• Journal of electromagnetic engineering and science
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• 제11권2호
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• pp.113-121
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• 2011

Multiple-input multiple-output with orthogonal frequency division multiplexing technology (MIMO-OFDM) is considered to be the ultimate solution for increasing system throughput and for enhancing communication reliability. In this paper, we propose to increase the uplink (UL) throughput by assigning the same UL resources to multiple single-antenna mobile stations. This leads to the loss of orthogonality among sub-carriers. Thus, at the base station (BS), MIMO-OFDM detection techniques are used to separate the streams of different users assigned the same UL resources. To obtain a realistic performance evaluation, different channel scenarios are applied with different correlation values among the antennas of the users. Simulation results show that the proposed MIMO-OFDM system linearly increases the uplink capacity of the OFDM system while maintaining a mobile station transmitter as simple as that used in a conventional OFDM system. For instance, when 4 users are assigned the same UL resources, the throughput of the proposed system is 3.07 times that achieved by a conventional single input single output OFDM system.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2007년도 학술대회
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• pp.46-49
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• 2007

Multiple Antenna Technologies such as Multiple-Input Multiple-Output (MIMO) and Beamforming provide the increase of channel capacity and the reliability of wireless link. To obtain these advantages, WiBro, Mobile WiMAX and $4^{th}$ Generation System are employing multiple antenna technologies. There exist, however, many technical issues in considering the application of the technologies or the providing of services using them. In this paper, various technical topics are discussed and simple solutions are proposed. Beamforming has several technical issues which include coverage imbalance, difficulties in providing Multicast-Broadcast Service (MBS). In Addition, network planning is a critical point from a cell extension and initial network entry point of view. In case of MIMO, network deployment is discussed in that cellular data network such as WiBro has many repeaters. MIMO mode selection for maximizing the cell capacity is also covered.

• 한국통신학회논문지
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• 제34권1C호
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• pp.1-8
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• 2009

Cooperative diversity is a novel technique to improve diversity gains, capacity gains, and energy saving. This technique involves multiple terminals sharing resources in order to build a virtual antenna array in a distributed fashion. In this paper, we propose a multi-user cooperative diversity protocol called Relay-assisted Multiple Access Channel(R-MAC) that allows multiple source terminals to transmit their signals simultaneously and the relay terminal forwards the aggregated signal received from the source terminals to the destination terminal. The proposed protocol converts the distributed antenna channels into an effective MIMO channel by exploiting a relay, increasing both diversity gain and system throughput. We investigate the performance of the proposed protocol in terms of outage probability and diversity-multiplexing tradeoff where we assume block fading channel environment. Our simulation results show that the proposed protocol outperforms direct transmission in the high spectral efficiency regime where the conventional cooperative diversity protocols cannot outperform direct transmission.

• Journal of Communications and Networks
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• 제9권2호
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• pp.141-149
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• 2007

Multiple-input multiple-output (MIMO) transmit pre-coding/beamforming can significantly improve system spectral efficiency. However, several obstacles prevent precoding from wide deployment in early wireless networks: The significant feedback overhead, performance degradation due to feedback delay, and the large storage requirement at the mobile devices. In this paper, we propose a precoding method that addresses these issues. In this approach, only 3 or 6 bits feedback is needed to select a precoding matrix from a codebook. There are fifteen codebooks, each corresponding to a unique combination of antenna configuration (up to 4 antennas) and codebook size. Small codebooks are prestored and large codebooks are efficiently computed from the prestored codebook, modified Hochwald method and Householder reflection. Finally, the feedback delay is compensated by channel prediction. The scheme is validated by simulations and we have observed significant gains comparing to space-time coding and antenna selection. This solution was adopted as a part of the IEEE 802.16e specification in 2005.

• Journal of Positioning, Navigation, and Timing
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• 제13권3호
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• pp.277-287
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• 2024

In satellite systems, efficient communication and observation require identifying of specific signal arrival points using onboard antenna systems. When utilizing massive array antennas to estimate the angle of arrival (AOA) of signals, traditional high-performance AOA estimation algorithms such as Multiple Signal Classification (MUSIC) encounter extremely high complexity due to the numerous individual antenna elements. Although, in order to improve this computational complexity problem, the cascade AOA estimation algorithm with CAPON and beamspace-MUSIC was recently proposed, the comparison of the computational complexity of the proposed algorithm across different massive array antenna configurations has not yet been conducted. In this paper, we provide the analyzed results of the computational complexity of the proposed cascade algorithm based on various massive array antennas, and determine an optimal antenna configuration for the efficient AOA estimation in satellite systems.

• 한국전자파학회논문지
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• 제26권2호
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• pp.127-134
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• 2015

본 논문에서는 2.6 GHz의 단일 대역의 MIMO(Multiple Input Multiple Ouput) 무지향 안테나를 제안한다. 2.6 GHz 단일 LTE(Long Term Evaluation) 대역 Up-link 2.52~2.54 GHz, Down-link 2.64~2.66 GHz에 동작하는 옥내용(in-building) MIMO 무지향 안테나로서 폴디드 루프(folded loop) 안테나 4단을 빔 합성을 통해 수평 편파를 구현하고, 폴디드 단극자(folded monopole) 안테나를 이용하여 수직 편파를 구현하였다. 폴디드 루프 안테나의 높이를 접지면으로부터 ${\lambda}/13.5$로 설계하여 MIMO 무지향 안테나의 높이를 최소화 하였으며, 수직편파 및 수평면파에서 각각 2.89 dBi 및 2.07 dBi 이득, 포트 분리도(port isolation) 19.32 dB의 우수한 MIMO 무지향 안테나 측정 특성을 얻었다.

• Journal of electromagnetic engineering and science
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• 제6권4호
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• pp.222-228
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• 2006

In this paper, the performance of a multiuser diversity system combined with a multi-element transmit antenna system is analyzed under the assumption of independent Rayleigh fading. A measure of system .level performance is an average channel capacity as a function of the number of users and antennas. Average channel capacity is obtained from the instantaneous signal-to-noise ratio(SNR) distribution combined by both transmit diversity(TD) at each link and multiuser diversity at system level. Numerical results show that closed-loop antenna techniques provide an additional gain with multiuser diversity system due to array gain, even though space diversity gain reduces multiuser diversity gain. On the other hand, the space-time block coding(STBC) that provides full order space diversity gain only has a destructive influence on multiuser diversity.

• Journal of electromagnetic engineering and science
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• 제19권1호
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• pp.13-19
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• 2019

This paper proposes a systematic method for estimating detection performances of a frequency-modulated continuous wave radar using electromagnetic simulations. The proposed systematic method includes a radar system simulator that can obtain range-Doppler images using the electromagnetic (EM) simulations in conjunction with a test setup employed for performance evaluation of multiple targets at different velocities in a traffic environment. This method is then applied for optimizing the half-power beamwidths of the antenna array using an evaluation metric defined to improve the detection strengths for the multiple targets. The optimized antenna has vertical and horizontal half-power beam widths of $10^{\circ}$ and $60^{\circ}$, respectively. The results confirm that that the proposed systematic method is suitable to improve the radar detection performance with the enhanced radar-Doppler images.

• 한국통신학회논문지
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• 제36권4A호
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• pp.337-344
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• 2011

본 논문은 모든 노드가 다중 안테나를 갖는 다중 안테나 (MIMO, multiple-input and multiple-output) 공간 다중화 (SM, spatial multiplexing) 릴레이 시스템을 비트 오율 (BER, bit error rate) 관점에서 연구한다. 제한된 전력 자원을 효율적으로 이용하기 위해서는 각 노드와 안테나에서 최적화된 전력 할당 전략이 필요하다. 본 논문은 이런 관점에서 다중 안테나 공간 다중화 릴레이 시스템을 위한 비트 오율 최소화에 기반을 둔 전력 할당 알고리즘을 제안한다. 제안된 알고리즘은 평균 비트 오율을 직접 최소화하여 얻어지며, 노드 간 (inter-node) 전력 할당 알고리즘과 안테나 간 (inter-antenna) 전력 할당 알고리즘으로 구성된다. 비트 오율 성능에 있어서, 기존의 균등 전력 할당 (EPA, equal power allocation) 알고리즘보다 추가적인 전력 소비 없이도 월등한 성능을 보인다.

• 한국전자파학회논문지
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• 제19권8호
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• pp.820-825
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• 2008

본 논문에서는 $2.3{\sim}2.4$ GHz 대역 무선 휴대 단말기용 내장형 MIMO 안테나 시스템의 격리도를 향상시키는 방법을 제시하였다. 제안된 MIMO 안테나 시스템은 2개의 안테나 사이의 그라운드 기판에 다수 개의 L-slot으로 구성된 multi-slots를 위치시키며, multi-slots가 대역 차단 필터처럼 작용하여 안테나 간의 상호 결합을 억제시켜 격리도를 향상시킨다. 6쌍의 L-slots를 채택한 MIMO 안테나 시스템은 -26.4 dB의 반사 손실과 -37.5 dB의 격리도를 나타내었다.