22 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use of both outdated and instantaneous CSIT.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
On the Fundamental Feedback-vs-Performance Tradeoff over the MISO-BC with Imperfect and Delayed CSIT
This work considers the multiuser multiple-input single-output (MISO)
broadcast channel (BC), where a transmitter with M antennas transmits
information to K single-antenna users, and where - as expected - the quality
and timeliness of channel state information at the transmitter (CSIT) is
imperfect. Motivated by the fundamental question of how much feedback is
necessary to achieve a certain performance, this work seeks to establish bounds
on the tradeoff between degrees-of-freedom (DoF) performance and CSIT feedback
quality. Specifically, this work provides a novel DoF region outer bound for
the general K-user MISO BC with partial current CSIT, which naturally bridges
the gap between the case of having no current CSIT (only delayed CSIT, or no
CSIT) and the case with full CSIT. The work then characterizes the minimum CSIT
feedback that is necessary for any point of the sum DoF, which is optimal for
the case with M >= K, and the case with M=2, K=3.Comment: An initial version of this paper has been reported as Research Report
No. RR-12-275 at EURECOM, December 7, 2012. This paper was submitted in part
to the ISIT 201
On the Vector Broadcast Channel with Alternating CSIT: A Topological Perspective
In many wireless networks, link strengths are affected by many topological
factors such as different distances, shadowing and inter-cell interference,
thus resulting in some links being generally stronger than other links. From an
information theoretic point of view, accounting for such topological aspects
has remained largely unexplored, despite strong indications that such aspects
can crucially affect transceiver and feedback design, as well as the overall
performance.
The work here takes a step in exploring this interplay between topology,
feedback and performance. This is done for the two user broadcast channel with
random fading, in the presence of a simple two-state topological setting of
statistically strong vs. weaker links, and in the presence of a practical
ternary feedback setting of alternating channel state information at the
transmitter (alternating CSIT) where for each channel realization, this CSIT
can be perfect, delayed, or not available.
In this setting, the work derives generalized degrees-of-freedom bounds and
exact expressions, that capture performance as a function of feedback
statistics and topology statistics. The results are based on novel topological
signal management (TSM) schemes that account for topology in order to fully
utilize feedback. This is achieved for different classes of feedback mechanisms
of practical importance, from which we identify specific feedback mechanisms
that are best suited for different topologies. This approach offers further
insight on how to split the effort --- of channel learning and feeding back
CSIT --- for the strong versus for the weaker link. Further intuition is
provided on the possible gains from topological spatio-temporal diversity,
where topology changes in time and across users.Comment: Shorter version will be presented at ISIT 201