Tuesday, November 27, 2007

Weekly papers - back again

Finally, back with the weekly papers segment after a rough beginning of November. Perhaps it was dodging reactions from INFOCOM reviews and how it went with various folks. More on that later when I have time to do a length post.

Diversity and multiplexing: a fundamental tradeoff in multiple-antenna channels This paper comes from our weekly papers meeting two weeks ago from discussions regarding our INFOCOM reviews regarding the relevance of MIMO to our current work. Transactions on Information Theory is a bit out of our normal purview so kudos to Dave for taking the time to digest the paper in its entirety.

The paper looked at the tradeoffs in a multi-antenna environment with regards to reliability versus capacity. The most relevant portion of the paper is the strong dropoff with regards to either dimension, i.e. if you choose to do both, you will not get a solution that is strong in either dimension. Not exactly a shocking result but the work in the paper is quite sound and a nice discussion point to discuss why our current work on wireless reliability is very interesting.

Near as I can tell, industry has gone the route of capacity over reliability meaning that our results regarding channel reliability are especially apt. In short, our most recent work has been looking at if the reliability of the channel for nodes in close proximity. If loss is primarily from the medium, losses should be correlated in nearby spaces but not necessarily correlated across larger spaces. In contrast, if losses are not correlated in a tight area, it means that it is likely an individual device going crazy, not the medium itself. Most of the works in the literature regarding burstiness / etc. seem to trust that the device itself is good and that the packet got corrupted before arriving, not that the device itself may be a significant source of the packet errors.

While previous works such as SRD by Balakrishnan reached what would be a similar conclusion, the works reached their conclusion for quite different reasons. Put simply, the physical sensors were highly scattered (i.e. APs over 30 feet+ apart) allowing for multi-path effects for different loss probabilities. In contrast, we showed that losses tended to also show a lack of correlation in short distances regardless of orientation, small distance between, and heavy background traffic. Moreover, there were also "weird" periodicity aspects to some of the devices that bear further investigation (Intel Centrino chipset).

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CresceNet said...
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