Spread spectrum (SS) communication systems have been studied and developed for commercial applications such as mobile communications, consumer communications and so on. The reason is that SS communication systems have various characteristic features, such as, robust immunity to interference and jamming, achieving privacy in communication and random access capability (spread spectrum multiple access: SSMA). The performance of the systems, mainly, depends on modulation method of spreading the spectrum. This paper introduces recent several methods of modulation in SS communication systems. First, direct-sequence (DS), which is a fundamental modulation in SS communication system, and M-ary/SSMA, which can increase the number of multiple access users, are described. For increasing the data rate per user, parallel SS, parallel combinatory SS and a code division multiplex using orthogonal Manchester coded M-sequences are introduced. Second, frequency hopping (FH), in which the spectrum of signal is spread by hopping carrier frequency, and related systems are shown. Finally, from a viewpoint of communication theory, spectral efficiency (i.e., data rate the number of multiple access users/bandwidth) of systems relating spreading codes are discussed. As a result, maximum spectral efficiency can be obtained by appropriate spreading factor for each spreading code.

A method for sweeping frequency ranges of over 130GHz within a tuning range of 30nm, without mode hopping, has been realized. The optical frequency is swept with a fine translation-rotation grating drive which uses a new, simplified operation method and a thermally controlled semiconductor laser system.

This paper describes the design of a 38-GHz high power MMIC amplifier using an improved load-pull technique. We improved the load-pull technique accuracy by using MMIC transtormers to match the input and output impedances of a GaAs MESFET to about 50 ohms. We used this technique to measure the large-signal load impedance of a FET with a 600-µm-wide gate. Using the data obtained, we developed an MMIC amplifier composed of two of these FET cells. At 38 GHz, the amplifier has an output power of 23.5 dBm for a 1 dB gain compression level.

General estimation technique using covariance information is proposed for white Gaussian and white Gaussian plus coloured observation noises in linear stationary stochastic systems. Namely, autocovariance data of signal and coloured noise appear in a semi-degenerate kernel, which represents functional expression of the autocovariance data, in the current technique. Then the signal is estimated by directly using autocovariance data of signal and coloured noise. On the other hand, in the previous technique, the covariance information is expressed in the form of a semi-degenerate kernel, but its elements do not include any autocovariance data.

Fading is unavoidable in many communication systems such as urban and mobile radio systems. Fading, in principle, results in increased error in data communications. However, the random variation of received signal envelope due to natural fading divides the received signals into many different power level, a method known to improved utilization of ALOHA network due to capture effects. In this paper, we consider Nakagami fading model for the radio channel. We derive the exact form of capture probabilities and show that the probabilities can be modeled as semi-exponential model. Thus we can determine the channel capacity of ALOHA system with capture channel.

In this paper we study the problem of scheduling parallel program modules onto an MPS (message passing multiprocessor system) so as to minimize the total execution time. Each node in the interconnection network of the MPS has buffers at its input ports to store messages waiting for the transmission. An algorithm for finding a route which minimizes the communication delay of a message to be sent between a processor-pair is first given. Next, we present heuristic algorithms for scheduling program modules onto the MPS. These algorithms use the above routing algorithm. The performances of the proposed algorithms are estimated by using simulation experiments.

We propose the coherent subcarrier multiplexed (SCM) system with distributing local oscillator (LO) in local loop. The proposed system can realize multichannel transmission with one optical carrier by using the SCM technique and has no need to have LO at each station. Therefore the proposed system becomes cost-effective. The proposed SCM system uses bandpass filter to select a specific channel. We analyze CNR of the system with frequency-shift keying (FSK) in a multioctave configuration. First, the general expression of CNR is derived and is shown for the following parameters such as the number of channels, the position of station on the loop, and the number of stations on the loop. Second, optimal phase modulation (PM) index is derived, and the optimal CNR, minimum required power of lasers, and maximum number of stations that the proposed system can serve are shown by using it. Moreover CNR of the proposed system is compared with that of the system having LO at each station in local loop. It is shown that the proposed system can obtain good performance at the expense of slight increase of the output power of only two lasers at the central station. Therefore the proposed system is cost-effective and practical.

The optimal coding strategy for signal detection in the correlated gaussian noise is established for the distributed sensors system with essentially zero transmission rate constraint. Specifically, we are able to obtain the same performance as in the situation of no restriction on rate from each sensor terminal to the fusion center. This simple result contrasts with the previous ad hoc studies containing many unnatural assumptions such as the independence of noises contaminating received signal at each sensor. For the design of optimal coder, we can use the classical Levinson-Wiggins-Robinson fast algorithm for block Toeplitz matrix to evaluate the necessary weight vector for the maximum-likelihood detection.

Fourier holographic image storage and reconstruction using BaTiO3 photorefractive crystal waveguide is investigated. The phase conjugation technique, which compensates image distortion caused by modal phase dispersion, successfully retores images stored in a test BaTiO3 crystal waveguide.

In this paper, voltage-input current-output Membership Function Circuit (MFC) and Normalization Locked Loop (NLL) are proposed. They are useful building blocks for the current-mode analog fuzzy hardware. The voltage-input current-output MFC consists of one source coupled type Operational Transconductance Amplifier (OTA). The MFC is used in the input parts of the analog fuzzy hardware system. The fuzzy hardware system can execute the singleton fuzzy control algorithm. In the algorithm, the weighted average operation is processed. When the weighted average operation is directly realized by analog circuits, a divider must be implemented. Here, the NLL circuit, which can process the weighted average operation without the divider, is implemented using one source coupled type OTA. The proposed circuits were designed by using 2 µm CMOS design rules and its operations were confirmed using SPICE simulations.

This paper extends an earlier study on the T-Model neural network to its collective computational properties. We present arguments that it is necessary to use the half-interconnected T-Model networks rather than the fully-interconnected Hopfield model networks. The T-Model has been generated in response to a number of observed weaknesses in the Hopfield model. This paper identities these problems and show how the T-Model overcomes them. The T-Model network is essentially a feedforward network which does not produce a local minimum for computations. A concept for understanding the dynamics of the T-Model neural circuit is presented and its performance is also compared with the Hopfield model. The T-Model neural circuit is implemented and tested with standard CMOS technology. Simulations and experiments show that the T-Model allows immense collective network computations and does not produce a local minimum. High densities comparable to that of the Hopfield model implementations have also been achieved.

This paper analyzes the performance of the capacity controlled digital radio system, which controls the number of modulation levels according to the amount of traffic. These analyses are performed under thermal noise and co-channel interference. As a result, the throughput improvement is approximately 16 times comparing with the fixed capacity system which has the designed outage probability of 0.1%. Theoretical results are applied to the future mobile communication system which utilizes TDMA access method or burst co-dec, and it is found that the reuse distance can be improved to 1/5 times when the designed outage probability is 0.1%.

This paper describes the waveform relaxation (WR) algorithm with the under relaxation method based on the virtual state formulation (VSF) technique and the effect of multirate behavior in this algorithm. First, we present the virtual state relaxation method using VSF technique. Next, we introduce the VSF method into WR algorithm in order to exploit the multirate behavior. Furthermore, we construct the relaxation-based circuit simulator DESIRE2 and apply this simulator to the transient analysis of MOS circuits. Finally, we show that the present technique enables to use efficiently the multirate integration method in VSR and reduce the total simulation time without losing the waveform accuracy.

This paper proposes parallel VLSI processors for robotics based on multiple processing elements organized around multiple bus interconnection networks. The advantages of multiple bus interconnection networks are generality, simplicity of implementation and capability of parallel communications between processing elements, therefore it is considered to be suitable for parallel VLSI systems. We also propose the optimal scheduling formulated in an integer programming problem to minimize the delay time of the parallel VLSI processors.

An intermediate-frequency-combining (IF-combining) polarization diversity using frequency conversion is proposed. The proposed diversity requires no phase controller as opposed to the conventional IF-combining diversity. It has been theoretically clarified that this diversity has polarization insensitive bit-error-rate (BER) characteristics. The effectiveness has been confirmed by experiments in which the sensitivity dependence on the polarization is suppressed to within 0.8dB and a stable 101km fiber transmission at 600Mbit/s is achieved.

A study on the limitation of optical communication systems has received much attention. A method to overcome the standard quantum limit is to apply non-standard quantum state, especially squeezed state. However, the advantage of the non-standard quantum state is degraded by the transmission energy loss. To cope with this problem, we have proposed a concept of the received quantum state control (RQSC), but the realization has some difficulties. In this paper, we propose a new system to realize the received quantum state control system, employing injection locked laser (ILL) system. Then we show that our new system can overcome the standard quantum limit.

High-speed digital land mobile communications suffer from frequency-selective fading due to a long delay difference. Several techniques have been proposed to overcome the multipath propagation problem. Among them, an adaptive array antenna is suitable for very high-speed transmission because it can suppress the multipath signal of a long delay difference significantly. This paper describes the LMS adaptive array antenna for frequency-selective fading reduction and a new diversity technique. First, we propose a method to generate a reference signal in the LMS adaptive array. At the beginning of communication, we use training codes for the reference signal, which are known at a receiver. After the training period, we use detected codes for the reference signal. We can generate the reference signal modulating a carrier at the receiver by those codes. The carrier is oscillated independently of the incident signal. Then, the carrier frequency of the reference signal is in general different from that of the incident signal. However, the LMS adaptive array works in such a way that the carrier frequency of the array output coincides with that of the reference signal. Namely, the frequency difference does not affect the performance of the LMS adaptive array. Computer simulations show the proper behavior of the LMS adaptive array with the above reference signal generator. Moreover, we present a new multipath diversity technique using the LMS adaptive array. The LMS adaptive array reduces the frequency-selective fading by suppressing the multipath components. This means that the transmitted power is not used sufficiently. We propose a multiple beam antenna with the LMS adaptive array. Each antenna pattern receives one of the multipath components, and we combine them adjusting the timing. Then, we realize the multipath diversity. In addition to the multipath fading reduction, we can improve a signal-to-noise ratio by the diversity technique.

A new set of self-consistent linear equations is presented for the analysis of the startup characteristics of gyrotron oscillators with an open cavity consisting of weakly irregular waveguides. Numerical results on frequency detuning and oscillation starting current for a whispering-gallery-mode gyrotron are described in which these equations were utilized. Experiments for making a check on the effectiveness of the derived equations showed that they well express the operation of gyrotrons in comparison with the linear theory using an empty cavity field as the wave field.

The encoding of high quality and super high definition images requires new approaches to the coding problem. The nature of such images and the applications in which they are used prohibits the introduction of perceptible degradation by the coding process. In this paper, we discuss techniques for the perceptually transparent coding of images. Although technically lossy methods, images encoded and reconstructed using these techniques appear identical to the original images. The reconstructed images can be postprocessed (e.g., enhanced via anisotropic filtering), due to the absence of structured errors, commonly introduced by conventional lossy methods. The compression, ratios obtained are substantially higher than those achieved using lossless means.

This paper discusses the design, implementation, and performance of a bus-connected multiprocessor, called Presto, for a Rete-based production system. To perform a match, which is a major phase of a production system, a Presto match scheme exploits the subnetworks that are separated by the top two-input nodes and the token flow control at these nodes. Since parallelism of a production system can only increase speed 10-fold, the aim is to do so efficiently on a low-cost, compact bus-connected multi-processor system without shared memory or cache memory. The Presto hardware consists of up to 10 processisng elements (PEs), each comprising a commercial microprocessor, 4 Mbytes of local memory, and two kinds of newly developed ASIC chips for memory control and bus control. Hierarchical system software is provided for developing interpreter programs. Measurement with 10 PEs shows that sample programs run 5-7 times faster.