672 research outputs found
Degrees of Freedom for the MIMO Multi-way Relay Channel
This paper investigates the degrees of freedom (DoF) of the L-cluster, K-user
MIMO multi-way relay channel, where users in each cluster wish to exchange
messages within the cluster, and they can only communicate through the relay. A
novel DoF upper bound is derived by providing users with carefully designed
genie information. Achievable DoF is identified using signal space alignment
and multiple-access transmission. For the two-cluster MIMO multi-way relay
channel with two users in each cluster, DoF is established for the general case
when users and the relay have arbitrary number of antennas, and it is shown
that the DoF upper bound can be achieved using signal space alignment or
multiple-access transmission, or a combination of both. The result is then
generalized to the three user case. For the L-cluster K-user MIMO multi-way
relay channel in the symmetric setting, conditions under which the DoF upper
bound can be achieved are established. In addition to being shown to be tight
in a variety of scenarios of interests of the multi-way relay channel, the
newly derived upperbound also establishes the optimality of several previously
established achievable DoF results for multiuser relay channels that are
special cases of the multi-way relay channel.Comment: submitted to IEEE Transactions on Information Theor
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
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
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
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
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