Sooyong Choi

Yonsei University, Sŏul, Seoul, South Korea

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Publications (105)72.08 Total impact

  • Sangjoon Park · Sooyong Choi ·
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    ABSTRACT: This paper proposes an iterative equalizer based on Kalman filtering and smoothing (IEKFS) for multiple-input multiple-output inter-symbol interference (MIMO-ISI) channels. A state-space model with a priori information and the corresponding Kalman filtering (KF) and Kalman smoothing (KS) operations are developed. The KF operations perform a linear minimum mean-square error (MMSE) equalization procedure with soft interference cancellation. In addition, the KF and KS operations produce and exchange the updated extrinsic information. During this IEKFS process, the soft estimate of a desired symbol does not participate in the equalization procedures for the desired symbol; only the feedback information of the other transmit symbols is used. Therefore, the proposed IEKFS performs iterative linear MMSE equalization based on the Kalman framework and turbo principle. The complexity of the IEKFS is linear with respect to the number of transmit signal vectors in a transmission block, and simulation results show that the IEKFS can achieve near-optimum bit error rate performances approaching the matched filter bound (MFB) of the channel in various environments.
    IEEE Transactions on Signal Processing 10/2015; 63(19):5111-5120. DOI:10.1109/TSP.2015.2457399 · 2.79 Impact Factor
  • Sangjoon Park · Sooyong Choi ·

    09/2015; 40(9):1728-1730. DOI:10.7840/kics.2015.40.9.1728
  • Sangjoon Park · Sooyong Choi ·

    09/2015; 40(9):1725-1727. DOI:10.7840/kics.2015.40.9.1725
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    ABSTRACT: In this paper, we propose a uplink (UL) non-orthogonal multiple access (NOMA) systems equipped with multiple antennas to enhance the sum capacity of UL. In the proposed UL NOMA system, a base station (BS) with N antennas can support 2N users by sharing the space resource. However, sharing the space resource leads to interference between users. Therefore, to mitigate the interference and improve the sum capacity, we additionally propose a set selection algorithm and power control scheme. The set selection algorithm, which selects 2N users based on orthogonality and gain-difference between their channels, reduces the interference between users. Furthermore, the power control scheme can maximize the sum capacity with ensuring minimum target rate. Numerical results show that the proposed system improves the sum capacity over that of the conventional orthogonal multiple access (OMA) system.
  • Sooyong Choi · Sangjoon Park ·
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    ABSTRACT: A QR decomposition aided belief propagation (QR-BP) detector for multiple-input multiple-output (MIMO) systems is proposed. Before the iterative message passing process, linear transformation is performed by using the unitary matrix obtained from the QR decomposition of the original MIMO channel matrix. Then, the original MIMO channel matrix is replaced by an upper triangular channel matrix after the linear transformation and the proposed QR-BP detector operates over the new bipartite graph from the upper triangular channel matrix. Therefore, the number of cycles in the new bipartite graph is significantly decreased when compared with the fully connected bipartite graph from the original MIMO channel matrix. In addition, since the unitary matrix is utilised for the linear transformation, there is no information loss on the likelihoods estimated from noisy observations. Simulation results verify that the proposed QR-BP detector outperforms existing BP detectors and achieves near-optimum performance close to the maximum-likelihood detector in terms of bit error ratio.
    Electronics Letters 05/2015; 51(11). DOI:10.1049/el.2015.0378 · 0.93 Impact Factor
  • Kyungsik Min · Taehyoung Kim · Sangjoon Park · Sooyong Choi ·

    10/2014; 39B(10):664-673. DOI:10.7840/kics.2014.39B.10.664
  • Taehyoung Kim · Kyungsik Min · Sooyong Choi ·

    10/2014; 39A(10):622-624. DOI:10.7840/kics.2014.39A.10.622
  • Sangjoon Park · Sooyong Choi ·

    10/2014; 39A(10):619-621. DOI:10.7840/kics.2014.39A.10.619
  • Sangjoon Park · Sooyong Choi ·

    09/2014; 39A(9):566-568. DOI:10.7840/kics.2014.39A.9.566
  • Yeonhee Pak · Kyungsik Min · Sooyong Choi ·
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    ABSTRACT: In this paper, we study the effective small-cell deployment scenarios to improve the system performance. We consider three deployment strategies - the random deployment, the deployment for the worst-performance user, and the cell-edge deployment [1]. From the system level simulation results, we suggest the effective small-cell deployment strategy in terms of the signal-to-interference plus noise ratio performance.
    2014 International Symposium on Consumer Electronics (ICSE); 06/2014
  • Hyungju Nam · Moonchang Choi · Chanhong Kim · Daesik Hong · Sooyong Choi ·
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    ABSTRACT: A filter-bank multicarrier - quadrature amplitude modulation (FBMC-QAM) system with two prototype filters for transmitting QAM signal is proposed. The proposed transmitter performs separate filtering for the even-numbered sub-carrier symbols and the odd-numbered sub-carrier symbols. We derive the orthogonality conditions for a FBMC-QAM system without the intrinsic interference. In order to satisfy the suggested orthogonality conditions, we perform a kind of block interleaving for the odd-numbered sub-carrier filtering. The receiver structure is the counterpart to the transmitter. Numerical results showed that the proposed FBMC-QAM system has almost the same bit error rate (BER) performance compared to the FBMC-OQAM and the orthogonal frequency division multiplexing (OFDM) system. with the proposed FBMC-QAM, multiple-input multiple-output transmission schemes and channel estimation schemes can be utilized similarly as in OFDM.
    ICC 2014 - 2014 IEEE International Conference on Communications; 06/2014
  • Gyuyeol Kong · Sooyong Choi ·
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    ABSTRACT: A new read channel architecture achieving diversity effects for bit patterned magnetic recording is proposed in this paper. In the proposed channel architecture, a new channel model generating several different channels for the desired symbols and the diversity achieving detection schemes are proposed to obtain performance gains with a simple structure. By using the proposed channel model, M different channels for the M desired symbols can be generated from the M reading operations and then M different channels can be exploited to obtain spatial diversity gains with the diversity achieving detection schemes. For the diversity achieving detection schemes, a single-track interference cancellation scheme is proposed based on ordered successive interference cancellation algorithm. To consider interference from the side-tracks, a multi-track interference cancellation (MTIC) scheme is also proposed. Simulation results show that the MTIC scheme with a simpler structure yields more than 1.5 dB gains over the conventional schemes when an areal density is 3 Tb/in2.
    Journal of Applied Physics 04/2014; 115(17). DOI:10.1063/1.4867344 · 2.18 Impact Factor
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    ABSTRACT: In this paper, we propose a load balancing and a dynamic overlay clustering procedures including the fusion procedure. The proposed load balancing gets some loss for the throughput of the overall system but it improves the throughput of the cell-edge users. Through the simulations, we verify that the load and the number of users of the proposed system are changed uniformly. In addition, we demonstrate that the proposed system can improve the quality of service for cell-edge users while guaranteeing user fairness.
    2014 International Conference on Information Networking (ICOIN); 02/2014
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    ABSTRACT: In this paper, we propose a non-orthogonal multiple access-based multiuser beamforming (NOMA-BF) system designed to enhance the sum capacity. In the proposed NOMA-BF system, a single BF vector is shared by two users, so that the number of supportable users can be increased. However, sharing a BF vector leads to interference from other beams as well as from the other user sharing the BF vector. Therefore, to reduce interference and improve the sum capacity, we additionally propose a clustering and power allocation algorithm. This clustering algorithm, which selects two users with high correlation and a large gain-difference between their channels, can reduce the interference from other beams and from the other user as well. Furthermore, power allocation ensures that each user's transmit power is allocated so as to maximize the sum capacity. Numerical results verify that the proposed NOMA-BF system improves the sum capacity, compared to the conventional multiuser BF system.
    MILCOM 2013 - 2013 IEEE Military Communications Conference; 11/2013
  • Young Rok Jang · Yongok Kim · Jang-Won Lee · Daesik Hong · Sooyong Choi ·
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    ABSTRACT: There are two important factors for the nodes of Wireless Body Area Network (WBAN): the lasting lifetime and the low loss of significant biometric data. Therefore, the stabilities of both the data queue and the energy queue are an important point on the WBAN nodes. In this paper, Minimum Distance Adaptive Allocation (MDAA) is proposed which is an adaptive queue management scheme to maintain the stabilities of both the data queue and the energy queue. MDAA adjusts the time ratio between energy harvesting and data transmission to minimize the Euclidean distance between the next state and the ideal state. The performance of the proposed scheme is evaluated and takes positive assessments rather than that of the control group.
    Proceedings of the 8th International Conference on Body Area Networks; 09/2013
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    ABSTRACT: This paper investigates a dynamic spectrum access (DSA) scheme for low power wireless sensor networks (WSN) in an open spectrum where multiple systems coexist and interfere with each other. Low transmission power and a simple communication protocol are significant obstacles to the operation of low power WSN in the open spectrum. As a result, available spectrum is more scarce for a low power WSN than for the other coexisting systems. To address this, we are proposing a new DSA scheme with an energy efficient channel switching criterion that can improve the expected throughput by chasing the low interference channel. OPNET-based system level simulation results, designed under the framework of ZigBee and IEEE 802.15.4, demonstrates that the proposed DSA scheme shows improved energy efficiency and throughput compared to conventional ZigBee systems.
    Proceedings of the 8th International Conference on Body Area Networks; 09/2013
  • Source
    Minchae Jung · Sooyong Choi ·
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    ABSTRACT: In this paper, we analyze a performance of multiuser massive multiple-input and multiple-output (MIMO) system. We derive the ergodic cell capacity based on a downlink frame structure and analyze the ergodic cell capacity with respect to the number of base station (BS) antennas and the number of users. This paper shows that the ergodic cell capacity is a concave function with respect to the number of BS antennas and the number of users, and also derives the optimal numbers of BS antennas and users for the maximum cell capacity. The simulation results verify the derived analyses and show that the derived numbers of BS antennas and users provide the maximum cell capacity.
    08/2013; 38A(8). DOI:10.7840/kics.2013.38A.8.724
  • Minchae Jung · Younsun Kim · Juho Lee · Sooyong Choi ·
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    ABSTRACT: The optimal number of users achieving the maximum sum throughput is analyzed in zero-forcing (ZF) based multiuser multiple-input multiple-output (MIMO) systems with a large number of base station (BS) antennas. By utilizing deterministic ergodic sum rates for the ZF-beamforming (ZF-BF) and ZF-receiver (ZF-R) with a large number of BS antennas [1], [2], we can obtain the ergodic sum throughputs for the ZF-BF and ZF-R for the uplink and downlink frame structures, respectively. Then, we can also formulate and solve the optimization problems maximizing the ergodic sum throughputs with respect to the number of users. This paper shows that the approximate downlink sum throughput for the ZF-BF is a concave function and the approximate uplink sum throughput for the ZF-R is also a concave function in a feasible range with respect to the number of users. The simulation results verify the analyses and show that the derived numbersof users provide the maximum sum throughputs for the ZF-BF as well as ZF-R in multiuser MIMO systems with a large number of BS antennas.
    Journal of Communications and Networks 08/2013; 15(4):362-369. DOI:10.1109/JCN.2013.000067 · 1.01 Impact Factor
  • Minchae Jung · Sooyong Choi ·

    07/2013; 38A(7):571-579. DOI:10.7840/kics.2013.38A.7.571
  • Taehyung Kim · Gyuyeol Kong · Xi Weiya · Sooyong Choi ·
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    ABSTRACT: Cell-to-cell interference compensation schemes using reduced symbol pattern of interfering cells for multilevel cell (MLC) NAND flash memory are proposed in this paper. The proposed schemes consist of three procedures, estimation of cell-to-cell interference, compensation for cell-to-cell interference, and generation of log-likelihood ratio (LLR). First, reduced symbol pattern of interfering cells is used to estimate cell-to-cell interference by modifying the levels of the threshold voltage shift from multi page programming to two levels. Second, based on this estimation, cell-to-cell interference is compensated by modifying the read voltage considering the estimated cell-to-cell interference in the proposed scheme 1 and by subtracting the estimated cell-to-cell interference from the sensed voltage in the proposed scheme 2. Finally, after conducting compensation, LLR is calculated for low-density parity check (LDPC) codes in the assumption of free cell-to-cell interference since interference between cells is mitigated by the compensation procedure. By using these techniques, cell-to-cell interference can be relaxed with a simple structure and a high reliability. The bit error rate (BER) performances of the proposed schemes are compared with the conventional schemes on 8-level MLC NAND flash memory. Simulation results show that the proposed schemes show the improved BER performances by more than an order of magnitude compared with the conventional LDPC scheme.
    IEEE Transactions on Magnetics 06/2013; 49(6):2569-2573. DOI:10.1109/TMAG.2013.2251417 · 1.39 Impact Factor

Publication Stats

487 Citations
72.08 Total Impact Points


  • 1997-2014
    • Yonsei University
      • Department of Electrical and Electronic Engineering
      Sŏul, Seoul, South Korea
  • 2004
    • National University (California)
      San Diego, California, United States
    • CSU Mentor
      Long Beach, California, United States
  • 2002-2003
    • University of California, San Diego
      • Institute for Neural Computation (INC)
      San Diego, California, United States
  • 1998
    • Dongguk University
      • Division of Electronics and Electrical Engineering
      Seoul, Seoul, South Korea