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For a system comprised of multiple Web servers that provide the same content, this paper proposes a method for the dynamic selection of servers that process requests, based on periodically obtained load information on servers. Previously proposed methods select servers probabilistically based on the weights calculated from server load information, and consequently, a server with a heavy load is selected by chance, often resulting in decreased performance. In contrast, the present method, instead of employing probabilistic server selection, selects servers by a round-robin scheme after eliminating any difference in load among the servers. A comparison of performance based on simulation studies with the conventional method indicates that the proposed method is immune to the impact of the intervals at which load information is acquired or the number of servers involved, and that it produces a low average response time even under heavy load conditions. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(10): 1–12, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20309

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 considers a connectionless (CL) packet switching network, such as IP, and proposes a method in which unused addresses are used as labels for packet flows with various granularities, which are transferred along explicitly specified routes. Generally, in CL packet-switched networks, the next packet is selected and relayed to arrive at the destination host on the basis of the destination address attached to the packet. Consequently, it is impossible to transfer packets which have the same destination address but different requirements along separate routes. One technique for performing such a transfer is multi-protocol label switching (MPLS) and is based on a different transfer paradigm. The cost of this method is high because the transfer schemes of each participating router must be modified. To address this problem, this paper proposes a method for flow-based explicit route transfer. In the proposed method, a particular packet flow is allocated to an unused address so that an explicit route is composed from the unused address and the destination address of the packet is translated. In this method, the transfer scheme is kept essentially the same and explicit route transfer is realized only through a simple extension to the router. Depending on the mode of application, it is unnecessary to modify internal routers; the method can easily be applied to existing networks. In this paper, an application of the method to IP, as a typical CL packet switching network, is described, and the features of the proposed method are discussed. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(9): 78–89, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20308

Web services are a unified framework that enables the exchange of information among distributed applications using existing World Wide Web communications technologies. Web services offer the benefit of simplifying the sharing of information among different applications that are operated via remote terminals. However, when multiple services exist that provide the same functionality, a mechanism for automatically selecting the most appropriate service from those on offer is necessary. Unfortunately, the majority of automatic selection mechanisms are designed to use a fixed set of indicators as the selection criteria and are therefore unable to adapt to the diverse demands of users. In this paper we propose a new mechanism for automatically performing such service selection that integrates a wide range of different indicators. Specifically, we assign attributes to each of the services that can be used as evaluation criteria; we then gather these attributes at the user's client. We can compute a rating for each service on the basis of the attributes that have been collected and select the service that is assigned the highest rating. In this paper we introduce the concept of an attribute database (an attribute repository) and define a new communications protocol to enable the registration and searching of attributes in order to deal with variation in the attributes used by different services. In addition, using a simulation of a distributed applications environment, we perform evaluations and demonstrate that the proposed selection mechanism is able to reduce execution times as compared to a random selection mechanism. We also implement the proposed mechanism in an experimental environment and show that it can be used in practice for automatically selecting services on the basis of attribute values. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(8): 40–49, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20284 Copyright © 2004 Wiley Periodicals, Inc.Copyright © 2007 Wiley Periodicals, Inc.

A Virtual Output Queuing (VOQ) input buffer type switch provided with a buffer in each input port is proposed in this paper as an input buffer type switch that avoids Head-of-Line (HoL) blocking. A scheduling algorithm for a multiple VOQ input buffer type switch is also proposed. As a representative algorithm we use a Two-Dimensional Round Robin (2DRR) scheduling algorithm that achieves low-delay and has iSLIP to avoid starvation as well as high fairness between ports. This paper also proposes a layered scheduling algorithm for a VOQ input buffer type switch with an objective of fairness between ports and switching with lower delay. The frequency of packets not being output is reduced regardless of whether an output port is empty by using up patterns of all I/O pairs in N input N output switches. The N input N output switching is divided into smaller units. Fairness between the units is achieved by successively shifting the order of priority of each unit that will be switched. Simulations were used to evaluate the effectiveness of the proposed scheduling algorithm. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(6): 43–52, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20313

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

A new pulse compression filter design technique to realize theoretical minimum S/N loss with zero range sidelobe was indicated in our previous paper. In succession, we have verified in this paper the performance of this pulse compression filter applied to discrete phase-coded waveforms modulated by Barker code or P4 code via numerical simulations. As a result, we have concluded that the filter derived by our proposed formula surely realizes zero range sidelobe even in the case of oversampling in one code chip, the compressed pulse width is almost the same as the code chip length, and the degradation caused by the Doppler effect is inevitable but equivalent to traditional pulse compression filters. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(3): 10–20, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20263

The demand for video service in mobile communications systems is increasing. In response to this demand, wireless P-MP (Point-to-MultiPoint) video transmission, in which a given video is transmitted to several moving terminals via a single channel, has been studied. This scheme can make effective use of bandwidth, power, and spreading codes. In this paper, as wireless P-MP video transmission schemes effective in the CDMA system, we propose MCAP (MultiCode Assignment algorithm for P-MP transmission) and the P-MP video transmission system. In MCAP, the mobile terminals receiving the identical video are divided into two groups, high quality and low quality, based on the channel quality. By performing transmission power and transmission rate control for each group, the transmission rate can be improved. Also, by using multicode transmission, transmission rate control and the channel allocation are carried out in a unified fashion. In this paper, by means of simulations, it is demonstrated that the proposed scheme can substantially improve the transmission rate without increasing the number of spreading codes and the power. Several schemes are compared as power control base selection schemes needed for MCAP. An optimum scheme is determined from the comparative evaluation results. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(8): 14–25, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20280

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

MUSIC superresolution algorithm can estimate the DOAs (directions of arrival) of multiple waves closing less than the beam width. However, the MUSIC algorithm is usually applied to a DBF (digital beam forming) array antenna, and it was difficult to apply the method to scanning beam radar, which has simpler structure and lower cost than DBF radar. This paper proposes a MUSIC DOA estimation algorithm intended to improve DOA estimation performance by separating mixed signals in a scanning beam radar. In this paper, we assume a scanning beam radar transmitting and receiving FMCW modulated waves, which are often used for modulation. The principle of the proposed method is described. The accuracy and resolution of DOA estimation by the proposed estimation method are evaluated by computer simulation, and it is verified that a resolution 5 times as great as that of the conventional method can be achieved. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(10): 24–33, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20289

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

In this paper, a layered network that interconnects a distributed queue subnetwork with another distributed queue bridge network is considered. As slot control scheme in this network, a loopback retransmission scheme preventing slot discarding and an adaptive node load control function are proposed. In the communication within the subnetwork, no transmitted slot is discarded during processing. However, it is necessary to consider protection against discarding due to buffer overflow in the bridge of the distributed queue bridge network interconnecting the subnetworks. In order to prevent reduction of slot use efficiency caused by discarding in the bridge, it is desirable to eliminate discarding. Also, in order to prevent discarding of slots arriving at the bridge from the subnetworks, slot transmission at each node must be controlled. In this paper, in order to prevent slot discarding caused by buffer overflow of the bridge, a method is proposed for loopback retransmission of the slot on the bridge network or subnetwork. It is shown that discarding can be eliminated. Also, the effectiveness of the method is confirmed by computer simulation. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(11): 35–45, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20267

Delay variation of packets is a significant performance measure in IP networks. Both active and passive measurements can evaluate delay variation. Among these, passive measurement is more advantageous because it can monitor the performance experienced by users without disturbing network load. Meanwhile, a shortcoming of using passive measurement is an extremely large storage space required to record packets and timestamps. This problem is solved by feeding a portion of each packet to a hash function as its input and recording the output to identify the packet. Since the data length of the hash function output is very short, such an approach effectively decreases the storage space. However, this approach still needs a considerably large storage space to record time-stamps. Additionally, the collisions among hash output values may bring unacceptable measurement errors. This paper proposes a method to decrease the storage space required to record timestamps for hash-based delay variation measurement. This decrease is achieved by a variable length coding of timestamps. The paper also presents methods to avoid measurement errors brought by hash value collisions. Through experiments, it is shown that the proposed techniques correctly measure delay variation as well as effectively reduce the storage space. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(3): 21–32, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20328

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

The purpose of this paper is to speed up handover processing. The handover process is first analyzed. Based on the result of analysis, an extension of the protocol is proposed, in which adjustment of the timer value, a mechanism to report the link layer information to the network layer, and a speed-up of DAD processing are considered. The extended protocol is implemented. A problem in the operating system is identified by experiments, and solutions are presented. This paper also presents the tool constructed for the handover experiment, which produces a network shift at the desired time and timing. The handover time was measured and evaluated using the tool in an experimental environment, and it was shown that the handover time is drastically reduced compared to the system based on the standard IPv6 specification. The effect of the handover time on the application was evaluated, and it was demonstrated that the proposed method can realize handover with little effect on the application, although the environment is prepared by emulating wireless communications by cable communications. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(11): 44–53, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20213

In this paper, a method for weight control of an adaptive array is proposed for a system using a cyclic prefix in single carrier wireless communications (SC-CP). In the SC-CP system, the delayed wave within the guard interval (GI) can be equalized by discrete frequency domain equalization. Therefore, it is to be expected that the characteristics can be improved with respect to the received signal power by reception of several arriving waves within the GI. On the other hand, reception of several arriving waves leads to generation of zero points in the frequency response so that noise enhancement may be a problem for a discrete frequency domain equalizer with a zero forcing (ZF) reference. Also caused in the SC-CP system are the intersymbol interference (ISI) and interblock interference (IBI) due to the delayed wave exceeding the GI length. In this paper, a weight control method is proposed that simultaneously realizes enhanced received signal power by reception of several arriving waves and avoidance of noise enhancement due to ZF reference equalizer. At the same time, the weight control method to suppress delayed waves outside the GI is theoretically derived and its characteristics are evaluated by a computer simulation. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(9): 38–48, 2005; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/ecja.20189

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, the electrical constitutive parameters of various amorphous mixed materials are derived. The effective permittivity of the mixed materials can be expressed simply by the geometric mean of the permittivity of the series combination and that of the parallel combination of each material according to a dielectric layered model. In this expression, it is not necessary to specify the host material as was previously the case. The solution of various mixed materials can be directly expressed in the closed form. It is shown that there is a significant difference between the effective permittivity in this paper and that in the conventional theory depending on permittivity and loss of mixing materials. The validity of the approach is confirmed experimentally. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(10): 1–9, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20229

In the video and speech transmission using packets, the media synchronization control is applied, especially in the system for real-time transmission. In the system containing the media synchronization, the allowable time delay is defined, and the packet after this delay limit is discarded. In protocols such as ARQ (automated repeat request), where the packet retransmission is executed for error correction, if the delay or the error rate of the channel is large, the packet delay is greatly increased when an error occurs. The packet is discarded when the packet delay exceeds the allowable delay, which produces degradation of quality. This paper proposes an adaptive protocol relay system considering the allowable delay, in order to cope with this problem. In the adaptive protocol relay system, the protocol relay is executed at the relay node, when a certain condition for each packet is satisfied. By reducing the time spent in the packet retransmission due to the error, the number of packets that do not arrive at the receiving terminal within the allowable delay is reduced. This paper examines the effect of the protocol relay on the packet discard rate, when the proposed method is used. The condition for the adaptive control at the relay node is also discussed. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(8): 50–59, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10031

In multicast delivery in a network environment with various bandwidth limitations, it is effective to apply the layered multicast technique, which realizes delivery at a reception rate matched to each receiver, although the rate is set discretely. This paper assumes a multimedia session such as a multichannel broadcast or a video conference, composed of multiple streams. In such an application, it is desirable from the viewpoint of efficient use of bandwidth that not only should the streams be transmitted with stable quality, but that the rate should be assigned according to requests, such as attention to the speaker. However, it is difficult to achieve the above goal by directly applying the conventional layered multicast rate control technique, since each stream controls the rate independently. From such a viewpoint, this paper presents a session level mechanism covering multiple layered streams. A multiple streams controller (MSC) is introduced into each receiver, and each MSC autonomously controls the reception rate with interstream coordination in the session. The MSC monitors the reception state of the multiple streams simultaneously and estimates the bandwidth information on the bottleneck link and the set of transiting streams, based on the detected congestion data. Based on the estimation, the learning efficiency of the reception rate is improved and rate assignment control over the streams is applied. An evaluation is performed by computer simulation, and it is shown that the reception quality of the stream is improved by applying the proposed method, and that the reception rate can be coordinated among the streams. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(8): 18–31, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20142

This paper discusses methods of sending messages from a source that created a mobile agent (MA) to the MA, which has moved. These methods include the Home-Proxy method and Broadcast method. However, with these techniques, it is possible that the transmitted messages may not be delivered to an MA that is frequently moving around on the network. A method for resolving this problem has been proposed by Murphy and Picco (hereafter termed the Murphy method). Although the Murphy method can reliably deliver messages to the MA, it does not take into consideration the time that elapses until the messages are delivered to the MA. The authors propose a method for delivering messages in the shortest possible time (hereafter termed the clustering method) by partitioning the entire network into multiple areas (clusters) to improve this Murphy method. This paper, proposes the clustering method precisely and in detail. In addition, the validity of this method is certified by performing a logical verification. Simulation experiments are performed to compare the method and Murphy method to prove the effectiveness of the method by verifying that the time required to deliver messages to the MA decreases if the time that an MA stays at a node is not short and that the number of messages decreases if the time that an MA stays at a node is short. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(1): 67–80, 2006; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/ecja.20184

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 discusses a radiation-immunity test method using an amplitude-modulated low-speed rotating-polarization electromagnetic field (rotating electromagnetic field). By using the amplitude-modulated electromagnetic field as the applied electromagnetic field in the radiation-immunity test, it is possible to simulate the phenomenon of unintentional detection in an electronic device under applied interference, with noise appearing in the final stage of the device (such as the voice output). This paper describes a method for generation of an amplitude-modulated rotating electromagnetic field and its fundamental characteristics with a view to application as the applied electromagnetic field in the radiation-immunity test. Further, a radiation-immunity test of a low-frequency amplifier using the present electromagnetic field is performed as an example. The effectiveness of the radiation-immunity test method using the amplitude-modulated rotating electromagnetic field is demonstrated. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(9): 45–53, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10196

FRN (flexible radio network) is an ad hoc network product that can realize a wide-area data collection network. This paper discusses a performance improvement method when TCP is applied to the transport layer in FRN. It is shown that even when the terminal is not moving as in FRN, the throughput can be improved in radio link failure due to noise or obstacles by combining ELFN (explicit link failure notification), which is proposed as a method for TCP performance improvement in ad hoc networks, with routing information. The proposed method is evaluated by simulation in this paper. A further objective is to reduce the performance degradation due to packet collision. The delayed ACK and the ACK retransmission with priority in the case of packet collisions are analyzed and the effectiveness of the method is demonstrated. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(11): 99–107, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10134

The λ/4 wave absorber is expected to be useful for indoor wireless LAN because of its simple structure and ease of design. However, this type of wave absorber has the deficiency that the thickness cannot be less than 1/4 of the wavelength within the spacer used. In this paper, an FSS (Frequency Selective Surface) is inserted in tandem with a resistive film as an absorbing film in the spacer section of the λ/4 wave absorber. By varying the phase within the spacer, thickness reduction of the absorber is attempted. In this case, it is necessary to understand the impedance of the FSS at the design frequency. In this paper, the impedance is first derived by the FDTD method. Substituting this result into an electric equivalent circuit, the insertion position of the FSS and the surface resistivity of the resistive film maximizing the absorbing characteristic are determined. A thin λ/4 wave absorber of this type is designed and fabricated and the absorption is measured. It is confirmed that a λ/4 wave absorber can be realized with approximately half the conventional thickness. Basic data on the frequency characteristics and angular dependence of this type of absorber can be obtained. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(11): 77–86, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10180

This paper considers the selective-repeat ARQ scheme, which is a typical error control scheme used in data communication systems, and analyzes the performance of the scheme in which the number of frame retransmissions is limited. In the proposed scheme, messages such as image for which information loss can be tolerated to some extent are transmitted after being divided into multiple frames. If the retransmission of a frame reaches the preset limit, the receiver accepts that frame even if an error is present, and the error is processed as noise or distortion. By this scheme, an upper limit can be defined for the time from the start to the end of the message transmission. This paper analyzes the proposed scheme using the discrete-time queuing model and derives the distribution of the message transmission delay. The throughput and the required receiver buffer capacity are also derived. It is shown by numerical examples that the throughput can be improved and the receiver buffer capacity can be reduced. If the strict analysis is continued, however, the state space of the Markov chain is enlarged with the increase in the number of parameters such as the round-trip propagation delay and the number of message divisions. Thus, the numerical calculation of the transmission delay becomes difficult. The approximate analysis of the message transmission delay and its properties are discussed in Ref. 1. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(6): 1–11, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10181

This paper considers the stored MPEG video multi-channel transmission, and discusses the design of dynamic band assignment scheme considering the picture quality, together with the result of implementation. In the proposed scheme, the parameter representing the picture degradation characteristic of each video picture is used in numerical form, in the assignment of the band to the streams. By preparing the transmission schedule beforehand, which indicates the band assignment to the streams along the time-axis direction, the change of the picture degradation characteristic due to the scene changes in each stream is handled. There arises, however, the following problem. Since GOP (group of pictures) of the stream is not synchronized, the transmission following the schedule may become impossible, if the scene changes occur very frequently, due to the increase of the streams. From such a viewpoint, this paper proposes a scheme where the whole streams are partitioned into groups, and each group executes the independent transmission process. Furthermore, a method to estimate the optimal number of groups is proposed, which minimizes the picture degradation, based on the parameters, such as the average scene length and GOP length. Those control schemes are implemented on LAN and the transmission experiment is run on the stored MPEG video, and the effectiveness of the proposed band assignment method in the multichannel transmission is demonstrated. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(10): 81–92, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10155

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

This paper proposes an authentication architecture for collaboration among agents in a network environment without security assurance. The architecture requires that there should exist at least one secure node (oasis node). The oasis node generates the same number of authentication codes as the number of objects of authentication, using random numbers and agent information, and distributes the codes among the agents. The agents gather at the specified oasis node and obtain verification by the oasis node, based on the distributed random value and the authentication code. In the authentication architecture proposed in this paper, the random number and the authentication code are publicized information which can be compromised by eavesdropping. But the algorithm for generation and verification of the authentication code is not publicized. The architecture is suited for handling authentication processing in ad hoc collaboration among an unspecified number of agents. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(5): 11–19, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10165

We explain a tracking method that uses a linear filter to estimate the true values of the position and the velocity with the target position as the radar observation. One representative example is a Kalman filter for three-dimensional space. The α-β filter with its easily analyzed performance is widely used in one-dimensional space. In a tracking method, the tracking precision must be evaluated when sufficient time has elapsed since the initial calculation, that is, in the steady state. The equation for calculating the variance of the errors in the predicted position in the steady state has been reported for radar observations of a constant-velocity linear motion target by an α-β filter. In addition, a Kalman filter can obtain the variance of the errors in the predicted position in the steady state by the Riccatti equation. In this case, however, a premise is the presence of drive noise that indicates the ambiguity of the motion model. There is no equation for calculating the variance of the errors in the predicted position in the steady state for the radar observations of a constant-velocity linear motion target. In this paper, we present an equation for calculating the covariance matrix of the prediction errors in the steady state of the position and velocity for the radar observations of the constant-velocity linear motion target in a 3D spatial linear filter. The results calculated in this paper present an extension of a conventional α-β filter. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(12): 68–77, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10186

This paper considers the ubiquitous environment, in which a tremendous number of objects, such as physical devices, multimedia contents, and software components, exist everywhere. In order to provide and utilize various services transparently in such an environment, there must be a service synthesis technique that can dynamically construct services by mutually connecting objects. The realization of service synthesis requires a position-independent naming service which can securely and transparently call from the network the functions (functional objects) that act as the service component. The authors designed an interface-based naming service which can perform transparent calling of functional objects on the basis of interface information on the objects. The interface-based naming service not only can call functional objects efficiently from the network, but also can provide several useful features of service synthesis support: when two functional objects are interconnected, the required supplementary functional object is automatically determined, and when a function cannot be found, that function is realized equivalently by using multiple functional objects. This paper describes the architecture of the interface-based naming service, together with its algorithm. The approach is evaluated by simulation and it is shown that the interface-based naming service is a useful system in a ubiquitous environment with an increased number of objects and an enlarged network scale. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(3): 63–75, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10177

In this paper, we propose a noise reduction method for synthetic aperture radar (SAR) images that uses a Kalman filter. The noise in SAR images is primarily generated by speckle and appears as salt-and-pepper noise. Speckle noise is known to have the multiplicative statistical property, but this property may not hold depending on the region. Consequently, adequate noise removal is difficult. In radar, the expected values of the backscattered waves change due to the type of reflecting object. The proposed method segments an image into several regions based on the texture and varies the parameters in Kalman filtering in response to the region. By varying the parameters, the processing can account for the noise generated primarily by speckle in actual SAR images and the changes in the statistical properties of the backscattered waves. In this paper, we apply the proposed method to synthetic test images and to actual SAR images to quantitatively evaluate the noise reduction and present the results. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(10): 21–32, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10065

A fiberoptic strain sensor is being developed that exploits the fact that the difference between the central frequency of Brillouin scattering, which is a type of back scattering that occurs in optical fibers, and the incident light frequency depends on the strain of the optical fiber. The measurement of the central frequency of the Brillouin scattering requires an estimation of the power spectrum distribution of the Brillouin scattering. An improvement in distribution estimation accuracy can potentially improve both the accuracy of central frequency measurements and the precision of strain measurements. Focusing on the problem of the power spectrum distribution of the Brillouin scattering, this paper proposes a weighted repetition least mean square algorithm. The paper also examines the stability of the proposed repetition algorithm and demonstrates the effectiveness of the proposed approach through simulations. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(1): 72–80, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1183

This paper is concerned with the realization of a ubiquitous computing network designed to improve the reachability of communications and to eliminate complex setup and manipulation related to communications. The new communication system EAPEC (environment-adaptive personal communications) is proposed. The communications context of the user, which changes from time to time, is automatically acquired. Based on that information, the communications terminal and the communications service/medium that are optimal for the receiver to receive the message are automatically selected. Then, according to the selection, the communications service or the communications medium is automatically converted. It is shown in this paper that EAPEC can be realized under the 3GPP (third-generation partnership project) IP network architecture. Placement of five functional modules in the network and the automatic acquisition procedure for communications context are described. As a means of performance evaluation, the call setup delay is evaluated by simulation, and guidelines for network design are obtained. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(1): 34–47, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10087

As video compression technology advances and hardware prices drop, real-time applications using digital video such as video conferencing systems have been put to practical use. Some of these kinds of applications require extremely high transmission quality such as program distribution for digital TV broadcasting. Various compression methods with a variety of compression rates are used for digital video. Although ATM is suitable for efficiently transmitting these kinds of real-time signals with a variety of speeds, the implementation of a transmission method that does not allow the video or audio to be interrupted or distorted even when a chance transmission channel failure or bit error occurs is becoming a key issue. Therefore, this paper proposes a method of implementing a “failure-resistant ATM transport (FRAT) method” for the transmission of high-quality real-time applications, which can compensate for random errors without causing information loss even when a transmission channel failure occurs and can prevent buffer underflow at the receiving terminal by minimizing delay variation even if a failure occurs. In addition, this paper shows the effectiveness and characteristics of the proposed method. Specifically, this paper presents an overview of the proposed method and describes the method of implementing it in detail. Also, a trial transmission device based on this implementation method is used to verify the operation of the proposed method, and the characteristics of this device are shown by comparing theoretical values with experimental values for the amount of delay variation, which is considered the most important factor in the transmission of real-time signals. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(9): 90–101, 2003; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/ecja.1176

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 discusses the method for direction-of-arrival estimation by an application of 2D-ESPRIT to a triangular planar array with an equilateral triangular lattice arrangement often used as a phased array for direction finding. It is difficult to apply the 2D-Unitary ESPRIT to the triangular array due to its element arrangement. Instead, the 2D-ESPRIT based on the standard ESPRIT is used. As the paring method for a multidimensional ESPRIT, the complex pairing (CP) method, simultaneous Schur decomposition (SSD), and mean eigenvalue decomposition (MEVD) have been proposed. In the case of 2D-Unitary ESPRIT, the simple CP method can be used for an extremely accurate estimation. Since CP cannot be used for the standard ESPRIT, SSD with a high computational load and MEVD requiring introduction of a reliability test need to be used. In this paper, as a pairing method of the signal parameters, a complex mean eigenvalue expansion method is proposed that does not require a reliability test and has a low computational cost. Through computer simulation, the azimuth angle and the elevation angle of multiple waves are estimated simultaneously so that the method's effectiveness is verified. A radiation pattern synthesis for separate reception of multiple waves is attempted with multiple beam forming weights obtained in the process of 2D-ESPRIT. The effectiveness of the synthesis method is confirmed. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(6): 59–68, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10016

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

In order to more accurately extract desired signals, it is necessary to suppress interference such as reflection and clutter more strictly. This paper discusses a method of suppressing sidelobes adaptively by placing a receive-only array around a high-gain array. The output power minimization method (DCMP) has been proposed as an adaptive clutter suppression method. When this method is applied to a high-gain array, there is a danger of destroying the directivity of the high-gain array. In this paper, a constraint on the weight not destroying the receiving pattern of the high-gain array is added to the DCMP, resulting in a norm-constrained DCMP (DCMP-CN). By using this method, adaptive sidelobe suppression is possible regardless of the intensity of the input signals. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(3): 11–18, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10178

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

With the rapid expansion of Internet use and the recent development of multimedia, improving the quality of the Internet is becoming a crucial issue. To construct a network system with high performance for cost, an effective analysis must be made of the characteristics of the traffic flowing on the network, the processing performance of the Web server, and the processing performance of the proxy server with caching functions, and the resources must be allocated with good balance. In this paper, we present a modeling and performance evaluation of an entire Web system, including the Web server and proxy server. In particular, this paper presents basic data on the processing performance of the caching function of the proxy server acquired by benchmarking. A model of processing performance is presented. Then, taking account of past results, a performance evaluation model for the entire Web based on the newly constructed model is presented. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(4): 94–106, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1161

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