Sooyong Choi

Yonsei University, Sŏul, Seoul, South Korea

Are you Sooyong Choi?

Claim your profile

Publications (101)74.44 Total impact

  • Sooyong Choi · Sangjoon Park
    [Show abstract] [Hide abstract]
    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 · 1.07 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
  • [Show abstract] [Hide abstract]
    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
  • Yeonhee Pak · Kyungsik Min · Sooyong Choi
    [Show abstract] [Hide abstract]
    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
  • Gyuyeol Kong · Sooyong Choi
    [Show abstract] [Hide abstract]
    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 · 2.19 Impact Factor
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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
    [Show abstract] [Hide abstract]
    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
    [Show abstract] [Hide abstract]
    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 · 0.75 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
    [Show abstract] [Hide abstract]
    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 · 1.21 Impact Factor
  • Moonchang Choi · Sooyong Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we propose a novel receiver structure for cancelling self-mixed interferences in direct conversion receivers. The proposed receiver structure is based on the adaptive interference cancellation (IC) using an adaptive algorithm such as a least-mean-square (LMS). The reference signal for the adaptive IC is obtained from the received signal itself. Thus, the proposed method can mitigate the self-mixed interference without any additional information on the self-mixed interference. Moreover, the signal-to-interference ratio (SIR) performance of the proposed cancellation method is theoretically analyzed. The simulation results indicate that the numerical SIR performance is well matched with the theoretical SIR performance. Also, the proposed cancellation method cancel the self-mixed interference almost perfectly even when the power of the received interference signal is 50dB larger than that of the received desired signal.
    IEEE Transactions on Consumer Electronics 05/2013; 59(2):310-315. DOI:10.1109/TCE.2013.6531111 · 1.16 Impact Factor
  • Moonchang Choi · Sooyong Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: A novel method for cancelling the time-varying offset due to self-mixed interferences in direct conversion receivers is proposed. The proposed method is based on the adaptive interference cancellation using the least mean square adaptation algorithm. Some simulation results show that the proposed method cancel the self-mixed interference almost perfectly.
    Consumer Electronics (ICCE), 2013 IEEE International Conference on; 01/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, an asymptotic distribution for the sum rate capacity is derived in zero-forcing beamforming (ZF-BF) based multiuser MIMO systems with a large number of base station (BS)antennas. By utilizing the characteristics of a large number of antennas and the central limit theorem, we prove that the asymptotic distribution for the sum rate capacity follows Gaussian distribution. Also we derive the mean and variance values for the asymptotic Gaussian distribution. Based on the asymptotic Gaussian distribution, we also obtain the outage probability for the sum rate capacity as a closed form. Simulation results show that the asymptotic Gaussian distribution is well follows the actual sum rate capacity, and the both asymptotic mean and variance value are also very accurate.
    Vehicular Technology Conference (VTC Spring), 2013 IEEE 77th; 01/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper analyzes the pilot power ratio (PPR) in multiuser multiple-input multiple-output (MU-MIMO) systems with a large number of receive antennas (M) at the base station (BS). We consider zero-forcing based MU-MIMO orthogonal frequency division multiplexing (OFDM) systems. Based on the deterministic uplink sum-rate approximation for imperfect channel state information, we can formulate the optimization problems in terms of the PPR to maximize the ergodic uplink sum-rate subject to the per-slot or per-symbol power constraint. Under the per-slot power constraint, the optimal PPR can be obtained in a closed form while under the per-symbol power constraint, we propose an iterative algorithm which generates a suboptimal PPR. Simulation results show that the proposed PPRs perform close to the optimal performance in terms of the sum-rate. Also, it is shown that the proposed PPRs outperform the equal power allocation. In particular, in the ZF-R based MU-MIMO OFDM system with 8 users and M=32 under the per-slot power constraint, the proposed PPR can achieve about 8bps/Hz performance gain compared to the equal power allocation.
    Vehicular Technology Conference (VTC Fall), 2013 IEEE 78th; 01/2013

Publication Stats

439 Citations
74.44 Total Impact Points

Institutions

  • 1997–2014
    • Yonsei University
      • Department of Electrical and Electronic Engineering
      Sŏul, Seoul, South Korea
  • 2004
    • CSU Mentor
      Long Beach, California, United States
  • 2003
    • University of California, San Diego
      San Diego, California, United States
  • 1998
    • Dongguk University
      • Division of Electronics and Electrical Engineering
      Seoul, Seoul, South Korea