# Postdoc positions at UT Austin

The ECE department at The University of Texas at Austin seeks highly qualified candidates for postdoctoral fellowship positions, lasting up to two years, in the information sciences, broadly defined. Applicants should have, or be close to completing, a PhD in ECE, CS, Math, Statistics or related fields.

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# i’m in ur protocolz, jammin ur cellphonez

Krish Eswaran sent me a story about how a group at Virgina Tech described how LTE networks are susceptible to a certain kind of jamming strategy:

“An example strategy would be to target specific control or synchronization signals, in order to increase the geographic range of the jammer and better avoid detection,” the Wireless @ Virginia Tech research group said in a filing (PDF) submitted to the National Telecommunications and Information Administration. “The availability of low-cost and easy to use software-defined radios makes this threat even more realistic.”

Color me unsurprised! For my PhD, I studied arbitrarily varying channels (AVCs), which are information-theoretic models for communication against adversarial interference. There are a couple of design insights one can distill from considering the AVC model:

• Separating protocol and payload makes schemes susceptible to spoofing.
• Lack of synchronization/coordination between sender and receiver can be a real problem in adversarial settings.

Here we have a case where the protocol is easy to spoof/disrupt, essentially because the control information in unprotected.

This separation between control information and payload is often suboptimal in other senses. See, for example, Tchamkerten, Chandar and Wornell.

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# Postdoc job openings

Some people have told me about postdoctoral position openings that are opening up, and I figured I’d repost some of them here as they come along. Of course, there are other places to post announcements, but I find that postdoc opportunities are a bit harder to advertise/hear about. I think a lot of systems EE people applying for academic positions right out of grad school tend to put off applying for postdocs until they hear back about their faculty interviews — I’d tend to say this is a mistake:

• If your graduation date may be a little flexible, pinging someone early on (e.g. in the fall) about possible postdoc opportunities can be a good plan. NSF grant deadlines are in the fall, and so they could write a postdoc position into a current proposal.
• Of course you’re going to apply for faculty positions, and the people you’re talking to about postdoc positions know that. However, if you get to May and haven’t talked to anyone about postdoc options, you may find that those positions have filled up.
• Don’t think of a postdoc as a “fallback plan” (akin to a “safety school”) — it’s an opportunity and a chance to make a strategic decision. Do you want to switch areas or learn about something new? Do you want to dig deeper into things you’ve already been working on? Do you want a springboard to get a job in a specific country? Do you want to build closer ties to industry? Do you want closer mentorship?

I went to a panel at Allerton once on “whether you should do a postdoc” starring (among other people) Aaron Wagner and Todd Coleman, I believe. Everyone was very enthusiastic about doing a postdoc. Everyone on the panel had faculty positions lined up for after their postdoc and deferred their start date to do that postdoc. This is the best of all possible worlds but is pretty unusual, so don’t count on it.

This is all dodging the issue of whether or not you should even do a postdoc. That might be a topic for a different post (or a debate for the comments) — I know people have strong feelings on both sides. I tend to think our system is broken or veering into brokenness.

However, more information is more power, so if you have a postdoc announcement (details are helpful) and want me to post it here, please do send it my way. You can also try to post to the IT Society website.

# ITA Workshop 2012 : Talks

The ITA Workshop finished up today, and I know I promised some blogging, but my willpower to take notes kind of deteriorated during the week. For today I’ll put some pointers to talks I saw today which were interesting. I realize I am heavily blogging about Berkeley folks here, but you know, they were interesting talks!

Nadia Fawaz talked about differential privacy for continuous observations : in this model you see $x_1, x_2, x_3, \ldots$ causally and have to estimate the running sum. She had two modifications, one in which you only want a windowed running sum, say for $W$ past values, and one in which the privacy constraint decays and expires after a window of time $W$, so that values $W$ time steps in the past do not have to be protected at all. This yields some differences in the privacy-utility tradeoff in terms of the accuracy of computing the function.

David Tse gave an interesting talk about sequencing DNA via short reads as a communication problem. I had actually had some thoughts along these lines earlier because I am starting to collaborate with my friend Tony Chiang on some informatics problems around next generation sequencing. David wanted to know how many (noiseless) reads $N$ you need to take of a genome of of length $G$ using reads of length $L$. It turns out that the correct scaling in this model is $L/\log G$. Some scaling results were given in a qualitative way, but I guess the quantitative stuff is being written up still.

Michael Jordan talked about the “big data bootstrap” (paper here). You have $n$ data points, where $n$ is huge. The idea is to subsample a set of size $b$ and then do bootstrap estimates of size $n$ on the subsample. I have to read the paper on this but it sounds fascinating.

Anant Sahai talked about how to look at some decentralized linear control problems as implicitly doing some sort of network coding in the deterministic model. One way to view this is to identify unstable modes in the plant as communicating with each other using the controllers as relays in the network. By structurally massaging the control problem into a canonical form, they can make this translation a bit more formal and can translate results about linear stabilization from the 80s into max-flow min-cut type results for network codes. This is mostly work by Se Yong Park, who really ought to have a more complete webpage.

Paolo Minero talked about controlling a linear plant over a rate-limited communication link whose capacity evolves according to a Markov chain. What are the conditions on the rate to ensure stability? He made a connection to Markov jump linear systems that gives the answer in the scalar case, but the necessary and sufficient conditions in the vector case don’t quite match. I always like seeing these sort of communication and control results, even though I don’t work in this area at all. They’re just cool.

There were three talks on consensus in the morning, which I will only touch on briefly. Behrouz Touri gave a talk about part of his thesis work, which was on the Hegselman-Krause opinion dynamics model. It’s not possible to derive a Lyapunov function for this system, but he found a time-varying Lyapunov function, leading to an analysis of the convergence which has some nice connections to products of random stochastic matrices and other topics. Ali Jadbabaie talked about work with Pooya Molavi on non-Bayesian social learning, which combines local Bayesian updating with DeGroot consensus to do distributed learning of a parameter in a network. He had some new sufficient conditions involving disconnected networks that are similar in flavor to his preprint. José Moura talked about distributed Kalman filtering and other consensus meets sensing (consensing?) problems. The algorithms are similar to ones I’ve been looking at lately, so I will have to dig a bit deeper into the upcoming IT Transactions paper.

# Some deals from Cambridge

Network Information Theory by Abbas El Gamal and Young-Han Kim is out! I saw copies in Young-Han’s office earlier this month when I was visiting San Diego. Having been at UCSD while the book was being written, I can attest to the comprehensiveness, attention to detail, and clarity of the writing. A must-have!

In addition, Cambridge is having a sale — many books for \$10 softcover and \$20 hardcover. Most of them are not comm/SP/IT related, so you won’t have to spend all of your money… One warning is that the website is INCREDIBLY SLOW and there is no real search interface for the sale, so you have to get through pages of “MRS Symposium Proceedings.” Titles that may be of interest:

and others, including sensor nets titles and miscellaneous wireless comm titles. Just use ENGR11 as the discount code.

# APIs for hardware : architecting cellphones and networks

We had two talks by here at UCSD on Tuesday. The first was Cell Phones: How Power Consumption Determines Functionality by Arvind, and the second was Software-Defined Networks by Nick McKeown. These talks had a lot in common: they were both about shifting paradigms for designers, and about approaching the architecture of hardware from a software point of view.

# CTW 2010

Playa Norte on Isla Mujeres

I was lucky enough to get invited to present at the Communications Theory Workshop (CTW) in Cancun last month. Since the conference started on a Monday I took the weekend before to do a little sightseeing, hang out on the beach (see above), and visit Chichen Itza, which was pretty amazing. CTW is a small conference — single track, 2.5 days, and plenty of time for panels, discussions, etc. I had a great time there, and it was really nice to meet new people who were working on interesting problems that I hadn’t even heard about.

The first day was focused on wireless data services, the explosion thereof, and the lack of capacity to support it all. Add more relays, femtocells, interference management and alignment, putting more antennas for MIMO gains. Reinaldo Valenzuela was pretty pessimistic — according to him we are pretty much at the point where service providers are losing money by providing data over wireless. He seemed to think the only way out now is to change pricing models or really try to exploit network MIMO.

The second day was on cognitive radio, where the picture also seemed a bit pessimistic. Michael Marcus kind of laid into academics for not participating in the FCC comment process. The criticism is valid — if we care about cognitive radio and its potentials and so on, we should try to persuade the regulators to do smart things and not piecemeal things. As things stand now, it’s unclear how much additional capacity is available in the TV bands, given the current requirements for operating there. The sensing requirements nigh unreasonable, and if you do detect a primary you have to stay silent for 30 minutes. That makes it kind of hard to run a commercial service.

Another thing I learned during that day was that wireless microphones in the US operate in the TV bands, and are grandfathered in to the existing rules for cognitive radio. This means you have to detect if you will interfere with a wireless mic, which seems quite tough. Steve Shellhammer talked about a contest Qualcomm ran to build a detector for this problem. In addition, a large fraction of wireless microphone users are not licensed and hence their use is illegal, but nobody’s enforcing that.

The second half of the day was on emerging topics, followed by a panel called “Is Communication Theory Dead?” I think the pessimism and despair of the first two days needed to be let out a little, and there was a pretty spirited discussion of whether communication theorists were answering the right questions or not. It was like group therapy or something. Luckily there was the banquet after the panel so people could forget their woes…

The last day of the workshop was the session I spoke in, which were 5 talks on wireless networks, but from vastly different perspectives. Tara Javidi talked about routing, Daniela Tuninetti about information theory and cognitive interference channels, Elza Erkip about game theory models for the interference channel, and Anna Scaglione about cooperative information flooding. For my part, I talked about (very) recent work I have done with Tara on distributed consensus with quantized messages. We have some nice first-order results but I’m still hammering away at better bounds on the convergence rate.

# US drones’ video feed was wiretapped

From Bobak I saw that US drones in Iraq have been hacked because “the remotely flown planes have an unprotected communications link” but “there was no evidence that they [insurgents] were able to jam electronic signals from the aircraft.”

This illustrates nicely the difference between eavesdropping and jamming. However, a nice by-product of anti-jamming codes using shared encryption keys (here they can be easily agreed upon before the drone takes off) is that sometimes you can get both eavesdropping and jamming protection at the same time.