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Cyclic Interference Alignment and Cancellation in 3-User X-Networks with Minimal Backhaul
We consider the problem of Cyclic Interference Alignment (IA) on the 3-user
X-network and show that it is infeasible to exactly achieve the upper bound of
degrees of freedom for the lower bound of n=5
signalling dimensions and K=3 user-pairs. This infeasibility goes beyond the
problem of common eigenvectors in invariant subspaces within spatial IA.
In order to gain non-asymptotic feasibility with minimal intervention, we
first investigate an alignment strategy that enables IA by feedforwarding a
subset of messages with minimal rate. In a second step, we replace the proposed
feedforward strategy by an analogous Cyclic Interference Alignment and
Cancellation scheme with a backhaul network on the receiver side and also by a
dual Cyclic Interference Neutralization scheme with a backhaul network on the
transmitter side.Comment: 8 pages, short version submitted to ISIT 201
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