32,934 research outputs found
The Approximate Capacity of the MIMO Relay Channel
Capacity bounds are studied for the multiple-antenna complex Gaussian relay
channel with t1 transmitting antennas at the sender, r2 receiving and t2
transmitting antennas at the relay, and r3 receiving antennas at the receiver.
It is shown that the partial decode-forward coding scheme achieves within
min(t1,r2) bits from the cutset bound and at least one half of the cutset
bound, establishing a good approximate expression of the capacity. A similar
additive gap of min(t1 + t2, r3) + r2 bits is shown to be achieved by the
compress-forward coding scheme.Comment: 8 pages, 5 figures, submitted to the IEEE Transactions on Information
Theor
On a New Approach for Constructing Wormholes in Einstein-Born-Infeld Gravity
We study a new approach for the wormhole construction in Einstein-Born-Infeld
gravity, which does not require exotic matters in the Einstein equation. The
Born-Infeld field equation is not modified from "coordinate independent"
conditions of continuous metric tensor and its derivatives, even though the
Born-Infeld fields have discontinuities in their derivatives at the throat in
general. We study the relation of the newly introduced conditions with the
usual continuity equation for the energy-momentum tensor and the gravitational
Bianchi identity. We find that there is no violation of energy conditions for
the Born-Infeld fields contrary to the usual approaches. The exoticity of
energy-momentum tensor is not essential for sustaining wormholes. Some open
problems are discussed.Comment: Minor revision to improve the clarity, Corrected typos, Added
reference and footnot
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