arXiv subjects

Hiroshi Saito

Publications and source records attributed to Hiroshi Saito.

11 recordsLinked to original sources

arXiv2021

Theoretical Analysis for Determining Geographical Route of Cable Network with Various Disaster-Endurance Levels

This paper theoretically analyzes cable network disconnection due to randomly occurring natural disasters, where the disaster-endurance (DE) levels of the network are determined by a network entity such as the type of shielding method used for a duct containing cables. The network operator can determine which parts have a high DE level. When a part of a network can be protected, the placement of that part can be specified to decrease the probability of disconnecting two given nodes. The maximum lower bound of the probability of connecting two given nodes is explicitly derived. Conditions decreasing (not decreasing) the probability of connecting two given nodes with a partially protected network are provided.

cs.NI↗

arXiv2019

Spatio-Temporal Correlation of Interference in MANET Under Spatially Correlated Shadowing Environment

Correlation of interference affects spatio-temporal aspects of various wireless mobile systems, such as retransmission, multiple antennas and cooperative relaying. In this paper, we study the spatial and temporal correlation of interference in mobile ad-hoc networks under a correlated shadowing environment. By modeling the node locations as a Poisson point process with an i.i.d. mobility model and considering Gudmundson (1991)' s spatially correlated shadowing model, we theoretically analyze the relationship between the correlation distance of log-normal shadowing and the spatial and temporal correlation coefficients of interference. Since the exact expressions of the correlation coefficients are intractable, we obtain their simple asymptotic expressions as the variance of log-normal shadowing increases. We found in our numerical examples that the asymptotic expansions can be used as tight approximate formulas and useful for modeling general wireless systems under spatially correlated shadowing.

cs.NI↗

arXiv2019

Theoretical Performance Analysis of Vehicular Broadcast Communications at Intersection and their Optimization

In this paper, we propose an optimization method for the broadcast rate in vehicle-to-vehicle (V2V) broadcast communications at an intersection on the basis of theoretical analysis. We consider a model in which locations of vehicles are modeled separately as queuing and running segments and derive key performance metrics of V2V broadcast communications via a stochastic geometry approach. Since these theoretical expressions are mathematically intractable, we developed closed-form approximate formulae for them. Using them, we optimize the broadcast rate such that the mean number of successful receivers per unit time is maximized. Because of the closed form approximation, the optimal rate can be used as a guideline for a real-time control-method, which is not achieved through time-consuming simulations. We evaluated our method through numerical examples and demonstrated the effectiveness of our method.

cs.PF↗

arXiv2018

Estimating Shape of Target Object Moving on Unknown Trajectory by Using Location-Unknown Distance Sensors: Theoretical Framework

By using directional distance sensors that have unknown locations, this paper proposes a method of estimating the shape of a location-unknown target object $T$ moving with unknown speed on an unknown straight line trajectory. Regardless of many unknown factors, the proposed method can estimate the shape by using each sensor's continuous report of the measured distance to $T$ without using side information or additional mechanisms such as locations of anchor sensors and angle-of-arrival measurements. By using the sensor reports, the proposed method estimates (i) the moving speed of $T$, (ii) the length and direction of an edge of $T$, and (iii) the order of consecutive edges. As a result, we can obtain the shape of $T$.

eess.SP↗

arXiv2018

Theoretical Framework for Estimating Target-Object Shape by Using Location-Unknown Mobile Distance Sensors

This paper proposes a theoretical framework for estimating a target-object shape, the location of which is not given, by using mobile distance sensors the locations of which are also unknown. Typically, mobile sensors are mounted on vehicles. Each sensor continuously measures the distance from it to the target object. The proposed framework does not require any positioning function, anchor-location information, or additional mechanisms to obtain side information such as angle of arrival of signal. Under the assumption of a convex polygon target object, each edge length and vertex angle and their combinations are estimated and finally the shape of the target object is estimated. To the best of our knowledge, this is the first result in which a target-object shape was estimated by using the data of distance sensors without using their locations.

eess.SP↗

arXiv2017

Estimating Target-Object Shape Using Location-Unknown Mobile Fixed-Direction Distance Sensors

This paper proposes a method of estimating a target-object shape, the location of which is unknown, through the use of location-unknown mobile distance sensors. The direction of the sensor is fixed from the moving direction. Typically, mobile sensors are mounted on vehicles. Each sensor continuously measures the distance from it to the target object. The estimation method does not require any positioning function, anchor-location information, or additional mechanisms to obtain side information such as angle of arrival of signal. Under the assumption of a polygon target object, each edge length and vertex angle and their combinations are estimated to completely estimate the shape of the target object.

eess.SP↗

arXiv2017

Geometric Analysis of Observability of Target Object Shape Using Location-Unknown Distance Sensors

We geometrically analyze the problem of estimating parameters related to the shape and size of a two-dimensional target object on the plane by using randomly distributed distance sensors whose locations are unknown. Based on the analysis using geometric probability, we discuss the observability of these parameters: which parameters we can estimate and what conditions are required to estimate them. For a convex target object, its size and perimeter length are observable, and other parameters are not observable. For a general polygon target object, convexity in addition to its size and perimeter length is observable. Parameters related to a concave vertex can be observable when some conditions are satisfied. We also propose a method for estimating the convexity of a target object and the perimeter length of the target object.

cs.IT↗

arXiv2017

Nitrogen-vacancy centers created by N$^+$ ion implantation through screening SiO$_2$ layers on diamond

We report on an ion implantation technique utilizing a screening mask made of SiO$_2$ to control both the depth profile and the dose. By appropriately selecting the thickness of the screening layer, this method fully suppresses the ion channeling, brings the location of the highest NV density to the surface, and effectively reduces the dose by more than three orders of magnitude. With a standard ion implantation system operating at the energy of 10 keV and the dose of 10$^{11}$ cm$^2$ and without an additional etching process, we create single NV centers close to the surface with coherence times of a few tens of $μ$s.

cond-mat.mtrl-sci↗

arXiv2014

Theoretical Evaluation of Offloading through Wireless LANs

Offloading of cellular traffic through a wireless local area network (WLAN) is theoretically evaluated. First, empirical data sets of the locations of WLAN internet access points are analyzed and an inhomogeneous Poisson process consisting of high, normal, and low density regions is proposed as a spatial point process model for these configurations. Second, performance metrics, such as mean available bandwidth for a user and the number of vertical handovers, are evaluated for the proposed model through geometric analysis. Explicit formulas are derived for the metrics, although they depend on many parameters such as the number of WLAN access points, the shape of each WLAN coverage region, the location of each WLAN access point, the available bandwidth (bps) of the WLAN, and the shape and available bandwidth (bps) of each subregion identified by the channel quality indicator in a cell of the cellular network. Explicit formulas strongly suggest that the bandwidth a user experiences does not depend on the user mobility. This is because the bandwidth available by a user who does not move and that available by a user who moves are the same or approximately the same as a probabilistic distribution. Numerical examples show that parameters, such as the size of regions where placement of WLAN access points is not allowed and the mean density of WLANs in high density regions, have a large impact on performance metrics. In particular, a homogeneous Poisson process model as the WLAN access point location model largely overestimates the mean available bandwidth for a user and the number of vertical handovers. The overestimated mean available bandwidth is, for example, about 50% in a certain condition.

cs.PF↗

arXiv2014

Spatial Design of Physical Network Robust against Earthquakes

This paper analyzes the survivability of a physical network against earthquakes and proposes spatial network design rules to make a network robust against earthquakes. The disaster area model used is fairly generic and bounded. The proposed design rules for physical networks include: (i) a shorter zigzag route can reduce the probability that a network intersects a disaster area, (ii) an additive performance metric, such as repair cost, is independent of the network shape if the route length is fixed, and (iii) additional routes within a ring network does not decrease the probability that all the routes between a given pair of nodes intersect the disaster area, but a wider detour route decreases it. Formulas for evaluating the probability of disconnecting two given nodes are also derived. An optimal server placement is shown as an application of the theoretical results. These analysis results are validated through empirical earthquake data.

cs.NI↗

arXiv2013

Analysis of Geometric Disaster Evaluation Model for Physical Networks

A geometric model of a physical network affected by a disaster is proposed and analyzed using integral geometry (geometric probability). This analysis provides a theoretical method of evaluating performance metrics, such as the probability of maintaining connectivity, and a network design rule that can make the network robust against disasters. The proposed model is of when the disaster area is much larger than the part of the network in which we are interested. Performance metrics, such as the probability of maintaining connectivity, are explicitly given by linear functions of the perimeter length of convex hulls determined by physical routes. The derived network design rule includes the following. (1) Reducing the convex hull of the physical route reduces the expected number of nodes that cannot connect to the destination. (2) The probability of maintaining the connectivity of two nodes on a loop cannot be changed by changing the physical route of that loop. (3) The effect of introducing a loop is identical to that of a single physical route implemented by the straight-line route.

cs.NI↗