10 research outputs found
The Degrees-of-Freedom of Multi-way Device-to-Device Communications is Limited by 2
A 3-user device-to-device (D2D) communications scenario is studied where each
user wants to send and receive a message from each other user. This scenario
resembles a 3-way communication channel. The capacity of this channel is
unknown in general. In this paper, a sum-capacity upper bound that
characterizes the degrees-of-freedom of the channel is derived by using
genie-aided arguments. It is further shown that the derived upper bound is
achievable within a gap of 2 bits, thus leading to an approximate sum-capacity
characterization for the 3-way channel. As a by-product, interesting analogies
between multi-way communications and multi-way relay communications are
concluded.Comment: 5 pages, ISIT 201
MIMO Multiway Relaying with Clustered Full Data Exchange: Signal Space Alignment and Degrees of Freedom
We investigate achievable degrees of freedom (DoF) for a multiple-input
multiple-output (MIMO) multiway relay channel (mRC) with clusters and
users per cluster. Each user is equipped with antennas and the relay with
antennas. We assume a new data exchange model, termed \emph{clustered full
data exchange}, i.e., each user in a cluster wants to learn the messages of all
the other users in the same cluster. Novel signal alignment techniques are
developed to systematically construct the beamforming matrices at the users and
the relay for efficient physical-layer network coding. Based on that, we derive
an achievable DoF of the MIMO mRC with an arbitrary network configuration of
and , as well as with an arbitrary antenna configuration of and .
We show that our proposed scheme achieves the DoF capacity when and .Comment: 13 pages, 4 figure
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