This paper describes an improved complementary beamforming microphone array based on the new noise adaptation algorithm. Complementary beamforming is based on two types of beamformers designed to obtain complementary directivity patterns with respect to each other. In this system, during a pause in the target speech, two directivity patterns of the beamformers are adapted to the noise directions of arrival so that the expectation values of each noise power spectrum are minimized in the array output. Using this technique, we can realize the directional nulls for each noise even when the number of sound sources exceeds that of microphones. To evaluate the effectiveness, speech enhancement experiments and speech recognition experiments are performed based on computer simulations with a two-element array and three sound sources under various noise conditions. In comparison with the conventional adaptive beamformer and the conventional spectral subtraction method cascaded with the adaptive beamformer, it is shown that (1) the proposed array improves the signal-to-noise ratio (SNR) of degraded speech by more than 6 dB when the interfering noise is two speakers with the input SNR of below 0 dB, (2) the proposed array improves the SNR by about 2 dB when the interfering noise is bubble noise, and (3) an improvement in the recognition rate of more than 18% is obtained when the interfering noise is two speakers or two overlapped signals of some speakers under the condition that the input SNR is 10 dB.

This paper describes a scheme to capture a wide-view image using a camera setup with uncalibrated cameras. The setup is such that the optical axes are pointed in divergent directions. The direction of view of the resulting image can be chosen freely in any direction between these two optical axes. The scheme uses eight-parameter perspective transformations to warp the images, the parameters of which are obtained by using a relative orientation algorithm. The focal length and scale factor of the two images are estimated by using Powell's multi-dimensional optimization technique. Experiments on real images show the accuracy of the scheme.

This paper describes how voltage fluctuation in the DC power supply of a digital IC can be reduced, by means of molding the package-pin in a ferrite-resin composite. The voltage fluctuation of the DC power supply, when the input terminal was driven by a 40 MHz, 5 Vp-p pulse wave, was measured using an oscilloscope. Simultaneously, the voltage spectrum of the fluctuation was measured using a spectrum analyzer. As a result, the voltage fluctuation was decreased by about 50 % when the IC package-pins were molded in a ferrite-resin composite, in which the µiac of the ferrite powder equalled 100, and the powder content was 80 weight-%. In the same IC, there was the reduction effect of the voltage spectrum of the fluctuation was recognized in the frequency range 40 MHz to 1 GHz.

This study is to clear how the impedance and the current of a simple printed line model involve to the near field electromagnetic noise radiation, by computer simulation and experiment. Frequency characteristics of the impedance and the current of the printed line and the near field noise are considered, from low to high frequency components. The model size 225 60 0.51 mm3, length of the line is 185 5 mm2 and 1 kΩ termination resistance is connected as non-matching load. FDTD method is used to calculate the impedance, the current waveform and the near field noise. Measurements of the line impedance and the near field noise spectrum by clock pulse are compared with simulations. It is cleared that using FDTD method, the characteristic of impedance of the printed line model, the current waveform, and the near field noise can be calculated at the same simulator. As results, from calculation and measurement, the near field noise has a relationship with impedance of printed line model. Emission at frequency less than 200 MHz, which is near the wavelength of λ/4, is observed at significant intensity. So, it is suggested that near field noise emission should be discussed from low to high frequency and analysis of the characteristics of the printed line and magnetic near field noise using FDTD method and measurement is useful to basic examination of complex PCB models.

This paper proposes a new protocol for ad hoc based CDMA wireless local area networks, Hierarchy Schedule Sensing (HSS) protocol. It adopts hierarchical sensing to schedule transmission requests to avoid collisions. Multi-level group spreading codes are used to reduce scheduling delay. The network performance under the HSS protocol is evaluated using a two-dimensional Markov chain model in consideration of collided packets capture effect at receivers. The paper also focuses on the impacts of multiple packet collisions on the performance. A closed formula of the average collision rate is derived explicitly. The results show that the HSS protocol offers a robust performance with low hardware requirement.

Heartbeat interval time series is an example of natural signals with 1/f characteristics. The exponent α of the 1/fα spectrum has some clinical significance. But sometimes the 1/f components is superimposed by some sinusoid components in the signal. To estimate the slope accurately, the 1/f component must be extracted from the signal. The singular spectrum analysis (SSA) method is recruited here to perform the task. Experimental results on data from real patients are satisfactory.

It is proposed a novel method that optimizes nonlinear filters by unsupervised learning using a novel definition of morphological pattern spectrum, called "morphological opening/closing spectrum (MOCS)." The MOCS can separate smaller portions of image objects from approximate shapes even if the shapes are degraded by noisy pixels. Our optimization method analogizes the linear low-pass filtering and Fourier spectrum: filter parameters are adjusted to reduce the portions of smaller sizes in MOCS, since they are regarded as the contributions of noises like high-frequency components. This method has an advantage that it uses only target noisy images and requires no example of ideal outputs. Experimental results of applications of this method to optimization of morphological open-closing filter for binary images are presented.

This paper presents a 7th-order channel-select filter for a spread-spectrum wireless receiver operating with a minimum power supply of 2.5 V. The channel-select filter implements a sharp transition from 2 MHz to 4 MHz and a stopband attenuation of 50 dB. The 7th-order filter is realized by a cascade of a passive RC integrator, a 3rd-order leapfrog filter, an operational amplifier based differentiator, a 2nd-order notch filter, and a 1st-order allpass filter. It is designed in a 0.35 µm single-poly BiCMOS process. Simulation results show feasibility of the proposed filter.

The wall admittance of an arbitrarily shaped microstrip antenna is generally formulated. As examples, elliptical microstrip antennas with and without a circular slot are calculated. The wall admittance is determined by the spectral domain analysis in order to consider the effect of the dielectric substrate. The electromagnetic fields within the cavity are expanded in terms of the eigenfunctions in the cylindrical coordinate system and their expansion coefficients are determined by applying the impedance boundary condition at the aperture in the sense of the least squares. The calculated input impedance and axial ratio agree fairly well with the experimental data. The proposed method is valid for the microstrip antennas with a patch whose geometry deviates from the particular coordinate system, such as single-feed circularly polarized microstrip antennas.

Watermarking methods that employ orthogonal transformations are very robust against non-geometrical modifications such as lossy compression, but attaining robustness against image translation or cropping is difficult. This report describes a watermarking method that increases robustness against geometrical modifications such as image translation and cropping by embedding watermark data in the frequency component of an image and detecting that data by considering the phase difference of the coefficients that results from translation of the image. Experimental results demonstrate the robustness of this method against both non-geometrical image changes and image translation and cropping.

In this paper, we propose the introduction of space diversity techniques to the code acquisition of a direct-sequence spread-spectrum signal. In this scheme, both a transmitter and a receiver have multiple antennas and the signals corresponding to all the combinations of the transmitter and receiver antennas are combined at the acquisition circuit of the receiver. The performance is evaluated for an indoor packet radio communication system from the viewpoints of the average time for acquisition, the probability of success of acquisition, and the necessary preamble length. As the result, we show great performance improvements by the proposed scheme under slow and flat Rayleigh fading environment.

In inter-vehicle communication (IVC) expectation for spread spectrum techniques is high. However, in a decentralized network environment, power control is difficult and until now perfect power control has been assumed. In this paper the use of sector antennas are proposed as a solution to the problems of power control in inter-vehicle communication. Results are shown for an IVC protocol in both no power control and imperfect power control environments in a realistic fading channel. Omni-directional, uniform sector antennas and non-uniform sector antennas are examined by computer simulation. Non-uniform sector antennas are shown to be the best solution and to have high packet reception rates even for no power control environments.

We have two goals in this paper. One is the comparison of Spread Spectrum (SS) CDMA and Spread Time (ST) CDMA. The other is to propose a new SS-ST CDMA system, which is an adaptive CDMA with both merits of SS and ST CDMA. SS and ST CDMA are compared from the view point of two dimensional space "frequency (B Hz)-time (T Sec)" together with their communication capacity. A primary modulation is assumed to be PPM in ST CDMA, and FSK in SS CDMA which is regarded as PPM in frequency axis. Both SS and ST CDMA are combined to give the proposed SS-ST CDMA, where transmitted signals are spread both in time and frequency domain. In order to realize the proposed system, a transmitter model is presented, and two receiver structures are discussed. The discrete Fourier transform (DFT) is employed for the system flexibility. Although SS, ST and SS-ST CDMA are shown to have the same capacity of 0.7213, the combined SS-ST CDMA has a merit of adaptability to adjust spreading gain of ST and SS according to property of channels, an impulsive noise dominated or a CW interference dominated channel. Numerical results of DFT are also shown to illustrate the waveform and spectrum of the proposed SS-ST CDMA system. Finally the symbol error probability performance of ST PPM, SS FSK and combined SS-ST systems in CW and impulsive environment is presented.

This paper discusses factorization of bent function type complex Hadamard matrices of order pn with a prime p. It is shown that any bent function type complex Hadamard matrix has symmetrical factorization, which can be expressed by the product of n matrices of order pn with pn+1 non-zero elements, a matrix of order pn with pn non-zero ones, and the n matrices, at most. As its application, a correlator for M-ary spread spectrum communications is successfully given, which can be simply constructed by the same circuits with reduced multiplicators, before and behind.

This paper proposes a novel spread spectrum (SS) modem for random access satellite communication systems that employs digital matched filters. The proposed modem employs a parallel structure to ensure detection of packet arrival. Code timing detection with a combination of a coarse detector and a fractional error detector reduces the sampling rate while maintaining the BER performance. An in-symbol pilot multiplexing scheme is also proposed for fast and stable carrier synchronization with a simple hardware. A performance evaluation shows that the proposed modem achieves the UW miss-detection probability of 10-4 at the Eb/No of 0 dB. The overall BER performance achieved in experiments well agrees simulation.

This paper describes a digital delay-lock Loop (DLL) to which delta-sigma (Δ Σ) modulation technique is applied in order to reduce circuit elements. The DLL is evaluated in both transient and steady-state behavior by theoretical analysis, computer simulations and circuit experiments. Not deteriorated by the internally generated Δ Σ-modulation noise, the DLL shows good tracking performance in transient response and steady-state RMS jitter of phase error against additive white Gaussian noise. Using the proposed DLL most parts of receiving circuits are realized by digital integrated circuits. After realizing the circuit, power-line communication system with spread spectrum is possibly expected in a small size with low cost.

Recently portable computers and mobile communications have been developed rapidly. Along with the developments of mobile computing environment, the demands of transmitting images over wireless channels are growing. However, high efficiency image coding techniques are not designed for the wireless communication channels. The use of variable length codes (VLCs) in those coding techniques makes a receiver hard to synchronize with the codewords on the noisy channel. On the other hand, a variable length code transmission technique utilizing multicode CDM (Code Division Multiplex) has been proposed. In this paper, the multicode CDM technique is applied to wireless transmission of images compressed by the H. 263 algorithm. Especially, the proposed technique is employed for motion vector transmission. In consequence, the proposed transmission technique reduces the required Eb/N0 as compared with the conventional transmission technique.

In this letter, the bit error probability of a hybrid DS/SFH-SS (Direct-Sequence/Slow-Frequency-Hopped Spread-Spectrum) system is derived for a Nakagami fading channel in the presence of multiple tone jamming. At a low JSR (jamming-to-signal power ratio), a pure DS-SS system can achieve lower bit error probability than a hybrid DS/SFH-SS system. But at a high JSR, a hybrid DS/SFH-SS system is shown to be superior to a pure DS-SS system. Especially, the worst case performance of a hybrid DS/SFH-SS system is almost equal to that of a pure DS-SS system.

In this paper, the use of optimal Karhunen-Loeve (KL) transform for quantization of speech line spectrum frequency (LSF) coefficients is studied. Both scalar quantizer (SQ) and vector quantizer (VQ) schemes are developed to encode efficiently the transform parameters after operating one or two-dimensional KL transform. Furthermore, the SQ schemes are also combined with entropy coding by using Huffman variable length coding (VLC). The basic idea in developing these schemes is utilizing the strong correlation of LSF parameters to reduce the bit rate for a given level of fidelity. Since the use of global statistics for generating the coding scheme may not be appropriate, we propose several adaptive KL transform systems (AKL) to encode the LSF parameters. The performance of all systems for different bit rates is investigated and adequate comparisons are made. It is shown that the proposed KL transform coding systems introduce as good as or better performance for both SQ and VQ in the examined bit rates compared to other methods in the field of LSF coding.

This paper proposes applications of a code-division multiplexing technique to VLSI systems free from interconnection problems. We employ a pseudo-random orthogonal m-sequence carrier as a multiplexable information carrier to achieve efficient data transmission. Using orthogonal property of m-sequences, we can multiplex several computational activities into a single circuit, and execute in parallel using multiplexed data transmission with reduced interconnection. Also, randomness of m-sequences offers the high tolerance to interference (jamming), and suppression of dynamic range of signals while maintaining a sufficient signal-to-noise ratio (SNR). We demonstrate application examples of multiplex computing circuits, neural networks, and spread-spectrum image processing to show the advantages.