다중 사용자의 경우에 있어서는 심각한 성능 저하 (error floor)를 보이는 것으로 알려져 있다. 본 논문에서 제안한 수신기는 다중 사용자 환경에서 이러한 성능 저하를 보이지 않으며, 다단계 연산을 통해서 보다 더 나은 성능을 얻을 수 있다. 또한, 제안한 방법은 chip interleaving을 하는 경우, 다단계 연산을 통해 단일 사용자 환경에 대해서도 V-BLAST보다 더 나은 성능을 보인다. 제안한 방법에 대한 이와 같은 성능은 컴퓨터 모의 실험을 통해서 확인해 본다.

• Journal of Communications and Networks
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• 제17권3호
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• pp.267-274
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• 2015

Due to the difficulty of coordination in the cellular uplink, it is a practical challenge how to achieve the optimal throughput scaling with distributed scheduling. In this paper, we propose a distributed and opportunistic user scheduling (DOUS) that achieves the optimal throughput scaling in a single-input multiple-output interfering multiple-access channel, i.e., a multi-cell uplink network, with M antennas at each base station (BS) and N users in a cell. In a distributed fashion, each BS adopts M random receive beamforming vectors and then selects M users such that both sufficiently large desired signal power and sufficiently small generating interference are guaranteed. As a main result, it is proved that full multiuser diversity gain can be achieved in each cell when a sufficiently large number of users exist. Numerical evaluation confirms that in a practical setting of the multi-cell network, the proposed DOUS outperforms the existing distributed user scheduling algorithms in terms of sum-rate.

• Journal of Communications and Networks
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• 제18권1호
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• pp.27-39
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• 2016

This paper derives and analyzes a novel block fast Fourier transform (FFT) based joint detection algorithm. The paper compares the performance and complexity of the novel block-FFT based joint detector to that of the Cholesky based joint detector and single user detection algorithms. The novel algorithm can operate at chip rate sampling, as well as higher sampling rates. For the performance/complexity analysis, the time division duplex (TDD) mode of a wideband code division multiplex access (WCDMA) is considered. The results indicate that the performance of the fast FFT based joint detector is comparable to that of the Cholesky based joint detector, and much superior to that of single user detection algorithms. On the other hand, the complexity of the fast FFT based joint detector is significantly lower than that of the Cholesky based joint detector and less than that of the single user detection algorithms. For the Cholesky based joint detector, the approximate Cholesky decomposition is applied. Moreover, the novel method can also be applied to any generic multiple-input-multiple-output (MIMO) system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권9호
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• pp.2120-2133
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• 2013

In this paper, we address the problem of linear minimum mean-squared error (MMSE) transmitter design for the cognitive radio (CR) multi-user multiple-input single-output (MU-MISO) broadcasting channel (BC), where the cognitive users are subject to not only a sum power constraint, but also a interference power constraint. Evidently, this multi-constraint problem renders it difficult to solve. To overcome this difficulty, we firstly transform it into its equivalent formulation with a single constraint. Then by utilizing BC-MAC duality, the problem of BC transmitter design can be solved by focusing on a dual MAC problem, which is easier to deal with due to its convexity property. Finally we propose an efficient two-level iterative algorithm to search the optimal solution. Our simulation results are provided to corroborate the effectiveness of the proposed algorithm and show that this proposed CR MMSE-based scheme achieves a suboptimal sum-rate performance compared to the optimal DPC-based algorithm with less computational complexity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권10호
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• pp.2601-2619
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• 2012

A differencing multiuser detection (MUD) method is proposed for multiple-input multiple-output (MIMO) direct sequence (DS) ultra-wideband (UWB) system to cope with the multiple access interference (MAI) and the computational efficiency in Nakagami fading channel. The method, which combines a multiuser-interference-cancellation-based decision feedback equalizer using error feedback filter (MIC DFE-EFF), a coefficient optimization algorithm (COA) and a differencing algorithm (DA), is termed as MIC DFE-EFF (COA) with DA for short. In the paper, the proposed MUD method is illuminated from the rudimental MIC DFE-EFF to the advanced MIC DFE-EFF (COA) with DA step by step. Firstly, the MIC DFE-EFF system performance is analyzed by minimum mean square error criterion. Secondly, the COA is investigated for optimization of each filter coefficient. Finally, the DA is introduced to reduce the computational complexity while sacrificing little performance. Simulations show a significant performance gain can be achieved by using the MIC DFE-EFF (COA) with DA detector. The proposed MIC DFE-EFF (COA) with DA improves both bit error rate performance and computational efficiency relative to DFE, DFE-EFF, parallel interference cancellation (PIC), MIC DFE-EFF and MIC DFE-EFF with DA, though it sacrifices little system performance, compared with MIC DFE-EFF (COA) without DA.

• 대한전자공학회논문지TC
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• 제46권7호
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• pp.6-12
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• 2009

본 논문에서는 다중 사용자 환경 다중 안테나 시스템에서 고유값 기반 스케줄링을 수행하기 위한 채널 정보(CSI: channel state information)를 각 사용자의 채널 상태에 따라 선택적(opportunistic)으로 피드백하기 위한 기법을 제안하고 있다. 3GPP(3rd generation partnership project) SMC(spatial multiplexing channel) 채널 모델에 의하면 도심지역에서 다중 사용자 다중 입출력(MU-MIMO: multiuser multiple input multiple output) 시스템은 안테나간의 높은 상관도(correlation)에 의해 시스템 용량(capacity)이 크게 저하된다. 이를 해결하기 위해 제안된 고유값 기반 스케줄링 기법의 경우 상관도에 의한 시스템 용량 저하를 완화시킬 수 있지만, 다중 사용자 다이버시티 이득(multiuser diversity gain)을 충분히 얻지 못하는 단점이 있다. 본 논문에서는 고유값 기반 스케줄링 기법을 바탕으로 다중 사용자 다중 입출력 시스템에서 평균적인 피드백 용량의 증가가 크지 않으면서, 다중 사용자 다이버시티 이득을 크게 향상 시킬 수 있는 선택적 채널 정보 피드백 기법을 제안하고 있다. 컴퓨터 모의 실험 결과를 통해서 본 논문에서 제안한 선택적 피드백 기법을 통해 시스템 용량 개선 효과를 확인할 수 있다.

• ETRI Journal
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• 제38권1호
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• pp.62-69
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• 2016

In this paper, we propose two novel user selection algorithms for multiuser multiple-input and multiple-output downlink wireless systems, in which both a base station (BS) and mobile stations (MSs) are equipped with multiple antennas. Linear transmit beamforming at the BS and receive combining at the MSs are used to avoid interference between users and find a better sum-rate capacity performance. An optimal technique for selecting users would entail an exhaustive search, which in practice becomes computationally complex for a realistic number of users. Suboptimal algorithms with low complexity are proposed for a coordinated beamforming scheme. Simulation results show that the performance of the proposed algorithms is better than that provided by previous algorithms and is very close to an optimal approach with reduced complexity.

• 전자공학회논문지
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• 제50권8호
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• pp.53-60
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• 2013

이 논문에서는 Pre-FFT 빔 형성기를 가진 MIMO(Multi-Input Multi-Out)-OFDM(Orthogonal Frequency Division Multiplexing)시스템 구조에 적합한 적응 빔 형성기법과 결합된 전력제어 기법을 제안한다. 제안된 전력제어 기법과 적응 빔 형성기법이 결합되어 송신전력을 제어하는 과정과 빔형성기 계수를 갱신하는 과정이 시간적으로 함께 iterative하게 이루어져서 수렴하게 되면 원하는 방향으로 빔이 형성되고 각 부반송파별로 원하는 SNIR 값에 수렴하게 되어 다중 사용자 환경에서 성능개선 효과를 얻을 수 있다. Pre-FFT 빔 형성기를 가진 MIMO-OFDM 시스템에 전력 제어기법을 결합할 경우 시스템의 성능 개선 효과를 모의 실험을 통하여 확인한다.