9,938 research outputs found
Feedback Capacity of the Compound Channel
In this work we find the capacity of a compound finite-state channel with
time-invariant deterministic feedback. The model we consider involves the use
of fixed length block codes. Our achievability result includes a proof of the
existence of a universal decoder for the family of finite-state channels with
feedback. As a consequence of our capacity result, we show that feedback does
not increase the capacity of the compound Gilbert-Elliot channel. Additionally,
we show that for a stationary and uniformly ergodic Markovian channel, if the
compound channel capacity is zero without feedback then it is zero with
feedback. Finally, we use our result on the finite-state channel to show that
the feedback capacity of the memoryless compound channel is given by
.Comment: 34 pages, 2 figures, submitted to IEEE Transactions on Information
Theor
Optimal Use of Current and Outdated Channel State Information - Degrees of Freedom of the MISO BC with Mixed CSIT
We consider a multiple-input-single-output (MISO) broadcast channel with
mixed channel state information at the transmitter (CSIT) that consists of
imperfect current CSIT and perfect outdated CSIT. Recent work by Kobayashi et
al. presented a scheme which exploits both imperfect current CSIT and perfect
outdated CSIT and achieves higher degrees of freedom (DoF) than possible with
only imperfect current CSIT or only outdated CSIT individually. In this work,
we further improve the achievable DoF in this setting by incorporating
additional private messages, and provide a tight information theoretic DoF
outer bound, thereby identifying the DoF optimal use of mixed CSIT. The new
result is stronger even in the original setting of only delayed CSIT, because
it allows us to remove the restricting assumption of statistically equivalent
fading for all users
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