Seungwon Choi

Hanyang University, Sŏul, Seoul, South Korea

Are you Seungwon Choi?

Claim your profile

Publications (79)79.85 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents an optimum placement of Gateways operating in Wireless Sensor Networks (WSNs). The full search method of Gird deployment requires tremendous amount of computation. A novel algorithm for resolving the complexity problem is proposed. The new algorithm utilizes the Cross Entropy Method (CEM) for the maximum network performance with a lot less operations compared to the full search method. Applying the proposed method to various practical situations such as health care system, Electronic Shelf Labeling (ESL), etc, we have verified the superb throughput performance of the proposed algorithm using OPNET simulator. Compared to the full search, which is ideal method, the proposed method provides nearly 98% throughput in various experimental tests.
    2014 International Symposium on Consumer Electronics (ICSE); 06/2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper introduces an implementation of GPU-based beamforming antenna module consisting of 4 elements. The proposed system can be mounted on top of the next generation base station system to reduce the radiating power at the base station. The transmitting power at base station is reduced proportionally to the number of antenna elements, due to the pencil beam provided between the base station and receiving terminal. Conversely, received signal at the terminal is enhanced by 4 times if the transmit power is maintained the same. Through various experimental tests, we have verified the proposed system consisting of 4 antenna elements provides nearly 12dB improvement in the receiving power at the terminal.
    2014 International Symposium on Consumer Electronics (ICSE); 06/2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we present an implementation of a long term evolution (LTE) system on a software defined radio (SDR) platform using a conventional personal computer that adopts a graphic processing unit (GPU) and a universal software radio peripheral2 (USRP2) with a URSP hardware driver (UHD) to implement an SDR software modem and a radio frequency transceiver, respectively. The central processing unit executes C++ control code that can access the USRP2 via the UHD. We have adopted the Ettus Research UHD due to its high degree of flexibility in the design of the transceiver chain. By taking advantage of this benefit, a simple cognitive radio engine has been implemented using libraries provided by the UHD. We have implemented the software modem on a GPU that is suitable for parallel computing due to its powerful arithmetic and logic units. A parallel programming method is proposed that exploits the single instruction multiple data architecture of the GPU. We focus on the implementation of the Turbo decoder due to its high computational requirements and difficulty in parallelizing the algorithm. The implemented system is analyzed primarily in terms of computation time using the compute unified device architecture profiler. From our experimental tests using the implemented system, we have measured the total processing time for a single frame of both transmit and receive LTE data. We find that it takes 5.00 and 8.58 ms for transmit and receive, respectively. This confirms that the implemented system is capable of real-time processing of all the baseband signal processing algorithms required for LTE systems.
    Analog Integrated Circuits and Signal Processing 03/2014; 78(3). · 0.55 Impact Factor
  • Source
    Donghyun Kum, Daegeun Kang, Seungwon Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a novel user selection method based on the signal-to-interference-plus-noise ratio (SINR), which is approximated using limited feedback data at the base stations (BSs) of multiple user multiple-input multiple-output (MU-MIMO) systems. In the proposed system, the codebook vector index, the quantization error obtained from the correlation between the measured channel and the codebook vector, and the measured value of the largest singular value are fed back from each user to the BS. The proposed method not only generates precoding vectors that are orthogonal to the precoding vectors of the previously selected users and are highly correlated with the codebook vector of each user but also adopts the quantization error in approximating the SINR, which eventually provides a significantly more accurate SINR than the conventional SINR-based user selection techniques. Computer simulations show that the proposed method enhances the sum rate of the conventional SINR-based methods by at least 2.4 (2.62) bps/Hz when the number of transmit antennas and number of receive antennas per user terminal is 4 and 1(2), respectively, with 100 candidate users and an SNR of 30 dB.
    Etri Journal 01/2014; 36(1). · 0.74 Impact Factor
  • Kyunghoon Kim, Hyunwook Yang, Seungwon Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: This letter presents a novel method of user selection in a downlink multi-user multiple input multiple output (MU-MIMO) system employing the precoding procedures of zero forcing or block diagonalization (BD). The proposed technique utilizes the cross-entropy method (CEM) in order to maintain a performance level comparable to that of the full search (FS) method with reasonable complexity. With the CEM, the proposed system can select multiple users at once instead of selecting a single user at each step. From various computer simulations, it has been verified that the proposed method exhibits nearly 98 % of the sum-rate compared to the FS method, which implies that the proposed method far outperforms conventional methods such as semi-orthogonal user selection (SUS) or the capacity-based suboptimal user selection (CBSUS) algorithm. Compared to CBSUS, the proposed technique enhances the sum-rate by approximately 1.1 bps/Hz with about half the complexity when each user is equipped with two receiving antennas. In the case where each user is equipped with a single antenna, the proposed method outperforms the method of SUS by about 0.3 bps/Hz, at the expense of a complexity increase of $$O(2M)$$O(2M) times.
    Wireless Personal Communications 01/2014; 74(2):789-802. · 0.43 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this work, a novel lattice reduction (LR) precoding method is proposed. The technique combines conventional LR precoding with a method of reducing the singular value coefficients of the LR-reduced basis matrix. The performance of the new technique was comparable to that of sphere encoding, while its complexity was lower than that of other sub-optimal methods.
    Wireless Personal Communications 05/2013; 70(1). · 0.43 Impact Factor
  • Hyunwook Yang, Seungwon Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose a novel precoding algorithm that is a zero-forcing (ZF) method combined with adaptive beamforming in the Worldwide Interoperability for Microwave Access (WiMAX) system. In a Multiuser Multiple-Input Multiple-Output (MU-MIMO) system, ZF is used to eliminate the Multiple Access Interference (MAI) in order to allow several users to share a common resource. The adaptive beamforming algorithm is used to achieve the desired SNR gain. The experimental system consists of a WiMAX base station that has 2 MIMO elements, each of which is composed of three-array antennas and two mobile terminals, each of which has a single antenna. Through computer simulations, we verified that the proposed method outperforms the conventional ZF method by at least 2.4 dB when the BER is 0.1%, or 1.7 dB when the FER is 1%, in terms of the SNR. Through a hardware implementation of the proposed method, we verified the feasibility of the proposed method for realizing a practical WiMAX base station to utilize the channel resources as efficiently as possible.
    International Journal of Antennas and Propagation 04/2013; 2013. · 0.68 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper introduces an anti-jamming technology for satellite communication that can cancel terrestrial jammers. In this paper, we first consider the Conjugate Gradient Method (CGM) as the first adaptive algorithm. Using this method, the attainment of the depth of the nulls and the rate of convergence are shown to be excellent. We also introduce a second novel adaptive algorithm, the hardware complexity of which for real-time implementation remains within the capacity of an off-the-shelf serial processor. A simulator based on the proposed adaptive algorithms is then illustrated to verify the performance of an adaptive system designed for implementation on a geostationary satellite. Finally, we demonstrate a hardware implementation of the adaptive system for canceling terrestrial jammers. Detailed hardware descriptions of an implemented adaptive system - such as the antenna array module, the beamforming module, and the controller module - are illustrated, along with the results of the performance obtained in laboratory tests.
    IEEE Antennas and Propagation Magazine 02/2013; 55(1):32-48. · 1.18 Impact Factor
  • Kyunghoon Kim, Hyunwook Yang, Seungwon Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper proposes a novel user selection algorithm to enhance the system performance of a multi-user, multiple-input, multiple-output (MU-MIMO) system. The proposed algorithm first selects a primary user set using a predetermined threshold, and selects sub-users for each primary user to define user groups that maximize the determinant of the channel matrix consisting of selected user(s) and a candidate user. The user group that provides the maximum sum rate is then determined. According to computer simulation results, the proposed algorithm improves the system sum rate, compared to the conventional algorithm, by approximately 0.5bps/Hz.
    ICT Convergence (ICTC), 2013 International Conference on; 01/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: A novel calibration method using the Zadoff-Chu (ZC) sequence as a test signal is proposed. Using this technique, the timing information of the received test signal that contains the phase characteristics of each antenna path can be accurately estimated. Performance of the proposed method is first analyzed through computer simulation. Then, the proposed calibration algorithm is implemented on a Field Programmable Gate Array (FPGA) board to verify its excellent performance in terms of the estimation accuracy for both the amplitude characteristics and the phase characteristics of each antenna path of a given array system.
    ICT Convergence (ICTC), 2013 International Conference on; 01/2013
  • Jaeho Chung, Yusuk Yun, Seungwon Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents field experiments on a Multi-Input Multi-Output (MIMO) system that combines Adaptive Beamforming (ABF) and Spatial Multiplexing (SM) procedures. The combination of SM signal processing with ABF is applied to WiBro, the South Korean Orthogonal Frequency Division Multiplexing (OFDM) system that follows the IEEE 802.16e standard. The field experimental results show that ABF-MIMO OFDM system outperforms a simple MIMO OFDM system by 2dB (1.5dB) in the signal to noise ratio (SNR) for 16-QAM (64-QAM) under low correlated fading channel and 4dB (2.5dB) in the SNR for 16-QAM (64-QAM) under highly correlated fading channel, respectively, at the frame error rate (FER) of 1%. Details on the implementation of ABF-MIMO OFDM system is also presented in this paper. Through the system implementation and its field experimental results, we verify that the combination of MIMO OFDM system with ABF provides improved performance over a simple MIMO OFDM system in real propagation channel environment and, in particular, it is more effective in highly correlated fading channel. KeywordsMIMO–Adaptive beamforming (ABF)–OFDM–IEEE 802.16e–WiBro
    Telecommunication Systems 01/2013; · 1.03 Impact Factor
  • Hyunwook Yang, Seungwon Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we present an algorithm for reducing the transmit normalization factor by perturbing the transmit signal in a Multi-User Multiple Input Multiple Output (MU-MIMO) system which uses the channel inverse matrix as its precoding matrix. A base station must normalize unnormalized transmit signals due to the limitation of the constant transmit power. This paper defines the norm of the unnormalized transmit signal as the transmit normalization factor used to normalize the transmit signal. Recalling that the transmit normalization factor consists of a combination of the singular values from the channel inverse matrix, we provide a codebook that successively reduces the coefficients of these singular values. Through computer simulations, the proposed algorithm is compared to sphere encoding in terms of the Bit Error Rate (BER) and the outage probability in a MU-MIMO signal environment. Sphere encoding is known to be an optimal solution amongst the perturbation methods that reduce the transmit normalization factor [1]. This work demonstrates that the proposed algorithm is has very good performance, comparable to that of sphere encoding, while its computational load is nearly 200 times less. Since the codebook in our algorithm depends only on the given channel, the difference in the computational complexity becomes even greater when the channel state is not changed, because the codebook can be reused. Furthermore, the codebook exhibits the characteristic of robustness to the maximum Doppler shift.
    IEICE Transactions on Communications. 01/2012; E95.B(7):2405-2413.
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study presents an implementation of the standard smart antenna (SA) application programming interface (API) and Transceiver API developed by the wireless innovation forum’s (WINNF) smart antenna working group (SAWG). The API is implemented using the open-source SCA implementation-embedded (OSSIE) developed at Virginia Tech. Our implementation verified that the SA API can be utilized in software communication architecture (SCA)-based software defined radio (SDR) systems. We also verified that the Transceiver API can be realized with a real radio frequency (RF) transceiver module such as universal software radio peripheral2 (USRP2). The SA API enables various functions of multi-antenna systems such as beamforming and multiple input multiple output (MIMO) of spatial multiplexing. These are core technologies prevalent in 4G mobile communication systems. In order to support multi-antenna structures, the Transceiver API has first been extended for multichannel use. The paper details how the API is extended using OSSIE and the current status of the API as a standard within the Wireless Innovation Forum. KeywordsSDR–Smart antenna–Transceiver–SCA
    Analog Integrated Circuits and Signal Processing 12/2011; 69(2):219-226. · 0.55 Impact Factor
  • Jinho Choi, Seungwon Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: Cell-edge users in cellular systems suffer from intercell interference (ICI), and their data rates are usually lower than those of the users who are close to base stations (BSs). Since data rates cannot be improved by merely increasing transmission power in the presence of ICI, the interference management and alignment become crucial for cell-edge users. However, when channel state information (CSI) is not available at BSs, it is difficult to apply interference alignment techniques. In this paper, we consider a simple approach where each BS in coordination transmits signals to a dedicated user through multiple subcarriers shared by adjacent BSs, which results in an interference channel, so that higher diversity can be exploited for better performance. Using joint detection at users, we show that a reasonable performance can be achieved.
    IEEE Transactions on Vehicular Technology 06/2011; · 2.06 Impact Factor
  • Jaeho Chung, Yusuk Yun, Seungwon Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper details the downlink performance analysis of a MIMO (Multi-Input Multi-Output) system that combines adaptive beamforming (ABF) and spatial multiplexing (SM) procedures. The combination of MIMO signal processing with ABF is applied to WiBro (Wireless Broadband), the South Korean orthogonal frequency division multiple access (OFDMA) system that follows the IEEE 802.16e standard. Performance analysis is based on the results of experiments and simulations obtained from a prototype system implementation and fixed-point simulator. Both the prototype experiments and simulations demonstrate that the ABF-MIMO OFDMA system improves the required signal to noise ratio (SNR) over the conventional MIMO OFDMA system by 3 dB (QPSK)/2.5 dB (16-QAM) for the frame error rate of 1% in the WiBro signal environments. From the implementation of the prototype system and its experimental results, we verify the feasibility of the ABF-MIMO technology for realizing a practical WiBro base station. Copyright © 2011 John Wiley & Sons, Ltd.
    International Journal of Communication Systems 01/2011; 24:1627-1646. · 1.11 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Conventional communication systems have been implemented using digital signal processors (DSPs) and/or field programmable gate arrays (FPGAs), especially for software defined radio (SDR) functionality. We propose a scheme that uses a graphics processing unit (GPU) in place of the conventional DSPs or FPGAs for the implementation of an SDR-based communication system. The GPU, a high-speed parallel processor with multiple arithmetic logic units, is adopted for the signal processing of the physical layer required for the parallel processing in an SDR system. The compute unified device architecture (CUDA) based on the C language provides a software development kit (SDK) for the modem application of the GPU. Therefore we utilize the CUDA SDK to implement the real-time modem function. This paper presents an implementation of a 2×2 multiple-input multiple-output (MIMO) WiMAX system employing a GPU as the real-time modem. By installing a radio frequency module on top of the GPU modem, we implement a real-time transmission system for video data. The performance of the proposed GPU-based system is demonstrated by comparing its operation time against that of the conventional DSP-based system. KeywordsSDR–GPU–CUDA–WiMAX–MIMO
    Analog Integrated Circuits and Signal Processing 01/2011; 69(2):107-117. · 0.55 Impact Factor
  • Changeui Shin, Hyunsung Go, Seungwon Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: Efficient User Scheduling Algorithm for Enhancing Zero-Forcing Beamforming in MIMO Broadcast Channels
    IEICE Transactions. 01/2011; 94-B:2908-2911.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we study the power allocation for multiband coded OFDM systems. With limited feedback, we propose an effective power allocation method across OFDM bands to maximize the throughput and achieve the quality of service target. To facilitate the proposed method, two optimization algorithms based on greedy and dynamic programming principles are discussed. The trade-off between performance and complexity is provided. Simulation results show that the proposed power allocation mechanism allows a signal to noise ratio gain of 2 dB at a goodput of 2.5 bit per second per Hz over the multiband OFDM systems with equal power allocation.
    Proceedings of the 74th IEEE Vehicular Technology Conference, VTC Fall 2011, 5-8 September 2011, San Francisco, CA, USA; 01/2011
  • Jinho Choi, Seungwon Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: Cooperative communications in wireless multiuser systems, e.g., cellular systems, can improve the spectral efficiency. Through cooperation between distributed receivers, a better per- formance can be obtained by exploiting the spatial diversity gain. In this paper, we derive distributed iterative receiver (DIR) algo- rithms using a factor graph. DIR algorithms are message-passing algorithms where messages are exchanged through an intracom- munication network between distributed receivers. To take into account the limited bandwidth of the intracommunications, we also derive DIR algorithms with quantized messages and partial connections between distributed receivers. Through simulations, we show that the performance is improved as more collaboration (i.e., iteration) takes place.
    IEEE Transactions on Vehicular Technology 01/2011; 60(7):3066-3075. · 2.06 Impact Factor
  • J. Kim, Seungheon Hyeon, Seungwon Choi
    [Show abstract] [Hide abstract]
    ABSTRACT: This article presents a novel procedure of implementing software defined radio modem using a graphics processing unit instead of conventional digital signal processors and/or field programmable gate arrays. Considering that modern GPU is suitable for parallel computing due to its numerous powerful arithmetic logic units, we suggest a proper architecture of hardware and software platform for the SDR modem to be implemented on GPU. Then, we show a design example of mobile WiMAX terminal implemented on the proposed GPU platform. In our experimental tests, we observed that the GPU-driven modem is nearly 90 times faster than the conventional 8-way Very Long Instruction Word architectured DSP-driven modem for the application of Viterbi decoder implementation of mobile WiMAX terminal.
    IEEE Communications Magazine 04/2010; · 3.66 Impact Factor

Publication Stats

485 Citations
79.85 Total Impact Points

Institutions

  • 1993–2014
    • Hanyang University
      • • Department of Electronics and Computer Engineering
      • • Department of Electronic and Electrical Engineering
      Sŏul, Seoul, South Korea
  • 2011
    • Swansea University
      • College of Engineering
      Swansea, WLS, United Kingdom
  • 2002–2006
    • Yong-in Songdam College
      Sŏul, Seoul, South Korea
    • Feng Chia University
      • Department of Electrical Engineering
      臺中市, Taiwan, Taiwan
  • 2001–2006
    • Kyungpook National University
      • • School of Computer Science and Engineering
      • • Department of Electrical Engineering
      Taegu, Daegu, South Korea
  • 2003
    • University of South Wales
      Понтиприте, Wales, United Kingdom
  • 1995–1997
    • Syracuse University
      • Department of Electrical Engineering and Computer Science
      Syracuse, NY, United States