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This paper discusses a λ/4-type wave absorber for the microwave band made with conductive paper, which is paper with a coating of conductive material. A simplified wave absorber of this type is first designed and constructed for the X band and Ku band. Using the resulting absorption characteristics, experimental formulas are derived for the relative permittivity and surface resistance. These formulas are then used to design and construct a more practical wave absorber, whose absorption characteristics are measured. Excellent absorption characteristics, better than 20 dB, are verified in the intervals from 8.2 to 10.6 GHz and from 14.1 to 17.2 GHz for wave absorption in the X band and Ku band, respectively, although there is a difference of approximately 0.4 dB between the designed matching frequency and the measured value. Design guidelines for such a microwave absorber using a conductive coating are then presented. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(10): 100–107, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1180

When an adaptive array antenna is used in cellular and other mobile communication base stations for the purpose of improving SINR, the array antenna itself sometimes falls into a fading valley, resulting in failure to obtain an adequate improvement effect. While this problem can be solved by increasing the aperture length of the array antenna, simply increasing the aperture length alone increases the number of antenna elements, so that a large-scale adaptive array antenna becomes required, leading to the problem of failure of the weighting to track changes in the environment during fast fading. In this paper, we try to solve the first issue by making the element spacing nonuniformly aligned, reducing the number of elements. For the second issue, the weighting is divided into two layers, resolving the problem through both use of MMSE to eliminate interference and use of EGC for diversity combining. In a slow fading environment, however, favorable characteristics can be obtained when the entire weighting is controlled by MMSE. In this paper, we estimate the fading speed by the amount of envelope fluctuation in the desired signal after elimination of interference by the initial layer MMSE, and propose during slow fading the use of MMSE batch control, and during fast fading a control that incorporates both MMSE and EGC diversity combining. Finally, we use a computer simulation to evaluate the validity. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 13–21, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20397

In this paper, the authors propose a new control scheme in which the output voltage is fed back into a triangle waveform of a control circuit to improve the transient response of a switching converter. The circuit structure of the proposed system is very simple and will therefore reduce the size and weight of the apparatus and have reduced production costs. Also, because an error amplifier is not used, the circuit is not affected by switching noise or the like and the circuit is easy to design. In this paper, the proposed system is applied to a synchronous rectifying buck converter; the basic properties are analyzed and the system is verified experimentally. As a result, it was confirmed that the proposed scheme has superior regulation properties and transient response characteristics. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(7): 52–59, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20256

This paper presents the results of a study of the OFDM adaptive modulation technique. The adaptive modulation technique, which selects the modulation scheme according to the transmission conditions, is effective in improving system throughput. Then, it is important to study evaluation function under various propagation conditions. In this paper, we propose an adaptive modulation technique using the instantaneous DUR (desired signal to undesired signal ratio) per packet as the performance measure of the transmission path, in which the intersymbol interference (ISI) and intercarrier interference (ICI) power of delayed waves exceeding the guard interval are used under the assumption of convolution coding and soft-decision Viterbi decoding. A DUR estimation method is also proposed. The effectiveness of the approach is confirmed by numerical simulation. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(3): 36–45, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20254

Bluetooth is a short-range wireless system using the 2.4-GHz band, but has the problem of degradation of communication quality caused by the noise radiated by microwave ovens which share the same frequency band. In this paper, we theoretically and experimentally study the impact of microwave oven noise on Bluetooth. Time variations in the bit error rate with a fixed channel frequency are theoretically evaluated applying the time domain oven noise model represented by frequency and amplitude modulated wave to the theoretical equation of the bit error probability for frequency shift keying (FSK). The average bit error rate and the average packet error rate with the frequency hopping spread spectrum (FH-SS) scheme are also evaluated. The results of theoretical study show that (1) microwave oven noise using an inverter power supply (inverter-type) degrades average packet error rate more seriously than does a microwave oven not using an inverter power supply (transformer-type), and that (2) FH-SS is less effective in mitigating interference from inverter-type oven noise compared with transformer-type oven noise. Experiments are conducted using Bluetooth terminals. Error rates are measured using actual ovens and oven noise simulator based on the noise model. The effectiveness of the noise model applied in this paper in the evaluation of the Bluetooth transmission characteristics during microwave oven noise interference is demonstrated. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(11): 24–34, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20275

Application of the UWB technology to Wireless Personal Area Network (W-PAN) systems and high-speed wireless Local Area Network (LAN) systems is currently being studied. This paper proposes a thin and compact antenna with very wide band characteristics for UWB systems. Antennas for UWB systems must have good wideband characteristics while being thin and compact because they need to be built into UWB system candidates, such as wireless TVs, hard disk video-recorders, and personal computers. Traditional wideband antennas had to be three dimensional or have a large ground plane, making installation in the above types of equipment difficult. This paper describes the flat-type UWB antenna, which consists of a large elliptical element with a hole, a small elliptical element, and an element shaped like an inverted U, which realizes excellent wideband characteristics. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(12): 54–61, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20301

An SCM optical FM method can obtain an FM gain, so it is effective on employing an RoF link which transfers a broad-band or multicarrier RF signal. However, the RF signal quality is degraded by intermodulation distortions due to the nonlinearity of LDs and optical frequency discriminator. The nonlinear compensation technique in the RoF link has been investigated in order to obtain a higher RF signal quality. This paper proposes an insertion-type distortion nonlinear compensation. In the proposed scheme, a nonlinear device is inserted between transmitter and receiver and we propose an optical chirp controller as the nonlinear device. The proposed scheme suppresses the higher order intermodulation distortion which degrades RF signal quality in the adaptive transmittance control method. In this paper we theoretically analyze the SFDR of the optical FM method using the optical chirp controller and show that improvement in the SFDR at 9 and 5 dB compared to methods without nonlinear compensation and the adaptive transmittance control method, respectively, can be obtained. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(12): 1–11, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20322

This paper considers multiple beamforming in the transmitter and receiver in MIMO channels and discusses the weight control procedure. The first half of the paper describes the transmitter and receiver weight conditions for realizing large capacity, for the cases with and without interference signals from other users. The second half proposes a weight control method which can realize high capacity in a real environment. In the proposed system, the control signal is exchanged between the transmitter and the receiver and the transmitter and receiver weights are determined. Using the proposed method, a satisfactory transmission weight can be determined even if the transmitter does not know the propagation information. As a result of simulation, we see that the proposed method is less affected by the propagation path and can assure stable throughput. We also find that the proposed method can achieve high throughput even if a control error occurs. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(6): 55–70, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20145

OFDM AMS/MTPC (OFDM-based Adaptive Modulation Scheme with Multilevel Transmit Power Control) using multilevel transmit power control schemes to set the modulation levels and transmitted power of each subcarrier of an OFDM (Orthogonal Frequency Division Multiplexing) system can significantly improve the throughput in an isolated cell environment. This paper takes advantage of the property that OFDM AMS/MTPC allows high throughput by using the frequency selectivity of the received SINR (Signal to Interference plus Noise power Ratio) in the presence of interference, and a one-cell reuse TDMA (Time Domain Multiple Access) system using simple wireless resource control is proposed. In this system, it is necessary to limit dynamic variations of the interference power level associated with transmit power control in such a way that control of the OFDM AMS/MTPC can be appropriately carried out depending on the interference among the cells. In this paper, it is confirmed that an effective cell reuse value of 1.46 can be achieved by optimization with regard to the application of diversity reception, the control period of adaptive modulation, and the spacing of the required SINR of the modulation level. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(12): 50–60, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20195

This paper considers a multicarrier system performing burst transmission and discusses the channel estimation method, together with the estimation accuracy. In a multicarrier system such as OFDM, the channel state information of each subcarrier is estimated using a known signal, and then the signal is detected. Consequently, the accuracy of channel estimation has a large effect on transmission performance. Furthermore, in an MC-CDMA system in which OFDM is combined with code spreading in the frequency domain, the signal is also synthesized by using subcarriers in the receiver on the basis of the subchannel information. Thus, the signal quality after despreading depends greatly on the accuracy of channel estimation, and it is an important issue to establish a channel estimation method suited to a multicarrier system and to evaluate its accuracy. This paper considers channel estimation in the time domain based on correlation calculation for the known signal and channel estimation in the frequency domain using the FFT of the known signal. The accuracy of estimation is derived analytically, and a method of reducing the computational complexity is proposed. Finally, the receiver performance is derived quantitatively by computer simulation, assuming that these channel estimation procedures are applied, and the effects of these methods on the quality of the received signal are analyzed. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(4): 10–21, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20261

In this paper, we discuss techniques for transmitting signals over the same frequency by synchronizing multiple base stations in order to achieve both high communication quality and excellent spectral efficiency in broadcast (P-MP: Point to Multipoint) communication (single-frequency, multistation simultaneous transmission). Specifically, in this paper, we propose a communication technique that uses the concept of transmission diversity and converts beat interference to intersymbol interference to suppress beat interference, which becomes a problem in single-frequency, multistation simultaneous transmission. The proposed technique features (1) controlling the transmit timing or waveform of the signal transmitted from each base station, and (2) using an adaptive equalizer to compensate for intersymbol interference produced during transmission. Finally, we assume a high-speed Rayleigh fading environment in addition to a beat interference environment in computer simulations and demonstrate the effectiveness of the proposed technique when maximum likelihood sequence estimation based on per-survivor processing is adopted. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(6): 12–21, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10167

The accurate and rapid identification or detection of the electrical noise sources causing noise malfunctions in communication equipment is an important issue in determining corrective measures. In this paper, we explain an improvement in the frequency extraction accuracy of linear predictive analysis for noise waveforms in order to identify the noise sources from noise waveforms such as the audible noise generated by communication equipment like telephones and noise currents penetrating into the communication equipment. In this study, we propose an improvement of the frequency extraction accuracy of linear predictive analysis by using correlation and integration. This method preserves specific frequency components of the original noise waveforms although correlation and integration are performed. In this paper, we divide the noise waveform into finite-length segments, correlate and integrate the time series data within a given segment, and formulate dynamic frequency analysis (time–frequency analysis) based on linear predictive analysis for the time series data in the postprocessing. We also verify the effectiveness of the proposed method by using known noise waveforms. The result of applying the proposed method to a noise waveform that convolved white noise with sine wave signals having known frequencies was clearly the ability to extract the frequencies of the sine waves included in the noise waveform even for a signal-to-noise ratio (SNR) of 0 dB with an error range of about 10 to 15%. This assumes that the frequencies of the sine waves included in the noise can be extracted even under the worst case SNR due to the suppression of white noise by the correlation and the emphasis of the low-frequency components by the integration. Thus, we show that the characteristic frequencies in the noise waveform can be accurately extracted by using linear predictive analysis combining correlation and integration, and present the remaining issues. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(1): 1–11, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20153

This paper proposes a packet switch architecture with scalability suitable for handling Internet traffic. The basis of the architecture is a multistage switch consisting of a combination of bufferless unit switches. In the conventional multistage switches, one problem is resistance to hot spots. A hot spot is generated by the best-effort traffic characteristic of the Internet. In this paper, a method of control of the multistage switch with resistance to hot spots is proposed. Further, mechanisms for facilitating the installation of multistage switches are also proposed, including prevention of out-of-sequence transmission of the packets and reduction of the speed-up factor. The proposed switch architecture is evaluated by simulation and its effectiveness is confirmed. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(9): 78–89, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1175

This paper describes the design of a narrow bandpass filter with attenuation poles used at high frequencies. The filter circuit is new and consists of coupled lines and resonators. This paper analyzes how the filter characteristics vary with these circuit parameters. A bandpass filter designed with the results is fabricated and tested. It is confirmed that a narrow bandpass filter with a relative bandwidth of 0.3% is obtained at a center frequency of 1 GHz. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(6): 19–24, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10067

This paper analyzes the down-link of a DS-CDMA system and clarifies the relationship between the system capacity and base station transmitter power, while taking handover and transmission quality into account, when the base station transmitter power control is suitably controlled so that the instantaneous SIR of mobile stations will be uniform in relation to traffic channels in a model that simultaneously considers the traffic channels and common control channel. This paper also shows that system parameters can be easily optimized if the derived equations are used. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(6): 84–103, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1167

In cellular communication systems, every call is carried through a base station, and when the communication path to the base station is obstructed by buildings or other obstacles, the communication may not be established. It is expected that ad hoc relaying of such an obstructed call will increase the performance of the network as a whole. This paper discusses how to theoretically analyze the communication traffic performance of a cellular system with ad hoc networking and shows that the network performance can be increased even with relatively small range of relaying capability of terminals. This paper also shows by simulation that multihop relaying does not give significantly greater performance improvement than that by two-hop relaying. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(11): 1–10, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10135

The use of magnetic materials has drawn attention as a method of simultaneously realizing suppression of electromagnetic (EM) noise radiated from information devices and improvement of the immunity of such equipment against the EM noise from these devices. Suppression effect of the electromagnetic noise radiated from printed circuit boards (PCB) traces and cables by ferrite cores and sheets has been studied. However, little is known about the relationship between the mounting location of the ferrite materials and the noise suppression effect. In this paper, a transmission line on the ground plane for the transverse electromagnetic mode is treated. The radiated field at a sufficient distance relative to the transmission line length is analyzed. It is shown that the field level in this case is proportional to the spatial average value of the current distribution on the transmission line in the length direction and hence that reduction of the field level is possible by suppressing the average value of the current. Next, a computational formula is derived for the field level from the ferrite core-attached transmission line. Using this formula, the suppression effect of the field level by core attachment is numerically studied. It is found that a suppression effect is recognizable if the ferrite core is installed at the near end of the transmission line. On the other hand, the field level actually increases if the ferrite core is installed at the far end. These numerical results are confirmed to agree well with experimental results obtained in a six-surface anechoic chamber. Hence, the formula derived in this paper is valid. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(5): 12–20, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10050

This paper proposes a beam pattern selection diversity technique using an adaptive array antenna. In the system using an adaptive array antenna, beam control in the uplink is carried out for all terminals in the cell. Hence, it is necessary to determine the antenna weights for all terminals at the base station, so that the amount of computation is increased and the base station configuration becomes complex in a cellular system that seeks to be capable of handling as many terminals as possible. In this paper, the beam patterns are generated only for a limited number of terminals in the cell, while other terminals share the generated radiation patterns, so that the amount of computation can be reduced substantially. In general, in a system using an adaptive array antenna, the interference suppression capability is significantly affected by the angle of arrival of the propagation channel. In this paper, the angle of arrival of the channel is modeled by a normal distribution and the proposed system is investigated in a micro-cell environment. As a result of numerical simulation, it is found that the proposed method can reduce the processing effort by 20% in the micro-cell environment, while the characteristics are sufficiently competitive with the results obtained when optimum radiation patterns are generated for all terminals. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(5): 32–41, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10020

Research and development have been carried out extensively on the MUSIC and ESPRIT algorithms, based on the eigenfunction expansion of the correlation matrix, for high-resolution direction-of-arrival estimation using array antennas. A factor hindering the best performance of these high-resolution algorithms in real array antennas is nonuniformity of the element patterns caused by element coupling in an array configuration. In this paper, it is assumed that the array antenna is operated in a single mode and that the initial deviations of the transmitted amplitude and phase of the feed system and errors such as interelement coupling can be represented by a single coupling matrix with complex elements. Under such assumptions, this paper proposes a method for compensating the error of the center of rotation of the rotating table on which the device under test for calibration data measurement is installed, and estimates the coupling matrix. By computer simulation in the case of a receiving array antenna, it is found that the coordinates of the rotating center and the coupling coefficient can be estimated and that received signals with the initial deviation and interelement coupling compensated can be obtained by multiplying by the inverse of the coupling matrix estimated for the received signals. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(3): 59–73, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10126

Mobile IP has gained attention as a technology that can provide mobility to universal users independently of the access network. The introduction of Mobile IP in mobile core networks is currently under investigation. This paper discusses route optimization methods when Mobile IP technology is applied to mobile core networks. More specifically, it discusses means of resolving the “Triangle Routing” problem, which occurs when communications from a correspondent node to a mobile node must be routed through a Home Agent (HA). This paper first describes the conventional route optimization method being investigated by the Internet Engineering Task Force (IETF) and indicates problems with that method. It then proposes a new Mobile IP Border Gateway (MBG) method for solving the problems of the conventional method. The MBG method enables packets that arrive from another network to be directly received at the mobile node by having a Border Gateway router maintain Binding Information consisting of the care-of address and home address that were originally being maintained by the Home Agent for the communicating node. This paper also shows that introducing the MBG method enables the mean route length within the network to be shortened and the traffic volume routed through the Home Agent to be reduced. Finally, it shows methods of reducing the burden of registering Binding Information at the Mobile IP Border Gateway and indicates the applicability of the MBG method to large-scale mobile communications networks. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(2): 31–41, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1151

This paper considers a network in which one of the links is the bottleneck of communication, and the speed of that link is upgraded. A simple method of calculation is proposed for the effect of the upgrading on the throughput of the TCP communication passing through the link. As the first step, a formula for the TCP communication throughput is proposed, which is a function of the mean window size of the TCP flow control, the round-trip time, and the loss ratio of the packet. The waiting time in the router, which is the major factor determining the round-trip time, is approximated by the M/M/1/m queue. By combining those two expressions, the change of the throughput by upgrading the link speed is calculated. In order to verify the validity of the throughput calculation and the router model, the change of the TCP communication throughput in upgrading the speed of the bottleneck link is calculated, and the result is compared to the result of actual measurement in the experimental network composed of PPP and Ethernet. It is seen that the model proposed in this paper agrees well with the actual measurement although it is simple. The method is applied to the network between Mie University and SINET. The effect of the link speed upgrading on TCP throughput is examined and verified. The result obtained in this paper is expected to be useful in the network design, in estimating the link speed required in dissolving the bottleneck. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(1): 65–73, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1147

In this paper, we propose a method of implementation of a remote access system to controllers in a manufacturing line via the Internet. In order to reduce development cost, we adopt the method of not modifying user interface-related programs in existing controller access software, but modifying communication processing programs in it. We designed three types of implementation methods according to the communication protocol translation between the controller access communication protocols and TCP/IP. From the qualitative analysis of these three methods, we determined that the TCP/IP data wrapping method is the best among the three implementations. This paper also describes our prototype implementation of a remote access system based on TCP/IP data wrapping method and evaluates the results of our proposed method. © 2002 Scripta Technica, Electron Comm Jpn Pt 1, 85(6): 23–32, 2002

For the cellular systems used in portable telephones, down beam tilting is required from base station antennas. The authors have reported a design method of wire antennas with one or two loads for deriving the loading impedances to realize the tilt angle and directive gain provided as a condition. In the present paper, a method of design of a beam tilting antenna with more than three loads for better characteristics is discussed. In such a loaded wire antenna, determination of the locations for the loads and the antenna length is important. This paper proposes a method of determining the locations of the loads and the antenna length. In addition, by including a previously reported method of determining the loading impedance, a design method that achieves the desired tilt angle and high gain with suppressed sidelobes is presented. © 2002 Scripta Technica, Electron Comm Jpn Pt 1, 85(5): 1–10, 2002

Subsurface radar to detect buried objects from the ground surface by using electromagnetic waves has been used widely for detection of buried pipes since a shallow subsurface zone of up to 2 to 3 m can be visualized with high resolution at high speed. On the other hand, deeper subsurface detection is required in searching for archaeological ruins. In this paper, a delay correlation-type subsurface radar using monocycle pulse signals modulated by M-sequence codes is proposed with a view to expanding the search range by increasing the average energy of the transmitted signals. With a test setup, a steel pipe buried 2.5 m below the ground surface was detected with a transmitting power of 1 mW. In regard to the maximum detectable range of the subsurface radar using this type of coded signals, this paper carries out a study from the point of view of both the time side-lobe and S/N. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(2): 8–16, 2002

For economical construction of access networks, the passive double star (PDS) transmission system using optical fiber is promising. In the PDS transmission system, multiplexing of different transmission systems is possible due to wavelength division multiplexing (WDM). This system has drawn attention because addition of new service is easily accomplished. In this paper, an approach is proposed that is effective for wavelength division multiplexing in PDS transmission systems. When several systems with different transmit/receive level differences are transmitted over one fiber by wavelength division multiplexing, the transmission line length and the number must be adjusted to the system in which the transmit/receive level difference is the smallest in the conventional method. Hence, the application range of the system is degraded. On the other hand, in this paper, a method is proposed in which the loss distributions can be independently designed by cascading several star couplers when each system is wavelength division multiplexed. The method's procedure, evaluation of the efficiency of the accommodations, and an experimental example of an actual system are presented. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(7): 66–73, 2001

Self-healing has been investigated as a technique for efficient path failure restoration in VP-based networks. This paper discusses self-healing in networks with multiple reliability classes, and evaluates restoration performance of different failure recovery procedures that introduce priority orders in the failure recovery process based on the reliability class for each failed path. The authors present a composite-type restoration procedure in which preplanned-type and flooding-type procedures are combined. This paper also presents a bumping added-type restoration procedure. The authors evaluated the performance of the above proposed techniques assuming various failure modes. The simulation results revealed that the proposed methods show improved performance. In addition, we propose an enhanced technique that introduces a subsidiary priority criterion in the paths belonging to the same reliability class, in order to increase the number of paths to be recovered. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(7): 1–17, 2001

This paper discusses the problem of coexistence of DS-CDMA (direct sequence code division multiplex access) and TDMA (time division multiple access) systems where their signals are transmitted in the same frequency band. The DS-CDMA signal is robust against narrowband interference, but there is a limit to its immunity against interference. This paper proposes, from such a viewpoint, a method using a complex multirate filter bank, as a way to reject TDMA signals, which act as narrowband interference to the DS-CDMA signal, in the coexistence system. By the proposed method, a notch filter can be composed with an arbitrary frequency resolution at an arbitrary frequency, by constructing the complex version of the conventional multirate filter bank. It is shown that, by eliminating the TDMA signal by the proposed method, the bit error rate of the DS-CDMA signal is improved, indicating that the proposed system is useful in the coexistence problem. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(5): 34–41, 1999

In feeding parallel plate slot arrays with plane waves propagating between parallel conductor plates, a dielectric plate lens or a parabolic cylindrical reflector is often used to generate the plane waves. Such a lens or a reflector requires a point source at its focus, since these lenses are designed by using a geometrical optics approach and actually are fed by H-plane sectoral horns. However, it is impossible to regard the horn as a point source, because its aperture is generally several wavelengths. Thus it is essential to determine the phase center of the sectoral horn in order to put the feeding system to practical use. Moreover, the lens and reflector are usually placed in the Fresnel region of the horn and are designed to operate at the widest feeding angle possible. In this paper a method to determine the phase center of the horn that is applicable in the wide angle Fresnel region is proposed, and several charts for its location are presented. This method is ascertained to be fully practical by means of several numerical and experimental investigations. A trial-fabricated plate dielectric lens and an offset parabolic cylindrical reflector were tested and found to operate approximately in accordance with the principles of geometrical optics, if their focii are arranged on the phase centers given in this paper. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(3): 28–38, 1999

In this paper, an adaptive soft-output Viterbi equalizer (SOVE) is proposed for fast time-varying frequency-selective fading. The demodulator can make a symbol-by-symbol or bit-by-bit soft-decision based on a posteriori probabilities. The proposed adaptive SOVE has the following advantages: (1) it has a superior tracking ability for fast time-varying frequency-selective fading, (2) it works in blind if the coding rules are suitably designed, and (3) a good BER is obtained at the output of the decoder by introducing interleaves. In this paper, these advantages are confirmed by computer simulations. In particular, in the presence of frequency-selective fading, we can show that the proposed method is superior to adaptive maximum-likelihood sequence estimation which carries equalizing and decoding simultaneously. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(4): 31–39, 1998

The electric field sensor using an optical modulator makes possible accurate measurement without disturbing the electromagnetic field to be measured and is expected to have applications in EMC measurement. In this paper, a theoretical analysis of the sensitivity of the electric field sensor using an LiNbO3 modulator and the error factors are described. First, the electric field sensor consisting of a rod, an optical modulator, an optical source, and an optical detector is expressed by an equivalent circuit. Next, of the equivalent circuit parameters, those related to the sensor rod are derived by a numerical analysis using the method of moments. Those related to the optical modulator are derived by the theoretical analysis and measurement. A method is presented for determination by measurement in regard to the optical source and the detector. An electric field sensor is fabricated and its characteristics are evaluated. It is found that the difference between the measured value and the theoretical value of the sensitivity is about 8.2 dB. The causes of the difference are the input capacitance and the insertion loss of the optical modulator. These two parameters are measured beforehand and used in the calculation. Then, the sensitivity of the electric field sensor can be estimated with an accuracy of 1 dB. The analysis method used in this paper is found to be effective for sensitivity analysis of the electric field sensor. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(12): 79–89, 1997

In this paper, a design method is presented for a base station dual-beam antenna appropriate for the six-sector wireless zone configuration in mobile communication. Two radiating elements are installed on the main reflector. These radiating elements are formed by hybrid circuits. The dual-beam antenna is characterized by its superiority in reducing the number of antennas to be installed and in cost effectiveness. In this paper, the beamwidth in the horizontal plane is 60°. With a view to reducing the wind load, antenna structural parameters (main reflector width, spacing of the radiating elements, and spacing between the main reflector and the radiating elements) are found so that the antenna width becomes as small as possible. In addition, the structural parameters reducing the sidelobe level are obtained. Further, the sidelobe level is reduced by about 5 dB by installing side reflectors on the main reflector. By installing a parasitic element in front of the radiating element, the main reflector width is reduced from 1.1λ to 0.75λ, so that the antenna size is reduced by about 25%. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(12): 38–46, 1997

Finding a clear and simple method which gives steady state response of a linear antenna system with nonlinear loads is very important in the research field of electromagnetic compatibility (EMC). This paper concerns the EMI problem of electrical equipment exposed to electromagnetic surroundings. The problem is reduced to calculating the steady state response of a nonlinearly loaded multiport electrical circuit with multitone sinusoidal excitation. Several studies using Volterra series and multi-dimensional Fourier transform pairs have been made, but the method is very complicated due to the theoretical difficulty and computational complexity, so it is not conclusive in practical use. In this paper we introduce a simpler and more efficient method based on the nonlinear steady state response method. A characteristic of our new method is that we can easily and effectively apply it to the above problems and can obtain results equivalent to those obtained with the Volterra method. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(6): 8–16, 1997

This paper addresses some solutions to overcome the problems that arise when optical time domain reflectometry (OTDR) is applied to optical amplifier submarine transmission systems. It designs a backscatter path that feeds the backscattering into the opposite line without causing any degradation in the main signal transmission. This paper proposes a new modulation format, FSK-ASK, and confirms that the proposed approach can both eliminate optical surge generation and improve OTDR performance. An FSK-ASK OTDR is applied to an 890-km commercial amplifier submarine transmission system with a 90-km span. Field trials successfully demonstrate that the OTDR can locate a fault in all spans with a spatial resolution of 1 km after averaging the sum of 220 measurements. The FSK-ASK OTDR proves to be very useful in maintaining a reliable submarine transmission system because it can locate subtle fiber anomalies along the entire length from a terminal end.

As an effective traffic control mechanism of the asynchronous transfer mode (ATM) local area network (LAN) which has been getting attention as the next-generation high-speed LAN, the reactive congestion control is considered. In this paper, to obtain such a traffic control mechanism, a scheme to add the function of backpressure to an ATM switch having buffers in both the input side and the output side is evaluated. Also in this paper, the maximum throughput of an ATM switch with backpressure function for burst traffic is analyzed mathematically. Further, a uniform traffic load and a mixture of such traffic occupying the bandwidth in a peak rate as voice and video are analyzed. Moreover, with some numerical data examples, the effect of the output buffer size and the burstiness of the arriving traffic on the system performance is analyzed.

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.

This paper discusses flight-path planning for an aircraft flying at low altitude while avoiding terrain crashes. In a past study, several algorithms based on exploratory procedures have been proposed; however, they do not generate practical paths that take into account aircraft inertia. This paper proposes a new algorithm to generate a flight path taking account of the aircraft's inertia; this algorithm does not generate the flight path directly, but determines the aircraft's steering acceleration at every point along the way and then generates the flight path based on the steering acceleration. This algorithm extracts feature parameters representing a relation between the aircraft and the terrain, determines steering acceleration by fuzzy reasoning using the feature parameters, and updates state variables of the aircraft. Furthermore, this paper also proposes a learning algorithm to design the membership values in the fuzzy reasoning from reference flights since it is difficult to optimize them by trial and error. The flight-path planning by the proposed algorithm is compared with that based on the exploratory procedure. The learning algorithm of the membership values is validated through computer simulations.

This paper proposes a new configuration for an interference cancellation system for spread-spectrum communications and will verify its performance. In the proposed system, a pilot signal with a known code is spread modulated without altering the data and sent to the common reverse link. Blind deconvolution is avoided because the characteristics of the radio channel are determined from the received pilot signal. The new configuration is simpler and offers improved interference cancellation. A filtering system is proposed for the estimated and the correlated signals using a time-variant model to alter the characteristics of the radio channel along with the operation of the personal station. A sequential configuration system is proposed for interference cancellation (simply called cancellation). This is considered to be equivalent to the basic configuration that has been previously proposed, yet it further simplifies the configuration. The cancellation system is based on the system stated above. The path-diversity combination of the delay wave and the data and the amount of interference on the destination and interfering channels are estimated, and interference from other channels is removed. This paper discusses, first, the estimation system for time-variant multipath radio channels and, second, the configuration of sequential cancellation and its management. Based on the above, a cancellation system is proposed and the effectiveness of the proposed system is verified.

To achieve efficient and highly reliable network operation requires a mechanism to monitor and control the states of remote terminals (nodes) automatically by the central operation system (OpS). This paper is an attempt to obtain such a mechanism. Operation and maintenance (OAM) cell is defined that contains the connection information for remote monitoring and the control path to be set. By successively transferring OAM cells according to the connection information, remote monitoring and control virtual paths (VPs) can be obtained autonomously. Based on the proposed idea, this paper discusses the structure of the OAM cell, the functions to be provided in the cross-connect system, and transmission algorithms for the OAM cell. The proposed system well utilizes the unique feature of the ATM cell. The cell routing information (VPI) is transferred within itself.

Telecommunications networks are designed and managed based on statistical traffic data including basic traffic obtained at peak traffic hours. Network links are also designed based on the basic traffic. the network is designed so that the quality of services (network blocking) is at a certain level when basic traffic is applied to the network and the network is managed so that quality of services is maintained for the basic traffic. This conventional method is universal and simple because the required data for design and management are very small. On the other hand, recent telecommunication systems have the ability to measure and collect detailed traffic data. This paper proposes a new network design method in which time-series traffic data rather than statistical traffic data is used for network design. Combining the time-series traffic data and the tariff data for each hour, we can design a network based on total revenue. Unlike the conventional method, the proposed method makes it possible to estimate revenues, costs, and damages. Using time-series traffic data obtained for every hour of the year, a method is devised that optimizes the number of circuits (i.e., for optimizing network blocking) and thus maximizes profits. This paper also presents a new methodology for traffic data and a new network structure that effectively uses the proposed method.

This paper considers the modem which has the features of high precision, high-level functions, adjustment-free operation, and low cost, to provide high-capacity transmission and to cope flexibly with various radio communication systems. A fully digitized modem is investigated, in which the digital signal processing techniques are applied up to the IF band. This paper shows the effects of the quantization level, the aperture effect and the clock jitter, which are the major deteriorating factors of digital signal processing (DSP), on the multilevel modem. an analysis method based on the equivalent C/N degradation is proposed, and fixed degradation of the modulation/demodulation systems is calculated quantitatively. It is verified as a result that when the method is applied to the devices on the market, the fixed degradation is approximately 2 dB in 256 QAM, which is nearly the same as in the modem with the conventional configuration. It is seen also that the effect of the degrading factors depends on the number of levels. When the number of levels is small, the quantization level has the dominant effect, and when the number of levels is large, the aperture effect, as a factor for the waveform distortion, is the dominant effect. Finally, a fully digital modem is constructed experimentally. As a result of the performance evaluation, the validity of the analysis method is verified by experiment.

A variety of multiaccess optical communication systems with common carrier have been reported recently. This paper proposes a new type of multiaccess coherent optical communication system with star configuration in which a common optical carrier from a single source is distributed by a star coupler. In this system, the carrier is phase-modulated at each user by an external modulator through a subcarrier signal and the signal is received by an optical heterodyne receiver. A feature of the system is that the distributed optical carrier and the modulated light are directional-division multiplexed. Theoretical analysis of the carrier-to-noise power ratio (CNR) of the system is carried out in this paper taking into account the effect of interference light caused by reflections, backscattering, or insufficient isolation of a circulator used in the system, followed by discussions on the allowable value of the signal-to-interference light power ratio and on the relation between transmitter power and maximum user numbers.

In the communication system using a constant modulus signal, a constant modulus algorithm (CMA) adaptive array antenna is effective for elimination of the frequency-selective fading generated in multiple propagation paths. On the other hand, in the system in which CMA adaptive loops are installed for each antenna element in an array with more than 10 elements used for mobile satellite communication, the computing time and the amount of hardware become excessive. In this paper, a beam-space CMA adaptive array antenna (BSCMA) is proposed in which a portion of the multibeam output is selected to form a CMA adaptive array. In the BSCMA, first, a multibeam is formed by means of a fast Fourier transform (FFT) and only the beams whose output power exceeds a threshold level are selected. an adaptive process is carried out with the CMA as a guiding principle only for the selected beam outputs. the BSCMA has an advantage of carrying out the capture of the desired wave and the elimination of the interference wave effectively with degrees of freedom corresponding to the number of arriving waves. the method is effective for an adaptive antenna system applied to an array antenna constructed with many antenna elements. In this paper, the configuration of the BSCMA is shown and its characteristics are investigated by the numerical simulation.

With the rapidly increasing demand for leased service, an important issue in the future telecommunication network will be efficient utilization of leased circuits. This paper considers the network configuration for leased circuits in the metropolitan area, where the demand for such circuits is increasing. This paper also discusses the allocation of cross-connect (XC) nodes in the construction of the network for low-speed leased circuits and the segregation/sharing of public and leased circuits from the viewpoint of economy. First, the system configuration for the low-speed leased circuits and the network topology for the efficient operation of the leased circuits are discussed. As a result, allocation schemes for XC nodes and schemes for fiber segregation and transmission capacity are proposed. Then the relation between the number of XC nodes and the network cost, as well as the relation between the transmission capacity and the network cost, are discussed from the viewpoints of the segregated and the shared configurations for the leased and public circuits. From this discussion, the optimal XC node allocation and the optimal transmission capacity are shown. Finally, a comprehensive assessment is described and the optimal area for each of the proposed network configurations is shown quantitatively for the case where the demand for the leased circuit or the equipment cost is varied.

Efficient handover during both mobile telephone and portable telephone communication is a technology essential in implementing ideal mobile communications. However, there exists the possibility of a transmission data slip during the process of circuit switching, which has become a problem in communication using terminal machines such as data modems and FAX machines connected to mobile telephones and portable telephones. In this paper, a transmission data slip accompanying route changes inside digital exchanges in a handover during telephone communications is assumed; it is shown on the basis of this assumption that a lag in synchronism occurs in the receiver terminal equipment. Then a sync lag of the receiver terminal modem during handover has been confirmed by tests using actual analog cellular phones and a transmission data slip has been shown on the basis of the results of the tests. In this paper, a synchronism control method minimising the sync lag has been studied. The efficacy of this method has been confirmed as a result of applying the method to a mobile telephone FAX modem.

This paper evaluates the performance of the two-way message transmission system on the meteor burst channel developed and tested by the authors. First, the usual channel model is simplified and then the system is analyzed. It is shown through simulations that the errors introduced by the new channel model and by the approximated analysis method are negligible and the proposed method can be used to design and evaluate the system. The performance of the system having packets with subblocks is compared to that of one with usual packets. It is shown that, by using packets with subblocks, robustness of the system performance against changes of channel parameters as well as a shorter time needed to transmit a message can be obtained. The method of performance evaluation shown in this paper has adequate generality and is also applicable to many other meteor burst communication (MBC) systems.

This paper describes the S-band intersatellite communication (SIC) antenna to be carried on the Engineering Test Satellite VI scheduled for launch in 1994, to undertake the first intersatellite data relay experiments in Japan. The SIC antenna is an on-board formed multibeam phased array antenna, the first of this kind in the world to be carried on a satellite. The SIC antenna is capable of simultaneous data relays to several orbiting satellites (user satellites) by means of an electrically scanned beam. With an on-board microprocessor, the location of a user satellite can be computed, and the beam is pointed toward that direction automatically. In comparison with the system used in the data relay satellite of the United States, the on-board beam-forming system has several advantages, such as the effective use of power and frequency in the case in which the number of user satellites is small, as in Japan. In this paper, the function and the configuration of an SIC antenna are described first. Next, analysis of the antenna is presented, including the effect of the phase and amplitude errors caused by temperature fluctuations. Further, as the main components, the newly developed broadband microstrip antenna, a small beam-forming network with small phase errors, and the phase shifter controller making the computation of the orbit of the user satellite are presented. Finally, the total test results of the on-board model of the SIC antenna are described.

Intensive efforts have been observed in recent years on the development of data communication technology, aiming at the effective utilization of such existing transmission lines as the in-house distribution line. The automatic consumption meter reading, for example, uses the low-voltage distribution line as the transmission channel. This paper aims at the improvement of the receiver demodulation performance in the data transmission using the low-voltage distribution line and proposes the phase-diversity reception using two phases (red and black) of the single-phase, three-wire system. In the data transmission using the low-voltage distribution line, stray signals are produced between the two phases of the single-phase, three-wire lines and two signals with different signal-to-noise (SN) ratios are received. If a simple scheme such as the addition is employed, a problem arises in that the reliability of the demodulated data is deteriorated. To cope with this problem, this paper proposes a phase-diversity reception, where the time-varying phase difference is adjusted to zero using an adaptive phase shifter and the SN ratio is improved by synthesizing the two-phase received signals. The proposed scheme is implemented on a digital signal processor (DSP), and a robustness against the channel noise and the periodic attenuation is realized by the feedback (FB) control. As a result of an experimental evaluation, it is shown that the SN ratio is improved by 2.7 dB at the maximum for the stationary phase error, compared to the traditional simple addition and the addition/subtraction selection schemes. Thus, it is verified that the receiver demodulation performance of the low-voltage distribution line data transmission can be improved.

Previously, the authors have proposed a design method of a shaped dual-reflector contoured-beam antenna with virtual multihorns with a view to applications to the broadcast satellite BS-3. In such a design, there were discontinuities on the main reflector. In this paper, a method for eliminating these step discontinuities is studied for the dual-reflectors. The current distribution on the main reflector corresponding to the desired radiation pattern is determined by optimization depending on the constraint gain of the far field. Note that the optimization method for the aperture phase distribution was known for a single smoothly shaped contoured-beam antenna. Also, in this paper, an optimization method for the amplitude distribution is proposed anew. Further, by adding a restriction to the phase difference between the adjacent elements in the optimization of the phase distribution, the step discontinuity on the reflector is eliminated. By means of this method, an antenna made of a main reflector with an aperture diameter of 2.3 m is designed at 12 GHz which is the frequency of the downlink of the broadcast satellite. Most of Hokkaido, Honshu, Shikoku, Kyushu, and Okinawa is covered by a radiation pattern with more than 40 dBi and other remote islands with more than 28 dBi. A one-half scale model is fabricated and the radiation pattern is measured at 22 GHz. The results agree well with the numerical results. Also, the sidelobe and the cross-polarization characteristics of this antenna sufficiently satisfy the technical standards in RR.AP 30.

This paper proposes an interference cancellation method called the in-band power minimizing method (IPMM), and describes the use of the method in satellite communication earth stations. In this method, an interfering signal arriving from an earth station antenna is combined by a cancellation circuit with an interfering signal received by an auxiliary antenna and the two interfering signals are arranged to have equal amplitudes but opposite phase. To achieve this condition, the amplitude and phase are adjusted so that the signal power of the output signal from the cancellation circuit contained in the desired signal frequency band is to be a minimum. This method is characterized by the fact that a simple circuit can be used to detect interference rapidly and accurately even at low C/N ratios. This paper also discusses the principle of IPMM and examines the results obtained when it is applied to small earth stations. It was found that IPMM is quite effective in this application.

With the advent of the radio relay system and multilevel modulation, the multicarrier system and variable capacity transmission system are proposed to realize excellent performance in the fading channel. Accordingly, it is desired to realize a highly functioned MODEM which can cope with those systems in a flexible way. On the other hand, intensive studies have been made on digital signal processing in the modulation and demodulation in the field of data modem. However, these methods consider the low-rate system of less than 100 Kbaud and are difficult to apply directly to the system where the transmission rate of 10 Mbaud or above is required. For the foregoing reasons, this paper considers the realization of the all-digital modulator which can realize the high-capacity transmission of over 10 Mbaud for the multilevel modulation system, such as 256 QAM. This paper discusses the design of the digital filter with excellent intersymbol interference. The condition for the carrier frequency for a given clock rate is presented. Then a variable multilevel modulator with a simple correction circuit is proposed which can be applied to the variable-capacity transmission system. Finally, the proposed circuit is constructed and it is confirmed that an excellent modulation performance is obtained without adjustment in various multilevel modulation systems.