Shigeo Shioda

Medium-term centralized virtual-path bandwidth control based on traffic measurements

The paper presents a centralized virtual path bandwidth (VPB) control scheme for ATM networks which satisfies mainly three specifications: a) optimality during a medium-term control interval, b) fast time response so as to absorb the medium-term traffic fluctuations, and c) easy implementation. The paper mainly points at the impact of direct, on-line traffic measurements on bandwidth control. The control objective is to rearrange the installed bandwidth of the virtual paths according to the offered traffic so as to minimize the maximum call blocking probability of the whole network. Network simulation shows that a sophisticated VPB controller which relies on simple measurements of the offered traffic can substantially improve the performance of an ATM network. The necessary bandwidth rearrangement time is also examined by simulation. >

Fundamental characteristics of connectivity in vehicular ad hoc networks

We study the connectivity in vehicular ad-hoc networks, where the motion of vehicles is constrained on a lattice-shaped road network. First, we theoretically investigate the connectivity under the Poisson-positioning assumption, where vehicles are positioned according to a Poisson process on each road at any arbitrary instants. We find that the Poisson-positioning assumption allows the existence of the finite critical-vehicle density; that is, if (and only if) the density of vehicles is greater than the finite critical density, then there exists a large (theoretically infinite) cluster of vehicles and an arbitrary pair of vehicles in the set is connected in single or multiple hops. We obtain an analytical expression for the critical density as a function of the transmission range of each vehicle and the distance between intersections. Next, we consider the connectivity under more realistic movement patterns of vehicles where the Poisson-positioning assumption does not hold. We numerically find that, even in non-Poisson-positioning cases, there exists the critical vehicle density. The critical density in non-Poisson-positioning cases is, however, larger than the one under the Poisson-positioning assumption. We also gain some insight on the efficiency of roadside-relay-station deployment to provide better connectivity between vehicles.

Shape Estimation Using Networked Binary Sensors

An estimation method for the shape and size of a target object by using networked binary sensors whose locations are unknown is proposed. Each of those sensors, which individually are incapable of monitoring the target objects shape and size, sends only binary data describing whether or not it detects at every moment the target object. By using these data and the explicit formulas derived in this paper, we can estimate the size and the perimeter length of the target object even without sensor location information. An additional parameter, which is a function of the shape of the target object, can also be estimated when the target object is non-convex.

Estimating Parameters of Multiple Heterogeneous Target Objects Using Composite Sensor Nodes

We propose a method for estimating parameters of multiple target objects by using networked binary sensors whose locations are unknown. These target objects may have different parameters, such as size and perimeter length. Each sensors, which is incapable of monitoring the target objects parameters, sends only binary data describing whether or not it detects target objects coming into, moving around, or leaving the sensing area at every moment. We previously developed a parameter estimation method for a single target object. However, a straight-forward extension of this method is not applicable for estimating multiple heterogeneous target objects. This is because a networked binary sensor at an unknown location cannot provide information that distinguishes individual target objects, but it can provide information on the total perimeter length and size of multiple target objects. Therefore, we propose composite sensor nodes with multiple sensors in a predetermined layout for obtaining additional information for estimating the parameter of each target object. As an example of a composite sensor node, we consider a two-sensor composite sensor node, which consists of two sensors, one at each of the two end points of a line segment of known length. For the two-sensor composite sensor node, measures are derived such as the two sensors detecting target objects. These derived measures are the basis for identifying the shape of each target object among a given set of categories (for example, disks and rectangles) and estimating parameters such as the radius and lengths of two sides of each target object. Numerical examples demonstrate that networked composite sensor nodes consisting of two binary sensors enable us to estimate the parameters of target objects.

Stochastic Geometric Filter and Its Application to Shape Estimation for Target Objects

We investigated how to estimate the shape of a target object. For this problem, we propose pair-line composite sensor nodes consisting of multiple sensors on a pair of line segments, where each sensor generates binary information whether it detects the target object or not. We show that the proposed pair-line composite sensor nodes, which are randomly placed, can detect a certain range of angles; therefore, we also call them stochastic geometric filters. By random distribution of pair-line composite sensor nodes without GPS functions or careful placement at known locations, the information sent from the nodes enables us to estimate the boundary angles of the target object as well as its size and perimeter length. A composite sensor node can be conceptualized as between a sensor node equipped with GPS functions, or carefully placed sensors at known locations, and randomly deployed simple sensors without GPS functions.

Optimal virtual path bandwidth management assuring network reliability

The impact of virtual path bandwidth (VPB) management on the network performance in the expected environment of broadband integrated service digital network (B-ISDN) has been recognized, and several VPB control schemes have been proposed. The authors present the optimal VPB management which minimizes the worst call blocking probability of all VPs in the network. They solve a large network optimization problem by a rigorous analytical procedure. The optimization model comprises bandwidth distribution schemes assuring network reliability. The demand for reliability requires considerably larger bandwidth to be installed in the backbone network, and therefore optimal VPB management is essential. As an application example, a model asynchronous transfer mode (ATM) network is examined.<<ETX>>

Path coverage properties of randomly deployed sensors with finite data-transmission ranges

We analyze the path coverage properties of a sensor network, where numerous sensors are randomly deployed. We characterize the path coverage in terms of three metrics: fraction of coverage, probability of complete coverage, and probability of partial coverage. We derive the expressions for the three coverage metrics as functions of the sensor density, the sensing range of a sensor, and the data-transmission range of a sensor. Based on the derived expressions, we study the impact of the data-transmission range on the path coverage and show, for example, that a sensor should have a long data-transmission range in order to achieve high detectability of intruding objects (partial coverage probability of the trajectories of objects) with a modest sensor density.

Departure Process of the MAP/SM/1 Queue

We study the departure process of a single server queue with Markovian arrival input and Markov renewal service time. We derive the joint transform of departure time and the number of departures and, based on this transform, we establish several expressions for burstiness (variance) and correlation (covariance sequence) of the departure process. These expressions reveal that burstiness and correlation of the arrival process have very little impact on the departure process when a queueing system is heavily loaded. In contrast, both burstiness and correlation of the service-time process greatly affect those of the departure process regardless of the load of the system. Finally, we show that, even when an arrival process is short-range dependent, the departure process could has long-range dependence if a service-time process is long-range dependent.

Magnetic field effects on the specific heat of nearly ferromagnetic metals

The magnetic field dependence of the specific heat due to spin fluctuations in nearly ferromagnetic metals is quantitatively discussed over the wide temperature and field ranges based on the self-consistent renormalization theory of spin fluctuations. It is shown that for TiBe 2 , good agreement is obtained between the theory and experiment both for the susceptibility and the specific heat.

A new approach to the bottleneck bandwidth measurement for an end-to-end network path

We propose a new technique for measuring the bottleneck bandwidth of a network path between end hosts. Our proposal is based on the packet-pair technique and uses a simple statistical procedure for filtering out the cross traffic effect. We explain the basic mechanism of our proposal and its implementation in two different types of tools, single end-point and double end-point tools. The former runs in one end-point of the path, assuming that the other end-point or intermediate routers should reply to each received packet using ICMP (Internet control message protocol) packets. The latter works under the cooperation of both source and destination hosts. We have extensively conducted several experiments on nationwide and international networks to show that our proposal outperforms existing tools, such as Pathchar and Nettimer, in terms of accuracy and robustness of measurement.