Cognitive radio, which utilizes the radio frequency spectrum efficiently by recognizing radio resource availability, is an attractive technology for overcoming the shortage of radio frequency. From the perspective of networking, cognitive radio technologies are also useful since they allow flexible network construction. This paper proposes base station networks using cognitive radio technologies. In order to achieve efficient utilization of the radio frequency spectrum and flexible network construction, we also propose a topology management and route control method for our proposed base station network. Our method shares the status of the wireless links along with topology information and establishes routes by using this information. Through simulation, we evaluate that our method significantly improves the throughput by efficient utilization of the radio frequency spectrum. Moreover, we demonstrate that our method works well when the size of the network gets larger.

The directional MAC protocols improve spatial reuse, but require the exact location of destination and have the problem of deafness. In this paper, we propose a dual-channel MAC protocol with directional antennas for mobile ad-hoc networks. In the proposed MAC protocol, RTS/CTS are sent omnidirectionally as nodes do not have the exact location of the destination in mobile environments. Omnidirectional transmissions on control channel overcome deafness, but have low spatial reuse. We propose a new blocking algorithm to improve spatial reuse on control channel. We use the negative CTS (NCTS) to solve the exposed terminal problem. We confirm throughput of the proposed MAC protocol by simulations using Qualnet ver. 3.8 simulator.

In ad-hoc networks, mobile nodes are limited by a range of radio coverage and have an irregular source of power due to their battery. In ad-hoc networks, there are a lot of situations that all mobile nodes need to agree on their key not at the same time but in part and then merge themselves subsequently. This is because ad-hoc networks have specific features such as mobility and allow various conditions during configuration. In this thesis, we propose MCP (Merging Clusters Protocol), a simple key agreement scheme that can effectively deal with merging different adjacent clusters in mobile ad-hoc networks. When nodes of each cluster have already agreed on their own group keys and intend to merge themselves for further secure communications, MCP can be used in an efficient and secure way. In addition, it can be utilized for efficient group key agreement in a large ad-hoc network. We analyze the security and efficiency of MCP and discuss the experimental results according to practical implementation scenarios.

Previous routing algorithms for mobile ad-hoc networks (MANETs) have focused on finding short-distance path(s) between communicating nodes. However, due to the dynamic and unreliable communication nature of MANETs, previously determined paths can easily become disconnected. Although dynamic routing can be used to circumvent this problem, determining a new route each time a packet needs to be sent involves a lot of overhead. An alternative form of dynamic routing involves maintaining valid routes in routing tables, which can be dynamically updated whenever network changes are detected. This paper proposes a new routing algorithm, referred to as pseudo-distance routing (PDR), that supports efficient routing table maintenance and dynamic routing based on such routing tables.

Since mobile ad-hoc networks have certain constraints, including power shortages, an unstable wireless environment, and node mobility, more power-efficient and reliable routing protocols are needed. Accordingly, this paper propose a new routing protocol, PERRA (Power Efficient Reliable Routing protocol for mobile Ad-hoc networks), that includes the advantages of on-demand protocols, while also providing power- efficient and reliable packet transmission. PERRA uses a new cost function to select the optimum path based on considering the minimum residual energy of the nodes on a path, the total energy consumed by a path to transmit and process a packet, and the path's stability in accordance with the node mobility. As a result, the proposed method increases the power efficiency, decreases the route-reconstructions due to residual power shortages and node mobility, and provides effective route maintenance mechanisms. The performance of PERRA is evaluated by simulations under various conditions.

This paper discusses effective configuration methods for peer-to-peer (P2P) network topologies within a mobile ad-hoc network. With recent progress in mobile ad-hoc network technology promoting the creation of new and attractive services, we are examining and developing P2P network systems for operation within ad-hoc networks. Our focus is on identifying methods of network-topology control that provide the best balance between performance and availability. We evaluate three methods through computer simulation and field trials from the viewpoints of resource consumption and network integrity, and clarify their domains of applicability. The results are expected to contribute to the design of future P2P networks for operation in mobile ad-hoc networks.

Bluetooth is reputed as a wireless networking technology capable of forming ad-hoc networks between digital devices. In particular, the Bluetooth scatternet will be an essential part of the fully distributed ad-hoc networks. However, scatternet is not fully described in the Bluetooth specification. This has been the topic of discussion among researches in relation to the formation algorithm, scheduling scheme, etc. Most of the proposed algorithms reported in past researches on scatternet formation are too large and complex to be implemented in a real commercial Bluetooth hardware. Therefore, the verifications of the proposed algorithms reported in past researches were done through only simulations. In addition, the formation process takes too long and these past researches had been conducted only in static environment where no node enters or leaves the scatternet. In this paper, therefore, we propose a new scatternet formation algorithm called Node Ring Scatternet (NRS), emphasizing on two aspects, i.e. implementation and dynamic property of the algorithm. The algorithm is very simple and compact and is verified to be easily implementable in a real commercial Bluetooth device. For the dynamic properties, the NRS entails relatively short formation delay and a reformation algorithm in a dynamic environment was designed. Therefore, the network of the NRS can be scalable and flexible. In addition, a new protocol called SFMP (Scatternet Formation & Management Protocol) was designed and is presented herein. Using this protocol, the NRS algorithm was implemented in a real Bluetooth device, and the performance was verified through hardware experiments. Based on the experimental results, it was found that the NRS composed of up to 20 nodes is formed and the proposed algorithm has shown improvement in terms of formation delay, formation probability and reformation.

Flooding is usually utilized to find a multi-hop route toward a node which is not within transmission range. However, existing flooding schemes deteriorate the performance of network because of periodic message exchanges, frequent occurrence of collisions, and redundant packet transmission. To resolve the problem, a lightweight and novel flooding scheme is proposed in this paper. The scheme employs ongoing packets for constructing a cluster architecture as the existing on-demand clustering scheme. Unlike to the existing schemes, it makes use of unicast packet transmission to reduce the number of collisions and to find the flooding candidates easily. As a result, the proposed scheme yields fewer flooding nodes than other schemes. Simulation results prove that it causes fewer packet transmissions and fewer collisions than those of two other schemes.

This paper proposes a user revocation scheme for decentralized networks. User revocation is a method to distribute a group decryption key that is shared by n users in a group so that all but d revoked users can obtain the key. In decentralized networks such as ad-hoc networks, mesh networks, and Peer to Peer (P2P) networks, a sender should revoke the access of a dishonest user or an unauthorized user as soon as possible to protect the security of group communication. However, if the sender distributes the group key to all users aside from the revoked user, it would take a long time to revoke a user in a large group. In addition, users must set shared group keys for each user without a privileged center. We propose a scheme in which the amount of transmission and the key storage of each user are small.

Mobile ad-hoc networks consist of mobile nodes interconnected by multihop path that has no fixed network infrastructure support. Due to the limited bandwidth and resource, and also the frequent changes in topologies, ad-hoc network should consider these features for the provision of security. We present a secure routing protocol based on identity-based signcryption scheme. Since the proposed protocol uses an identity-based cryptosystem, it does not need to maintain a public key directory and to exchange any certificate. In addition, the signcyption scheme simultaneously fulfills both the functions of digital signature and encryption. Therefore, our protocol can give savings in computation cost and have less amount of overhead than the other protocols based on RSA because it uses identity-based signcryption with pairing on elliptic curve. The effectiveness of our protocol is illustrated by simulations conducted using ns-2.

A flooding algorithm is an indispensable and fundamental network control mechanism for achieving some tasks, such notifying all nodes of some information, transferring data with high reliability, getting some information from all nodes, or to reserve a route by flooding the messages in the network. In particular, the flooding algorithm is greatly effective in the heterogeneous and dynamic network environment such as so-called ubiquitous networks, whose topology is indefinite or changes dynamically and whose nodal function may be simple and less intelligent. Actually, it is applied to grasp the network topology in a sensor network or an ad-hoc network, or to retrieve content information by mobile agent systems. A flooding algorithm has the advantages of robustness and optimality by parallel processing of messages. However, the flooding mechanism has a fundamental disadvantages: it causes the message congestion in the network, and eventually increases the processing time until the flooding control is finished. In this paper, we propose and evaluate methods for producing a more efficient flooding algorithm by adopting the growth processes of primitive creatures, such as molds or microbes.

Topology of a network greatly affects the network performance. Depending on the purpose of a network, a specific topology may perform much better than any other topologies. Since the ad hoc networks are formed for a specific purpose, determining, and constructing the network topology based on the application requirements will enhance system performance. This paper proposes Bluetooth scatternet forming protocol in which the network topology is determined by three parameters. The parameters affecting the topology are the number of maximum slaves in a piconet, the number of maximum piconets that a gateway Bluetooth device can service, and the number of loops needed in the formed scatternet. These parameters can be read from a script file prior to the network formation. This process of reading the important parameters from the file would give users freedom in determining the network topology. The proposed protocol also includes a role negotiation process to accommodate different capabilities of the participating devices. The negotiation process of the protocol allows the resource-limited nodes to participate in the network. Different types of scatternet topologies like star, mesh, ring and line can be formed by specifying the parameters. This paper also discusses theoretical information necessary for calculating network topologies in detail. The protocol is verified with help of simulations, and implementations using commercially available Bluetooth devices. The detailed results are also presented in this paper.

In this paper, a novel carrier-sense multiple-access (CSMA) scheme for UWB ad-hoc network is proposed and evaluated. UWB is a kind of spread spectrum communication and it is possible to detect the distance between the nodes. With this positioning capability of the UWB systems, DS-CDMA (DS-UWB) scheme with variable spreading factor is used. In this paper, a novel CSMA scheme that employs the correlation of the spreading code is proposed.

A multi-hop wireless local area network (LAN) is an ad-hoc wireless network that connects to the Internet backbone via an access point. Routing paths between mobile hosts and a fixed host can be divided into two sub-paths, wireless and wired. In this paper, we apply the Hierarchical Routing Tree (HRT) concept to finding wireless sub-paths. That is, by constructing an HRT, each mobile host can find a routing path to an access point (i.e., the HRT root) quickly and thus gain the access to Internet. In addition, we choose the Ad-hoc On-demand Distance Vector (AODV) routing protocol as a point-to-point routing method for sources and destinations located in the same ad-hoc network in order to improve upon a weakness in the HRT method. Numerical experiments are given to show the effectiveness of the hybrid routing method.

The single path routing protocol, known as the Ad Hoc On-demand Distance Vector, has been widely studied for use in mobile ad hoc networks. AODV requires a new route discovery whenever a path breaks. Such frequent route discoveries cause a delay due to route discovery latency. To avoid such inefficiency, a multipath routing protocol has been proposed that attempts to find link-disjoint paths in a route discovery. However, when there are two or more common intermediate nodes on the path, the protocol can not find a pair of link-disjoint paths even if the paths actually exist. To reduce this route discovery latency, it is necessary to increase the opportunities for finding a pair of link-disjoint paths. In this paper, we focus on AODV and propose an AODV-based new multipath routing protocol for mobile ad hoc networks. The proposed routing protocol uses a new method to find a pair of link-disjoint paths by selecting a route having a small number of common intermediate nodes on its path. Using simulation models, we evaluate the proposed routing protocol and compare it with AODV and the existing multipath routing protocol. Results show that the proposed routing protocol achieves better performance in terms of delay than other protocols because it increases the number of cases where a pair of link-disjoint paths can be established.

We have been developing new cycling environments by using knowledge sharing and speech communication. We have offered multimodal knowledge contents to share knowledge on safe and exciting cycling. We accumulated 140 contents, focused on issues such as riding techniques, trouble shootings, and preparations on cycling. We have also offered a new way of speech communication using an ad-hoc wireless LAN technology for safe cycling. Group cycling requires frequent communication to lead the group safely. Speech communication achieves spontaneous communication between group members without looking around or speaking loudly. Experimental result through actual cycling has shown the effectiveness of sharing multimodal knowledge contents and speech communication. Our new developed environment has an advantage of increasing multimodal knowledge through the accumulation of personal experiences of actual cycling.

In this paper, we propose a modeling framework for supporting QoS routing in mobile ad-hoc wireless networks. The basic motivations of the proposed modeling approach stem from the commonality observed in the location uncertainty in mobile ad-hoc wireless networks and the concept of entropy. These common characteristics have motivated our work in developing an analytical modeling framework using entropy concepts and utilizing mobility information as the corresponding variable features, in order to support and evaluate route stability in self-organizing mobile ad-hoc wireless networks. The corresponding methodology, results and observations can be used by the routing protocols to select the most stable route between a source and a destination, in an environment where multiple paths are available, as well as to create a convenient performance measure to be used for the evaluation of the stability and connectivity in a mobile ad-hoc wireless networks.

The performance of a mobile ad hoc network (MANET) is related to the efficiency of the routing protocol in adapting to changes in the network topology and the link status. However, the use of many different mobility models without a unified quantitative "measure" of the mobility has made it very difficult to compare the results of independent performance studies of routing protocols. In this paper, a mobility measure for MANETs is proposed that is flexible and consistent. It is flexible because one can customize the definition of mobility using a remoteness function. It is consistent because it has a linear relationship with the rate at which links are established or broken for a wide range of network scenarios. This consistency is the strength of the proposed mobility measure because the mobility measure reliably represents the link change rate regardless of network scenarios.

A new distributed medium access control (MAC) protocol--Soft Reservation Multiple Access with Priority Assignment (SRMA/PA) protocol--is introduced for supporting the integrated services of real-time and non-real-time applications in mobile ad-hoc networks. The SRMA/PA protocol allows the distributed nodes to contend for and reserve time slots with RTS/CTS-like "collision-avoidance" handshake and "soft reservation" mechanism augmented with distributed and dynamic access priority control. The SRMA/PA protocol realizes distributed scheduling for guaranteeing QoS requirements of integrated services and maximizes statistical multiplexing gain. We have demonstrated by simulation studies that the multiplexing gain can be improved significantly without unduly compromising on system complexity. Moreover, we have shown that the proposed back-off mechanism designed for delay-constrained services is useful for further improving utilization of the channel.