Thursday, February 20, 2014

Leveraging Location

So this became a thing on the internet today:
DIDO white paper
Artemis
I read the paper and it made me very happy. One, it was a well written paper, two, it made it clear to me roughly what is going on in this wireless architecture, and three, the architecture is beautiful in concept.

The first swipe at an analogy I thought of was for some reason public key cryptography. You have this seemingly unintelligible stream of data moving in a volume, but at certain locations, it all makes sense. It coheres into something intelligible.

But that really doesn't work as an analogy, so I went very basic to the classic destructive/constructive interference model: the double-slit experiment. But in reverse. But this isn't really instructive to what DIDO is actually doing.

Then I thought of a really good analogy in the mechanical world. One company I met with last year was working on a new touch screen architecture where they planned to use the cover glass as a big vibrational surface. They place a few piezo vibrators under the glass to set up a small vibrational mode, and a few displacement sensors under the perimeter of the glass in order to gather data about its vibrational modes. When you touch the glass, disturb the natural vibrational mode of the glass. The sensors pick up this disturbance and their custom silicon can perform the intensive calculations to figure out where your fingers were located to cause that particular mode disturbance. 

Even cooler would be if you could set up standing vibrational modes that your finger could feel in order to provide haptic feedback. The vibrator actuators would dynamically adjust their inputs to move the standing wave (coherence) around as you moved your finger across the surface.  I feel like I saw a paper where they almost did this, but not quite. With normal haptics, you only have one actuator that affects the entire touch surface (no localization).

It is probably pretty hard to localize haptic feedback on such a small surface in such a stiff material. However, you can do it with electromagnetic waves. This is what DIDO does. You have a bunch of distributed access points (piezo actuators in my mechanical world). It doesn't matter where they are except that they must be in range of the client device and must know where they are relative to one another (this can be done via triangulation). The client devices (fingers) move around in the area (glass surface) covered by these access points. The access points know where the clients are at all times (also via triangulation). The access points are not exactly distributed, because they must all talk to a central server (CPU) that organizes what signals they send out. The server computes the 3D signal pattern (vibrational mode) necessary to create a particular coherence at each of the client devices (kinda like a phased array antenna but firing in multiple directions at once). The access points all broadcast their assigned outputs such that you get constructive interference with the appropriate, specific data (haptic waveform) at all of the client locations and gibberish everywhere else. Woo insane.

This was also a serendipitous announcement because I was recently thinking a lot about wireless networks. Scott and I were talking about mobile ad hoc networks as a means to create directional antennae for mobile devices (which Josh had originally got me thinking about).

Outstanding related question: phased N-arrays are great at being directional, but how are they more efficient than a single antenna at Nx the power? The radiation energy that isn't going in the desired direction isn't saved. It's just cancelled out destructively.


In other news, I need to start writing more again, so I plan to lower my already low quality standards for blog posts.

It makes me miss MIT when I hear via popular news about something so lovely that was first published more than 2 years ago. 










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