In this paper, three issues concerning the linear adaptive receiver using the LMS algorithm for single-user demodulation in direct-sequence/code-division multiple-access (DS/CDMA) systems are considered. First, the convergence rate of the LMS algorithm in DS/CDMA environment is considered theoretically. Both upper and lower bounds of the eigenvalue spread of the autocorrelation matrix of receiver input signals are derived. It is cleared from the results that the convergence rate of the LMS algorithm becomes slow when the signal power of interferer is large. Second, fast converging technique using a prefilter is considered. The LMS based adaptive receiver using an adaptive prefilter adjusted by a Hebbian learning algorithm to decorrelate the input signals is proposed. Computer simulation results show that the proposed receiver provides faster convergence than the LMS based receiver. Third, the complexity reduction of the proposed receiver by prefiltering is considered. As for the reduced complexity receiver, it is shown that the performance degradation is little as compared with the full complexity receiver.

The proposed high-power-factor converter is constructed with a flyback converter, and locates the energy-storage capacitor on the secondary side of the transformer. A high power-factor can be obtained without needing to detect any current, and the ZVS operation can be achieved without auxiliary switches. To make the best use of these advantages in the converter, ZVS operations and power-factor characteristics in the converter were analyzed. From the analytical results, the effective control method for achieving ZVS was examined. Using a bread-board circuit controlled by this method, a power-factor of 0.99 and a conversion efficiency of 88% were measured.

In this paper, we analyze overload and stability in the charge-pump phase locked loop (PLL). We propose a new computational model that can be applied for the precise estimation of the physical limits of charge-pump, the leakage current of loop filter and waveform distortion of charge-pump PLL operating in high speed. We derive the exact mathematical expressions of the parameters describing the steady-state behavior of the PLL as well as the transient-state behavior. Performance comparisons with the conventional model are provided through numerical results. Algorithms for approximate analysis is also provided. The new model is particularity useful for analyzing the cases that the charge-pump PLL operates in high- speed or the loop filter has large leakage current.

In this paper, we discuss the use of convolutional codes with a multi-antenna transmission scheme for DS/CDMA systems. The binary input data to a rate 1/M encoder produces M coded bits, which, in turn, are assigned to M different antennas and transmitted from each antenna simultaneously. An intentional delay of several chips duration is introduced at each antenna before transmission, which enables a receiver to distinguish the signals from different antennas. Because the proposed scheme utilizes spatial and time domains for coding, it can achieve not only implicit time-diversity through the use of coding with interleaving, but also space-diversity through the transmission from multiple antennas. Multi-antenna schemes with convolutional codes can perform better than conventional single antenna schemes with the same codes and transmission diversity technique with the same number of transmitting antennas, especially when a fading is relatively slow and interleaving size is limited.

It is well known that M-ary/spread spectrum (M-ary/SS) system is superior to direct-sequence spread spectrum system under AWGN, and can achieve high spectral efficiency. On the other hand, however, the main drawback of this system is that the synchronization acquisition is difficult. In this paper, we propose a new synchronization acquisition method of M-ary/SS system. This method acquires the code synchronization by introducing a symmetrical property in spreading sequences, and detecting this property with the differential decoding technique. As spreading sequences, a set of orthogonal sequences and a set of non-orthogonal sequences are considered. The strong features of proposed systems are that the systems can acquire the code synchronization in carrier band and can reduce the complexity of calculation greatly. Among the comparison results of the systems with newly proposed orthogonal and some specific non-orthogonal spreading sequences, it is especially noted that the latter can reduce the mean acquisition time and calculation complexity much greater than the former.

ITU (International Telecommunication Union) has issued request for submission of candidate technologies for IMT (International Mobile Telecommunication)-2000/FPLMTS radio interface in April 1997. In order to propose a candidate technology and to contribute to the production of a world wide standard of IMT-2000, ARIB (Association of Radio Industries and Businesses) has studied radio transmission technologies for IMT-2000. This paper shows the recent study results on IMT-2000 radio transmission technologies in ARIB. Now in ARIB detailed study to produce necessary specifications and prepare of a proposal on candidate radio transmission technology to ITU are being conduced based on wide band DS-CDMA technologies.

This paper is concerned with CDMA applied to personal and mobile communications on a global basis using multiple low earth orbital satellites (LEOS). We focus our attention on some unique aspects of LEOS systems and discuss their influences on the CDMA system performance as well as the techniques for coping with these aspects. We deal with three kinds of important items that are unique to LEOS systems; Doppler frequency shift due to satellite movement, propagation delay affecting packetized data transmission and geographical nonunifomity in traffic.

In this paper, we study and analyze the overall acquisition performance of the combined acquisition-tracking synchronization loop for direct-sequence spread-spectrum (DS-SS) signals in the presence of Doppler shift. We consider both the change of effective search rate and the impact on the detection probability due to Doppler for the acquisition loop. We also determine the acquisition behavior of the digital delay lock loop (DDLL) in the presence of code Doppler. As a result, the influence of the DDLL's acquiring capability on the complete acquisition process is investigated and some numerical results are presented to demonstrate the acquisition performances of this combined loop which are quite different from the previous reports.

In this paper, a simple frame synchronization system for M-ary Spread Spectrum (M-ary/SS) communication system is analyzed. In particular, synchronization performance, bit error rate performance, and Spread Spectrum Multiple Access (SSMA) performance are analyzed. The frame synchronization system uses the racing counters. The transmitted signal contains framing chips that are added to spreading sequences. In the receiver, the framing chips are detected from several frames. The authors have proposed the simple frame synchronization system that detects framing chips from consecutive 2 frames. In this system, as the number of framing chips increases, synchronization performance improves and bit error rate performance degrades. In this paper a frame synchronization system that improves bit error rate performance is treated and analyzed. As the rusult, when the number of reference frames is 3, the bit error rate is much improved than the conventional system.

This paper presents a method to examine the effect of introducing data application services on existing wireless CDMA networks where conventional voice communications service is being provided. Since the total number of channels used in a cell is limited in the interfering cellular environments, some voice-traffic channels should be sacrificed when an additional channel is introduced for data services. We investigate this trade-off by analyzing the interference the forward link channels generate. It is also an objective of this paper to examine the forward link capacity in terms of the numbers of paging and voice-/data-traffic channels so as to determine the impact of introducing data services via paging and traffic channels. Different capacity regions are plotted for various cellular environments.

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 letter proposes and investigates a method of estimating the direction of arrival (DOA) of wideband signals such as spread spectrum signals, in a multipath channel. The DOA estimation method can reduce the effect of signal distortion due to bandwidth of signals by creating a spatial spectrum wihch satisfies the sampling theory in the time domain. The DOA estimate calculated from this spatial spectrum is robust against signal distortion due to multipath. Computer simulations numerically evaluate the proposed method. In comparison with conventional MUSIC algorithm, the proposed method achieves superior performance in a multipath channel.

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.

We propose concepts of Paley-Wiener multiresolution analysis and Paley-Wiener wavelet frame based on general, not limited to dyadic, dilations of functions. Such a wavelet frame is an extension both of the Shannon wavelet basis and the Journe-Meyer wavelet basis. A concept of "natural" Paley-Wiener wavelet frame is also proposed to clarify whether a Paley-Wiener wavelet frame can naturally express functions from the point of view of the multiresolution analysis. A method of constructing a natural Paley-Wiener wavelet frame is given. By using this method, illustrative examples of Paley-Wiener wavelet frames with general scales are provided. Finally, we show that functions can be more efficiently expressed by using a Paley-Wiener wavelet frame with general scales.

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.

This paper presents a technique to determine prime implicants in multi-level combinational networks. The method is based on a graph representation of Boolean functions called AND/OR reasoning graphs. This representation follows from a search strategy to solve the satisfiability problem that is radically different from conventional search for this purpose (such as exhaustive simulation, backtracking, BDDs). The paper shows how to build AND/OR reasoning graphs for arbitrary combinational circuits and proves basic theoretical properties of the graphs. It will be demonstrated that AND/OR reasoning graphs allow us to naturally extend basic notions of two-level switching circuit theory to multi-level circuits. In particular, the notions of prime implicants and permissible prime implicants are defined for multi-level circuits and it is proved that AND/OR reasoning graphs represent all these implicants. Experimental results are shown for PLA factorization.

We present a method for learning classification functions from pre-classified training examples and hypotheses written roughly by experts. The goal is to produce a classification function that has higher accuracy than either the expert's hypotheses or the classification function inductively learned from the training examples alone. The key idea in our proposed approach is to let the expert's hypotheses influence the process of learning inductively from the training examples. Experimental results are presented demonstrating the power of our approach in a variety of domains.

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.

In supervisory control, discrete event dynamic systems (DEDSs) are modeled by finite-state automata, and their behaviors described by the associated formal languages; control is exercised by a supervisor, whose control action is to enable or disable the controllable events. In this paper we present a general stability concept for DEDSs, stability in the sense of Lyapunov with resiliency, by incorporating Lyapunov stability concepts with the concept of stability in the sense of error recovery. We also provide algorithms for verifying stability and obtaining a domain of attraction. Relations between the notion of stability and the notion of fault-tolerance are addressed.