Monday, July 7, 2008

ISIT Liveblog: July 7

8:48 AM: I'm in Calderbank's very interesting plenary on sensing and detection in the context of algebraic codes. Carefully designed waveforms with good autocorrelation properties can be used in radar sensing. I saw an earlier version of this talk in Edmonton at CWIT 2007. Calderbank likes Blahut's coding book, and commented: "Classical coding theory and Fourier analysis are two sides of the same coin". But, as a "modern" coding theorist, I'll have to think a bit about what that means.

10:21 AM: Skipping between Iterative Decoding and the Wiretap Channel. Nice talk about bilayer LDPC codes, designed with respect to a rate constraint, in Iterative Decoding. In Wiretap Channels, I saw "Physical Layer Encryption with Stream Ciphers". I'm a little confused about this paper: using ciphers, there seems to be no reason to enhance traditional cryptography with physical layer security; and they claim the eavesdropper can obtain the key via plaintext attacks (which is true traditionally, and what if the transmitted data is compressed or otherwise equiprobable 1/2-1/2?). I think the contribution here is more along the lines of protecting encrypted text with error-correcting codes.

10:35 AM: Neat paper by Gunduz, Erkip and Poor on multiterminal compression with security constraints: eavesdropper can observe a subset of the terminals; only the "decipherer" (i.e., destination) can see all of them.

I think I get the wiretap channel now: given a side channel that is secure (e.g., secured with traditional cryptography, or otherwise private), it is possible to use information theory to make a much larger system private.

12:13 PM: In "Wireless Networks", a very interesting generalization to scaling laws by Ozgur et al., revealing a new operating regime for a wireless network that ignores the area density of nodes.

5:35 PM: Here's something I didn't know (if I remember it right): if z = x+y, then 2^(2H(Z)) >= 2^(2H(X)) + 2^(2H(Y)), with equality if and only if x, y, and z are Gaussian.

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