Lien-Wu Chen

Exploiting Spectral Reuse in Routing, Resource Allocation, and Scheduling for IEEE 802.16 Mesh Networks

The IEEE 802.16 standard for wireless metropolitan area networks (WMANs) is defined to meet the need for wide-range broadband wireless access at low cost. The objective of this paper is to study how to exploit spectral reuse in resource allocation in an IEEE 802.16 mesh network, which includes routing tree construction (RTC), bandwidth allocation, time-slot assignment, and bandwidth guarantee of real-time flows. The proposed spectral reuse framework covers bandwidth allocation at the application layer, RTC and resource sharing at the medium access control (MAC) layer, and channel reuse at the physical layer. To the best of our knowledge, this is the first paper that formally quantifies spectral reuse in IEEE 802.16 mesh networks and exploits spectral efficiency under an integrated framework. Simulation results show that the proposed schemes significantly improve the throughput of IEEE 802.16 mesh networks.

Dynamic Traffic Control with Fairness and Throughput Optimization Using Vehicular Communications

Traffic congestion in modern cities seriously affects our living quality and environments. Inefficient traffic management leads to fuel wastage in volume of billion gallons per year. In this paper, we propose a dynamic traffic control framework using vehicular communications and fine-grained information, such as turning intentions and lane positions of vehicles, to maximize traffic flows and provide fairness among traffic flows. With vehicular communications, the traffic controller at an intersection can collect all fine-grained information before vehicles pass the intersection. Our proposed signal scheduling algorithm considers the flows at all lanes, allocates more durations of green signs to those flows with higher passing rates, and also gives turns to those with lower passing rates for fairness provision. Simulation results show that the proposed framework outperforms existing works by significantly increasing the number of vehicles passing an intersection while keeping average waiting time low for vehicles on non-arterial roads. In addition, we discuss our implementation of an Zigbee-based prototype and experiences.

Exploiting Spectral Reuse in Resource Allocation, Scheduling, and Routing for IEEE 802.16 Mesh Networks

The IEEE 802.16 standard for wireless metropolitan area networks (WMAN) has been created to meet the need of wide-range broadband wireless access at low cost. The objective of this paper is to study how to exploit spectral reuse in an IEEE 802.16 mesh network through timeslot allocation, bandwidth adaptation, hierarchical scheduling, and routing. To the best of our knowledge, this is the first work which formally quantifies spectral reuse in IEEE 802.16 mesh networks and which exploits spectral efficiency under an integrated framework. Simulation results show that the proposed spectral reuse scheduling and load-aware routing significantly enhance the network throughput performance in IEEE 802.16 mesh networks.

Surveillance on-the-road: Vehicular tracking and reporting by V2V communications

Abstract Vehicular networks have attracted a lot of attention recently. One potential application of vehicular networks is to use video cameras embedded in vehicles to support video surveillance, which we call “ surveillance on-the-road ”. Traditional surveillance systems only rely on fixed stations on the roads to monitor road conditions. With vehicular cameras, deeper and richer road conditions may be tracked. In this paper, we study the related communication issues to support such “on-the-road” surveillance scenarios. We use monitoring and tracking suspicious vehicles (such as stolen cars) on the road through license plate recognition (LPR) as an example (our results should be applicable to other scenarios as well). We show how vehicles can work cooperatively through vehicle-to-vehicle (V2V) communications to achieve this goal. With a tracking and a reporting modules, our solution does not rely on infrastructure networks. The tracking module allows handoff of a tracking job to neighboring vehicles as necessary and report of suspicious vehicles to nearby police cars. The reporting module can help guide message flows to avoid flooding the network. Simulation results verify the message efficiency of our approach. We also show how our framework can be applied to the developing WAVE/DSRC (Wireless Access in Vehicular Environments/Dedicated Short Range Communications) standards.

A lane-level cooperative collision avoidance system based on vehicular sensor networks

In this paper, we design and implement a lane-level cooperative collision avoidance (LCCA) system using vehicle-to-vehicle communications. The LCCA system applies vehicular sensor networks to preventing chain vehicle collisions, which allows vehicles with merely onboard sensors to prevent such collisions on the road because of sharp stops. To the best of our knowledge, this is the first CCA system that does not use inaccurate GPS locations and costly roadside infrastructures to avoid chain vehicle collisions. LCCA employs inter-vehicle communications and onboard sensing to form warning groups, where each warning group is a set of vehicles that drive along the same lane and every pair of adjacent cars is within a certain distance. Only single-hop transmissions are needed to join/leave a warning group, thus keeping the group maintenance overhead low. When a sudden braking is taken in a warning group, LCCA can quickly propagate warning messages among group members. This paper demonstrates our current prototype.

Design and analysis of contention-based request schemes for best-effort traffics in IEEE 802.16 networks

The IEEE 802.16 standard is designed to meet the need of metropolitan-area broadband wireless access. This work studies two collision-resolution requesting schemes for best-effort (BE) traffics in IEEE 802.16 networks. One is the exponential backoff scheme defined in the standard and the other is a piggyback mechanism enhanced by single-frame backoff, called the Request Piggyback (RPB) scheme. We analyze and compare their performance in terms of the request success probability and the packet delivery delay under Poisson traffic. The results show that the RPB scheme outperforms the exponential backoff scheme and can reduce request collision.

Intelligent file transfer for smart handheld devices based on mobile cloud computing

Summary Most methods of file transfer between mobile devices have to take considerable time to obtain and input target identifiers. To speed up file sharing of mobile devices, an intelligent file transfer framework is designed based on mobile cloud computing. Only single-finger action is performed in the proposed framework, which just drags the file to the target face on the touchscreen of a mobile device. The dragged file can be transmitted to the target receiver who can either get the file immediately as her/his mobile device is online or receive the file later after connecting to the Internet. Our framework provides the following features: (i) users do not need to know the target identifier in advance; (ii) users do not need to input identity information by themselves; and (iii) users can select a specific target among multiple candidates from the camera of a mobile device. The intelligent file transfer framework reveals an efficient architecture and innovative user interfaces to transfer files between mobile devices, which can significantly reduce the complexity and difficulty of file sharing. An Android-based prototype is implemented to verify the feasibility and superiority of our framework. Experimental results show that our approach outperforms existing schemes and can save large amounts of time in file sharing for mobile users. Copyright

A vehicular surveillance and sensing system for car security and tracking applications

In this paper, we propose a Vehicular Surveillance and Sensing System (VS3), which targets at car security and tracking applications. VS3 can be triggered by events detected inside or outside a car, such as abnormal air quality, potential burglary, and identification of some target vehicles (such as stolen cars). Via a 3G module, a user can interact with VS3 via multimedia communications. For security applications, we show how VS3 detects an abnormal CO2 level or potential car burglary, notifies the vehicle owner, and then interacts with the owner. For tracking applications, we show how VS3 identifies potential stolen vehicles, transmits reports to the police department, and get neighboring cars involved to cooperatively track suspicious vehicles. This paper demonstrates our current prototype.

LEGS: A Load-balancing Emergency Guiding System based on wireless sensor networks

LEGS is a Load-balancing Emergency Guiding System using a wireless sensor network. In LEGS, we design a load-balancing guiding scheme and derive an analytical model in order to reduce the total evacuation time of people. The proposed guiding scheme can provide the fastest path to an exit based on the evacuation time estimated by the derived analytical model. To the best of our knowledge, LEGS is the first system which takes the corridor capacity and length, exit capacity, and people distribution into consideration for analyzing evacuation time and planning escape paths. Through LEGS, the congestion of certain corridors and exits can be released to significantly reduce the evacuation time of people. Analytical and simulation results show that LEGS outperforms existing works, which can prevent people from following the local optimal guiding direction with the longer evacuation time in total. LEGS thus demonstrates an efficient emergency guiding system for public safety.

Distributed Emergency Guiding with Evacuation Time Optimization Based on Wireless Sensor Networks

This paper proposes a load-balancing framework for distributed emergency guiding based on wireless sensor networks. A load-balancing guiding scheme is designed and an analytical model is derived to reduce the total evacuation time of people indoors. The guiding scheme can provide the fastest path for people to reach an exit according to the evacuation time estimated using the analytical model. Based on thorough research, this is the first distributed solution in which corridor capacity and length, exit capacity, and the concurrent movement and distribution of people are considered in estimating the evacuation time and planning escape paths. Using the proposed framework, congestion in corridors and at exits can be eased to substantially reduce the total evacuation time. Analytical and simulation results show that this approach outperforms existing schemes and can prevent people from following localoptimal guiding directions that increase the evacuation time. A prototype called the Load-balancing Emergency Guiding System (LEGS) is implemented; this system can be used to compare the evacuation times and guiding directions provided by existing schemes and the proposed scheme for various distributions of people.