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A New Capacity Result for the Z-Gaussian Cognitive Interference Channel
This work proposes a novel outer bound for the Gaussian cognitive
interference channel in strong interference at the primary receiver based on
the capacity of a multi-antenna broadcast channel with degraded message set. It
then shows that for the Z-channel, i.e., when the secondary receiver
experiences no interference and the primary receiver experiences strong
interference, the proposed outer bound not only is the tightest among known
bounds but is actually achievable for sufficiently strong interference. The
latter is a novel capacity result that from numerical evaluations appears to be
generalizable to a larger (i.e., non-Z) class of Gaussian channels
On the Symmetric Feedback Capacity of the K-user Cyclic Z-Interference Channel
The K-user cyclic Z-interference channel models a situation in which the kth
transmitter causes interference only to the (k-1)th receiver in a cyclic
manner, e.g., the first transmitter causes interference only to the Kth
receiver. The impact of noiseless feedback on the capacity of this channel is
studied by focusing on the Gaussian cyclic Z-interference channel. To this end,
the symmetric feedback capacity of the linear shift deterministic cyclic
Z-interference channel (LD-CZIC) is completely characterized for all
interference regimes. Using insights from the linear deterministic channel
model, the symmetric feedback capacity of the Gaussian cyclic Z-interference
channel is characterized up to within a constant number of bits. As a byproduct
of the constant gap result, the symmetric generalized degrees of freedom with
feedback for the Gaussian cyclic Z-interference channel are also characterized.
These results highlight that the symmetric feedback capacities for both linear
and Gaussian channel models are in general functions of K, the number of users.
Furthermore, the capacity gain obtained due to feedback decreases as K
increases.Comment: Accepted for publication in IEEE Transactions on Information Theor
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