• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.6B
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• pp.579-585
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• 2002

The investigation into the effect of various feedback errors on system performance can help the robust feedback channel design and transmission of exact feedback channel information as well. In this paper, we address the algorithm that determines space combining weight vector maximizing received signal power at mobile on frequency flat fading channel and investigate the performance degradation by feedback channel delay in the FDD/CDMA systems employing transmit beamforming. We observe the effect of feedback channel delay corresponding to the number of transmit antennas and the temporal/spatial correlation of channel. The results show that performance is more sensitive to feedback delay with the larger number of antennas when fadings at transmit antennas are not spatially correlated.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.4 s.346
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• pp.31-38
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• 2006

In this paper, we propose an efficient preceding scheme for STBC-Spatial Muiltiplexing OFDM systems. In MIMO systems, the precoder is designed on the assumption that feedback channel information is perfectly known to transmitter and receiver. However, feedback delay and link errors in real environment make the transmitter use the incorrect channel information and consequently cause the performance degradation. The proposed precoder is designed to compensate for the performance degradation by the diversity gain provided by STBC. At the transmitter, the precoder for each subcarrier is constructed by using the index of codebook, subcarrier correlation, and auto correlation of channel. From the simulation results, STBC-spatial multiplexing OFDM outperforms the preceded-spatial multiplexing OFDM at $SER=10^{-3}$ when the Doppler frequency is greater than 60Hz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.7A
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• pp.1152-1161
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• 2001

본 논문에서는 이동국 수신 신호의 SINR을 최대화하는 빔 성형 알고리듬을 이용하여, 폐쇄 루프 송신 빔 성형기술을 적용한 순방향 링크 CDMA 시스템에서의 안테나 수, 귀환 채널의 구조, 귀환 지연 등과 시스템 성능과의 상관관계를 연구하였다. 폐쇄 루프 전송 빔 성형에서는 이동국이 각 안테나가 겪는 채널을 추정하여 수신 SINR을 최대화시키는 가중치 벡터를 계산하고, 귀환채널을 통해 가중치 벡터의 양자화된 진폭과 위상정보를 전송한다. 컴퓨터 모의 실험 결과는 송신 안테나가 2개, 3개, 4개로 늘어남에 따라 빔 성형 이득은 단일 송신 안테나와 비교해 $10^{-5}$ BER 근방에서 4.2dB, 5.8dB, 7dB로 증가하지만 양자화 오류에 의한 성능 저하 또한 0.1dB, 0.6dB, 1.3dB로 커지는 것을 보여준다. 또한 순방향 채널의 최대 도플러 주파수가 100Hz일 때에는 귀환 채널을 통한 소신 가중치 벡터를 보다 빠르게 갱신하는 것이 가중치 벡터의 양자화 레벨의 수를 늘여주는 것보다 $10^{-5}$ BER 근방에서 0.6dB 더 좋은 성능을 보이며, 최대 도플러 주파수가 10Hz일 때에는 가중치 벡터의 갱신 속도를 늘이기 보다 양자화 레벨의 수를 늘여주어 정확한 가중치 벡터를 전송하는 편이 0.9dB의 성능 향상을 보인다. 두 전력제어 그룹 길이의 귀환지연으로 인한 성능저하는 채널의 최대 도플러 주파수가 50Hz인 경우가 채널의 최대 도플러 주파수가 100Hz인 경우보다 $10^{-5}$ BER 근방에서 0.3dB 정도 더 작다. 또한 AOS가 3$^{\circ}$인 경우가 AOS가 $10^{\circ}$인 경우보다 $10^{-5}$ BER 근방에서 1.9dB 정도, 주파수 선택적 페이딩 채널이 주파수 비선택적 페이딩 채널보다 $10^{-5}$ BER 근방에서 1dB 정도 귀환 지연으로 인한 성능의 저하가 작다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.3A
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• pp.111-118
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• 2003

The transmit adaptive array requires the forward link channel information for evaluating the optimum transmit weight vector in which a feedback channel provides transmitter with the forward link channel information. The larger transmit adaptive array is, the higher required rate of feedback channel is. Therefore we consider the system that the N-transmit antenna system is expanded to the 2N-transmit antenna system, while the feedback channel is maintained as that of N-transmit antenna system. The increase of the number of antennas can produce the additional diversity gain, however the insufficient feedback bits assigned to each antenna aggravates the quantization error. In this paper, we propose the transmit antenna selection in order to improve the performance of transmit adaptive array having an insufficient feedback channel information. The effective method to transmit the weight vector is also introduced. System performances are investigated for the case of N=4 corresponding to the antenna selection diversity schemes on the flat fading channel and the multipath fading channel. The simulation results show that the proposed scheme can improve the system performance by 1 dB when the N is expanded to the 2N, while the feedback channel is restricted to that of N-transmit antenna system.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.909-914
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• 2005

This paper proposes an efficient antenna selection scheme for PRT (Personal Rapid Transit) remote control in a wireless MIMO-OFDM systems. Using high correlation among neighboring sub-carriers, transmit antennas are selected by calculation based on the channel response of the center sub-carrier in each subgroup. This scheme reduces complexity of selection algorithm and significantly reduces the feedback channel information with small performance degradation. Especially, when feedback channel rate between a control base and a train is fixed, the proposed scheme can provide a significant advantage in high mobility.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.9 s.339
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• pp.41-48
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• 2005

In this paper, we suggest the scheme combining long-term feedback and short-term feedback in MIMO multi-user system and analyze its system performance. At the beginning of communication, long-term feedback is fed back to transmitter such as the number of active antennas, constellations, and transmission powers which are determined to satisfy the given target symbol error and target data rate for each user. After this, short-term feedback of active antenna index is fed back periodically Simulation results show the proposed scheme outperforms better than long-term feedback or short-term feedback information scheme.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.3
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• pp.473-479
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• 2005

A key issue toward mobile multimedia communications is to create technologies for broadband signal transmission that ran support high quality services. Such a broadband mobile communications system should be able to overcome severe distortion caused by time-varying multi-path fading channel, while providing high spectral efficiency and low power consumption. For these reasons, an adaptive suboptimum decision feedback equalize. (DFE) for the single-carrier short-burst transmissions system is considered as one of the feasible solutions. For the performance improvement of the system with the short-burst format including the short training sequence, in this paper, the multiple-training least mean square (MTLMS) based DFE scheme with soft decision feedback is proposed and its performance is investigated in mobile wireless channels throughout computer simulation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.950-953
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• 2006

A key issue toward mobile multimedia communications is to create technologies for broadband signal transmission that can support high quality services. Such a broadband mobile communications system should be able to overcome severe distortion caused by time-varying multi-path fading channel, while providing high spectral efficiency and low power consumption. For these reasons, an adaptive suboptimum decision feedback equalizer (DFE) for the single-carrier short-burst transmissions system is considered as one of the feasible solutions. For the performance improvement of the system with the short-burst format including the short training sequence, in this paper, the multiple-training least mean square (MTLMS) based DFE scheme with soft decision feedback is proposed and its performance is investigated in mobile wireless channels throughout computer simulation.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.776-781
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• 2005

In this paper, using received channel information, we analyze performance in MIMO multiuser system in low-to-medium mobile speed by selecting each user's constellations, powers, and transmit antennas. Given a target of symbol error, we determine each user's constellations, powers, selected tranprobability smit antennas such that the required signal-to-noise(SNR) is minimized for MMSE, V-BLAST receiver according to each user's information and channel estimation information. When we do power control with antenna selection technique through uplink channels of MIMO system in low-to-medium mobile speed, we analyze system performance with wireless channel information from Base-Station(BS) to Users. By simulation, it has been shown that the proposed antenna selection scheme for transmitting data offer better performance improvement than all transmit antennas for transmitting data.

• Journal of the Institute of Convergence Signal Processing
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• v.3 no.2
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• pp.53-57
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• 2002

Recently, digital communication system becomes high speed, as communication demand dose not only increases sharply, but an image, voice various kinds data also comes multimedia. In transmitting data at a high speed, the main problem is fading by multipath. A linear or nonlinear distortion arise In multipath channel fading from ISI(Intersymbol Interference). For restoring this distorted signal, A lot of equalizer and adaptive algorithm is introduced. This paper compares and analysises, for improving communication quality in channel which is long delay spread, performance of decision feedback equalizer by RLS algorithm, a channel estimation by RLS-MLSE and viterbi equalizer Particularly, there Is exactly channel estimation of impluse response and excellent property of equalization about channel, which delay spread is long impluse response comparatively and is property of non-minimun phase.