50,999 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
CSI Feedback Reduction for MIMO Interference Alignment
Interference alignment (IA) is a linear precoding strategy that can achieve
optimal capacity scaling at high SNR in interference networks. Most of the
existing IA designs require full channel state information (CSI) at the
transmitters, which induces a huge CSI signaling cost. Hence it is desirable to
improve the feedback efficiency for IA and in this paper, we propose a novel IA
scheme with a significantly reduced CSI feedback. To quantify the CSI feedback
cost, we introduce a novel metric, namely the feedback dimension. This metric
serves as a first-order measurement of CSI feedback overhead. Due to the
partial CSI feedback constraint, conventional IA schemes can not be applied and
hence, we develop a novel IA precoder / decorrelator design and establish new
IA feasibility conditions. Via dynamic feedback profile design, the proposed IA
scheme can also achieve a flexible tradeoff between the degree of freedom (DoF)
requirements for data streams, the antenna resources and the CSI feedback cost.
We show by analysis and simulations that the proposed scheme achieves
substantial reductions of CSI feedback overhead under the same DoF requirement
in MIMO interference networks.Comment: 30 pages, 7 figures, accepted for publication by IEEE transactions on
signal processing in June, 201
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
Interference Alignment (IA) and Coordinated Multi-Point (CoMP) with IEEE802.11ac feedback compression: testbed results
We have implemented interference alignment (IA) and joint transmission
coordinated multipoint (CoMP) on a wireless testbed using the feedback
compression scheme of the new 802.11ac standard. The performance as a function
of the frequency domain granularity is assessed. Realistic throughput gains are
obtained by probing each spatial modulation stream with ten different coding
and modulation schemes. The gain of IA and CoMP over TDMA MIMO is found to be
26% and 71%, respectively under stationary conditions. In our dense indoor
office deployment, the frequency domain granularity of the feedback can be
reduced down to every 8th subcarrier (2.5MHz), without sacrificing performance.Comment: To appear in ICASSP 201
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