Research Activites

|| Home | Publication List | Teaching | Calit2 | Networking Lab | Curriculum Vitae ||

Prof. Bao's research interests extend over five areas in wireless networks, based on both analytic frameworks and empirical results.
  1. MAC protocol design and evaluation
  2. Routing protocols
  3. Mobility management
  4. Localization algorithms
  5. Network security provisioning
In additional to using the widely adopted network simulators, such as NS2 and NCTUns, our research laboratory establishes and utilizes wide array of experimental testbeds, such as SDR nodes based on GNU Radio and USRP, multiple wireless mesh routers based on COTS devices and open-source projects, as well as the public PlanetLab site at UCI.

1) MAC Protocol Design

Wireless networks, especially in multi-hop networking scenarios, are constrained by the limited communication channel capacity, governed by Shannon’s law. On the other hand, ever-increasing demands on data throughput squeeze out any budget dedicated to channel access coordination functions in the distributed environments. Traditional approaches to efficient channel access control have branched out in two directions – randomized that allows collision-tolerant distributed channel access control, or scheduled that generates conflict-free transmission schedule at the cost of high system coordination overhead. An ideal solution that achieves efficient conflict-free transmission schedule with minimum amount of system coordination overhead is the “Holy Grail” in MAC protocol design area. We have made significant contributions towards the goal.

Besides the traditional channel access coordination problems in homogeneous wireless networks, we brought up new MAC problems for heterogeneous wireless systems, in which different wireless systems, such as WiFi and GSM, share the same channel in a TDMA fashion, uniquely different from cognitive radio to solve the spectrum scarcity problem. Heterogeneous wireless system coexistence is supported by NSF (2007-2010).

  • L. Bao and S. Liao, “Temporal Spectrum Access Scheduling in Heterogeneous Wireless Systems”, accepted for publication in The International Conference on Information Networking (ICOIN), Busan, Korea, 2009.
  • S. Liao and L. Bao, “Spatial Spectrum Reuse in Heterogeneous Wireless Systems”, accepted for publication in The International Conference on Information Networking (ICOIN), Busan, Korea, 2009.
  • L. Bao and S. Liao, “Spectrum Access Scheduling among Heterogeneous Wireless Systems”, accepted for publication as a book chapter in Emerging Wireless Networks: Concepts, Techniques and Applications, ed. C. Makaya and S. Pierre, Auerbach Publications, Taylor & Francis Group, 2009.
  • L. Bao and S. Liao, "Scheduling Heterogeneous Wireless Systems for Efficient Spectrum Access", accepted for publication in EURASIP Journal on Wireless Communications and Networking, special issue on Wireless Network Algorithms, Systems, and Applications, 2010.
  • L. Bao, S. Liao and E. Bozorgzadeh, "Spectrum Access Scheduling among Heterogeneous Wireless Systems", accepted for publication by SDR Forum Technical Conference and Product Exposition (SDR), Washington, DC, 2009.
  • S. Liao and L. Bao, "Implementing a Base Station Using the SDR Platform for Coexistence of Heterogeneous Wireless Systems", Demo accepted for presentation in SDR Forum Technical Conference and Product Exposition (SDR), Washington, DC, 2009.
  • A. Gholamipour, E. Bozorgzadeh and L. Bao, "Seamless Sequence of Software Defined Radio Designs through Hardware Reconfigurability of FPGAs", The International Conference on Computer Design (ICCD), Lake Tahoe, CA, Oct. 12-15, 2008.

Additionally, we also designed channel sharing scheme in the SDMA (spatial division multiple access) fashion for heterogeneous wireless systems coexistence, and derived analytic and experimental results in order to deploy DSSS-based WiFi systems in the communication channels used by the GSM systems.

2) Routing Protocol Design

We have done extensive research in designing routing protocols for wireless ad hoc and sensor networks under special constraints, such as unidirectional link, underground tunnel environments or dense ad hoc and sensor network deployments. A related topic, topology management, was extensively studied in our research group as well. One of the publications on topology management was actually one of three key references in the DoD Navy SBIR proposal solicitation Topic N08-198 SPAWAR, directed by Mr. Steve Stewart.

3) Mobility Management

Freedom to roam in wireless networks comes at the complexity of mobility management on both end-user mobile devices and the network infrastructure backbone. Among possible solutions at each layer of the networking stack, we addressed the issues at layer-2, the DLL (data link layer), and proposed a Personal AP protocol to hide the mobility management details from the mobile devices by moving the layer-two mobile-to-network communication contexts to the APs that currently associate with the mobile station.

In order to track the topology locations of mobile hosts, we also proposed a distributed packet traceback mechanism using Bloom filters, called CAPTRA (CoordinAted Packet Traceback), by taking advantage of open-air transmission characteristics of wireless media so that wireless nodes observing packets in the channel may help packet tracking and tracing operations later.

  • D. Sy and L. Bao, " CAPTRA: CoordinAted Packet TRAceback", The Fifth International Conference on Information Processing in Sensor Networks (IPSN), Nashville, TN, April 19-21, 2006.

4) Localization Algorithms

Location information is crucial in wireless network management and applications. we have worked on two localization algorithms for target tracking and networking mapping, respectively. These applications present opposite goals for localization algorithms – the first one usually uses multiple reference locations to collectively identify the location of a single node, whereas the latter uses a single mobile node to identify the locations of multiple other network stations, sometimes even without the knowledge of the number of these target nodes.

  • D. Wu, L. Bao and R. Li, "UWB-Based Localization in Wireless Sensor Networks", International Journal of Communications, Network and System Sciences  (IJCNS), Scientific Research Publishing, Inc. 2009.
  • D. Wu, R. Li and L. Bao, "UWB-Based Localization in Wireless Sensor Networks", The 5th International Conference on Mobile Ad-hoc and Sensor Networks (MSN), 2009.
  • Y. Zhang, L. Bao, M. Welling and S.H. Yang, "Base Station Localization in Search of Empty Spectrum Spaces for Cognitive Radio Networks", The 5th International Conference on Mobile Ad-hoc and Sensor Networks (MSN), 2009.
  • D. Wu and L. Bao, "Design and Evaluation of Localization Protocols and Algorithms in Wireless Sensor Networks Using UWB", in Proc. of the 27th International Performance Computing and Communications Conference (IPCCC), Austin, TX, Dec. 7-9, 2008.

A derivative work on the localization algorithms was to solve the location-dependent network coverage problems in WSNs. we have designed probabilistic algorithms to maintain sufficient sensing coverage in the network while reducing the energy consumption of WSNs. One of the papers received the IFIP Best Paper Award in EUC’05.

5) Network Security

Our work on provisioning network security focused on two areas – anonymous routing and network access control in wireless ad hoc networks. Our work on anonymous routing was the first to use Bloom filters as a routing mechanism in wireless networks.

Our work on network access control was a novel application of our prior research on mobility management (Personal AP) for location-based network access control purposes.

Lichun Bao