Chiung-Ying Wang

A novel efficient power-saving MAC protocol for multi-hop MANETs

Following recent advances in the performance of ad hoc networks, the limited life of batteries in mobile devices poses a bottleneck in their development. Consequently, how to minimize power consumption in the Medium Access Control (MAC) layer of ad hoc networks is an essential issue. The power-saving mode (PSM) of IEEE 802.11 involves the Timing Synchronization Function to reduce power consumption for single-hop mobile ad hoc networks (MANETs). However, the IEEE 802.11 PSM is known to result in unnecessary energy consumption as well as the problems of overheating and back-off time delay. Hence, this study presents an efficient power-saving MAC protocol, called p-MANET, based on a Multi-hop Time Synchronization Protocol, which involves a hibernation mechanism, a beacon inhibition mechanism, and a low-latency next-hop selection mechanism for general-purpose multi-hop MANETs. The main purposes of the p-MANET protocol are to reduce significantly the power consumption and the transmission latency. In the hibernation mechanism, each p-MANET node needs only to wake up during one out of every N beacon interval, where N is the number of beacon intervals in a cycle. Thus, efficient power consumption is achieved. Furthermore, a beacon inhibition mechanism is proposed to prevent the beacon storm problem that is caused by synchronization and neighbor discovery messages. Finally, the low-latency next-hop selection mechanism is designed to yield low transmission latency. Each p-MANET node is aware of the active beacon intervals of its neighbors by using a hash function, such that it can easily forward packets to a neighbor in active mode or with the least remaining time to wake up. As a consequence, upper-layer routing protocols can cooperate with p-MANET to select the next-hop neighbor with the best forwarding delay. To verify the proposed design and demonstrate the favorable performance of the proposed p-MANET, we present the theoretical analysis related to p-MANET and also perform experimental simulations. The numerical results show that p-MANET reduces power consumption and routing latency and performs well in extending lifetime with a small neighbor discovery time. Copyright

Mobile IPv6-based ad hoc networks: its development and application

The Internet protocol version 6 (IPv6)-enabled network architecture has recently attracted much attention. In this paper, we address the issue of connecting mobile ad hoc networks (MANETs) to global IPv6 networks, while supporting IPv6 mobility. Specifically, we propose a self-organizing, self-addressing, self-routing IPv6-enabled MANET infrastructure, referred to as IPv6-based MANET. The proposed self-organization addressing protocol automatically organizes nodes into tree architecture and configures their global IPv6 addresses. Novel unicast and multicast routing protocols, based on longest prefix matching and soft state routing cache, are specially designed for the IPv6-based MANET. Mobile IPv6 is also supported such that a mobile node can move from one MANET to another. Moreover, a peer-to-peer (P2P) information sharing system is also designed over the proposed IPv6-based MANET. We have implemented a prototyping system to demonstrate the feasibility and efficiency of the IPv6-based MANET and the P2P information sharing system. Simulations are also conducted to show the efficiency of the proposed routing protocols.

Mobility management in ubiquitous environments

Ubiquitous computing is aiming at providing users with intelligent human-centric context-aware services at anytime anywhere. However, mobility increases dynamism and uncertainty conditions. This study therefore explores the management and uses of various contexts for automatically providing appropriate services to individual users. This issue is explored from an open framework perspective referred to as ubiquitous gate (U-gate). In this framework, a distributed context management architecture and a communication model based on standard protocols are proposed. To fit user requirements and to achieve complete mobility management, a context-aware path planning mechanism (UbiPaPaGo) and a context-aware handoff mechanism (UbiHandoff) are proposed based on context stored in an open and distributed context management server U-gate. Based on the path planning results of UbiPaPaGo, UbiHandoff derives a minimum access point (AP) handoff plan that satisfies multiple QoS requirements for individual users and services. The UbiHandoff mechanism includes multiple-attribute decision making method (MADM)–based handoff planning, referred to as MADM-based UbiHandoff, and genetic algorithm (GA)–based handoff planning, referred to as GA-based UbiHandoff. In the proposed MADM-based UbiHandoff, analytic hierarchy process (AHP) and technique for order preference by similarity to ideal solution (TOPSIS) provide efficient and seamless AP handoff to gain higher QoS performance. In GA-based UbiHandoff, genetic algorithm is employed to minimize handoff by finding appropriate APs along the path under QoS constraints. Finally, the effectiveness of the proposed mechanisms is evaluated through simulations. Numerical results demonstrate that both mechanisms minimize handoffs and ensure compliance with QoS requirements.

UbiPhone: Human-Centered Ubiquitous Phone System

Emerging rich wireless networking modalities facilitate the development of new intelligent, innovative services on smart phones. The authors propose a ubiquitous phone (UbiPhone) system that demonstrates innovative context-aware human-centric phone services, which could become available on smart phones. UbiPhones features include UbiCall, AnyCall, and an emergency contact service.

p-MANET: Efficient Power Saving Protocol for Multi-Hop Mobile Ad Hoc Networks

In this paper, we propose an efficient power saving protocol for multi-hop mobile ad hoc networks, called p-MANET. Our design is expected as a new foundation MAC layer power saving protocol. The main goals of p-MANET protocol are to reduce significant power consumption and transmission latency, and to achieve efficient power saving. Each mobile node in p-MANET only needs to become active during one beacon interval for every n interval where n is the size of a super frame. Thus, efficient power saving is expected. p-MANET also yields low transmission latency because that every mobile node is aware of the active beacon intervals of its neighbors such that it can easily choose a neighbor in active mode or with the least remaining time to wake up to forward packets. Simulations are also conducted to show the efficiency of the proposed p-MANET

UbiPaPaGo: Context-aware path planning

The increased prevalence of digital devices with communication capability heralds the era of ubiquitous computing, as predicted by Mark Weiser. Ubiquitous computing aims to provide users with intelligent human-centric context-aware services at anytime anywhere. Optimal path planning in a ubiquitous network considers the needs of users and the surrounding context. This approach is very different from that applied by existing research on car navigation and mobile robots. This study proposes a context-aware path planning mechanism based on spatial conceptual map (SCM) and genetic algorithm (GA), referred to as UbiPaPaGo. The SCM model is adopted to represent the real map of the surrounding environment. The optimal path is planned using a GA, which is a robust metaheuristic algorithm. UbiPaPaGo attempts to automatically find the best path that satisfies the requirements of an individual user. A prototype of UbiPaPaGo is implemented to demonstrate its feasibility and scalability. Experimental results validate the effectiveness and the efficiency of UbiPaPaGo in finding the optimal path.

Context-awareness handoff planning in heterogeneous wireless networks

This paper addresses a context-awareness handoff planning mechanism in heterogeneous wireless networks for seamless ubiquitous access. The proliferation of digital devices with communication capability heralds the era of ubiquitous computing, as predicted by Mark Weiser. Mobile devices with multi-mode interfaces can access heterogeneous wireless networks, such as wireless local area network (WLAN), worldwide interoperability for microwave access (WiMAX) network and third generation (3G) network. In heterogeneous wireless networks, different network provides different network capability, transmission range, data rate, access cost, security policy and quality of service. Therefore, a ubiquitous access aims to provide users intelligent human-centric context-aware handoff mechanism in heterogeneous wireless networks at anytime anywhere is gradually become an important issue. Optimal handoff planning in heterogeneous wireless networks considers the needs of users, accessing service and the surrounding context. However, most of existing handoff mechanisms only considered few contexts that lead to not able to select the most suitable network for individual user. In this paper, we propose a human-centric context-aware solution to access most appropriate network that satisfies individual users requirement, fulfills seamless data transmission and reduces handoff delay. We develop two integrated approaches for context-awareness handoff planning mechanisms, namely MADM approach and GA approach. The MADM approach contains initial process and decision process. Initial process weights context by Analytic Hierarchy Process (AHP) method while decision process selects the most appropriate network by Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). The GA approach uses Genetic Algorithm to minimize handoff under given QoS constraints. Performance of proposed mechanisms is evaluated under different services with different QoS considerations. Our simulation results show that both mechanisms are able to derive a proper network handoff plan which guarantees QoS requirements and reduces delay, jitter, and number of handoffs.

An Open Framework for Distributed Context Management in Ubiquitous Environment

In this paper, we aim to propose an open framework for ubiquitous environment. In this framework, a distributed context management architecture and a communication model based on standard protocols are proposed. With this framework, a smart device is able to join to the ubiquitous environment and search for context-aware services based on standard protocols, such as UPnP and DNS. A service is also easily deployed into the system through standard protocols and distributed context managers. A prototype of the framework has been implemented to demonstrate the feasibility of the framework. The major contribution of this paper is to propose an open, efficient, and distributed framework for ubiquitous computing environment which provides digital devices an open interface to access any kind of services and context.

Ubiquitous Phone System

Portable smart devices, such as Pocket PC Phones and Smartphones, have become common devices in our daily life. However, they still provide technology-oriented human interface. In future ubiquitous environment, context-awareness is the key to make the human interface of smart devices become human-centric. In this paper, we design and develop a ubiquitous phone system, referred to as UbiPhone, which provides context-aware, human-centric phone service based on rich context acquired from various sensing sources. The most unique feature of UbiPhone is that a user only needs one click, UbiPhone will automatically choose the right communication channel and device to connect to the callee. UbiPhone also provides intelligent feedback service when the callee is not available, such as when to call back according to callees calendar, whether to automatically dial back when the callee becomes available, who to contact with if this is an emergency call and the callee is not reachable. In particular, social network is adopted to reason who would be the most appropriate person to help the caller find the callee immediately. Prototype of UbiPhone has been developed to show its feasibility.

Development of a context-aware messaging system over heterogeneous wireless networks

Integration of messaging services in heterogeneous wireless networks plays an important role in facilitating personal communications. Furthermore, supporting context-awareness drives wireless messaging services to the ubiquitous and human-centric extent. In this article we introduce a context-aware wireless messaging system in ubiquitous networking environment. The key concepts are (1) heterogeneous wireless data are accessed and translated by a gateway with corresponding networking interfaces or terminals; (2) a messaging service with always-best-connected capability is provided according to the context information collected by users mobile or handheld devices; and (3) a Resource Description Framework (RDF) context server is used to manage all kinds of context information. With our system, users can enjoy the cost-effective and near-real-time communication even when they face network heterogeneity in the ubiquitous networking environment. This paper also describes the implementation of the system prototype to demonstrate the effectiveness of the proposed system.