Yuh-Shyan Chen

The broadcast storm problem in a mobile ad hoc network

Broadcasting is a common operation in a network to resolve many issues. In a mobile ad hoc network (MANET) in particular, due to host mobility, such operations are expected to be executed more frequently (such as finding a route to a particular host, paging a particular host, and sending an alarm signal). Because radio signals are likely to overlap with others in a geographical area, a straightforward broadcasting by flooding is usually very costly and will result in serious redundancy, contention, and collision, to which we call the broadcast storm problem. In this paper, we identify this problem by showing how serious it is through analyses and simulations. We propose several schemes to reduce redundant rebroadcasts and differentiate timing of rebroadcasts to alleviate this problem. Simulation results are presented, which show different levels of improvement over the basic flooding approach.

A mobile scaffolding-aid-based bird-watching learning system

In this paper, we develop a mobile scaffolding-aid-based bird-watching learning system, which aims to construct an outdoor mobility-learning activity under the up-to-date wireless technology. The proposed bird-watching learning (BWL) system is designed on the wireless mobile ad-hoc network. In the BWL system, each learner device has PDA (personal digital assistances) with a Wi-Fi (IEEE 802.11b) card, within a WLAN environment. Specially, the BWL system contains a mobile learn sheet sub-system, which integrates the scaffolding-aid learn model into the BWL system. Finally, we conduct a formative evaluation to provide statistical results, which is evaluated for the following two purposes; (1) to explore the possible roles and scaffolding aids that the mobile PDA of the BWL system can play and offer in the bird-watching activities, (2) to investigate if the affective and cognitive learning could be possibly benefited from the mobility, portability, and individualization of the mobile PDA of the BWL system.

Routing Protocols in Vehicular Ad Hoc Networks: A Survey and Future Perspectives

Vehicular Ad hoc Network (VANET), a subclass of mobile ad hoc networks (MANETs), is a promising approach for the intelligent transportation system (ITS). The design of routing protocols in VANETs is important and necessary issue for support the smart ITS. The key difference of VANET and MANET is the special mobility pattern and rapidly changeable topology. It is not effectively applied the existing routing protocols of MANETs into VANETs. In this investigation, we mainly survey new routing results in VANET. We introduce unicast protocol, multicast protocol, geocast protocol, mobicast protocol, and broadcast protocol. It is observed that carry-and-forward is the new and key consideration for designing all routing protocols in VANETs. With the consideration of multi-hop forwarding and carry-and-forward techniques, min-delay and delay-bounded routing protocols for VANETs are discussed in VANETs. Besides, the temporary network fragmentation problem and the broadcast storm problem are further considered for designing routing protocols in VANETs. The temporary network fragmentation problem caused by rapidly changeable topology influence on the performance of data transmissions. The broadcast storm problem seriously affects the successful rate of message delivery in VANETs. The key challenge is to overcome these problems to provide routing protocols with the low communication delay, the low communication overhead, and the low time complexity. The challenges and perspectives of routing protocols for VANETs are finally discussed.

DeuceScan: Deuce-Based Fast Handoff Scheme in IEEE 802.11 Wireless Networks

The IEEE 802.11 standard has enabled low-cost and effective wireless local area network (WLAN) services. It is widely believed that WLANs will become a major portion of the fourth-generation cellular system. The seamless handoff problem in WLANs is a very important design issue to support the new astounding and amazing applications in WLANs, particularly for a user in a mobile vehicle. The entire delay time of a handoff is divided into probe, authentication, and reassociation delay times. Because the probe delay occupies most of the handoff delay time, efforts have mainly focused on reducing the probe delay to develop faster handoff schemes. This paper presents a new fast handoff scheme (i.e., the DeuceScan scheme) to further reduce the probe delay for IEEE-802.11-based WLANs. The proposed scheme can be useful to improve wireless communication qualities on vehicles. A spatiotemporal approach is developed in this paper to utilize a spatiotemporal graph to provide spatiotemporal information for making accurate handoff decisions by correctly searching for the next access point. The DeuceScan scheme is a prescan approach that efficiently reduces the layer-2 handoff latency. Two factors of stable signal strength and variable signal strength are used in our developed DeuceScan scheme. Finally, simulation results illustrate the performance achievements of the DeuceScan scheme in reducing handoff delay time and packet loss rate and improving link quality.

An on-demand, link-state, multi-path QoS routing in a wireless mobile ad-hoc network

The peer-to-peer multimedia applications have recently generated much interest in wireless network infrastructure with supporting the quality-of-service (QoS) communications. In this paper, we propose a new on-demand QoS routing, namely link-state multi-path QoS routing, protocol in a wireless mobile ad-hoc network (MANET). Our proposed scheme offers a bandwidth routing protocol for QoS support in a multihop mobile network. Our QoS routing protocol determines the end-to-end bandwidth calculation and bandwidth allocation at the destination. Our protocol collects link bandwidth information from source to destination in order to construct a network topology with the information of link bandwidth at the destination. To satisfy a given bandwidth requirement, the bandwidth calculation of the QoS route are determined at the destination to accurately determine the QoS uni-path or multi-path route depending on the status of network bandwidth. Our routing scheme may offer a multi-path route if a MANET with the insufficient network bandwidth, and provide a uni-path route if the network bandwidth is sufficient. The destination eventually determines the QoS multi-path routes and replies to the source host to perform the bandwidth reservation. Our routing scheme obviously improves the success rate of identifying a QoS route, and the simulation result demonstrates this improvement.

Network mobility protocol for vehicular ad hoc networks

The goal of the network mobility management is to effectively reduce the complexity of handoff procedure and keep mobile devices connecting to the Internet. When users are going to leave an old subnet and enter a new subnet, the handoff procedure is executed on the mobile device, and it may break off the real-time service, such as VoIP or mobile TV, because of the mobility of mobile devices. Because a vehicle is moving so fast, it may cause the handoff and packet loss problems. Both of the problems will lower down the throughput of the network. To overcome these problems, we propose a novel network mobility protocol for vehicular ad hoc networks. In a highway, because every car is moving in a fixed direction at a high speed, a car adopting our protocol can acquire an IP address from the vehicular ad hoc network through the vehicle-to-vehicle communications. The vehicle can rely on the assistance of a front vehicle to execute the prehandoff procedure, or it may acquire a new IP address through multihop relays from the car on the lanes of the same or opposite direction and thus may reduce the handoff delay and maintain the connectivity to the Internet. Simulation results have shown that the proposed scheme is able to reduce both the handoff delay and packet loss rate. Copyright

Realizing Outdoor Independent Learning with a Butterfly-Watching Mobile Learning System

In this article, we describe the development of a mobile butterfly-watching learning (BWL) system to realize outdoor independent learning for mobile learners. The mobile butterfly-watching learning system was designed in a wireless mobile ad-hoc learning environment. This is first result to provide a cognitive tool with supporting the independent learning by applying PDA with wireless communication technology to extend learning outside of the classroom. Independent learning consists of self-selection, self-determination, self-modification, and self-checking. To support independent learning, we designed useful butterfly-watching learning subsystems to offer the self-selection, self-determination, self-modification, and self-checking functionality. The study sample consisted of 24 five-year students who enrolled in natural science course in the Fall of 2003 in Taiwan. The study lasted fourth months (one semester). During the butterfly-watching activity, each learner arbitrarily took a distinct butterfly picture and entered it into his own PDA to acquire the butterfly knowledge anytime and anywhere through wireless communication. The potential impacts, limitations, and lessons learned from this study are discussed from both the educational and technological points of view. Mobile outside classroom learning potentially extends the scope of learning activities and with more flexibility than in traditional school curriculum. This work shows that the concept of applying PDA with wireless communication technology is a “new cognitive learning tool” to personally access, analyze, interpret, and organize their personal knowledge anytime and anywhere.

A cross-layer protocol of spectrum mobility and handover in cognitive LTE networks

Abstract Cognitive radio technique is the next step toward efficient wireless bandwidth utilization. While some of the spectrum bands (unlicensed band) have been increasingly used, most of the other spectrum resources (licensed band) are underutilized. This drives the challenges of open spectrum and dynamic spectrum access concepts, which allows unlicensed users (or called secondary users, SUs) equipped with cognitive radios to opportunistically access the spectrum not used by licensed users (or called primary users, PUs). Most existing results mainly focus on designing the lower-layer cognitive radio problems. In the literature, this is the first result to investigate the higher-layer solution for cognitive radio networks. In this paper, we present a cross-layer protocol of spectrum mobility (layer-2) and handover (layer-3) in cognitive LTE networks. With the consideration of the Poisson distribution model of spectrum resources, a cross-layer handoff protocol with the minimum expected transmission time is developed in cognitive LTE networks. Performance analysis of the proposed handoff protocol is investigated. Finally, simulation results illustrates the proposed handoff protocol significantly reduces the expected transmission time and the spectrum mobility ratio.

DIR: diagonal-intersection-based routing protocol for vehicular ad hoc networks

In this paper, we present a diagonal-intersection-based routing (DIR) protocol for vehicular ad hoc networks. The DIR protocol constructs a series of diagonal intersections between the source and destination vehicles. The DIR protocol is a geographic routing protocol. Based on the geographic routing protocol, source vehicle geographically forwards data packet toward the first diagonal intersection, second diagonal intersection, and so on, until the last diagonal intersection, and finally geographically reach to the destination vehicle. For given a pair of neighboring diagonal intersections, two or more disjoint sub-paths exist between them. The novel property of DIR protocol is the auto-adjustability, while the auto-adjustability is achieved that one sub-path with low data packet delay, between two neighboring diagonal intersections, is dynamically selected to forward data packets. To reduce the data packet delay, the route is automatically re-routed by the selected sub-path with lowest delay. The proposed DIR protocol allows the mobile source and destination vehicles in the urban VANETs. Experimental results show that the DIR protocol outperforms existing solutions in terms of packet delivery ratio, data packet delay, and throughput.

Seamless session mobility scheme in heterogeneous wireless networks

The next generation wireless communication system will likely be heterogeneous networks, as various technologies can be integrated on heterogeneous networks. A mobile multiple-mode device can easily access the Internet through different wireless interfaces. The mobile multiple-mode device thus could switch to different access points to maintain the robustness of the connection when it can acquire more resources from other heterogeneous wireless networks. The mobile multiple-mode device therefore needs to face the handover problem in such environment. This work introduces Session Initiation Protocol (SIP)-based cross-layer scheme to support seamless handover scheme over heterogeneous networks. The proposed scheme consists of a battery lifetime-based handover policy and cross-layer fast handover scheme, called the SIP-based mobile stream control transmission protocol (SmSCTP). This work describes the major idea of the proposed scheme and infrastructure. The proposed scheme has been implemented in Linux system. The simulation and numerical results demonstrate that the proposed SmSCTP scheme yields better signaling cost, hand-off delay time, packet loss and delay jitter than SIP and mSCTP protocols. Copyright