Linkage

Badass women cartographers!

Looking back on Shoes.

At a DARPA PI meeting recently, I met some folks from Cybernetica who told me about the hot new startup CountryOS! (EDIT: it’s not their startup).

A recent 99% Invisible episode describes the history of the SIGSALY, a secure communication system developed during WWII that used white noise one-time pads printed on vinyl to analog-encrypt communications lines.

Thanks to The Allusionist, I learned about EuroSpeak and discovered this guide on Misused English words and expressions in EU publications, which is hilarious.

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Signal boost: Postdoc positions at Tel Aviv University

Two postdoctoral research positions are now available in the Department of Electrical Engineering – Systems at Tel Aviv University, Israel, in the fields of information theory and interactive communications. Starting immediately for up to two years. Funded by the European Research Council (ERC).

We offer two postdoctoral fellowships for researchers in the broad area of information theory, with special emphasis on interactive communications. Specific topics of interest include single-user and multiuser communications with noisy feedback, iterative-refinement coding for two-way channels, interactive coding and its relations to dynamical systems and stochastic control, resource-limited interactive communications, distributed function computation, and combinatorial aspects of multiuser interactive communications. The research will be conducted in close collaboration with Dr. Ofer Shayevitz and his group, and is funded by a grant from the European Research Council (ERC).

The positions are available immediately and for a period of up to two years. Applicants should hold a PhD in either electrical engineering, computer science, or mathematics, and are expected to have a strong background in information theory or closely related fields. Remuneration is highly competitive and commensurate with skills and track record. To apply, please send your CV along with a short statement of research interests to Dr. Ofer Shayevitz at ofersha@eng.tau.ac.il.

Detection and Estimation: book recommendations?

It’s confirmed that I will be teaching Detection and Estimation next semester so I figured I would use the blog to conjure up some book recommendations (or even debate, if I can be so hopeful). Some of the contenders:

  • Steven M. Kay, Fundamentals of Statistical Signal Processing – Estimation Theory (Vol. 1), Prentice Hall, 1993.
  • H. Vincent Poor, An Introduction to Signal Detection and Estimation, 2nd Edition, Springer, 1998.
  • Harry L. Van Trees, Detection, Estimation, and Modulation Theory (in 4 parts), Wiley, 2001 (a reprint).
  • M.D. Srinath, P.K. Rajasekaran, P. K. and R. Viswanathan, Introduction to Statistical Signal Processing with Applications, Prentice Hall, 1996.

Detection and estimation is a fundamental class for the ECE graduate curriculum, but these “standard” textbooks are around 20 years old, and I can’t help but think there might be more “modern” take on the subject (no I’m not volunteering). Venu Veeravalli‘s class doesn’t use a book, but just has notes. However, I think the students at Rutgers (majority MS students) would benefit from a textbook, at least as a grounding.

Srinath et al. is what my colleague Narayan Mandyam uses. Kay is what I was leaning to before (because it seems to be the most widely used), but Poor’s book is the one I read. I think I am putting up the Van Trees as a joke, mostly. I mean, it’s a great book but I think a bit much for a textbook. So what do the rest of you use? Also, if you are teaching this course next semester, perhaps we can share some ideas. I think the curriculum might be ripe for some shaking up. If not in core material, at least in the kinds of examples we use. For example, I’m certainly going to cover differential privacy as a connection to hypothesis testing.

SPCOM 2014: some more talks (and a plenary)

I did catch Greg Wornell’s plenary at SPCOM, which was called When Bits Absolutely, Positively, Have to be There as Soon as Possible, a riff on this FedEx commercial, which is older than I am. The talk was on link-aware PHY-layer design– basically looking at how ARQ enables incremental redundancy, and how to do a sort of layered superposition + incremental redundancy scheme in the sequential setting as well as a “multi-path” setting where blocks can arrive out of order. This was really digging into the signal issues in a way that a lot of non-communication engineering information theorists may get squeamish about. The nice thing is that I think the engineering problem is approachable without knowing a lot of heavy-duty math, but still requires some careful analysis.

Communication and Compression Via Sparse Linear Regression
Ramji Venkataramanan
This was on building codewords and codebooks out of a lower-complexity code dictionary A \in \mathbb{R}^{n \times ML} where each codeword is a superposition of L columns, one each from groups of size M. Thus encoding is A \beta where \beta is a sparse vector. I saw a talk by Barron and Joseph from a previous ISIT about this, but the framework extends to rate distortion (achieving the rate distortion function), and channel coding. The main point is to lower the complexity of the code at the expense of the gap to optimal rate — encoding and decoding are polynomial time but the rate gap for rate-distortion goes to zero as 1/\log n. Ramji gave a really nice and clear talk on this — I hope he puts the slides up!

An Optimal Varentropy Bound for Log-Concave Distributions
Mokshay Madiman; Liyao Wang
Mokshay’s talk was also really clear and excellent. For a distribution f(X) on \mathbb{R}^n, we can define \tilde{h}(X) = - \log f(X). The entropy is the expectation of this random variable, and the varentropy is the variance. Their main result is a upper bound on the varentropu of log concave distributions f(X). To wit, \mathrm{Var}(\tilde{h}) \le n. This bound doesn’t depend on the distribution and is sharp if f is a product of exponentials. They then use this to prove a universal bound on the deviation of \tilde{h} from its expectation, which gives a AEP that doesn’t really assume anything about the joint distribution of the variables except for log-concavity. There was more in the talk, but I eagerly await the paper.

Event-triggered Sampling and Reconstruction of Sparse Real-valued Trigonometric Polynomials
Neeraj Sharma; Thippur V. Sreenivas
This was on non-uniform sampling where the sampler tries to detect level crossings of the analog signal and samples at that point — the rate may not be uniform enough to use existing nonuniform sampling techniques. They come up with a method for reconstructing signals which are real-valued trigonometric polynomials with a few nonzero coefficients (e.g. sparse) and it seems to work pretty decently in experiments.

Removing Sampling Bias in Networked Stochastic Approximation
Vivek Borkar; Raaz Dwivedi
In networked stochastic approximation, the intermittent communication between nodes may mean that the system tracks a different ODE than the one we want. By modifying the method to account for “local clocks” on each edge, we can correct for this, but we end up with new conditions on the step size to make things work. I am pretty excited about this paper, but as usual, my notes were not quite up to getting the juicy bits. That’s what paper reading is for.

On Asymmetric Insertion and Deletion Errors
Ankur A. Kulkarni
The insertion/deletion channel model is notoriously hard. Ankur proposed a new model where 0‘s are “indestructible” — they cannot be inserted or deleted. This asymmetric model leads to new asymptotic bounds on the capacity. I don’t really work on this channel model so I can’t get the finer points of the results, but once nice takeaway was that asymptotically, each indestructible 0 in the codeword lets us correct around 1/2 a deletion more.

ISIT 2014: two more plenaries

As I wrote before, I took pretty woeful notes during ISIT this year, so I don’t have much to write about. Andrea Goldsmith’s plenary was about how we always say IT/Comm is dead, but she thinks we should be more sanguine about it. She presented a glimpse of some recent work with Stefano Rini on a unified approach for providing achievable results for single-hop networks using a graph to represent superposition coding and binning operations among the auxiliary variables. If it is actually as easy to use as advertised, it might save over the 23+ rate inequalities defining some achievable rate regions. The moral of the story is that it’s sometimes better to clean up our existing results a bit. I think the El-Gamal and Kim book did a great job of this for basic multiterminal IT, for example.

Vijay Kumar’s plenary was on codes for distributed storage and repair-bandwidth tradeoffs, focusing on extensions of the model. There was a lot of discussion of other code constructions, and how asking for certain properties (such as “locality”) can cost you something in the tradeoff. This is important when you can’t repair a code from arbitrary nodes in the network/data center — because there’s an underlying network which supplies the data for repair, codes should probably respect that network. At least that was the moral I took from this talk. Since I don’t work on coding, some things were a little over my head, but I thought he did an excellent job of keeping it accessible with nice concrete examples.

Postdoc opening at UCSB

There’s an opening in Professor Madhow’s group at UC Santa Barbara:

We are looking for a postdoctoral researcher with a strong background in communications/signal processing/controls who is interested in applying these skills to a varied set of problems arising from a number of projects. These include hardware-adapted signal processing for communications and radar, neuro-inspired signal processing architectures, and inference in online social networks. In particular, familiarity with Bayesian inference is highly desirable, even if that is not the primary research area for his/her PhD. There are also opportunities to work on problems in next generation communication systems, including millimeter wave networking and distributed communication. While the researcher will be affiliated with Prof. Madhow’s group in the ECE Department at UCSB, depending on the problem(s) chosen, he/she may need to interact with faculty collaborators in other disciplines such as circuits, controls, computer science and neuroscience, as well as with colleagues with expertise in signal processing and communications. Thus, in addition to technical depth and talent, a flexible attitude and openness to interdisciplinary collaboration is essential.

Interested candidates should send a brief statement of research experience and interests and a CV (including the names and contact info for at least three references) to Prof. Upamanyu Madhow.

A poem in lieu of a post

I’ve not been posting because I have been visiting Japan for the last week (and for another week after this). I am teaching one week of a machine learning course at the Toyota Technological Institute (豊田工業大学, Toyota Kōgyō Daigaku), which is the main campus — TTI-Chicago is just a satellite campus. Between jet lag, sightseeing, and lesson prep I haven’t had much of a chance to post about anything.

My friend Celeste posted a link to the poem Telephone Repairman, by Joseph Millar.

Some people who read this blog work on communications. It’s worth taking a pause occasionally to contemplate, as the character in the poem does:

He thinks of the many signals
flying in the air around him
the syllables fluttering,
saying please love me,
from continent to continent
over the curve of the earth.