Hyunchul Ku

A route optimization via recursive coa substitution for nested mobile networks

In nested mobile networks, the undesirable effects due to nonoptimal routing tends to get aggravated, leading to excessively long packet sizes and transfer delays. In this paper, in order to resolve the non-optimal routing problem, also known as ‘pinball routing problem’ in the literature, we propose a new route optimization scheme where the care-of address (CoA) in each binding update (BU) message is recursively substituted by the intermediate mobile routers in the mobile network. Through qualitative and numerical analyses, we show that the proposed scheme indeed demonstrates a greatly reduced signaling overhead in terms of packet sizes and number of BU messages required, thereby reducing the RO setup time and end-to-end transfer delay. We also show that the proposed scheme can be a good solution for the so-called intra-MoNET routing problem.

Closed-form expression of IMD considering input/output frequency responses in nonlinear RF power amplifiers for digital predistortion

In this paper, a novel closed-form expression of the intermodulation distortion (IMD) of nonlinear RF power amplifier (PA) considering input and output frequency responses is proposed. A transmitter including nonlinear PA is modeled with three-box (Wiener-Hammerstein type) model to include input and output frequency responses. To verify the closed-form expression of IMD, the analytical results are compared with the simulated results by changing frequency responses of filters in three-box model. The analytical IMDs show exact agreement with the simulated ones. The proposed analytical description can be applied to accurate PA modeling and predistortion design.

Development of web-based remote laboratory for education and research on RF engineering

This paper presents the design of a remote laboratory platform using web-based technologies for radio frequency (RF), microwave measurements and their analysis. The developed RF remote laboratory system is easy to operate using web-based graphical user interfaces in controlling the test equipments and displaying the test results. The various measurement and analysis engines for RF devices, circuits, and systems are developed using graphical language, LabView. The remote RF laboratory system with the developed user interfaces and engines is used in education and research on RF engineering. The developed system can increase efficiency of education and research on RF engineering cost-effectively by providing similar environment with an actual laboratory using web-based technologies.

Multiband wireless transmitter using nonlinear characteristics of power amplifier and harmonic-tuning predistorter

A new technique to send a signal in m-th harmonic band with a harmonic-tuning digital predistortion (DPD) scheme is presented. A nonlinear relationship between an input complex envelope and an output complex envelope of m-th harmonic zone is theoretically analyzed. The AM/AM m and AM/PM m are defined and extracted. The suggested analysis is verified with a fundamental-fundamental and fundamental-third harmonic measurements for a InGaP power amplifier (PA). A novel numerical and look-up table (LUT) based DPD algorithm to linearize output signal on m-th harmonic zone is developed. For a 16-QAM input signal, a predistortion for third harmonic signal is implemented, and output spectrum and signal constellation are measured. The results show that a proposed harmonic-tuning DPD scheme works. The proposed nonlinear analysis and predistortion scheme can be applied to multiband software defined radio (SDR) / cognitive radio (CR) wireless system.

Analysis and Identification of Wiener-Hammerstein System in Frequency Domain Using Two-Tone Measurements for Nonlinear RF Transmitters

This paper presents analysis and identification method of Wiener-Hammerstein system to characterize a nonlinear RF transmitter in fundamental frequency zone. A two-tone signal is used to analyze and identify a Wiener-Hammerstein model. A RF signal is converted to baseband-equivalent complex signal, and Wiener-Hammerstein model is considered to have a baseband equivalent complex polynomial and linear filters. For a two-tone input signal, closed form descriptions of the output signal in the time domain and frequency domain are developed using a newly suggested nonlinearly modulated two-tone phasors (NMTP). The relationship between frequency terms of input and output signals in RF transmitters are represented with linear matrix-vector equation based on NMTP analysis. An advantage of the proposed method is its simplicity using closed form analysis and linear approximation. In addition, we can model a wideband system with relatively narrowband measurements by sweeping two-tone signal. The prediction of spectral regrowth and the predistortion performance for WiBro 1FA signal demonstrate the validity of the proposed approach in identifying the nonlinear RF transmitters.

Characterization of Electrical Memory Effects in Power Amplifier using Multi-tone Measurement

In this paper, an efficient method to characterize electrical memory effects arising from the interaction between the static nonlinearity and the frequency response is proposed using a multi-tone measurement. A transmitter system with nonlinear power amplifier (PA) is modeled with two box Wiener structure that consists of a static Saleh model and a linear filter. A nonlinear least square method with a multi-tone measurement is used to extract frequency response and nonlinear characteristics. The proposed method is verified with a simulation and experiment with a 10W class AB gallium-nitride (GaN) HEMT PA.

Modeling and impedance matching for radio frequency driven plasma lamp considering cold and hot states

A new dual-state impedance matching scheme for a microwave driven plasma lamp using a solid-state power amplifier (SSPA) is presented. The impedance of the plasma lamp depends on the amount of input radio frequency (RF) energy, and therefore has very different values for hot and cold states. First, a method for effectively modeling the electrical characteristics of a plasma lamp that depends on RF power has been proposed. Second, a new technique has been proposed to achieve dual-state impedance matching for two state impedances at two very close frequencies using a T-shaped matching network with two section shunt stub and additional transmission line. The proposed method can achieve dual state impedance matching in two frequency bands located very closely when compared to the conventional methods. The accuracy of the proposed model and the effectiveness of the proposed dual-state matching are verified via a plasma lamp system with a 2.45 GHz 300 W GaN SSPA.

A 12 mW ADPLL Based G/FSK Transmitter for Smart Utility Network in 0.18 ㎛ CMOS

This paper presents low power frequency shift keying (FSK) transmitter using all digital PLL (ADPLL) for smart utility network (SUN). In order to operate at low-power and to integrate a small die area, the ADPLL is adopted in transmitter. The phase noise of the ADPLL is improved by using a fine resolution time to digital converter (TDC) and digitally controlled oscillator (DCO). The FSK transmitter is implemented in 0.18㎛ 1-poly 6-metal CMOS technology. The die area of the transmitter including ADPLL is 3.5 ㎟. The power consumption of the ADPLL is 12.43 ㎽. And, the power consumptions of the transmitter are 35.36 ㎽ and 65.57 ㎽ when the output power levels are -1.6 ㏈m and +12 ㏈m, respectively. Both of them are supplied by 1.8 V voltage source. The frequency resolution of the TDC is 2.7 ㎰. The effective DCO frequency resolution with the differential MOS varactor and sigma-delta modulator is 2.5 ㎐. The phase noise of the ADPLL output at 7.8㎓ is -121.17 ㏈c/㎐ with a 1㎒ offset.

Design of Efficient Reconfigurable Digital Compensator for Advanced Wireless Transmitter Using Computational Digital Signal Processing

This paper presents an efficient digital compensator that can be used for adjustment of gain and phase imbalances in linear amplification with nonlinear components (LINC) transmitters. The proposed compensator is designed in signal component separator (SCS) block using computational digital signal processing (DSP). Complex baseband equivalent signals and systems are considered to analyze error vector magnitude (EVM) and adjacent channel power ratio (ACPR) of the transmitter. Look up tables (LUT) based on the analyzed EVM and ACPR are used to compensate gain/phase imbalances of RF paths in the LINC transmitter. The suggested method is efficient to implement using computational software and DSP, and thus the compensator is reconfigurable for various input signals and RF transmitters. The LINC transmitter with the proposed compensator is implemented, and the suggested scheme is verified by showing the improvement of EVM and ACPR performance for the transmitted signals.

Design of Current-Mode Class-D 900 MHz RF Power Amplifier Using Inverse Class-F Technology

In this paper, Current-Mode Class-D(CMCD) RF Power Amplifier(PA) is designed and implemented at 900 MHz. Conventional CMCD PA has output parallel resonator to reconstruct a fundamental frequency component of the output signal. However the resonator can be removed by connecting inverse class-F PAs because even-harmonic components can be removed by CMCD PA`s push-pull structure. Using load-pull, inverse class-F PA with GaN transistors is designed, and CMCD PA with the inverse class-F PA is implemented. The CMCD PA has 64.5 % drain efficiency, 34.2 dBm output power. Comparing with the drain efficiency of a CMCD PA with parallel resonator, the CMCD with the inverse class-F technology has 13.6 % improved drain efficiency.