Catálogo de publicaciones - libros

Specifically ubiquitous computing paradigm is based on seamless connectivity. And also to guarantee the seamless connectivity, an intelligent network management between heterogeneous network interfaces, called vertical handoff (VHO), should be designed. Besides, conventional VHO schemes are based on network information only, and do not provide any service manage-ment scheme for seamless service. For this reason, this paper proposes a middleware architecture supporting efficient seamless connectivity with service management. In this architecture, we define modules to perform VHOs in accordance with contexts of services, user intention as well as network information. And also we define profiles used to express the contexts related to the process of VHOs and service management. With the proposed scheme, we can reduce the number of unnecessary VHOs and application failures significantly. This leads to around 130% of enhancement in data throughput, and also 85% of application failures can be reduced.

In this paper, we present SBAC (Soft Bound Admission Control) algorithm considering critical bandwidth ratio to reduce handover blocking probability over WLAN and WAAN (Wide Area Access Network). SBAC algorithm utilizes dynamically optimized resource allocation scheme to decrease the blocking probability of vertical handover connections within the limited capacity of system. Based on SBAC algorithm, we derive the handover blocking probability as new traffic load and handover traffic load increase. In order to evaluate the performance, we compare SBAC algorithm against traditional non-bounded and fixed bound schemes. Numerical results show that the SBAC scheme improves handover blocking probability in ubiquitous environment.

In this study, an adaptive handoff algorithm with a dynamic hysteresis value, based on the distance between the mobile station and the serving base station, is proposed for cellular communications. Handoff probability is calculated to evaluate handoff algorithms analytically. The proposed handoff algorithm is compared with an algorithm with fixed hysteresis, an algorithm using both threshold and hysteresis, and a handoff algorithm based on distance and hysteresis. Performance is evaluated in terms of the average number of handoffs, average handoff delay, standard deviation of handoff location, average signal strength during handoff, and probability of link degradation. Numerical results and simulations demonstrate that the proposed algorithm outperforms other handoff algorithms. The effect of distance error is also discussed.

Despite the importance of seamless connectivity in ubiquitous computing, research for seamless connectivity has not been considered properly. To provide seamless connectivity, this paper proposes an application execution model for seamless services with an intelligent context-aware handoff scheme based on context information, such as user intentions and application requirements as well as issues of network layer. In this paper, we define several profiles reflecting various context informations and design basic modules organizing middleware architecture for seamless service management and efficient vertical handoff (VHO) management. Consequently, the proposed seamless service management with context-aware handoff scheme provides service continuity in ubiquitous computing environment by preventing unnecessary handoffs, changing application service modes adaptively, and eventually maintaining optimal network configuration. And also simulation results show about 38% enhanced performance in the processing rate, about 13% enhanced performance from service continuity, and about 29% enhanced performance in the processing time, compared with conventional schemes.

In this paper, an adaptive soft handoff algorithm, which dynamically calculates the threshold values for soft handoff based on the received signal strength, is proposed for mobile cellular communication systems. An analytical model is developed to study the performance of soft handoff algorithms. Performance is evaluated in terms of the average number active set updates, the mean size of the active set, the mean time of soft handoff, the average signal quality and link degradation probability, where a link degradation is defined to be the event that the signal strength falls below a level required for satisfactory communication. The adaptive soft handoff is shown to yield a significantly better tradeoff than the handoff algorithm with static thresholds.

This paper presents a Bandwidth Broker (BB) based admission control and traffic engineering model for Diffserv supported MPLS networks. The proposed model uses a multi-path model in which several paths are pre-established between each ingress-egress router pair. As a central agent in each domain, the BB performs admission control on behalf of its entire domain via pre-established paths. The proposed model reduces the network congestion by adaptively balancing the load among multiple paths based on measurement of path utilization state. It increases the network core scalability by minimizing the core routers’ state maintenance and signaling operation. The experimental results are provided to verify the achievements of our model.

We propose a new method to determine the optimal TXOP duration (TD) of scheduling algorithm for VBR traffics that guarantees delay and loss probability in IEEE 802.11e HCCA. In this algorithm, the TXOP Duration for each Traffic Stream (TS) is determined by the number () of packets to be transmitted during a TXOP duration, which is found by analyzing //1/× queueing system where the delay bound of the TS is times the Service Interval having length. Numerical results show that the number of admitted TSs with guaranteed loss probability by new method is greater than the number of admitted TSs by other known schemes.

The provision of ubiquitous services in Mobile Ad-hoc Networks (MANETs) is a great challenge, considering the bandwidth, mobility, and computational-resources constraints exhibited by these networks. Incorporation of modern delay-sensitive applications has made the task even harder. The traditional Quality of Service (QoS) provisioning techniques are not applicable on MANETs because such networks are highly dynamic in nature. The available QoS provisioning algorithms are either not efficient or are embedded into routing protocols adding a high computation and communication load. In this paper, we propose a Network State Adaptive QoS provision algorithm (NETSAQ) that works with many underlying routing protocol. It ensures the QoS provisioning according to the high level policy. NETSAQ is simple to implement yet minimizes the degradation of the best effort traffic at a considerable level. Our simulation results show that NETSAQ adapts well in MANET environments where multiple services are contending for limited resources.

In this paper, we model the end-to-end QoS provisioning mechanisms in the WLAN and 3GPP interworking network. For the end-to-end QoS guaranteed service, we model the control plane and user plane considering the WLAN and 3GPP interworking network. And we propose the QoS parameter/class mapping and DPS packet scheduler. By the simulation results, DPS can provide the low end-to-end delay of voice traffic, even though a traffic load increases by 96%. Especially, the end-to-end delay of voice is much smaller when the QoS parameter/class mapping and DPS are applied to the interworking network.

In this paper, we propose the localized adaptive QoS routing scheme using POMDP(partially observable Markov Decision Processes) and Exploration Bonus. In order to deal with POMDP problem, we use CEA(Certainty Equivalency Approximation) technique that involves using the mean value of random variables, since it is intractable to determine the optimal solution. And we present a new path selection using the Exploration Bonus method in order to find detour path, which is better than current path and more adaptive to network environment. Also we evaluate performances of service success rate and average hop count which varies with and performance parameters, which are defined as exploration count and intervals.