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Bi-Directional Use of Spatial Resources and Effects of Spatial Correlation
Hyungsik Ju,Xiaohu Shang,Poor, H. V.,Daesik Hong IEEE 2011 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.10 No.10
<P>In multiple antenna systems, spatial fading correlation causes a significant degradation in performance. In this work, a method for reducing the sensitivity to spatial fading correlation through the bi-directional use of spatial resources is investigated. Firstly, the concept of bi-directional use of spatial resources is introduced and the fading characteristics of the proposed bi-directional multiple-input multiple-output (B-MIMO) system are investigated. The achievable rates of the B-MIMO system are then investigated and compared with those of conventional MIMO systems for beamforming and full rank transmission. Based on those results, conditions needed for the B-MIMO system to demonstrate a larger average achievable rate are evaluated. B-MIMO systems are found to efficiently reduce the sensitivity to spatial fading correlation, while supporting comparable achievable rates in spatially white environments.</P>
Ju, Hyungsik,Gwak, Donghyuk,Kim, Tae-Joong Electronics and Telecommunications Research Instit 2020 ETRI Journal Vol.42 No.1
In this paper, we describe a simultaneously transmitted jamming (ST-jamming) for bi-directional in-band full-duplex (IFD) system to improve information security at the physical layer. By exploiting ST-jamming, each legitimate user transmits data samples and jamming samples together in one orthogonal frequency division multiplexing symbol according to given traffic asymmetry. Regardless of the traffic difference in both directions in IFD communication, eavesdropping of confidential information is prevented in both directions simultaneously without the loss of data rate. We first propose an encoding scheme and the corresponding decoding scheme for ST-jamming to be used by the legitimate users. In addition, we study a transceiver structure of the legitimate users including a baseband modem uniquely designed for the use of ST-jamming. The leakage of confidential information at an eavesdropper is then quantified by studying the mutual information between the confidential transmit signals and the received signals of the eavesdropper. Simulation results show that the proposed ST-jamming significantly reduces the leakage of legitimate information at the eavesdropper.
Hyungsik Ju,Eunsung Oh,Daesik Hong IEEE 2009 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.8 No.8
<P>This letter presents a new full duplex relay (FDR) system that features more efficient use of time resource and antennas. The proposed FDR system is constructed based on time and antenna-sharing and elimination of underlying interference. The underlying interference caused by time- and antenna-sharing is eliminated using precoding. We propose a design for the precoder and decoder, and investigate the achievable rate of the proposed FDR system when the precoder and decoder are applied. Simulation results show improved achievable rate and BER performances with the proposed FDR system compared to half duplex and conventional full duplex relay systems.</P>
Bi-Directional Beamforming and its Capacity Scaling in Pairwise Two-Way Communications
Hyungsik Ju,Dongkyu Kim,Poor, H. V.,Daesik Hong IEEE 2012 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.11 No.1
<P>Recent developments in various devices and applications require pairwise communications in an ad-hoc manner. Such systems are mostly interference-limited and suffer from capacity degradation caused by two-way communication. This paper investigates improvement of capacity performance in pairwise two-way communication through bi-directional use of spatial resources when beamforming is employed as the transmission scheme and instantaneous channel information is not available. This system is called a 'bi-directional beamforming' system. The primary approach to showing improvement in capacity performance in the bi-directional beamforming system involves focusing on the scaling of its achievable sum rate. Lower and upper bounds on the achievable sum rate are derived to evaluate the scaling of the achievable sum rate. Then, a condition is derived under which the bi-directional beamforming system outperforms the conventional beamforming system in the pairwise two-way communication environment. As a result, when the bi-directional beamforming system is employed, results show that the achievable sum rate scales twice as fast as that when conventional beamforming is employed.</P>
Full Duplexity in Beamforming-Based Multi-Hop Relay Networks
Hyungsik Ju,Sungmook Lim,Dongkyu Kim,Poor, H. V.,Daesik Hong IEEE 2012 IEEE journal on selected areas in communications Vol.30 No.8
<P>This work investigates the effects of full duplexity on delay and throughput in interference-limited multi-hop networks. It is assumed that channel state information is not available at transmitters and beamforming is employed as the transmission scheme. A closed-form expression is developed for hop success probability in networks of this type. The delay and throughput of multi-hop networks employing full duplex and half duplex beamforming are than compared. The delay and throughput are studied in two cases: when full duplexity is used for full duplex relay (FDR), and bi-directional beamforming (BBF). For FDR, employing full duplex beamforming is more beneficial if a low rate constraint is required or if interferers are rare. However, this benefit diminishes as the required data rate or the interferer density increases. For BBF, the use of full duplex beamforming is always more beneficial because it leads to a reduction in the required rate constraint. Specifically, this benefit becomes more significant as the required rate rises and interferers become rarer.</P>
주형식(Hyungsik Ju),이성은(Sungeun Lee),홍대식(Daesik Hong) 대한전자공학회 2008 電子工學會論文誌-TC (Telecommunications) Vol.45 No.1
본 논문에서는 다중 안테나(MIMO)를 사용하는 환경에서 보호 자원(보호 시간 및 보호 대역)을 필요로 하지 않는 새로운 양방통신(duplex) 방법을 제안한다. 이 양방 통신 방식에서는, 보호 자원을 사용하지 않기 위해, 송, 수신단 사이의 다중 안테나 채널을 선부호화, 후부호화하여 공간 영역(spatial domain)에서 두 개의 가상 채널(virtual-channels)을 생성하여 양방 링크에 할당한다. 제안된 양방 통신 방법은 선부호화기와 후부호화기를 적절히 선택해 줌으로써 채널 용량을 더 증대시킬 수 있는 장점을 가지며, 이렇게 향상된 채널 용량은 보호 대역, 보호 시간이 사용되지 않은 기존 양방 통신 방식보다 우수함을 보인다. We propose a new duplex which does not require guard resources in MIMO environments. In the proposed duplex, two virtual channels in spatial domain are generated by precoding and postcoding MIMO channels, not to use guard resources in either the time or frequency domain. The capacity can be improved by properly selecting precoder and postcoder. We show the improved capacity of the proposed duplex outperforms conventional duplexes even without guard resources.
주형식(Hyungsik Ju),이성은(Sungeun Lee),홍대식(Daesik Hong) 大韓電子工學會 2011 電子工學會論文誌-TC (Telecommunications) Vol.48 No.8
다중 안테나 통신 시스템에서 채널의 correlation은 심각한 성능 열화를 일으킨다. 본 논문에서는 공간 자원을 양방향으로 활용함으로써 채널 correlation에 대한 민감도를 줄일 수 있는 방법을 다룬다. 먼저 공간 자원의 양방향 활용에 대한 개념을 제시한 후, 사용 가능한 eigenmode를 분석함으로써 이 기술이 채널 correlation에 대한 민감도를 어떻게 줄이는지에 대해 다루도록 한다. 마지막으로 시뮬레이션 결과를 통해 이 기술이 채널 correlation에 대한 민감도를 효과적으로 줄임을 보인다. In multiple antenna systems, spatial facing correlation causes a significant degradation in performance. In this work, a method for reducing the sensitivity to spatial fading correlation through the bi-directional use of spatial resources is investigated. Firstly, the concept of bi-directional use of spatial resources is introduced. Then, the ability of this technique to reduce the sensitivity to spatial fading correlation is then shown through an analysis of the number of usable eigenmodes (UEMs). This system is found to efficiently reduce the sensitivity to spatial fading correlation.