Paper at Queen's: PDF

It was a beautiful day in Kingston on Wednesday, which I mostly spent indoors listening to talks.

Here are the PDF and citation of the QBSC paper I mentioned earlier:

S. E. T. Hadley, A. W. Eckford, and W. H. Gage, “Power saving in a biomechanical sensor network using activity detection,” in Proc. 25th Biennial Symposium on Communications, Kingston, ON, pp. 173-176, 2010.

Summertime, and the living is busy

I love it when I tell someone that I'm a professor, and they respond with something like, "Oh, it must be great to have the whole summer off!" Especially today: with my spring grading finally out of the way, I'm making up my lengthy summer to-do list. Some highlights:

• Clean up my office disaster
  
• Attend this conference (and attend an executive committee meeting)
• Attend and speak at this conference
  
• Finally get the revisions done for this paper (which should have been done months ago)
• Write a journal version of this paper
• Get a grant proposal done
• Read and edit theses as two students get ready to defend
• Get some chapters done for a textbook project that were promised for months ago
• Make some headway on a new consulting contract
• Lots more that I'm forgetting, for sure

Yep. Another lazy, coronas-on-the-beach summer.

Paper at Queen's

My paper at the Queen's Biennial Symposium on Communications:

Power Saving in a Biomechanical Sensor Network Using Activity Detection
Scott E. T. Hadley, Andrew W. Eckford, and William H. Gage
Wednesday, May 12, 4:50-6:10 PM (second talk in session), Walter Light Hall rm. 210

This is the first paper out of an interdisciplinary project with Will Gage in Kinesiology. The basic idea is to place accelerometers on stroke patients to monitor their recovery in walking, but the main challenge is to design a system with the robustness, endurance, and ease of use to be used in the home, rather than in the therapist's office. It's a practical project with lots of neat signal processing, and we just got a grant to continue it.

One of the key issues is to reduce power consumption and extend battery life. In this paper, we show that signal processing can help with power saving: we use activity detection to scale the sampling rate based on what the patient is doing. As a result, we strike a nice balance between power saving and data loss: switching modes, we lose about a second of data (about one step -- because it takes that long to detect acceleration with the reduced sampling rate), whereas we would lose about 30 seconds by putting the node to sleep and waking it up.

Scott will be presenting the paper. I'll be at Queen's for Wednesday only, so I hope to see you there. PDF of the paper will be posted shortly.

What's the worst noise?

It's a well-known theorem of information theory that, of all additive noise channels with constant noise variance (i.e., constant noise power), the Gaussian channel has the minimum capacity. I learned this long ago, and over time the concept was distilled in my memory down to "Gaussian is the worst noise".

I was trying to use this "property" to find a quick lower bound for the capacity of a new binary-input channel. But after some funny results, my grad student found an old paper of Shamai and Verdú, which -- much to my surprise and dismay -- shows that Gaussian noise is not worst-case if the input distribution is constrained! In particular, if the input is binary {+1,-1}, the worst constant-power distribution is supported on the discrete set {...,-2,0,+2,...}, and can't generally be expressed in closed form.

For more details, see:

S. Shamai and S. Verdú, "Worst-case power-constrained noise for binary-input channels," IEEE Trans. Info. Theory, vol. 38, no. 5, pp. 1494--1511, 1992.

Video: Writing on Tiny Paper

Here's the video for my talk at UIUC on Monday (this is a playlist). More details here.

Steve Munro Misses the (Swan?) Boat

Some Toronto-specific stuff now. There are days when I wonder whether Steve Munro is this city's most overrated blogger, today for example: here he is arguing that the Toronto Board of Trade was full of it by saying Toronto’s commute times are the worst in the world.

Go read Munro's post and see if you can piece together his rambling argument. The best I could do: the Board of Trade study is wrong because it used a metric, namely average commute time, which under-emphasized proper urban development. But development is important, and development goes hand in hand with transit, so the government should invest in transit.

It's important to bear in mind that the report was hugely in favor of transit investment, stating unequivocally:

... congestion threatens Toronto’s viability over the long-term and serves as an argument for increased investment in public transit and policies that encourage Torontonians to leave their cars behind.

So Munro is spectacularly missing the point on two fronts. The first is the current political context: the provincial government just postponed (and maybe killed) Transit City, of which Munro is a staunch promoter. The Board of Trade report, coming on the heels of this announcement, is an obvious political win for Transit City advocates. Other commentators are picking up on the obvious ways to shame the province, and keep the issue in the public eye. Not Munro, though - he’d rather quibble about metrics, and take a far more convoluted route to argue about transit funding.

The second is that Munro completely misunderstands the report, by failing to see the value of time. The economic impact of commuting is most acutely felt in the time spent commuting, not in the distance or speed, since a long commute is both time and effort diverted from other (potentially money-making) tasks. If you’re going to argue that the province should invest in transit, surely the return on the investment should be largely economic, especially since an economic boost will return to the province’s coffers in the form of tax revenues.

Talk at UIUC: "Writing on Tiny Paper"

I'll be giving a seminar next Monday, April 5, at UIUC. Thanks to Todd for the invite. Here are the title and abstract:

Writing on tiny paper: Towards information-theoretic analysis of molecular communication

In molecular communication, messages are transmitted as a pattern of molecules propagating from a transmitter to a receiver. This form of communication is useful where electromagnetic communication is impractical, such as in a lab-on-chip device. In this talk, we review current approaches to molecular communication. We also present some of our own results on modelling and analyzing these channels from an information-theoretic perspective, looking at molecular channels both as timing channels and as mass-transport channels.