A new beamforming method based on simplex downhill optimaization process has been presented for the reverse link CDMA systems. The proposed system performs code-filtering at each antenna for each user. The new beamforming method gives lower computations and faster convergence properties than existing algorithms. The simulation results show that the proposed algorithm has a better BER performance in the case of the time-varing channel.

A novel scheme of subband adaptive array for multicode Direct Sequence Code Division Multiple Access (DS-CDMA) is proposed in this paper. The proposed scheme has a flexible configuration which allows basestation to be able to dynamically adapt to multirate transmission requests from subscribers. It is shown that the novel scheme can effectively suppress multiple access interferences (MAI) by appropriately forming main beam toward the desired user while pointing beampattern nulls toward MAI sources. Moreover, the combination of the subband adaptive array with the so-called cyclic prefix spreading code CDMA is also proposed to mitigate multipath fading and maximize diversity gain in multipath fading environment.

The joint histogram of second order scale space differential invariants of natural images (including textures) is typically clustered about parabolic surface patches, whereas symmetrical elliptical patches (local convexities or concavities) are very rare and symmetrical hyperbolical patches also occur less frequently than parabolic patches. We trace the origin of this striking effect in the context of Gaussian random noise. For this case one may derive the joint histogram of curvedness and shape index analytically. The empirical observations are fully corroborated. In deriving these results we introduce a polar coordinate system in the space of second order scale space derivatives that turns out to be particularly useful in the study of the statistics of local curvature properties. The empirical observations apply also to non-Gaussian noise (e.g., Brownian noise) as well as to photographs of natural scenes. We discuss general arguments that help explain these observations.

In this paper, we study a delay transmit diversity system combined with antenna diversity reception that transmits the time-delayed and weighted versions of the same signal from multiple antennas. At a receiver, multiple receive antennas are used and all delayed signals received on multiple antennas are coherently combined by a Rake receiver. The set of optimum antenna weights for maximizing the received signal-to-noise power ratio (SNR) after Rake combining is theoretically analyzed to show that the optimum solution is to transmit only from the best antenna that has the maximum equivalent channel gain seen after Rake combining. The bit error rate (BER) performance is theoretically analyzed and evaluated by computer simulation. The combined effect of transmit diversity and transmit power control (TPC) is also investigated.

This Letter presents a fast codeword search algorithm based on ordered Hadamard transform. Before encoding, the ordered Hadamard transform is performed offline on all codewords. During the encoding process, the ordered Hadamard transform is first performed on the input vector, and then a new inequality based on characteristic values of transformed vectors is used to reject the unlikely transformed codewords. Experimental results show that the algorithm outperforms many newly presented algorithms in the case of high dimensionality, especially for high-detail images.

In this paper, we derive spatial correlation functions of linear and circular antenna arrays for three types of angular energy distributions: a Gaussian angle distribution, the angular energy distribution arising from a Gaussian spatial distribution, and uniform angular distribution. The spatial correlation functions are investigated carefully. The spatial correlation is a function of antenna spacing, array geometry and the angular energy distribution. In order to emphasize the research and their applications in diversity reception, as an example, performance of the antenna arrays with MRC in correlated Nakagami fading channels is investigated, in which analytical formulas of average BER for the spatial correlation are obtained.

In this paper, we describe our study on a novel high-frequency magnetic field probe based both on the BiRIG rotation magnetization (RM) phenomenon and the third-generation optical probing scheme. First, we explain our experimental investigation on RF sensitivity and frequency response of the RM-based Faraday effect in a commercially available Bi-substituted rare-earth iron garnet plate. Second, we report on the implementation of fiber-optic magneto-optic (MO) probe heads with bandwidths of 10 GHz or broader, which have been brought about by careful arrangement of the magnetization axis of a single-domain crystal and the highly sensitive fiber-edge optical probing scheme. Third, we describe a few RF magnetic field distribution measurements carried out successfully over GHz-band microstrip line circuits. The results of the study imply the substantial potential of the present MO probe head for the RF current visualization.

We report on several photoconductive (PC) geometries for the generation of both guided-wave and free-space terahertz (THz) waveforms. It is found that guided-wave THz electrical waveforms can be produced through both PC self-switching and frozen wave generation--eliminating the need for an ultrashort carrier lifetime in the semiconductor substrate. The concept of PC switching is also applied to the generation of free-space THz waveforms, and various ZnSe detectors are investigated as potential electro-optic THz sensors.

This review paper addresses an emerging aspect of the relationship between optics and microwave electronics: the application of short pulses of laser light to the sensing and measurement of continuous-wave microwave fields. In particular, very short duration optical pulses can take on the role of ultrafast sampling gates within the framework of the electro-optic sampling technique in order to realize unprecedented temporal resolution, measurement bandwidth, and probing flexibility. As a result, in numerous instances electro-optic sampling has been demonstrated, primarily within the research laboratory, to be an effective tool in the field of diagnostic testing and the determination of the electrical characteristics of microwave components. Recently, with the emergence of new applications such as microwave electric-field mapping in wireless and radar environments, and as the ultrafast time domain has gained in importance for the area of optical telecommunications, added attention has been directed to electro-optic sampling. Herein, an abbreviated historical perspective of the history of electro-optic field mapping is presented, along with the fundamental concepts that are utilized in the technique. The effectiveness of an optical-fiber-mounted electro-optic probe in a scanning electric-field-mapping system is highlighted in several diagnostic measurements on microwave and millimeter-wave antenna arrays, and a combined electric-field and thermal-imaging capability is also introduced.

In the image recognition problem, it is very important how we represent the image. Considering this, we propose a new representational method of images based on the stability in scale-space. In our method, the image is segmented and represented as a hierarchical region graph in scale-space. The object is represented as feature graph, which is subgraph of region graph. In detail, the region graph is defined on the image with the relation of each segment hierarchically. And the feature graph is determined based on the "life-time" of the graph of the object in scale-space. This "life-time" means how long feature graph lives when the scale parameter is increased. We apply our method to the face detection problem, which is foundmental and difficult problem in face recognition. We determine the feature graph of the frontal human face statistical point of view. We also build the face detection system using this feature graph to show how our method works efficiently.

Large number of electronic connectors are widely used in various electronic and telecommunication systems. No matter whether it is optical telecommunications or mobile phone systems, connectors are important links for electronics. Unfortunately connector contacts are exposed in air, they are different from any other electronic components, the contacts are greatly influenced by the environment where they operate. In China, dust and corrosion products are the main contaminants to cause contact failure. Evidently the failed contacts seriously deteriorate the reliability of electronic and telecommunication systems. This paper summarizes the recent achievements obtained by our Lab on the effect of dust and corrosion products to the connector contact failure. Since dust contamination is a very complex problem which is not only popular in China, but also happened in many countries. Continuous studies will be very useful to improve the contact reliability of connectors, setting up new and effective testing methods and standards, building up experimental and computer simulation systems.

In an attempt to improve the performance under frequency selective fading environment, we develop in this paper an orthogonal frequency division multiplex (OFDM) system in which adaptive interleaving is applied. The adaptive interleaving is a method that assigns symbols adaptively to the subcarriers in order to cope with frequency selective fading based on a channel state information (CSI) sent back from the reception end. The concept of adaptive interleaving is to maximize a free Euclidean distance in the limited interleave size. In this paper, we extend the method by an introduction of bit interleaving and multiple trellis coded modulation (MTCM). MTCM assigns two or more symbols to one trellis branch and shows good performance in frequency selective fading. If we could assign those set of symbols with an aid of the adaptive interleaving, the performance improvement can be expected. Another improvement method considered in this paper is the use of bit interleaving. The bit interleaving techniques randomize the effect of channel more efficiently compared to the case of symbols interleaving. Thus the further performance improvement is expected. One draw back is that since the interleaving process is done in bit level, bit interleaving can not be applied to TCM nor MTCM. In this paper, we mainly focus on adaptive bit and symbol interleaving and discuss the performance from the point of interleaving effect, and the error correcting code (convolutional code and MTCM).

In this paper, we propose a new multistage (iterative) structure where Kalman channel estimation and parallel interference cancellation multiuser detection are conducted in every stage (iteration). The proposed scheme avoids the complexity of the decorrelator in front of Kalman channel estimator, and has better performance than the previous scheme.

Nowadays electronic devices and systems are widely used in various dynamic environments. However, they cause electrical contact instability that can easily be ignored. This phenomenon is considered as contact failure caused by a dynamic influence. In this paper, the investigation of contact failure caused by dynamic influences and analysis method for such contact failure are discussed. The results show that a dynamic influence could not be well covered in the experimental testing for a new product.

This paper presents an extension of the database query language SQL to include queries against a database with natural language annotations. The proposed scheme is based on Concept Coupling Model, a language model for handling natural language sentence structures. Integration of the language model with the conventional relational data model provides a unified environment for manipulating information sources comprised of relational tables and natural language texts.

As a new material, silver (Ag) coated fabric has been developed, and its use for shielding electromagnetic radiation is expected. In this paper, seven kinds of Ag coated fabrics, woven, knitted and nonwoven by Ag coated fibers, are prepared, and placed over a PCB with a microstrip line, which is used as a noise source. By measuring the input impedance of the microstrip line, the distance between the PCB and the fabric is fixed to 8 mm to reduce the coupling paths. The shielding effect SE of those fabrics was compared by measuring the magnetic near-field with a small shielded-loop probe. In the results, the resonance frequency is dependent on the fabric's length, as well as the case of a copper sheet. Comparing the texture, the SE of woven and nonwoven fabrics is larger than the knitted fabric. Comparing with the copper sheet, the SE of the fabrics is smaller below 200 MHz, but elsewhere is almost the same.

The key elements of sub-100 nm MOSFET modeling for circuit simulation are accurate representation of new physical phenomena arising from advancing technologies and numerical efficacy. We summarize the history of MOSFET modeling, and address difficulties faced by conventional methods. The advantage of the surface-potential-based approach will be emphasized. Perspectives for next generations will be also discussed.

This paper deals with the wave scattering from a periodic surface with finite extent. Modifying a spectral formalism, we find that the spectral amplitude of the scattered wave can be determined by the surface field on only the corrugated part of the surface. The surface field on such a corrugated part is then expanded into Fourier series with unknown Fourier coefficients. A matrix equation for the Fourier coefficients is obtained and is solved numerically for a sinusoidally corrugated surface. Then, the angular distribution of the scattering, the relative power of each diffraction beam and the optical theorem are calculated and illustrated in figures. Also, the relative powers of diffraction are calculated against the angle of incidence for a periodic surface with infinite extent. By comparing a finite periodic case with an infinite periodic case, it is pointed out that relative powers of diffraction beam are much similar in these of diffraction for the infinite periodic case.

Wireless LAN (WLAN) systems transmit and receive via a common frequency band. In this band, signals of other wireless applications operate on a WLAN beamformer as interferences, and so the problem in adaptive antenna is increasing the canceling performance in the presence of moving interference sources. The performance of conventional adaptive beamformer is severely degraded and the robust adaptive beamformer must be equipped with additional sensors to obtain desired performances. Therefore, in order to avoid having to install additional sensors, an efficient algorithm is necessary. In this paper, we introduce a fast adaptive algorithm with variable forgetting factor, which does not require any further additional modifications. Through computer simulations, we can obtain better performances than those of other techniques under a variety of operating conditions.

Two implementation schemes for a two-step SOVA (Soft Output Viterbi Algorithm) decoder are proposed and verified in a chip. One uses the combination of trace back (TB) logic to find the survivor state and double trace back logic to find the weighting factor of a two-step SOVA. The other is that the reliability values are divided by a scaling factor in order to compensate for the distortion brought by overestimating those values in SOVA. We introduced a fixed scaling factor of 0.25 or 0.33 for a rate 1/3 and designed an 8-state Turbo decoder with a 256-bit frame size to lower the reliability values. The implemented architecture of the two-step SOVA decoder allows important savings in area and high-speed processing compared with the one-step SOVA decoder using register exchange (RE) or trace-back (TB) method. The chip is fabricated using 0.65 µm gate array at Samsung Electronics and it shows higher SNR performance by 2 dB at the BER 10-4 than that of a two-step SOVA decoder without a scaling factor.