Hiroaki Morino

Performance study of channel allocation schemes for beyond 4G cognitive femtocell-cellular mobile networks

The demand of beyond 4th Generation (4G) mobile communications includes not only high transmission rate but also the capability to provide QoS guaranteed services to high user density areas under the constraint of limited radio spectrum. Cognitive radio is considered as a core technology for future wireless communications in which the wireless spectrum can be dynamically shared between primary mobile network operators and secondary networks. Femtocell is a new mobile technology proposed for providing wireless voice and broadband services to customers in small areas such as the home, office or designated locations. In the paper, we present a cognitive femtocell-cellular network model which we consider as a mobile network model used for beyond 4G mobile communications. We will discuss selected channel allocation schemes and compare their performance obtained by computer simulation.

A Novel Managed Wireless Mesh Architecture for Community Service Platform

This paper identifies communication system functions and technologies that a local region, individuals living in that region, and various communities to which each individual belongs require and propose a community communication service platform for providing those functions and technologies. To provide a variety of services suited to the characteristics of a region or community, the local region itself or individuals, communities, or organizations that are not the conventional telecommunications carriers should be able to deploy, operate, and manage the communications network within that region and should be able to easily construct and provide various services on it. The proposed system, which is based on open specifications, establishes logical paths with a many-to-many mesh topology on a physical wireless mesh network to implement multiple services each of which uses the paths based on its own policy.

Fast Recovery from Link Failures and Blackout of a Managed Wireless Mesh for NerveNet

A managed wireless mesh for infrastructure-level, stable regional mesh network has been studied. NerveNet, which we have been proposing, is a concept of future regional platform network that covers local regions and provides various context-aware services with the shared use of sensors and actuators. The managed wireless mesh developed for materializing NerveNet features auto-configuration of multiple, different routes between any two base stations for high capacity and reliability. The managed wireless mesh of ten base stations was implemented on PCs and commercial L2 switches. Performance evaluation showed that route switching after one or two link failures had been detected was completed in no later than 70 milliseconds while it takes a few to tens of seconds with existing adhoc routing-based mesh networks. It was also shown that the restart of the network took only about three minutes, enabling urgent recovery of communication in emergency situations.

Unidirectional Ad Hoc Routing Protocol with Area-controlled Flooding Using Overheard Neighbor Node Information

In ad hoc networks, wireless links can be unidirectional due to the difference of transmission range of each node. Particularly for temporally formed ad hoc networks, routing protocols should support route construction using unidirectional links to provide high connectivity in various network configurations. Although existing DSR have a mode of two way flooding to support route construction using unidirectional links, it involves substantial control traffic and should be avoided in the high node density environment. This paper proposes a novel routing protocol supporting unidirectional links called FOCUS2 (flooding based ad hoc routing protocol controlled with overheard control information to support unidirectional links). FOCUS2 employs an area-controlled two way flooding that adaptively limiting flooding area. Performance evaluation by simulation shows that FOCUS2 reduces the number of control packets by approximately 50 % as compared with existing two way flooding DSR and that the degradation of route construction performance is small

A key management scheme for mobile ad hoc networks based on threshold cryptography for providing fast authentication and low signaling load

Providing secure communications is a crucial task for the success of future ubiquitous mobile communication systems. Using public key infrastructure (PKI) is considered as a good solution to fulfill the task. However, as mobile ad hoc networks (MANET) inherit unique characteristics such as dynamic topology, non-infrastructure architecture, centralized PKI architectures are not suitable for dynamic MANET. The use of distributed PKI models is more appropriate but requires additional modifications to adapt with network changes. In this paper, we introduce a novel key management scheme for MANET, which exploits advantages of threshold cryptography. The major innovative aspect of this scheme is the use of temporal substitute certificate authorities (SCA), which form a PKI model of multi SCA groups. Performance results obtained by computer simulation show that the proposed key management scheme can reduce the latency of authentication, certificate update delay and the signaling load.

Sensor-Terminal-Network Cooperative Architecture for Context-Aware Services

A new-generation access network should be able to transport various kinds of dynamically changing sensor information about specific localities or private individuals to different destination servers in a secure manner for processing so that the various processed information can be used in an integrated manner to provide advanced context-aware services. After classifying the various kinds of sensor information related to individuals, we propose a communication architecture in which sensors placed in the environment, mobile terminals owned by users, and the new generation access network operate cooperatively. It features secure transport of sensor information via mobile terminals by establishing communication channels to sensors and the sensor database.

Sensor Application Platform on a Novel Managed Wireless Mesh

We propose a sensor application platform using a managed wireless mesh network for providing a variety of services that are demanded by individuals living in a local region and various communities to which each individual belongs and that conventional telecom networks or sensor networks are not able to provide at a reasonable cost. The proposed system, which is based on openness, establishes logical paths with a many-to-many mesh topology on a physical wireless mesh network, providing logically different service domains. This makes a variety of sensor applications/services available on a single platform. Mechanisms of the platform and operation models of the platform are presented.

The multi-agent system for dynamic network routing

The single-hop communication method of the current wireless network cannot meet new demands in the domain such as intelligent transport systems (ITS) and Home LAN. Even though the ad-hoc network architecture is expected to solve this problem, the nature of a dynamic topology makes this routing hard to realize. This paper introduces a new ad-hoc routing algorithm, which is inspired by the cooperating mobile agents for dynamic network routing of Miner et al. (see Software agents for future communicating systems, p.287-304, Springer, 1999). In their system, some control agents explore the network and update routing tables on their own knowledge. Using these routing tables, other agents deliver messages. They considered the feasibility of the agent-based routing system, but did not refer to an efficient algorithm. We consider that algorithm without increasing the network load. We propose multiplying each entry in the routing table to store much more information from agents and evaluating them to make better use of information, which succeeded in raising the network connectivity by about 40% by simulation.

AD HOC Routing Protocol with Flooding Control using Unidirectional Links

In ad hoc networks, unidirectional links between nodes exist due to differing propagation patterns or wireless interferences. Routing protocols for bidirectional links must cause the decline of connectivity. In recent years, some routing protocols considering unidirectional links have been proposed. However, these protocols have a problem: the broadcast traffic for backward path discovery increases. This paper proposes a novel routing protocol for ad hoc networks that positively uses unidirectional links and that drastically reduces the number of control packets. Our protocol improves network connectivity and reduces the number of control traffic.

Load-balanced multipath routing for wireless mesh networks: A step by step rate control approach

Wireless mesh network has been increasingly attracting attentions as enabling technology not only for access network to the Internet but for application oriented network. To strengthen reliability of wireless mesh network, adaptive loadbalanced routing to avoid congestion will be the key technology. This paper presents a novel concept of multipath routing with load balancing capability based on periodical packet distribution rate control. Packet distribution rate of each route adapts to delay cost calculated by using channel utilization of base stations on this route. Compared with existing load-balanced routing, the advantage of the proposed scheme is that it adapts to both sparse networks and dense networks. Results of performance evaluation by computer simulation demonstrate the advantages of the proposed scheme quantitatively. They show that it reduces average end-to-end delay by about 30% compared to loadbalanced singlepath routing scheme and simple multipath routing scheme.