Zhiwei Cen

QoS aware wireless bandwidth aggregation (QAWBA) by integrating cellular and ad-hoc networks

Some mobile devices are beginning to support both cellular and IEEE 802.11 based network interfaces. Although rates are increasing, current cellular networks provide relatively low bandwidth that do not meet the QoS requirements of many high-demanding multimedia applications. In this paper, we propose an integrated network architecture that utilizes both wireless interfaces to provide better QoS support by QoS aware wireless bandwidth aggregation (QAWBA). Via QAWBA, mobile nodes form a mobile ad hoc network (MANET) using their IEEE 802.11 interfaces to share their cellular link capacity. Some mobile nodes act as proxies to contribute their idle cellular links to support a QoS request that may exceed the available bandwidth of any individual mobile node. A K-path proxy discovery algorithm is proposed for fast and efficient proxy discovery. Simulation results show that QAWBA can significantly improve network utilization and the admission rate of QoS requests.

Using cooperative multiple paths to reduce file download latency in cellular data networks

Current cellular data networks provide relatively low throughput, which results in long delays when downloading large files. We propose a cooperative parallel file downloading scheme to reduce latency in cellular data networks. Mobile nodes form a mobile ad hoc network (MANET) via their IEEE 802.11-based links to share their cellular link capacity. A file is split into pieces and downloaded simultaneously by the client and several neighbor nodes that act as relay proxies. The proxies then use the MANET to forward packets to the client. Thus, the client uses multiple paths for parallel downloading. No special hardware or modifications on the base stations are needed. An on-demand proxy discovery algorithm is proposed for fast and efficient proxy discovery. Experimental and simulation results show that cooperative parallel file downloading may significantly improve cellular network utilization and file download performance

Supermedia transport for teleoperations over overlay networks

In real-time Internet based teleoperation systems, the operator controls the robot and receives feedback through the Internet. Supermedia refers to robotic control commands, video, audio, haptic feedback, and other sensory information in the control system. Traditional transport services may not be able to meet the timely transmission requirements and dynamic priority changes of supermedia streams. Supermedia TRansport for teleoperations over Overlay Networks (STRON) uses multiple disjoint paths and forward error correction encodings to reduce end-to-end latency for supermedia streams. Network routes and encoding redundancy may be adjusted dynamically to meet the supermedia QoS requirements. NS2 simulations and evaluations using available bandwidth traces from globally distributed computing nodes show that STRON can significantly reduce latency compared with available transport services.

Modeling and design of mobile surveillance networks using a mutational analysis approach

Networked surveillance systems provide an extended perception and distributed reasoning capability in monitored environments through the use of multiple networked sensors. The challenge for such large scale networked systems is to design an efficient modeling and analysis tool and devise stable control algorithms for accomplishing the surveillance task. Current feature (point) based visual servo and tracking techniques generally employed do not provide an optimal solution for the surveillance task. This paper presents a mutational analysis approach for shapes, and shape based control to model and design mechanisms for such active surveillance systems. The techniques of image based Hausdorff tracking and cooperative Hausdorff tracking are introduced. Finally, experimental results demonstrate the efficacy of the proposed approach for tracking targets over a large area.

Relocation of hopping sensors

Hopping sensors are a class of mobile sensors whose mobility design are inspired by creatures such as grasshoppers. Such sensors are able to maintain mobility in harsh terrains but may lack movement accuracy of those sensors that are powered by wheels. We examine the opportunities and challenges for utilizing the mobility of low cost hopping sensors to ensure coverage and maintain energy efficiency within a sensing field. We focus on the problem of transporting a number of hopping sensors from multiple sources to a destination. Probabilistic methods are used to contain the movement inaccuracies along the hopping course. We also consider the impact of wind under an aerodynamic setting. Two transport schemes are designed to minimize the number of hops needed while considering other constraints, such as sustaining the capability of relocating sensors within the whole network. In one scheme we use upper and lower hopping limits to apply the network mobility constraints. The other scheme uses a balancing coefficient to construct a new optimization target to meet the requirement of path optimality and network mobility dynamically. Simulation results show that both schemes work well regardless of the wind factors, while the dynamic scheme is also shown to be resilient to topological changes of the network.

QoS management of supermedia enhanced teleoperation via overlay networks

In supermedia enhanced Internet based teleoperation systems, the data flowing between the operator and the robot include robotic control commands, video, audio, haptic feedback and other media types. The difference between an Internet based teleoperation system and other Internet applications are that (1) there are many media types involved in teleoperation systems and each of them has a particular quality of service (QoS) requirement; and (2) some media types are very latency sensitive. Overlay networks have been proposed to improve the QoS of teleoperation applications. However efficient use the overlay network resources and the distribution of these resources optimally to all supermedia streams remains an important problem. This paper aims to provide a framework of QoS management for teleoperation systems over overlay networks. The validity and performance of the system is evaluated using the PlanetLab overlay network.

Improving the Operation Efficiency of Supermedia Enhanced Internet Based Teleoperation via an Overlay Network

For Internet based real-time teleoperation systems, random time delay can cause instability in the closed loop control system and hence hinder task accomplishment. Event based control systems have been proposed to overcome the instability caused by the random time delay. High latency at the transport layer can still impede effective and reliable execution of tasks with high dexterity requirements. Network QoS based dynamic resource allocation has been proposed to increase the efficiency and reliability of task execution. However, these approaches only try to mitigate or overcome the effects of random time delay and do not address the cause of latency issues in the communication channel. This paper addresses the efficiency and reliability requirements for supermedia enhanced teleoperated systems by reducing the end-to-end transmission latency through the use of overlay networks. The proposed system reduces the transmission latency by using multiple, disjoint paths in overlay networks. The proposed system facilitates reliable and efficient task completion for tasks with high dexterity requirements. Experimental validation of the proposed teleoperated system using the PlanetLab Network is provided for the task of teleoperating a mobile manipulator system.

Supermedia Interface for Internet-based Telediagnostics of Breast Pathology

We present our development of a supermedia interface for telediagnostics of breast pathology via the Internet. Supermedia is the incorporation of multiple media and data streams, such as audio, video, ultrasound images, and tactile and haptic sensor data for enhanced telepresence capabilities. Our supermedia interface comprises an anthropomorphic arm/hand equipped with haptic and tactile sensing, ultrasound imaging capabilities, a physician interface capable of rendering both haptic and tactile information, and two-way audio and video. The supermedia interface was tested via the Internet and enables telediagnostics. Preliminary experiments with silicone breast models have demonstrated the e fectiveness of the supermedia interface for telediagnostics. The interface is expected to enhance and improve the diagnostic performance of breast pathology as well as promote telediagnostics in remote areas and for patients with cultural barriers.

Cooperative multi-target surveillance using a mutational analysis approach

Networked surveillance systems provide an extended perception and distributed sensing capability in monitored environments through the use of multiple networked sensors. The task of tracking multiple targets in a surveillance network is a challenging problem because of the following reasons: (1) multiple targets need to be monitored and tracked continuously so that they would not leave the view of at least one of the sensors; (2) the view of the sensors needs to be optimized so that at a given time the targets are observed with a discernable resolution for feature identification; (3) it is important to devise stable control algorithms for accomplishing the surveillance task. Current feature (point) based visual surveillance and tracking techniques generally employed do not provide an adequate framework to express a surveillance task. This paper presents a mutational analysis approach for shape based control to model a multi-target surveillance scenario. It further presents an optimal multiple sensor task planning algorithm based on the target resolution and priority, to achieve optimal coverage of multiple targets in the sensing region of the surveillance network. Finally, experimental results demonstrate the efficacy of the proposed approach for tracking multiple targets over a large area

Improved transport service for remote sensing and control over wireless networks

In a bilateral teleoperated system, the signal transmissions between the operator and the slave manipulators have different QoS requirements in comparison to traditional network traffic. Running teleoperated systems over wireless networks poses more challenges in comparison to wired networks. The media streams involved differentiate themselves from other media types in that they require both reliable and smooth delivery. Reliable delivery requires the transport service to have TCP style semantics. By being smooth, the transport service should be able to deliver the control and sensing data with bounded and reduced latency and its variation. For example, we have conducted numerous teleoperated experiments using our system. We have found in some of our applications that if the end-to-end latency variance becomes larger than 0.3 second, the operator has difficulty maintaining smooth control of the slave manipulator. However, our simulations show that using TCP, the end-to-end latency variance can be as much as 2.5 seconds in an ad hoc wireless network. This paper proposes an improved transport service for remote sensing and control (TRSC). The service reduces the end-to-end latency and latency variance (jitter) for real-time reliable media in mobile ad hoc networks by using forward error correction encoding and multiple network paths. Simulation using NS2 shows the approach performs well under different wireless scenarios