• Journal of information and communication convergence engineering
• /
• 제2권2호
• /
• pp.67-70
• /
• 2004

In this paper, we propose two novel high-rate high-performance space-time codes for multiple-input multiple-output (MIMO) systems. When $n_T$ transmit antennas and When $n_R$ ＝ When $n_T$ receive antennas are deployed, the two proposed codes respectively offer transmission rates of (When $n_T$ -1) and (When $n_T$ -2) symbols per channel use and diversity orders of 3 and 5. As a consequence, our proposed codes allow the MIMO systems to employ a simple detection technique based on QR decomposition. Moreover, for equal or even higher spectral efficiencies, our proposed codes always provide much better bit error rate (BER) performances than V-BLAST architecture does when When $n_R$ ＝ When $n_T$. Computer simulation is given to verify performances of our proposed codes.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제12권11호
• /
• pp.5382-5403
• /
• 2018

In this paper, for a spectrum sensing purpose, we heuristically established a test statistic (TS) from a sample covariance matrix (SCM) for multiple antennas based cognitive radio. The TS is formulated as a scaled-energy which is calculated as a sum of scaled diagonal entries of a SCM; each of the diagonal entries of a SCM scaled by corresponding row's Euclidean norm. On the top of that, by combining theoretical results together with simulation observations, we have approximated a decision threshold of the TS which does not need prior knowledge of noise power and primary user signal. Furthermore, simulation results - which are obtained in a fading environment and in a spatially correlating channel model - show that the proposed method stands effect of noise power mismatch (non-uniform noise power) and has significant performance improvement compared with state-of-the-art test statistics.

• International Journal of Internet, Broadcasting and Communication
• /
• 제15권3호
• /
• pp.14-23
• /
• 2023

The cooperative communication systems using MIMO(multiple input multiple-output) relay are known as one of the most promising techniques to improve the performance and coverage of wireless communication systems. In this paper, we propose the cooperative communication systems using the relay with multi-antennas and DSTC(distributed space time coding) for decode-and-forward protocol. As using DSTC for DF(decode-and-forward), we can minimize the risk of error propagation at the wireless system using relay system. Also, the MIMO channel cab be formed by multi-antenna and DSTC at the MS(mobile station)-RS(relay station) and at the RS-BS(base station).Therefore, obtaining truly constructive the MIMO diversity and cooperative diversity gain from the proposed approach, the performance of system can be more improved than one of conventional system (relay with single antenna, no relay). The improvement in bit error rate is investigated through numerical analysis of the cooperative communication system with the proposed approach.

• 한국통신학회논문지
• /
• 제42권2호
• /
• pp.291-298
• /
• 2017

본 논문에서는 송신단 채널 정보가 없는 다중안테나 Z-간섭 채널에서 수신단의 재구성 안테나를 통해 얻을 수 있는 자유도(DoF: degrees of freedom) 이득을 구한다. 수신단이 가지는 재구성 안테나의 안테나 모드 스위칭 패턴 디자인을 통해 간섭 신호는 정렬하고 원하는 신호를 위해 충분한 신호부공간(signal subspace)을 남겨두는 새로운 선형 기법을 제안한다. 제안하는 기법의 핵심은 송신단에서 일정 구간동안 신호를 보내지 않음으로써 수신단에서 그 동안 받은 간섭신호를 부가 정보(side information)로 간섭 제거에 활용하는 것이다. 결론적으로, 수신단이 가지는 재구성 안테나를 활용해 재구성 안테나 모드의 개수가 RF 체인의 수 보다 클 때 더 큰 자유도 이득을 얻을 수 있음을 밝힌다.

• Journal of Communications and Networks
• /
• 제7권2호
• /
• pp.157-170
• /
• 2005

The combination of multiple antennas and multi-carrier code division multiple-access (MC-CDMA) is a strong candidate for the downlink of the next generation mobile communications. The study of such systems in scenarios that model real-life trans-missions is an additional step towards an optimized achievement. We consider a realistic MIMO channel with two or four transmit antennas and up to two receive antennas, and channel state information (CSI) mismatches. Depending on the mobile terminal (MT) class, its number of antennas or complexity allowed, different data-rates are proposed with turbo-coding and asymptotic spectral efficiencies from 1 to 4.5 bit/s/Hz, using three algorithms developed within the European IST-MATRICE project. These algorithms can be classified according to the degree of CSI at base-station (BS): i) Transmit space-frequency prefiltering based on constrained zero-forcing algorithm with complete CSI at BS; ii) transmit beamforming based on spatial correlation matrix estimation from partial CSI at BS; iii) orthogonal space-time block coding based on Alamouti scheme without CSI at BS. All presented schemes require a reasonable complexity at MT, and are compatible with a single-antenna receiver. A choice between these algorithms is proposed in order to significantly improve the performance of MC-CDMA and to cover the different environments considered for the next generation cellular systems. For beyond-3G, we propose prefiltering for indoor and pedestrian microcell environments, beamforming for suburban macrocells including high-speed train, and space-time coding for urban conditions with moderate to high speeds.

• 한국산학기술학회논문지
• /
• 제10권10호
• /
• pp.2646-2650
• /
• 2009

본 논문은 디코이(Decoy) 안테나를 사용하여 레이다를 보호하기 위한 레이다 전파회피 기술에 대한 것이다. 디코이 안테나의 효과를 알아보기 위해 대방미사일(ARM) 수신기에 도달하는 감시 레이다 신호와 디코이 신호의 합성 신호의 위상과 진폭을 분석하였다. 그리고 다수 디코이의 배치 방법과 배치 거리에 따른 ARM의 요격효과를 시뮬레이션 하고, ARM 방어를 위한 효과적인 디코이 배치 방법 및 배치거리를 제안한다.

• Journal of electromagnetic engineering and science
• /
• 제17권4호
• /
• pp.228-232
• /
• 2017

The radiation properties and fabrication precautions of a 3D printed, electrically small folded spherical meander wire monopole antenna are investigated. The antenna is self-resonant and shows sufficiently high radiation efficiency at an electrical size ka of 0.4, with the radiation quality factor Q approaching the lower physical bound. In antenna fabrication, the possible structural deformation due to gravity is examined before the antenna frame is 3D-printed. The required conductivity is achieved by multiple manual paintings of a silver paste. The radiation efficiency and pattern show very good agreement with the computed expectations, whereas the resonant frequency deviates by 11.8%. The method to minimize such a fabrication error when using 3D printing technology for wire antennas is discussed.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2002년도 ITC-CSCC -3
• /
• pp.1960-1963
• /
• 2002

Transmit diversity schemes we an effective capacity improvement method for down link of wideband code division multiple access (W-CDMA) systems. In this paper, we propose to use transmit antenna subset selection scheme in conjunction with closed loop transmit adaptive array (TxAA). The proposed scheme selects N$\_$s/ optimum antennas among N$\_$${\gamma}$/(>N$\_$s/) transmit antennas in order to maximize diversity gain from selected antennas, and also reduces the cost of RE chains by employing two different types of RF modules fur the selected and the unselected antenna group, respectively. Computer simulation results show performance improvement by the proposed scheme over the conventional TxAA when considering up link control information feedback.

• 전자통신동향분석
• /
• 제37권3호
• /
• pp.41-51
• /
• 2022

This article presents an overview of the key technologies in the communications payload of broadband LEO satellite communications systems. In recent years, new developments have been realized for LEO satellite communications. SpaceX's Starlink, a technology leader in this field, offers premium services with satellites carrying in-house developed communications payloads. OneWeb, Amazon, Telesat, and Boeing are also developing LEO satellite communications payloads. The communications payload consists of user link antennas, inter-satellite link communications equipment, feeder link antennas, and a digital processor. Highly sophisticated technologies of compact active phased array antennas for generating multiple hopping beams and light laser communication equipment for ultra-high-speed inter-satellite communication will be applied to next- generation payloads.

• 한국통신학회논문지
• /
• 제31권10C호
• /
• pp.981-990
• /
• 2006

본 논문에서는 OFDM 기반의 셀룰러 시스템에서 실제 다중 수신안테나를 사용하지 않고 부반송파를 가상의 다중 수신안테나로 간주하여 MIMO 기법을 적용할 수 있는 부반송파 기반 가상 수신안테나 기법을 기술한다. 부반송파 기반 가상 안테나 기법은 단일 수신안테나에서도 셀간 간섭 제거 또는 SDMA를 수행할 수 있는 기법으로 송수신단에서 다중 안테나를 사용하는 경우에도 쉽게 확장가능하다. 부반송파 기반 가상 안테나 기법은 스마트 안테나 기법을 적용한 가상 스마트 안테나 기법과 MIMO 기법을 적용한 가상 다중 안테나 기법으로 분류된다. 특히 수신단이 주파수 재 사용률이 1인 셀 경계지역에 있을 때 인접 셀의 간섭을 효과적으로 제거할 수 있는 기법으로 간섭의 정도에 따라 유동적으로 자원할당이 가능한 방법이다. 모의실험을 통해 동일한 데이터 전송률에서 기존 셀간 간섭 제거 기법보다 부반송파 기반 가상 안테나 기법이 우수함을 보인다.