Mihiro Sasaki | Nanzan University (original) (raw)

Papers by Mihiro Sasaki

In this paper, we present a new formulation of one-stop capacitated hub-and-spoke model as a natu... more In this paper, we present a new formulation of one-stop capacitated hub-and-spoke model as a natural extension of the uncapacitated one-stop model. The model involves arc capacity constraints as well as hub capacity constraints, which enables us to incorporate some practical factors into the model. We also present a branch-and-bound based exact solution method with Lagrangian relaxation bounding strategy, and report some results of numerical experiments using real aviation data. Computational results show the practical significance of the proposed capacitated model.

In this paper, we consider the design of large-scale hub-and-spoke transportation networks in a c... more In this paper, we consider the design of large-scale hub-and-spoke transportation networks in a competitive environment. We adopt the hub arc location model that locates arcs with discounted transport costs connecting pairs of hub facilities. Two firms compete for customers in a Stackelberg framework where the leader firm locates hub arcs to maximize its revenue, given that the follower firm will subsequently locate its own hub arcs to maximize its own revenue. Several mechanisms are presented to allocate traffic between the two firms based on the relative utility of travel via the competing hub networks. Results with up to three hub arcs for each competing firm show the role of a competitive environment in designing transportation systems. key words: Hub location, competition, transportation, Stackelberg 1

Journal of the City Planning Institute of Japan, 2014

Recent years, in Japan supply insufficiency of medical service becomes important issue caused by ... more Recent years, in Japan supply insufficiency of medical service becomes important issue caused by aging society. Public services such as ambulance service are required to serve as equitably and efficiently as possible. For measuring or comparing sufficiency of service, supply quantity per capita and/or per area is generally used. This kind of indices is suitable for regions which are large enough to be considered as uniform density. In this paper, we propose an index representing supply-and-demand gap, which is generalization of supply sufficiency above. Then, we discuss features of proposed index considering numerical examples and iterative procedure how to calculate it. Finally, we adapt it to numbers of beds of acute hospitals in Kanagawa Prefecture, and visualize it.

In this paper, we consider the design of airline network in Asia where optimal locations of the g... more In this paper, we consider the design of airline network in Asia where optimal locations of the gateways and local hubs are established. We report some results using the demand data reported by IATA in 2005. The results show interesting features of gateway locations in Asia.

In this paper, we consider a multi-hop wireless sensor network, where the network topology is a t... more In this paper, we consider a multi-hop wireless sensor network, where the network topology is a tree, time division multiple access (TDMA) is employed as medium access control, and all data generated at sensor nodes are delivered to a sink node located on the root of the tree through the network. It is reported that if a transmission schedule that avoids interference between sensor nodes completely can be computed, TDMA is preferable to others in performance. However, solving the scheduling problem for TDMA is difficult, especially, in large-scale multi-hop sensor networks. In this paper, based on graph theory, we propose new formulation for the TDMA scheduling problem.

Journal of the Operations Research Society of Japan, 2012

One of the important issues in wireless sensor networks is how to save power consumption and exte... more One of the important issues in wireless sensor networks is how to save power consumption and extend the network lifetime. Foi this purpose, various network topology construction algorithms haMe been studied. However, most ef them are based on a method repeating single round optimization. In other words, by considering the energy dissipation of sensor nodes only in the next round, a network topology in the next round is constructed in a round-by-round manner. The set of the topology constructlons based on such a round-by-rouiid view may be far frem the optimal solution to maximize the network lifetime. [Eb address this issue, we take the energy dissipation ef sensor nodes over multiple rounds into account, and we consider the problem as a multi-dimensional knapsack problem, which enables us to find optimal network topologies until at least one sensor nede exhausts its battery power. Wle also propose a solution method to maximize the network Iifetime. The computational experiments show that the proposed approach provides eMcient topology construction in the wireless sensor network in terms of network lifetime compared to the cluster-based approach.

Journal of the Operations Research Society of Japan, 2009

In this paper, we study mathematical formulations for clustering problems which arise in wireless... more In this paper, we study mathematical formulations for clustering problems which arise in wireless sensor networks as examined from the standpoint of focility location theoTy. Following facility location theory, LEACH-C, one of the principal studies on cluster-based network organizations, formulates the clustering problem as a p-median problem, In this paper, we examine some drawbacks to the formulation put forward in LEACH-C. We t･hen formulate the problem as an uncapacitated facility location problem to overcome thcse drawbacks. Computational experiments show that compared to LEACH-C, the proposed algorithm based on our formulation can extend the total lifetime of sensor networks.

Journal of the Operations Research Society of Japan, 2005

wr consider a hub network design model based on the Stackelberg hub location model, where two fir... more wr consider a hub network design model based on the Stackelberg hub location model, where two firms compete with each other to maximize their own profit, The firm as a leader first locates p hubs and decides which OD pairs should be in services on the cendition that the other firm as a fo11ower locates q hubs and decides its strategies in a similar way after that. Tb avoid the possibility of unprofitable services, we incorporate fiow threshold constraints into the model. We formulate the leader's problem as a bilevel progTamming problem with the fo11ower's problem as a lower level problem. We solve the problem with the complete enumeration method and a greedy heuristic. The main objective is to make it clear how the network structure can be affected by the flow threshold constraints and the competitor's strategies.

Journal of the Operations Research Society of Japan, 2001

Ab,strfict Ln this papf'r. "'e ('"Tislcier a rie"' conipetitive hi]b location tnodel ca[ied Stnck... more Ab,strfict Ln this papf'r. "'e ('"Tislcier a rie"' conipetitive hi]b location tnodel ca[ied Stnckell)e. rg hub locaLion problern where n, tjig firin conipet,es wit,h several tnediuni fin"s to inaxisriizc' it,s own profiL XVe assuine t,h;it t･he rnodiuin tirnis7 service seLs are niutunlly diejoi"t and there is no competii,ion ainollg t,hein. Thc big firm first, }oft,at/es a ne"r hub on a plarte as a lcadcr on the ('otLclition that, t,he ot,her firrns locate their ne"' hubs afLer t･hat. SN':e fcn'niulate the le:{,der's probloin as a bilevel progra,nirning probLem with followers7 problern as lo-'er level prc')1)lenis. and so[ve it. iisirig SQP inethorl. Clon]put,ationul results show the sigTTifi('ance of the proposed ('{}riipetit,ive hub lo('at,ion in-del, A, Suzuki and Z, Drezner: On the airline hub problem: The continuous model, ,JouTnal of the Qperations Rescarch Society of Japan, 40 (1997) 62-T4.

Journal of the Operations Research Society of Japan, 2003

In this paper, we present a new formulation of onestop capacitated hub-and-spoke model as a natur... more In this paper, we present a new formulation of onestop capacitated hub-and-spoke model as a natural extension of the uncapacitated onestop model. The model involves arc capacity constraints as well as hub capacity constraints, which enables us to incorporate some practical factors irtto the model. We also present a branch-and-bound based exact solution method with Lagrangian relaxation bounding strategy, and report seme results of numerical experiments using real aviation data. Computational results sh(Jw t･he practical significance of the proposed capacitated model.

One of the important issues in wireless sensor networks is how to save power consumption and exte... more One of the important issues in wireless sensor networks is how to save power consumption and extend the network lifetime. For this purpose, various network topology construction algorithms have been studied. However, most of them are based on a myopic method, where the topology construction is carried out round-by-round. To address this issue, we take the energy dissipation of sensor nodes over multiple rounds into account, and we consider the problem as a multi-dimensional knapsack problem, which enable us to find optimal network topologies until at least one sensor node exhausts its battery power. We also propose a solution method to maximize the network lifetime. The computational experiments show that the proposed approach provides ecient topology construction in the wireless sensor network in terms of network lifetime compared to the cluster-based approach.

In this paper, we study clustering algorithms for wireless sensor networks from a view of facilit... more In this paper, we study clustering algorithms for wireless sensor networks from a view of facility location theory. From this view, we can consider that LEACH-C, which is one of the principal studies on cluster-based network organization, formulates the clustering problem as a p-median problem. We point out drawbacks of the formulation in LEACH-C. To overcome the drawbacks, we formulate the problem as an uncapacitated facility location problem. Computational experiments show that the proposed algorithm can extend the lifetime of sensor networks, compared to LEACH-C.

Proceedings of the 6th International Wireless Communications and Mobile Computing Conference on ZZZ - IWCMC '10, 2010

ABSTRACT In this paper, we consider a multi-hop sensor network, where the network topology is a t... more ABSTRACT In this paper, we consider a multi-hop sensor network, where the network topology is a tree, TDMA is employed as medium access control, and all data generated at sensor nodes are delivered to a sink node located on the root of the tree through the network. It is reported that if a transmission schedule that avoids interference between sensor nodes completely can be computed, TDMA is preferable to CSMA/CA in performance. However, solving the scheduling problem for TDMA is difficult, especially, in large-scale multi-hop sensor networks. In this paper, to formulate the scheduling problem for TDMA, we propose min-max model and min-sum model. While the min-max model yields the shortest schedule under the constraints, the min-sum model does not guarantee providing the shortest schedule. Numerical examples show that the min-sum model can provide good schedules in a reasonable CPU time, even when the min-max model fails to compute the shortest schedule in a reasonable CPU time.

2007 Wireless Telecommunications Symposium, 2007

We present a new heuristic method for a clustering problem of sensor networks. The heuristic meth... more We present a new heuristic method for a clustering problem of sensor networks. The heuristic method is using the uncapacitated facility location problem formulation for the clustering problem of sensor networks. It is an iterative method based on the Voronoi diagram. We also propose a parallel version of the heuristics to reduce the time to obtain a solution. The proposed algorithms are investigated for the quality of their approximate solutions and computational time to obtain them. By comparing the approximate solutions to the exact solutions for examples of one hundred sensors, we found that the quality of the approximate solutions is almost the same as that of the exact ones. The computational time to obtain the approximate solutions is a thousandth of that of obtaining the exact solution. For examples of ten thousand sensors, the computational time to obtain a solution is about 9.

International Transactions in Operational Research, 2008

We consider hierarchical facility location problems on a network called Multiple Location of Tran... more We consider hierarchical facility location problems on a network called Multiple Location of Transfer Points (MLTP) and Facility and Transfer Points Location Problem (FTPLP), where q facilities and p transfer points are located and each customer goes to one of the facilities directly or via one of the transfer points. In FTPLP, we need to find an optimal location of both the facilities and the transfer points while the location of facilities is given in MLTP. Although good heuristics have been proposed for the minisum MLTP and FTPLP, no exact optimal solution has been tested due to the size of the problems. We show that the minisum MLTP can be formulated as a p-median problem, which leads to obtaining an optimal solution. We also present a new formulation of FTPLP and an enumeration-based approach to solve the problems with a single facility.

Computers & Operations Research, 2014

In this paper, we consider the design of large-scale multiple allocation hub-and-spoke transporta... more In this paper, we consider the design of large-scale multiple allocation hub-and-spoke transportation networks in a competitive environment. We adopt a generic hub arc location model that locates arcs with discounted transport costs connecting pairs of hub facilities. Two firms compete for customers in a Stackelberg framework where the leader firm locates hub arcs to maximize its revenue, given that the follower firm will subsequently locate its own hub arcs to maximize its own revenue. We present an optimal solution algorithm that allocates traffic between the two firms based on the relative utility of travel via the competing hub networks. Results for each competing firm with up to three hub arcs show the important role of competition in designing hub-based transportation systems.

Computers & Operations Research, 1999

... Ltd. All rights reserved. Cited By in Scopus (12). Permissions & Reprints. ... algorithm.... more ... Ltd. All rights reserved. Cited By in Scopus (12). Permissions & Reprints. ... algorithm. We report computational results for problems with airline passenger interactions between 25 US cities in 1970 evaluated by the Civil Aeronautics Board. ...

In this paper, we consider the design of large-scale hub-and-spoke transportation networks in a c... more In this paper, we consider the design of large-scale hub-and-spoke transportation networks in a competitive environment. We adopt the hub arc location model that locates arcs with discounted transport costs connecting pairs of hub facilities. Two firms compete for customers in a Stackelberg framework where the leader firm locates hub arcs to maximize its revenue, given that the follower firm will subsequently locate its own hub arcs to maximize its own revenue. Several mechanisms are presented to allocate traffic between the two firms based on the relative utility of travel via the competing hub networks. Results with up to three hub arcs for each competing firm show the role of a competitive environment in designing transportation systems.

In this paper, we present a new formulation of one-stop capacitated hub-and-spoke model as a natu... more In this paper, we present a new formulation of one-stop capacitated hub-and-spoke model as a natural extension of the uncapacitated one-stop model. The model involves arc capacity constraints as well as hub capacity constraints, which enables us to incorporate some practical factors into the model. We also present a branch-and-bound based exact solution method with Lagrangian relaxation bounding strategy, and report some results of numerical experiments using real aviation data. Computational results show the practical significance of the proposed capacitated model.

In this paper, we consider the design of large-scale hub-and-spoke transportation networks in a c... more In this paper, we consider the design of large-scale hub-and-spoke transportation networks in a competitive environment. We adopt the hub arc location model that locates arcs with discounted transport costs connecting pairs of hub facilities. Two firms compete for customers in a Stackelberg framework where the leader firm locates hub arcs to maximize its revenue, given that the follower firm will subsequently locate its own hub arcs to maximize its own revenue. Several mechanisms are presented to allocate traffic between the two firms based on the relative utility of travel via the competing hub networks. Results with up to three hub arcs for each competing firm show the role of a competitive environment in designing transportation systems. key words: Hub location, competition, transportation, Stackelberg 1

Journal of the City Planning Institute of Japan, 2014

Recent years, in Japan supply insufficiency of medical service becomes important issue caused by ... more Recent years, in Japan supply insufficiency of medical service becomes important issue caused by aging society. Public services such as ambulance service are required to serve as equitably and efficiently as possible. For measuring or comparing sufficiency of service, supply quantity per capita and/or per area is generally used. This kind of indices is suitable for regions which are large enough to be considered as uniform density. In this paper, we propose an index representing supply-and-demand gap, which is generalization of supply sufficiency above. Then, we discuss features of proposed index considering numerical examples and iterative procedure how to calculate it. Finally, we adapt it to numbers of beds of acute hospitals in Kanagawa Prefecture, and visualize it.

In this paper, we consider the design of airline network in Asia where optimal locations of the g... more In this paper, we consider the design of airline network in Asia where optimal locations of the gateways and local hubs are established. We report some results using the demand data reported by IATA in 2005. The results show interesting features of gateway locations in Asia.

In this paper, we consider a multi-hop wireless sensor network, where the network topology is a t... more In this paper, we consider a multi-hop wireless sensor network, where the network topology is a tree, time division multiple access (TDMA) is employed as medium access control, and all data generated at sensor nodes are delivered to a sink node located on the root of the tree through the network. It is reported that if a transmission schedule that avoids interference between sensor nodes completely can be computed, TDMA is preferable to others in performance. However, solving the scheduling problem for TDMA is difficult, especially, in large-scale multi-hop sensor networks. In this paper, based on graph theory, we propose new formulation for the TDMA scheduling problem.

Journal of the Operations Research Society of Japan, 2012

One of the important issues in wireless sensor networks is how to save power consumption and exte... more One of the important issues in wireless sensor networks is how to save power consumption and extend the network lifetime. Foi this purpose, various network topology construction algorithms haMe been studied. However, most ef them are based on a method repeating single round optimization. In other words, by considering the energy dissipation of sensor nodes only in the next round, a network topology in the next round is constructed in a round-by-round manner. The set of the topology constructlons based on such a round-by-rouiid view may be far frem the optimal solution to maximize the network lifetime. [Eb address this issue, we take the energy dissipation ef sensor nodes over multiple rounds into account, and we consider the problem as a multi-dimensional knapsack problem, which enables us to find optimal network topologies until at least one sensor nede exhausts its battery power. Wle also propose a solution method to maximize the network Iifetime. The computational experiments show that the proposed approach provides eMcient topology construction in the wireless sensor network in terms of network lifetime compared to the cluster-based approach.

Journal of the Operations Research Society of Japan, 2009

In this paper, we study mathematical formulations for clustering problems which arise in wireless... more In this paper, we study mathematical formulations for clustering problems which arise in wireless sensor networks as examined from the standpoint of focility location theoTy. Following facility location theory, LEACH-C, one of the principal studies on cluster-based network organizations, formulates the clustering problem as a p-median problem, In this paper, we examine some drawbacks to the formulation put forward in LEACH-C. We t･hen formulate the problem as an uncapacitated facility location problem to overcome thcse drawbacks. Computational experiments show that compared to LEACH-C, the proposed algorithm based on our formulation can extend the total lifetime of sensor networks.

Journal of the Operations Research Society of Japan, 2005

wr consider a hub network design model based on the Stackelberg hub location model, where two fir... more wr consider a hub network design model based on the Stackelberg hub location model, where two firms compete with each other to maximize their own profit, The firm as a leader first locates p hubs and decides which OD pairs should be in services on the cendition that the other firm as a fo11ower locates q hubs and decides its strategies in a similar way after that. Tb avoid the possibility of unprofitable services, we incorporate fiow threshold constraints into the model. We formulate the leader's problem as a bilevel progTamming problem with the fo11ower's problem as a lower level problem. We solve the problem with the complete enumeration method and a greedy heuristic. The main objective is to make it clear how the network structure can be affected by the flow threshold constraints and the competitor's strategies.

Journal of the Operations Research Society of Japan, 2001

Ab,strfict Ln this papf'r. "'e ('"Tislcier a rie"' conipetitive hi]b location tnodel ca[ied Stnck... more Ab,strfict Ln this papf'r. "'e ('"Tislcier a rie"' conipetitive hi]b location tnodel ca[ied Stnckell)e. rg hub locaLion problern where n, tjig firin conipet,es wit,h several tnediuni fin"s to inaxisriizc' it,s own profiL XVe assuine t,h;it t･he rnodiuin tirnis7 service seLs are niutunlly diejoi"t and there is no competii,ion ainollg t,hein. Thc big firm first, }oft,at/es a ne"r hub on a plarte as a lcadcr on the ('otLclition that, t,he ot,her firrns locate their ne"' hubs afLer t･hat. SN':e fcn'niulate the le:{,der's probloin as a bilevel progra,nirning probLem with followers7 problern as lo-'er level prc')1)lenis. and so[ve it. iisirig SQP inethorl. Clon]put,ationul results show the sigTTifi('ance of the proposed ('{}riipetit,ive hub lo('at,ion in-del, A, Suzuki and Z, Drezner: On the airline hub problem: The continuous model, ,JouTnal of the Qperations Rescarch Society of Japan, 40 (1997) 62-T4.

Journal of the Operations Research Society of Japan, 2003

In this paper, we present a new formulation of onestop capacitated hub-and-spoke model as a natur... more In this paper, we present a new formulation of onestop capacitated hub-and-spoke model as a natural extension of the uncapacitated onestop model. The model involves arc capacity constraints as well as hub capacity constraints, which enables us to incorporate some practical factors irtto the model. We also present a branch-and-bound based exact solution method with Lagrangian relaxation bounding strategy, and report seme results of numerical experiments using real aviation data. Computational results sh(Jw t･he practical significance of the proposed capacitated model.

One of the important issues in wireless sensor networks is how to save power consumption and exte... more One of the important issues in wireless sensor networks is how to save power consumption and extend the network lifetime. For this purpose, various network topology construction algorithms have been studied. However, most of them are based on a myopic method, where the topology construction is carried out round-by-round. To address this issue, we take the energy dissipation of sensor nodes over multiple rounds into account, and we consider the problem as a multi-dimensional knapsack problem, which enable us to find optimal network topologies until at least one sensor node exhausts its battery power. We also propose a solution method to maximize the network lifetime. The computational experiments show that the proposed approach provides ecient topology construction in the wireless sensor network in terms of network lifetime compared to the cluster-based approach.

In this paper, we study clustering algorithms for wireless sensor networks from a view of facilit... more In this paper, we study clustering algorithms for wireless sensor networks from a view of facility location theory. From this view, we can consider that LEACH-C, which is one of the principal studies on cluster-based network organization, formulates the clustering problem as a p-median problem. We point out drawbacks of the formulation in LEACH-C. To overcome the drawbacks, we formulate the problem as an uncapacitated facility location problem. Computational experiments show that the proposed algorithm can extend the lifetime of sensor networks, compared to LEACH-C.

Proceedings of the 6th International Wireless Communications and Mobile Computing Conference on ZZZ - IWCMC '10, 2010

ABSTRACT In this paper, we consider a multi-hop sensor network, where the network topology is a t... more ABSTRACT In this paper, we consider a multi-hop sensor network, where the network topology is a tree, TDMA is employed as medium access control, and all data generated at sensor nodes are delivered to a sink node located on the root of the tree through the network. It is reported that if a transmission schedule that avoids interference between sensor nodes completely can be computed, TDMA is preferable to CSMA/CA in performance. However, solving the scheduling problem for TDMA is difficult, especially, in large-scale multi-hop sensor networks. In this paper, to formulate the scheduling problem for TDMA, we propose min-max model and min-sum model. While the min-max model yields the shortest schedule under the constraints, the min-sum model does not guarantee providing the shortest schedule. Numerical examples show that the min-sum model can provide good schedules in a reasonable CPU time, even when the min-max model fails to compute the shortest schedule in a reasonable CPU time.

2007 Wireless Telecommunications Symposium, 2007

We present a new heuristic method for a clustering problem of sensor networks. The heuristic meth... more We present a new heuristic method for a clustering problem of sensor networks. The heuristic method is using the uncapacitated facility location problem formulation for the clustering problem of sensor networks. It is an iterative method based on the Voronoi diagram. We also propose a parallel version of the heuristics to reduce the time to obtain a solution. The proposed algorithms are investigated for the quality of their approximate solutions and computational time to obtain them. By comparing the approximate solutions to the exact solutions for examples of one hundred sensors, we found that the quality of the approximate solutions is almost the same as that of the exact ones. The computational time to obtain the approximate solutions is a thousandth of that of obtaining the exact solution. For examples of ten thousand sensors, the computational time to obtain a solution is about 9.

International Transactions in Operational Research, 2008

We consider hierarchical facility location problems on a network called Multiple Location of Tran... more We consider hierarchical facility location problems on a network called Multiple Location of Transfer Points (MLTP) and Facility and Transfer Points Location Problem (FTPLP), where q facilities and p transfer points are located and each customer goes to one of the facilities directly or via one of the transfer points. In FTPLP, we need to find an optimal location of both the facilities and the transfer points while the location of facilities is given in MLTP. Although good heuristics have been proposed for the minisum MLTP and FTPLP, no exact optimal solution has been tested due to the size of the problems. We show that the minisum MLTP can be formulated as a p-median problem, which leads to obtaining an optimal solution. We also present a new formulation of FTPLP and an enumeration-based approach to solve the problems with a single facility.

Computers & Operations Research, 2014

In this paper, we consider the design of large-scale multiple allocation hub-and-spoke transporta... more In this paper, we consider the design of large-scale multiple allocation hub-and-spoke transportation networks in a competitive environment. We adopt a generic hub arc location model that locates arcs with discounted transport costs connecting pairs of hub facilities. Two firms compete for customers in a Stackelberg framework where the leader firm locates hub arcs to maximize its revenue, given that the follower firm will subsequently locate its own hub arcs to maximize its own revenue. We present an optimal solution algorithm that allocates traffic between the two firms based on the relative utility of travel via the competing hub networks. Results for each competing firm with up to three hub arcs show the important role of competition in designing hub-based transportation systems.

Computers & Operations Research, 1999

... Ltd. All rights reserved. Cited By in Scopus (12). Permissions & Reprints. ... algorithm.... more ... Ltd. All rights reserved. Cited By in Scopus (12). Permissions & Reprints. ... algorithm. We report computational results for problems with airline passenger interactions between 25 US cities in 1970 evaluated by the Civil Aeronautics Board. ...

In this paper, we consider the design of large-scale hub-and-spoke transportation networks in a c... more In this paper, we consider the design of large-scale hub-and-spoke transportation networks in a competitive environment. We adopt the hub arc location model that locates arcs with discounted transport costs connecting pairs of hub facilities. Two firms compete for customers in a Stackelberg framework where the leader firm locates hub arcs to maximize its revenue, given that the follower firm will subsequently locate its own hub arcs to maximize its own revenue. Several mechanisms are presented to allocate traffic between the two firms based on the relative utility of travel via the competing hub networks. Results with up to three hub arcs for each competing firm show the role of a competitive environment in designing transportation systems.