bluuebunny/crossref_metadata_2025 huggingface dataset:
Very low latitude whistlers and the effect of earth‐ionosphere waveguide propagation
Authors: Ohta Kenji , Shimizu Akio , Hayakawa Masashi , Shimakura Shin
Published: July 2007

When a sonogram of the nighttime whistlers observed in Wuchang, China, at a low latitude (at a geomagnetic latitude of 19.4°N) was studied in detail, whisker‐type spectral components were observed, which may be due to the waveguide propagation effect of the second‐ and third‐order modes, in the spectra of intense whistlers accompanied by echo trains. By applying the field analysis direction‐finding method to this part, the propagation characteristics are derived and the results exhibited a tendency identical to that of the characteristics of tweek atmospherics. It was found that the whistlers transmitted through the ionosphere at a very low latitude in Zhanjiang (geomagnetic latitude of 10.0°N) and exhibited an extremely rare waveguide mode propagation after subionospheric propagation of over approximately 1000 km.
Dual‐frequency corner‐reflector antennas fed by elements connected to parallel feed lines
Authors: Maruyama Tamami , Kagoshima Kenichi
Published: July 2007

The dual‐frequency antenna with the same beam‐width is well suited to the mobile communication base station antenna. One candidate is a corner reflector antenna whose elements are connected to a parallel feed line. However, no design equations or analysis have been published. This paper corrects this deficiency through analysis of the characteristics after integration of the two factors, spatial coupling and transmission line, for this antenna. A two dual‐frequency corner reflector antenna is designed. One uses co‐phase feedlines and is a wide band sector‐beam antenna with a 3 dB beamwidth difference of 30° in the field pattern of horizontal plane and a return loss of less than ‐15 dB over a wide frequency range (from 900 MHz to 1.5 GHz). the other uses antiphase feed lines and its beamwidths can be varied by changing the corner angle while the beamwidths are coincident at two frequencies.
A reconfiguration method for fiber optic subscriber loops
Authors: Imanaka Hideo , Iwashita Motoi , Yamamoto Hideo
Published: July 2007

A fiber optic subscriber loop provides many services that require high quality for a large number of subscribers. This means that it is necessary to establish a highly reliable, economical subscriber network.

A method for high‐reliability network construction has been proposed. In this method, the amount of equipment is reduced by utilizing a fiber access module (FAM), which allows fiber lines between the adjacent loops to be connected in the optical subscriber loop. to realize the function of the FAM inexpensively, manual cross‐connection is indispensable. However, the restoration time in the event of cable failure is quite long for manual crossconnection.

This paper proposes a reconfiguration method, the selected node reconfiguration method (SRM), which has a shorter restoration time than the conventional method, assuming a manual cross‐connection FAM. to further shorten the restoration time, a cross‐connection method is proposed in which several fibers are switched at the same time. the efficiency of this method and the functional structure of the FAM will be shown.
Optical digital cross‐connect system using photonic switch matrices and optical amplifiers
Authors: Shiragaki Tatsuya , Fujiwara Masahiko , Suzuki Syuji , Burke Conrad , Shiozawa Takahiro
Published: July 2007

An optical digital cross‐connect system (DCS) comprised of both photonic switching networks and electric DCSs is proposed for applications in network‐failure restorations. Optical DCSs exhibit excellent characteristics in restorations of multiple failures and when compared against their electrical counterparts, size‐reduced apparatus can be expected. the design of DCSs for applications in metropolitanarea networks are investigated and it is shown that such DCSs can be realized using LiNbO3photonic switch matrices together with traveling wave optical amplifiers (TWA).

With respect to the problem arising from the polarization dependency of TWA gain, it was solved using the output power controller (APC) which is shown theoretically to cause no difficulty in the noise characteristics. the optical DCS is designed and manufactured using LiNbO3switch matrices and TWA, by which its basic operation properties are verified. Using this trial system, it is confirmed that the network failures can be restored by changing the optical routes.
A spread spectrum communication system without a reference signal for a frequency‐selective fading channel
Authors: Miyatani Tetsuhiko , Akaiwa Yoshihiko
Published: July 2007

In a spread spectrum communication system (SS), RAKE reception is effective as a measure against frequency‐selective fading. Channel impulse response should be known for RAKE reception. In a conventional system where a reference signal is added to a transmission signal to obtain an impulse response, a decrease in transmission efficiency occurs under fast fading.

This paper proposes a scheme that does not use the reference signal by allocating different codes to information signals. In addition, a channel‐estimation scheme that alleviates effects of undesired autocorrelation values or cross‐correlation values of spreading codes is proposed. This scheme subtracts cross‐correlation values or excess autocorrelation values from a matched filter (MF) in measuring a channel impulse response and eliminates responses lower than a given threshold. Computer simulations under two‐path fading were performed. the error characteristics were improved with the proposed channel‐estimation scheme. It is shown that the proposed scheme is better than the scheme using a reference signal.
Performance of DS/FH‐CDMA over fading channels with near‐far problem
Authors: Shinkaji Yasuhiko , Yamazato Takaya , Katayama Masaaki , Ogawa Akira
Published: July 2007

The performance of a hybrid direct‐sequence/frequency‐hopping code‐division multiple‐access (DS/FHMA) system is investigated in the presence of both the near‐far problem and multipath fading. It is confirmed that the error‐correcting technique is essential lessening the effect of the near‐far problem and that the coded DS/FH system employing the Reed‐Solomon forward error‐correcting code preforms better than the coded DS system. It is shown also that the path‐diversity technique is effective in reducing the degradation caused by multipath fading.

As a result of this study, it is concluded that the DS/FH‐CDMA with the error‐control code and the path‐diversity technique is better suited to solve both near‐far problem and multipath fading than DS‐CDMA in which an accurate power control is difficult to achieve in such an environment.
Evaluation of handover performance in DS/CDMA systems
Authors: Kudoh Eisuke
Published: July 2007

This paper considers the performance of traffic capacity and handover frequency in a DS/CDMA system under imperfect handover. the effect experienced when the number of base stations observed by the personal station is restricted is estimated. Furthermore, the effect of handover hysteresis also is considered. Simulation models are presented which can evaluate the traffic capacity and the handover frequency under these imperfections. System performance is evaluated by computer simulations using these models.

It is found that if the number of observed base stations is 3 and the standard deviation of short‐distance medium value variance is 6 dB, the reverse‐link traffic capacity is reduced to about 90 percent and the forward‐link traffic capacity is reduced to about 85 percent, while the handover frequency is about 90 percent of the frequency of the short‐distance medium value variance.

It is found also that if the handover hysteresis is 4 dB and is 6 dB, the reverse‐link traffic capacity is reduced by about 10 percent while the handover frequency is about 60 percent of the frequency of the shortdistance medium value variance.
Throughput evaluation of multicast error control schemes with maximum distance separable codes
Authors: Salcakibara Katsumi , Kasahara Masao
Published: July 2007

One of the important issues in the multicast error control scheme is how to suppress the deterioration of the throughput due to the increase of the number of receivers. This paper proposes two multicast error control schemes, where the deterioration of the performance is ameliorated by generating the retransmission frame based on the maximum distance separable (MDS) code. One is the scheme which uses the MDS code with the fixed code length, and the other is the scheme to use the MDS code with the fixed minimum distance.

The throughput performance of the proposed scheme is derived analytically, and the result is compared with that of the conventional multicast error control scheme using the MDS code with the fixed number of information symbols. It is shown as a result that the throughput performance is better in the order of the scheme with fixed code length, the scheme with fixed number of information symbols, and the scheme with fixed minimum distance.
Orthogonal multicarrier frequency hopping‐code division multiple access scheme for frequency‐selective fading
Authors: Ohkawa Mitsugu , Kohno Ryuji , Imai Hideki
Published: July 2007

To improve frequency efficiency or user capacity in land mobile communication systems, orthogonal multi‐carrier frequency hopping‐code division multiple access (FH‐CDMA) is introduced and investigated. Such improvement is achieved by combining orthogonal frequency division multiplexing (OFDM) with FH‐CDMA. the theoretical analysis includes bit error rate (BER), required S/N, and maximum bit rate.

A modified scheme allowing transmission power to be controlled according to the number of simultaneously accessing users also is discussed. This scheme improves BER performance for frequency‐selective fading when the number of simultaneously accessing users in a cellular zone is small.
A method for observing the three‐dimensional patterns of electromagnetic power absorbed by the human body‐the gel phantom of the human body used to study the electromagnetic environmental problem
Authors: Miyakawa Michio , Takahashi Naoki , Hoshina Shinichiroh
Published: July 2007

By adding salt to highly molecular materials such as polyacrylamide and gellan gum, it is possible to construct a physical model for the biological system called “phantom,” which has nearly the same conductivity and relative dielectric constant close to that of biological tissue and is highly transparent at room temperature. If the nonionic surface active agent is added to such a gel, the following property is realized. When the phantom is heated and a small region reaches the temperature called a clouding point, the surface active agent is segregated, making the phantom white and opaque. When the phan tom is irradiated by the electromagnetic wave, the white and opaque region is produced according to the absorbed energy, making the three‐dimensional distribution of the absorbed power visible from the outside. Since the material is high molecular gel, there is no convection. It is also possible to construct a biological model without a container. This paper reports on the method for fabrication of such a phantom and a typical example is applied to the electromagnetic environmental problem.
Number of wavelengths required for constructing large‐scale optical path networks
Authors: Nagatsu Naohide , Hamazumi Yoshiyuki , Sato Ken‐Ichi
Published: July 2007

Photonic networks that exploit the abundant optical bandwidth capability are needed to realize a truly effective B‐ISDN. We have proposed two optical path schemes, the wavelength path (WP) scheme and the virtual wavelength path (VWP) scheme, wherein wave length division multiplexing/frequency division multiplexing (WDM/FDM) technologies are employed in the path layer of the transport networks. Although wave lengths are precious resources in photonic networks, the number of wavelengths required for any network has never been evaluated because of the NP‐completeness of the wavelength assignment problem. In this paper, we propose heuristic optical path accommodation design algorithms that can minimize the wavelength requirements in the network. We also evaluate the wavelength requirements for large‐scale and irregularly structured physical network topologies utilizing the proposed algorithms. Accordingly, we elucidate, for the first time, that the wavelength requirements for the WP and VWP schemes are almost the same regardless of physical network topologies and path demand distribution patterns.
A method of applying message sequence chart specifications for services with variant process structure
Authors: Moriyasu Kenji , Hirakawa Yutaka
Published: July 2007

Message sequence charts have recently been the focus of considerable attention as formal specification descriptions and become standardized. However, At is difficult to use them for specifying services with variant process structure, such as interrupt services.

This paper proposes a method that allows the number of processes in a service to change by selecting a suitable message sequence chart and switching the operation of each process over from the previous message sequence chart according to a specific procedure. Using this method, conventional synthesizing and verification techniques that deal with services with constant process structure can be applied to services with variant process structure.
A structure and control method of the fast re‐arrangeable nonbiocking (FAN) switch
Authors: Kim Dongwhee , Take Keijiro , Tominaga Hideyoshi
Published: July 2007

We propose a new self‐routing switch network, the fast rearrangeable nonbiocking (FAN) switch, and its control algorithm. the FAN switch is a rearrangeable switch network and is applicable to asynchronous transfer mode (ATM) switching because rearranging and routing are performed by hardware on the same time. the FAN switch has a modular structure that is constructed by connecting 4 × 4 elementary switches that consists of 2 × 4, 2 × 2, and 4 × 2 elements. We prove that the FAN switch with its characteristic control algorithm is a nonblocking network and compare it to other self‐routing switch networks.
Wideband phase‐locked loop synthesizer using linear frequency variation direct digital synthesizer as reference oscillator
Authors: Itoh Kenji , Lida Akio , Kanagawa Yousuke
Published: July 2007

A wideband phase‐locked loop (PLL) synthesizer is proposed in which a linear frequency variation direct digital synthesizer (LFDDS) is used as a reference oscillator and a frequency variation band can be widened up to the full tunable range of voltage controlled oscillator (VCO) by frequency hopping within the lock‐in range of PLL. A. theoretical study is made and experimental results are explained. At first, assuming continuous frequency variation of LFDDS, transient behavior of frequency difference between two input signals of phase comparator of PLL is determined. Next, the condition for frequency variation speed of LFDDS is derived so that phase locking can be obtained using the maximum value of this frequency difference. Then the quantized frequency variation of LFDDS is assumed, transient behavior of the frequency difference is determined, and its difference from the continuous variation is clarified. A 6‐GHz band PLL synthesizer is fabricated, and the theory's validity is confirmed through experiments. Using LFDDS, a frequency setting time for a PLL synthesizer increases less than 10 percent for five times wider operation bandwidth. Performing experiments in 79 6‐GHz band. we obtained an operation bandwidth of 23 percent and so frequency hopping can be performed. Moreover, a frequency setting time of 50 μs and spurious level of ‐55 dBc were obtained.
Tracking ability of decision feedback equalizer for time‐varying channel characteristics
Authors: Serizawa Mutsumu , Namekata Minoru , Murakami Junzo
Published: July 2007

The magnitude of the delay difference due to multihop wave propagation is such that it cannot be ignored compared to the inverse of the transmission speed, and it is capable of degrading transmission characteristics in TDMA digital mobile communications. It is known that adaptive equalizers are effective in preventing this problem; however, the tracking characteristics of such equalizers with respect to high‐speed variations of mobile communications transmission paths are not adequate.

This paper is an attempt to clarify the factors that degrade the tracking ability of such equalizers and to develop counter measures to protect against them. Specifically, the fact that the equalizer cannot track a time varying channel and evaporates when a decrease in the received signal level occurs due to the effects of wave propagation, etc., is a major contributor to the deterioration of equalization characteristics. This assertion is demonstrated analytically by simulations using the two‐ wave Rayleigh model and the one‐wave model in which the amplitude changes linearly with respect to time. In addition, to decrease the level of deterioration, a symbol‐ selective double‐directional equalizing system has been proposed; the efficacy of this system is demonstrated by simulation.
Parameter design of dynamic connection admission control in asynchronous transfer mode networks
Authors: Kawamura Yosbinori , Saito Hiroshi , Chaki Shinichiro
Published: July 2007

Dynamic connection admission control (dynamic CAC) has been proposed as one of the connection admission controls for asynchronous transfer mode (ATM) networks. Dynamic CAC uses the distributions of the number of cells arriving during a fixed interval. This distribution is renewed by exponential forecasting with smoothing parameter α This paper proposes a parameter design method that will enable this control to provide high utilization while suppressing VP GOS deterioration due to excess VC connections.
Optimal assignment of carrier frequency for frequency division multiple access using multibeam satellite
Authors: Nakamura Hajime , Mizuike Takeshi
Published: July 2007

This paper presents a new mathematical model for carrier frequency assignment of frequency division multiple access (FDMA) systems using a multibeam satellite. the model deals with carrier assignment of multiple transponders to minimize both intermodulation and cochannel interference simultaneously. As this problem requires a great deal of computation, the segmentation of a frequency band for efficient modeling is introduced. Based on this formulation, a new efficient algorithm is proposed using a branch‐and‐bound method with parallel processing. the algorithm is implemented and its efficiency is evaluated. Improvement of transmission quality as a result of the proposed model has been verified through numerical examples.
Coupled mode analysis of electromagnetic wave propagation in a laterally nonuniform duct in altitude with an even power N profile
Authors: Kawaguchi Yoshinari , Oka Eiichi
Published: July 2007

This paper theoretically analyzes the effect of an inverted atmospheric layer, nonuniform in the lateral direction, on wave propagation by means of the coupled mode theory. A grounded duct, an inverted atmospheric model, was employed in which a 2n power N profile (height) a located under standard atmosphere and the lowest layer with a linear profile. In terms of distance, the depth of the lowest layer is assumed to vary slowly with distance. the nonuniform atmosphere varying continuously in the distance is replaced by a staircase approximation. Numerical examples are given for the coupling coefficient of the neighboring atmospheres. the coupled mode becomes maximum immediately before the trapping mode and the mode conversion is more conspicuous for a larger n. the spatial distributions of the propagation characteristics are shown in the nonuniform duct made of uniform, nonuniform; and uniform sections in the distance direction. It was found that the variation of the received electric field changes significantly according to the change in duct height in the distance direction and that the effect of the order a is extremely significant.
Fundamental investigation of stimulated brillouin scattering suppression by fiber cabling
Authors: Imai Takeshi , Yoshizawa Nobuyuki , Tanifuji Tadatoshi
Published: July 2007

One of the main factors preventing the increase of the input power of optical fibers is the saturation of the input power by stimulated Brillouin scattering (SBS). In this paper, theoretical and experimental investigations are performed of three methods for suppressing SBS. the first method is to enlarge the optical fiber Brillouin gain bandwidth by applying a periodic strain distribution in the longitudinal direction of an optical fiber using the structure of the optical fiber cables. the second method is to shift the frequency of the Brillouin gain spectrum by connecting fibers with different core dopant concentrations. the third method is the combination of the two methods described above.

In the cable described in this paper, a sinusoidal strain distribution was induced in the fibers with a maximum strain amplitude of 0.4 percent and a pitch of 600 mm by using a double‐stranded structure. By doing so, the Brillouin gain bandwidth could be enlarged up to 400 MHz. Also, a frequency difference of 580 MHz is induced by connecting fibers with a dopant difference of a maximum of 4.4 percent between each fiber. It is shown that the SBS can be suppressed upto a CW optical input power of +17.4 dBm by widening the bandwidth and connecting optical fibers with shifted bandwidths. There fore, it is concluded that the proposed method is effective and practical for SBS suppression.
Medium access control protocol for intervehicle communication network using spread‐spectrum technique
Authors: Inoue Yasuhiko , Nakagawa Masao
Published: July 2007

With the severe traffic situation in recent years as the background, there are intensive studies on the inter‐vehicle communication system, aiming at the safety improvement of the road traffic system and the smooth control of the traffic flow. the spread‐spectrum communication is very useful in the realization of such a system since the data for the distance between vehicles are obtained, which is very important in driving the vehicle, as well as the communication.

This paper considers the intervehicle communication network using the spread‐spectrum system and proposes the medium access control (MAC) protocol for the autonomous distributed access control. to evaluate the performance of the proposed system, a computer simulation is executed for the environment where the vehicles run freely on a highway. It is shown that stable information exchange can be realized with vehicles running in nearby positions.
Transmission bandwidth control schemes for direct sequence/spread spectrum systems in the presence of periodic partial‐band interference
Authors: Aoyagi Yasushi , Kohno Ryuji , Imai Hideki
Published: July 2007

When a processing gain of a direct sequence spread spectrum (DS/SS) system is too small to suppress nar rowband interferences and the interference power is much higher than that of the desired signal, an adaptive filter [5‐7] cannot compensate for the uncorrelated interference signals because the filter coefficients cannot be updated. In this case, if the interfered bands are known, a notch or bandpass filtering is useful. However, such frequency domain filtering in the receiver may suppress not only the interfering signals but also the desired one. Prefiltering in the transmitter [8] cannot achieve the same performance as DS/SS systems without a bandpass‐fllter in the absence of interference.

This paper proposes and investigates a scheme of controlling the transmission bandwidth and its power spectral density using two spreading sequences in order to improve the performance in the presence or absence of high‐power periodical partial‐band interference. Two concrete systems also are proposed: a spreading sequence serial transmission system using different spreading 81 sequences; and a spreading sequence selectable ARQ system. In the former system, the transmitter does not consider the phase of the periodical partial‐band interfer ence in the receiver. Therefore, the system is realized easily because of the rather loose timing control require ment on the penalty of bit rate and because it does not require backward channels. On the other hand, in the latter system, 75 percent of the transmitted data are not degraded by the interference because of the more careful channel state selection at the transmitter than the former system.
A performance analysis of the slotted ring protocol for a voice/data integrated network environment
Authors: Fuwa Yasushi , Shimizu Hidetaka , Imura Hiroshi
Published: July 2007

A performance analysis of the slotted ring protocol for a voice/data integrated network environment is presented. At each node two types of packet generation (data and voice) are assumed and a model to provide dedicated buffers for storing each type of packet is constructed. Packet transmission is performed according to the slotted ring protocol with priority given to the voice packets. In particular, an on‐off model reflecting real behavior for the generation of voice packets is defined and finite capacities for the packet buffers are assumed to allow for the calculation of buffer overflow probabilities. In communication systems that handle voice packets, receiving nodes are normally equipped with buffers for accommodating the delays in packet transmission to prevent degradation of audio quality, although excessive delays can cause packets to expire and be discarded. This paper provides for the analysis of the rate at which voice packets are discarded at such nodes and discusses in detail the performance of voice packet transmission. the analysis of this model is based on the method of the equilibrium point analysis. the accuracy of these results are verified by comparing them with the results of simulation. Furthermore, one example of an application of these findings is to examine the effects of changing slot lengths on the performance of a network.
CLAD implementation and experimental results in ATM networks
Authors: Uematsu Hitoshi , Ueda Hiromi , Maki Kazumitsu , Kasai Hiroyuki
Published: July 2007

In ATM networks, CLAD functions convert the information source signal to cells and disassemble the ATM cells to yield the original signal. This paper implements a CLAD utilizing synchronous residual time stamp (SRTS) from the one in the method based upon AAL type 1. That transmits signals whose timing is independent of that of the network. It is clarified that the SRTS method generates low‐frequency jitter of the same order as the stuff multiplexing method. the SRTS jitter of the prototype CLAD is measured. A high‐quality NTSC motion picture is transmitted as DS3 (44.736 Mbits/s) coded signals. Furthermore, communication between two FDDI LANs is tested using DS3 data routers. These tests confirm that the CLAD works well.
Distribution feedback laser chirp depending on pulse pattern in high‐speed modulation and transmission performance
Authors: Amemiya Masaki
Published: July 2007

The wavelength generated by a single mode distribution feedback (DFB) laser varies over time inside pulses generated at high modulation speeds (chirp). This worsens the transmission characteristics of a long‐distance communication link that uses the laser as a light source. Because the modulation of the DFB laser is used to produce a pulse train signal to be transmitted, it is important to determine the dependence of the wavelength fluctuation on the modulated pulse pattern. The dependence of the chirp on the pulse pattern and its degrading effect on the transmission characteristics will be demonstrated here. It will be shown that the pulse pattern dependent wavelength fluctuation is due both to temperature variations caused by the pulse density and carrier storage effects at gigabit per second order modulation speed. The carrier storage effect of the pattern on the wavelength dependence can be reduced by increasing the bias current above the threshold value. However, raising the bias current does not improve the thermal dependent wavelength fluctuation. For example, it will be shown that for a modulation current of 90 mA, the generated center wavelength varies on the order of 0.08 nm. A model for the degradation of the transmission characteristics due to the wavelength fluctuation of the light source through the interaction with chromatic dispersion in the fiber will be presented. Degradation will be quantified experimentally and analytically.
Transition models for the number of broadcast viewers in broadband integrated services digital network
Authors: Tanaka Yoshiaki , Usui Tetsuya
Published: July 2007

When broadband integrated services digital network (B‐ISDN) service is implemented, the choice of a routing algorithm for broadcast services will be an important issue. Routing is the problem of deciding which of several nodes already connected to the broadcast node will be advantageous for the connection of new calls. In this respect, the number of viewers on each node would be important information. This paper uses broadcast traffic simulations to examine a method for determining a change in the number of viewers with the minimum number of calculations. The conventional approach would calculate the call transitions until the desired moment, but here the goal is to shorten the calculation time by determining the number of viewers directly at the desired moment. In this examination, under the two conditions M(N)/M/N and N, M(N)/D/N, two models are proposed for the duration of the ON state of the node (a situation where there is more than one viewer): the exponential distribution approximation and the hypercharacteristic distribution approximation. The number of viewers is modeled by the birth‐death process approximation and the normal distribution approximation. The amount of time needed for the calculation depends on the interval to calculate the traffic intensity and the number of viewers, but this is much less than the time needed when the conventional method is used.
Transmission power control effects for quasi‐millimeter microwave access systems
Authors: Manabe Toshihiro , Yoshida Teruaki , Murase Takehiro
Published: July 2007

In the quasi‐millimeter radio access system, the links are installed radially from the central station (CS) to the outstation (OS). Therefore, the interference characteristics of the CS are deteriorated at the time of rain.

This paper proposes a transmission power control method with a view to reducing the deterioration of the interference characteristics at the CS in rain. The effect of compensation of the level ratio of a desired wave to an undesired wave (D/U) degradation at the CS in the rain can be reduced by 11.5 dB by the transmission power control (TPC) of 20 dB. Further, the speed of the rain attenuation was found which is a propagation parameter needed for the TPC. The trailing speed of the rain attenuation in the proposed TPC algorithm is 67 dB/s, which is much larger than the maximum speed of the 3 dB/s of the rain attenuation. Hence, the proposed TPC algorithm can sufficiently follow the rain attenuation.
Range sidelobe suppression by locally weighting filter
Authors: Ehara Naoki , Sasase Iwao , Mori Shinsaku
Published: July 2007

One of the important technologies in the pulsed radar is the pulse compression by means of chirp signals. This technology simultaneously satisfies the contradicting requirements of increased search distance, or the increase of the average transmission power, and of range resolution. However, the waveform after pulse compression has a range sidelobe in the range direction and a small object existing near an object with a large radar cross section is hidden in the range sidelobe so that its detection becomes difficult.

To suppress the range sidelobes, a method has been considered to provide weights to the frequency characteristics of the pulse compression radar. In this paper, the wavelet transform as a tool for time frequency analysis is used for the analysis of pulse compression waveform. A range sidelobe suppression method in which a filter with a wavelet localized on the time and frequency axis as an impulse response is placed behind the compression filter is proposed since the frequency components near the main lobe and near the sidelobes are different. In this method, the local weighting is carried out.

As a result of the convolution of the pulse compressed waveform with the wavelet with a scale corresponding to the frequency components near the main lobe, i.e., the filtering, it is shown by computer simulation that the correlation is reduced in the range sidelobe region and the maximum sidelobe level is reduced by about 10 dB. The proposed method can be combined with the weighting of the frequency characteristics of the pulse compression filter. Further, the dc offset of the I/Q signal can be eliminated.
An analysis of single‐feed circularly polarized microstrip antenna using boundary element method
Authors: Ohmine Hiroyuki , Sunahara Yonehiko
Published: July 2007

This paper presents an analysis method of a singlefeed circularly polarized microstrip antenna (MSA) by means of the boundary element method. When the boundary element method is applied to such open planar circuits as the microstrip antenna, the loss due to radiation must be taken into consideration. As the radiation loss, it is proposed that the radiation admittance obtained from the radiated field from a microstrip antenna with a basic shape be used as the load. This radiation admittance can be derived easily without any complicated calculations.

As examples of the application of this analysis method, the computed values of the input impedance and the axial ratio are compared for the circular and rectangular MSAs with small sectors to remove the degeneracy and for the circular MSA with a shorting pin inside so that the effectiveness of the method is demonstrated. Also, an impedance matching method is proposed at the frequency for the minimum axial ratio by cancelling the inductance of the feed pin by means of the change of the positional relationship of the feed point and the small sectors.
Beam scanning characteristics of an optically controlled array antenna fed by a fiber optic array
Authors: Konishi Yoshihiko , Chujo Wataru , Fujise Masayuki , Yamada Ken‐Ichi
Published: July 2007

For an optically controlled array antenna in which the microwave excitation distribution is generated and controlled in the optical domain by means of the optical Fourier transform and the optical/electrical (O/E) conversion, element antenna excitation, and the radiation characteristics are theoretically and experimentally studied in the case in which the image mask is shifted from the optical axis of the Fourier transforming lens for an intended beam scanning. A planar fiber optic array was constructed and the excitation profile and the radiation pattern were experimentally investigated by means of a fiber optic array. First, the excitation profile and the beam scan angle were theoretically expressed in the case in which the circular aperture image mask shift and beam scan angle is derived. From the excitation profile experiment using a type of two‐laser optically controlled array system, it is shown that the excitation profile necessary for the beam scanning can be obtained. From the calculation of the radiation pattern, the beam scanning corresponding to the computed value is possible. A 61‐element fiber optic array was then designed for trial. By using the excitation profile experiment with this array, it is shown that the excitation profile and the beam scanning characteristics can be obtained with the fiber optic array if the transmission loss of the fiber optic array is compensated for.
Geometrical optics in dissipative media—uniform plane wave approximation
Authors: Tokumaru Shinobu
Published: July 2007

The conventional ray optics theory in a lossless medium is extended to an inhomogeneous medium with slight dissipation including the circular polarization decomposition of the field. To extend this theory, a complex eikonal is introduced. Next, as a physical quantity to express the energy relationship, an absolute value Poynting flux is introduced. Having introduced these quantities, the wave propagation in the lossy medium is assumed to be a locally uniform plane wave. From the complex eikonal and the absolute value Poynting flux, the wavefront normal is defined and the absolute value Poynting ray also is defined. The amplitude of this absolute value ray is derived. It is shown that this ray satisfies Format's principle.
Path diversity technology based on multipath selection for a spread spectrum communication system
Authors: Moriyama Eimatsu
Published: July 2007

Land mobile communications systems that implement spread spectrum are being actively researched. With direct‐sequence spread spectrum, performance is predicted to improve by dividing a multipath delay wave into separate paths, using path diversity combining, and so‐called path diversity receiver.

Generally, although performance improves with an increase in the number of branches in a path diversity system, a small number of branches is preferred with the implementation of a receiver. Hence, this paper analyzes the performance whenn= 2 for a model of a path diversity receiver wherenpaths are selected fromMcandidate paths in order of the largest instantaneous signal‐to‐noise (S/N) ratio, and bearing in mind the receiver that produces the maximal ratio combining. The results show that there is no significant difference betweenn= 4 andn= 2 whenM= 4. The average power delay profile shows the number of effective branches when applying a system ofn= 2 branches to path diversity for both the exponential and rectangular models. Also, the theoretical value for the BPSK and FSK average bit error rate performance is determined for a primary modulation system with the rectangular model.
Direct sequence/code‐division multiple‐access adaptive interference canceller on differential detection for fast fading channel
Authors: Yoshida Shousei , Ushirokawa Akihisa , Yanagi Shuzo , Furuya Yukitsuna
Published: July 2007

This paper proposes the differential detection type direct sequence/code‐division multiple‐access (DS/ CDMA) adaptive interference canceller (AIC) that can track the fast fading. The proposed AIC is composed of the fractionally chip‐spaced code‐orthogonalizing filter (COF) with tap length corresponding to several bit periods and the differential detector. The COF makes adaptively the tap weight orthogonal to all spreading codes of other users as a despreading code of the desired user so that the interferences from other users are cancelled and the signal component of the desired user is extracted. The differential detector compensates the carrier phase variation due to fading in the desired user's signal at the COF output. By such a structure, the tracking performance of AIC to the channel variation can be improved to the limit of the tracking performance of the differential detector.

This paper evaluates the basic ability of the proposed AIC in the fast‐fading channel. The AIC is especially expected to be utilized in the DS/CDMA mobile communications since the receiver is of the single‐user type, where no information concerning other users is needed.
A filter for reducing speckle in synthetic aperture radar images
Authors: Kobayashi Nobuyoshi , Hirosawa Haruto
Published: July 2007

A filter for reducing the speckle in synthetic aperture radar (SAR) images is proposed. This filter is based on the most likelihood method and consists of the following procedures. First, by using ann X nwindow, a spatial averaging is carried out and two‐dimensional data composed of sets of average value μ and variance o2are generated. Next, by also applying then X nwindow, the samples, without being affected by edges are extracted among the samples contained in the window based on a criterion derived from the statistical characteristic of the speckles. For the extracted samples, the average value of μ is computed and the derived value is given as the output for the pixel at the center of the window. For this filter, smoothing characteristics and the operation at an edge are evaluated by simulation. Applying the filter to the SAR images allows it to be confirmed that the filter operates correctly.
Evaluation of radio frequency immunity test facilities based on the scattered field of a conductive sphere
Authors: Akiyama Yoshiharu , Kuwabara Nobuo , Ideguchi Tsuyoshi , Tokuda Masamitsu
Published: July 2007

In the radiation immunity test for telecommunication equipment, an electromagnetic applicator such as chamber, a transmission electron microscopy (TEM) cell and a general transmission electron microscopy (GTEM) cell are used. Characteristics that include a semianechoic uniformity of the electromagnetic field without a device under test have been evaluated. However, characteristics that include an electromagnetic field in the presence of the device under test have not been reported.

In this paper, it is recognized that these electroamgentic applicators are designed in such a way that they can generate an electromagnetic field simulating a plane wave. Based on the electric field distribution generated by the plane wave incident on a conducting sphere, the electric field is evaluated and compared in the case in which the device under test is placed within the applicator. Further, evaluation results are included for the size of the device under test for which the immunity test is possible in each applicator. The evaluation method first derives the theoretical value of the scattered electric field when a plane wave is incident on the conducting sphere in free space.

Next, these theoretical values are compared with the measured electric field values around the conducting sphere in each electromagnetic applicator. It was found that the difference between the measured and the theoretical results is the smallest and the frequency dependence is the lowest in a semianechoic chamber. In the case of a TEM cell and a GTEM cell, it was found that the difference between the measured and the theoretical values is less than +6 dB if the magnitude of the device under test is less than one‐third the spacing between the inner and outer conductors.
Real‐time air traffic flow management: Expectations and probabilities of delay
Authors: Qiao Mu , Morikawa Hiroyuki , Mizumachi Moriyuki
Published: July 2007

Air traffic flow management is carried out with a view to maintaining smooth aircraft traffic. Real‐time air traffic flow control is to carry out the air traffic flow control responsive to a real situation in real time by express use of the present situation of the desired terminal region and the radar information.

With a view to such real‐time air traffic flow management, this paper derives equations for the holding delay time expectation value of aircraft requesting take‐off, the delay time expectation value within the terminal, holding generating probability, delay generating probability in the terminal, and the flight delay generating probability. If in the future any departure‐regulating procedure for reducing the flight delay time of the aircraft requesting take‐off is developed based on the values found from these equations, it becomes possible to carry out the air traffic flow management adaptively to a real situation.
Application of millimeter‐wave radar traffic observation system
Authors: Shimoi Nobuhiro , Nakamura Yatsuka
Published: July 2007

Traffic monitoring systems employ, as sensors, infrared image systems, visible light image systems, and so on. But observation with such monitoring systems are limited to highway interchange areas and intersections of large roads. Also, such systems often fail to detect vehicles hidden by obstacles such as roadside trees because the sensors are easily affected by weather conditions such as rain and dense fog.

This paper discusses sensors using 94‐GHz millimeter‐wave radar in traffic observation systems. These sensors make it possible to observe hidden cars and to reduce the influence of weather and are unaffected by night and day conditions.

In addition, it is possible to improve the observation ability by using both the current system and the 94‐GHz millimeter‐wave radar for unattended observation of traffic within the range of 1 km.
Still image transmission using unequal error protection coding in mobile radio channel
Authors: Matoba Naoto , Yoshida Susumu
Published: July 2007

With the advent of multimedia mobile communication, image transmission in the fading channel is becoming more and more important. This paper discusses the highly efficient coding where the image coding and the channel coding are integrated. More precisely, the following hierarchical image transmission is proposed. Assuming Joint Photograph Experts Group (JPEG) progressive image coding, discrete cosine transform (DCT) transform coefficients or the bit planes are divided into groups so that the unequal channel coding rates are assigned according to the effect of the channel error on the image quality. The proposed system is examined and evaluated by a computer simulation. As a result, it is shown that the reconstructed image suffers from less deterioration compared to the case where the channel coding rate is assigned uniformly.
Traffic design method for switched telecommunication networks with double homing and combined switching
Authors: Mase Kenichi , Kawano Hiromichi
Published: July 2007

This paper proposes the concept of partially combined switching which is useful in a network design with double homing and combined switching. Partially combined switching makes some of the switches that are found in a certain switch office play the same role as in a different switching office. With partially combined switching, both improvement in switch utilization efficiency and reduction in the number of switches are expected. The concept of hierarchy, such as traffic network, circuit network, etc., is introduced; within this framework the theory of network design with partially combined switching is developed. The changes in network topology and routing tables necessary in order to realize partially combined‐switching are shown here. A traffic assignment method is also shown for circuit networks with partially combined switching. It is pointed out that techniques such as one‐sided homing and combined hierarchy used for the present digital telephone network are examples of partially combined switching. Finally, numerical examples are presented to show that the partially combined switching is effective to reduce the number of switches in the network.
A fast traffic simulation method using vector operation
Authors: Tanaka Yoshiaki , Shimizu Sheyu , Kojima Akihiro , Tomochika Takeshi
Published: July 2007

The supercomputer is used widely at present in various research institutions, and it is quite usual to employ the supercomputer in the simulation. The performance of the supercomputer is improved steadily. A problem in the conventional traffic simulation, however, is that little vector computation is included and the speed of improvement of the simulation has been difficult even if a supercomputer is used.

This paper aims at the effective use of the supercomputer in the traffic simulation. A vectorized simulation method is proposed where the simulation clock is advanced for each unit of time, and the call origination and the use of link are represented by a matrix or a vector.

Simulation models actually are considered for the circuit‐switching network and the packet‐switching network. The vectorized simulation is applied to those models, and the performances are assessed, compared to those of the conventional method, in terms of the computation time, the call loss probability and the waiting probability. It is shown as a result that the execution speed is improved greatly within a certain range of the error, indicating that the proposed vectorized simulation is effective.