43 research outputs found
Algebraic lattice constellations: bounds on performance
In this work, we give a bound on performance of any full-diversity lattice constellation constructed from algebraic number fields. We show that most of the already available constructions are almost optimal in the sense that any further improvement of the minimum product distance would lead to a negligible coding gain. Furthermore, we discuss constructions, minimum product distance, and bounds for full-diversity complex rotated Z[i]/sup n/-lattices for any dimension n, which avoid the need of component interleaving
End-to-End Joint Antenna Selection Strategy and Distributed Compress and Forward Strategy for Relay Channels
Multi-hop relay channels use multiple relay stages, each with multiple relay
nodes, to facilitate communication between a source and destination.
Previously, distributed space-time codes were proposed to maximize the
achievable diversity-multiplexing tradeoff, however, they fail to achieve all
the points of the optimal diversity-multiplexing tradeoff. In the presence of a
low-rate feedback link from the destination to each relay stage and the source,
this paper proposes an end-to-end antenna selection (EEAS) strategy as an
alternative to distributed space-time codes. The EEAS strategy uses a subset of
antennas of each relay stage for transmission of the source signal to the
destination with amplify and forwarding at each relay stage. The subsets are
chosen such that they maximize the end-to-end mutual information at the
destination. The EEAS strategy achieves the corner points of the optimal
diversity-multiplexing tradeoff (corresponding to maximum diversity gain and
maximum multiplexing gain) and achieves better diversity gain at intermediate
values of multiplexing gain, versus the best known distributed space-time
coding strategies. A distributed compress and forward (CF) strategy is also
proposed to achieve all points of the optimal diversity-multiplexing tradeoff
for a two-hop relay channel with multiple relay nodes.Comment: Accepted for publication in the special issue on cooperative
communication in the Eurasip Journal on Wireless Communication and Networkin
On the Transmit Beamforming for MIMO Wiretap Channels: Large-System Analysis
With the growth of wireless networks, security has become a fundamental issue
in wireless communications due to the broadcast nature of these networks. In
this work, we consider MIMO wiretap channels in a fast fading environment, for
which the overall performance is characterized by the ergodic MIMO secrecy
rate. Unfortunately, the direct solution to finding ergodic secrecy rates is
prohibitive due to the expectations in the rates expressions in this setting.
To overcome this difficulty, we invoke the large-system assumption, which
allows a deterministic approximation to the ergodic mutual information.
Leveraging results from random matrix theory, we are able to characterize the
achievable ergodic secrecy rates. Based on this characterization, we address
the problem of covariance optimization at the transmitter. Our numerical
results demonstrate a good match between the large-system approximation and the
actual simulated secrecy rates, as well as some interesting features of the
precoder optimization.Comment: Published in Lecture Notes in Computer Science 8317, pp. 90-102,
2014. (Proceedings of International Conference on Information-Theoretic
Security (ICITS), Singapore, November 2013
How to obtain division algebras used for fast-decodable space-time block codes
We present families of unital algebras obtained through a doubling process from a cyclic central simple algebra D, employing a K-automorphism tau and an invertible element d in D. These algebras appear in the construction of iterated space-time block codes. We give conditions when these iterated algebras are division which can be used to construct fully diverse iterated codes. We also briefly look at algebras (and codes) obtained from variations of this method
Secrecy capacity of a class of orthogonal relay eavesdropper channels
The secrecy capacity of relay channels with orthogonal components is studied
in the presence of an additional passive eavesdropper node. The relay and
destination receive signals from the source on two orthogonal channels such
that the destination also receives transmissions from the relay on its channel.
The eavesdropper can overhear either one or both of the orthogonal channels.
Inner and outer bounds on the secrecy capacity are developed for both the
discrete memoryless and the Gaussian channel models. For the discrete
memoryless case, the secrecy capacity is shown to be achieved by a partial
decode-and-forward (PDF) scheme when the eavesdropper can overhear only one of
the two orthogonal channels. Two new outer bounds are presented for the
Gaussian model using recent capacity results for a Gaussian multi-antenna
point-to-point channel with a multi-antenna eavesdropper. The outer bounds are
shown to be tight for two sub-classes of channels. The first sub-class is one
in which the source and relay are clustered and the and the eavesdropper
receives signals only on the channel from the source and the relay to the
destination, for which the PDF strategy is optimal. The second is a sub-class
in which the source does not transmit to the relay, for which a
noise-forwarding strategy is optimal.Comment: Submitted to Eurasip Journal on Wireless Communications and
Networking special issue on Wireless physical layer security, Dec. 2008,
Revised Jun. 200
Secured Communication over Frequency-Selective Fading Channels: a practical Vandermonde precoding
In this paper, we study the frequency-selective broadcast channel with
confidential messages (BCC) in which the transmitter sends a confidential
message to receiver 1 and a common message to receivers 1 and 2. In the case of
a block transmission of N symbols followed by a guard interval of L symbols,
the frequency-selective channel can be modeled as a N * (N+L) Toeplitz matrix.
For this special type of multiple-input multiple-output (MIMO) channels, we
propose a practical Vandermonde precoding that consists of projecting the
confidential messages in the null space of the channel seen by receiver 2 while
superposing the common message. For this scheme, we provide the achievable rate
region, i.e. the rate-tuple of the common and confidential messages, and
characterize the optimal covariance inputs for some special cases of interest.
It is proved that the proposed scheme achieves the optimal degree of freedom
(d.o.f) region. More specifically, it enables to send l <= L confidential
messages and N-l common messages simultaneously over a block of N+L symbols.
Interestingly, the proposed scheme can be applied to secured multiuser
scenarios such as the K+1-user frequency-selective BCC with K confidential
messages and the two-user frequency-selective BCC with two confidential
messages. For each scenario, we provide the achievable secrecy degree of
freedom (s.d.o.f.) region of the corresponding frequency-selective BCC and
prove the optimality of the Vandermonde precoding. One of the appealing
features of the proposed scheme is that it does not require any specific
secrecy encoding technique but can be applied on top of any existing powerful
encoding schemes.Comment: To appear in EURASIP journal on Wireless Communications and
Networking, special issue on Wireless Physical Security, 200
Secret Sharing over Fast-Fading MIMO Wiretap Channels
Secret sharing over the fast-fading MIMO wiretap channel is considered. A
source and a destination try to share secret information over a fast-fading
MIMO channel in the presence of a wiretapper who also makes channel
observations that are different from but correlated to those made by the
destination. An interactive authenticated unrestricted public channel is also
available for use by the source and destination in the secret sharing process.
This falls under the "channel-type model with wiretapper" considered by
Ahlswede and Csiszar. A minor extension of their result (to continuous channel
alphabets) is employed to evaluate the key capacity of the fast-fading MIMO
wiretap channel. The effects of spatial dimensionality provided by the use of
multiple antennas at the source, destination, and wiretapper are then
investigated.Comment: Revision submitted to EURASIP Journal on Wireless Communications and
Networking, Special Issue on Wireless Physical Layer Security, Sept. 2009.
v.3: Fixes to proofs. Matthieu Bloch added as co-author for contributions to
proof