• Information and Communications Magazine
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• v.32 no.4
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• pp.93-96
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• 2015

기존 MIMO 시스템에서는 안테나의 개수가 늘어날수록 선형적으로 RF 모듈의 개수도 늘어나 전체 시스템의 복잡도와 전력소모가 심하다. 이를 해결하기 위해 단일 RF 송신구조가 제안되었고, 본 논문에서는 임피던스를 가변하여 안테나에서 방사되는 패턴을 조절하는 기술을 제안한다. 기존 MIMO 시스템의 RF 회로부가 가지는 복잡도와 전력 효율 문제를 해결하기 위해 임피던스 로딩 부분의 실험시제품 제작 및 검증을 수행한다. BPSK와 QPSK 변조방식을 지원하는 임피던스 로딩 보드를 제작하고, 3 m거리에서 무선 송수신 실험을 성공적으로 수행하였다.

• Information and Communications Magazine
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• v.32 no.6
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• pp.59-61
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• 2015

기존 MIMO 시스템에서는 안테나의 개수가 늘어날수록 선형적으로 RF 모듈의 개수도 늘어나 전체 시스템의 복잡도와 전력 소모가 심하다. 이를 해결하기 위해 단일 RF 송신구조가 제안되었고, 본 논문에서는 임피던스를 가변하여 안테나에서 방사되는 패턴을 조절하는 기술을 제안한다. 기존 MIMO 시스템의 RF 회로부가 가지는 복잡도와 전력 효율 문제를 해결하기 위해 임피던스 로딩 부분의 실험시제품 제작 및 검증을 수행한다. BPSK와 QPSK 변조방식을 지원하는 임피던스 로딩 보드를 제작하고, 3 m거리에서 무선 송수신 실험을 성공적으로 수행하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.10
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• pp.947-955
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• 2012

In this paper, we propose iterative algorithms to obtain the transmit and the receive vectors for interference alignment in cellular network. Although the conventional interference alignment algorithms for interference channels can be applied to cellular network, the number of iterations required to achieve a high sum rate is very large. The key idea in the proposed algorithms is to ignore intra-cell interference in updating the transmit vector for uplink and the receive vector for downlink. Numerical results show that the proposed algorithms achieve higher sum rates than the conventional algorithms for given iteration numbers when multiple antennas and a single carrier are used for interference alignment. It is also shown that the proposed algorithms outperform the conventional algorithms when a single antenna and multiple subcarriers are used for interference alignment.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.7
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• pp.1271-1277
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• 2008

This paper proposes the code acquisition scheme on a MIMO channel for preamble search in a CDMA-MIMO uplink system. The multiple transmit/receive antennas are used for beamforming. The performance of a ML code acquisition technique based on transmit and receive beamforming is analyzed by considering rho detection probability. The acquisition performance and MAT for a MIMO code acquisition system are numerically evaluated. It is shown that multiple transmit antennas can give the code acquisition system a transmit beamforming gain and result in much better performance than a SIMO case.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9A
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• pp.749-754
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• 2005

It is well-known that mobile communication systems are usually limited in their performance and capacity by three major impairments, which are multipath fading, delay spread and co-channel interference (CCI). OFDMA (OFDM-FDMA) system can cope with the multipath fading and delay spread easily due to the beneficial properties of OmM technology. Though OFDMA scheme avoids intra-cell interference using the orthogonality among subcarriers, the scheme contains difficulty of reducing co-channel interference. Therefore, in this paper, adaptive antenna techniques are deployed into OFDMA/TDD system to minimize the co-channel interference induced by adjacent cells and to enhance the uplink performance. For the improvement of downlink performance, we apply TxAA (Transmit Adaptive Array), a kind of transmit diversity technique, utilizing preamble symbols for training antenna may into OFDMA/TDD transmitter side. Simulation results show that the uplink and downlink performance under multipath Rayleigh fading channel improved 9dB and 7dB each compared with the case of single antenna system at target BER $10^{-3}$ .

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.3A
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• pp.223-231
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• 2011

It has been shown that the performance of multiple-input multiple-output (MIMO) spatial multiplexing systems is significantly degraded when spatial correlation exists between transmit and receive antenna pairs. In this paper, we investigate designs of a new statistical precoder for spatial multiplexing systems with maximum likelihood (ML) receiver which requires only correlation statistics at the transmitter. Two kinds of closed-form solution precoders based on rotation and power allocation are proposed by means of maximizing the minimum E tlidean distance of joint symbol constellations. In addition, we extend our results to linear receivers for correlated channels. We provide a method which yields the same profits from the proposed precoders based on a simple zero-forcing (ZF) receiver. The simulation shows that 2dB and 8dB gains are achieved for ML and ZF systems with two transmit antennas, respectively, compared to the conventional systems.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.2
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• pp.32-38
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• 2012

In this paper, we design on nonliner 3 user Dirty Paper Precoding for MIMO adjacant interference signal cancellation based on 3 GPP LTE Release 10. In this paper, in order to reduce the inter-channel interference at the transmitted side, we propose the Dirty Paper Precoding scheme for 3-user MIMO wireless systems using LQ decomposition and Gram-Schmidt algorithm based in its orthonormal basis.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.4
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• pp.95-103
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• 2009

In this paper, a generation method of transmit and receive beamforming vectors based on base station cooperation is proposed which maximizes the user SINR in mobile cellular multi-user MIMO systems. There are two main sources of interference which deteriorate the performance of the system, i.e. the inter-user interference caused by the usage of the same radio resource for multiple users in the system, and the inter-cluster interference from neighboring base stations which are not participating in cooperative transmission. The proposed scheme cancels out the inter-user interference by using the block diagonalization(BD) method, and mitigate the inter-cluster interference by using optimal transmit and receive beamforming vectors based on optimal combining(OC) with the statistic information of inter-cluster interference. We perform computer simulations to verify the performance of the proposed scheme, and compare the result to the conventional performance obtained from utilizing the receiver side information only or utilizing the information from neither sides. The performance evaluations are conducted not only over the independent MIMO channels, but over correlated MIMO channels to demonstrate the robustness of the proposed scheme over the channels with correlation among antennas.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.12
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• pp.6478-6483
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• 2013

This paper presents the idea of interpolating between multiple sounding bursts to estimate the individual channels of a MIMO scenario. The performance of the proposed technique depends on the $f_dT$ product and the number of transmit and receive antennas. In particular, this technique can be effective if the $f_dT$ product is not too high and the number of antennas is not too large. Furthermore, there is a considerable difference in the performance of the 16 channels in the $4{\times}4$ MIMO case because the sounding bursts spread farther apart with time, meaning that the Doppler in the channel causes a greater error for the channels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6A
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• pp.640-650
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• 2004

Channel estimation schemes are proposed for Multiple Input-Multiple output Orthogonal Frequency Division Multiplexing(MIMO-OFDM) systems based on the physical layer specification of the IEEE 802.1 la. By combining the space-time block coding(STBC)/ space-frequency block coding(SFBC) techniques with the transform domain interpolation, the proposed algorithms achieve more accurate channel coefficients for the MIMO channels such that improve the BER performance. The performance improvements of the proposed algorithms are evaluated by simulations under the various multipath fading channel environments and various transmission rates.