1,504,063 research outputs found
Opportunistic Interference Alignment in MIMO Interference Channels
We present two interference alignment techniques such that an opportunistic
point-to-point multiple input multiple output (MIMO) link can reuse, without
generating any additional interference, the same frequency band of a similar
pre-existing primary link. In this scenario, we exploit the fact that under
power constraints, although each radio maximizes independently its rate by
water-filling on their channel transfer matrix singular values, frequently, not
all of them are used. Therefore, by aligning the interference of the
opportunistic radio it is possible to transmit at a significant rate while
insuring zero-interference on the pre-existing link. We propose a linear
pre-coder for a perfect interference alignment and a power allocation scheme
which maximizes the individual data rate of the secondary link. Our numerical
results show that significant data rates are achieved even for a reduced number
of antennas.Comment: To appear in proc. IEEE PIMRC 2008 - Workshop in Emerging Network
Perspectives in Multiuser and Cooperative MIMO (NWMIMO). 5 pages and 4
figure
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
Capacity Region of Vector Gaussian Interference Channels with Generally Strong Interference
An interference channel is said to have strong interference if for all input
distributions, the receivers can fully decode the interference. This definition
of strong interference applies to discrete memoryless, scalar and vector
Gaussian interference channels. However, there exist vector Gaussian
interference channels that may not satisfy the strong interference condition
but for which the capacity can still be achieved by jointly decoding the signal
and the interference. This kind of interference is called generally strong
interference. Sufficient conditions for a vector Gaussian interference channel
to have generally strong interference are derived. The sum-rate capacity and
the boundary points of the capacity region are also determined.Comment: 50 pages, 11 figures, submitted to IEEE trans. on Information Theor
Mesoscopic interference
We analyze a double-slit experiment when the interfering particle is
"mesoscopic" and one endeavors to obtain Welcher Weg information by shining
light on it. We derive a compact expression for the visibility of the
interference pattern: coherence depends on both the spatial and temporal
features of the wave function during its travel to the screen. We set a bound
on the temperature of the mesoscopic particle in order that its quantum
mechanical coherence be maintained.Comment: 16 pages, 14 figure
Interference Automata
We propose a computing model, the Two-Way Optical Interference Automata
(2OIA), that makes use of the phenomenon of optical interference. We introduce
this model to investigate the increase in power, in terms of language
recognition, of a classical Deterministic Finite Automaton (DFA) when endowed
with the facility of optical interference. The question is in the spirit of
Two-Way Finite Automata With Quantum and Classical States (2QCFA) [A. Ambainis
and J. Watrous, Two-way Finite Automata With Quantum and Classical States,
Theoretical Computer Science, 287 (1), 299-311, (2002)] wherein the classical
DFA is augmented with a quantum component of constant size. We test the power
of 2OIA against the languages mentioned in the above paper. We give efficient
2OIA algorithms to recognize languages for which 2QCFA machines have been shown
to exist, as well as languages whose status vis-a-vis 2QCFA has been posed as
open questions. Finally we show the existence of a language that cannot be
recognized by a 2OIA but can be recognized by an space Turing machine.Comment: 19 pages. A preliminary version appears under the title "On a Model
of Computation based on Optical Interference" in Proc. of the 16-th
Australasian Workshop on Combinatorial Algorithms (AWOCA'05), pp. 249-26
Capacity Regions and Sum-Rate Capacities of Vector Gaussian Interference Channels
The capacity regions of vector, or multiple-input multiple-output, Gaussian
interference channels are established for very strong interference and aligned
strong interference. Furthermore, the sum-rate capacities are established for Z
interference, noisy interference, and mixed (aligned weak/intermediate and
aligned strong) interference. These results generalize known results for scalar
Gaussian interference channels.Comment: 33 pages, 1 figure, submitted to IEEE trans. on Information theor
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