ISIT 2007 : multi-user IT and cognitive radio

A Linear Interference Network with Local Side-Information (M. Wigger, S. Shamai (Shitz), and A. Lapidoth) : This model was a chain ofinterference channels with K total transmit-receive pairs in a kind of ladder, and looked at behavior of the prelog in the sum-capacity expression when each transmitter knows the J earlier messages in the ladder. For the achievable scheme, they silence some of the sensors and use dirty paper coding, and for the converse they use some interference-cancellation arguments. The bounds match and they get floor(K/(J+2)) for the prelog.

A Broadcast Approach to Multiple Access with Random States (P. Minero and D. Tse) : This paper looks at a kind of “compound MAC” problem, when the receiver has channel information (about the fading state for example). If the encoded information is “layered” via superposition coding, the decoder can opportunistically extract the data at a rate that the channel can support. By making each setting of the states into one virtual receiver, we get a broadcast version of the MAC. They look at two problems — the slow fading compound channel problem, and the “random access” model, where the number of users is variable. For the fading system, superposition is optimal for the sum rate, but for random access it is not.

On InterFerence Channel with Generalized Feedback (IFC-GF) (D. Tuninetti) : This looks at an interference channel with two additional outputs that are fed back to the transmitters. These outputs could be some internal part of the channel, or could be a noisy version of the channel outputs. For a Gaussian setting with the feedback being independently faded and noisy copies of the other transmitter’s signal, she exhibited a block Markov encoding scheme using backward decoding and showed that if there a common message can get a power boost.

Bounds on the capacity region of a class of interference channels (I. Telatar and D. Tse) : Although this talk was the last talk of the conference and I was pretty exhausted, it was one of my favorites. The class of channels being references are those in which the interference for user 1 is user 2’s signal passed through a channel and then a deterministic function. For example the channel could be “fade and add noise.” They derive outer bounds that are quite similar in form to the inner bound due to Chong-Motani-Garg, and can give some bounds on the tightness of that achievable region in the flavor of the “within 1-bit” result of Etkin-Tse-Wang.

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