This paper proposes a bandwidth division type parallel combinatory (PC) spread spectrum (SS) modulation scheme. In the proposed system, a given system bandwidth for the conventional single-carrier PC-SS system is divided into H subbands, and H PC-SS signals are transmitted in parallel. We evaluate the frame error rate (FER) of the proposed system under the asynchronous CDMA environment. We show that the proposed scheme provides a smaller FER than the single-carrier PC-SS system for a given information bit rate. We also show that the proposed scheme attains a higher information bit rate than the single-carrier PC-SS system for a given FER.

In this paper, the error performances of several reliability based decoding algorithms over the Rayleigh fading channel with coherent detection are evaluated. The algorithms for which the theoretical bounds are evaluated are the Generalized Minimum Distance (GMD), Chase-type, combined GMD and Chase-type and ordered statistic decodings. All derived bounds are relatively tight and require the same computational effort.

Stability of slotted ALOHA systems with retransmission cutoff, in which a packet is discarded after the certain number of unsuccessful transmissions, is investigated on slow-frequency-hopped channels with the aid of the catastrophe theory. The result of this paper can be viewed as extension of the result derived by Kim. The balance function is first formulated. Then, the cusp point and the bifurcation sets are numerically evaluated. We visualize how retransmission cutoff effects on bistable region. Using the result, we can design parameters of slotted ALOHA systems with retransmission cutoff such that the system operates with the unique stable equilibrium point.

We proposed a simple technique for measuring the effective zero-dispersion wavelength. In this study, we measured the effective zero-dispersion wavelength of a 25-km-long dispersion-shifted fiber (DSF) using the four-wave mixing (FWM) of a spectrum-sliced fiber amplifier light source, and then compared our results with other conventional techniques to confirm the validity of our method.

Due to the advancements in Information Technology, such as the Internet and the presence of fierce competition in the market, the business environment is changing rapidly. To cope with these dynamic changes, heterogeneous systems are now required to integrate in order to form alliances with different business units or within individual business units. Since business operations can not be stopped to carry out these changes in the existing systems, the systems are required to integrate flexibly, preserving each constituent's individual characteristics. By implementing Atomic Action through a gateway and across constituent systems in a Heterogeneous Autonomous Decentralized System (HADS), higher degrees of assurance can be achieved through cooperation. However, if all the transactions are passed through a gateway, the response time worsens and the result cannot be obtained within an appropriate timeframe. Hence, a new technique of suppressing the flow passing through the gateway, while achieving a maximum number of successful transaction within the appropriate timeframe, is required.

In this paper, we propose a new type of hybrid ARQ protocol, in which a channel-adaptive variable rate channel coding scheme is combined with a multi-copy retransmission strategy so as to enhance the system performance under the delay constraint of real-time ATM services in broadband radio access networks. The main feature of a multi-copy retransmission strategy in this scheme is to improve the average throughput for a given Forward Error Correction (FEC) rate, subject to the prescribed cell loss requirement of the real-time wireless ATM services, while augmenting the reliability of channel state information required for a channel-adaptive FEC scheme. Our analysis shows that under a harsh fading channel, the proposed approach is useful for achieving the prescribed cell loss performance without significantly degrading the average throughput performance.

This paper proposes a precise method of realizing simultaneous measurement of microscopic defects and the macroscopic three-dimensional shapes of planar objects having specular reflection surfaces. The direction vector field of surface tilt is evaluated directly by the introduction of a moving slit-light technique based on computer graphic animation. A reflected image created by the moving slit-light is captured by a video camera, and the image sequence of the slit-light deformation is analyzed. The obtained direction vector field of the surface tilt recovers the surface shape by means of integration. Two sample objects, a concave mirror and a plane plastic injection molding, are tested to measure the performance of the proposed method. Surface anomalies such as surface dent and warpage are detected quantitatively at a high resolution (about 0.2 [µm]) and a high accuracy (about 95%) in a wide area (about 15 [cm]) of the test object.

We consider iterative soft-decision decoding algorithms in which bounded distance decodings are carried out with respect to successively selected input words, called search centers. Their error performances are degraded by the decoding failure of bounded distance decoding and the duplication in generating candidate codewords. To avoid those weak points, we present a new method of selecting sequences of search centers. For some BCH codes, we show the effectiveness by simulation results.

A positive integer code EXEb,h,d(b1, h1,d0) is proposed. Its codeword for a positive integer n consists of three kinds of information: (1) how many times the number of n's digits can be subtracted by the terms of a progression including a geometric progression, (2) the rest of the subtractions, and (3) given value of the positive integer n. EXEb,h,d is a non-recursive type code. It is an asymptotically optimal code (for d1) and preserves the lexicographic,length, and number orders (for bh+2). Some examples of EXEb,h,d are also presented. Their codeword lengths are found to be shorter than the Amemiya and Yamamoto code CEk except for small positive integers.

An analytic equation was derived for the time jitter of digital NRZ signals due to inter-symbol interference in the PCB transmission lines loaded by DRAM chips which are located in uniform spacing. The inter-symbol interference is caused by a low-pass filtering effect of the loaded transmission line. Good agreements were observed between the equation and measurements with an average error of 17.5%.

Packet-based and stream-based traffic will be widely accommodated in third generation mobile systems. In direct sequence code division multiple access (DS-CDMA) systems, the impact of packet-based traffic is different from stream-based traffic because of different power control schemes adopted in a multipath fading environment. In this paper, a closed-loop like power control scheme is considered for packet-based traffic on the reverse link. The concept of packet cost is introduced that represents how packet traffic consumes the link capacity of stream-based traffic. The effects of the response delay, the fading maximum Doppler frequency, and the number of resolvable paths on the packet cost for a single cell system are investigated by using Markov modeling for a multipath fading channel with a uniform power delay profile.

This paper presents a fast inversion method for electromagnetic imaging of cylindrical dielectric objects with the optimal regularization parameter used in the Levenberg-Marquardt method. A novel procedure for choosing the optimal regularization parameter is proposed. The method of moments with pulse-basis functions and point matching is applied to discretize the equations for the scattered electric field and the total electric field inside the object. Then the inverse scattering problem is reduced to solving the matrix equation for the unknown expansion coefficients of a contrast function, which is represented as a function of the relative permittivity of the object. The matrix equation may be solved in the least-squares sense with the Levenberg-Marquardt method. Thus the contrast function can be reconstructed by the minimization of a functional, which is expressed as the sum of a standard error term on the scattered electric field and an additional regularization term. While a regularization parameter is usually chosen according to the generalized cross-validation (GCV) method, the optimal one is now determined by minimizing the absolute value of the radius of curvature of the GCV function. This scheme is quite different from the GCV method. Numerical results are presented for a circular cylinder and a stratified circular cylinder consisting of two concentric homogeneous layers. The convergence behaviors of the proposed method and the GCV method are compared with each other. It is confirmed from the numerical results that the proposed method provides successful reconstructions with the property of much faster convergence than the conventional GCV method.

The European Commission, through RACE, ACTS and now the IST programmes, has funded numerous consortium based research projects addressing capacity enhancement by means of Smart or Adaptive Antenna Technology. In addition to capacity enhancement, these projects have also considered the additional operational benefits, such as multipath mitigation and range extension, that this technology can offer to wireless network deployments. This paper provides an overview of the results obtained from the test-bed and field trial evaluations conducted under the ACTS TSUNAMI project. Here, a test-bed facility was developed by the project partners in order to appraise the potential merits of a Smart antenna facet deployment at the base-station cell site of a DCS1800 network. Details of the test-bed hardware and adaptive control algorithms are given, as well as results from the user tracking, traffic bearer quality assessments and range extension experiments. These results help substantiate many of the claims put forward by the proponents of Smart antenna technology, as well as ranking the relative performance of the family of adaptive control algorithms evaluated here. Further, new research activities, which embody Smart Antenna Technology, now supported under IST funding are also introduced.

This paper deals with the radiation phenomenon from bent transmission lines numerically and experimentally. At first, the radiation loss for different types of bent transmission lines has been estimated by using the method of moments (MoM), in order to suggest the most optimal design for a bent line in terms of a radiation loss. So, the simplest line with a right-angle bend is recommended. Then, the radiation patterns from such a right-angle bent transmission line have been numerically calculated, which may indicate that the radiation is originated mainly at the bend, but other parts are also found to contribute to the overall pattern with many extra lobes. All of the numerical results were confirmed by the corresponding experiment.

We studied a three-wave coupling process occurring in microwave power transmission (MPT) experiment in the ionospheric plasma by performing computer experiments with one-dimensional electromagnetic PIC (Particle-In-Cell) model. In order to examine the spatial variation of the coupling process, we continuously emitted intense electromagnetic wave from an antenna located at a simulation boundary. In the three-wave coupling, a low-frequency electrostatic wave is excited as the consequence of a nonlinear interaction between the forward propagating pump wave and backscattered one. In the computer experiments, low-frequency electrostatic bursts are discontinuously observed in space. The discontinuity of the electrostatic bursts is accounted for by the local electron heating due to the bursts and associated modification of the wave dispersion relation. In a case where the pump wave propagates along the geomagnetic field Bext, several bursts of Langmuir waves are observed. Since the first burst consumes a part of the pump wave energy, the pump wave is weakened and cannot trigger the three-wave coupling beyond the region where the burst occurs. Since the dispersion relation of the Langmuir wave is variable due to the local electron heating by the burst, the coupling condition eventually becomes unsatisfied and the first interaction becomes weak. Another burst of Langmuir waves is observed at a different region beyond the location of the first burst. In the case of perpendicular propagation, the upper hybrid wave, one of the mode branches of the electron cyclotron harmonic waves, is excited. Since the dispersion relation of the upper hybrid wave is less sensitive to the electron temperature, the coupling condition is not easily violated by the temperature increase. As a result, the three-wave coupling periodically takes place in time and eventually the transmission ratio of the microwaves becomes approximately 20% while almost no attenuation of the pump waves is observed after the first electrostatic burst in the parallel case.

This paper shows a comparison between several procedures to represent the Physical Optics (PO) current density into a hybrid Moment-Method-Physical-Optics (MM-PO) code. Some numerical results demonstrate that a set of basis functions suitable for the Method of Moments (MM) may be inappropriate to model the PO currents. A new evaluation of the PO operator is proposed. The radiation can be analytically determined and, since it includes a linear interpolation of the phase, it can be applied over large triangular domains. This allows a drastic reduction of the computational cost, maintaining or even improving the level of accuracy.

In this paper, we propose new approaches to speech enhancement based on soft decision. In order to enhance the statistical reliability in estimating speech activity, we introduce the concept of a global speech absence probability (GSAP). First, we compute the conventional speech absence probability (SAP) and then modify it according to the newly proposed GSAP. The modification is made in such a way that the SAP has the same value of GSAP in the case of speech absence while it is maintained to its original value when the speech is present. Moreover, for improving the performance of the SAP's at voice tails (transition periods from speech to silence), we revise the SAP's using a hang-over scheme based on the hidden Markov model (HMM). In addition, we suggest a robust noise update algorithm in which the noise power is estimated not only in the periods of speech absence but also during speech activity based on soft decision. Also, for improving the SAP determination and noise update routines, we present a new signal to noise ratio (SNR) concept which is called the predicted SNR in this paper. Moreover, we demonstrate that the discrete cosine transform (DCT) enhances the accuracy of the SAP estimation. A number of tests show that the proposed method which is called the speech enhancement based on soft decision (SESD) algorithm yields better performance than the conventional approaches.

In this paper, we propose an ECG waveform compression technique based on the matching pursuit. The matching pursuit is an iterative non-orthogonal signal expansion technique. A signal is decomposed to atoms in a function dictionary. The constraint to the dictionary is only the over-completeness to signals. The function dictionary can be defined to be best match to the structure of the ECG waveform. In this paper, we introduce the multiscale analysis to the implementation of inner product computations between signals and atoms in the matching pursuit iteration. The computational cost can be reduced by utilization of the filter bank of the multiscale analysis. We show the waveform approximation capability of the matching pursuit with multiscale analysis. We show that a simple 4-tap integer filter bank is enough to the approximation and compression of ECG waveforms. In ECG waveform compression, we apply the error feed-back procedure to the matching pursuit iteration to reduce the norm of the approximation error. Finally, actual ECG waveform compression by the proposed method are demonstrated. The proposed method achieve the compression by the factor 10 to 30. The compression ratio given by the proposed method is higher than the orthogonal wavelet transform coding in the range of the reconstruction precision lower than 9% in PRD.

In this paper, a CMOS down-conversion double-balanced mixer is presented with the modified low voltage design technique. The frequencies of the radio frequency (RF) signal, local oscillator (LO) and intermediate frequency (IF) are 2.4 GHz, 2.3 GHz and 100 MHz, respectively. Measurement results of the proposed mixer exhibit 6.7 dB of conversion gain, -18 dBm of input 1 dB compression point (P-1 dB), -8 dBm of input-referred third-order intercept point (IIP3), and 14.7 dB single-side band (SSB) noise figure (NF) while applying -8 dBm LO power and consumes 3.3 mA from 1.8 V supply voltage. It can provide 0.7 dB conversion gain when the supply voltage reduces to 1.3 V. This mixer was fabricated in a 0.35 µm 1P4M standard digital CMOS process and the die size is 1.5 1.1 mm2.

This paper presents a digital reaction-diffusion system (DRDS)--a model of a discrete-time discrete-space reaction-diffusion dynamical system--for designing new image processing algorithms inspired by biological pattern formation phenomena. The original idea is based on the Turing's model of pattern formation which is widely known in mathematical biology. We first show that the Turing's morphogenesis can be understood by analyzing the pattern forming property of the DRDS within the framework of multidimensional digital signal processing theory. This paper also describes the design of an adaptive DRDS for image processing tasks, such as enhancement and restoration of fingerprint images.