374 research outputs found
Regularized ZF in Cooperative Broadcast Channels under Distributed CSIT: A Large System Analysis
Obtaining accurate Channel State Information (CSI) at the transmitters (TX)
is critical to many cooperation schemes such as Network MIMO, Interference
Alignment etc. Practical CSI feedback and limited backhaul-based sharing
inevitably creates degradations of CSI which are specific to each TX, giving
rise to a distributed form of CSI. In the Distributed CSI (D-CSI) broadcast
channel setting, the various TXs design elements of the precoder based on their
individual estimates of the global multiuser channel matrix, which intuitively
degrades performance when compared with the commonly used centralized CSI
assumption. This paper tackles this challenging scenario and presents a first
analysis of the rate performance for the distributed CSI multi-TX broadcast
channel setting, in the large number of antenna regime. Using Random Matrix
Theory (RMT) tools, we derive deterministic equivalents of the Signal to
Interference plus Noise Ratio (SINR) for the popular regularized Zero-Forcing
(ZF) precoder, allowing to unveil the price of distributedness for such
cooperation methods.Comment: Extended version of an ISIT 2015 submission. Addition of the proofs
omitted due to space constrain
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
Degrees of Freedom of Certain Interference Alignment Schemes with Distributed CSIT
In this work, we consider the use of interference alignment (IA) in a MIMO
interference channel (IC) under the assumption that each transmitter (TX) has
access to channel state information (CSI) that generally differs from that
available to other TXs. This setting is referred to as distributed CSIT. In a
setting where CSI accuracy is controlled by a set of power exponents, we show
that in the static 3-user MIMO square IC, the number of degrees-of-freedom
(DoF) that can be achieved with distributed CSIT is at least equal to the DoF
achieved with the worst accuracy taken across the TXs and across the
interfering links. We conjecture further that this represents exactly the DoF
achieved. This result is in strong contrast with the centralized CSIT
configuration usually studied (where all the TXs share the same, possibly
imperfect, channel estimate) for which it was shown that the DoF achieved at
receiver (RX) i is solely limited by the quality of its own feedback. This
shows the critical impact of CSI discrepancies between the TXs, and highlights
the price paid by distributed precoding.Comment: This is an extended version of a conference submission which will be
presented at the IEEE conference SPAWC, Darmstadt, June 201
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