722 research outputs found
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
Gapped boundary of (4+1)d beyond-cohomology bosonic SPT phase
In this work we study gapped boundary states of bosonic
symmetry-protected topological (SPT) phases in 4+1d, which are characterized by
mixed -gravity response, and the closely related phases protected
by rotation symmetry. We show that if , any
symmetry-preserving boundary theory is necessarily gapless for the root SPT
state. We then propose a 3+1d gauge theory coupled to fermionic
matter as a candidate boundary theory for , where the anomalous
symmetry is implemented by invertible topological defects obtained from gauging
2+1d chiral topological superconductors. For the case, we present an
explicit construction for the boundary states for , and argue that
the construction fails for other values of .Comment: 15 pages, 4 figures; v2: added discussions on the group structure of
SPT phases, and more on the case. More references adde
- …