Enhancement of inversion-layer mobility and inversion-layer capacitance becomes more important in realizing scaled CMOS, from both viewpoints of higher performance and lower power consumption. This paper presents an engineering scenario of the subband structure in inversion layer for the enhancement of inversion-layer mobility and capacitance in MOSFETs. A key factor for the electron mobility enhancement is to increase the energy difference in the subband energy between the two-fold and the four-fold valleys and the resultant electron occupancy of the two-fold valleys. The electrical characteristics of two device structures based on this subband engineering, strained-Si MOSFETs and ultra-thin SOI MOSFETs, are studied. Also, it is shown that the reduction in SOI films down to less than inversion-layer thickness of bulk MOSFETs is an effective way to increase inversion-layer capacitance.

We studied various types of 2D and 3D Si-based photonic crystal structures that are promising for future photonic integrated circuit application. With regard to 2D SOI photonic crystal slabs, we confirmed the formation of a wide photonic bandgap at optical communication wavelengths, and used structural tuning to realize efficient single-mode line-defect waveguides operating within the bandgap. As regards 3D photonic crystals, we used a combination of lithography and the autocloning deposition method to realize complicated 3D structures. We used this strategy to fabricate 3D full-gap photonic crystals and 3D/2D hybrid photonic crystals.

We have developed a distributed optical fiber strain sensor for detecting the collapse of river embankments. The sensor uses a Brillouin optical time domain reflectometer (BOTDR) and consists of an optical fiber cable and pieces of nonwoven cloth. Pieces of cloth are fixed to the cable at 1.5-meter intervals and it is then embedded in a U-shaped configuration in a river embankment. The pieces of cloth are displaced when there is movement of the soil in which they are embedded. If one of two adjacent pieces of cloth remains stationary while the other moves, the optical fiber between the two pieces is stretched. The collapse of an embankment can be detected by using a BOTDR to monitor any such stretching in the 1.5-m lengths of fiber. The developed sensor operates at a sensitivity of 0.025%/kgf, which is equivalent to 0.067%/mm, and is thus capable of detecting soil movements of a few mm in river embankments. The sensor is also able to provide effective advance warning of the collapse of a river embankment resulting from water penetration. We subjected the sensor system to field tests that demonstrated the effectiveness of its construction and its long-term stability. The developed sensor system is an effective tool for use in river management systems of the very near future.

The Lorentzian-shape filter response of a microring resonator filter is not suitable to the practical use in WDM systems, because of the lack of pass band flatness, high cross talk, and the large wing in the stop band. Therefore, the tailoring of filter response shape is required to improve the performance. In this paper, the authors designed and demonstrated the box-like filter response of microring resonator filter by using the supermodes of stacked double microring resonators. The thicknesses of microrings and the separation between them were optimally designed to give the maximally flat response. A fine fabrication process was developed to achieve the deep and very smooth side wall. The shape factor, which is defined by the ratio of -1 dB bandwidth to -10 dB bandwidth, was successfully improved by three factors from 0.17 of Lorentzian shape to 0.51.

In this paper, we propose the multirate repeating method for alias free subband adaptive filters (AFSAFs) and consider its convergence property. It is shown that we can adjust the convergence speed and the final error of the adaptive filters by varying its two parameters according to the requirements of the applications where the method is applied. The proposed method has two parameters, namely, the number of channel and the number of repetition. We show that by increasing the number of channels we can reduce the final error, and this property is preferred when the signal-to-noise ratio (SNR) is low. On the other hand, we show that the convergence speed of the AFSAF approaches to that of the affine projection algorithm (APA) by increasing the number of repetition. Through the computer simulations, we show the effect of the proposed method.

In this article we present the subject of wideband channel modeling and simulation, stressing the method of orthogonalization. We compare the performance of this simulation method using Karhunen-Loeve, Wavelets and other basis over radio channels represented via the Input-Delay Spread Bello Function.

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.

In the literature, the optimum discrete interpolation approximation is presented. However, this approximation is the optimum for the union of the set of band-limited signals and the set of the corresponding approximation errors. In this paper, under several assumptions, we present two optimum extended discrete interpolation approximations such that the set of the corresponding approximation errors is included in the set of signals if we ignore some negligible component of error. In this paper, we assume that the decimated sampling interval T satisfies T M, where M is the number of paths of the filter bank. The maximally distinct or under sampled filter banks treated in this paper have FIR analysis filters with or without a continuous pre-filter and FIR synthesis filters with a band-limited continuous D/A filter. The first discussion is useful for designing a kind of down-converter which transforms HDTV signal with wide band-width to SDTV signal with narrow band-width, for example. In this discussion, we assume that the SDTV signal is limited in |ω|π/T and the Fourier spectrum of the HDTV signal has wider band but is approximately included in the corresponding narrow band of the SDTV signal. In the well-known scalable coding of signals, if the spectrum of a signal with higher resolution is not included approximately in the spectrum of the corresponding signal with lower resolution, the quality of the quantized output signal with lower resolution will become quite low practically. As shown in [3], however, scalable coding has received much attention recently in the fields of HDTV/SDTV compatibility. Therefore, it will be natural to consider that the spectrum of HDTV signal with higher resolution is similar to and is included approximately in the corresponding spectrum of SDTV signal with lower resolution. The analysis filters are FIR filters with a continuous pre-filter approximately band-limited in |ω|π/T. To improve the quality of the SDTV signal, the whole spectrum component of the HDTV signal is used in the presented down-converter. Another discussion is a general theory of approximation for filter banks using the prescribed analysis filters. In this discussion, although some modification for the band-width is introduced in the process of analysis, the final band-width of the receiver is limited in |ω| π. The FIR analysis filters do not have pre-filter. The condition imposing on the set of signals is more general than the corresponding condition in the first optimum approximation theory. Finally, we present the optimum transmultiplexer TR. In general, under the condition that the receiver filters are prescribed, a transmultiplexer has approximation error between the original signal and the transferred signal. However, the presented TR minimizes approximately the supreme value of arbitrary positive measures of approximation error that can be defined, totally or separately, with respect to all the channels. Note that, in the presented discussion, we can prescribe the degree of FIR filters used in TR, strictly.

We have proposed an intracell uplink of a spread-spectrum code-division multiple-access (SS-CDMA) flexible wireless network based on approximately synchronized (AS) CDMA. Since the AS-CDMA has no co-channel interference, complicated transmission power control (TPC) is not required. A modem of the AS-CDMA has been designed and implemented for the Japanese 2.4 GHz industrial, scientific and medical (ISM) band. Using the implemented modem, the degradation of Eb/N0 from the theoretical limit is 1.0 dB at a bit error rate (BER) of 10-3. Under 2-user environment, the degradation of carrier-to-noise ratio (CNR) is 0.5 dB at a BER of 10-3 when the desired-to-undesired signal ratio (DUR) is -20.3 dB. We have evaluated BER performances in cases of varying carrier frequency offset and median DUR with computer simulation. Under 8-user environment, at the carrier frequency offset of 0.3 ppm, the BER with the DUR of -16 dB is found to be 10-3. Using the AS-CDMA with a 4-step open-loop TPC technique, the design of intracell uplink is available.

The Orthogonal Frequency Division Multiplexing (OFDM) system is one of several suitable candidates for use in broadband wireless communications. However, due to multipath propagation, the received signal suffers from frequency-selective fading which causes significant degradation of system performance. Antenna diversity reception is widely used to solve this problem. However, this approach is not suitable for the downlink, because it increases the complexity and power consumption of the mobile station (receiver). In this paper, we consider closed-loop mode transmit diversity for OFDM, instead of diversity reception, to improve the performance in the downlink. The base station (transmitter) has several transmit antennas and each antenna is weighted by a weighting factor calculated based on feedback information (FBI). This system is a closed loop, since the FBI is fed back from the receiver. We propose a new weight generation scheme by making use of the correlation between adjacent OFDM subcarriers. The performance is evaluated under a broadband wireless channel model by computer simulation. The results show that the proposed weight generation scheme exhibits better performance than the conventional weight generation scheme without increasing the number of the FBI bits in the uplink.

New bandpass filters (BPFs) with stub resonators are proposed for creating multiple attenuation poles. Firstly, the stub-dependent characteristics of the distributed-element stubs are examined theoretically. Secondly, the new BPFs with resonators of combined stubs are proposed. An advantage of these filters is the possibility of controlling the number of attenuation poles. The design of the proposed filter is carried out based on the general filter design with the narrow-band approximation technique. The transmission and reflection characteristics of the proposed BPFs are also examined theoretically and experimentally. The miniaturization of the filters is also carried out using the resonator with loaded-element stubs. The discussions lead us to the conclusion that the proposed design method of the filters are useful for controlling the number of attenuation poles of the BPF.

This paper describes a simple design of a broad-band four-way power divider with 45-degree phase differences between output ports. In the first stage of our work, we present a new broad-band 90-degree power divider. The phase error of the power divider here is less than one-tenth of the conventional 90-degree branch-line hybrid. Next, an experimental UHF-band four-way power divider using a broad-band 90-degree power divider and two broad-band 45-degree power dividers is presented. Over the frequency range from 0.86 to 1.06 GHz, the experimental four-way power divider exhibits power splits of -6.420.25 dB, return losses of greater than 15 dB, errors in the desired relative-phase difference between output ports of less than 1 degree, and isolation between output ports of greater than 15 dB. This divider is useful for realizing low distortion and high efficiency amplifiers without the need for an isolator.

We propose the new and highly accurate design theory of the high Tc superconducting (HTS) miniaturized coplanar waveguide (CPW) bandpass filters (BPFs) with highly packed meanderlines. BPFs are designed using the external quality factor (Qe) and coupling constant (k) (Q-k method). These parameters are estimated from the transmission coefficient obtained by the 2.5-dimensional electromagnetic field simulator. Moreover, the Q-k method is compared with the J-b method (designed using admittance inverter and susceptance slope parameter) presented previously; in this way we confirmed that the Q-k method has higher accuracy than the J-b method. We realized the design of a the highly packed meanderline CPW BPF (5 pole, center frequency = 2 GHz, fractional band width = 15 MHz, ripple = 0.1 dB) in a 3.5 mm 8 mm substrate.

A new structure of a low-loss high temperature superconducting (HTS) filter is proposed by using quarter-wavelength coplanar waveguide (CPW) resonators. A 4-pole Chebyshev band-pass filter with the center frequency 5.0 GHz and the 0.01 dB-ripple fractional bandwidth 3.2% is designed based on the theory of direct-coupled resonator filters using K- and J-inverters. This filter is fabricated by using a high-Tc superconductive YBCO film deposited on a MgO dielectric substrate. The frequency response of the filter measured at 60 K agrees very well with the theoretical one. The insertion loss is 0.22 dB. The insertion loss of this filter is the lowest in HTS-CPW filters presented so far.

In leased line services used by ISPs (Internet Service Providers) the bandwidth is fixed, but the traffic changes dynamically. Therefore, there is a necessity for ISPs to accommodate extra capacity to meet peak usage demands; many resources are not used in off-peak hours. To address this, we propose an auction method for the dynamic allocation of bandwidth to ISPs sharing backbone networks. By this method, backbone networks can be used effectively as each ISP is able to secure bandwidth according to its own policy. The Internet users can also be expected to receive good services, as it enables them to obtain information about all ISPs, such as the access fee and QoS (quality of service) provided, and to select congenial ISPs from among all ISPs according to this information. In this study, we compare a dynamic bandwidth allocation service with a leased line service (fixed allocation of bandwidth to ISPs) by using the users' utility to estimate the effectiveness of the proposed method.

This paper proposes list Viterbi equalizers (LVEs) that use two kinds of metric criteria for wide-spread time-dispersive channels to achieve a good trade-off between complexity and bit error rate (BER) performance. For Viterbi equalization employing a state-reduction algorithm, the modified metric criterion proposed by Ungerboeck is not always equivalent to the squared Euclidean distance metric criterion. This paper proposes the following two schemes for the LVE: (1) to combine two kinds of metric criteria like combining diversity; (2) to select the metric criterion like selection diversity according to the channel impulse response. Finally, computer simulation shows that the proposed schemes improve BER performance on wide-spread frequency selective fading channels, even if the proposed schemes have smaller complexity than the conventional one.

This paper describes 2.4-GHz-band front-end building circuits--a down conversion mixer (DCM), a dual-modulus divide-by-4/5 prescaler, a transmit/receive antenna switch (SW), a power amplifier (PA), and a low noise amplifier (LNA). They are fabricated using a standard bulk 0.18 µm CMOS process with a lower current consumption than bipolar circuits, and can operate at the low supply voltage of 1.8 V. Meshed-shielded pads are adopted for lower receiver circuit noise. Pads shielded by metals become cracked when they are bounded, therefore silicided active areas are used as shields instead of metals to avoid these cracks. The meshed shields achieve lower parasitic pad capacitors without parasitic resistors, and also act as dummy active areas. The proposed DCM has a high IP3 characteristic. The DCM has a cascode FET configuration and LO power is injected into the lower FET. By keeping the drain-source voltage of the upper transistor large, the nonlinearity of the drain-source transconductance is reduced and a low distortion DCM is realized. It achieves a higher input referred IP3 with a higher conversion gain for almost the same current consumption of a conventional single-balanced mixer. The output referred IP3 is higher 5.0 dB than the single-balanced mixer. The proposed dual-modulus prescaler employs a fully-differential technique to achieve stable operation. In order to avoid errors, the fully-differential circuit gives the logic voltage swing margins. In addition, the differential technique also reduces the noise effect from the supply voltage line because of the common-mode signal rejection. The maximum operating frequency is 3.0 GHz, and the one flip-flop power consumption normalized by the maximum operating frequency is 180 µW/GHz.

A novel optical transmission line consisted of fibers characterized by positive and negative medial dispersion of NZ-DSF and SMF was designed and fabricated. Both P-MDF and N-MDF have achieved the medial dispersion and low non-linearity simultaneously. Total characteristics were confirmed to be suitable for the future high-bit-rate transmission.

In this paper, a new multi-engine architecture for the baseband modem LSI of W-CDMA systems is proposed. The developed test chip with this architecture is also presented. In the multi-engine architecture, processors and wired logic are combined to obtain both flexibility and low power dissipation. Multiple processors are used in the LSI to lower its operating frequency by distributed processing. A customized processor is used to lower the overhead of multiple processors in terms of LSI scale. The test chip was fabricated with a 0.25-µm process. Its measured power dissipation for simultaneous 384 kbit/s downlink reception and 64 kbit/s uplink transmission was 160 mW.

The provisioning of QoS in the Internet is gaining an increasing attention, thus the importance of methods capable of estimating the bandwidth requirement of traffic flows is constantly growing. This information can be used for a wide range of purposes. Admission control, QoS routing and load sharing all need the same basic information in order to be able to make decisions. This paper describes a number of methods that can be used to arrive at precise estimates of the bandwidth requirement focusing on those that are based on the theory of large deviations. A methodology is presented that allows the reformulation of earlier solutions based on the estimation of some form of an overflow probability so that their output becomes a bandwidth-type quantity, the format preferred by Internet control applications. The methodology provides two tracks for the conversion: an indirect method that encapsulates the overflow probability-type approach as an embedded calculation and a direct method that immediately results in the estimate of the bandwidth requirement. The paper introduces a novel method for the direct computation of the bandwidth requirement of Internet traffic flows using the many sources asymptotic regime of the large deviation theory. The direct bandwidth estimator method reduces the computational complexity of the calculations, since it results directly in the bandwidth requirement, allowing the omission of the frequent and costly computation of the buffer overflow probability. The savings arising from the reduction in computational complexity are demonstrated in a numerical example.