491 research outputs found
On the Feasibility of Linear Interference Alignment for MIMO Interference Broadcast Channels with Constant Coefficients
In this paper, we analyze the feasibility of linear interference alignment
(IA) for multi-input-multi-output (MIMO) interference broadcast channel
(MIMO-IBC) with constant coefficients. We pose and prove the necessary
conditions of linear IA feasibility for general MIMO-IBC. Except for the proper
condition, we find another necessary condition to ensure a kind of irreducible
interference to be eliminated. We then prove the necessary and sufficient
conditions for a special class of MIMO-IBC, where the numbers of antennas are
divisible by the number of data streams per user. Since finding an invertible
Jacobian matrix is crucial for the sufficiency proof, we first analyze the
impact of sparse structure and repeated structure of the Jacobian matrix.
Considering that for the MIMO-IBC the sub-matrices of the Jacobian matrix
corresponding to the transmit and receive matrices have different repeated
structure, we find an invertible Jacobian matrix by constructing the two
sub-matrices separately. We show that for the MIMO-IBC where each user has one
desired data stream, a proper system is feasible. For symmetric MIMO-IBC, we
provide proper but infeasible region of antenna configurations by analyzing the
difference between the necessary conditions and the sufficient conditions of
linear IA feasibility.Comment: 14 pages, 3 figures, accepted by IEEE Trans. on Signal Processin
On the Degrees of Freedom of Asymmetric MIMO Interference Broadcast Channels
In this paper, we study the degrees of freedom (DoF) of the asymmetric
multi-input-multi-output interference broadcast channel (MIMO-IBC). By
introducing a notion of connection pattern chain, we generalize the genie chain
proposed in [11] to derive and prove the necessary condition of IA feasibility
for asymmetric MIMO-IBC, which is denoted as irreducible condition. It is
necessary for both linear interference alignment (IA) and asymptotic IA
feasibility in MIMO-IBC with arbitrary configurations. In a special class of
asymmetric two-cell MIMOIBC, the irreducible condition is proved to be the
sufficient and necessary condition for asymptotic IA feasibility, while the
combination of proper condition and irreducible condition is proved to the
sufficient and necessary condition for linear IA feasibility. From these
conditions, we derive the information theoretic maximal DoF per user and the
maximal DoF per user achieved by linear IA, and these DoFs are also the DoF per
user upper-bounds of asymmetric G-cell MIMO-IBC with asymptotic IA and linear
IA, respectively.Comment: 6 pages, 3 figures, submitted to ICC 201
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