329 research outputs found
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
Achievable Sum DoF of the K-User MIMO Interference Channel with Delayed CSIT
This paper considers a -user multiple-input-multiple-output (MIMO)
interference channel (IC) where 1) the channel state information obtained by
the transmitters (CSIT) is completely outdated, and 2) the number of transmit
antennas at each transmitter, i.e., , is greater than the number of receive
antennas at each user, i.e., . The usefulness of the delayed CSIT was
firstly identified in a -phase Retrospective Interference Alignment (RIA)
scheme proposed by Maddah-Ali et al for the Multiple-Input-Single-Output
Broadcast Channel, but the extension to the MIMO IC is a non-trivial step as
each transmitter only has the message intended for the corresponding user.
Recently, Abdoli et al focused on a Single-Input-Single-Output IC and solved
such bottleneck by inventing a -phase RIA with distributed overheard
interference retransmission. In this paper, we propose two -phase RIA
schemes suitable for the MIMO IC by generalizing and integrating some key
features of both Abdoli's and Maddah-Ali's works. The two schemes jointly yield
the best known sum Degrees-of-Freedom (DoF) performance so far. For the case
, the achieved sum DoF is asymptotically given by
when
Elements of Cellular Blind Interference Alignment --- Aligned Frequency Reuse, Wireless Index Coding and Interference Diversity
We explore degrees of freedom (DoF) characterizations of partially connected
wireless networks, especially cellular networks, with no channel state
information at the transmitters. Specifically, we introduce three fundamental
elements --- aligned frequency reuse, wireless index coding and interference
diversity --- through a series of examples, focusing first on infinite regular
arrays, then on finite clusters with arbitrary connectivity and message sets,
and finally on heterogeneous settings with asymmetric multiple antenna
configurations. Aligned frequency reuse refers to the optimality of orthogonal
resource allocations in many cases, but according to unconventional reuse
patterns that are guided by interference alignment principles. Wireless index
coding highlights both the intimate connection between the index coding problem
and cellular blind interference alignment, as well as the added complexity
inherent to wireless settings. Interference diversity refers to the observation
that in a wireless network each receiver experiences a different set of
interferers, and depending on the actions of its own set of interferers, the
interference-free signal space at each receiver fluctuates differently from
other receivers, creating opportunities for robust applications of blind
interference alignment principles
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