• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6A
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• pp.551-557
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• 2011

We investigate lattice-reduction-aided precoding techniques using Look-Up table (LUT) for multi-user multiple-input multiple-output(MIMO) systems. Lattice-reduction-aided vector perturbation (VP) gives large sum capacity with low encoding complexity. Nevertheless lattice-reduction process based on the LLL-Algorithm still requires high computational complexity since it involves several iterations of size reduction and column vector exchange. In this paper, we apply the LUT-aided lattice reduction on VP and propose a scheme to generate the LUT efficiently. Simulation results show that a proposed scheme has similar orthogonality defect and Bit-Error-Rate(BER) even with lower memory size.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.12 s.115
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• pp.1224-1230
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• 2006

In this paper, for spatial multiplexing with limited feedback, a precoding scheme is proposed based on the joint use of minimal instantaneous feedback and long-term feedback of a small number of bits, wherein the long-term feedback is used to convey a selected preceding matrix within a precodercodebook consisting of a number of unitary matrices, and the active column vectors of the selected unitary matrix are conveyed to the transmitter using instantaneous feedback. Focusing on the case of dual multi-input multi-output(MIMO) systems, precoder codebook design for maximizing the average throughput of a spatial multiplexing system with a zero-forcing(ZF) receiver is proposed. It is shown that the proposed scheme provides a considerable throughput enhancement over multi-mode antenna selection and multi-mode basis selection only with the additional long-yterm feedback of a small number of bits. For example, the throughput increases by 11.5 % than antenna selection and 5.1% than basis selection, respectively, when SNR=20 dB.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.11
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• pp.33-39
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• 2014

We propose an optimal number of transmit antennas which maximizes energy-efficiency (EE) in multi-user massive multiple-input multiple-output (MIMO) downlink system with the maximal ratio transmission (MRT) precoding. With full channel state information at the transmitter (CSIT), we find a closed form solution by partial differential function with proper approximations using average channel gain, independence of individual channels, and average path loss. With limited feedback, we get a solution numerically by the bisection with approximations in the same manner, and analyze an effect of feedback bits on the optimal number of transmit antennas. Simulation results show that the optimal numbers of transmit antenna getting from proposed closed form solution and exhaustive search are nearly same.

• ETRI Journal
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• v.34 no.5
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• pp.655-665
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• 2012

Based on wideband precoding (WBP) in the multiple-input multiple-output orthogonal frequency division multiplexing system, an adaptive nonuniform codebook is presented in this paper. The relationship between the precoder distribution and spatial correlation is analyzed at first. A closed-form expression based on overlapped isosceles triangles is proposed as an approximation of the precoder distribution. Then, the adaptive codebook design is derived with the approximate distribution to minimize quantization errors. The capacity and bit error rate performance demonstrate that the adaptive codebook with WBP outperforms the conventional fixed uniform codebook.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2013.06a
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• pp.29-31
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• 2013

본 논문에서는 기존라디오(primary) 네트워크와 스펙트럼을 공유하는(spectrum sharing) 인지라디오(cognitive radio) 네트워크에서 비재생적(non-regenerative) 다중안테나 중계 (relay) 시스템을 위한 소스(source) 및 중계기 프리코딩(precoding) 기법을 제안한다. 제안된 기법은 소스와 중계기 프리코딩 행렬의 최적해를 구하기 위해 QCQP(Quadratically Constrained Quadratic Programming) 문제를 통해 구한다. 제안된 기법은 기존라디오 수신기에서의 간섭세기 제한을 만족하면서 낮은 MSE(Mean squared error)와 높은 MI(Mutual Information)를 달성함을 모의실험결과를 통해 보인다. 또한 아주 빠른 속도로 최적해로 수렴함을 보이고 있다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5A
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• pp.347-354
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• 2009

In this paper, we propose a new transmit diversity technique for multiple-input multiple-output (MIMO) systems to improve the link level performance of open-loop systems. By cyclically applying a predetermined set of preceding weight vectors, artificially induced fluctuation is created to achieve additional diversity gain in flat fading channels. To design the set of the precoding vectors, we exploit the knowledge on the distribution of near optimum Preceding vectors observed in a beamforming scheme based on the rotation transformations. Simulation results demonstrate that the proposed open-loop diversity scheme with an arbitrary number of transmit antennas achieves a full diversity gain with computational complexity comparable to a single-input single-output (SISO) system.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.1
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• pp.45-50
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• 2023

In order to improve a total system throughput when a base station (BS) transmits data to user equipments (UEs), we propose a scheme to apply multiuser multiple-input multiple-output (MU-MIMO), space-time block coding (STBC), and non-orthogonal multiple access (NOMA) together. An MU-MIMO is applied to two UEs near the BS and STBC is applied to a UE far from the BS because of the difficulty of obtaining the channel information. Also NOMA is applied to differentiate the data from the near UE and the far UE. Two orthognal precoding vectors are used for the MU-MIMO UEs and it causes no interference between them. The STBC technique with the two procoding vectors are also used for the far UEs. Through performance analysis and simulation, we show that the proposed scheme has higher total system throughput than the conventional ones.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.7
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• pp.431-436
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• 2014

In this paper, we propose a compressive sensing-based channel quantization feedback mechanism that is appropriate for practical massvie multiple-input multiple-output (MIMO) systems. We assume that the base station (BS) has a compact uniform square array that has a highly correlated channel. To serve multiple users, the BS uses a zero-forcing precoder. Our proposed channel feedback algorithm can reduce the feedback overhead as well as a codebook search complexity. Numerical simulations confirm our analytical results.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.8
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• pp.12-18
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• 2012

In this paper, we propose an improved analysis of transmission power of BTHP applied into the downlink multi-user (MU) multi-input multi-output (MIMO) system. On the contrary to the conventional analysis that adopts the strong interference assumption for every users in the system, the proposed analysis approximates the characteristics of the actual interference components so that provides more accurate approximation of the transmission power than that from the conventional analysis. By computer simulations, it is observed that the proposed approximation is more accurate than the conventional one, especially in the case of 4-QAM modulation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.7
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• pp.3010-3025
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• 2016

Lattice reduction (LR) has been used widely in conventional multiple-input multiple-output (MIMO) systems to enhance the performance. However, LR is hard to be applied to the relay systems which are important but more complicated in the wireless communication theory. This paper introduces a new viewpoint for utilizing LR in multiuser MIMO relay systems. The vector precoding (VP) is designed along with zero force (ZF) criterion and minimum mean square error (MMSE) criterion and enhanced by LR algorithm. This implementable precoder design combines nonlinear processing at the base station (BS) and linear processing at the relay. This precoder is capable of avoiding multiuser interference (MUI) at the mobile stations (MSs) and achieving excellent performance. Moreover, it is shown that the amount of feedback information is much less than that of the singular value decomposition (SVD) design. Simulation results show that the proposed scheme using the complex version of the Lenstra--Lenstra--Lovász (LLL) algorithm significantly improves system performance.