Emergency workers: "can you hear me now?"

We've all heard stories about how emergency workers (aka first responders) have had trouble communicating at disaster sites because their equipment was not "interoperable," that is, operated at different frequencies or use incompatible methods. But disasters in big cities have other problems, even when the interoperability one is solved. There are so many physical obstacles -- buildings, steel girders, possibly rubble or wreckage -- that create barriers or echoes or other problems that prevent workers from speaking to each other even when they are close by. An article, still in press at IEEE Transactions on Antennas and Propagation by Young et al., the National Institute of Standards and Technology (NIST), proposes a novel solution to the problem: a random antenna array. Since the paper is not yet published I haven't read it (and anyway, realistically I not much of an antenna expert), but there is a good account of it via ScienceDaily. It is just the kind of idea I like: solving one problem, in emergency services, using an approach from a very distant discipline (antenna engineering).

Here's the idea. Use an array of small antennas connected to low power signal repeaters that are synchronized with each other and the transmitter used by the first responder. Where would you put these smaller antennas? The surprising answer: wherever. "Wherever" is my colloquial version of "randomly," although in the sense I get from the paper's method, it really means, "unsystematically". Synchronized here means "in phase," that is, each of the random array antenna-repeater combinations have to be sending out the exact same part of the signal at the exact same time. When there are a lot of echoes from signals bouncing around, that is not a given, so some kind of phase matching circuitry will be required in the little repeater-antenna combo.

In simulations and experiments the NIST engineers were able to demonstrate that unsystematic dispersal of as little as four of these little guys produced a 5 fold increase in median received power compared to a single transmitter of equivalent power. Making sure the signals were in-phase made a real difference, somewhere between 2.5 and 4 fold difference in median signal compared to unsynced signals. If you have a hard time envisioning what this system might look like, the project leader supplies this description:

Project leader Chris Holloway envisions portable transmitter devices shaped like hockey pucks, incorporating a small antenna and phase-shifting electronics, which could be thrown on the ground or stuck on a wall with the antenna always upright. “The idea is that someone, or even a robot, would have a bag of these things and would drop them off as they go through a building,” Holloway says. (ScienceDaily)

The unsystematic placement of the four repeaters is an important element, not because it performs better than a systematically designed one but because in an emergency situation putting these things "wherever" is probably the best you can do. What this work shows is that it works if you roughly match the signals. If you don't, it doesn't work or works poorly. The matching of phases allows the signals to reinforce each other, leading to the boost in received power.

Maybe you have to be geeky to find to take pleasure in this (I plead guilty), but the underlying problem for emergency workers at a physically challenging disaster scene is deadly serious. This is the kind of relatively simple, innovative and clever solution that saves lives. These little phase-matching repeater devices shouldn't be expensive to make and may have many other uses, including routine low power communication within physically complex settings.

My favorite kind of technological solution: cheap and effective.