We have experimentally observed the dynamics of laser outputs in a microchip laser with frequency-modulated feedback light. We have observed rich dynamics that can be interpreted as three types of dynamics at different frequencies: (1) periodic bursts at twice of the frequency of the modulation of the external mirror, (2) chaotic pulsations at the relaxation oscillation frequency, and (3) clusters at the instantaneous Doppler-shifted frequency. We have confirmed these rich dynamics by using numerical simulations.

Microstrip antennas with meshed ground planes are suitable for radiation elements of large satellite phased array antennas. Although they have some mechanical advantages such as the possibility of antenna weight reduction, they also cause electrical problems such as the resonant frequency shift and F/B ratio degradation. The first purpose of this paper is the analytical understanding of the resonant frequency shift, for which two perturbational methods are proposed. One has a closed form expression that provides some useful design data. The other is to solve the integral equations by using the periodicity of the meshed ground plane, which gives more accurate results. The second purpose of this paper is to investigate the backward radiation from the meshed ground plane analytically, for which we derive an analysis method from the calculated results of the resonant frequency shift. The proposed methods are verified with the measured ones.

This paper proposes a multi-hop wireless link system for radio access networks (RANs) of new generation mobile communication systems. The performance of the multi-hop wireless link system is evaluated from the viewpoints of total output power, co-frequency interference characteristics, and the system frequency bandwidth based on a comparison with that of the single-hop wireless link system, which is currently used as a RAN. The proposed system is effective in realizing an enormous approach link capacity from both the total output power and the co-frequency interference viewpoints. From the system frequency bandwidth viewpoint, the optimum number of relays in the multi-hop connection is determined to be three hops in a line-of-sight propagation environment in order to minimize the frequency bandwidth for transferring traffic. We conclude that the multi-hop wireless link system is suitable for new generation mobile communication systems.

In this paper, we propose a novel higher order time-frequency distribution (GDH) for a discrete time signal. This distribution is defined over the original discrete time-frequency grids through a delicate discretization of an equivalent expression of a higher order distribution, for a continuous time signal, in [4]. We also present a constructive design method, for the kernel of the GDH, by which the distribution satisfies (i) the alias free condition as well as (ii) the marginal conditions. Numerical examples show that the proposed distributions reasonably suppress the artifacts which are observed severely in the Wigner distribution and its simple higher order generalization.

Methods that precisely compensate for propagation distortion using pilot symbols are widely used in mobile communications. We describe such a pilot-symbol-assisted technique for precise compensation of flat fading and frequency offset. This technique provides a wide range of offset compensation. Conventional methods using fast Fourier transform (FFT) compensate for both slow and fast fading, but their tolerable range of frequency offset is very limited. By composing a system with an approximate frequency estimator, we can estimate and compensate for fading and a large frequency offset at the same time. The estimation and compensation are carried out by periodic pilot symbols and no other index sequences are needed. This method enables high-data-rate transmission. We describe the method and provide a theoretical analysis for the compensable range of fading and frequency offset for a transmission frame structure with pilot symbols. Then, we evaluate the method by computer simulation.

In an orthogonal frequency division multiplexing (OFDM) system, the bit error performance is degraded in the presence of multiple propagation paths whose excess delays are longer than the Guard Interval (GI), because the orthogonality between subcarriers cannot be maintained. Therefore, the GI has to be long enough for an expected delay spread of the channel. On the other hand, a long GI causes a decrease in transmission efficiency. In this paper, we propose a new OFDM demodulation method with a variable effective symbol duration, in order to improve the bit error performance in the presence of multipaths whose excess delays are longer than the GI. The proposed method can realize more stable radio communication systems under a multipath propagation environment even if a propagation path whose excess delay is longer than the GI exists. In other words, the proposed method can improve transmission efficiency without performance degradation by a shortened GI under the same environment. The principle of the proposed method is explained, and the bit error probability of the proposed method is analyzed theoretically in an AWGN channel and a multipath fading channel. The performance of the proposed method is then evaluated by computer simulation. The results show that the proposed method improves the system availability under more various multipath fading environments without changing the system parameters.

This paper describes a single-chip RF transce-iver LSI for 2.4-GHz-band Bluetooth applications. This chip uses a 0.5 µm BiCMOS process, which provides 23 GHz fT. The LSI consists of almost all the required RF and IF building blocks--a power amplifier (PA), a low noise amplifier (LNA), an image rejection mixer (IRM), channel-selection filters, a limiter, a received signal strength indicator (RSSI), a frequency discriminator, a voltage controlled oscillator (VCO), and a phase-locked loop (PLL) synthesizer. The transceiver consumes 34.4 mA in TX mode (PA, VCO, PLL) and 44.0 mA in RX mode (LNA, IRM, channel-selection filters, limiter, RSSI, frequency discriminator, VCO, PLL). Direct-up conversion with a frequency doubler is used for the TX architecture. In order to avoid the VCO pulling, we used a 1.2 GHz VCO with the frequency doubler. In the receiver section, a low-IF single conversion RX architecture is employed for the integration of the channel-selection filters. The transceiver has a proposed linear frequency discriminator with a wide input range. The wide input-frequency range discriminator is required to realize the lower IF RX architecture because of the higher ratio of frequency deviation to the center IF frequency. The discriminator is the delay line type, and consists of a mixer and a delay line circuit with a locked loop. The delay line connects to one input terminal of the mixer. By using the delay locked at one fourth of the period of the IF frequency, a quadrature phase shift IF signal is applied to the mixer input terminal. For the frequency discriminator, the DC output voltage changes in proportion to the input frequency and a wide input range is achieved. This RF transceiver sufficiently satisfies all the target specifications for short-range Bluetooth applications. By using this chip, a -80 dBm sensitivity is obtained for the 10-3 BER, and the transceiver can deliver an output power of over 0.0 dBm.

The optical pulses of 50 MHz has been obtained from an organic light emitting diode (OLED) based on the Alq3 emissive layer with the active area of 0.01 mm2. We demonstrate that the OLEDs can be applied to fields of optical communication as the electro-optical conversion device for transmitting the signals of moving picture.

This paper proposes a novel space diversity reception scheme suitable for packet-based orthogonal frequency division multiplexing (OFDM) wireless access systems that achieves large diversity gain by improving the accuracy of both carrier frequency synchronization and phase tracking. Phase tracking compensates the phase rotation caused by residual carrier frequency error and phase noise and is necessary for high data rate OFDM systems that use coherent detection. In the proposed scheme, the accuracy of carrier frequency synchronization is improved by combining the information of the carrier frequency offset detected on all diversity branches; the accuracy of phase tracking is improved by using pilot signals whose signal to noise ratio (SNR) is raised by maximal ratio combining of the pilot signals extracted from all branches. Computer simulation results show that the proposed scheme effectively improves the diversity gain even in severe environments such as those with low carrier to noise ratios (CNR) and large delay spreads.

We propose a subchannel power control scheme in the OFDM system, which transmits data with a variable power level for each subchannel based on the received SNR. The OFDM system, employing the D-QPSK modulation and the proposed subchannel power control with a grouping coefficient equal to 3, gives about 2.3 dB gain in Eb/N0 comparing with the conventional OFDM system, under the two-ray multipath channel with the mean value of the second-ray's attenuation coefficient equal to 0.25, for the required BER equal to 10-5.

Cutoff frequencies and the modal fields in hollow conducting waveguides of arbitrary cross section are frequently calculated by the method of solving integral equations. This paper presents some improvements for the method by the integral equations. The improved method can calculate the cutoff frequencies and the modal fields only by using the real number, and this method can remove extraneous roots when calculating the cutoff frequencies. The former method calculates the cutoff frequency and the fields only at the cutoff frequency, but the improved method can calculate the fields at arbitrary phase constants.

In this paper, a time-to-digital converter in which the digital output is obtained without delay time is proposed. The circuit consists of a time-to-voltage converter, voltage-to-frequency converter, and counter. In the time-to-voltage converter, a capacitor is charged with a constant current during the input time interval. The change in the capacitor voltage is proportional to the input time and the capacitor voltage can be converted into a pulse signal with the voltage-to-frequency converter. The frequency of the pulse signal is directly proportional to the peak capacitor voltage and the pulse signals are counted to obtain the digital output. In the proposed circuit, the input time interval can be easily controlled and the resolution of the digital output can be improved by controlling the passive devices such as the capacitor and resistor.

We propose a set of Fabry-Perot etalons integrated in a planar lightwave circuit (PLC-FPE) designed for a unified system for broadcasting and communication. A PLC-FPE containing four etalons having different cavity lengths is fabricated and their loss and frequency characteristics are investigated. The total loss and the maximum finesse were found to be 8 dB and 34, respectively.

In this paper, a CMOS data recovery PLL for DVD-ROM is described. Some techniques have been introduced to alleviate the specifications required to analog circuits. A new phase detector alleviates the timing specification of a delay line and a pulse generator. A new frequency detector increases the capture range up to 8% of the center frequency. We have achieved to realize the data recovery PLL that operates at DVD-ROMx14 speed.

In this paper, a novel method to reduce additive time-varying noise is proposed. Unlike the previous methods, the proposed method requires neither the assumption about noise nor the estimate of the noise statistics from any pause regions. The enhancement is performed on a band-by-band basis for each time frame. Based on both the decision on whether a particular band in a frame is speech or noise dominant and the masking property of the human auditory system, an appropriate amount of noise is reduced in time-frequency domain using modified spectral subtraction. The proposed method was tested on various noisy conditions: car noise, F16 noise, white Gaussian noise, pink noise, tank noise and babble noise. On the basis of segmental SNR, inspection of spectrograms and MOS tests, the proposed method was found to be more effective than spectral subtraction with and without pause detection in reducing noise while minimizing distortion to speech.

Recent advances make it possible to mitigate a number of drawbacks of conventional phase locked loops. These advances permit the design of phase tracking system with much improved characteristics that are sought after in modern communication system applications. A new phase tracking system is outlined which reduces the effects of VCO phase noise to an insignificant level. This fact permits extremely narrow bandwidth phase tracking systems to be realized, even when a VCO with poor phase noise characteristics is employed. The improvement in performance over conventional phase locked loops is analyzed. The new phase tracking system also has other benefits such as precise centre frequency and elimination of peaking in the transfer function. To implement the phase tracking system requires a frequency measurement. We outline a new highly integrated frequency measurement method suitable for narrow bandwidth applications. Experimental results from a prototype confirms theoretical results.

The constant-Q based wavelet transform is the most effective means of quantitatively characterizing high frequency transient signals. This study develops a novel non constant-Q based multi-resolution transform (NCQM) and provides a precision analysis descriptor for both low and high frequency transients. The properties of this novel NCQM kernel are thoroughly examined and then the striking conceptual resemblance, energy conservation characteristic, and power spectrum close forms are derived. The rapid algorithm of NCQM is also presented and its excellent performance in noisy environments is demonstrated.

We have fabricated and characterized two types of high-Tc planar SQUID gradiometers having different line width of pickup loops. The device worked in flux-locked loop (FLL) operation even in laboratory environment without any shielding. A magnetic field gradient resolution of a parallel-type device in a lightly shielded room was about 0.5 pT/cmHz1/2 at 1 kHz and 2 pT/cmHz1/2 at 1 Hz. The device was possible to record magnetocardiograms in a shielded room. QRS-complex peaks of about 10 pT PP/4mm are clearly observed. For a mesh-type device, the increase of low frequency noise in the open laboratory environment was less than that for a parallel-type.

In this letter, an algorithm that estimates one of the most important channel parameters, maximum Doppler frequency, fD, is proposed. The algorithm uses phase variations of received pilot signals, which is strongly related with fD in a fading environment. In addition, a phase variation measurement method for binary phase shift keying (BPSK) modulated signals is also proposed and it makes possible to estimate fD from BPSK modulated information signals as well as unmodulated pilot signals. The results show that the proposed algorithm is very simple and shows good performance over wide Doppler frequency range.

This paper describes the circuit design procedure of the zero-current soft switching (ZCS) high frequency inverter for induction heating uses. Its output power can be regulated from its maximum to minimum by the instantaneous current vector control scheme using phase shift control between switching units at a fixed frequency. In addition, it can be safely operated since no extraordinarily high voltage or current results even at a short-circuit period at the load. Also, its overall efficiency reaches 90%. The detailed load and frequency characteristics of the inverter are elucidated by the computer-aided simulation. Then, the circuit design procedure is presented, and practical numerical examples are obtained according to this procedure which reveal that the inverter is highly practical and the design procedure is effective. The trial inverters yielding 2 kW or 4 kW were actually prepared. The observed values of the voltages and currents of the inverters were found to be in good agreement with the calculated ones. These facts certificate the validity of the proposed design procedure.