• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1A
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• pp.27-33
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• 2009

This paper proposes transmit power control techniques with fading channel prediction scheme based on recurrent neural network for high-speed mobile communication systems. The operation result of recurrent neural network which is derived interpretively solves complexity problems of neural network circuit, and channel gain of multiple transmit antenna is derived with maximum ratio combining(MRC) by using the operation result, and this channel gain control transmit power of each antenna. simulation results show that proposed method has a outstanding performance compared to method that is not to be controlled power based on channel prediction. Most of legacy studies are for robust receive technique of fading signals or channel prediction of fading signals limited low-speed mobility, but in open loop Power control, proposed channel prediction method decrease system complexity with removal of fading effect in transmitter.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.12
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• pp.1380-1387
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• 2012

The transmit/receive(T/R) module is a key component in the active phased array system. The brick-type T/R module has been widely used and the miniaturization has been an important factor to get the flexibility of the system configuration. For the miniaturization, multi-function chips(MFC) having a common leg configuration are suitable to reduce the number of required MMICs and a high isolation between transmit and receive paths is necessary for the high gain T/R modules. In this work, we propose a bias timing scheme for the compact T/R module and show the optimum timing based on measurements, in order to improve the feed-back path loop problem and the consequent isolation problem of the common leg configuration. We have implemented high power(7 W/channel) and high T/R gain(35 dB transmit and 30 dB receive gains) within the half size($140{\times}80{\times}16mm^3$) of the conventional T/R modules.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.229-234
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• 2006

Acquisition is to detect the presence of the GPS signal. Once the signal is detected, the estimated frequency and code phase are passed to a tracking loop to demodulate the navigation data. In order to detect the weak signal, multiple length of data integration is always needed. In this paper, we present five different acquisition approaches based on circular correlation and Fast Fourier Transform (FFT), using coherent as well as non-coherent integration techniques for the multiple length of collected GPS satellite signal. Moreover a general approach of determining the acquisition threshold is introduced based on noise distribution which has been proved effective, and independent of the hardware. In the end of this paper, the processing speed and acquisition gain of each method are illustrated, compared, and analyzed. The results show that coherent approach is much more time consuming compared to noncoherent approaches, and in the case of multiple length of data integration from 2ms to 8ms, the processing times consumed by the fastest non-coherent acquisition method are only 25.87% to 1.52% in a single search, and 34.76% to 1.06% in a global search of those in the coherent acquisition. However, coherent acquisition also demonstrates its better performance in the acquisition gain, and in the case of 8ms of data integration it is 4.23 to 4.41 dB higher than that in the non-coherent approaches. Finally, an applicable scheme of combining coherent and non-coherent acquisition approaches in the development of a real-time Software GPS receiver in the University of Tokyo is provided.

• Journal of Advanced Navigation Technology
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• v.8 no.2
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• pp.184-190
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• 2004

A feedforward linear power amplifier (FLPA) has been developed for UHF-band RFID reader applications. The main and error amplifiers are composed of a 2 stage so that linearity of the FLPA can be improved. The FLPA has been implemented on an FR-4 substrate (Er=4.7 and thickness=0.8 mm) with 3-dB and 10-dB hybrid couplers for input/output power divider and combiner. For 2-tone measurement (input level=-11 dBm at $f_1$=915 MHz and $f_2$=916 MHz), the FLPA exhibits a -18.52 dBm of $IMD_3$, which indicates that $IMD_3$ cancellation with feedforward loop is more than 27 dB. From 890 to 960 MHz, 1-dB gain compression output power and power gain of the FLPA are higher than 30 dBm and 40 dB, respectively.

• Smart Structures and Systems
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• v.13 no.2
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• pp.281-303
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• 2014

In order to suppress the wind-induced vibrations of the Canton Tower, a pair of active mass driver (AMD) systems has been installed on the top of the main structure. The structural principal directions in which the bending modes of the structure are uncoupled are proposed and verified based on the orthogonal projection approach. For the vibration control design in the principal X direction, the simplified model of the structure is developed based on the finite element model and modified according to the field measurements under wind excitations. The AMD system driven by permanent magnet synchronous linear motors are adopted. The dynamical models of the AMD subsystems are determined according to the open-loop test results by using nonlinear least square fitting method. The continuous variable gain feedback (VGF) control strategy is adopted to make the AMD system adaptive to the variation in the intensity of wind excitations. Finally, the field tests of free vibration control are carried out. The field test results of AMD control show that the damping ratio of the first vibration mode increases up to 11 times of the original value without control.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.7 s.98
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• pp.671-680
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• 2005

The CFL linearisation chip which is one of key devices in ultra-narrowband mobile radio transmitter using CQPSK digital modulation method is designed and implemented with $0.35{\mu}m$ CMOS technology. The reduced size and low cost of transmitter are available by the use of direct-conversion and CFL ASIC chip, which improve the power effi챠ency and linearity of transmitting path. In addition, low power operation is possible through CMOS technology The performance test results of transmitter show -25 dBc improvement of IMD level at the 3 kHz frequency offset and then satisfy FCC 47 CFR 90.210 E emission mask in the operation of CFL ASIC chip. At that time, the transmitting power is about PEP(Peak-to-Envelope Power) 5 W. The main parameters to improve the transmitting characteristic and to compensate the distortion in feed back loop such as DC-offset, loop gain and phase value are interfaced with notebook PC to be controlled with S/W.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.42 no.6
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• pp.23-36
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• 2005

PLLs have been widely used for many applications including communication systems. This paper presents a VCO with an improved negative skewed delay scheme and a PLL using this VCO. The proposed VCO and PLL are intended for replacing traditional LC oscillators and PLLs used in communication systems and other applications. The circuit designs of the VCO and PLL are based on 0.18um CMOS technology with 1.8V supply voltage. The proposed VCO employs subfeedback loops using pass-transistors and needs two opposite control voltages for the pass transistors. The subfeedback loops speed up oscillation depending on the control voltages and thus provide a high oscillation frequency. The two voltage controls have opposite frequency gain characteristics and result in low phase-noise. The 7-stage VCO in 0.18um CMOS technology operates from $3.2GHz\~6.3GHz$ with phase noise of about -128.8 dBc/Hz at 1MHz frequency onset. For 1.8V supply voltage, the current consumption is about 3.8mA. The proposed PLL has dual loop-filters for the proposed VCO. The PLL is operated at 5GHz with 1.8V supply voltage. These results indicate that the proposed VCO can be used for radio frequency operations replacing LC oscillators. The circuits have been designed and simulated using 0.18um TSMC library.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.9
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• pp.741-749
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• 2005

This paper presents a nonlinear controller design for optical disk drive systems to improve anti-shock performance. The nonlinear anti-shock controller is added parallel to the original linear servo control loop. In the previous work, a dead-zone nonlinear element is used for the nonlinear controller and a PID control method is used for the linear controller. Although this parallel structure of the controller improves anti-shock performance, it has a narrow stability bound. In this paper, the dead-zone with saturation nonlinear element is proposed for the nonlinear controller. Since this nonlinear element improves stability margin, we can use higher slope gain of dead-zone than that of nonlinear controller using dead-zone only. In the linear controller design, it is shown that the lead-lag control has an improved stability margin over PID control. Numerical simulation results and experimental results show that the proposed method can get better performance to the external shock than previously proposed methods.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1901-1904
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• 2003

MPC or model predictive control is representative of control methods which are able to handle physical constraints. Closed-loop stability can therefore be ensured only locally in the presence of constraints of this type. However, if the system is neutrally stable, and if the constraints are imposed only on the input, global aymptotic stability can be obtained; until recently, use of infinite horizons was thought to be inevitable in this case. A globally stabilizing finite-horizon MPC has lately been suggested for neutrally stable continuous-time systems using a non-quadratic terminal cost which consists of cubic as well as quadratic functions of the state. The idea originates from the so-called small gain control, where the global stability is proven using a non-quadratic Lyapunov function. The newly developed finite-horizon MPC employs the same form of Lyapunov function as the terminal cost, thereby leading to global asymptotic stability. A discrete-time version of this finite-horizon MPC is presented here. The proposed MPC algorithm is also coded using an SQP (Sequential Quadratic Programming) algorithm, and simulation results are given to show the effectiveness of the method.

• Journal of Power Electronics
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• v.15 no.5
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• pp.1274-1285
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• 2015

This paper deals with model reference adaptive system (MRAS) speed estimators based on a secondary flux for linear induction motors (LIMs). The operation of these estimators significantly depends on an adaptation mechanism. Fixed-gain PI controller is the most common adaptation mechanism that may fail to estimate the speed correctly in different conditions, such as variation in machine parameters and noisy environment. Two adaptation mechanisms are proposed to improve LIM drive system performance, particularly at very low speed. The first adaptation mechanism is based on fuzzy theory, and the second is obtained from an LIM mechanical model. Compared with a conventional PI controller, the proposed adaptation mechanisms have low sensitivity to both variations of machine parameters and noise. The optimum parameters of adaptation mechanisms are tuned using an offline method through chaotic optimization algorithm (COA) because no design criterion is given to provide these values. The efficiency of MRAS speed estimator is validated by both numerical simulation and real-time hardware-in-the-loop (HIL) implementations. Results indicate that the proposed adaptation mechanisms improve performance of MRAS speed estimator.