In this paper, we present orthogonal multi-code CDMA systems with the constant amplitude transmission. In general, the dynamic range of the amplitude of the transmitting signal is very large in the case of orthogonal multi-code CDMA systems. In order to realize the constant amplitude transmission for orthogonal multi-code CDMA systems, we propose a constant amplitude coding. First, we show the basic concept of the constant amplitude coding. And then, we show that the constant amplitude transmission can be realized by the combination of the conventional orthogonal multi-code CDMA and the constant amplitude coding. Finally, the effectiveness of the proposed method is evaluated in terms of the bit error rate performance and it is shown that the proposed method is robust to the non-linear distortion caused by a high power amplifier (HPA).

Considering that the application of the direct-sequence slotted spread ALOHA communications system to access/control channel is effective in communications systems with traffic channels operating at CDMA mode, the spread ALOHA communications system is discussed in terms of the system configuration and transmission efficiency. The transmission efficiency of the spread ALOHA communications system using a unified spread code is derived by means of two methods. One is based on the simulation of demodulation algorithm, and the other is based on the approximation by modeling. It becomes obvious from quantitative evaluation in terms of the probability of packet success and the throughput performance that the approximated results coincide with the simulated results, and that the modeling is very effective to estimate the transmission efficiency of the spread ALOHA communications system.

This paper proposes and investigates a vehicular radar system that can measure the distance to, the relative speed of and the direction of arrival (DOA) of the reflected waves from multiple targets or vehicles using the direct-sequence spread spectrum (DS-SS) technique. In particular, we propose a DOA estimation scheme using a multi-beam antenna. In order to show that the proposed system can accurately measure the above mentioned quantities, the performance is evaluated numerically in a multipath environment. Moreover, optimal multi-beam pattern is derived to minimize error probability of DOA estimation.

The efficiency and reliability of an ultrasonic motor, operating in longitudinal-torsional degenerate-mode, are investigated. It is essential to miniaturize both longitudinal and torsional mode piezoelectric ceramic elements, in order to produce low-cost ultrasonic motors, and to realize a motor with low battery power consumption. The ultrasonic motor is designed with an accurate mechanical equivalent circuit, which can produce high design precision notwithstanding low computation cost. It is important in this design that the resonant frequencies of longitudinal mode and torsional mode coincide with each other under the pertinent rotor pressing force and longitudinal and torsional mode piezoelectric ceramic elements are located in the vibration nodes for the longitudinal mode and the torsional mode, respectively. As a result, the fabricated motor, whose rotor diameter was 12 mm, produced 480 r.p.m. no-load revolution speed, 0.55 kgfcm maximum torque, 50% maximum efficiency, 2.5 W consumed power and a lifetime over 1000 hours with continuous rotation.

This paper proposes an analysis method of scaling-factor-quantization error in fractal image coding using a state-space approach with the statistical analysis method. It is shown that the statistical analysis method is appropriate and leads to a simple result, whereas the deterministic analysis method is not appropriate and leads to a complex result for the analysis of fractal image coding. We derive the output error variance matrix for the measure of error and define the output error variance by scalar quantity as the mean of diagonal elements of the output error variance matrix. Examples are given to show that the scaling-factor-quantization error due to iterative computation with finite-wordlength scaling factors degrades the quality of decoded images. A quantitative comparison of experimental scaling-factor-quantization error with analytical result is made for the output error variance. The result shows that our analysis method is valid for the fractal image coding.

A switched-capacitor Wien bridge oscillator and its automatic gain controller are discussed for low-frequency generation. The dc voltage Vs related to the amplitude of oscillation is obtained from the voltage differences in the frequency-determining arm. Theoretical analysis of the ripples in Vs is reported.

This paper describes the 10-bit 50 MS/s pipelined CMOS A/D Converter using a "reference feed-forward architecture." In this architecture, reference voltage generated in a reference generator block and residual voltage from a DA/subtractor block are fed to the next stage. The reference generator block and DA/subtractor block are constructed using resistive-load, low-gain differential amplifiers. The high-gain, high-speed amplifiers consuming much power are not used. Therefore, the power consumption of this ADC is reduced. The gain matching of the reference voltage with the internal signal range is achieved through the introduction of the reference generator block having the same characteristics as a DA/subtractor block. Each offset voltage of the differential amplifier in the reference generator block and the DA/subtractor block is canceled by the offset cancellation technique, individually. In addition, the front-end sample/hold circuit is eliminated to reduce power consumption. Because of the introduction of high-speed comparators based on the source follower and latch circuit into the first stage A/D subconverter, analog bandwidth is not degraded. This ADC has been fabricated in double-polysilicon, double-metal, 0.5µm CMOS technology, and it operates at 50 MS/s with a 300-mW (Vdd=3.0 V) power consumption. The differential linearity error of less than +/-1 LSB is obtained.

This paper presents a distributed power control scheme for next-generation multiservices CDMA systems. CDMA has inherent capability to control the quality-of-service (QoS) requirements by assigning different power levels to each traffic type. Toward this, optimum power control schemes have been investigated. The main drawback of the previously proposed algorithms is that they would require all users' transmission state necessiating a complicated control process or peak-rate badnwidth allocation. To overcome this, we exploit the Markovian property to obtain the statistics of the traffic. The statistical formulation is presented for allocating power distributedly so as to keep the "collision" probability below a predefined probability. Numerical examples show that the distributed power control scheme allows better utilization of wireless resources through statistical multiplexing than peak-rate bandwidth assignment, and it does not require a complicated control process while keeping total transmitted power at slightly greater than optimum power control.

A wireless communications system with a transmission rate of 10 Mbit/s using Japanese ISM band (2471-2497 MHz) is presented. This system employs a novel spread spectrum multiple access method named "CFO-SS (Carrier Frequency Offset-Spread Spectrum)" method. In the CFO-SS system, a single PN code is commonly assigned to all the multiple carriers, and the frequency offset between the carriers is determined by the information symbol rate, which is small as compared with the spread bandwidth of the signal. Bit error rate performance of the proposed CFO-SS system under multipath environments is investigated by computer simulation, and the performance of the CFO-SS method is confirmed for wireless LAN systems using the 2.4 GHz ISM band.

The performance of a constrained (that is, minimal order) Yule-Walker (CYW) single tone frequency estimator is studied. A closed form expression for the asymptotic error variance is derived. It is shown that CYW does not satisfactorily utilize the informaiton in data, and estimators with improved performance are proposed. Simulation results which lend support to the theoretical findings are included.

Recently, progress has been made in the area of electrical modeling of conductors embedded in arbitrary dielectrics using circuit oriented techniques. These models usually occur in conjunction with VLSI type circuits. Many different applications exist today for such models in the EMI, EIP (Electrical Interconnect and Package) analysis as well as for the microwave circuit area. Practical problems involve a multitude of hardware components and they demand a wide spectrum of both time as well as frequency domain solution techniques. In this paper we consider circuit oriented techniques for the solution of these problems. Specifically, we give an outline of the three dimensional Partial Element Equivalent Circuit (PEEC) full wave modeling approach and review the recent progress in this area.

A novel block coding scheme based on complementary sequences which is capable of both error correction and peak to average power ratio reduction has been proposed for M-ary PSK multicarrier systems. Generator matrices for the number of carriers N = 2k where k = 2,3,...are derived. The effectiveness of the scheme has been confirmed by computer simulations.

The EMC-adequate design of microelectronic systems includes all actions intended to eliminate electromagnetic interference in electronic systems. Challenges faced in the microelectronic area include a growing system complexity, high integration levels and higher operating speeds at all levels of integration (chip, MCM, printed circuit board and system). The growing complexity, denser design and higher speed all lead to a substantial increase in EMC problems and accordingly the design time. EMC is not commonly accepted as a vital topic in microelectronic design. Microelectronic designers often are of the opinion that EMC is limited to electrical and electronic systems and the mandatory product regulations instead of setting requirements also for the integrated circuit they are designing. In this contribution a concept for an EMC-adequate design of electronic systems will be introduced. This concept is based on a generalized development process to integrate EMC-constraints into the system design. A prototype of an environment to analyse signal integrity effects on PCB based on a workflow oriented integration approach will be presented. Based on this approach the generation of user specific design and analysis environments including various set of EMC-tools is possible.

In this paper, a quite general systematic procedure is presented for defining incremental field contributions, that may provide effective tools for describing a wide class of scattering and diffraction phenomena at any aspect, whthin a unitary, self-consistent framework. This is based on a generalization of the localization process for cylindrical canonical problems with elementary source illumination and arbitrary observation aspects. In particular, it is shown that the spectral integral formulation of the exact solution may also be represented as a spatial integral convolution along the axis of the cylinder. Its integrand is then directly used to define the relevant incremental field contribution. This procedure, that will be referred to as a ITD (Incremental Theory of Diffraction) Fourier transform convolution localization process, is explicitly applied to both wedge and circular cylinder canonical configurations, to define incremental diffiraction and scattering contributions, respectively. These formulations are asymptotically approximated to find closed form high-frequency expression for the incremental field contributions. This generalization of the ITD lacalization process may provide a quite general, systematic procedure to find incremental field contributions that explicitly satisfy reciprocity and naturally lead to the UTD ray field representation, when it is applicable.

The H-polarized diffraction by a wedge consisting of perfect conductor and lossless dielectric is investigated by employing the dual integral equations. Its physical optics diffraction coefficients are expressed in a finite series of cotangent functions weighted by the Fresnel reflection coefficients. A correction rule is extracted from the difference between the diffraction coefficients of the physical optics field and those of the exact solution to a perfectly conducting wedge. The angular period of the cotangent functions is changed to satisfy the edge condition at the tip of the wedge, and the poles of the cotangent functions are relocated to cancel out the incident field in the artificially complementary region. Numerical results assure that the presented correction is highly effective for reducing the error posed in the physical optics solution.

In this paper, scattering problem of the directional coupler for the slab waveguides are analyzed by the mode-matching method in the sense of least squares for the lowest order even TE mode incidence. It is considered that the analysis of this coupler for the slab waveguides presents the fundamental data to design the directional coupler for the three dimensional waveguides. This directional coupler is composed of three parallel slabs which are placed at equal space in the dielectric medium. Respective slabs are core regions of three respective waveguides. The periodic groove structure of finite extent is formed on the both surfaces of core region of the central waveguide among them. The power of incident TE mode is coupled to other two waveguides through periodic groove structure. The coupled TE mode propagates in the other waveguides to the same or opposite direction for the direction of incident mode which propagates in the waveguide having periodic structure when the Bragg condition is selected appropriately. The scattered field of each region of this directional coupler is described by the superpositions of the plane waves with bandlimited spectra, respectively. These approximate wave functions are determined by the minimization of the mean-square boundary residual. This method results in the simultaneous Fredholm type integral equations of the second kind for these spectra. The first order approximate solutions of the integral equations are derived and the coupling efficiency and scattered fields are analyzed on the basis of those solutions in this paper.

A new optical wavelength demultiplexer using quasi-phase-matched sum-frequency-generation (QPM-SFG) is proposed. The device consists of an optical deflector using Pockels effect and a nonlinear crystal with a periodic structure. The demultiplexing characteristics of the device composed of a LiNbO3 crystal are analyzed theoretically. Wavelength demultiplexing can be made simply by changes in the electric field applied to the deflector.

This paper presents a method of analyzing the electromagnetic field inside an equipment housing. The electromagnetic field is assumed to be coming from outside and coupled into the housing through an aperture on the housing surface. The analysis is based on the transmission-line modeling method. Results of the analysis show a good agreement with the results of measurement. Also, it is found that the coupling through the aperture shows peaks at some frequencies that depend almost only on the structure of the housing and aperture and, therefore, can be estimated at the time of equipment design.

Recently, the low earth orbit satellite communications has been attracting much attention. These communications have many strong features, however, the communication performances are influenced by carrier frequency offset (CFO) and, particularly, it is hard to acquire the synchronization. A large number of publications have so far been made on the synchronization acquisition of DS/SS systems under CFO and most of them make use of the maximum likelihood decision in finding the maximum values of Fourier transform outputs. However, the implementations of Fourier transforms usually require high cost and large space. In this paper, we propose a new simple acquisition scheme using half-symbol differential decoding technique for DS/SS systems under CFO. This scheme makes use of the addition and subtraction of baseband signals and their delayed versions, (omitting Fourier transforms), together with integrations by recursive integrators, and thus resulting in much simpler implementation. In general, it is shown that the proposed scheme can acquire the code synchronization under carrier frequency offset with much smaller computational complexities and the sacrifice of longer acquisition time.

Bit-interleaving can enhance performance of a trellis coded modulation system over a fading channel. A combined system with decision feedback equalization is proposed. In the system, TCM decoded symbols are fed back for equalization. To avoid a bad effect of decoding delay, a deinterleaver is utilized effectively. Information sequence is divided into three subsequences and encoded by three encoders. Among the 3 code vectors from the encoders, bits are interleaved and decoding proceeds in parallel. Simulation results show that the proposed system realizes 0.6 dB more coding gain than a symbol interleaved system. A calculation method of a branch metric for decoding is proposed. Performance with the branch metric is shown to be nearly independent from the desired/undesired power ratio of a intersymbol interference channel. An approximate upper bound is analyzed for the proposed system, and the optimum code is searched.