Mission
Research
Publication
People
Funding
RESEARCH
 

Current projects

Past work

Data dissemination in vehicular ad hoc networks: Vehicular ad hoc networks (VANET) have been envisioned to be useful in road safety and many commercial applications. Although data dissemination techniques have been widely studied in the database community and the network community, many unique characteristics of VANET bring out new research challenges. The specific goal of this project is to provide a unified data dissemination framework for VANET. The proposed research addresses four intertwined issues. First, for infrastructure-assisted data dissemination, we design and evaluate service scheduling protocols, and protocols to efficiently utilization the bandwidth. We also propose a data pouring scheme to push data to the users to reduce the query delay. Second, for infrastructureless data dissemination, we design and evaluate vehicle-assisted data delivery protocols for sparsely connected VANET. Our solution makes use of the predictable mobility in VANET, which is limited by the traffic pattern and the road layout. Third, besides using network support for data dissemination, we also look into user-centric data dissemination to maximize data accessibility to individual users. Finally, we investigate mobility characterization techniques which enable individual vehicles to characterize the fine-grained mobility patterns of their neighbors, which can be used for clustering or finding a stable multi-hop route.

SELECTED PUBLICATIONS (COMPLETE LIST)

  • J. Zhao and G. Cao, "VADD: Vehicle-Assisted Data Delivery in Vehicular Ad Hoc Networks," IEEE Transactions on Vehicular Technology, Vol. 57, No. 3, May 2008. [[PDF]] (Early version appeared in infocom'06).

  • Y. Zhang, J. Zhao, and G. Cao, "On Scheduling Vehicle-Roadside Data Access," The Fourth ACM International Workshop on Vehicular Ad Hoc Networks (VANET) , 2007. [[PDF]]

  • J. Zhao, Y. Zhang, and G. Cao, "Data Pouring and Buffering on The Road: A New Data Dissemination Paradigm for Vehicular Ad Hoc Networks," IEEE Transactions on Vehicular Technology , Volume 56, Issue 6, pp. 3266-3277, November, 2007. [[PDF]]

  • J. Zhao, T. Arnold, Y. Zhang and G. Cao, "Extending Drive-Thru Data Access by Vehicle-to-Vehicle Relay," ACM International Workshop on Vehicular Ad Hoc Networks (VANET) , 2008. [[PDF]]

  • Y. Zhang, J. Zhao and G. Cao, "Roadcast: A Popularity Aware Content Sharing Scheme in VANETs", IEEE International Conference on Distributed Computing Systems (ICDCS), 2009. [[PDF]]

Supporting multi-missions in wireless sensor networks: Wireless sensor networks have been adopted to many military and commercial applications. However, the sensor network envisioned so far is targeted for a single mission and often designed for some particular application. As sensors become widely deployed, multiple missions, each with different requirements, may share common sensors to achieve their goals. Each mission may have its own requirements for the type of data being reported, the sampling rate, accuracy, and location of the sampling. From resource management point of view, it will be cost effective for the wireless sensor network to support multiple missions instead of a single mission. The specific goal of this project is to support multi-missions in wireless sensor networks. The project addresses four intertwined issues: (i) various mission-driven scheduling protocols which can optimize the sensor coverage will be designed, implemented, and evaluated; (ii) novel techniques will be developed to disseminate the mission switch code/command to the affected sensor nodes quickly and efficiently; (iii) mission-driven sensor assignment schemes will be designed to maximize the network utility; (iv) mission-specific network configurations will be investigated to meet the real-time requirements of data transfer for dynamic and competing missions.

SELECTED PUBLICATIONS (COMPLETE LIST)

  • C. Liu and G. Cao, "Minimizing the Cost of Mine Selection Via Sensor Networks," IEEE INFOCOM, 2009. [[PDF]]

  • L. Su, C. Liu, H. Song, and G. Cao, "Routing in Intermittently Connected Sensor Networks," IEEE International Conference on Network Protocols (ICNP) , 2008 [[PDF]]

Security in cellular networks: With the introduction of the iPhone, Openmoko and Android smartphones amongst several others, we see an increasing trend in the mobile devices domain to keep the user always connected to the Internet. At the same time, surveys and research show that there is an increasing number of mobile phone malware. Besides viruses, other types of malware like worms, spyware, adware, trojan horses, backdoors etc. are emerging. Moreover, these mobile phones can be used to exploit the vulnerabilities of the cellular network to launch Denial of Service attacks and battery attacks. Despite the severity of these threats, research on security in cellular networks has not received much attention and many research challenges remain open. This research will investigate device-side and network-side solutions for defending against various security attacks in cellular networks.

SELECTED PUBLICATIONS (COMPLETE LIST)

  • Z. Zhu, G. Cao, S. Zhu, S. Ranjan, A. Nucci, "A Social Network Based Patching Scheme for Worm Containment in Cellular Networks," IEEE INFOCOM, 2009. [[PDF]]

  • B. Zhao, C. Chi, W. Gao, S. Zhu, G. Cao, "A Chain Reaction DoS Attack on 3G Networks: Analysis and Defenses," IEEE INFOCOM, 2009. [[PDF]]

Collaborative data access in wireless P2P networks: Wireless P2P networks such as ad hoc networks, mesh networks and sensor networks have received considerable attention due to their potential applications in many civilian and military environments such as disaster recovery, wireless office, battlefield and outdoor assemblies. Design of such networks considering performance and power optimization has become a recent research focus. As nodes in wireless P2P networks may perform similar tasks using common data sets, cooperative data access, which allows sharing and coordination of cached or replicated data among multiple nodes, can be used to reduce the bandwidth and power consumption. The specific goal of this project is to provide a collaborative data access framework for wireless P2P networks. The proposed research addresses four intertwined issues. First, we design and evaluate two cooperative caching schemes, called CachePath and CacheData. We identify the tradeoffs between these two schemes, and rely on HybridCache to further improve the system performance. Second, various cache replacement and cache admission control algorithms are proposed and evaluated to balance the tradeoffs between access latency and data accessibility. Third, to further reduce the access latency and increase the data accessibility, data replication techniques are designed and evaluated. Finally, we identify possible security violations to maintain data consistency and propose solutions to defend against such attacks.

SELECTED PUBLICATIONS (COMPLETE LIST)

Secure wireless sensor networks: It is a big challenge to secure wireless sensor networks because of the network scale, the highly constrained system resource, and the fact that sensor networks are often deployed in unattended and hostile environments. The objective of this project is to develop a framework for defending against node compromises in unattended sensor networks. The framework consists of a suite of security mechanisms spanning three phases: prevention, detection, and reaction. This research will provide fundamental security services covering key management, authentication, compromise detection, and revocation. These services are essential for the successful deployment of sensor networks. In addition, most of the proposed solutions are designed and implemented in a distributed manner, where no central authority is involved. This distributed property is critical for unattended sensor networks deployed in adversarial environments because the central authority is a single point of failure from security and performance perspectives.

SELECTED PUBLICATIONS (COMPLETE LIST)

  • W. Zhang and G. Cao, "Group Rekeying for Filtering False Data in Sensor Networks: A Predistribution and Local Collaboration-Based Approach," IEEE INFOCOM, March 2005. [PDF]

  • W. Zhang, H. Song, S. Zhu, and G. Cao, "Least Privilege and Privilege Deprivation: Towards Tolerating Mobile Sink Compromises in Wireless Sensor Networks," ACM MOBIHOC, May 2005. [PDF]

  • Y. Yang, X. Wang, S. Zhu, and G. Cao, "SDAP: A Secure Hop-by-Hop Data Aggregation Protocol for Sensor Networks," ACM MobiHoc, May 2006. [PDF]

  • M. Shao, S. Zhu, W. Zhang, and G. Cao, "pDCS: Security and Privacy Support for Data-Centric Sensor Networks," IEEE INFOCOM, 2007. [[PDF]]

  • M. Shao, Y. Yang, S. Zhu, and G. Cao, "Towards Statistically Strong Source Anonymity for Sensor Networks," IEEE Infocom, 2008. [[PDF]]

  • Y. Yang, S. Zhu, and G. Cao. "Improving Sensor Network Immunity under Worm Attacks: A Software Diversity Approach." ACM Mobihoc 2008. [[PDF]]

Mobile sensor networks: Traditional sensor networks have limitations when applied to support multiple missions or when the network conditions change. Mobile sensors can be used to address these problems as mobility can significantly increase the capability of the sensor network by making it resilient to failures, reactive to events, and be able to support disparate missions with a common set of sensors. To support mobility in sensor networks, this project investigates various research issues in mobility assisted sensing, network monitoring, mobility assisted routing, and integrated mobility management for sensing and routing. The expected results from this project are: (i) Significant theoretical and technical advances in supporting mobility in sensor networks; (ii) Understanding various performance and power tradeoffs in designing and implementing sensor relocation protocols; (iii) Development of network monitoring protocols, coverage hole estimation and failure effect estimation protocols; (iv) Theoretical advances on mobility assisted routing; and (v) Understanding of how sensing and routing interact and how to satisfy different mission requirements and maximize the network capability.

SELECTED PUBLICATIONS (COMPLETE LIST)

  • G. Wang, G. Cao, T. La Porta, and W. Zhang, "Sensor Relocation in Mobile Sensor Networks," IEEE INFOCOM, March 2005. [PDF]

  • G. Wang, G. Cao, and T. La Porta, ``Movement-Assisted Sensor Deployment,'' IEEE Transactions on Mobile Computing, Vol. 5, No. 6, pp. 640 - 652, June 2006. [PDF]

  • G. Wang, G. Cao, P. Berman, and T. La Porta, "Bidding Protocols for Deploying Mobile Sensors," IEEE Transactions on Mobile Computing, Vol. 6, No. 5, pp. 515-528, May 2007. [[PDF]]

Data centric sensor networks: Sensor nodes are limited in sensing capacity and are prone to failure, drift and loss of calibration, and hence we can not rely on a single sensor node to obtain reliable data. Instead, multiple nodes should be deployed in close proximity with the target of interest to obtain fine-grained and high-precision data. The involvement of many senor nodes in a sensing task and the constrained energy supply of the sensor nodes pose new challenges for designing scalable, self-organizing, and energy efficient data collection and dissemination schemes in sensor networks. The specific goal of this proposal is to provide a data-centric framework for mobile target tracking and data dissemination in sensor networks. The proposed research addresses three intertwined issues. The first part focuses on building a dynamic convoy tree-based framework for data collection. Tree reconfiguration protocols and collaborative failure detection and recovery schemes will be designed and evaluated considering the energy efficiency and scalability issues. The second part proposes an index-based data dissemination framework. Considering the scalability and reliability issues, an adaptive ring-based index solution will be designed and evaluated. The final part attempts to build a heterogeneous storage structure which allows the collected sensing data to be saved locally. Protocols will be designed to help sensor nodes find local storage, and the tradeoffs between data quality and cost will be investigated.

SELECTED PUBLICATIONS (COMPLETE LIST)

Cache invalidation and power-aware data access: Caching is an effective technique to reduce the query latency, bandwidth and power consumption in mobile environments. When cache is used, cache consistency issues must be addressed. One attractive approach is based on invalidation reports (IR), where the server periodically broadcasts an IR in which the changed data items are indicated. The IR-based solution is attractive because it can tolerate client disconnections and it has good scalability. However, it has some drawbacks such as long query latency and low bandwidth utilization. To reduce the query latency, we proposed to replicate the IR several times. Since the IR contains a large amount of update history information, we proposed an optimization technique which is called updated invalidation report (UIR), to remove the redundancy [Mobicom00]. With the UIR-based model, we designed and evaluated stateful and stateless server approaches to improve the bandwidth utilization by actively prefetching the right data into the local cache. In the stateful server approach [Monet02], a counter is used to identify the most frequently accessed data. Techniques are also proposed to deal with client and server failures. In the stateless server approach [TC02], we proposed novel solutions to organize the broadcast channel to help clients prefetch the right data. Since prefetch consumes power, we investigated the tradeoffs between performance and power [Twireless04], and extended the solution to achieve a balance between performance and power considering various factors such as access rate, update rate, and data size.

SELECTED PUBLICATIONS (COMPLETE LIST)

Resource management in wireless networks: Putting the wireless network interface (WNI) into sleep when the WNI is idle is an effective technique to save power. To support streaming applications, existing techniques cannot put the WNI into sleep due to strict delay requirements. we have proposed a novel power-aware and QoS-aware service model [infocom04b], where mobile nodes use proxies to buffer data so that the WNIs can sleep for a long time period. To achieve power-aware communication while satisfying the delay requirement of each flow, a scheduling scheme is designed to decide which flow should be served at which time. To deal with channel errors, a novel adaptive technique is developed to adjust the sleep time of the WNI according to the channel condition. We are also investigating techniques to improve the performance of Wireless LANs through scheduling. Since wireless LAN supports multiple data rates in response to different channel conditions, data packets may be delivered faster through a relay node than through a direct link if the direct link has low quality and low rate. To enable MAC layer relay, we have designed and evaluated protocols [infocom05] to help mobile nodes collect information about the channel conditions, and notify each other which data rate to use and whether to transmit the data through a relay station.

SELECTED PUBLICATIONS (COMPLETE LIST)

Distributed fault-tolerant computing: Coordinated checkpointing is an attractive approach for transparently adding fault tolerance to distributed applications. We have developed a theory of ``z-dependency'' [TPDS98] to catch the essence of coordinated checkpointing and proved that there does not exist a non-blocking algorithm, which forces only a minimum number of processes to take their checkpoints. Based on this impossibility result, we have proposed a min-process algorithm which relaxes the non-blocking condition while tries to minimize the blocking time, and a non-blocking algorithm [TPDS01] which relaxes the min-process condition while minimizing the number of checkpoints saved on the stable storage. The proposed non-blocking algorithm is based on a novel concept called ``mutable checkpoint'' which is neither a tentative checkpoint nor a permanent checkpoint. Mutable checkpoints can be saved anywhere; e.g., the main memory or local disk of the mobile nodes. In this way, taking a mutable checkpoint avoids the overhead of transferring large amount of data to the stable storage at the base station over the wireless network. We have also designed and evaluated techniques to minimize the number of mutable checkpoints.

SELECTED PUBLICATIONS (COMPLETE LIST)

 

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