103 research outputs found
Interference alignment for the MIMO interference channel
We study vector space interference alignment for the MIMO interference
channel with no time or frequency diversity, and no symbol extensions. We prove
both necessary and sufficient conditions for alignment. In particular, we
characterize the feasibility of alignment for the symmetric three-user channel
where all users transmit along d dimensions, all transmitters have M antennas
and all receivers have N antennas, as well as feasibility of alignment for the
fully symmetric (M=N) channel with an arbitrary number of users.
An implication of our results is that the total degrees of freedom available
in a K-user interference channel, using only spatial diversity from the
multiple antennas, is at most 2. This is in sharp contrast to the K/2 degrees
of freedom shown to be possible by Cadambe and Jafar with arbitrarily large
time or frequency diversity.
Moving beyond the question of feasibility, we additionally discuss
computation of the number of solutions using Schubert calculus in cases where
there are a finite number of solutions.Comment: 16 pages, 7 figures, final submitted versio
Retrospective Interference Alignment for the 3-user MIMO Interference Channel with delayed CSIT
The degrees of freedom (DoF) of the 3-user multiple input multiple output
interference channel (3-user MIMO IC) are investigated where there is delayed
channel state information at the transmitters (dCSIT). We generalize the ideas
of Maleki et al. about {\it Retrospective Interference Alignment (RIA)} to be
applied to the MIMO IC, where transmitters and receivers are equipped with
antennas, respectively. We propose a two-phase transmission scheme
where the number of slots per phase and number of transmitted symbols are
optimized by solving a maximization problem. Finally, we review the existing
achievable DoF results in the literature as a function of the ratio between
transmitting and receiving antennas . The proposed scheme improves
all other strategies when .Comment: Draft version of the accepted manuscript at IEEE ICASSP 1
On the Degrees of freedom of the K-user MISO Interference Channel with imperfect delayed CSIT
This work investigates the degrees of freedom (DoF) of the K-user
multiple-input single-output (MISO) interference channel (IC) with imperfect
delayed channel state information at the transmitters (dCSIT). For this
setting, new DoF inner bonds are provided, and benchmarked with
cooperation-based outer bounds. The achievability result is based on a
precoding scheme that aligns the interfering received signals through time,
exploiting the concept of Retrospective Interference Alignment (RIA). The
proposed approach outperforms all previous known schemes. Furthermore, we study
the proposed scheme under channel estimation errors (CEE) on the reported
dCSIT, and derive a closed-form expression for the achievable DoF with
imperfect dCSIT.Comment: Draft version of the accepted manuscript at IEEE ICASSP 1
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