1,392 research outputs found
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
MIMO Multiway Relaying with Pairwise Data Exchange: A Degrees of Freedom Perspective
In this paper, we study achievable degrees of freedom (DoF) of a
multiple-input multiple-output (MIMO) multiway relay channel (mRC) where
users, each equipped with antennas, exchange messages in a pairwise manner
via a common -antenna relay node. % A novel and systematic way of joint
beamforming design at the users and at the relay is proposed to align signals
for efficient implementation of physical-layer network coding (PNC). It is
shown that, when the user number , the proposed beamforming design can
achieve the DoF capacity of the considered mRC for any setups. % For
the scenarios with , we show that the proposed signaling scheme can be
improved by disabling a portion of relay antennas so as to align signals more
efficiently. Our analysis reveals that the obtained achievable DoF is always
piecewise linear, and is bounded either by the number of user antennas or
by the number of relay antennas . Further, we show that the DoF capacity can
be achieved for and
, which
provides a broader range of the DoF capacity than the existing results.
Asymptotic DoF as is also derived based on the proposed
signaling scheme.Comment: 13 pages, 7 figure
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
Degrees of Freedom of the 3-User Rank-Deficient MIMO Interference Channel
We provide the degrees of freedom (DoF) characterization for the -user
multiple-input multiple-output (MIMO) interference channel (IC)
with \emph{rank-deficient} channel matrices, where each transmitter is equipped
with antennas and each receiver with antennas, and the interfering
channel matrices from each transmitter to the other two receivers are of ranks
and , respectively. One important intermediate step for both the
converse and achievability arguments is to convert the fully-connected
rank-deficient channel into an equivalent partially-connected full-rank MIMO-IC
by invertible linear transformations. As such, existing techniques developed
for full-rank MIMO-IC can be incorporated to derive the DoF outer and inner
bounds for the rank-deficient case. Our result shows that when the interfering
links are weak in terms of the channel ranks, i.e., , zero forcing is sufficient to achieve the optimal DoF. On the other
hand, when , a combination of zero forcing and
interference alignment is in general required for DoF optimality. The DoF
characterization obtained in this paper unifies several existing results in the
literature.Comment: 28 pages, 7 figures. To appear in IEEE transactions on wireless
communication
Interference Alignment for Cognitive Radio Communications and Networks: A Survey
Β© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Interference alignment (IA) is an innovative wireless transmission strategy that has shown to be a promising technique for achieving optimal capacity scaling of a multiuser interference channel at asymptotically high-signal-to-noise ratio (SNR). Transmitters exploit the availability of multiple signaling dimensions in order to align their mutual interference at the receivers. Most of the research has focused on developing algorithms for determining alignment solutions as well as proving interference alignmentβs theoretical ability to achieve the maximum degrees of freedom in a wireless network. Cognitive radio, on the other hand, is a technique used to improve the utilization of the radio spectrum by opportunistically sensing and accessing unused licensed frequency spectrum, without causing harmful interference to the licensed users. With the increased deployment of wireless services, the possibility of detecting unused frequency spectrum becomes diminished. Thus, the concept of introducing interference alignment in cognitive radio has become a very attractive proposition. This paper provides a survey of the implementation of IA in cognitive radio under the main research paradigms, along with a summary and analysis of results under each system model.Peer reviewe
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