Catálogo de publicaciones - libros

In a mobile environment, it is desirable for mobile applications to adapt their behaviors to the changing context. However, adaptation mechanism may emphasize more on overall system performance, while neglecting the needs of individual. We present a generalized Adaptive Middleware Infrastructure (AMI) to cater for individual needs in a fair manner, while maintaining optimal system performance. Furthermore, due to the vagueness in context nature and uncertainty in context aggregation for adaptation, we propose a Fuzzy-based Service Adaptation Model (FSAM) to achieve generality and improve the effectiveness of service adaptation. By fuzzification of the context and measuring the fitness degree between the current context and the optimal situation, FSAM adopts the most appropriate service. We have evaluated the FSAM inference engine within the middleware AMI by an application Campus Assistant. The performance is analyzed and compared with a conventional threshold-based approach.

Context aware service which provides best suitable services for a user by analyzing user’s needs and situational information, will be one of the promising next generation (NG) mobile services. In this paper, we propose the NG mobile service environment based on the NG mobile service platform and evolutional phases of context aware services in the NG mobile service environment. We then introduce the Context Aware Follow-me (CAF) service developed as a prototype of promising NG context aware mobile service followed by introduction of testbed system developed to investigate feasibility of the CAF service.

Internet users are increasingly becoming more and more demanding, expecting Internet access anytime, anywhere, making ubiquitous, next generation networks a requirement. Uninterrupted connection, even in the case of moving networks, is expected. It is important for a vehicle network to reduce signaling traffic in wireless channels and have fast handover. To achieve these requirements, in this paper, a MRP based rouging scheme for network mobility, is proposed. In order to achieve fast handover, a candidate FA if found, which a mobile network is attached to, making an initial virtual connection to a Mobile Router (MR). In addition, the throughput of a wireless channel is upgraded, by reducing signaling traffic through load balancing. The performance of the proposed scheme is evaluated through a series of simulations using Network Simulator (ns-2).

Mobile IPv6 represents a global solution, providing mobility management for a wide variety of radio technologies, devices, and applications. In particular, Network Mobility basic support protocol is the one of fundamental solutions in MIPv6 which reduces the number of binding update messages issued from mobile network nodes except mobile routers. That is, it never reduces the number of binding update messages which mobile router issues. Significant research results relating to Network Mobility have been reported over last several years. However, practical and common issues exist within the technology; specification of Binding Update Lifetime has a substantial impact the system performance. The binding update message should be delivered periodically for the purpose of user location notification and binding authorization. If the lifetime is too short, the traffic load resulting from the messages may be significant. In addition, issues related to authorization can be problematic. In this paper, therefore, Network Mobility considering arrival time is devised to solve the binding update explosion of mobile routers without security problem in Network Mobility.

Service-oriented device anycasting using quality first search (DA-QFS) approach is proposed to coordinate various portable devices for providing wireless personal area network (WPAN) services. We adopt a cross-layer design standing on not only the lower (network and data link) layer’s point of view but also higher (application) layer’s point of view to provide quality WPAN services. In DA-QFS the service profile (SP) of a WPAN service is well-represented by the proposed characterized task graph (CTG). The proposed weighted device anycasting (WDA) process then takes connectivity, implicit distance, work degree, and mobility as the criteria to select the most quality device according to the information embedded in CTG. The simulation results on energy consumption, packet loss rate, average delay, and re-start time show that DA-QFS is an efficient approach, especially in the environment with highly mobile devices and multiple users.

In recent years, extensive research effort has been devoted to TCP congestion control in hybrid wired-wireless networks. A general agreement is that the TCP sender should respond differently to wireless losses and disconnection, i.e., not slow down as drastically as for congestion losses. Thus, research focus for wireless TCP congestion control is the discrimination between the wireless inherent packet losses and the network congestion packet losses in wired network. In addition, researchers attempt to detect temporary or lengthy wireless disconnection. This paper proposes a simple but novel strategy, dubbed (Base Station Assisted TCP), (1) to accurately discriminate wireless losses from wired network congestion losses and (2) to detect and notify a TCP sender about wireless disconnections. The key distinctive feature of the proposed scheme is its general use for most issues at stake for TCP over wireless: loss discrimination, wireless disconnection and handoffs. It also circumvents the asymmetric problem that acknowledgements might follow different paths from those of data packets. Such asymmetry problem is common to mechanisms that buffer and retransmit wireless lost data packets locally at the base station. The proposed method also addresses energy efficiency.

This paper proposes dynamic clustering for coverage-time maximization (DC-CTM) in sensor networks. The coverage-time is defined as the time until one of cluster heads (CHs) runs out of energy in clustering-based sensor networks. DC-CTM regulates cluster radii for balanced energy consumption among CHs for coverage-time maximization. By using DC-CTM, three advantages can be achieved. The first one is balanced energy consumption among CHs. The second one is minimized energy consumption in each CH. The last one is the consideration of mobility on CHs. The novelty of proposed scheme, DC-CTM scheme, is shown by various simulation-based performance analyses.

For handoff in wireless ATM networks, a call might be rerouted because ATM basically provides connection-oriented service. We propose an enhanced hybrid rerouting scheme (EHRS) for handoff in wireless ATM networks, which combines the concepts of multicast rerouting, anchor rerouting, path extension and dynamic rerouting methods to effectively reduce handoff call dropping ratio, new call blocking ratio, and handoff delay. An analytical model and simulation experiments obtain performance measurements. According to the results, EHRS performs better than the different schemes.

Wireless ad-hoc networks are commonly supposed to be a key technology for future ubiquitous computing environments. The dynamic nature of such networks demands mechanisms that allow the users to assess the availability of given network connections. In this paper we present a novel connection stability heuristic based on neighborhood information of intermediary network nodes. This heuristic identifies nodes that are able to bridge broken network links and thus improve connection stability. Extensive simulation experiments are presented that show the applicability of the heuristic, even though it does not require any special hardware equipment or exact signal strength measurements. Moreover, it imposes only negligible additional effort for the nodes and for the network.

Sensor nodes in wireless sensor network are severely energy-constrained. This has been a key factor to limit its performance. So far, many energy-efficient routing protocols have been proposed. Cluster-based routing protocols have been paid much attention because of their advantages. However, the cluster-based routing protocols require information on the locations of the sensor nodes in the network to construct clusters. Due to cost, it is not feasible to know the locations of all sensor nodes in the network. In this paper, we propose (BCSP) which requires no location information of the sensor nodes. Instead, BCSP utilizes information on the remaining energy of each sensor node and the number of cluster heads which is changed depending on the circumstance of the sensor network. From performance experiments, BCSP shows better performance than (LEACH).