221 research outputs found
Optimal DoF Region of the Two-User MISO-BC with General Alternating CSIT
In the setting of the time-selective two-user multiple-input single-output
(MISO) broadcast channel (BC), recent work by Tandon et al. considered the case
where - in the presence of error-free delayed channel state information at the
transmitter (delayed CSIT) - the current CSIT for the channel of user 1 and of
user 2, alternate between the two extreme states of perfect current CSIT and of
no current CSIT.
Motivated by the problem of having limited-capacity feedback links which may
not allow for perfect CSIT, as well as by the need to utilize any available
partial CSIT, we here deviate from this `all-or-nothing' approach and proceed -
again in the presence of error-free delayed CSIT - to consider the general
setting where current CSIT now alternates between any two qualities.
Specifically for and denoting the high-SNR asymptotic
rates-of-decay of the mean-square error of the CSIT estimates for the channel
of user~1 and of user~2 respectively, we consider the case where for any two positive current-CSIT quality exponents
. In a fast-fading setting where we consider communication over
any number of coherence periods, and where each CSIT state is present
for a fraction of this total duration, we focus on the
symmetric case of , and derive
the optimal degrees-of-freedom (DoF) region. The result, which is supported by
novel communication protocols, naturally incorporates the aforementioned
`Perfect current' vs. `No current' setting by limiting .
Finally, motivated by recent interest in frequency correlated channels with
unmatched CSIT, we also analyze the setting where there is no delayed CSIT
On the Degrees of Freedom of time correlated MISO broadcast channel with delayed CSIT
We consider the time correlated MISO broadcast channel where the transmitter
has partial knowledge on the current channel state, in addition to delayed
channel state information (CSI). Rather than exploiting only the current CSI,
as the zero-forcing precoding, or only the delayed CSI, as the Maddah-Ali-Tse
(MAT) scheme, we propose a seamless strategy that takes advantage of both. The
achievable degrees of freedom of the proposed scheme is characterized in terms
of the quality of the current channel knowledge.Comment: 7 pages, 1 figure, submitted to ISIT 2012, extended version with
detailed proof
Degrees of Freedom of Time Correlated MISO Broadcast Channel with Delayed CSIT
We consider the time correlated multiple-input single-output (MISO) broadcast
channel where the transmitter has imperfect knowledge on the current channel
state, in addition to delayed channel state information. By representing the
quality of the current channel state information as P^-{\alpha} for the
signal-to-noise ratio P and some constant {\alpha} \geq 0, we characterize the
optimal degree of freedom region for this more general two-user MISO broadcast
correlated channel. The essential ingredients of the proposed scheme lie in the
quantization and multicasting of the overheard interferences, while
broadcasting new private messages. Our proposed scheme smoothly bridges between
the scheme recently proposed by Maddah-Ali and Tse with no current state
information and a simple zero-forcing beamforming with perfect current state
information.Comment: revised and final version, to appear in IEEE transactions on
Information Theor
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
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