295 research outputs found
The Degrees of Freedom Region of Temporally Correlated MIMO Networks With Delayed CSIT
We consider the temporally-correlated Multiple-Input Multiple-Output (MIMO)
broadcast channels (BC) and interference channels (IC) where the transmitter(s)
has/have (i) delayed channel state information (CSI) obtained from a
latency-prone feedback channel as well as (ii) imperfect current CSIT,
obtained, e.g., from prediction on the basis of these past channel samples
based on the temporal correlation. The degrees of freedom (DoF) regions for the
two-user broadcast and interference MIMO networks with general antenna
configuration under such conditions are fully characterized, as a function of
the prediction quality indicator. Specifically, a simple unified framework is
proposed, allowing to attain optimal DoF region for the general antenna
configurations and current CSIT qualities. Such a framework builds upon
block-Markov encoding with interference quantization, optimally combining the
use of both outdated and instantaneous CSIT. A striking feature of our work is
that, by varying the power allocation, every point in the DoF region can be
achieved with one single scheme. As a result, instead of checking the
achievability of every corner point of the outer bound region, as typically
done in the literature, we propose a new systematic way to prove the
achievability.Comment: Revised to IEEE Trans. Inf. Theory. A new simple and unified
framework is proposed, allowing to attain optimal DoF region for general
antenna configurations and current CSIT qualities. A striking feature is
that, every corner point in the DoF region can be achieved with one single
scheme, and hence a new systematic way is proposed to prove the achievability
instead of checking every corner poin
Secure Degrees of Freedom of MIMO X-Channels with Output Feedback and Delayed CSIT
We investigate the problem of secure transmission over a two-user multi-input
multi-output (MIMO) X-channel in which channel state information is provided
with one-unit delay to both transmitters (CSIT), and each receiver feeds back
its channel output to a different transmitter. We refer to this model as MIMO
X-channel with asymmetric output feedback and delayed CSIT. The transmitters
are equipped with M-antennas each, and the receivers are equipped with
N-antennas each. For this model, accounting for both messages at each receiver,
we characterize the optimal sum secure degrees of freedom (SDoF) region. We
show that, in presence of asymmetric output feedback and delayed CSIT, the sum
SDoF region of the MIMO X-channel is same as the SDoF region of a two-user MIMO
BC with 2M-antennas at the transmitter, N-antennas at each receiver and delayed
CSIT. This result shows that, upon availability of asymmetric output feedback
and delayed CSIT, there is no performance loss in terms of sum SDoF due to the
distributed nature of the transmitters. Next, we show that this result also
holds if only output feedback is conveyed to the transmitters, but in a
symmetric manner, i.e., each receiver feeds back its output to both
transmitters and no CSIT. We also study the case in which only asymmetric
output feedback is provided to the transmitters, i.e., without CSIT, and derive
a lower bound on the sum SDoF for this model. Furthermore, we specialize our
results to the case in which there are no security constraints. In particular,
similar to the setting with security constraints, we show that the optimal sum
DoF region of the (M,M,N,N)--MIMO X-channel with asymmetric output feedback and
delayed CSIT is same as the DoF region of a two-user MIMO BC with 2M-antennas
at the transmitter, N-antennas at each receiver, and delayed CSIT. We
illustrate our results with some numerical examples.Comment: To Appear in IEEE Transactions on Information Forensics and Securit
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