Carnegie Mellon University

Tim Brown

Tim Brown

Distinguished Service Professor, Engineering and Public Policy
Electrical and Computer Engineering

Bio

2013 - present         Visiting Professor: Carnegie Mellon University Africa

1995 - present         Professor: University of Colorado, Boulder

2008 - 2012            Director: Interdisciplinary Telecommunications Program, University of Colorado, Boulder

1992 - 1995            Member Technical Staff: Bell Communications Research, Morristown

1990 - 1992            Member Technical Staff: Jet Propulsion Laboratory, Pasadena

Education

  • Ph.D. in Electrical Engineering, California Institute of Technology, Pasadena 1991
    Thesis: Neural Network Design for Switching Network Control
  • M.S. in Electrical Engineering, California Institute of Technology, Pasadena, 1987
  • B.S. in Physics, Pennsylvania State University, University Park, 1986

Research

Dr. Brown's research seeks to understand so-called challenged networks. Starting from traditional cellular mobile telephone networks we "challenge" this paradigm along several dimensions that allows us to better understand their behavior. Current wireless networking trends are pushing along these dimensions and so we can better understand how to build out these future networks. Here are several examples of these dimensions:

1. What happens when the basic infrastructure of base stations becomes more and more sparse?
With more sparseness, connectivity starts to depend on peer relaying and physically carrying messages to get them to their destination. If there is mobility, some network resources can be dynamically repositioned to maintain connectivity. How do we control these mobile resource? What protocols are required? If mobile nodes are, for instance, autonomous unmanned aerial vehicles, what role does the FAA play?

2. What happens when there is insufficient spectrum to communicate? 
Dynamic spectrum access allows a network to draw on a broader set of spectrum resources. One model of dynamic spectrum access is so-called policy-based radios. How are these spectrum policies generated and specified? How do we avoid harming other radio services? How is harm even defined?

3. What happens when networks are set up with little or no planning?
The good old days of homogeneous base stations arranged in regular grids are long gone. Tiny femto cells mix with big macro cells, Cellphones mix with WiFi. Base stations are placed wherever they are needed. How do we make sense of this? Should we expect it to work? Will I have good coverage and throughput? How does this compare to the good old days? Will the billions of sensors in the Internet of Things be the technology that finally makes it fall apart?

Cutting across these questions we try to understand (a) how they will really work through building prototypes and designing implementation architectures, (b) the effect on performance through analyzing the underlying theory, (c) the policy implications as we impact on existing systems, and (d) the security considerations as each of these challenges opens up new attack surfaces.

His recent research funding includes NSF, DOE, and industry. Projects include the role of mobility in network control of unmanned aircraft, denial of service vulnerabilities in wireless protocols, spectrum policy frameworks for cognitive radios, and stochastic geometry applied to wireless networks. He is a recipient of the NSF CAREER Award, and the GWEC Wireless Educator of the Year Award.

Publications

M. Saint, T. X Brown, "A New Spectrum License for Old Circumstances: A Retrospective Look at the Nextel Interference Proceedings," Research Conference on Communications, Information and Internet Policy (TPRC), Sept. 7, 2017.

E. Ogbo, T. X Brown, D. Sicker, "Mobile Service Substitution. A Wall or a Bridge for Internet Penetration Growth in Rural Africa? A Case Study in Nigeria," Research Conference on Communications, Information and Internet Policy (TPRC), Sept. 7, 2017.

S. Hayat, E. Yanmaz, T. X Brown, C. Bettstetter, "Connectivity and coverage trade-offs in UAV path planning," Robotics: Science and Systems, Cambridge, MA, Jul. 2017. (4 pages)

S. Hayat, E. Yanmaz, T. X Brown, C. Bettstetter, "Multi-objective UAV path planning for search and rescue," IEEE International Conference on Robotics and Automation (ICRA), Singapore, May 2017. (6 pages)

M. Saint, T. X. Brown, "The dynamic policy license," International Symposium on Dynamic Spectrum Access Networks (DySPAN), Baltimore, MD, Mar. 2017. (9 pages)

H. Mauwa, A. Bagula, M. Zennaro, E. Pietrosemoli, A. Lysko, T. X Brown "Analysis of Geo-Location and Spectrum Sensing as Access Methods to TV White Space," Journal of ICT Standardization, v. 4, n. 1, 2017. pp. 147{176, 28p.

T. X Brown, D. C. Sicker, "Spectrum Sharing Vulnerability and Threat Assessment," in J. D. Matyjas, S. Kumar, F. Hu, eds., Spectrum Sharing in Wireless Networks: Fairness, Efficiency and Security, CRC Press, April 2016. (21 pages)

P. Madhusudhanan, Refereed J. G. Restrepo, Y. Liu, T. X Brown, "Analysis of Downlink Connectivity Models in a Heterogeneous Cellular Network via Stochastic Geometry," IEEE Transactions on Wireless Communication, v. 15, n. 6, Jun. 2016. pp. 3895-3907, 13 p.

M. Saint, J. Hoyos, T. X Brown, "Securing Power Systems," in A.-S. Khan Pathan, ed., Securing Cyber-Physical Systems, CRC Press, Oct. 2015, (27 pages)

D. T. Bennett, T. X Brown, "Simple Receding Horizon Approach to Scheduling Mobile Wireless Clients with Uncertainty," Proc. IEEE Wireless Communications and Networking Conference  (WCNC), New Orleans, Mar. 10, 2015.

P. Madhusudhanan, Refereed J. G. Restrepo, Y. Liu, T. X Brown, K. Baker, "Downlink Performance Analysis for a Generalized Shotgun Cellular System," IEEE T. on Wireless Communication, v. 13, n. 11, Dec. 2014. pp. 6684-6696, 13p.

T. X Brown, E. Pietrosemoli, M. Zennaro, A. Bagula, H. Mauwa. S. M. Nleya, "A survey of TV white space measurements," Proc. Sixth Int. Conf. on e-Infrastructure and e-Services for Developing Countries (Africomm). Kampala, Uganda, Nov. 24, 2014.

P. Madhusudhanan, Y. Liu, T. X Brown, "On Primary User Coverage Probabilities and Faulty Cognitive Radios," IEEE T. on Wireless Communication, v. 13, n. 11, Nov. 2014. pp. 6207-6218, 12p.

P. Madhusudhanan, J. G. Restrepo, Y. Liu, T. X Brown, "Downlink analysis for a heterogeneous cellular network," Proc. Tenth Workshop on Spatial Stochastic Models for Wireless Networks (SpasWiN), Hammamet, Tunisia, May 16, 2014.

T. X Brown, J. M. Peha, "Policy-Based Radios," in E. Pietrosemoli, M. Zennaro eds., TV White Spaces: A Pragmatic Approach, ICTP, Dec. 2013, pp. 51-66. (16 pages)

T. X Brown, "Policy-Based Radios for Spectrum Sharing," IST-Africa Conference and Ex-hibition (IST-Africa), Nairobi, May 30 2013, (9 pages).

S. Brown, M. Saint, T. X Brown, "Study of SMS Air Interface Delay in the Presence of Strong and Weak Signals," IST-Africa Conference and Exhibition (IST-Africa), Nairobi, May 29, 2013, (12 pages).

P. Madhusudhanan, Xing Li, Youjian Liu, T. X Brown, "Stochastic geometric modeling and interference analysis for massive MIMO systems," in Proc. of 11th Inter. Symp. on Modeling and Optimization in Mobile, Ad Hoc and Wireless Networks (WiOpt),  2013 pp. 15-22, Tsukuba, Japan May 12, 2013. (8 pages, invited paper)

M. Stachura, J. Elston, E.W. Frew, B. Argrow, T. X. Brown, C. Dixon, "Multi-UAS Testbed for Wireless Communication Experiments," in Proc. of IEEE International Conference on Robotics and Automation (ICRA) , Karlsruhe, May 8, 2013. (4 pages)

T. X Brown, M. McHenry, S. Jaroonvanichkul, "Cognitive Radio Architectures for Unmanned Aircraft Systems," in K. P. Valavanis, G. J. Vachtsevanos, eds., Handbook of Unmanned Aerial Vehicles, Springer, 2013.

B. Pearre, T. X Brown, "Model-Free Trajectory Optimisation for Unmanned Aircraft Serving as Data Ferries for Widespread Sensors," Remote Sensing. 2012; v. 4, n. 10, pp. 2971-3005, 35 p.

T. X Brown, S. Jaroonvanichkul, "Policy-based radios for UAS operations," Proc. IEEE Third International Workshop on Wireless Networking for Unmanned Autonomous Vehicles: Architectures, Protocols and Applications,  (Wi-UAV) Anaheim, CA, Dec. 7 2012.

P. Madhusudhanan, J. Restrepo, Y. Liu, T. X Brown, "Downlink Coverage Analysis in a Heterogeneous Cellular Network," Proc. IEEE Global Communications Conf. (Globecom), Anaheim, CA Dec, 3-7 2012.

B. Pearre, T. X Brown, "Energy conservation in sensor network data ferrying: a reinforcement metalearning approach," Proc. IEEE Global Communications Conf. (Globecom), Anaheim, CA, Dec. 3-7 2012.

P. Madhusudhanan, T. X Brown, Y. Liu, "Coverage in the Downlink of an OFDMA Cellular Network with Maximum SIR Connectivity," Proc. IEEE International Workshop on Emerging Technologies for LTE-Advanced and Beyond-4G  (B4G), Anaheim, CA Dec. 3 2012.

P. Madhusudhanan, J. G. Restrepo, Y. Liu, T. X Brown, K. Baker, "Stochastic Ordering based Carrier-to-Interference Ratio Analysis for the Shotgun Cellular Systems," IEEE Wire-less Communications Letters, v. 1, n. 6, Dec. 2012. pp. 565-568, 4 p.

J. Hoyos, M. Dehus, T. X Brown, "Exploiting the GOOSE protocol: A practical attack on cyber-infrastructure," Proc. IEEE Workshop on Smart Grid Communications: Design for Performance  (SGComm), Anaheim, CA, Dec. 3 2012.

P. Madhusudhanan, J. Restrepo, Y. Liu, T. X Brown, "Heterogeneous Cellular Network Performance Analysis under Open and Closed Access," Proc. IEEE The 4th IEEE International Workshop on Heterogeneous and Small Cell Networks  (HetSNets), Anaheim, CA Dec. 3 2012.

D. Bennett, T. X Brown, "Optimal Data Scheduling of Mobile Clients Serviced using Beamforming Antennas," Proc. IEEE Military Communications Conference (MilCom), Orlando, Nov. 1, 2012.

B. Pearre, T. X Brown, "Self-monitoring Reinforcement Metalearning for Energy Conservation in Data-ferried Sensor Networks," Proc. The Sixth International Conference on Sensor Technologies and Applications (SensorComm), Aug. 19-24, Rome 2012.

D. Bennett, T. Brown, "Wireless Data Scheduling of Clients Serviced using UAV Mounted Beamforming Antennas," Proc. AIAA Infotech Aerospace Conf. Garden Grove, California, 19-21 June 2012.

P. Madhusudhanan, T. X Brown, Y. Liu, "Interference characteristics and success probability at the primary user in a cognitive radio network," Proc. Eighth Workshop on Spatial Stochastic Models for Wireless Networks (SpasWiN), Paderborn, Germany, May 14, 2012.

T. X Brown, N. M. Balasubramanya, "Dynamic Outage, Availability, and Interference Models for Mobile Cognitive Radios," Proc. IEEE Global Communications Conf. (Globecom), Houston, TX, Dec. 6-8, 2011.

P. Madhusudhanan, J. Restrepo, Y. Liu, T. X Brown, K. Baker, "Multi-tier Network Performance Analysis using a Shotgun Cellular System," Proc. IEEE Global Communications Conf. (Globecom), Houston, TX, Dec. 6-8, 2011.

P. Madhusudhanan, T. X Brown, Y. Liu, "On the Interference to Multiple Low Power Primary Users from Cooperative Cognitive Radios," Proc. 49th Annual Allerton Conference on Communication, Control, and Computing, Sep. 28-30, 2011.

M. Heusse, G. Urvoy-Keller, T. X Brown, A. Duda, "Least Attained Recent Service for Packet Scheduling over Access Links," Pervasive and Mobile Computing, v. 7, n. 4, Aug. 2011. pp. 479-494, 16 p.

B. Pearre, T. X Brown, "Fast, Scalable, Model-free Trajectory Optimization for Wireless Data Ferries," IEEE International Conference on Computer Communication Networks (IC-CCN 11), Maui, Hawaii, Jul. 31-Aug. 4, 2011.

M. Heusse, S. Merritt, T. X Brown, A. Duda. "Two-way TCP connections: old problem, new insight," ACM SIGCOMM Comput. Commun. Rev., v. 41, n. 2, Apr. 2011, pp. 5-15,11 p.