Human tissues conduct electricity about as well as semiconductors. However, there are large differences between tissues which have recently been shown to be determined mainly by the structure of the tissue. For example, the impedance spectrum of a layered tissue such as skin is very different to that of the underlying tissues. The way in which the cells are arranged and also the size of the nucleus are both important. Some of the recent developments in measurement and modelling techniques are described and the relationship between tissue structures and impedance spectra is outlined. The illustrations and examples look at the effect of premalignant changes on localised impedance spectra measured from cervical tissues. Electrical Impedance Tomographic measurements on lung tissue are used to show the maturational changes of lung structure in neonates. The conclusion contains some speculation as to what further research outcomes might occur over the next few years.

For multimedia communications, the computational scalability of a multimedia codec is required to match with different working platforms and integrated services of media sources. In this paper, two condensed stochastic codebook search approaches are proposed to progressively reduce the computation required for the algebraic code excited linear predictive (ACELP) and multi-pulse maximum likelihood quantization (MP-MLQ) coders. By reducing the candidates of the codebook before search procedure, the proposed methods can effectively diminish the computation required for the ITU-T G.723.1 dual rate speech coder. Simulation results show that the proposed methods can save over 50 percent for the stochastic codebook search with perceptually intangible degradation in speech quality.

We have developed a 200-channel imaging system that enables measurement of changes in oxygenation and blood volume and that covers a wider area (45 cm 15 cm) than that covered by conventional systems. This system consisted of 40 probes of five channels, a light-emitting diode (LED) driver, multiplexers and a personal computer. Each probe was cross-shaped and consisted of an LED, five photo diodes, and a current-to-voltage (I-V) converter. Lighting of the LEDs and acquisition of 200-channel data were time-multiplexed. The minimum data acquisition time for 200 channels, including the time required for calculation of oxygenation and monitoring of a few traces of oxygenation on a computer display, was about 0.2 s. We carried out exercise tests and measured the changes in oxy- and deoxy-hemoglobin concentrations in the thigh. Working muscles in exercises could be clearly imaged, and spatio-temporal changes in muscle oxygenation during exercise and recovery were also shown. These results demonstrated that the 200-channel imaging system enables observation of the distribution of muscle metabolism and localization of muscle function.

The frequency- and time-domain expressions are derived for the signal-to-noise power ratio (SNR) of an ideal Rake combiner output in a direct sequence spread spectrum (DS-SS) mobile communication system. The derived SNR expressions make it possible to estimate the SNR statistics after Rake combining for an arbitrary spreading chip rate in the frequency-selective multipath channel.

A new objective speech quality measure, Bark Coherence Function is presented. The Coherence Function was used for evaluating the non-linear distortion of low-to-medium rate speech coders. However, it is not well suited for quality estimation in modern speech transmission, especially, CDMA mobile communication system. In the proposed method, Coherence Function is newly defined in psycho-acoustic domain as the cognition module of perceptual speech quality measure and evaluates the perceptual non-linear distortion of mobile system. The experimental results showed that the proposed method has good performance over CDMA PCS and digital cellular system.

We have developed optical encoding devices for processing femtosecond pulses. These devices are based on spectral separation devices and light modulators with fiber gratings. Experiments were made to encode a light pulse in the spectral domain. These experiments utilize the characteristics that a femtosecond light pulse has a very broad spectrum. An input femtosecond light pulse is decomposed into a series of wavelength components. Each wavelength component with narrow spectra <1 nm width is successfully extracted into a single mode fiber. Light modulators corresponding to wavelength components are assigned to the 1st bit, the 2nd bit, the 3rd bit, , the nth bit, respectively. All of the encoded wavelength components are again recombined into a single time-varying signal and transmitted through an optical fiber. Decoding at receiving site is made by the reverse operation. Encoding and decoding for 2-bit and 4-bit signals were demonstrated for 200 fs input light pulse with about 40 nm spectral width.

This study is intended to realize an in-situ gas sensor based upon the principle of millimeter/submillimeter wave spectroscopy. In-situ gas sensor will be attractive because of gas selectivity, multiple parametric measurement such as gas temperature, pressure and density, and of the in-situ measurement capability. One of the major technical problem to be solved is to develop an instrument accurate enough to discern the spectrum change due to the variation of parameters such as temperature. In this paper a proposed gas absorption measurement system is investigated, which schematically consists of Fabry-Perot type gas cell for effective long path length, and vector signal processing to reject leak signal coupled between resonator input and output ports so as to achieve precise absorption measurement. Also included is an parametric study of oxygen absorption characteristics, which is served as the predicted value in the evaluation of the instrument. The experiment at 60 GHz and 120 GHz bands using oxygen demonstrates the effectiveness of the current system configuration.

This paper described a new method to generate a spread spectrum clock for the purpose of EMI reduction. This method uses two phase-locked loops (PLL). The output of the first PLL is locked to its input of 14.318 MHz. The VCO in this PLL is used to produce 32 outputs with the same frequency and each with 11.25 degrees phase variation. A digital spread spectrum generator uses these 32 signals to generate the desired spread spectrum signal by phase hopping technique. These two circuits form a spread spectrum digital PLL (SSDPLL). The second PLL is configured as a conventional frequency synthesizer. It can be programmed to generate the desired frequencies. The second PLL also serves as a low pass filter of the output of the SSDPLL to smooth out frequency variation. This circuit was implemented with a 0.6 µm single poly CMOS process. The active areas of the SSDPLL and the synthesizer are 826396 µm2 and 790298 µm2, respectively. The total power consumption is 99 mW at 3.3 V supply. The peak power of the spread spectrum clock is reduced by 10 dBm at 14.318 MHz output with a 2.34% frequency spreading. The reduction of peak power increases with output frequency.

In this paper, we describe a frame synchronization method for bi-orthogonal modulation systems. In bi-orthogonal modulation systems, several bi-orthogonal sequences are used for data transmission. Frame synchronization in bi-orthogonal modulation systems is difficult because transmitted sequences can change every frame. In the proposed method, each bi-orthogonal sequence consists of two different inner sequences. Each bi-orthogonal sequence has the same arrangement of two different inner sequences. A receiver can track the frame timing by observing the arrangement of inner sequences. In this paper, we analyze the bit error rate performance that takes into account the tracking performance of a system we developed based on our method. The spectral efficiency of the proposed system in code division multiple access (CDMA) systems is also investigated. As a result, we found that the proposed system is effective in synchronous CDMA systems.

PSK coherent demodulation has difficulty in achieving high speed carrier extraction and symbol synchronization when implementing to slow FH-SS radio system. On the other hand, implementation to FPGA has the requirement of a small gate size to design because of FPGA cost issue. We developed a QPSK coherent demodulation digital modem for FH-SS radio systems using FPGA by solving problems. The designed modem performs symbol synchronization with no carrier extractions, under the limitation of the small gate size requirement. The modem employs shift arithmetic operation and a comb digital BPF to achieve very good synchronization lock-up performance with small gate size. In this paper, the symbol synchronization and the carrier tracking scheme are mainly discussed. Analysis of its performance and stability are also explained. The achievement of its very good performance is presented by experimental measurement.

Power-line communication (PLC) systems have been assumed as the systems of low speed and low reliability. The low qualities of the systems, however, are not inherent of PLC but the result of inadequate design strategy of the systems. The systems with proper considerations of the characteristics of power-line as a communication medium achieve reliable high-speed data transmission in power-lines. In fact, the activities on the standardization of high-speed PLC systems have recently started in many countries, and variety of high-speed PLC systems are being to be purchased off-the-shelf. Following this trend of PLC, this manuscript first describes the features of power-line for communications and then explains technical issues on the design of PLC systems of the next generations as the infrastructure of information-communication technology age.

Network bandwidth has rapidly increased, and high-speed networks have come into wide use, but overheads in legacy network protocols prevent the bandwidth of networks from being fully utilized. Even UDP, which is far lighter than TCP, has been a bottleneck on high-speed networks due to its overhead. This overhead mainly occurs from per-byte overhead such as data copy and checksum. Previous works have tried to minimize the per-byte overhead but are not easily applicable because of their constraints. The goal of this paper is to investigate how to fully utilize the bandwidth of high-speed networks. We focus on eliminating data copy because other major per-byte overhead, such as checksum, can be minimized through hardware. This paper introduces a new concept called Asynchronous UDP and shows that it eliminates data copy completely. We implement Asynchronous UDP on Linux with ATM and present the experiment results. The experiments show that Asynchronous UDP is much faster than the existing highly optimized UDP by 133% over ATM. In addition to the performance improvement, additional advantages of Asynchronous UDP include: (1) It does not have constraints that previous attempts had, such as copy-on-write and page-alignment; (2) It uses much less CPU cycles (up to 1/3) so that the resources are available for more connections and/or other useful computations; (3) It gives more flexibility and parallelism to applications because applications do not have to wait for the completion of network I/O but can decide when to check the completion.

In this letter, we describe the conditions for measuring the nonlinear refractive index n2 when using the self-phase modulation-based cw dual-frequency method. We clarify the appropriate measurement conditions for dispersion-shifted and conventional single-mode fibers both numerically and experimentally. We also show experimentally that the evaluated n2 values for conventional single-mode fiber depend on the signal wavelength separation.

This paper proposes iterative demodulation/decoding for parallel combinatorial spread spectrum (PC/SS) systems. A PC/SS system conveys information data by a combination of pre-assigned orthogonal spreading sequences with polarity. In this paper, convolutional coding with a uniform random interleaver is implemented in channel coding, just like as a serial concatenated coding. A 'soft-in/soft-out' PC/SS demodulator based on a posteriori probability algorithm is proposed to perform the iterative demodulation and decoding. Simulation results demonstrate that the proposed iterative demodulation/decoding scheme bring significant improvement in bit error rate performance. This proposed decoding scheme achieves high-speed transmission by two approaches. One is a puncturing operation, and the other is to increase the number of transmitting sequences. In the latter approach, lower error rate performance is achieved comparing with that the punctured convolutional code is used to increase the information bit rate.

This paper proposes an automatic dispersion equalization system using extracted clock power monitoring in order to facilitate the field installation of high-speed time-division multiplexed (TDM) systems over existing fiber cables. The proposed scheme adjusts the dispersion of a variable-dispersion equalizer so as to maximize the extracted clock power level. This scheme has a simple configuration, needs no communication channel between the transmitter and the receiver, and is sensitive to parameters such as initial chirping and fiber input power. The clock power dependence on the fiber dispersion is theoretically analyzed assuming that the return-to-zero (RZ) format is used and that pulse broadening is small compared to the bit duration. We show that the clock power is maximized when the dispersion-induced waveform distortion is minimized. Numerical simulations show that the proposed scheme is effective with the non-return-to-zero (NRZ) format and for the case that the optimum total dispersion deviates from zero due to initial and/or self-phase modulation (SPM)-induced chirping. The operation of the proposed automatic equalization system is experimentally confirmed in 20-Gbit/s transmission using both RZ and NRZ formats. Moreover, a 40-Gbit/s transmission experiment over 200 km of dispersion-shifted fiber (DSF) is successfully demonstrated using the proposed equalization scheme.

Spatiotemporal chaos in a multidomain regime in a Gunn-effect device is numerically investigated as an example of collective domain oscillations under global constraints. The dynamics of carrier densities are computed using a set of model partial differential equations. Numerical results reveal some distinctive and chaotic clustering features caused by the global coupling and boundary effects. The chaotic regime is then characterized in terms of a Lyapunov spectrum and Lyapunov dimension, the latter increasing with the size of the system.

A priming effect is studied for a three-electrode, surface-discharge AC-PDP, which has stripe barrier ribs of 0.22 mm pitch. It was found that by keeping the interval between the reset and address pulses within 24 µs, the data pulse voltage can be reduced while the data pulse width can be narrowed due to the priming effect. By adopting the primed addressing technique to the PDP, the data pulse voltage was reduced to 20 V when the data and scan pulse widths were 1 µs. Alternatively, the data pulse width could be narrowed to 0.33 µs when the data pulse voltage was 56 V. 69% of the TV field time could be assigned for the display periods with 12 sub-fields, assuring high luminance display.

Using a point matching method, we have numerically analyzed resonance frequencies and unloaded Q factor of whispering gallery modes in a millimeter wave region that are well known as an intrinsic mode of a dielectric disk resonator. We express field distributions of the resonance modes by a summation of spherical waves. Tangential electromagnetic fields inside the disk are matched to those outside the disk at appropriate matching points on a boundary. As the result, a 4N 4N (N; number of matching points) determinant is derived as an eigenvalue equation of the disk resonator. Since elements of the determinant are complex numbers, a complex angular frequency is introduced to make a value of the determinant zero. For a location of the matching points, we also introduce a new technique which is derived from a field expression of the whispering gallery modes. Since an azimuthal angle dependence of the field distributions with a resonance mode number m is presented by the associated Legendre function Pnm(cos θ), we define abscissas θi of the matching points as solutions of Pm+2N-1m (cos θ) = 0. Considering the field symmetry, we also modify the eigenvalue equation to a new eigenvalue equation which is expressed (4N - 2) (4N - 2) determinant. From the results of our numerical analysis, we can find that the resonance frequencies and unloaded Q factor well converge for number of matching points N. A comparison of numerical results and experimental ones, in a millimeter wave band (50 - 100 GHz), shows a good agreement with each other. It is found that our analysis is effective for practical use in the same wave band.

We proposed a simple technique for measuring the effective zero-dispersion wavelength. In this study, we measured the effective zero-dispersion wavelength of a 25-km-long dispersion-shifted fiber (DSF) using the four-wave mixing (FWM) of a spectrum-sliced fiber amplifier light source, and then compared our results with other conventional techniques to confirm the validity of our method.

InP-based high electron mobility transistors (HEMTs) with gate lengths reduced to 30 nm were fabricated and characterized, and the effect of the gate recess on the high-frequency characteristics was studied. The cutoff frequency, which is regarded as a function of the gate length and the average carrier velocity in a first-order approximation, depends on the size of the gate recess when the gate length becomes short. The size of the gate recess is optimized by taking the feed-back capacitance and the parasitic resistance into account. For HEMTs having the gate recess with an InP surface, an appropriate widening of the gate recess gives a record cutoff frequency of 368 GHz for the 30-nm-gate HEMTs with a lattice-matched channel.