17,238 research outputs found
A Systematic Approach for Interference Alignment in CSIT-less Relay-Aided X-Networks
The degrees of freedom (DoF) of an X-network with M transmit and N receive
nodes utilizing interference alignment with the support of relays each
equipped with antennas operating in a half-duplex non-regenerative mode
is investigated. Conditions on the feasibility of interference alignment are
derived using a proper transmit strategy and a structured approach based on a
Kronecker-product representation. The advantages of this approach are twofold:
First, it extends existing results on the achievable DoF to generalized antenna
configurations. Second, it unifies the analysis for time-varying and constant
channels and provides valuable insights and interconnections between the two
channel models. It turns out that a DoF of \nicefrac{NM}{M+N-1} is feasible
whenever the sum of the
A New DoF Upper Bound and Its Achievability for -User MIMO Y Channels
This work is to study the degrees of freedom (DoF) for the -user MIMO Y
channel. Previously, two transmission frameworks have been proposed for the DoF
analysis when , where and denote the number of antennas at
each source node and the relay node respectively. The first method is named as
signal group based alignment proposed by Hua et al. in [1]. The second is named
as signal pattern approach introduced by Wang et al. in [2]. But both of them
only studied certain antenna configurations. The maximum achievable DoF in the
general case still remains unknown. In this work, we first derive a new upper
bound of the DoF using the genie-aided approach. Then, we propose a more
general transmission framework, generalized signal alignment (GSA), and show
that the previous two methods are both special cases of GSA. With GSA, we prove
that the new DoF upper bound is achievable when . The DoF
analysis in this paper provides a major step forward towards the fundamental
capacity limit of the -user MIMO Y channel. It also offers a new approach of
integrating interference alignment with physical layer network coding.Comment: 6 pages, 3 figures, submitted to IEEE ICC 2015. arXiv admin note:
text overlap with arXiv:1405.071
The Ergodic Capacity of Phase-Fading Interference Networks
We identify the role of equal strength interference links as bottlenecks on
the ergodic sum capacity of a user phase-fading interference network, i.e.,
an interference network where the fading process is restricted primarily to
independent and uniform phase variations while the channel magnitudes are held
fixed across time. It is shown that even though there are cross-links,
only about disjoint and equal strength interference links suffice to
determine the capacity of the network regardless of the strengths of the rest
of the cross channels. This scenario is called a \emph{minimal bottleneck
state}. It is shown that ergodic interference alignment is capacity optimal for
a network in a minimal bottleneck state. The results are applied to large
networks. It is shown that large networks are close to bottleneck states with a
high probability, so that ergodic interference alignment is close to optimal
for large networks. Limitations of the notion of bottleneck states are also
highlighted for channels where both the phase and the magnitudes vary with
time. It is shown through an example that for these channels, joint coding
across different bottleneck states makes it possible to circumvent the capacity
bottlenecks.Comment: 19 page
Generalized Signal Alignment For MIMO Two-Way X Relay Channels
We study the degrees of freedom (DoF) of MIMO two-way X relay channels.
Previous work studied the case , where and denote the number of
antennas at the relay and each source, respectively, and showed that the
maximum DoF of is achievable when by
applying signal alignment (SA) for network coding and interference cancelation.
This work considers the case where the performance is limited by the
number of antennas at each source node and conventional SA is not feasible. We
propose a \textit{generalized signal alignment} (GSA) based transmission
scheme. The key is to let the signals to be exchanged between every source node
align in a transformed subspace, rather than the direct subspace, at the relay
so as to form network-coded signals. This is realized by jointly designing the
precoding matrices at all source nodes and the processing matrix at the relay.
Moreover, the aligned subspaces are orthogonal to each other. By applying the
GSA, we show that the DoF upper bound is achievable when ( is even) or ( is odd). Numerical results also demonstrate
that our proposed transmission scheme is feasible and effective.Comment: 6 pages, 6 figures, to appear in IEEE ICC 201
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