47 research outputs found
The DMT classification of real and quaternionic lattice codes
In this paper we consider space-time codes where the code-words are
restricted to either real or quaternion matrices. We prove two separate
diversity-multiplexing gain trade-off (DMT) upper bounds for such codes and
provide a criterion for a lattice code to achieve these upper bounds. We also
point out that lattice codes based on Q-central division algebras satisfy this
optimality criterion. As a corollary this result provides a DMT classification
for all Q-central division algebra codes that are based on standard embeddings.Comment: 6 pages, 1 figure. Conference paper submitted to the International
Symposium on Information Theory 201
Algebraic Hybrid Satellite-Terrestrial Space-Time Codes for Digital Broadcasting in SFN
Lately, different methods for broadcasting future digital TV in a single
frequency network (SFN) have been under an intensive study. To improve the
transmission to also cover suburban and rural areas, a hybrid scheme may be
used. In hybrid transmission, the signal is transmitted both from a satellite
and from a terrestrial site. In 2008, Y. Nasser et al. proposed to use a double
layer 3D space-time (ST) code in the hybrid 4 x 2 MIMO transmission of digital
TV. In this paper, alternative codes with simpler structure are proposed for
the 4 x 2 hybrid system, and new codes are constructed for the 3 x 2 system.
The performance of the proposed codes is analyzed through computer simulations,
showing a significant improvement over simple repetition schemes. The proposed
codes prove in addition to be very robust in the presence of power imbalance
between the two sites.Comment: 14 pages, 2 figures, submitted to ISIT 201
Fast-Decodable Asymmetric Space-Time Codes from Division Algebras
Multiple-input double-output (MIDO) codes are important in the near-future
wireless communications, where the portable end-user device is physically small
and will typically contain at most two receive antennas. Especially tempting is
the 4 x 2 channel due to its immediate applicability in the digital video
broadcasting (DVB). Such channels optimally employ rate-two space-time (ST)
codes consisting of (4 x 4) matrices. Unfortunately, such codes are in general
very complex to decode, hence setting forth a call for constructions with
reduced complexity.
Recently, some reduced complexity constructions have been proposed, but they
have mainly been based on different ad hoc methods and have resulted in
isolated examples rather than in a more general class of codes. In this paper,
it will be shown that a family of division algebra based MIDO codes will always
result in at least 37.5% worst-case complexity reduction, while maintaining
full diversity and, for the first time, the non-vanishing determinant (NVD)
property. The reduction follows from the fact that, similarly to the Alamouti
code, the codes will be subsets of matrix rings of the Hamiltonian quaternions,
hence allowing simplified decoding. At the moment, such reductions are among
the best known for rate-two MIDO codes. Several explicit constructions are
presented and shown to have excellent performance through computer simulations.Comment: 26 pages, 1 figure, submitted to IEEE Trans. Inf. Theory, October
201
Almost universal codes for fading wiretap channels
We consider a fading wiretap channel model where the transmitter has only
statistical channel state information, and the legitimate receiver and
eavesdropper have perfect channel state information. We propose a sequence of
non-random lattice codes which achieve strong secrecy and semantic security
over ergodic fading channels. The construction is almost universal in the sense
that it achieves the same constant gap to secrecy capacity over Gaussian and
ergodic fading models.Comment: 5 pages, to be submitted to IEEE International Symposium on
Information Theory (ISIT) 201
Number field lattices achieve Gaussian and Rayleigh channel capacity within a constant gap
This paper proves that a family of number field lattice codes simultaneously
achieves a constant gap to capacity in Rayleigh fast fading and Gaussian
channels.
The key property in the proof is the existence of infinite towers of Hilbert
class fields with bounded root discriminant. The gap to capacity of the
proposed families is determined by the root discriminant.
The comparison between the Gaussian and fading case reveals that in Rayleigh
fading channels the normalized minimum product distance plays an analogous role
to the Hermite invariant in Gaussian channels.Comment: Will be submitted to ISIT. Comments, suggestions for references etc.
are warmly welcome. Edit:Appendix adde