91,192 research outputs found
Secure Transmission with Multiple Antennas II: The MIMOME Wiretap Channel
The capacity of the Gaussian wiretap channel model is analyzed when there are
multiple antennas at the sender, intended receiver and eavesdropper. The
associated channel matrices are fixed and known to all the terminals. A
computable characterization of the secrecy capacity is established as the
saddle point solution to a minimax problem. The converse is based on a
Sato-type argument used in other broadcast settings, and the coding theorem is
based on Gaussian wiretap codebooks.
At high signal-to-noise ratio (SNR), the secrecy capacity is shown to be
attained by simultaneously diagonalizing the channel matrices via the
generalized singular value decomposition, and independently coding across the
resulting parallel channels. The associated capacity is expressed in terms of
the corresponding generalized singular values. It is shown that a semi-blind
"masked" multi-input multi-output (MIMO) transmission strategy that sends
information along directions in which there is gain to the intended receiver,
and synthetic noise along directions in which there is not, can be arbitrarily
far from capacity in this regime.
Necessary and sufficient conditions for the secrecy capacity to be zero are
provided, which simplify in the limit of many antennas when the entries of the
channel matrices are independent and identically distributed. The resulting
scaling laws establish that to prevent secure communication, the eavesdropper
needs 3 times as many antennas as the sender and intended receiver have
jointly, and that the optimimum division of antennas between sender and
intended receiver is in the ratio of 2:1.Comment: To Appear, IEEE Trans. Information Theor
Distributed Voltage and Current Control of Multi-Terminal High-Voltage Direct Current Transmission Systems
High-voltage direct current (HVDC) is a commonly used technology for
long-distance power transmission, due to its low resistive losses and low
costs. In this paper, a novel distributed controller for multi-terminal HVDC
(MTDC) systems is proposed. Under certain conditions on the controller gains,
it is shown to stabilize the MTDC system. The controller is shown to always
keep the voltages close to the nominal voltage, while assuring that the
injected power is shared fairly among the converters. The theoretical results
are validated by simulations, where the affect of communication time-delays is
also studied
Distributed PI-Control with Applications to Power Systems Frequency Control
This paper considers a distributed PI-controller for networked dynamical
systems. Sufficient conditions for when the controller is able to stabilize a
general linear system and eliminate static control errors are presented. The
proposed controller is applied to frequency control of power transmission
systems. Sufficient stability criteria are derived, and it is shown that the
controller parameters can always be chosen so that the frequencies in the
closed loop converge to nominal operational frequency. We show that the load
sharing property of the generators is maintained, i.e., the input power of the
generators is proportional to a controller parameter. The controller is
evaluated by simulation on the IEEE 30 bus test network, where its
effectiveness is demonstrated
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