12,578 research outputs found
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
Baryogenesis at a Lepton-Number-Breaking Phase Transition
We study a scenario in which the baryon asymmetry of the universe arises from
a cosmological phase transition where lepton-number is spontaneously broken. If
the phase transition is first order, a lepton-number asymmetry can arise at the
bubble wall, through dynamics similar to electroweak baryogenesis, but
involving right-handed neutrinos. In addition to the usual neutrinoless double
beta decay in nuclear experiments, the model may be probed through a variety of
"baryogenesis by-products," which include a stochastic background of
gravitational waves created by the colliding bubbles. Depending on the model,
other aspects may include a network of topological defects that produce their
own gravitational waves, additional contribution to dark radiation, and a light
pseudo-Goldstone boson (majoron) as dark matter candidate.Comment: 21 pages + 10 appendices & references, 3 figure
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