Research Interests and Projects  (Full list of publications)

• Cyber-Physical Systems
• Real-time and embedded systems
• Server, Data Center, and Internet technologies

• Lui Sha, Sathish Gopalakrishnan, Xue Liu, Qixin Wang, "Cyber-Physical Systems: A New Frontier," in Proceedings of the IEEE International Conference on Sensor Networks, Ubiquitous, and Trustworthy Computing (SUTC 2008), Taichung, Taiwan, 2008 
• Zhong Xu, Xue Liu, Guoqing Zhang, Wenbo He, Guanzhong Dai, Weihuan Shu, "A Certificateless Signature Scheme for Mobile Wireless Cyber-Physical Systems," in Proceedings of the First International Workshop on Cyber-Physical Systems, in conjunction with ICDCS 2008, Beijing, China. (Acceptance rate 27%) 

• Xue Liu, Jin Heo, Lui Sha, Xiaoyun Zhu, "Queueing-Model-Based Adaptive Control of Multi-Tiered Web Applications, " in IEEE Transactions on Network and Service Management, 2009
• Jianguo Yao, Xue Liu, Mingxuan Yuan, Zonghua Gu, "Online Adaptive Utilization Control for Real-Time Embedded Multiprocessor Systems," in Proceedings of the 6th International Conference on Hardware-Software Codesign and System Synthesis (CODES+ISSS'08), Atlanta, Georgia, 2008
• Xue Liu, Xiaoyun Zhu, Jianguo Yao, Zhikui Wang, Sharad Singhal, "Simplified Control for Complex IT Systems Using Dimension Reduction, " in Proceedings of the Third International Workshop on Feedback Control Implementation and Design (FeBID'08), in conjunction with ACM SIGMETRICS'08, Annapolis, Maryland, 2008
• Wenbo He, Klara Nahrstedt, Xue Liu, "End-to-End Delay Control of Multimedia Applications over Multi-hop Wireless Links," in ACM Transactions on Multimedia Computing, Communications and Applications (TOMCCAP),
• Xue Liu, Xiaoyun Zhu, Pradeep Padala, Zhikui Wang, Sharad Singhal, "Optimal Multivariate Control for Differentiated Services on a Shared Hosting Platform," in Proceedings of the 46th IEEE Conference on Decision and Control (CDC'07), New Orleans, LA, 2007. 
• Xue Liu, Wenbo He, "Active Queue Management Design Using Discrete-Event Control," in Proceedings of the 46th IEEE Conference on Decision and Control (CDC'07), New Orleans, LA, 2007. 
• Zhikui Wang, Xue Liu, Alex Zhang, Chris Stewart, Xiaoyun Zhu, Terence Kelly, Sharad Singhal, "AutoParam: Automated Control of Application-Level Performance in Virtualized Server Environments," in Second IEEE International Workshop on Feedback Control Implementation and Design in Computing Systems and Networks (FeBID'07), co-located with IM 2007 Munich, Germany, 2007.
• Wenbo He, Xue Liu, Klara Nahrstedt, "A Feedback Control Scheme for Resource Allocation in Wireless Multi-hop Ad Hoc Networks," in Proceedings of the Second Annual International Conference on Mobile and Ubiquitous Systems (MobiQuitous 2005), San Diego, California, 2005.
• Xue Liu, Xiaoyun Zhu, Sharad Singhal, Martin Arlitt, "Adaptive Entitlement Control to Resource Containers on Shared Servers," in Proceedings of the 9th IFIP/IEEE International Symposium on  Integrated Network Management (IM 2005), Nice, France, 2005. (Acceptance rate = 23.5%)
• Ying Lu, Tarek Abdelzaher, Chenyang Lu, Lui Sha, Xue Liu, "Feedback Control with Queueing-Theoretic Prediction for Relative Delay Guarantees in Web Servers," in Proceedings of the 9th IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS 2003), Washington DC, 2003.
• Lui Sha, Xue Liu, Ying Lu, Tarek Abdelzaher, "Queuing Model Based Network Server Performance Control,"  in Proceedings of the 23th  IEEE Real-Time Systems Symposium (RTSS 2002), Austin, TX, Dec., 2002.

• Jianguo Yao, Xue Liu, Mingxuan Yuan, Zonghua Gu, "Online Adaptive Utilization Control for Real-Time Embedded Multiprocessor Systems," in Proceedings of the 6th International Conference on Hardware-Software Codesign and System Synthesis (CODES+ISSS'08), Atlanta, Georgia, 2008
• Qixin Wang, Sathish Gopalakrishnan, Xue Liu, and Lui Sha, "A Switch Design for Real-Time Industrial Networks," in Proceedings of  the 14th IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS 2008), Saint Louis, MO, 2008
• Pavithra Prabhakar, Peter Csaba Olveczky, Xue Liu, "Formal Modeling and Analysis of Real-Time Resource-Sharing Protocols in Real-Time Maude," in Proceedings of  the 16th International Workshop on Parallel and Distributed Real-Time Systems (WPDRTS 2008), Miami, FL
• Qixin Wang, Xue Liu, Jennifer Hou, Lui Sha, "GD-Aggregate: A WAN Virtual Topology Building Tool for Hard Real-Time and Embedded Applications," in Proceedings of the 28th IEEE Real-Time Systems Symposium (RTSS'07), Tucson, Arizona, 2007.
• Chengdu Huang, Tarek Abdelzaher, Xue Liu, "On Dominating Set Allocation Policies in Real-Time Wide-Area Distributed Systems," in Proceedings of the the 19th Euromicro Conference on Real-Time Systems (ECRTS'07), Pisa, Italy, 2007. 
• Xue Liu, Tarek Abdelzaher, "Non-Utilization Bounds and Feasible Regions for Arbitrary Fixed-Priority Policies," in ACM Transactions on Embedded Computing Systems (TECS), to appear, 2007.
• Ramesh Chandra, Xue Liu, Lui Sha, "On the Scheduling of Flexible and Reliable Real-Time Control System," in Real-Time Systems Journal, Vol. 24 (2), 2003.

• Jin Heo, Dan Henriksson, Xue Liu, Tarek Abdelzaher, "Integrating Adaptive Components: An Emerging Challenge in Performance-Adaptive Systems and a Server Farm Case-Study," in Proceedings of the 28th IEEE Real-Time Systems Symposium (RTSS'07), Tucson, Arizona, 2007.
• Tibor Horvath, Tarek Abdelzaher, Kevin Skadron, Xue Liu, "Dynamic Voltage Scaling in Multi-tier Web Servers with End-to-end Delay Control," in IEEE Transactions on Computers (ToC), vol. 56, pp. 444-458, 2007. 

• Weihuan Shu, Xue Liu, Zonghua Gu, Sathish Gopalakrishnan, "Optimal Sampling Rate Assignment with Dynamic Route Selection for Real-Time  Wireless Sensor Networks, " in Proceedings of the 29th IEEE Real-Time Systems Symposium (RTSS 2008), Barcelona, Spain, 2008
• Wei Dong, Chun Chen, Xue Liu, Kougen Zheng, Rui Chu, Jiajun Bu, "FIT: A Flexible, LIght-Weight, and Real-Time Scheduling System for Wireless Sensor Platforms," in Proceedings of the 4th International Conference on Distributed Computing in Sensor Systems (DCOSS 2008), Santorini Island, Greece, 2008  (Acceptance rate 25%)
• Qixin Wang, Rong Zheng, Ajay Tirumala, Xue Liu, and Lui Sha, "Lightning: A Hard Real-Time, Fast, and Lightweight Low-End Wireless Sensor Election Protocol for Acoustic Event Localization," in IEEE Transactions on Mobile Computing (TMC),Vol. 7, Issue 5, pp570-584, May, 2008 (Selected as the Featured Article of IEEE TMC 2008 May Issue )
• Xue Liu, Qixin Wang, Wenbo He, Marco Caccamo, Lui Sha, "Optimal Real-Time Sampling Rate Assignment for Wireless Sensor Networks," in ACM Transactions on Sensor Networks (TOSN), Vol. 2(2), pp. 263-295, 2006

• Yuan Chen, Subu Iyer, Xue Liu, Dejan Milojicic, Akhil Sahai, "Translating Service Level Objectives to lower level policies for multi-tier services," in Journal of Cluster Computing, Springer Netherlands, 2008. (to appear)
• Jin Heo, Xue Liu, Lui Sha, Tarek Abdelzaher, "Autonomous Delay Regulation for Multi-Threaded Internet Servers", in 2006 International Symposium on Performance Evaluation of Computer and Telecommunication Systems (SPECTS 2006), Calgary, Canada.
• Xue Liu, Jin Heo, Lui Sha, "Modeling 3-Tiered Web Applications," in Proceedings of the 13th  IEEE International Symposium on Modeling, Analysis, and Simulation of Computer and Telecommunication Systems (MASCOTS 2005), Short Ppaer, Atlanta, Georgia, 2005.
• Xue Liu, Lui Sha, Yixin Diao, Steve Froehlich, Joseph Hellerstein, Sujay Parekh, "Online Response Time Optimization of Apache Web Server," in Proceedings of the 11th International Workshop on Quality of Service (IWQoS 2003), Monterey, CA, 2003. (Acceptance rate, 18.9% for 2002, 19.5% for 2004)

• Wenbo He, Hoang Nguyen, Xue Liu, Klara Nahrstedt, Tarek Abdelzaher "iPDA: An Integrity-Protecting Private Data Aggregation Scheme for Wireless Sensor Networks," in Proceedings of the 2008 Military Communications Conference (MILCOM 2008), San Diego, CA, 2008
•  Junhai Luo, Xue Liu, Yi Zhang, Danxia Ye, Zhong Xu, "Fuzzy Trust Recommendation Based on Collaborative Filtering for Mobile Ad-hoc Networks," in Proceedings of the 33rd Annual IEEE Conference on Local Computer Networks  (LCN 2008), Montreal, QC, Canada, 2008
• Wenbo He, Xue Liu, Hoang Nguyen, Klara Nahrstedt, Tarek Abdelzaher, "PDA: Privacy-preserving Data Aggregation in Wireless Sensor Networks, " in Proceedings of the 26th Annual IEEE Conference on Computer Communications (INFOCOM 2007), Anchorage, Alaska, May 2007. (Acceptance rate = 18%).  

• Xue Liu, Qixin Wang, Sathish Gopalakrishnan, Wenbo He, Lui Sha, Hui Ding, Kihwal Lee, "ORTEGA: An Efficient and Flexible Online Fault Tolerance Architecture for Real-Time Control Systems," in IEEE Transactions on Industrial Informatics (TII), Vol 4, No. 4, pp 213-224, 2008 ( Best Paper Award of  IEEE TII 2008)
• Long Zheng, Xue Liu, Jinglun Zhou, "Frequency-Domain Reliability Analysis and Modeling of Networked Control Systems,” in Proceedings of the Third International Workshop on Feedback Control Implementation and Design (FeBID'08), in conjunction with ACM SIGMETRICS'08, Annapolis, Maryland, 2008

• Qixin Wang, Xue Liu, Weiqun Chen, Lui Sha, Marco Caccamo, "Building Robust Wireless LAN for Industrial Control with DSSS-CDMA Cellphone Network Paradigm," in IEEE Transactions on Mobile Computing (TMC), vol. 6, pp. 706-719, 2007.
• Xue Liu, Hui Ding, Kihwal Lee, Lui Sha, Marco Caccamo, "Feedback Fault Tolerance of Real-Time Embedded Systems -- Issues and Possible Solutions," in ACM SIGBED Review, Vol 3(2), 2006

• Chen Tian, Xue Liu, Hongbo Jiang, Wenyu Liu, Yi Wang, "Improving BitTorrent Traffic Performance by Exploiting Geographic Locality", in Proceedings of the IEEE Global Communications Conference (GLOBECOM 2008), New Orleans, LA, 2008

• Chen Tian, Hongbo Jiang, Xue Liu, Wenyu Liu, Yi Wang, "Towards Minimum Traffic Cost and Minimum Response Latency: A Novel Dynamic Query Protocol in Unstructured P2P Networks, " in Proceedings of the 37th International Conference on Parallel Processing (ICPP-08), Portland, Oregon, 2008

• Qixin Wang, Wook Shin, Xue Liu, Zheng Zeng, Cham Oh, Bedoor K. Alshebli, Marco Caccamo, Carl A. Gunter, Elsa Gunter, Jennifer Hou, Karrie Karahalios, and Lui Sha, "I-Living: An Open System Architecture for Assisted Living", in Proceedings of the 2006 IEEE International Conference on Systems, Man, and Cybernetics (SMC 2006). Taipei, Taiwan. 2006.

• Chun Zhang, Xue Liu, “Tradeoff Between Sampling Rates and Data Accuracy,” in Proceedings of the 2008 American Control Conference (ACC'08), Seattle, WA
• Ramesh Chandra, Xue Liu, Lui Sha, "On the Scheduling of Flexible and Reliable Real-Time Control System," in Real-Time Systems Journal, Vol. 24 (2), 2003.
• Lui Sha, Xue Liu, Marco Caccamo, Giorgio Buttazzo, "Online Control Optimization Using Load Driven Scheduling," in Proceedings of the 39th Conference on Decision and Control (CDC '00), Vol. 1, Sydney, Dec., 2000.

• Jianguo Yao, Xue Liu, Xiaoyun Zhu, "Reduced Dimension Control Based on Online Recursive Principal Component Analysis, " in Proceedings of the 2009 American Control Conference (ACC'09), St. Louis, MO, 2009 
• Jianguo Yao, Xue Liu, "Asymptotically Stable Adaptive Critic Design for Uncertain Nonlinear System," in Proceedings of the 2009 American Control Conference (ACC'09), St. Louis, MO, 2009