A framework for deploying application-specific overlay networking is presented. It enables network protocols for transmitting data and agents to be naturally facilitated as mobile agents. It can also implement the deployment of mobile agent-based protocols within mobile agents. It can customize the deployment of network protocols as well as data transmission by migrating and replacing corresponding mobile agent-based protocols. It provides a self-deployment mechanism for the overlay network. This paper describes the system and its prototype implementation, which uses Java as both the implementation language and the protocol development language.

Lam, Chung, Gu and Sun (2003) proposed a lightweight security mechanism for mobile commerce transactions to meet the security needs in the face of the resource constraints of mobile devices. End-to-end security between the mobile device and the mobile commerce provider is established. However, its security builds on the assumption that customers can confirm every mobile commerce provider's public key by themselves before each transaction. Moreover, the mechanism still produces high overhead on the mobile device. This paper elucidates the causes of these drawbacks, and an enhanced mechanism is also proposed to protect mobile commerce transactions more effectively and efficiently.

This paper studies a multiband mobile communication system to support both high data rate services and wide service coverage, using high and low frequency resources with different propagation characteristics. In the multiband system, multiple frequency bands are managed by a base station and one of the frequency bands is adaptively allocated to a terminal depending on his channel quality. By limiting the low frequency resources to a terminal not covered by the higher frequencies, the presented multiband system can accommodate many terminals providing wide coverage area, as if all radio resources have low frequency. From numerical results, the multiband system can provide wide service coverage area for much larger number of terminals than conventional systems. It is also found that an appropriate balance of multiple frequency resources is essential to achieve high capacity.

It was previously shown that the number of array elements must exceed the number of sources for multiple target direction of arrival (DOA) tracking. This is clearly not practical for code-division multiple access (CDMA) communications since the number of mobile users is very large. To overcome the restriction, adaptive angle tracking approaches employing the code-matched filters and parallel Kalman/H∞ algorithms are presented in this paper. The proposed approaches are applied to the base station of a mobile communication system. Different from Kalman prediction algorithm which minimize the squared tracking error, the adaptive H∞ filtering algorithm is a worst case optimization. It minimizes the effect of the worst disturbances (including modeling error of direction matrix models and array structure imperfection, process noise, and measurement noise). Hence, the difficult problem of tracking the crossing mobiles can be successfully handled by using the code-matched filters. Computer simulation is provided for illustrating the effectiveness of the adaptive angle tracking approaches.

To obtain large capacity, high quality mobile satellite communication systems in the future, we must use a multi-beam that can cope with extremely high levels of frequency reuse. This paper describes a novel resource allocation algorithm for multi-beam satellite communication systems that can dynamically adapt to maximum communication capacity without compromising quality. The algorithm combines two resource allocation schemes that enable it to contend with the ever-changing user distribution and inter-beam interference conditions. The first scheme optimizes the resources amongst beams. To minimize interference, the optimal constraint conditions are clarified when all clusters share and occupy the same bandwidth completely. These constraints are used in the optimization algorithm. The second scheme manages the various required resources and adapts them to the beam gain and interference levels at various user locations within a single beam. We propose a fixed power adaptive modulation scheme to obtain stable communications. This two-layered scheme can satisfactorily allocate multi-beam satellite resources to contend with the increasing communication capacity and still improve the quality.

Micromobility management is a key issue for the deployment of broadband mobile communication services. The packet loss during handover and the handover latency need to be minimized to maintain the high quality of these services. We have previously proposed a mobility management scheme that addresses this issue in wide-area mobile networks that employed hierarchical multiple mobility management routers (Mobility Anchor Points or MAPs). Our scheme directs a Mobile Terminal (MT) to a suitable MAP to fully minimize packet loss during handover, and handover latency of the MTs. In our previous work, we confirmed the effectiveness of our scheme using a simple tree network. Actual networks however, always have densely meshed topologies to provide some redundancy for the elimination of single points of failure. In such networks, it is difficult to deduce the relationships between the MAPs, and this makes it difficult for our scheme to select a suitable MAP for an MT, because the selection is performed using both the MT's smoothed speed and the relationships existing between the MAPs located above the Access Router (AR), to which the MT is connected. In this paper, we propose a method to overcome this problem, by autonomously adjusting the selection criteria that are individually configured for use at a particular AR, and we evaluate this method using simulation experiments. The results show that our mobility management scheme works well in densely meshed networks using the proposed additional method.

The crucial issue for mobile Internet services is to provide the guaranteed mobile QoS for multicalls. In mobile networks, we should not only guarantee handoff dropping probability but also maximize resource utilization. In this paper, we propose a QoS admission control mechanism for macro Mobile QoS based on a dynamic resource reservation. We introduce the requirements for macro Mobile QoS as mobility features and predict required resources in each routing paths thorough the combined analysis of average movement pattern and pre-defined handoff dropping probability. Our simulation results show that the proposed scheme can guarantee the pre-defined handoff dropping probability and maintain lower call blocking probability and higher resource utilization than other schemes. The propose scheme gives a practical solution for mobile networks providing mobile Internet services.

The boundary of a distributed denial of service (DDoS) attack, one of the most threatening attacks in a wired network, now extends to wireless mobile networks, following the appearance of a DDoS attack tool targeted at mobile phones. However, the existing defense mechanisms against such attacks in a wired network are not effective in a wireless mobile network, because of differences in their characteristics such as the mobile possibility of attack agents. In this paper, we propose a proactive defense mechanism against IP spoofing traffic for mobile networks. IP spoofing is one of the features of a DDoS attack against which it is most difficult to defend. Among the various mobile networks, we focus on the Network Mobility standard that is being established by the NEMO Working Group in the IETF. Our defense consists of following five processes: speedy detection, filtering of attack packets, identification of attack agents, isolation of attack agents, and notification to neighboring routers. We simulated and analyzed the effects on normal traffic of moving attack agents, and the results of applying our defense to a mobile network. Our simulation results show that our mechanism provides a robust defense.

We describe a layer 3 diversity reception scheme that enhances the transmission characteristics of Ku-band mobile satellite communication systems. This scheme can realize high-speed communication for vehicles that experience shadowing caused by terrestrial obstacles such as tunnels, buildings and bridges, especially for trains that frequently experience shadowing from the trolley wire structures. Layer 3 diversity was chosen for long distance diversity to prevent signal shadowing caused by terrestrial obstacles while minimizing the alterations of existing receivers. The technology enables high-speed communication under shadowing conditions in a running train environment.

The fast handover protocol adopted in a IPv6 hierarchical structure provides a seamless handover in wireless IP networks by minimizing the handover latency. To reduce the handover latency, the fast handover uses anticipation based on layer 2 trigger. Nonetheless, a mobile node can still lose its connection with the old link during the fast handover procedures. Accordingly, this paper analyzes the handover latency and packet delivery costs associated with fast handover failure cases based on a timing diagram.

The Minimum Connected Dominating Set (MCDS) reduces the number of messages to destinations and the finding MCDS is considered as a NP-hard problem. Alzoubi's approximation algorithm is known as the best in terms of message-optimal CDS construction, but not for mobility management. We present a message-efficient mobility management scheme based on distributed spanning trees. The proposed method may generate more messages than Alzoubi's for message delivery, but it consumes significantly fewer messages for mobility management (to the ratio of 2.5). Thus, when highly mobile networks are assumed, the proposed scheme outperforms Alzoubi's in terms of total number of messages.

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.

We introduce a new hierarchical key management scheme which can be applied for secure Mobile IP registration protocol. Contrary to the previous schemes, AAA protocol used for registration key distribution is separated from the base registration protocol, so that the registration key distribution can be simplified and the delay caused by the AAA protocol can be avoided. Also proposed is the non-repudiation service based on a hash chain, which is useful for secure auditing.

Blood pressure is one of the most important indicators of human health condition. A patient with hypertension in long term tends to have various kinds of vessel pathological changes such as coronary heart disease, apoplexy, and nephropathy. Consequently, the blood pressure measurement is important in daily health care for hypertension patients. Traditionally, the design and implementation of blood pressure monitor mostly focuses on the accuracy of pressure measurement and does not deal with the requirement of hypertension health care services with two-way communication via instant messages between the patient and the medical center. In this paper, a mobile-care system integrated with Bluetooth blood pressure and pulse monitor, and cellular phone is designed and implemented to transmit the physiological parameters of the patient in real time via wireless networks. The health care provider can monitor the blood pressure, body temperature, and heart rate of the patient and provide services by intelligent health care systems. The intelligent system constantly manages the health care data and periodically reports the status of the patient to the patient's family members. By the above care mechanism, the patients with hypertension can easily obtain long-term and constant monitoring of the physiological parameters and thus better health care services. A questionnaire survey has been conducted among medical personnel in Taipei municipal Wang-Fang hospital to collect their opinions of using our proposed and implemented blood pressure monitor with Bluetooth transmission function. An average of 95% of the medical personnel agree that long-term monitoring of the patients' physiological information such as blood pressure can be helpful to reduce medical cost, to provide useful reference data, and to provide long-distance health care. This thus shows strong support of the usefulness of our proposed device. Our proposed and implemented device has also been submitted to US FDA for medical device approval.

In this paper, we present a novel forwarding scheme to enhance communication stability based on geographic routing in mobile ad hoc networks, which is called "Position-based Heuristic Forwarding" (PHF). For alternative solutions to traditional ad hoc routings, many geographic routing algorithms have been proposed. Most of the existing routings impose a certain restriction, planarity, on the graph structure of network for delivering messages to destination definitely. PHF achieves the guaranteed packet delivery over Unit Disk Graph, which is more widely employed graph model for the study of ad hoc networks. Accordingly, to eliminate the restriction of the routing algorithms enhances the probability to deliver messages successfully in networks with high nodes' mobility rate. In the simulation of PHF, we have evaluated the performance comparisons between PHF and its related work, Greedy Perimeter Stateless Routing (GPSR) and Dynamic Source Routing (DSR), which are the prominent geographic and conventional topology-based routing protocols, respectively. The results show that PHF provides higher packet delivery success rate indicating better communication stability and equal or less overhead than these work.

Recently with the high expectation of voice over WLAN service, to support fast inter-AP security transition in WLAN Access Point (AP) is one of the most actively investigating issues. It is also very important problem to minimize inter-AP security transition (IAPST) latency, while maintaining constantly the secure association from old AP when a station transits to new AP. With this background, this paper presents a novel association control mechanism whose objective pursues to minimize IAPST latency time and to take countermeasures against attacks of rogue transition station. Experiment shows that the proposed scheme outperforms the legacy AP over 70% with regard to the transition latency.

An RF adaptive array antenna (RF-AAA) configured with variable capacitors is proposed. This antenna system can control the power combining ratio and phase value of received signals. In this paper, we focus on the diversity effects of RF-AAA. First, we show the design methodology of the combiner circuit to realize the effective combining. Second, the perturbation method and the steepest gradient method are compared for the optimization algorithms to provide fast convergence and suboptimum solutions among the variable circuit constants. Finally, in simulation, we show the RF-AAA can achieve diversity antenna gains of 7.7 dB, 10.9 dB and 12.6 dB for 2-branch, 3-branch and 4-branch configuration, respectively, which have higher performance than the selection combining.

The Japan Aerospace Exploration Agency (JAXA) plans to launch a geostationary satellite called Engineering Test Satellite VIII (ETS-VIII) in FY 2006. In this paper, a microstrip line array antenna, which has a very simple structure, is introduced to radiate a circularly polarized wave aiming at ETS-VIII applications. This antenna consists of a triangular conducting line with its vertexes rounded off, located above a ground plane, with a gap on one of its side to produce a circular polarization. The proposed antenna is analyzed by numerical simulations for a single element as well as for a three elements array configuration and the possibility of beam-switching in the azimuth space is experimentally confirmed in the latter case. It is found that by properly feeding the elements constituting the array antenna, for an elevation angle El = 48in Tokyo area, three beams are created in the conical-cut direction with a minimum gain more than 6.6 dBic and an axial ratio less than 3 dB.

The Public Wireless Local Area Network (PWLAN) is an emerging service for wireless access to the Internet. However, the service coverage of the PWLAN is limited by the deployment of access points (APs) because only those who stay near the AP can access the PWLAN. A feasible way of extending the service coverage of a PWLAN is to deploy mobile ad hoc access networks (MAHANs) so that users who are not in an AP's radio coverage area can send their packets to the AP in a multihop manner. However, in a MAHAN, mobile nodes that intend to access the Internet have to discover routes to the AP first, which may result in considerable bandwidth cost. In this paper, we propose the Appointed BrOadcast (ABO) method to reduce the cost of route discovery in MAHANs. Using the ABO method can achieve this goal on the basis of packet overhearing. Functions that are necessary for network and data link layers to employ the ABO method are also discussed. Simulation results show that using the ABO method can significantly reduce the cost on route discoveries. Due to the widespread use of legacy IEEE 802.11 nodes, the problem of how ABO-enhanced and legacy IEEE 802.11 nodes can coexist in a MAHAN is also discussed.

Hierarchical Mobile IPv6 (HMIPv6) was proposed by the Internet Engineering Task Force (IETF) for efficient mobility management. HMIPv6 reduces the amount of signaling in the wired network link that exists in Mobile IPv6. But, HMIPv6 cannot reduce the signaling cost in the wireless link. In mobile networks, the wireless link has far less available bandwidth resources and limited scalability compared with the wired network link. Therefore, the signaling overhead associated with mobility management severely degrades the wireless link. In this paper, we propose virtual-IP (VIP) allocation scheme with dynamic VIP zone to reduce the wireless signaling cost in mobile networks. The performance of the proposed scheme is compared with HMIPv6. Based on the numerical analysis and simulation, we show that VIP allocation scheme reduces the wireless signaling cost under various system conditions.