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The authors designed an asynchronous messaging platform to facilitate the development of context-aware services that are triggered by state judgment results (contexts) obtained by using multiple kinds of information from different generation sources in an environment where information providers, who actively disseminate information, and information holders, who provide information according to requests, persistently exist on a network. This platform also uses information that is obtained by using synchronous inquiries to calculate the activation triggers that are sought by the service providers in a distributed environment and provide these triggers to the application logic without destroying the asynchronous information generation order. In addition, the authors adapted this platform to a ubiquitous computing environment according to a design that takes into consideration large-scale distribution. They measured the basic performance of this platform and obtained measurement results showing that the platform can support a large-scale increase in the number of participating nodes and volume of circulating messages. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 1– 12, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20403 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

In recent years, attention has focused on UWB (Ultra Wideband), which is suitable for high-speed, large-capacity near-distance wireless communication systems. Since UWB uses the 3.1- to 10.6-GHz bands, research and development into antennas capable of obtaining wideband characteristics has become active. Research has also accelerated on antennas that can be shared with wireless LAN and other wireless communication systems. In this paper, we propose a wideband characteristics method that uses trapezoidal conductors for planar dipole antennas that satisfy the ultrawide bandwidths required for UWB, and for planar asymmetric dipole antennas that can be used for both IEEE802.11b/g, a wireless LAN in the 2.4-GHz band, and UWB. We performed analysis and measurement of impedance characteristics, and of directionality in each frequency band, and confirmed that the analysis results and measurement results virtually match. We also performed measurement to study group delay characteristics. We used the proposed method to achieve an antenna that is effective for both UWB and the 2.4-GHz-band wireless LAN, and showed the validity of the wideband characteristics method. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 22–30, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20395 [ABSTRACT FROM AUTHOR]

Interstitial microwave hyperthermia is one of the modalities for cancer treatment that insert a thin microwave antenna into the affected part to selectively heat only the tumor. The authors are investigating this technique with an aim of clinical applications of this medical treatment for brain tumors. In the clinical treatment of brain tumors, it is more critical that “only the tumor parts be heated” than for the treatment of other tissues. Therefore, an antenna that can generate a localized heating pattern on the tumor is required. Although the heating pattern can be controlled here in the longitudinal direction of the antenna by using multiple antennas to form an array applicator, control of the heating pattern in the axial direction is relatively difficult. In this paper, to enable the heating pattern to be controlled in the axial direction, the authors introduced a coaxial-dipole antenna and improved its structure. In addition, they assumed that it was actually applied in the medical treatment of brain tumors and used a numerical calculation model that included a tumor created from MR images to verify the effectiveness of the improved coaxial-dipole antenna according to numerical calculations. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 31–38, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20390 [ABSTRACT FROM AUTHOR]

With developments in the technology and greater adoption of satellite positioning systems such as GPS, there has been much research into location information systems and services and their practical applications. Extremely weak power radio communications systems are small-scale and low-power devices that do not require a license and are rarely used for communications purposes because they are able to communicate only over small distances compared to other communications media; however, if the distance over which they can be used for communication could be increased, then it would be easy to construct communications systems with them. To take advantage of this we propose an extremely weak power radio communications system based on the DS-SS scheme that synchronizes chips using the pulse-per-second (PPS) signal that is output by a GPS receiver. This system is continuously able to have access to location information due to the use of the GPS receiver and we anticipate that by using this it should be possible to increase the communications distances and communications quality. In recent years there has been an increase in the number of accidents in small-scale ships with low-end communications systems have capsized while at sea or drifted. Small-scale location information systems that can be used for marine distress situations such as capsizing or drifting have become increasingly sought after and communications systems that use such extremely weak power radio communications devices for marine location information systems have been proposed. In this paper we first give an overview of our proposed marine location information system and then describe the extremely weak power radio DS-SS communications system used to implement the system. Following this we perform simple communications experiments. The results of our experiments show that a communications distance of 80 m can be improved to 800 m. From the above results we show that in addition to the marine location information system created using the proposed method, a wide range of different applications are possible. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 39–50, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20379 [ABSTRACT FROM AUTHOR]

As the uses of artificial satellites diversify, investigation of the propagation characteristics of electric waves surrounding the Earth has become an important task. These electric waves are strongly influenced by plasma, a propagation medium, but although on the one hand investigation of plasma in the ionosphere is proceeding with various different methods being used, current investigations into the density profile of plasma in the plasmasphere is not progressing since it is hampered by the fact that satellites produce only single point observations. In this paper we develop a method for estimating the density profile of the global electrical field of the plasmasphere from natural VLF band electromagnetic wave frequency spectra and propagation vector direction information observed by satellite by solving an ill-posed inverse problem. We confirm the uniqueness of the solution by performing a brute force search using a dictionary and investigate the applicability of our method to actual data by using pseudo-observation data. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 51–61, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20377 [ABSTRACT FROM AUTHOR]

This paper considers the sensor network based on IEEE 802.15.4, and proposes a method in which a probabilistic model of wireless propagation characteristics in a real environment is constructed, and the node position is estimated by maximum-likelihood estimation using the model. The performance of the proposed method is evaluated by simulation and position estimation experiments based on the probabilistic model obtained from the actual indoor measurement. It is shown that the proposed method is useful for indoor personnel location management. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 62–72, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20359 [ABSTRACT FROM AUTHOR]

This paper proposes a new system architecture which achieves stable HDTV distribution service using ISP multicast networks. With the recent spread of broadband access networks including FFTH, the distribution of broadcasting contents using IP multicast is becoming indispensable in the ISP service menu. The important issues in the development of such a content distribution service are to provide high service availability and to construct a highly flexible distribution system that can handle various distribution formats. The authors have proposed a nonstop IP multicast technique without modification of router implementation intended for the ISP network, and also a packet transmission control procedure which works independently of the distribution format. A prototype was implemented and a video distribution experiment is performed on an IP multicast network corresponding to digital HDTV broadcasting by satellite. It is shown that nonstop service can be provided using the prototype system, compensating the loss of approximately 27,500 packets, accompanied by detection and recovering of network failure at the router. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 73–85, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20346 [ABSTRACT FROM AUTHOR]

FMCW (frequency-modulated continuous wave) radar is a radar system which can achieve high resolution by relatively low signal processing load. The authors have reported on clutter suppression by FMICW (FM interrupted CW) radar, where the transmission/reception of FMCW radar in pulse waveform is switched in order to assure transmission/reception isolation and to suppress undesired waves from short distances. This paper proposes the FM staggered PRI system, in which the pulse repetition interval (PRI) is randomized for each pulse in order to suppress the interference when FMICW radars are congested within the search distance. The target-signal in the FM staggered PRI system is formulated. Conditions such as the average PRI and the possible range of staggering are derived from requirements such as the maximum search distance. The output S/I is statistically evaluated by computer simulation, with the average PRI, the pulse width, the number of interference waves, and the input S/I (signal-to-interference ratio) as variables. The effectiveness of the FM staggered PRI system is demonstrated. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 86–100, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20326 [ABSTRACT FROM AUTHOR]

Recently, with advances in cellular phones and wireless LAN technologies, mixed environments consisting of a fixed network and a wireless network have become commonplace. Also, information networks represented by the Internet are now indispensable for daily life. Hence, demands for highly reliable communications in a mixed environment of fixed and wireless networks have increased. However, wireless networks have the problem of easily generated packet loss due to various factors such as obstacles and interference. In a network consisting of a link with a high packet loss rate and high instability, the end-to-end packet arrival rate is significantly degraded. In addition, the entire network may become unstable due to frequency updating of the paths as a result of losses in routing control packets. To enhance the packet arrival rate, it is effective to use a multipath communications system in which several copies of the packets are sent by different paths. In this paper, based on path design considering the introduction of the intermittent state as a link condition, and introduction of the concepts of interruption-tolerant path and route calculation considering interference, a multipath communication system is proposed that enhances the end-to-end packet arrival rate while the control load is reduced in a network consisting of unstable links. By means of simulation it is shown that the control load can be kept small during communications while the packet arrival rate is improved over that in the conventional system. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(11): 1–11, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20405 [ABSTRACT FROM AUTHOR]

Recently, in the fields of network measurement and distributed control, synchronization accuracy of better than microsecond order is required. For highly accurate time synchronization, the skew (the variation of the clock rate) and the queuing delay in the packet switching network constitute problems. In this paper, Packet Arrival Interval-based time synchronization (PAI) is proposed. In the proposed system, based on the fact that the average arrival interval of the synchronized packets broadcast accurately at a certain interval is less likely to be affected by the queuing delay, the clock rate is accurately estimated. Also, the one-directional delay from the master to each client can be calculated accurately from prior knowledge of the constituent elements of the LAN. Wide-range synchronization is possible if the master is synchronized to GPS. An experiment confirms that synchronization accuracy of better than microsecond order can be realized even in the presence of cross traffic with a channel use rate of about 80%. In addition, the present system can be used even with small nodes such as a sensor network. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(11): 12–24, 2007; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/ecja.20402 [ABSTRACT FROM AUTHOR]

When communication signals are transmitted at high speed on balanced cable (UTP cable), signals may leak from the cable and affect the reception of wireless signals. To evaluate this effect, the radiated electromagnetic field from the balanced cable is measured by using a 4-port network at 300 MHz or less. Although this method has the advantage that it can be used to analyze line constants, it is not clear whether it can be applied in an analysis at a frequency greater than 300 MHz. In this paper, the authors investigate the applicability of this method at frequencies up to 1 GHz. As a result, they discuss a method of using a 4-port network to represent telecommunication equipment for increasing precision and a balun for simulating this equipment and also discuss the dependency of this method on the number of subdivisions of one twist of the cable. From the results of actually evaluating the radiated electromagnetic field by using a 3-meter length of UTP cable, it was apparent that this analysis method using a 4-port network was effective for obtaining the trends exhibited by the characteristics of the radiated electromagnetic field at up to 1 GHz by obtaining the 4-port network parameters of the terminal equipment parts and dividing one twist of the cable into 80 parts. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(11): 25–35, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20391 [ABSTRACT FROM AUTHOR]

In this paper, we improve On-Demand Multicast Routing Protocol (ODMRP), which is a multicast routing protocol for Mobile Ad hoc Network (MANET), and propose a new protocol decreasing the number of data forwarding without deteriorating communication reliability. The proposed protocol avoids unnecessary data forwarding by distinguishing each multicast source at every Forwarding Group (FG) Node used in ODMRP. Moreover, the proposed protocol utilizes Support Group (SG), which also distinguishes each multicast source, in order to retain substitute routes without any redundant data forwarding. Therefore, the proposed protocol can avoid deteriorating communication reliability. We evaluate the performance of ODMRP, ODMRP with SG, and the proposed protocol, and we show that the proposed protocol can decrease the number of data forwarding compared with the conventional protocols. We also show that the proposed protocol can restrain the deterioration of packet delivery ratio within allowable range except the case where the number of multicast sources and receivers is extremely large. Furthermore, we show that the proposed protocol can mitigate the deterioration of packet delivery ratio caused by traffic congestion in the case where the number of multicast sources is large. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(11): 36–47, 2007; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/ecja.20382 [ABSTRACT FROM AUTHOR]

Dynamic load balancing (DLB) making use of network transferable computers (NTC) and Mobile IP is a new approach to performing load balancing for network traffic. In client– server systems when access requests to a specific server become particularly high from time to time, excessive amounts of network traffic will be generated on the route connecting to the server. With a server that is receiving a high concentration of requests, the provision of a mirror server can help provide load balancing to deal with issues of host performance, but it is not necessarily the best approach when the objective is principally to balance the load of the traffic on the network. In the DLB approach, the server is given the capability to migrate across the network; the server can therefore be moved to a location from which the route over which request and response packets to the server are causing congestion can be avoided. Since this results in the corresponding traffic being eliminated from the given network route, it allows the load balancing of network traffic. The proposed method is constructed via the use of an NTC system, Mobile IP, and a server migration manager. The server migration manager system can provide the following functionality. First, it is able to analyze information obtained from the network in which the server is located and provide predictions necessary for determining migration decisions. Next it can determine whether or not the server should actually migrate and in the case that it does can determine the location to migrate to. We have conducted evaluations of this method in simulation experiments and confirmed that traffic was reduced on the targeted network route. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(11): 48– 60, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20345 [ABSTRACT FROM AUTHOR]

Broadband fixed wireless access (FWA) systems using submillimeter and millimeter bands are expected to function as large-capacity access circuits supplementing wired broadband access networks. However, a major issue in handling high-frequency bands such as the submillimeter and millimeter bands has been deterioration of circuit quality due to rain attenuation and the resulting degradation of operating efficiency. In order to deal with this issue, the authors proposed a multipoint-to-multipoint (MP-MP) FWA system using a mesh topology that organically combines point-to-point (P-P) wireless links, and quantitatively showed a diversity effect obtained on the mesh network to demonstrate the validity of the system. The proposed system was recommended for use as F.1704 by the ITU-R (International Telecommunication Union-Radiocommunication Sector), which promotes research into standardization of wireless communications and prepares recommendations. In this paper, we give theoretical evaluations of the diversity effect that formed the core of the recommendation, and present evaluation examples based on real data obtained from outdoor test networks, to demonstrate the validity of the diversity effect in the proposed system. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(11): 61–70, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20334 [ABSTRACT FROM AUTHOR]

GMPLS (Generalized Multi-Protocol Label Switching) is considered promising as the basic technology for forming the next-generation ISP (Internet Service Provider) backbone network. In an IP backbone network based on GMPLS, the optical layer and the packet layer are vertically integrated and operate in close collaboration. It is due to this collaborative operation of multiple layers that integrated network control such as path setting in the optical layer according to the IP traffic in the packet layer and fast recovery from faults is realized. However, there is a danger, due to the similarity of functions in the two layers or to mismatch of the parameters, that collaborative operation between layers may affect the stability of IP routing in the packet layer. This situation is mostly due to the fact that the time granularity in the change of path state in the optical layer is finer than that of the IP routing protocol processing in the packet layer. This paper discusses route stability in the packet layer during collaborative operation of layers. The situation is analyzed by simulation and a method of improving stability is proposed. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(11): 71–80, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20332 [ABSTRACT FROM AUTHOR]

In service in the ubiquitous networking environment, it is expected that flexible interaction between the user and the things (resource) in the real world will become important. In order to realize such an interaction, there must be a system in which the resource to be utilized can be searched for with its attribute information as keys. Consequently, this paper proposes a DHT (distributed hash table)-based P2P search system using a new indexing method called pseudo-candidate key indexing. A problem of the conventional DHT-based P2P search system is that a large amount of communication is needed in the search process. The proposed system attempts to deal with the problem by preparing an index for all search conditions which are useful to the user, thus reducing the amount of communication in the search. A simulation verifies that the proposed system is scalable. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(11): 81–94, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20317 [ABSTRACT FROM AUTHOR]

Because of the rapid development of mobile communications and ITS (intelligent transport systems), the electromagnetic wave propagation environment is becoming complex, and there is an increasing demand for techniques to estimate the direction of arrival with high resolution and to reduce the effect of interference waves. Among these, Cyclic MUSIC and Cyclic ESPRIT, in which the direction of the arriving wave can be estimated selectively by utilizing the periodic stationary property of the arriving wave, are attracting attention. The authors are proposing Cyclic ESPRIT based on the noise subspace (NS Cyclic ESPRIT) in order to remedy the performance degradation produced by the fact that the correlation matrix of the array input used in Cyclic ESPRIT is not a Hermitian matrix. However, when the number of snapshots is finite in the estimation of arrival direction by Cyclic MUSIC or Cyclic ESPRIT, the interference wave component remaining in the correlation matrix has an adverse effect on the accuracy of direction-of-arrival estimation. Consequently, adaptive spatial smoothing processing and generalized eigenvalue decomposition are introduced into NS Cyclic ESPRIT in this study, aiming at reduction of the remaining interference component and at performance improvement in direction-of-arrival estimation. A computer simulation verifies that the performance in direction-of-arrival estimation in NS Cyclic ESPRIT is improved. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(11): 95–104, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20304 [ABSTRACT FROM AUTHOR]

In this paper, we propose a modified calibration method to improve the accuracy of direction of arrival (DOA) estimation, and conduct simulations and experiments to verify the effectiveness of the proposed method. In a system for DOA estimation, because the accuracy of the DOA estimation is degraded by the mutual coupling among the antenna elements, these elements must be calibrated. Therefore, we propose a modified calibration method to implement these improvements while considering the mutual coupling among the elements and the manufacturing errors. We verify the effectiveness of the proposed method by simulations and improve the accuracy by about twofold compared to the conventional method in experiments. In addition, the estimation accuracy is degraded by changes in the directions of the angle of elevation and the angle of dip in the conventional method, but we demonstrate the ability to suppress degradation by applying the proposed method. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(10): 1– 13, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20398 [ABSTRACT FROM AUTHOR]

Orthogonal frequency division multiplexing (OFDM) can achieve high utilization efficiency. In this paper, the authors combine OFDM with wavelength division multiplexing (WDM) to investigate the optical fiber transmission characteristics of a WDM/OFDM hybrid system that can easily achieve high utilization efficiency even when the number of channels is high. They used intensity modulation (IM), differential binary phase-shift keying (DBPSK), and differential quadrature phase-shift keying (DQPSK) as modulation methods to show transmission characteristics related to multi-repeater and nonrepeater systems. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(10): 14– 24, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20387 [ABSTRACT FROM AUTHOR]

The detection of received radar signals uses Doppler filtering as the correlation process on the received echoes for many transmitted pulses in addition to the pulse compression process which is the correlation process in the range direction. Normal radar echoes become blips widened in the azimuth direction, but the Doppler filtering process is not the optimum process from the perspective of improving the signal-to-noise ratio. Furthermore, compression of the spread in the azimuth direction of the signal is demanded in order to detect the azimuth. In this paper, we show that the azimuth beam width compression process can be implemented by filtering which satisfies the maximum SNR based on the zero sidelobe constraint condition applied to pulse compression. In addition, we theoretically explain the weighting matrix derived by this design method and use simulations to compare with the pulse compression process of the characteristics of a zero sidelobe correlation function. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(10): 25– 35, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20373 [ABSTRACT FROM AUTHOR]

In the past few years, communication among clients, such as IP video telephony and file sharing, that is peer-to-peer (P2P) communication, has increased. P2P communication is often considered to be communication over relatively short geographic distances as in local communication. However, in P2P communication, the communication partner is not limited to belonging to the same Internet Service Provider (ISP) as oneself and communication may be routed over long paths known as routing through an Internet exchange (IX) even when geographically close. However, the problem becomes inefficient transmission. To solve this problem, we herein propose a multinetwork access method using multiple networks, implement efficient packet forwarding, and study the reduction in IX or ISP network traffic when this method is applied to an access network. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(10): 36– 46, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20368 [ABSTRACT FROM AUTHOR]

The expansion of a communication area and the provision of services to wide districts can be expected if ad hoc networks are connected to established networks. In this environment, two types of routes exist between mobile stations that compose ad hoc networks: routes using wireless links only and routes via base station and the established networks. However, most routing protocols decide a route simply by the minimum hop counts between mobile stations without taking the differences of communication performance between the established network and ad hoc networks into account. This paper presents a new routing protocol that uses simple formulas to decide which route is effective, a route using wireless links only, or a route via the established networks. The formulas are derived from the results of simulation on the communication performance of some routes that uses IEEE802.11b as wireless links and Ethernet of 100 Mb/s as wired links. The performance of our proposed routing protocol, which is realized as an extension of ad hoc on-demand distance vector (AODV), is evaluated by simulation. The results show that the proposed routing protocol is effective especially under a high data rate situation compared with AODV. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(10): 47– 56, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20363 [ABSTRACT FROM AUTHOR]

Satellite communications is suitable for multicast communications which can achieve one-to-many delivery because it can broadcast to multiple receiving stations over a wide area. However, packet retransmission is inefficient for satellite communications because of its large delay and bit error rate. In order to avoid packet retransmission, FEC (forward error correction) exploiting error correcting codes have been put to practical use in satellite multicasting. Tornado-type codes are well known as a kind of error correcting codes suitable for multicasting. Tornado-type codes are encoded and decoded in packets. As a result, they are effective for combatting packet losses by buffer overflow or congestion control. Furthermore, their coding and decoding have low time complexity. On the other hand, the bit errors in the packet are processed as a packet loss in decoding because the Tornado-type codes are decoded packet-wise. In this paper, we propose an effective decoding method for bit errors in the packets for Tornado-type codes. We show by computer simulation that the proposed method is effective in bit error environments. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(10): 57– 66, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20361 [ABSTRACT FROM AUTHOR]

In mobile ad hoc networks, due to the change of topology caused by the movement of hosts and the change of radio link status, it is difficult for mobile hosts to retain accessibility to data on other hosts. To solve such a problem, replica distribution methods which distribute replicas of data items to other mobile hosts and maintain them have been proposed. In this paper, we propose and evaluate a method to enhance the accessibility to data items that are associated with locations and requested by Geocast from hosts. This method is based on flooding of replicas of data items, and it uses the locations of mobile hosts and the associated locations of data items for controlling the range of the replications and the redundancy of the replicas. Furthermore, to keep the accessibility to such data high, replicas are dynamically relocated after the movement of hosts. We confirmed the effectiveness of the proposed method by detailed simulations including multiple data request models. Simulation results showed that the proposed method achieves high accessibility to location-dependent data especially when the storage size is small. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(10): 67– 80, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20320 [ABSTRACT FROM AUTHOR]

This paper investigates an intervehicle communication method as a safe driving support system for intersection collision avoidance warnings. In this kind of system, realization of highly reliable communications in the physical layer is an absolute requirement. As a result, we propose a new MIMO-STBC (Space-Time Block Coding) method based on intersection propagation channel characteristics. MIMO transmission characteristics are determined by the propagation channel characteristics. First, we use a ray-tracing method simulation to clarify the propagation channel conditions, and then model the intersection propagation channel. We use the characteristics of this propagation channel to propose a MIMO-STBC method that utilizes decision feedback channel estimation, and verify the effectiveness of the proposed method in computer simulations. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(9): 1–15, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20400 [ABSTRACT FROM AUTHOR]

In this paper, we propose an OVSF (Orthogonal Variable Spreading Factor) code allocation in OFCDM (Orthogonal Frequency and Code Division Multiplexing) system. In the proposed OVSF code allocation, codes which have a different ancestor code are allocated to users. When the proposed OVSF code allocation is used, a receiver can use a despreading which utilizes chips shorter than the spreading factor. Thus, symbols are generated. Furthermore, we propose a two-stage combining method. After first stage combining, by despreading, the symbols are multiplied by weights and combined in second stage combining. We show that the proposed scheme achieves better BER performance than the conventional scheme by computer simulations. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(9): 16– 24, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20381 [ABSTRACT FROM AUTHOR]

In general, it is difficult to measure short distances by radar, which has a minimum detection distance of several meters. The standing wave radar proposed by the present authors has a minimum detection distance of about 2 m when the frequency bandwidth is 76 MHz. A solution to reduce the minimum detection distance is to increase the frequency bandwidth. This is not realistic due to limits imposed by radio regulations. The authors have proposed a method with measurable distances down to 0 m without enlarging the bandwidth and have presented the configuration and the measurement principle. The measurement principle has been verified by numerical simulation. In the present paper, the measurement principle is experimentally verified by using an actual standing wave radar and the realizability of a standing wave radar with measurement capability down to 0 m is confirmed. It is shown that the distance to the target at locations closer than the minimum detection distance of 2 m (0.14, 0.3, 0.5, and 1 m) can be measured with an error of several centimeters for a frequency bandwidth of 76 MHz at 24 GHz. For distances less than 0.14 m, the target could not be placed closer than 0.14 m due to positional interference of the target and the antenna in the present experimental environment so that physical confirmation was not possible. However, at the confirmed distance, the range spectrum predicted from the theory is obtained. Hence, it is considered possible to make measurements without special restrictions. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(9): 25– 34, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20375 [ABSTRACT FROM AUTHOR]

For sidelobe suppression design of antennas, weighting with window functions has been traditionally used. The antenna gain is degraded if a low sidelobe level is sought, so that expansion of the antenna beamwidth is inevitable. Also, there have been discussions of using the convergent calculation in the derivation of a window function that realizes desired characteristics such as sidelobe-free conditions, but it has not been clear whether the theoretically maximum antenna gain is realized. This paper presents a method of analytical derivation of a weight vector satisfying the maximum achievable antenna gain while the desired beamwidth is obtained under the null sidelobe constraint for the sidelobe region output. In addition, we demonstrate the effectiveness of the method by simulation examples. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(9): 35–44, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20370 [ABSTRACT FROM AUTHOR]

For satellite observation of the electric fields of waves, a dipole antenna using a wire (wire antenna) is often used. An antenna with probes on both ends (probe antenna) is used for observation of the static electric field. For calibration of these antennas, the effective length of the antenna is a problem. In general, in AC wave observation, the effective length of the wire antenna is half the total length L and hence L/2. It has been verified that this is correct at frequencies of several hundred hertz or higher. However, in the GEOTAIL antenna, the same antenna is co-used for wave observation and the static field observation. Calibration is performed with an effective length of L/2 for wave observation with an effective length of L for static electric field measurement. Reliable data are obtained in both cases. This paper reports a rheometry experiment in which the output voltage of a small antenna is measured in water for the wire antenna, obtaining the frequency dependence of the effective length in the low-frequency region. It is found that the frequency dependence of the effective length depends on the antenna configuration. When a wire antenna with only its side surfaces insulation coated is placed in a conductive medium such as water or plasma, it is found that the effective length approaches L at low frequencies and L/2 at higher frequencies. This result is theoretically analyzed by means of an equivalent circuit and it is found that the phenomenon depends on the balance among surrounding medium, the insulation coating of the wire, and the input impedance of the receiver. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(9): 45–53, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20353 [ABSTRACT FROM AUTHOR]

This paper considers environment-adaptive content delivery in which an intermediary modifies the content between the content provider and the content user, and proposes a system in which the provider can securely control content modification by the intermediary in accordance with usage rules defined in the content. In order to have the intermediary follow the usage rules strictly, it is indispensable to provide a content protection technique in which tampering with content or usage rules by a third party is prevented while permitting content modification by intermediaries approved by the provider within the scope of the usage rules. The authors consider the hash-tree signature method in which data deletion by the intermediary is permitted, and propose a signature system with a place holder extension permitting data addition. A highly efficient realization of the proposed signature system based on the hash-sign-switch (HSS) method is presented. The effectiveness of the approach is shown by a quantitative evaluation using the implemented system. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(9): 54–66, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20341 [ABSTRACT FROM AUTHOR]

Deflection routing is considered as a method to avoid packet collisions in an optical packet switching system. Deflection routing is a method of avoiding collision by link substitution, in which the colliding packet is sent to an idle link. Thus, the load on the congested part of the network is distributed and the bandwidth can be utilized effectively. When excessively frequent deflections are performed, however, the load on the whole network is increased, which produces an adverse effect. Another problem is that sequence errors can occur in the same flow due to differences of transmission delay, since packets are sent to different routes. From these points of view, this paper proposes a deflection control method which can remedy the above problems, and applies the proposed method to an optical packet switching system. In the proposed control method, class separation is performed with respect to sequence error, and deflection is permitted to packets of nonpriority class. This improves performance by large-scale grouping. In order to alleviate the increase in load on the whole network, a control algorithm which can deal with changes of the link utilization and the number of traversed hops is devised. The effectiveness of the approach is shown by computer simulation. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(9): 67– 77, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20312 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

In this paper, we propose a method for decreasing cross-polarization in the tilt plane by optimizing the dielectric substrates of dual-polarized patch antennas. At the same time, we clarify the limit values for the cross-polarization level. First, we use a cavity model of the patch antenna to find cross-polarization dielectric characteristics in the tilt plane. We learn from this that the direction of cross-polarization increase or decrease in relation to the dielectric is reversed during horizontal polarized excitation and vertical polarized excitation. Therefore, if the cross-polarization level during horizontal polarized excitation and vertical polarized excitation is the same dielectric, the lowest cross-polarization level can be obtained in conditions where both horizontal polarization and vertical polarization are decreasing cross-polarization. Next, we investigate the case where parasitic elements are mounted on the patch antenna, and use the FDTD method and test to show that our method is valid. In addition, if the patch is positioned perpendicularly to the horizontal plane, we show that the optimum dielectric remains virtually unchanged in the tilt plane up to about 15° from the horizontal plane. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(8): 1–9, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20393 Copyright © 2004 Wiley Periodicals, Inc.Copyright © 2007 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We optimized orbital elements to minimize the squared deviation of the satellite position intermittently measured by an on-board GPS receiver from the satellite position measured from orbital elements using the SGP orbit model, and then reentered the results into the SGP orbital model to attempt an interpolation calculation of the satellite position and velocity at any given point in time. As a result of applying this system to data from a GPS receiver on board the Whale Ecology Observation Satellite (WEOS), we found that by using positions measured at several minute intervals over a period of about 2 hours, we could calculate the position of WEOS with an error of about 50 m at any given instant within the time frame, among other conclusions. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(8): 10–19, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20378 [ABSTRACT FROM AUTHOR]

The method of moments and the FDTD method have been widely used for the analysis of radiated electromagnetic fields. In comparison with the FDTD method, the method of moments calculates the electromagnetic field by a light computational load and analyzes the far field accurately. A wire grid model of the printed circuit board placed on the upper plane of the imitated equipment has been reported and it can calculate the electromagnetic field below 1 GHz. However, the wire grid model using the calculation above 1 GHz has not been reported. This paper proposes the analytical model that can analyze the radiated electromagnetic fields with horizontal polarization at frequencies above 1 GHz. Since the contribution of the current on a microstrip line (MSL) is significant in the case of horizontal polarization, the proposed method attempts to simulate the current distribution by inserting impedances and admittances into the wire grid model of MSL. As a result of the studies, it is found that an analysis is possible with an accuracy within ±5 dB of the measured results in the frequency range of 1 to 3 GHz when the current distribution, calculated by the FDTD method, is simulated by inserting inductance and capacitance into the wire grid model. It is also found that the result of calculation by the model is similar to that by the FDTD method, which requires a computation time about 4 times longer. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(8): 20–29, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20354 Copyright © 2004 Wiley Periodicals, Inc.Copyright © 2007 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

With a view to constructing a metropolitan network that can flexibly handle highly bursty traffic, an optical burst switched ring network with upstream prioritized switching and distributed fairness control is proposed. In optical burst switching, high burst drop rates at intermediate nodes constitute a problem. In the proposed system, burst signal dropping at the relay nodes is eliminated by means of upstream prioritized switching. At the same time, by using distributed fairness control, the problem of upstream prioritized switching-related unfairness, in which positional priority provides higher priority to more distant transmission nodes, is resolved. Further, by modifying the reservation of downstream nodes by using the trailer packet after disconnection of the transmission, unnecessary bandwidth is eliminated and the throughput is improved. By computer simulation, the throughput and the fairness with regard to the throughput are evaluated. It is shown that the proposed architecture exhibits excellent characteristics even in cases of hot-spot traffic, in which concentrated traffic occurs at a particular destination. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(8): 30–39, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20338 Copyright © 2004 Wiley Periodicals, Inc.Copyright © 2007 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

As broadband Internet access channels such as ADSL and FTTH become more widely used, network compression by power users becomes a problem. In order to deal with this problem, bandwidth control that assigns bandwidth among users in a fair manner is needed. In this paper, we studied the DRR method, which is known to allow fair bandwidth allocation and to be highly realizable. A new method that resolves the problem of realizability at high speeds in the range of gigabits and tens of gigabits typical of the DRR method is proposed. By this method, it is possible to realize fair allocation of bandwidth even if the channel speed is increased to several gigabits or several tens of gigabits. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(8): 50–56, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20266 Copyright © 2004 Wiley Periodicals, Inc.Copyright © 2007 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

In recent years attention has turned to LDPC codes, which show performance approaching communication path capacity. In the past, application of LDPC codes has mainly been BPSK-based proposals. In this paper, we propose a new design method for multilevel coding that uses LDPC codes as element codes. First, we focus on the possibility of freedom of design for LDPC codes in regards to any desired encoding rate, optimize a degree profile using Gaussian Approximation, and use the actual BER characteristics shown in LDPC codes of finite length formed by this degree file to find the differential SNRnorm up to the Shannon limit of SNR values at the time of some specific BER. With the SNRnorm for the encoding rate at several points, we calculate an SNRnorm approximation formula for a continuous, wide-range encoding rate, and use this approximation formula to propose a method for designing multivalue coded modulation based on multilevel coding. In addition, we demonstrate the results of a simulation of this proposed method using irregular EG-LDPC codes, and demonstrate that this method is effective for restricting deterioration of performance in actual usage. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(8): 57–68, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20173 Copyright © 2004 Wiley Periodicals, Inc.Copyright © 2007 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The transmission characteristics of a fiber Fabry-Perot etalon formed by mirror-finishing both ends of an optical fiber are dependent on the external stress applied. A theoretical study and an experimental confirmation of a fiber Fabry-Perot etalon with a ferrule diameter of 2.5 mm and a resonator length of 4 mm are carried out to investigate variations of the transmission frequencies as a function of the stress. It is confirmed that there is a proportional relationship of 1.5 GHz/N and -0.1 GHz/N in the transmission frequency variations versus the stress in the axial and radial directions. Arbitrary transmission frequencies within FSR can be obtained by adjustment of the stress at values less than 17 N, so that the fiber Fabry-Perot etalon can be used as a tunable optical frequency filter. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(7): 1– 8, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20386 [ABSTRACT FROM AUTHOR]

Mobile IP is a protocol which provides a function by which a mobile node (MN) continuously retains a single IP address and continues to use the same IP address, even if the MN moves from the network to which it originally connected (Home Network) to another network. This paper is a study of the advantages of IPsec for MIP applied to IP-VPN, with a small number of terminals per node and where the subject devices are integrated devices such as non-personal computer terminals. In order to apply MIP to such an IP-VPN, a new MFA mode is proposed, in addition to the FA mode and CoA mode which have previously been provided to Mobile IP. In the MFA mode, both the MN and MFA move together. Furthermore, it is proposed to include an autoconfiguration function as well. This can be expected to result in reduced terminal shipping costs. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(7): 9–17, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20385 [ABSTRACT FROM AUTHOR]

Recently, on-board distributed power systems consisting of bus converter and POL have usually been used for IT infrastructure equipment. However, even if each converter has stable operation, the bus voltage may oscillate and the system may be unstable, depending on the bus converter design; this has been a serious problem in recent years. Solution of the issue is highly desirable, and in order to improve the system stability various techniques have been discussed. This paper investigates the improvement of the system stability by the control method. The availability of full-regulated bus converter is especially examined. It is determined that the full-regulated method is the optimal control method for the bus converter because a full-regulated bus converter can reduce bus voltage oscillation and adjust to input voltage variations flexibly by regulation. A stability design process is proposed for an on-board distributed power system using a full-regulated bus converter. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(7): 18–25, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20356 [ABSTRACT FROM AUTHOR]

In recent years the amount of software running on mobile phones has increased dramatically due to the start of data network connection services for mobile phones. As a result it has sometimes become necessary to repair defects in such products after they have been shipped to market. In this context, services have been launched that enable software to be updated after a terminal has been sold. The time taken for software to be updated is made up of the time taken to transmit the data to the handset via a mobile network or from a PC (which in turn depends on the amount of data being transmitted) and the time taken to overwrite the data on flash memory. A standard method for making the amount of data that needs to be transmitted to the handset small, is to only send delta data corresponding to those parts of the new version of the software that differ from the old version; it is generally necessary to make this delta as small as possible. Following a description of existing techniques for extracting deltas, in this paper we make multiple proposals regarding delta extraction schemes that are designed with the structure of mobile phone software particularly in mind with a view to making the delta data transmitted to the handset when updating software as small as possible; we then describe results of evaluations with actual mobile phones immediately prior to shipping. Both of the schemes that we propose are shown to allow a reduction of approximately 30 percent in the size of the delta when compared with standard delta representation mechanisms. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(7): 26–37, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20348 [ABSTRACT FROM AUTHOR]

For conditions under which the channel conditions between the transmitting and receiving antennas are known on the transmitter side when TDD (Time Division Duplex) is used in the MIMO (Multi-Input Multi-Output) method, much attention has been devoted to E-SDM (Eigenbeam Space Division Multiplexing), in which the influence of CCI (Co-Channel Interference) is eliminated by making the different transmission signal sequences orthogonal in space by means of the eigenvectors of the channel matrix used as the transmission and reception weights. However, in such a system as E-SDM, in which eigenvectors of the channel matrix are used, more than two antennas are needed on the receiving side in order to perform eigenvalue decomposition of the channel matrix. In this paper, in order to realize a system using the eigenvectors as the transmission and reception weights even in a system with two transmitting antennas and one receiving antenna under TDD, the ETD (Eigenbeam Transmit Diversity) system is proposed. In this system, the concept of frequency diversity is applied, in which identical signals are transmitted on two subcarriers on one transmitting antenna, so that a MIMO system is virtually realized with subcarriers of the OFDM (Orthogonal Frequency Division Multiplexing) in place of receiving antennas in the row direction of the channel matrix. In the ETD system, the minimum eigenvalue of the channel matrix can be made larger by adaptively interchanging the signals among antennas and by transmission phase control. Hence, the BER characteristics of the signal sequence by which the minimum eigenvalue is multiplied can be improved. The characteristics are evaluated by computer simulations. It is shown that the proposed system is superior in terms of BER characteristics to the transmission diversity system in which transmission phase control is carried out among the antennas. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(7): 38–51, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20342 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

A new double-sided electromagnetic wave absorber allowing transmission is proposed. In the conventional permeable wave absorber, a resistive film is attached to a lossless dielectric layer. However, this is not nonreflective for an incident wave on the resistive film side. In the present paper, a basic structure is considered in which there is no reflection on both sides of the absorber. A simple structure made of two resistive films inserted between three dielectric layers is proposed. The nonreflection condition of the present wave absorber is derived by means of the equivalent circuit, and the reflection and transmission characteristics are derived for given permittivities of the dielectric layers. It is found that the bandwidth of the reflection coefficient does not significantly depend on the permittivity of the inner layer and that the permittivity of the outer layers is increased and that of the inner layer is decreased in order to make the transmission coefficient smaller. The wave absorber is fabricated and measured for confirmation of the validity of the theory. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(6): 1–8, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20369 [ABSTRACT FROM AUTHOR]

This paper discusses the modeling and broadband design of an indoor infrared wireless communication channel consisting of a nondirected diffusion system. The property of the nondirected diffuse link is analyzed by the ray tracing technique and the modified Monte Carlo method. The physical parameters are directly related to the impulse response of the link and are modeled by a gamma probability density function. The impulse response model and a simulation indicate that it is effective for the broadband link to narrow the radiation angle of the optical source and to expand the receiver field of view to match the ceiling area of the room. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(6): 9–19, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20352 [ABSTRACT FROM AUTHOR]

The impact of distributed Raman amplification (DRA) technologies on long-distance large-capacity transmission systems is discussed from the viewpoint of improving the signal-to-noise ratio (SNR). First, we show the characteristics of this technology, which has brought significant improvement to the SNR, and its trends, the basic configuration for our proposed DRA system (a DRA/EDFA hybrid configuration), and safety aspects for high-power pumped light. In addition, we show the merits of the DRA system, including the amount of improvement in the optical SNR, transmission fiber (DSF and SMF) dependence, and superiority of DSF over SMF (about 2 to 3 dB). Furthermore, in a long-distance large-capacity wavelength division multiplexing transmission field trial using DRA in the L band on DSF, we confirm good transmission characteristics. In other words, the impact of DRA technologies lies in the significant improvement of the SNR in terrestrial long-distance large-capacity optically amplified transmission systems with field-installed fibers, and in the improvement of performance in systems utilizing these technologies. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(6): 20–28, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20340 [ABSTRACT FROM AUTHOR]

In a multihoming communications environment in which multiple communications interfaces are connected to a single terminal to use multiple paths, if different paths are used for the going-out path and return path, more efficient information communications may be possible. To enable this to occur, one-way delay must be taken into account to select the appropriate interface. However, it is generally difficult to directly obtain an accurate one-way delay because the communications path load varies according to such factors as the time period and amount of communications, and the going-out path delay and return path delay cannot be easily separated. In this paper, the authors simply obtain the one-way approximate differential delays from multiple patterns of round-trip delay combinations and propose a method of selecting the path based on these differentials. This method has such features as control packets for measurement and synchronization with the communication destination which are unnecessary and it is extendable since it does not depend on the network layer. The authors also implemented the proposed method on a computer by using ICMP and evaluated it experimentally in various types of multihoming communications environments. The results showed that one-way path selection is possible and that the proposed method is effective. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(6): 29–42, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20321 [ABSTRACT FROM AUTHOR]