Seungwon Choi

Bio: Seungwon Choi is an academic researcher from Hanyang University. The author has contributed to research in topics: Smart antenna & Antenna (radio). The author has an hindex of 19, co-authored 147 publications receiving 1723 citations. Previous affiliations of Seungwon Choi include Syracuse University & KT Corporation.

Design and implementation of low-profile contactless battery charger using planar printed circuit board windings as energy transfer device

Abstract: This paper paper presents the practical details involved in the design and implementation of a contactless battery charger that employs a pair of neighboring printed circuit board (PCB) windings as a contactless energy transfer device. A prototype contactless battery charger developed for application with cellular phones is used as an example to address the design considerations for the PCB windings and energy transfer circuit, plus demonstrates the performance of the contactless charger adapted to a practical application system.

A novel adaptive beamforming algorithm for a smart antenna system in a CDMA mobile communication environment

Abstract: An alternative way of adaptive beamforming is presented. The main contribution of the new technique is in its simplicity with a minimal loss of accuracy. The total computational load for computing a suboptimal weight vector from each new signal vector is about O(2N/sup 2/+5N). It can further be reduced down to O(3N) by approximating the autocorrelation matrix with the instantaneous signal vector at each snapshot. The required condition on the adaptive gain for the proposed algorithm to converge is derived analytically. The proposed beamforming algorithm is applied to the base station of a code-division-multiple access (CDMA) mobile communication system. The performance of the proposed method is shown in multipath fading communication channels in terms of the signal-to-interference+noise ratio (SINR), the bit error rate (BER), and the achievable capacity of a given CDMA cell/sector.

Design of an adaptive antenna array for tracking the source of maximum power and its application to CDMA mobile communications

Abstract: This paper presents an alternative method of adaptive beamforming. Under an assumption that the desired signal is large enough compared to each of interfering signals at the receiver, which is preconditionally achieved in code division multiple access (CDMA) mobile communications by the chip correlator, the proposed technique provides for a suboptimal beam pattern that increases the signal-to-noise/signal-to-interference ratio (SNR/SIR) and eventually increases the capacity of the communication channel. The main advantages of the new technique are: (1) the procedure requires neither reference signals nor a training period; (2) the signal intercoherency does not affect the performance or complexity of the entire procedure; and (3) the total amount of computation is tremendously reduced compared to that of most conventional beamforming techniques such that the suboptimal beam pattern is produced at every snapshot on a real-time basis. In fact, the total computational load for generating a new set of weights including the update of an N-by-N autocovariance matrix is O(3N/sup 2/+12N). It can further be reduced down to O(11N) by approximating the matrix with the instantaneous signal vector.

Implementation of an SDR system using graphics processing unit

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.

A novel adaptive beamforming algorithm for antenna array CDMA systems with strong interferers

Abstract: Blind beamforming based on the maximum signal-to-noise ratio (MSNR) can improve the performance of an array system only when the processing gain of the given code-division multiple-access (CDMA) system is high enough such that the desired signal can become dominant after despreading (see Choi, S. and Shim, D., IEEE Trans. Veh. Technol., vol.49, p.1793-1806, 2000; Choi, S. and Yun, D., IEEE Trans. Antennas Propagat., vol.45, p.1393-1404, 1997). We consider a maximum signal-to-interference-plus-noise ratio (MSINR) beamforming. The MSINR performance criterion is chosen to deal with strong interferers effectively. It is shown that blind MSINR beamforming is possible by directly utilizing the input and output signals of correlators of the CDMA systems. In addition, we propose an adaptive beamforming algorithm at a lower computational complexity - about O(7.5N) - where N is the number of antenna elements of the array system. Simulation results are presented in various signal environments to show the performance of the proposed adaptive algorithm.

Application of antenna arrays to mobile communications. II. Beam-forming and direction-of-arrival considerations

Abstract: Array processing involves manipulation of signals induced on various antenna elements. Its capabilities of steering nulls to reduce cochannel interferences and pointing independent beams toward various mobiles, as well as its ability to provide estimates of directions of radiating sources, make it attractive to a mobile communications system designer. Array processing is expected to play an important role in fulfilling the increased demands of various mobile communications services. Part I of this paper showed how an array could be utilized in different configurations to improve the performance of mobile communications systems, with references to various studies where feasibility of apt array system for mobile communications is considered. This paper provides a comprehensive and detailed treatment of different beam-forming schemes, adaptive algorithms to adjust the required weighting on antennas, direction-of-arrival estimation methods-including their performance comparison-and effects of errors on the performance of an array system, as well as schemes to alleviate them. This paper brings together almost all aspects of array signal processing.

A Critical Review of Recent Progress in Mid-Range Wireless Power Transfer

Abstract: Starting from Tesla's principles of wireless power transfer a century ago, this critical review outlines recent magneto-inductive research activities on wireless power transfer with the transmission distance greater than the transmitter coil dimension. It summarizes the operating principles of a range of wireless power research into 1) the maximum power transfer and 2) the maximum energy efficiency principles. The differences and the implications of these two approaches are explained in terms of their energy efficiency and transmission distance capabilities. The differences between the system energy efficiency and the transmission efficiency are also highlighted. The review covers the two-coil systems, the four-coil systems, the systems with relay resonators and the wireless domino-resonator systems. Related issues including human exposure issues and reduction of winding resistance are also addressed. The review suggests that the use of the maximum energy efficiency principle in the two-coil systems is suitable for short-range rather than mid-range applications, the use of the maximum power transfer principle in the four-coil systems is good for maximizing the transmission distance, but is under a restricted system energy efficiency (<;50%); the use of the maximum energy efficiency principle in relay or domino systems may offer a good compromise for good system energy efficiency and transmission distance on the condition that relay resonators can be placed between the power source and the load.

Applications of antenna arrays to mobile communications. I. Performance improvement, feasibility, and system considerations

Abstract: The demand for wireless mobile communications services is growing at an explosive rate, with the anticipation that communication to a mobile device anywhere on the globe at all times will be available in the near future. An array of antennas mounted on vehicles, ships, aircraft, satellites, and base stations is expected to play an important role in fulfilling the increased demand of channel requirement for these services, as well as for the realization of the dream that a portable communications device the size of a wristwatch be available at an affordable cost for such services. This paper is the first of a two-part study. It provides a comprehensive treatment, at a level appropriate to nonspecialists, of the use of an antenna array to enhance the efficiency of mobile communications systems. It presents an overview of mobile communications as well as details of how an array may be used in various mobile communications systems, including land-mobile, indoor-radio, and satellite-based systems. It discusses advantages of an array of antennas in a mobile communications system, highlights improvements that are possible by using multiple antennas compared to a single antenna in a system, and provides details on the feasibility of antenna arrays for mobile communications applications.

Inductive power transfer

Abstract: A detection method for use in a primary unit of an inductive power transfer system, the primary unit being operable to transmit power wirelessly by electromagnetic induction to at least one secondary unit of the system located in proximity to the primary unit and/or to a foreign object located in said proximity, the method comprising: driving the primary unit so that in a driven state the magnitude of an electrical drive signal supplied to one or more primary coils of the primary unit changes from a first value to a second value; assessing the effect of such driving on an electrical characteristic of the primary unit; and detecting in dependence upon the assessed effect the presence of a said secondary unit and/or a foreign object located in proximity to said primary unit.

Inductive Power Transfer

Abstract: Inductive power transfer (IPT) was an engineering curiosity less than 30 years ago, but, at that time, it has grown to be an important technology in a variety of applications. The paper looks at the background to IPT and how its development was based on sound engineering principles leading on to factory automation and growing to a $1 billion industry in the process. Since then applications for the technology have diversified and at the same time become more technically challenging, especially for the static and dynamic charging of electric vehicles (EVs), where IPT offers possibilities that no other technology can match. Here, systems that are ten times more powerful, more tolerant of misalignment, safer, and more efficient may be achievable, and if they are, IPT can transform our society. The challenges are significant but the technology is promising.