19,787 research outputs found
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 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
The DoF of Network MIMO with Backhaul Delays
We consider the problem of downlink precoding for Network (multi-cell) MIMO
networks where Transmitters (TXs) are provided with imperfect Channel State
Information (CSI). Specifically, each TX receives a delayed channel estimate
with the delay being specific to each channel component. This model is
particularly adapted to the scenarios where a user feeds back its CSI to its
serving base only as it is envisioned in future LTE networks. We analyze the
impact of the delay during the backhaul-based CSI exchange on the rate
performance achieved by Network MIMO. We highlight how delay can dramatically
degrade system performance if existing precoding methods are to be used. We
propose an alternative robust beamforming strategy which achieves the maximal
performance, in DoF sense. We verify by simulations that the theoretical DoF
improvement translates into a performance increase at finite Signal-to-Noise
Ratio (SNR) as well
Retrospective Interference Alignment for Two-Cell Uplink MIMO Cellular Networks with Delayed CSIT
In this paper, we propose a new retrospective interference alignment for
two-cell multiple-input multiple-output (MIMO) interfering multiple access
channels (IMAC) with the delayed channel state information at the transmitters
(CSIT). It is shown that having delayed CSIT can strictly increase the sum-DoF
compared to the case of no CSIT. The key idea is to align multiple interfering
signals from adjacent cells onto a small dimensional subspace over time by
fully exploiting the previously received signals as side information with
outdated CSIT in a distributed manner. Remarkably, we show that the
retrospective interference alignment can achieve the optimal sum-DoF in the
context of two-cell two-user scenario by providing a new outer bound.Comment: 7 pages, 2 figures, to appear in IEEE ICC 201
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