Department of Computer Science and Technology

Joined Department: 2002

Email:renfy@tsinghua.edu.cn

Phone:+86-10-62772487

Fax:+86-10-62771138

Bachelor of Electrical Technology, Northwestern Polytechnical University, Xi'an, China, 1993;

Master of Industrial Automation, Northwestern Polytechnical University, Xi'an, China, 1996;

Ph.D. in Computer Science, Northwestern Polytechnical University, Xi'an, China, 1999.

China Computer Federation: Member of Sensor Networks Committee;

National Technical Standardization Committee of Sensor Networks: Member;

Journal of Ad Hoc & Sensor Wireless Networks: Area Editor.

Traffic Control and Management in Computer Networks, Data Center Networking

Wireless Sensor Network, Optimization for Transport System in Wireless Networks

Performance Evaluation, Control Theory in Computer Networks

National Pillar Project in Technologies: Research on Key Technologies of Sensor Networks (2009-2011);

National Basic Research Program of China (The 973 Program): Research on Real-time Transport Quality of Connectionless and Heterogeneous Networks (2009-2013);

National Basic Research Program of China (The 973 Program): Modeling Transport Management System in Networks and Designing Adaptive Traffic Control Mechanism (2003-2008);

National 863 High-Tech Program: Architecture for Wireless Sensor Networks (2007-2008);

National Natural Science Foundation of China: Active Queue Management based on Control Theory (2003-2005);

National Natural Science Foundation of China: Research on Mechanism and Algorithms of Time Synchronization in Wireless Sensor Network (2006-2008);

National Natural Science Foundation of China: Optimizing Transport Protocol for High Speed Networks (2008-2010);

National Natural Science Foundation of China: A Potential Field-based Dynamic Routing Protocol for Wireless Sensor Networks (2010-2012).

I have been mainly working in the following areas:

1. Traffic Control in Computer Networks. Many factors throw obstacles in building a refined dynamic model for transport subsystem in computer networks, such as diversity of traffic statistical distribution, nonlinear coupling imposed by protocols, and time-varying characteristics of network states. Although heuristic algorithms for traffic control can be obtained without the support of system model, they can only work normally under some special environments. Through limited simulations (even experiments), the comprehensive evaluation on performance of these heuristic algorithms is difficult to be conducted, and in-depth understanding and sensible insights are hardly to be obtained. In our work in this area, the network traffic control subsystem will be considered as a nonlinear time-varying delay closed-loop system. Using some proper approximation techniques, such as fluid flow and local linearization, the transport subsystems in computer networks are described by linear differential equations. Combining with these coarse-grained models, the classical analysis approaches in linear and nonlinear control theory, such as describing function, phase plane and Lyapunov function, are used to analyze the stability of typical transport subsystems in computer networks, including TCP/AQM, ATM/FECI, Ethernet/BCN, etc. The explicit criterions of system stability are deduced, which provide some valuable guidelines to parameter settings for stable network operation. Otherwise, these theoretical results also give a reasonable interpretation of some phenomena occurring in transport subsystem. For example, the queue oscillation with identical amplitude should be limit cycle caused by the nonlinear elements embedded into traffic control algorithms. On the other hand, borrowing population ecology evolution theory and utilizing the design techniques in robust control theory, such as internal model control, sliding mode variable structure control and fuzzy control, we develop a series of flow control and congestion control algorithms for heterogeneous computer networks, including ultra-high-speed, large delay, mobile and wireless networks.

2. Wireless Sensor Network Architecture and Protocols Design. The coherent architecture and common programming model are crucial for large scale deployment of applications based on wireless sensor networks (WSNs). Following the philosophy of active network, we construct a reference model for WSN architecture, which enables sensor nodes programmability, dynamic loading/unloading of protocols, and the online updating of codes. In addition, the new architecture can improve code reusability and reliability, and can shorten development and deployment cycle of large-scale commercial applications. Finally, it is capable of reducing management cost. On the other hand, exploiting the redundancy of densely deployed sensor nodes and the centripetal pattern (i.e. many-to-one) existing in traffic spatial distribution, and borrowing the concept of potential field in physics, we construct different potential fields referring to different state parameters in networks, and then superpose them into a virtual potential field to drive packets to move directionally in networks. This paradigm can realize the basic function of routing, while can endow additional attributes, including balancing energy consumption, alleviating congestion and assisting data aggregation. Additionally, the other related protocols in WSNs, such as reliable transport, time synchronization and congestion control, are developed.

China's 100 Most Influential Academic Papers (2008);

Science and Technology Progress Award by City of Beijing, Second Class (2007);

Science and Technology Progress Award by Ministry of Education, First Class (2005).

[1] F.Y. Ren, X.M. Huang, F. Liu, C. Lin, Improving TCP Throughput Over HSDPA Networks, IEEE Trans. Wireless Communication, vol.7(6),, June, 2008, pp1993~1999

[2] F.Y. Ren, C. Lin, F. Liu, Self-Correcting Time Synchronization Using Reference Broadcast in Wireless Sensor Network. IEEE Wireless Communications. Vol.15(4),Aug. 2008, pp79~85

[3] F.Y. Ren, C. Lin, B. Wei, A Nonlinear Control Theoretic Analysis to TCP-RED System, Computer Networks ,vol.49, 2005,pp580~592

[4] F.Y. Ren, C. Lin, B. Wei, A robust controller for active queue management in large delay networks, Computer Communications,Vol.28 (5) , 2005, pp485-493

[5] F.Y. Ren, Y. Ren, X.M.Shan. Design of a Fuzzy Controller for Active Queue Management, Computer Communications.vol.25,2002, pp874-883

[6] F.Y. Ren, W.C. Jiang, Phase Plane Analysis of Congestion Control in Data Center Ethernet Networks, in Proc. of the 30th International Conference on Distributed Computing Systems (ICDCS 2010), June 21~ 25, 2010, Genoa, Italy

[7] H.K Yang, F.Y Ren, C. Lin and J. Zhang. Frequency-Domain Packet Scheduling for 3GPP LTE Uplink , In Proc. of IEEE INFOCOM 2010, Mar.15~19, 2010,San Diego, CA, USA

[8] X.M. Huang, F.Y. Ren, G.W. Yang, Y.W. Wu, C.Lin. End-to-end Congestion Control for High Speed Networks Based on Population Ecology Models. In Proc. of the 28th International Conference on Distributed Computing Systems (ICDCS2008),June 17~20, 2008,Beijing, China,

[9]X.M. Huang, C. Lin, F.Y. Ren, P. D. Ungsunan, Improving the Convergence and Stability of Congestion Control Algorithm, In Proc. of15th IEEE International Conference on Network Protocols (ICNP 2007), October 16-19, 2007, Beijing, China

[10] F.Y. Ren, C. Lin, X.H. Yin, X.M.Shan. A Robust Active Queue Management Algorithm Based on Sliding Mode Variable Structure Control. In Proc. of IEEE INFOCOM2002, San Francisco, USA