Broadband fixed wireless access (FWA) systems offer significantly higher bit rates than current cellular systems to which adaptive arrays are partly applied. Digital beam forming is being eagerly explored on account of its flexibility, but it will be difficult to apply to the high-speed systems, because its digital signal processing requires huge resources and power consumption. Conventional phased arrays, on the other hand, utilize phase shifters through RF or IF signal lines, but the phase shifters are usually both bulky and expensive. The authors propose an adaptive array steered by IF local signal phase shifters in this paper. The phase shift and the frequency shift of the signal from each antenna element can be simultaneously accomplished at the down conversion stage by the phase-controlled local signal. A prototype receiver operated in the K-band with the proposed configuration and its beam pattern measurement results are also described.

To generalize characteristics of a received signal level distribution from narrow- to wide-bands in a mobile radio channel, a new propagation parameter called equivalent received bandwidth (2ΔfΔLmax) has been proposed. The distributions are discussed mainly with computer simulation results. The simulation results shows the level distribution depends on 2ΔfΔLmax and power ratio a of direct to indirect waves, and the value of 2ΔfΔLmax classifies the radio channel as narrow- or wide-bands transmission. To confirm these simulated results, a field test was performed with a 3.35 GHz radio wave. This paper describes that the field test demonstrated the simulation results. It is concluded that the equation representing received signal level in the computer simulation is valid. And the fading depth depends directly on 2ΔfΔLmax, and the 2ΔfΔLmax is effective for generalizing the received signal level distribution. Furthermore, a method for calculating the power ratio was found to be better for a peak level model.

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.

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 first gives the exact surface integral representation for PO diffracted electromagnetic fields from bounded flat plate through the deformations of the original surface by using field equivalence principle. This exact representation with the surface integral can be approximately reduced to novel line integral along the boundary of the plate by the use of Maggi-Rubinowicz transformation, which keeps a high accuracy even in near zone. Numerical results for the scattering of the electric dipole wave from the square planar plate are presented for demonstrating the accuracy.

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.

This work presents a novel channel assignment scheme for low earth-orbit (LEO) satellite-based mobile communication systems, in which any newly generated call will first be assigned an optimum channel and will no longer be reassigned even when it crosses the boundary of the cell. Thus, the compact reuse distance can be maintained and no handoff failure will occur owing to channel unavailability. Furthermore, a high quality service which guarantees successful handoff processes can be provided. The performance of the proposed strategy is analyzed and compared with the performances of the fixed channel assignment (FCA) scheme and dynamic channel assignment schemes.

A flexible noise generation algorithm using DCT is proposed. The proposed method outperforms the conventional methods when a noise model requires complicated PSD (Power Spectral Density) specifications. Also, it is shown that the proposed system can be used for the test of VDSL (Very high-speed Digital Subscriber Line).

Software defined radio (SDR) is receiving much attention as the key technology to realize the next generation wireless communication system. This paper proposes the concept of system diversity on SDR and investigates the effectiveness of system diversity by using a concrete simulation model. System diversity allows the wireless communication system being used to be dynamically changed in addition to the signal processing algorithm or modulation/coding scheme being used. To clarify the validity of system diversity, we examine a system simulation model consisting of three wireless communication systems; algorithms are introduced to show how system diversity can be controlled using the QoS parameters of received signal level, data transmission rate, and channel capacity. The process by which system diversity switching is triggered is elucidated, and a practical example is introduced. Simulation results confirm that system diversity offers higher performance in terms of data throughput and system channel capacity than existing wireless communication systems. Finally, a comprehensive algorithm is described that protects existing single-mode traffic from being degraded by SDR switching.

This paper presents the design of low sidelobe single-layer slotted waveguide arrays. The Taylor distribution with -25 dB sidelobe level is synthesized in two orthogonal directions in the aperture. The multiple-way power divider consisting of a cascade of novel π-junctions is introduced; each π-junction, two-way power divider, is so designed as to accept unequal power dividing by adopting an offset window. The smooth Taylor distribution is realized at the output of the multiple-way power divider, which was originally developed only for uniform distribution. A model antenna for Taylor distribution is tested at 76 GHz. The measured sidelobe level is below -24 dB in both E- and H-plane. The highest gain is 34.5 dBi with 50% efficiency which is only 15% lower than that for uniform aperture illumination.

A high quality speech synthesis technique based on the wavelet subband analysis of speech signals was newly devised for enhancing the naturalness of synthesized voiced consonant speech. The technique reproduces a speech characteristic of voiced consonant speech that shows unvoiced feature remarkably in the high frequency subbands. For mixing appropriately the unvoiced feature into voiced speech, a noise inclusion procedure that employed the discrete wavelet transform was proposed. This paper also describes a developed speech synthesizer that employs several random fractal techniques. These techniques were employed for enhancing especially the naturalness of synthesized purely voiced speech. Three types of fluctuations, (1) pitch period fluctuation, (2) amplitude fluctuation, and (3) waveform fluctuation were treated in the speech synthesizer. In addition, instead of a normal impulse train, a triangular pulse was used as a simple model for the glottal excitation pulse. For the compensation for the degraded frequency characteristic of the triangular pulse that overdecreases than the spectral -6 dB/oct characteristic required for the glottal excitation pulse, the random fractal interpolation technique was applied. In order to evaluate the developed speech synthesis system, psychoacoustic experiments were carried out. The experiments especially focused on how the mixed excitation scheme effectively contributed to enhancing the naturalness of voiced consonant speech. In spite that the proposed techniques were just a little modification for enhancing the conventional LPC (linear predictive coding) speech synthesizer, the subjective evaluation suggested that the system could effectively gain the naturalness of the synthesized speech that tended to degrade in the conventional LPC speech synthesis scheme.

This paper proposes serially arranged two parasitic elements above a fed dipole to obtain broad bandwidth in resonant frequency of a parasitic element. The above antenna can be used in triple-bands with one feed point. Its design method using FDTD is also presented. Next, application of the triple-bands antenna is proposed for 3-sector base station antenna. Its characteristics of return loss and radiation patterns are indicated. Calculated values are in good agreement with measured ones.

Analysis of a novel folded loop antenna for handset is described along with the advanced design concept for handset antennas. The design concept shown in this paper meets the foremost requirement for handset antennas such as (1) small size and yet (2) has capability of mitigating degradation of antenna performance due to the body effect, and (3) of reducing SAR value in the human head at the handset talk position, in addition to the indispensable requirements for handset antennas such as (4) low profile, and (5) light weight. The technology applied is to make this antenna (a) an integrated structure, which is a typical application of the fundamental concept of making antennas small and (b) a balanced structure which has been proved to be very effective to satisfy the requirements (2) and (3). The antenna is essentially a two-wire transmission line, folded at about a quarter-wavelength to form a half-wave folded dipole, and yet appears to be a loop of one-wavelength. It does not have really a balanced structure, as is fed with an unbalanced line; however, the antenna structure itself can eliminate the unbalanced current flow on the feed line as in the balanced antenna system. Both theoretical and experimental analyses have been shown and the usefulness of the antenna is discussed. This paper may suggest the advanced technology and design concept that will be applied to the development of handset antennas toward the future.

A polarization diversity planar inverted-F antenna (PIFA) on portable telephone in the practical use near the operator's body is investigated at 1,800 MHz under multipath urban environment. The antenna structure comprises a center-fed square patch with one permanent short-pin and two RF-switches on three corners. The RF-switches perform as the polarization branch switches for dominantly vertical polarization (VP) or dominantly horizontal polarization (HP) modes. The radiation efficiency of the polarization diversity PIFA is 58% and 53% for VP and HP modes, respectively, which is higher than the 52% efficiency of the reference λ/4 monopole antenna under the same condition. The mean effective gain (MEG) of VP and HP modes decrease with respect to the increasing cross-polarization power ratio (XPR). The correlation coefficient of two diversity branches is between 0.66 through all the possible XPR ranging from -10 dB to +10 dB. The diversity gain is computed from the MEG and correlation coefficient to determine the diversity antenna gain (DAG). The diversity gain, based on 10-3 BER for selective combining, is 7.5 dB over non-diversity reception. The DAG is -1.2+2.8 dBi which is approximately 4 dB lower than the case without human body. In other words, the presence of the human body degrades the communication performance by a half.

This paper presents a novel design method for reducing the complexity of the design procedure for diversity antennas on the hand-held phone. Recently, antenna selection diversity has been widely used for hand-held phones in order to overcome a problem of fading. A monopole antenna and an inverted-F antenna are the typical combination for this purpose. In the case of the conventional design method, the mutual coupling between two antennas are used for improving the diversity performance. However, strong mutual coupling often makes the diversity antenna design difficult and degrades the radiation performance. The proposed design method suppresses this coupling by tuning the terminating impedance on the unselected antenna and improves the diversity performance by modifying the shape of inverted-F antenna. The validity of the proposed method is investigated under the effect of the user's hand and head by FDTD simulation.

Beam reconfiguration by structural reconfigurable antenna, such as the small multi-panel reconfigurable reflector antenna, has an aspect of great concern, that is the effects due to the use of a number of small panels to form the reflecting surface. It is thus a matter of great interest to numerically investigate all possible factors affecting the performance of this type of antenna such as: neighboring panels blocking, diffraction. The "null-field hypothesis" and PTD are employed to account for the effects of both phenomena on the main beam steering ability and the cross-polar level. In addition, the transformation of the polygonal flat domains into the square domains is applied in calculating the PO radiation field due to the various irregular polygonal flat sections of the arbitrary initial approximate reflector e.g., the flat circular reflector and the paraboloidal reflector. It is found that the main contribution to the total cross polarization is depolarization due to the finite size of the panels. The maximum cross-polar gain predicted using PTD is around -30 dB. The blocking effect has minor influence on cross-polarization. Both effects cause distortion on the co-polar pattern for the observer far from boresight but blocking has more influence than edge diffraction. Both effects have minor influence on the co-polar gain. The co-polar gain has variation of less than or equal to 0.07 dB in the flat case and 0.16 dB in the paraboloid case.

An optically controlled beamforming technique is a very effect procedure for phased array antenna control. We have built a Fourier optical processing beamforming network. In the optical processor, we use optical waveguide arrays and a GRIN micro lens in order to reduce the size and weight of the processor, optical coupling losses, mechanical destabilization, and optical alignment difficulties. This paper describes the characteristics of a one-dimensional Fourier optical processor, and shows the configurations of both its transmitting and receiving modes, which we have constructed. We demonstrate multiple signal generation, and beam steering for transmission in the X-band. Furthermore, we configure the beamformer for reception using the phase information of local signals form the optical processor. We additionally demonstrate the beam steering of the received X-band RF signal. Experimental results confirm the feasibility of the Fourier optical processing beamforming network.

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.

A self-similar behavior characterizes the traffic in many real-world communication networks. This traffic is traditionally modeled as an ON/OFF discrete-time second-order self-similar random process. The self-similar processes are identified by means of a polynomially decaying trend of the autocovariance function. In this work we concentrate on two criteria to build a chaotic system able to generate self-similar trajectories. The first criterion relates self-similarity with the polynomially decaying trend of the autocovariance function. The second one relates self-similarity with the heavy-tailedness of the distributions of the sojourn times in the ON and/or OFF states. A family of discrete-time chaotic systems is then devised among the countable piecewise affine Pseudo-Markov maps. These maps can be constructed so that the quantization of their trajectories emulates traffic processes with different Hurst parameters and average load. Some simulations are reported showing how, according to the theory, the map design is able to fit those specifications.

This paper describes the implementation of a proposed image filter into a Discrete-Time Cellular Neural Network (DT-CNN). The three stages that compose the filter are described, showing that the resultant filter is capable of (1) erasing or detecting several concentric shapes simultaneously, (2) thresholding and (3) thinning of gray-scale images. Because the DT-CNN has to fill certain conditions for this filter to be implemented, it becomes a modified version of a DT-CNN. Those conditions are described and also experimental results are clearly shown.