Insoo Hwang

University of Texas at Austin, Austin, Texas, United States

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Publications (9)10.72 Total impact

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    ABSTRACT: Multicell cooperation may play an important role in achieving high performance in cellular systems. Multicell cooperation with a single receive antenna at the mobile station has been widely investigated. Applying cooperation with multiple receive antennas, allowed in several emerging wireless standards, has met with some challenges. This is primarily because the transmit precoding/beamforming vector and receive processing have to be jointly optimized in multiple cells to combat out-of-cell interference. In this article, we first discuss the role of the receive antennas in a multicell environment, and then review recently proposed multicell cooperative algorithms and receive antenna techniques for different interference statistics. Finally, we highlight recent work on the fundamental limits of cooperation and the possibility of overcoming such limits by using multiple receive antennas in multicell cooperative networks.
    IEEE Wireless Communications 02/2013; 20(1):50-58. DOI:10.1109/MWC.2013.6472199 · 6.52 Impact Factor
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    ABSTRACT: In this paper, we propose jointly optimized linear transceiver algorithms called interference aware-coordinated beamforming (IA-CBF) for a two-cell system where each base station is equipped with multiple transmit antennas. To generalize IA-CBF to more than two-cell scenarios, a new beam-switching mechanism combined with IA-CBF is proposed. For a two-cell system, we derive a minimum-mean-square-error-type IA-CBF algorithm based on a lower bound on the achievable sum rate. We propose optimal (under an assumption of zero other-cell interference) and suboptimal transmit/receive beamforming vectors through zero-forcing IA-CBF algorithms. We also investigate the optimality of the proposed IA-CBF algorithms with respect to the number of receive antennas. Numerical results confirm that the proposed system with two transmit/receive antennas achieves the full degrees of freedom (a.k.a. multiplexing gain) of the two-cell multiple-input multiple-output channel while showing a better sum rate performance than competitive solutions such as noncooperative eigen-beamforming and interference nulling. A three-dimensional ray tracing tool is also used to evaluate the proposed multi-cell IA-CBF algorithm.
    IEEE Transactions on Wireless Communications 10/2012; 11(10):3692-3703. DOI:10.1109/TWC.2012.081312.112119 · 2.76 Impact Factor
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    ABSTRACT: A new beamforming strategy is proposed for multiuser systems with N transmit antennas at the transmitter and M ⩽ N single antenna receivers. The proposed scheme remarkably improves on the classical spatial division multiple access, and achieves the same data rates as spatial multiplexing for all users but with significantly superior performance/diversity gain. When compared with the Bell labs layered space–time system, the symbol rate is the same and the performance is much superior because of the presence of diversity gain. In addition, unlike the Bell labs layered space–time system, the receivers do not need to know each other's vector channels. Finally, the proposed algorithm is based on dirty-paper coding, but does not require much complexity and is implementable. Copyright © 2011 John Wiley & Sons, Ltd.
    International Journal of Communication Systems 08/2012; 25(8):1091-1099. DOI:10.1002/dac.1310 · 1.11 Impact Factor
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    ABSTRACT: Jointly optimized interference aware coordinated beamforming (IA-CBF) algorithms for a two-cell system are investigated, where each base/mobile station is equipped with multiple transmit antennas. We first derive a minimum-mean-square-error IA-CBF algorithm based on a lower bound on the achievable sum rate. We next propose optimal (under an assumption of zero other-cell interference) and suboptimal transmit/receive beamforming vectors through zero-forcing IA-CBF algorithms. Numerical results confirm that the proposed system shows better sum rate performance than competitive solutions such as non-cooperative eigen-beamforming and interference nulling.
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    ABSTRACT: In this paper, we propose jointly optimized transceiver algorithms called interference aware coordinated beamforming (IA-CBF) for a two-cell system where each base station is equipped with multiple transmit antennas. The case of single stream transmission to two mobile stations with two or more receive antennas is considered. First we propose minimum-mean-square-error IA-CBF using a lower bound on the achievable sumrate. Next we derive optimal (under an assumption of zero other-cell interference) and suboptimal transmit beamforming vectors called zero-forcing IA-CBF. We also investigate the optimality of the proposed IA-CBF algorithms with respect to the number of receive antennas. Analytical and numerical results confirm that the proposed system with two transmit/receive antennas achieves full degrees of freedom (a.k.a. multiplexing gain) of the two-cell multiple-input multiple-output channel while showing a better sum rate performance than the conventional solutions such as non-cooperative eigen-beamforming and interference nulling. Engineering and Applied Sciences Accepted Manuscript
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    ABSTRACT: We propose a new broadcast strategy for a multiple-input multiple-output (MIMO) system with N transmit antennas at the transmitter and M ≤ N single antenna receivers. The proposed method, based on dirty-paper coding (DPC), spatially separates the M users but does not suffer from the power loss of classical spatial division multiple access (SDMA). For the special case of M = N = 2 and when the two single antenna receivers are assumed to be co-located, the proposed scheme produces a 2 transmit, 2 receiver antenna MIMO transmission system that doubles the symbol rate of MIMO space-time block code (STBC) systems from one to two symbol per transmission time. It is proved theoretically and experimentally that the proposed scheme provides the same performance level as that of MIMO STBC systems (i.e., the Alamouti scheme) for the first symbol, and the same performance as the Bell labs layered space-time (BLAST) system for the second symbol. When compared to the BLAST system, the proposed scheme has the same symbol rate, but achieves significantly better performance, since it provides 2 level diversity per symbol on the first symbol while the BLAST system does not provide any diversity.
    IEICE Transactions on Communications 02/2008; E91B(2). DOI:10.1093/ietcom/e91-b.2.613 · 0.33 Impact Factor
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    ABSTRACT: In this paper, we propose a new broadcast strategy for a MIMO system with N transmit antennas at the transmitter and M les N single antenna receivers. The proposed method spatially separates the M users but does not suffer from the power loss of classical SDMA. For the special case of M = N = 2 and when the two single antenna receivers are assumed to be co-located, the proposed scheme produces a 2 transmit, 2 receiver antenna MIMO scheme. This gives a MIMO transmission scheme that doubles the symbol rate of MIMO STBC systems (Alamouti scheme) from one to two symbol per transmission time. It is proved that it provides the same performance level as that of the Alamouti STBC for the first symbol, and the same performance as the BLAST system for the second symbol. When compared to the BLAST system, our scheme has the same symbol rate, but enjoys significant performance improvements, since it provides 2 level diversity per symbol on the first symbol while the BLAST system does not provide any diversity.
    Information Sciences and Systems, 2007. CISS '07. 41st Annual Conference on; 04/2007
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    ABSTRACT: Antenna selection strategies for multiple-input multiple-output (MIMO) wireless systems is presented. In our scheme, both transmit and receive antenna selection is done at the receiver, significantly reducing feedback information to the transmitter. Row/column probability density function (pdf) is used for antenna selection to reduce computational complexity without performance degradation. Unlike other schemes, we used two different antenna selection algorithms both for high SNR and low SNR regime, achieving additional performance gain in comparison with the single antenna selection algorithm. Simulation results show that our scheme nearly approaches to the optimal closed-loop capacity (known as water-filling capacity).
    Proceedings of IEEE International Conference on Communications, ICC 2007, Glasgow, Scotland, 24-28 June 2007; 01/2007
  • Insoo Hwang, Yungsoo Kim, J. Kim
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    ABSTRACT: We present a multiple-input multiple-output (MIMO) relay system with hybrid automatic repeat request (HARQ) protocols which can achieve better outage behaviors than simple MIMO cooperative diversity schemes. Using repetition based and Alamouti based HARQ scheme, we can achieve better diversity gains without increasing additional transmit power. This system can be a practical solution for a new system which requires lower deployment costs and limited power in each nodes
    Signal Processing Advances in Wireless Communications, 2006. SPAWC '06. IEEE 7th Workshop on; 08/2006

Publication Stats

52 Citations
10.72 Total Impact Points

Institutions

  • 2008–2013
    • University of Texas at Austin
      • Department of Electrical & Computer Engineering
      Austin, Texas, United States
  • 2012
    • Gyeongsang National University
      • Department of Computer Science
      Shinshū, South Gyeongsang, South Korea