ANANT SAHAI Electrical Engineering and Computer Sciences Assistant Professor sahai@eecs.berkeley.edu Official website
Research For prospective students Bio Teaching My Students	267 Cory Hall UC Berkeley 94720-1770 Spring 09 Office Hours: Tue 12:30-1:30pm, Fri 10-11AM in 258 Cory

Announcements:

No office hours during summer, except by appointment.

Welcome Communication Magazine Readers. A slight bug was introduced by the editors during the production process. Equation 1 should be .

A representative sample list of talks and the associated slides is now available This includes the slides for my tutorials at ISIT '07 and DySpAN '05, material on delay and feedback, control and communication, noisy feedback, cognitive radio, and the Witsenhausen counterexample.

My areas of interest span communications, control, and signal processing. Within that range, my focus is on the communications theory side, particularly in the areas of wireless and information theory. Within information theory, my main interest is in developing the conceptual tools needed to understand feedback, interaction, delay, reliability, and complexity. To that end, I am interested in distributed control systems as they provide well understood mathematical models that do not mesh with the classical notions from information theory. They also tell us why delay is important. On the wireless communication side, I am interested in power consumption and how multi-scale heterogenous wireless systems can coexist peacefully. Cognitive radio is of particular interest.

My research sits within the Wireless Foundations center, where we study the fundamental basis for the wireless technologies of the future. The following pages give more details about some of my research interests, with links to additional publications, etc.

• All publications categorized by subjective importance
• Representative talk slides
• UNI: Understanding Networks and Information
• RASP: Robust and Adaptive Signal Processing for cognitive radios
• Official publication/invited-talks list

It is imperfect and incomplete, but an alternative perspective can be found using a Google Scholar search for my work. A few key papers get missed in that search, so this and this and this and this and this should bring them up. This might help if you are looking for related work as well.

Key contributions from my group (Details can be found using the links above)

• Distributed Control
  1. Built a bridge between control theory and information theory by showing that anytime reliability is the right way to evaluate the quality of a noisy channel being used in a feedback loop for stabilization. Developed tight bounds for anytime reliability.
  2. Obtained the first provably positive results for the longstanding Witsenhausen counterexample in distributed control by demonstrating nonlinear control strategies that are within a constant factor of optimal for all problem parameters.
• Classical Communication
  1. Overturned prior assertions to show how feedback improves the tradeoff between delay and the probability of error. Even noisy/unreliable feedback helps. Moreover, the details of this illuminated an interesting duality between source and channel coding.
  2. Developed a new bound on how the probability of error must scale with "decoding neighborhood sizes" and used this to illuminate the implementation complexity of codes in terms of power consumption. This showed that for short-range communication, approaching Shannon capacity is probably the wrong thing to aim for.
• Dynamic Spectrum Sharing
  1. Showed that modeling uncertainties introduce fundamental limitations (SNR Walls) to spectrum sensing.
  2. Developed new metrics for evaluating spectrum sensing in the dynamic spectrum access context, introduced the key idea of the spatial overhead of sensing, and showed that diversity (from cooperative sensing) is required to reduce this overhead.
  3. Introduced a new paradigm for the light-handed regulation of cognitive radios inspired by criminal rather than civil law and explored the resulting regulatory overhead.

A few recent papers: (Descriptions and more can be found using the links above)

1. Pulkit Grover and Anant Sahai, "Time-division multiplexing for green broadcasting", ISIT 2009, Seoul, Korea, June 2009.
   
   
2. Anant Sahai, Rahul Tandra, and Mubaraw Mishra, "Spectrum Sensing: Fundamental Limits", draft chapter for a Springer Book: Cognitive Radios: System Design Perspective, June 2009.
   
3. Rahul Tandra, Mubaraq Mishra, and Anant Sahai, "What is a spectrum hole and what does it take to recognize one?", Proceedings of the IEEE special issue on Cognitive Radio, pp 824 - 848, May 2009 (published online April 2009)
   Rahul Tandra, Mubaraq Mishra, and Anant Sahai, "Extended Edition: What is a spectrum hole and what does it take to recognize one?", UC Berkeley EECS Technical Report No. UCB/EECS-2008-110, August 2008.
   
   
4. Pulkit Grover, Anant Sahai, Se Yong Park, "The finite-dimensional Witsenhausen counterexample," Extended Version of the paper to appear at ConCom 2009, Seoul Korea, June 2009.
   
5. Se Yong Park, Pulkit Grover, and Anant Sahai, "A constant-factor approximately optimal solution to the Witsenhausen Counterexample," Submitted to the 2009 Conference on Decision and Control, Mar 2009
   
   
6. Anant Sahai, Kristen Woyach, George Atia, and Venkatesh Saligrama, "A technical perspective on light-handed regulation for cognitive radios," IEEE Communications Magazine, pages 96-102, Mar 2009.
   A slight bug was introduced by the editors during the production process. Equation 1 should be .
   
   
7. Mubaraq Mishra and Anant Sahai, "How much white space is there?", Technical Report, January 2009. (To be submitted to the appropriate journal)
   
   
8. Anant Sahai, Mubaraq Mishra, Rahul Tandra, and Kristen Woyach, "Cognitive Radios for Spectrum Sharing," DSP Applications column in the IEEE Signal Processing Magazine,pages 140-146, January 2009.
   
   
9. Pulkit Grover and Anant Sahai, "Witsenhausen's counterexample as Assisted Interference Suppression", To appear in a Special Issue on "Information Processing and Decision Making in Distributed Control Systems" in the International Journal of Systems, Control and Communications, Revised Nov 2008.
   Pulkit Grover and Anant Sahai, "A vector version of Witsenhausen's counterexample: Towards the convergence of control, communication and computation," Conference on Decision and Control, Dec. 2008. (handout, slides)
   
   
10. George Atia, Anant Sahai, and Venkatesh Saligrama, "Spectrum Enforcement and Liability Assignment in Cognitive Radio Systems", IEEE Symposium on Dynamic Spectrum Access Networks (DySpAN), Oct 2008. (handout, slides)
    
    
11. Amin Gohari, Arash Parsa, and Anant Sahai "Exploiting Interference Diversity for Event-Based Spectrum Sensing", IEEE Symposium on Dynamic Spectrum Access Networks (DySpAN), Oct 2008. (handout, slides)
    
    
12. Rahul Tandra and Anant Sahai, "Noise calibration, delay coherence and SNR walls for signal detection", IEEE Symposium on Dynamic Spectrum Access Networks (DySpAN), Oct 2008. (handout, slides)
    
    
13. Kristen Ann Woyach, Anant Sahai, George Atia, and Venkatesh Saligrama, "Crime and Punishment for Cognitive Radios", (handout, slides) Allerton Sep 2008.
    Kristen Ann Woyach and Anant Sahai, "A toy-model for the regulation of cognitive radios", Preliminary report, June 2008.
    
    
14. Rahul Tandra and Anant Sahai, "Overcoming SNR walls through macroscale features", Allerton Sep 2008.
    
    
15. Parvathinathan Venkatisubramaniam and Anant Sahai, "Incentivizing anonymous `peer-to-peer' reviews", Allerton Sep 2008.
    
    
16. Pulkit Grover and Anant Sahai, "Little Green Codes: Energy-Efficient Short-Range Communication", 2008 International Symposium on Information Theory in Toronto
    
    
17. Cheng Chang and Anant Sahai, "Trade-off of lossless source-coding error exponents", 2008 International Symposium on Information Theory in Toronto
    
    
18. Anant Sahai and Stark Draper, "The `hallucination' bound for the BSC", 2008 International Symposium on Information Theory in Toronto
    
    
19. Stark Draper and Anant Sahai, "Variable-length coding with noisy feedback," European Transactions on Telecommunications special issue on New Directions in Information Theory, June 2008.
    
    
20. Anant Sahai, "Why do block length and delay behave differently if feedback is present?" IEEE Transactions on Information Theory. Pages 1860-1886, May 2008.
    Earlier Preprint: arXiv: cs.IT/0610138
    
    
21. Rahul Tandra and Anant Sahai, "SNR Walls for signal detection," IEEE Journal on Special Topics in Signal Processing, pages 4-17, Feb 2008.
    Rahul Tandra and Anant Sahai, "SNR walls for feature detectors," IEEE DySpAN 2007
    
    
22. Anant Sahai and Pulkit Grover, "The price of certainty: `waterslide curves' and the gap to capacity". Submitted to the IEEE Transactions on Information Theory, 2007.
    
    
23. Hari Palaiyanur, Cheng Chang and Anant Sahai, "The source coding game with a cheating switcher," Submitted to the IEEE Transactions on Information Theory, 2007.
    "Lossy compression of active sources" ISIT 2008
    Hari Palaiyanur and Anant Sahai, "On the uniform continuity of the rate-distortion function" ISIT 2008
    Preliminary version presented at IEEE ISIT 2007
    
    
24. Krish Eswaran, Anand Sarwate, Anant Sahai, and Michael Gastpar, "Limited feedback achieves the empirical capacity," submitted to the IEEE Transactions on Information Theory, 2007.
    Preprint: arXiv: arXiv:0711.0237
    Krish Eswaran, Anand Sarwate, Anant Sahai, and Michael Gastpar, "Binary additive channels with individual noise sequences and limited active feedback," IEEE ISIT 2007
    
    
25. Anant Sahai, "Balancing forward and feedback error correction for erasure channels with unreliable feedback," submitted to the IEEE Transactions on Information Theory, 2007.
    Preprint: arXiv: 0712.0871
    
    
26. Cheng Chang and Anant Sahai, "Universal Quadratic Lower Bounds on Source Coding Error Exponents," CISS 2007
    Cheng Chang and Anant Sahai, "Universal Fixed-Length Coding Redundancy," ITW 2007
    
    
27. Cheng Chang and Anant Sahai, "The price of ignorance: the impact on side-information for delay in lossless source coding," submitted to the IEEE Transactions on Information Theory, 2007.
    Preprint: arXiv:0712.0873
    
    
28. Pulkit Grover and Anant Sahai, "Writing on Rayleigh faded dirt: a computable upper bound to the outage capacity," IEEE ISIT 2007
    Pulkit Grover and Anant Sahai, "On the Need for Knowledge of the Phase in Exploiting Known Primary Transmissions," IEEE DySpAN 2007
    
    
29. Anant Sahai and Sanjoy Mitter, "Source coding and channel requirements for unstable processes," submitted to IT Transactions. Revised.
    Preprint: arXiv: cs.IT/0610151
    
    
30. Anant Sahai and Sanjoy Mitter, "The necessity and sufficiency of anytime capacity for control over a noisy communication link: Part I" IT Transactions, Pages 3369 - 3395, Aug 2006 and "Part II", submitted to IT Transactions Revised.
    preprints: arXiv: cs.IT/0601007 and arXiv: cs.IT/0610146
    
    

Before joining the faculty at Berkeley in 2002, I spent 2001 at the startup Enuvis, Inc. where I was on the theoretical/algorithmic side of a team that developed new techniques for GPS detection in very low SNR environments (such as those encountered indoors in urban areas). From 1994-2000, I was a graduate student at MIT studying Electrical Engineering and Computer Science (Course 6 in MIT-speak) and was based in the Laboratory for Information and Decision Systems under Prof. Sanjoy Mitter. My research interests there started in machine understanding but shifted toward the intersection of control and information theory. I did my undergraduate work in EECS here at the University of California at Berkeley from 1990-1994.

I also currently serve as the Treasurer for the IEEE Information Theory Society and the faculty adviser for the Berkeley chapter of Eta Kappa Nu.

• EECS 298: The time for the NET/COM/DSP (EE298) seminar has changed to Mondays 2:30-3:30pm to avoid conflicts with other courses. Please add yourself to the mailing list so that you get an announcement. I strongly recommend adding the Seminar's Google calendar to your calendar program.

  For one unit of credit, only attendance is required. For more than that, you will have to prepare a written report about one of the talks going into some more detail. Talk with me.

• EECS 121: Digital communication for undergrads.

Teaching History:

• Rahul Tandra: Master's thesis on limits to low SNR detection due to uncertainty. Finishing up his doctoral research in the area of opportunistic spectrum use and the fundamental metrics/limits for spectrum sensing. Did summer internship at Qualcomm in '06.
• S. Mubaraq Mishra: Finishing up his doctoral research on cooperation and architectural issues for cognitive radios. (Joint with Brodersen in BWRC) Summer internship at Wionics Research with Realtek in '06.
• Hari Palaiyanur: Master's thesis on applications of sequential decoding to anytime problems. Did summer internship at Nokia Research in '07. Currently exploring the information theory of active models of perception and how to understand channels with feedback.
• Pulkit Grover: Explored model uncertainty issues from an information theoretic perspective. Summer internship at Wionics Research with Realtek in '07. Currently working on understanding the computational complexity of iterative decoding from a power-consumption perspective. (Also did some work on Witsenhausen's counterexample)
• Kristen Ann Woyach: Great master's thesis on regulatory issues in cognitive radio and spectrum sharing. Continuing her explorations in this direction for her doctoral research.
• Se Yong Park: Exploring the intersection of control theory and information theory. Finishing up his Master's research on the Witsenhausen counterexample and intermittent Kalman Filtering.

Visitors:

• Hidekazu Miyoshi: visiting from SEI Innovation Core in Japan. Exploring cognitive radio issues.
• Mukul Agarwal: A student of Prof. Sanjoy Mitter in LIDS. Spent Summer '06 visiting me here in Wireless Foundations. Exploring the nature of information flows in systems.

Alums:

• Cheng Chang: Did a Master's thesis on UWB-based sensors: localization and positioning. Doctoral thesis on multiuser anytime information theory with a focus on multiterminal source coding. Joined HP Labs as postdoc in Jan 08 and is now at the hedge fund D. E. Shaw.
• Danijela Cabric: A student of Bob Brodersen whom I coadvised on spectrum sensing issues. Great thesis and is now at UCLA as an Assistant Professor.
• Niels Hoven: Master's thesis on power control for cognitive radios. Did summer internship at Philips Research in 06. Currently taking an indefinite break from graduate school.
• Stark Draper: Postdoc with myself, Kannan Ramchandran, and David Tse. Worked on feedback and delay issues, especially in the soft deadline context, as well as streaming Slepian Wolf problems. Spent a year at MERL in Cambridge, and is now at U. Wisconsin Madison as Assistant Professor.
• Qing Xu: Master's thesis on anytime capacity of erasure type channels. Currently at a Bay Area startup.
• Tunc Simsek: Brilliant doctoral thesis on anytime coding with feedback. Now at Mathworks. (Joint with Varaiya)
• Hansen Bow: Undergrad researcher with me who is now at MIT working on BioMEMS. With me, he did some of our earliest work on spectrum sharing as well as work on positioning in UWB systems.
• Moshe Malkin: Undergrad researcher with me who is now at Stanford working with Prof. Cioffi. With me, he did some work on positioning in UWB systems.
• Amirali Zohrenejad: Undergrad researcher with me who is now at Microsoft working in wireless networking. With me, he did some early work on randomized encoding strategies for tracking random walks.

Special thanks to our past and present research sponsors:

• United States National Science Foundation under grants: ANI-0230963, ANI-326503, CNS-403427, CCF-729122 as well as NSF Fellowships for my students.
• Unrestricted Gifts from Sumitomo Electric and Samsung Corporation
• Vodafone Foundation Fellowships for my students
• C2S2 and others supporting work done in the Berkeley Wireless Research Center.