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Selected Publications:

Spectrum Management and Optimization in Wireless Networks

The increased number of networked devices and the broadband nature of usage demands in next-generation heterogeneous wireless networks, coupled with the continuing scarcity of wireless bandwidth, will aggravate the need for efficient spectrum sharing. The goal of this research is to develop efficient network architecture and medium access control protocols that integrate the latest hardware and signal processing technologies for optimal bandwidth allocation and scheduling in high-throughput and hybrid/overlapped networking environments.

• M. Lotfinezhad, B. Liang, and E. Sousa, “On stability region and delay performance of linear-memory randomized scheduling for time-varying networks,” in press, to appear in the IEEE/ACM Transactions on Networking.
• M. Lotfinezhad, B. Liang, and E. Sousa, “Dynamic control of tunable sub-optimal algorithms for scheduling of time-varying wireless networks,” in Proceedings of the IEEE International Workshop on Quality of Service (IWQoS), Enschede, The Netherlands, June 2008.
• A. So and B. Liang, “Optimal placement and channel assignment of relay stations in heterogeneous wireless mesh networks by modified Bender's decomposition,” Elsevier Ad Hoc Networks, vol. 7, no. 1, pp. 118 – 135, January 2009. (invited from IFIP Networking 2007)
• B. Liang and M. Dong, “Packet prioritization in multihop latency aware scheduling for delay constrained communication,” IEEE Journal on Selected Areas in Communications, Special Issue on Cross-Layer Optimized Wireless Multimedia Communications, vol. 25, no. 4, pp. 819-930, May 2007.
• A. So and B. Liang, “Enhancing WLAN capacity by strategic placement of tetherless relay points,” IEEE Transactions on Mobile Computing, vol. 6, no. 5, pp. 522-535, May 2007.
• A. So and B. Liang, “An efficient wireless extension point placement algorithm in urban rectilineal WLANs,” IEEE Transactions on Vehicular Technology, vol. 47, no. 1, pp. 532 – 547, January 2008.
• J. Eshet and B. Liang, “Randomly ranked mini slots for fair and efficient medium access control in ad hoc networks,” IEEE Transactions on Mobile Computing, vol. 6, no. 5, pp. 481-493, May 2007.

Distributed Data Dissemination in Multihop Wireless Networks

The main challenge in large-scale multihop wireless networking is to ensure the reliable and efficient transmission of high-bandwidth and mission-critical data, across multiple hops of unstable wireless links and through energy-limited and potentially uncooperative peers. A successful system design must allow dynamic adaptation to the time-varying characteristics of different layers of the network protocol stack. The goal of this research is to develop novel distributed computing theories and techniques for peer-to-peer communication and to promote cross-layer design for optimal network operation.

• Y. Lin, B. Liang, and B. Li, “Passive loss inference in wireless sensor networks based on network coding,” to be presented in the IEEE Conference on Computer Communications (INFOCOM), Rio de Janeiro, Brazil, April 2009.
• Y. Lin, B. Liang, and B. Li, “Priority random linear codes in distributed storage systems,” accepted for publication in the IEEE Transactions on Parallel and Distributed Systems.
• Y. Lin, B. Li, and B. Liang. “CodeOR: opportunistic routing in wireless mesh networks with segmented network coding,” in Proceedings of the 16th IEEE International Conference on Network Protocols (ICNP), Orlando, Florida, October 2008.
• Y. Lin, B. Liang, and B. Li, "Geometric random linear codes in sensor networks," in Proceedings of the IEEE International Conference on Communications (ICC), Beijing, China, May 2008.
• Y. Lin, B. Li, and B. Liang, "Efficient network coded data transmissions in disruption tolerant networks," in Proceedings of IEEE INFOCOM, Pheonix, Arizona, April 2008.
• Y. Lin, B. Li, and B. Liang, "Stochastic analysis of network coding in epidemic routing," IEEE Journal on Selected Areas in Communications, Special Issue on Delay and Disruption Tolerant Wireless Communication Systems, vol. 26, no. 5, pp. 794 – 808, June 2008.
• Y. Lin, B. Li, and B. Liang, "Differentiated data persistence with priority random linear codes," in Proceedings of the IEEE International Conference on Distributed Computing Systems (ICDCS), June 2007.
• Y. Lin, B. Liang, and B. Li, "Data persistence in large-scale sensor networks with decentralized fountain codes," in Proceedings of IEEE INFOCOM, May 2007. (This version contains post-publication corrections.)
• B. Liang and M. Dong, “Balancing distance and lifetime in delay constrained ad hoc networks,” in Proceedings of the ACM International Symposium on Mobile Ad Hoc Networking and Computing (MobiHoc), Florence, Italy, May 2006, pp. 97 – 107. (Extended version in IEEE JSAC)
• B. Liang and Z. J. Haas, “Hybrid routing in ad hoc networks with a dynamic virtual backbone,” IEEE Transactions on Wireless Communications, vol. 5, no. 6, pp. 1392-1405, June 2006.
• B. Liang and Z. J. Haas, "Optimizing route-cache lifetime in ad hoc networks," in Proceedings of the 22th IEEE INFOCOM, San Francisco, CA, April 2003.
• Z. J. Haas, J. Deng, B. Liang, P. Papadimitratos, and S. Sajama, "Wireless Ad Hoc Networks," in Wiley Encyclopedia of Telecommunications, John G. Proakis, Editor, John Wiley & Sons, New York, 2002.
• B. Liang and Z. J. Haas, "Virtual backbone generation and maintenance for ad hoc network mobility management," in Proceedings of the 19th IEEE INFOCOM, Tel Aviv, Israel, March 2000.
• Z. J. Haas and B. Liang, “Ad-hoc mobility management with randomized database groups,” Proceedings of the IEEE International Conference on Communications (ICC), Vancouver, BC, Canada, June 1999. 
• Z. J. Haas and B. Liang, “Ad hoc mobility management with Uniform Quorum Systems,” IEEE/ACM Transactions on Networking, vol. 7, no. 2, pp. 228-240, April 1999.

Peer Cooperation in Wireless Communication Networks

Collaborative network participants can jointly achieve advanced networking functions beyond simple relaying of data packets. They enable distributed network reconfiguration and autonomous tuning of software and hardware among peers, to support diverse and evolving application requirements and networking environments. However, the combination of mutual interference, network scale, decentralized control, and possible multihop radio instability, brings new challenges to the paradigm of intelligent collaboration in future generation wireless networks. The goal of this research is to create new theories and technologies toward promoting intelligent collaboration among the peer devices in a wireless system. We aim toward achieving efficient provisioning of resources and services, leveraging the benefit of joint-communication and joint-processing power of multiple wireless devices in proximity.

• M. Hajiaghayi, M. Dong, and B. Liang, “Using limited feedback in power allocation design for a two-hop relay OFDM system,” to be presented in the IEEE International Conference on Communications (ICC), Dresden, Germany, June 2009.
• S. Vakil and B. Liang, “Effect of joint cooperation and multi-hopping on the capacity of wireless networks,” in Proceedings of the IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks (SECON), San Francisco, California, 2008. Extended version at http://arxiv.org/abs/0805.3569
• S. Vakil and B. Liang, "Decentralized multiuser diversity with cooperative relaying in wireless sensor networks," in Proceedings of the IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks (SECON), June 2007.
• S. Vakil and B. Liang, “Cooperative diversity in interference limited wireless networks,” IEEE Transactions on Wireless Communications, vol. 7, no. 8, pp. 3185 – 3195, August 2008.

Adaptive Mobility Management for Wireless Inter-networking

Wireless technologies beyond the third generation are evolving toward real-time multimedia information access across multiple platforms. In order to support the ubiquitous availability of broadband applications, multiple access technologies, including the wired Internet, cellular networks, wireless local area networks, and mobile ad hoc networks, are expected to co-exist and interoperate, since no single system meets the ideal of high bandwidth, universal availability, and low cost. The goal of this research is to provide innovative solutions to network inter-connectivity and wireless resource management, so as to allow efficient and transparent services to multimedia users across heterogeneous networking platforms.

• A. Farbod and B. Liang, “Structured admission control policies in heterogeneous wireless networks with mesh underlay,” to be presented in the IEEE Conference on Computer Communications (INFOCOM), Rio de Janeiro, Brazil, April 2009.
• A. H. Zahran, B. Liang, and A. Saleh, “Mobility modeling and performance evaluation of heterogeneous wireless networks,” IEEE Transactions on Mobile Computing, vol. 7, no. 8, pp. 1041 – 1056, August 2008.
• A. H. Zahran and B. Liang, “A generic framework for mobility modeling and performance analysis in next-generation heterogeneous wireless networks,” IEEE Communications Magazine, vol. 45, no. 9, pp. 92 - 99, September 2007.
• A. Farbod and B. Liang, “Efficient structured policies for admission control in heterogeneous wireless networks,” ACM/Springer Mobile Networks and Applications, vol. 12, no. 5, pp. 309 – 323, December 2007.
• A. H. Zahran, B. Liang, and A. Saleh, "Impact of technology overlap in next-generation wireless heterogeneous systems," in Proceedings of IFIP Networking, Atlanta, Georgia,  May 2007.
• A. H. Zahran, B. Liang, and A. Saleh, “Signal threshold adaptation for vertical handoff in heterogeneous wireless networks,” ACM/Spring Mobile Networks and Applications, Special Issue on Soft Radio Enabled Heterogeneous Networks, vol. 11, no. 4, pp. 625-640, August 2006.
  
• B. Liang and Z. J. Haas, “Predictive distance-based mobility management for multi-dimensional PCS metworks,” IEEE/ACM Transactions on Networking, vol. 11, no. 5, pp. 718-732, October 2003.

Transmission and Topology Control for Multimedia Streaming Applications and Services

Multimedia streaming applications and services impose difficult constraints on network design, requiring high bandwidth, low latency, and stable data transfer for smooth playback. These challenges are compounded with the prevalence of limited-bandwidth and unstable wireless access to support free mobility. The goal of this research is to develop new theories and algorithms for transmitting and receiving streaming data over time-varying pathways, based on a fundamental understanding of the tradeoffs among different system parameters including memory usage, playback delay, jitter tolerance, and computational complexity.

• G. Ji and B. Liang, “Buffer schemes for VBR video streaming over heterogeneous wireless networks,” to be presented in the IEEE International Conference on Communications (ICC), Dresden, Germany, June 2009.
• T. Small, B. Li, and B. Liang, "Topology affects the efficiency of network coding in peer-to-peer networks," in Proceedings of the IEEE International Conference on Communications (ICC), Beijing, China, May 2008.
• G. Liang and B. Liang, "Balancing interruption frequency and buffering penalties in VBR video streaming," in Proceedings of IEEE INFOCOM, Anchorage, Alaska, May 2007.
• T. Small, B. Liang, and B. Li. "Scaling laws and tradeoffs in peer-to-peer live multimedia streaming," in Proceedings of ACM Multimedia, Santa Barbara, California, October 2006.
• G. Liang and B. Liang, “Effect of delay and buffering on jitter-free streaming over random VBR channels,” IEEE Transactions on Multimedia, vol. 10, no. 6, pp. 1128 – 1141, October 2008.
• T. Small, B. Li, and B. Liang, “Outreach: peer-to-peer topology construction towards minimized server bandwidth costs,” IEEE Journal on Selected Areas in Communications, Special Issue on Peer-to-Peer Communications and Applications, vol. 25, no. 1, pp. 35-45, January 2007.

Cooperation and Clustering for Data Aggregation and Reconstruction in Sensor Networks

Cooperation and clustering are motivated by the need for scalability in large sensor networks, where the absence of centralized infrastructure and limited availability of power regeneration impose severe constraints on large-scale network operation. The goal of this research is to generate novel network architectures, network protocols, and analytical tools, for optimal distributed cooperation and clustering, in order to locally emulate centralized network functions and to leverage the correlation between different samples of a signal field.

• M. Lotfinezhad, B. Liang, and E. Sousa, “Adaptive cluster-based data collection in sensor networks with direct sink access,” IEEE Transactions on Mobile Computing, vol. 7, no. 7, pp. 884 – 897, July 2008.
• K. Yuen, B. Liang, and B. Li, “A distributed framework for correlated data gathering in sensor networks,” IEEE Transactions on Vehicular Technology, vol. 57, no. 1, pp. 578 – 593, January 2008.
• M. Lotfinezhad and B. Liang, “Effect of partially correlated data on clustering in wireless sensor networks,” in Proceedings of the IEEE International Conference on Sensor and Ad hoc Communications and Networks (SECON), Santa Clara, California, October 2004.

Data Caching and Prefetching for Multimedia Networking and System Integration

In order to optimize uninterrupted service within and across heterogeneous access networks, network and user data should be replicated at strategically chosen locations within an integrated system. Duplication and distribution are key to robust information storage and retrieval, particularly under the volatile communication environment prevalent in wireless networks. The goal of this research is to develop efficient caching and prefetching algorithms for optimal network integration.

• J. Lau and B. Liang, “Optimal pricing for selfish users and prefetching in heterogeneous wireless networks,” in Proceedings of the IEEE International Conference on Communications (ICC), June 2007.
• B. Liang, S. Drew, and D. Wang, “Performance of multiuser network-aware prefetching in heterogeneous wireless systems,” ACM/Springer Wireless Networks, vol. 16, no. 1, pp. 99 – 110, January 2009 (Online First edition appeared February 2007).
  
• Y. Fang, Z. J. Haas, B. Liang, and Y.-B. Lin, “TTL prediction schemes and effects of inter-update time distribution on wireless data access,” ACM/Kluwer Wireless Networks, vol. 10, no. 5, pp. 607–619, September 2004.