bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimal assignment of carrier frequency for frequency division multiple access using multibeam satellite
Authors: Nakamura Hajime , Mizuike Takeshi 
Published: July 2007

AbstractThis 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

AbstractThis 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

AbstractOne 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

AbstractWith 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

AbstractWhen 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

AbstractA 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

AbstractIn 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

AbstractThe 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

AbstractWhen 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

AbstractIn 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

AbstractOne 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

AbstractThis 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

AbstractFor 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

AbstractThe 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

AbstractLand 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

AbstractThis 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

AbstractA 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.