Showing papers in "Electronics and Communications in Japan Part I-communications in 2007"
TL;DR: In this article, the modeling and broadband design of an indoor infrared wireless communication channel consisting of a non-directed diffusion system is discussed, where the physical parameters are directly related to the impulse response of the link and are modeled by a gamma probability density function.
Abstract: 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
39 citations
TL;DR: In this paper, the authors examined how to study the antenna characteristics using the phantom when extended to a bandwidth including 900 MHz to 3 GHz and 6 to 10 GHz and performed a quantitative study focusing on the electrical constants of the phantom.
Abstract: Previously, the authors studied biological tissue equivalent phantoms able to simulate the electrical constants of the human body in the 3- to 6-GHz band in a single composition ratio. Therefore, in this paper, we examined how to study the antenna characteristics using the phantom when extended to a bandwidth including 900 MHz to 3 GHz and 6 to 10 GHz and performed a quantitative study focusing on the electrical constants of the phantom. The result clearly showed hardly any effect of divergence of the phantom's electrical constants from the target values on the antenna input impedance, radiation efficiency, and radiation directivity. Therefore, in the entire ultra-wideband (UWB), this phantom can be accurately evaluated through antenna characteristic measurements and is clearly effective. Furthermore, differences due to the divergence of the phantom's electrical constants from the target values in the entire UWB bandwidth (3 to 10 GHz) are within ±3% for the average local specific absorption rate (SAR) inside the phantom caused by the electromagnetic wave energy radiated from the antenna. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(5): 48–55, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20300
31 citations
TL;DR: In this paper, a path loss prediction model for over-rooftop propagation environments is proposed for suburban areas based on the propagation mechanism explained by using the geometrical optics and consists of the direct wave region, the reflected wave region and the diffracted wave region.
Abstract: It is desirable that the method used for outdoor path loss estimation at microwave frequencies be one for which a worldwide consensus can be obtained through an ITU-R international standard. In this paper, a path loss prediction model for over-rooftop propagation environments is proposed for suburban areas. This model is based on the propagation mechanism explained by using the geometrical optics and consists of the direct wave region, the reflected wave region, and the diffracted wave region. The boundary points of these regions can be determined uniquely from the antenna height and building environment and all regions are continuously connected. Hence, high-precision estimation of the path loss can be estimated from the short-distance line-of-sight region to the far-field non-line-of-sight region. The proposed model is useful for channel design of microwave-band wireless access systems. Further, the method contributes to the ITU-R international standardization described above. Finally, it is shown that the measured path loss and the value estimated by the present model agree well at 2.2, 5.2, and 19.4 GHz. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(1): 13–24, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20333
31 citations
TL;DR: It is shown that the proposed method is useful for indoor personnel location management and 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.
Abstract: 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
25 citations
TL;DR: In this paper, a system for lightning location from single station observations has been developed for localizing lightning (distance and direction) at rather short distances (several hundred kilometers), where a vertical component of the electric field and two horizontal components of the magnetic field of the VLF wave of sferics are observed.
Abstract: A system for lightning location from single station observations has been developed for localizing lightning (distance and direction) at rather short distances (several hundred kilometers). In this system, a vertical component of the electric field and two horizontal components of the magnetic field of the VLF wave of the sferics are observed. The sferics are usually observed as a pulse train. The first pulse is used for estimation of the direction. The second and subsequent pulses are multiple reflections between the ionosphere and the ground. The differences in arrival time of these reflected waves are determined by the propagation distance between the ground and the ionosphere. The reflection altitude of the ionosphere and the horizontal distance to the lightning location are estimated from the arrival time difference of more than two pulses. In this research, the electromagnetic pulses radiated from the lightning are first analyzed by the full wave method, considering the ionosphere, free space, and the ground, in order to evaluate the location estimation method. The lightning location is estimated by calculating the space discharge sferics waveform at the observation point. Observations were also carried out with the lightning location system for estimation of lightning locations. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(1): 25– 34, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20329
19 citations
TL;DR: In this article, the relationship between the control constants and the output voltage regulation characteristics of a buck DC/DC converter for a digital control system using P-I-D control, the minimum phase FIR filter, and the moving average constructed from digital signal processors was described.
Abstract: In this paper, we describe the relationship between the control constants and the output voltage regulation characteristics of a buck DC/DC converter for a digital control system using P-I-D control, the minimum phase FIR filter, and the moving average constructed from digital signal processors. Furthermore, the digital control method and its control constants were studied comparatively from the perspective of suppressing the oscillations based on the limit cycle. We found that when an 8-bit analog-to-digital (A-D) converter having a quantization width of about 80 mV was used, we could obtain excellent results similar to the minimum phase FIR filter and the moving average, achieve an excellent output voltage regulation of less than 1.3% for fluctuations from a light load to the rated 2 A for the target 10 V, and suppress oscillations to less than 20 mV. In the P-I-D control method, adequate output voltage regulation characteristics were obtained, but oscillations could not be suppressed. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(5): 1–10, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20357
15 citations
TL;DR: To enable the heating pattern to be controlled in the axial direction, the authors introduced a coaxial-dipole antenna and improved its structure and 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.
Abstract: 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
13 citations
TL;DR: Simulation results show that HRFA can efficiently utilize radio resources and can also achieve load balancing in IEEE802.11e WLAN networks.
Abstract: IEEE802.11 WLAN (Wireless LAN) has been widely used in enterprises and public spaces such as airports. In these large WLAN networks, RRM (Radio Resource Management) is necessary for efficient use of radio resources, and also load balancing among APs (Access Point) has to be taken into account. Since, in IEEE802.11, STA (Station) has the right to select an AP with which it will associate, the AP selection mechanism implemented in STA is important for load balancing. This paper proposes an association mechanism called HRFA (High-Rate First Association) in order to achieve load balancing and efficient use of radio resources. Furthermore, IEEE802.11e was developed by Task Group E of the IEEE802.11 working group and specified a MAC protocol to provide QoS in the MAC layer and to support real-time traffic over WLAN. In order for WLAN to be more widely used, the functionalities of IEEE802.11e must be provided in WLAN devices. Our proposed HRFA can be applied to WLANs compliant with IEEE802.11e. Since the HRFA can be implemented without any modifications in the IEEE802.11 and IEEE802.11e standards, it is useful from the implementation-cost and compatibility point of views. Simulation results show that HRFA can efficiently utilize radio resources and can also achieve load balancing in IEEE802.11e WLAN networks. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(4): 35–45, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20347
12 citations
TL;DR: This paper makes 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 and describes results of evaluations with actual mobile phones immediately prior to shipping.
Abstract: 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
10 citations
TL;DR: In this article, the authors proposed a new SDMA (Space Division Multiple Access) configuration in which the number of multitudes of SDMA can be increased by using dual polarization antennas at both the smart antenna base stations and the mobile terminals.
Abstract: In this paper, a new SDMA (Space Division Multiple Access) configuration is proposed in which the number of multitudes of SDMA can be increased by using dual polarization antennas at both the smart antenna base stations and the mobile terminals. In the proposed configuration, the smart antennas at the base stations constantly monitor the mutual correlations between the mobile terminals at the time of reception. Then, the polarization (vertical or horizontal) to be transmitted by each mobile terminal is determined in such a way that the mutual correlation between the mobile terminals connected at the same time is minimized. The mobile terminal used in the proposed system has a configuration in which the antennas with vertical and horizontal polarizations can be switched for transmission. Transmission is carried out with the polarization specified by the base station. The proposed configuration is expected not only to improve spatial division capability of SDMA by the smart antenna base station with vertical and horizontal polarizations but also to compensate the deterioration of the transmission quality along with the increase of multiplicity of SDMA by means of the switching configuration of the transmission polarization of the mobile terminal while the interference between the mobile terminals is taken into account. The proposed configuration can be applied to the uplinks in the TDD or FDD channels. By means of the numerical simulation, the basic characteristics of the proposed configuration are clarified in the case where the cross polarization discrimination (XPD) and the number of mobile terminals vary. In this way, it is demonstrated that the mobile terminal discrimination capability is improved over the conventional SDMA with the vertical polarization and the system is useful for increased multiplicity of SDMA. Further, the propagation characteristics (amplitude and phase) of the vertical and horizontal polarizations are obtained when the base station antenna and the mobile terminal antenna are placed on a steel tower and on a vehicle, respectively. The characteristics of the proposed configuration are presented where several mobile terminals exist. Usefulness of the proposed configuration in an actual environment for increased multiplicity of SDMA is presented. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(2): 33–45, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20287
9 citations
TL;DR: This paper proposes an alternative method of stochastic node placement that has as high a fault tolerance as power-law placement and can be achieved with a reasonable degree of complexity.
Abstract: One of the most important issues in wireless sensor networks is to develop the technology for improved fault tolerance, since sensor nodes are prone to failure (for mechanical reasons, for example) and have limited energy storage. The strategy for determining the positions in which sensor nodes are placed is very important, because it affects the likelihood that a target will be within the sensing range of a node, and that there will be a communication path from that node back to the base station. We have considered that when many sensor nodes are to be placed in a wide area, an effective approach is stochastic node placement, whereby sensors may be scattered in a controlled manner, such that their approximate positions are characterized by a probability density function. Then, as the first step of our research, we have proposed stochastic node placements in which the degrees of the nodes follow a power-law distribution (“power-law placement”). Through simulation studies, we have shown that power-law placement, with well-tuned parameters, shows a higher tolerance against random failures and failure through battery exhaustion than general stochastic node placement. However, this can be difficult to implement. As the second step of our research, this paper proposes an alternative method of stochastic node placement that has as high a fault tolerance as power-law placement and can be achieved with a reasonable degree of complexity. To this end, we first investigate the requirements necessary for other types of stochastic node placement to exhibit as high a fault tolerance as power-law placement. Next, we propose ways of achieving stochastic node placement that meets these requirements. Our proposal has theoretical basis that any stochastic node placement can be achieved by scattering sensor nodes many times from the air in a number of appropriately controlled operations. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(3): 42–53, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20319
TL;DR: In this article, a new measurement method which can determine the direction of arrival of a pulse electromagnetic wave with frequency dispersion characteristics has been developed, which can be used for continuous observation.
Abstract: A new measurement method which can determine the direction of arrival of a pulse electromagnetic wave with frequency dispersion characteristics has been developed. The direction of arrival is determined by conventional data analysis for an electric field component and two magnetic field components. The sensor system is composed of a vertical dipole antenna and two search coils oriented in perpendicular directions in the horizontal plane. The major part of the analysis of the detected signal is composed of the derivation of the spectrum with frequency dispersion from the pulse waveform and the calculation of the direction of arrival from the amplitude and the phase obtained for each frequency in the dispersion characteristics. By the proposed method, the direction of arrival can be determined even when a frequency-dependent delay is produced in propagation (frequency dispersion). The method is applied to lightning discharge pulses, and it is shown that the direction of arrival can be determined with high accuracy. Thus, the method can be used for continuous observation. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(5): 23–32, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20327
TL;DR: In this paper, the authors examined the practicality of M-quadrature amplitude modulation (M-QAM) where the number of signal points M is not a power of two.
Abstract: This study examines the practicality of M-quadrature amplitude modulation (M-QAM) where the number of signal points M is not a power of two. A practical problem is the complexity of the configuration because one symbol in an M-QAM signal does not correspond to an integer number of bits, and the symbol error does not simply convert to the bit error. Therefore, from the perspective of simplifying the configuration and minimizing bit error rate (BER) properties, multidimensional encoding (binary/M-ary conversion) for converting a binary sequence to correlated symbols is proposed and the theoretical formulas of the symbol error rate (SER) and the bit error rate (BER) are clarified. SER properties of 40QAM, 44QAM, 48QAM, 56QAM, and 60QAM fall between 32QAM and 64QAM. The configuration of a QAM scheme where the number of signal points becomes 3 × 2p−1 where p is an integer greater than or equal to 3 is shown, as are theoretical values for the SER properties of 12QAM and 24QAM in particular. Also shown are the theoretical values of the BER properties with and without differential encoding; these are verified with a computer simulation. A discussion based on these results concerns the effectiveness of M-QAM in the sense of expanding decision branches for adaptive modulation. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(2): 46–57, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20269
TL;DR: A scheduling algorithm which solves the problem in a multihop wireless network where differences arise in the throughput caused by the number of hops from the base station connected to wired networks by classified uplink packets and downlink packets into packets originated within the node and forwarded packets from adjacent wireless nodes and queued.
Abstract: Recently, attention has focused on multihop wireless networks capable of expanding the communication area by employing wireless relays between nodes and access points. However, the problem in a multihop wireless network is differences arise in the throughput caused by the number of hops from the base station connected to wired networks. In this paper, we propose a scheduling algorithm which solves this problem. In this proposal, the uplink packets and downlink packets are queued separately, and the uplink packets are classified into packets originated within the node and forwarded packets from adjacent wireless nodes and queued. When the node transmits a packet, the fairness among the nodes is improved by scheduling based on the source identifiers of the queued packets. The results of a performance evaluation using a network simulator verified a maximum tenfold improvement in the fairness among the subscribers compared to typical schemes. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(4): 11–22, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20364
TL;DR: In this article, the authors proposed 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.
Abstract: 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
TL;DR: In this paper, the authors combine OFDM with 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.
Abstract: 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
TL;DR: In this paper, the authors proposed to control the 20-MHz and 40-MHz STAs by setting NAV to them in the MAC layer, where transmission in both 20 MHz and 40MHz channel bandwidths is enabled.
Abstract: IEEE802.11-1999 Standard is widely known as a standard of WLAN and it has a number of amendments and supplements such as 802.11a, 802.11g, and 802.11i and also those under work in the current activities by the task groups (TGs). The one now attracting a great deal of attention is TGn, which is aimed at achieving high throughput. We are involved in this TGn standardization process. To achieve high throughput, MIMO technique is the main discussion point in the PHY layer in TGn. But another important point is the channel bundling method which extends the channel bandwidth from 20 MHz to 40-MHz. By doubling the channel bandwidth, the data rate can be increased. But when this channel bundling method is introduced, the question of how to cope with the legacy 20-MHz stations will arise. For this problem, we are proposing to control the 20-MHz and 40-MHz STAs by setting NAV to them in the MAC layer. This paper explains our coexistence proposal for the system where transmission in both 20-MHz and 40-MHz channel bandwidths is enabled. The performance is also examined to confirm the influence of applying our coexistence proposal. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(1): 1–12, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20335
TL;DR: In this paper, the authors proposed a standing wave radar with a minimum detection distance of about 2 m when the frequency bandwidth is 76 MHz and verified the measurement principle by numerical simulation.
Abstract: 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
TL;DR: In this article, a transmission line model considering the loss in the movable short is introduced and the efficiency dip phenomena are explained, and a method for avoiding the dip is presented, where two movable shorts on the left and right inserted into the waveguide are moved, an efficiency dip occurs at the resonant frequency of the cavity.
Abstract: When the efficiency of a monopole is measured by determining the radiation efficiency of a small antenna based on a waveguide and a movable short, there are dips at certain frequencies. In this paper, a transmission line model considering the loss in the movable short is introduced and the efficiency dip phenomena are explained. A method for avoiding the dip is presented. When two movable shorts on the left and right inserted into the waveguide are moved, an efficiency dip occurs at the resonant frequency of the cavity. Therefore, the movable range of the two movable shorts that will avoid the efficiency dip is investigated. When one of the movable shorts is fixed at an arbitrary location, there is a dip in the radiation efficiency at a specific frequency. Therefore, it is confirmed that the dip can be avoided by limiting the range of the fixed location of the movable short. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(1): 35–44, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20323
TL;DR: This paper proposes a DHT (distributed hash table)-based P2P search system using a new indexing method called pseudo-candidate key indexing, which attempts to deal with the problem of a large amount of communication in the search process by preparing an index for all search conditions which are useful to the user.
Abstract: 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
TL;DR: In this paper, a generalized mode vector that simultaneously uses the differential coefficient component of the mode vector has been proposed for estimating the direction of arrival of incident waves having angular spread, and a combined-type MUSIC algorithm was proposed to examine the performance of the two algorithms.
Abstract: A generalized mode vector that simultaneously uses the differential coefficient component of the mode vector has been proposed for estimating the direction of arrival of incident waves having angular spread. In this paper, the authors first examined this generalized mode vector and proposed a gradient-type MUSIC algorithm that uses the differential coefficient component of the mode vector independently for estimating the direction of arrival. Then they used a computer simulation in which the waves having angular spread were considered to be a group of scattered waves to compare this algorithm with regard to the performance for estimating the direction of arrival with an integral-type MUSIC algorithm that uses simple integration, which they proposed separately. To improve the estimation precision degradation that occurs when the signal correlation is low among scattered waves that exist within the angular spread when using the integral-type MUSIC algorithm, the authors proposed a combined-type MUSIC algorithm that incorporated the gradient-type MUSIC algorithm in the integral-type MUSIC algorithm and used this to examine the performance for estimating the direction of arrival and angular spread again. The results of the comparison of the gradient-type MUSIC algorithm and integral-type MUSIC algorithm confirmed that the two algorithms have conflicting properties related to the signal correlation among scattered waves that exist within the angular spread. Also, the investigation related to the combined-type MUSIC algorithm indicated that estimation precision degradation that occurs when the signal correlation is low among scattered waves when using the integral-type MUSIC algorithm was reduced as expected. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(6): 53– 64, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20208
TL;DR: This paper proposes and evaluates a method to enhance the accessibility to data items that are associated with locations and requested by Geocast from hosts based on flooding of replicas of data items and it achieves high accessibility to location-dependent data especially when the storage size is small.
Abstract: 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
TL;DR: T theoretical evaluations of the diversity effect that formed the core of the recommendation are given, and evaluation examples based on real data obtained from outdoor test networks are presented to demonstrate the validity of the Diversity effect in the proposed system.
Abstract: 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
TL;DR: In this article, a trapezoidal conductors for planar dipole antennas that satisfy the ultrawide bandwidths required for UWB and for asymmetric dipole antenna that can be used for both IEEE 802.11b/g, a wireless LAN in the 2.4-GHz band, and UWB was proposed.
Abstract: 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
TL;DR: An algorithm for generating evaluation networks with different ratios ofhidden terminals in order to evaluate the effect of hidden terminals on competitive MAC protocols is proposed and results are reported.
Abstract: Hidden terminals can significantly lower the throughput of such competitive MAC protocols as CSMA. Therefore, a large number of MAC protocols that implement different hidden terminal strategies have been developed. In this paper we propose an algorithm for generating evaluation networks with different ratios of hidden terminals in order to evaluate the effect of hidden terminals on competitive MAC protocols. In addition, we use the same algorithm to report results that elucidate the characteristics of throughput as the ratio of hidden terminals that exist in a network is varied for both CSMA, a representative competitive MAC protocol, and MACA, a MAC protocol that makes use of RTS/CTS control, a representative hidden terminal strategy. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(4): 46–55, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20343
TL;DR: In this article, the frequency dependence of the effective length depends on the antenna configuration and the balance among surrounding medium, the insulation coating of the wire, and the input impedance of the receiver.
Abstract: 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
TL;DR: In this article, the authors proposed a cyclic ESPRIT based on the noise subspace to remedy the performance degradation produced by the fact that the correlation matrix of the array input used in Cyclic ESP-RIT is not a Hermitian matrix.
Abstract: 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
TL;DR: The proposed OVSF code allocation in OFCDM (Orthogonal Frequency and Code Division Multiplexing) system achieves better BER performance than the conventional scheme by computer simulations.
Abstract: 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
TL;DR: 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 and the one-directional delay from the master to each client can be calculated accurately from prior knowledge of the constituent elements of the LAN.
Abstract: 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
TL;DR: The proposed ETD (Eigenbeam Transmit Diversity) system is proposed and 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.
Abstract: 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