Unloaded Q of a dielectric image resonator is discussed based on the electromagnetic field distribution. It is shown that a partial air gap and a dielectric sheet with low permittivity between the dielectric resonator and the shield case reduce both the dielectric loss and the conductor loss. Especially, reduction of the conductor loss is significant, since the magnetic field distribution moves from the conductor to the upper part of resonator. A half-cut image resonator with an air gap and dielectric spacer is simulated and measured. The unloaded Q of the dielectric resonator with low dielectric loss is improved by about two times from that of original image resonator.

Similar to direct sequence code division multiple access (DS-CDMA), site diversity can be applied to a multicarrier-CDMA (MC-CDMA) cellular system to improve the bit error rate (BER) performance for a user with weak received signal power, thus resulting in an increased link capacity. In this paper, the downlink site diversity reception using frequency-domain equalization based on minimum mean square error (MMSE) is considered for a MC-CDMA cellular system. A set of active base stations to be involved in the site diversity operation is determined based on the received signal power measurement by a mobile station. Downlink capacity with site diversity is evaluated by computer simulation. The impacts of path loss exponent and shadowing loss standard deviation on the site diversity effect are discussed. Furthermore, the performance improvement by antenna diversity reception is discussed.

This paper describes implementation and performance evaluation of simple SDM-COFDM (Space Division Multiplexed-Coded Orthogonal Frequency Division Multiplexing) prototype over fading MIMO (Multi-Input Multi-Output) channel in order to achieve higher frequency utilization efficiency. It employs ZF (Zero Forcing) type detection scheme for SDM transmission to reduce hardware implementation complexity, where ZF type detection scheme needs to only multiply the received data by the estimated inverse propagation coefficient matrix at each OFDM subcarrier. Moreover, in order to improve the performance degradation due to the increase of the transmitted data length per frame in fast fading environments, the inverse matrix tracking using STC (Space-Time Coded) pilot is proposed and implemented in the prototype. Experimental results show that the prototype with 22 antennas achieves about 90% increase of the frequency utilization efficiency compared to the SISO (Single-Input Single-Output) transmission.

We consider space division multiplexing in a MIMO-OFDM system for high data rate transmission. Channel estimation is very important for suppressing interference and demultiplexing signals. In a wireless LAN system such as IEEE 802.11a, only a few training symbols are inserted in each subcarrier. First, we propose a channel estimation method for a MIMO-OFDM system with two training symbols per subcarrier. The basic idea is to estimate the time-domain channel responses between the transmit and receive antennas. The array response vectors for each subcarrier are calculated by applying a fast Fourier transform to them. We then can obtain the adaptive weights to cancel the interference. We show that employing training symbols having a lower condition number of the matrix used for the channel estimation improves the estimation accuracy. Furthermore, we show the bit error rate for several signal detection schemes using the above estimated channel. It is shown that an ordered successive detection based on an MMSE criterion has excellent performance, that is, it can achieve higher-speed transmissions with a lower transmit power.

In MC-CDMA, the data rate can be increased by reducing the spreading factor SF or by allowing multicode transmission. In this paper, we examine by computer simulations which gives a better bit error rate (BER) performance--lower SF or multicode operation--when high level modulation is used in addition to error control coding. For a coded system in a frequency selective channel, there is a trade-off among frequency diversity gain due to spreading, improved coding gain due to better frequency interleaving effect and orthogonality distortion. It is found that for QPSK, the performance of OFDM (MC-CDMA with SF = 1) is almost the same as that of a fully spread MC-CDMA system. However, for 16QAM and 64QAM, the BER performance is better for lower SF unlike the uncoded system, wherein higher SF gives a better BER.

Tufts-Kumaresan (TK) method, which is based on linear prediction approach, is a standard algorithm for estimating the frequencies of sinusoids in noise. In this Letter, the TK algorithm is improved by attenuating the noise in the observation vector with the use of the reduced rank data matrix. It is shown that the proposed modification can provide smaller mean square frequency errors with lower threshold signal-to-noise ratios than the TK method and a total least squares solution.

A multi-band OFDM-MIMO system, in which the multi-band OFDM method is combined with the MIMO concept, has been developed. In this system, the spectra of multi-band OFDM signals are adaptively shared to improve the path gain for MIMO multiple transmission. The OFDM signal is divided into multi-bands, and the divided signals are transmitted on an appropriate beam in each multi-band. Multi-band transmission improves the overall transmission capacity by reducing the degradation of frequency-selective channels. In this paper, we report on our evaluation of the multi-band OFDM-MIMO system with frequency-selective fading channels.

This work describes a 2.4 GHz frequency synthesizer based on a delay-locked loop (DLL). Because the proposed frequency synthesizer is basically developed from a DLL, it has no jitter accumulation thereby resulting in a low close-in phase noise of -105 dBc/Hz. Although only 9 delay cells are used, the proposed delay cell reusing scheme realizes frequency multiplication factors greater than 240 and provides multiple frequency output with the resolution of phase detector (PD) comparison frequency. This architecture has been verified by implementing the synthesizer in a 0.18 µm CMOS technology.

In orthogonal frequency division multiplexing (OFDM) systems with differential phase shift keying (DPSK), it is possible to apply differential modulation either in the time or frequency domain depending on the condition of fading channels, such as the Doppler frequency shift and the delay spread. This paper proposes a simple calculation method, that is, an approximate closed-form equation of the bit error rate (BER) in DPSK/OFDM systems mentioned above over both time and frequency selective Rician fading channels. The validity of the proposed method is demonstrated by the fact that the BER performances given by the derived equation coincide with those by Monte Carlo simulation.

Radio frequency (RF) microwave can be used to predict glucose concentration in a sample. This paper presents preliminary results in determining the concentration by measuring relative permittivity in the solutions of distilled water, saline, human serum, and human blood containing glucose. In the experiments, sensitivity for detecting glucose concentration in blood solutions was almost 57 mg/dl at the frequency of approximately 5.8 GHz.

New Recommendation and Future Standards highlight the Power Factor Correction (PFC) converter as a basic requirement for switching power supplies. Most high-frequency power factor correctors use resistor emulation to achieve a near-unity power factor and a small line current distortion. This technique requires forcing the input current with an average-current-mode control to follow the input voltage. Stability of this system was discussed previously by using some linear models. However, in this paper, two nonlinear phenomena have been encountered in the PFC circuit, period doubling bifurcation and chaos. Detection of these new instability phenomena in the stable regions predicted by the prior linear PFC models makes us more susceptible towards them, and reveals the need to consider a nonlinear models. A nonlinear model performing the practical operation of a boost PFC converter has been developed. Then, a simplified and accurate nonlinear model has been proposed and verified experimentally. As a result from this model, instability maps have been introduced to determine the boundary between stable and unstable operating ranges. Then, the period doubling bifurcation has been studied through a new proposed technique based on the capacitor storage energy. It is cleared that, As the load lessens, a required extra storage power is needed to achieve the significant increase in the output voltage. Then, if the PFC system can provide this extra energy, the operation can reach stability with new zero-storage energy else the system will have double-line zero energy that is period doubling bifurcation.

This paper presents a dual-frequency microstrip antenna for both 2 GHz and 5 GHz for a dual-band receiver. For a simple structure and low cost design, the microstrip feed circuit is designed on the same substrate as the antenna elements. Each antenna element is directly fed by the microstrip line, and the open stubs are loaded on the feed line of 2 GHz to suppress the higher order mode resonances between 2 GHz and 5 GHz. The feed line length of each antenna is adjusted so as to change it to the open condition at the other element frequency at the feed point. In addition, we propose the antenna structure in which two antenna elements for 2 GHz are split and placed at either sides of the 5 GHz antenna to coincide with the center positions of each antenna element. We investigate the proposed antenna by calculations and measurements to show the combiner free design for the dual band antenna.

Discrete Wavelet Multi-carrier Transceiver (DWMT) system, which can be viewed as a kind of OFDM, has many advantages because it uses wavelets as its base functions. In this paper we present a new sub-carrier frequency offset correction method for DWMT systems with little assistant information. The essential ideal of this algorithm is: when an orthogonal multi-carrier system is of perfect frequency synchronize, the demodulated signals of different sub-carriers are independent of each other. Whereas when frequency offset exists, intercarrier interference will distort the demodulated signal, i.e. every demodulated signal is the sum of several modulated signals' projects on the demodulating frequency. So the adjacent demodulated signals consist of the element of the same modulated signal, and these demodulated signals are correlated with each other. The degree that they correlated with each other depends on sub-carrier relative frequency offset. Since that little assistant information is used in this algorithm the spectrum efficiency can be largely increased. Simulation results shown that if the number of the sub-carrier of the DWMT system is bigger than 1000, the relative frequency offset can be limited in 2%.

Borrowing the notion of instantaneous frequency that was developed in the context of time-frequency signal analysis, an instantaneous frequency amplitude spectrum (IFAS) is introduced for estimating fundamental frequency of speech signal in both noiseless and adverse environments. We define harmonicity measure as a quantity that indicates degree of periodical regularity in the IFAS and that shows substantial difference between periodic signal and noise-like waveform. The harmonicity measure is applied to estimate the existence of fundamental frequency. We provide experimental examples to demonstrate the general applicability of the harmonicity measure and apply the proposed procedure to Japanese continuous speech signals. The results show that the proposed method outperforms the conventional methods with or without the presence of noise.

In this paper, a novel type of the step-up high frequency transformer linked full-bridge soft-switching phase-shift PWM DC-DC power converter with ZVS and ZCS bridge legs is proposed for small scale fuel cell power generation systems, automotive AC power supplies. A tapped inductor filter with a freewheeling diode is implemented in the proposed soft-switching DC-DC power converter to minimize the circulating current in the high-frequency step-up transformer primary side and high-frequency inverter stage. Using a tapped inductor filter with a freewheeling diode makes possible to reduce the circulating current without any active switches and theirs gate-drive circuits. The operating principle of the proposed DC-DC power converter with each operation mode during a half cycle of the steady state operation is explained. The optimum design of the tapped inductor turns ratio is described on the basis of the circuit simulation results. Developing 1 kW 100 kHz prototype with power MOSFETs and 36 V DC source verifies the practical effectiveness of the proposed soft-switching DC-DC power converter. The actual efficiency of the proposed DC-DC power converter is obtained 94% for the wide load and output voltage variation ranges.

A stability of the cascade two-stage Power-Factor-Correction converter is investigated. The first stage is boost PFC converter to achieve a near unity power factor and the second stage is forward converter to regulate the output voltage. Previous researches studied the system using linear analysis. However, PFC boost converter is a nonlinear circuit due to the existence of the multiplier and the large variation of the duty cycle. Moreover, the effect of the second stage DC/DC converter on the first stage PFC converter adds more complexity to the nonlinear circuit. In this issue, low-frequency instability has been detected in the two-stage PFC converter assuring the limitation of the prior linear models. Therefore, nonlinear model is proposed to detected and explain these instabilities. The borderlines between stable and unstable operation has been made clear. It is cleared that feedback gains of the first stage PFC and the second stage DC/DC converters are the main affected parts to the total system stability. Then, a simplified nonlinear model is provided. Experiment confirm the two models with a good agreement. These nonlinear models have introduced new PFC design scheme by choosing the minimum required output capacitor and the feedback loop design.

In wide-area wireless access systems such as satellite communications systems and stratospheric platform systems, electric power supplies for radio communications are realized using solar photovoltaic cells and/or fuel cells. However, the on-board weight limits restrict the number of cells that can be equipped. In addition, the transmission power of such systems is limited taking account of issues and regulations on sharing the same frequency band with other systems. Hence, both the frequency band and electric power is limited, which are crucial radio resources for those systems. Although radio channel allocation methods taking account of the frequency constraint only or the power constraint only have been proposed, radio channel allocation methods taking account of both constraints simultaneously have been insufficiently studied. This paper proposes a radio channel allocation method that provides global optimum allocation results by utilizing the linear programming method. The proposed method has features such that the method first allocates radio channels in proportion to the traffic demand distributed over the service coverage area and then maximizes the total radio channels allocated to systems. Numerical results are presented for a stratospheric platform system that covers an area of Japan, as an example, to demonstrate that the proposed method optimally allocates radio channels taking account of both constraints while efficiently allocating excess resources. In addition, whether a system reaches either the frequency or power limit can be estimated, by investigating the radio channel allocation results. Furthermore, enhanced linear programming models based on a method aiming at practical use of the radio channel allocation results in operation are also introduced. The enhanced model is demonstrated to work effectively to avoid unbalanced radio channel allocations over geographical areas. The proposed method and linear programming models are useful not only for making pre-plans but also for determining the amount of necessary frequency and power resources in designing systems.

A new circuit technique based on pass-gate logic with dynamic supply-voltage and clock-frequency control is proposed for a low-power motion-vector detection VLSI processor. Since the pass-gate logic style has potential advantages that have small equivalent stray capacitance and small number of short-circuit paths, its circuit implementation makes it possible to reduce the power dissipation with maintaining high-speed switching capability. In case the calculation result is obtained on the way of calculation steps, additional power saving is also achieved by combining the pass-gate logic circuitry with a mechanism that dynamically scales down the supply voltage and the clock frequency while maintaining the calculation throughput. As a typical example, a sum of absolute differences (SAD) unit in a motion-vector detection VLSI processor is implemented and its efficiency in power saving is demonstrated.

Direct digital frequency synthesizers (DDFS) provide fast frequency switching with high spectral purity and are widely used in modern spread spectrum wireless communication systems. ROM-based DDFS uses a ROM lookup table to store the amplitude of a sine wave. A large ROM table is required for high spectral purity. However, a larger ROM uses more area and consumes more power. Several ROM compression methods, including Sunderland technique based on simple trigonometric identities and quantization & error compensation techniques, have been reported. In this paper, we suggest several new techniques to reduce the ROM size. One new technique uses more number of hierarchical levels in ROM structures. Another technique uses simple interpolation techniques combined with hierarchical ROM structures. Experimental results show that the new proposed techniques can reduce the required ROM size up to 24%, when compared to that of a resent approach.

The relation between resonant frequency of micromirror with vertical combdrives and applied voltage between the upper and lower comb teeth was analyzed. Resonant frequency of the micromirror was controlled by stiffness of the torsion hinge. Resonant frequency of the mirror was proportional to the applied voltage between the upper and lower comb teeth at the same tilt angle.