arXiv subjects

Thomas Unger

Publications and source records attributed to Thomas Unger.

21 records · Page 2Linked to original sources

arXiv2012

A hermitian analogue of the Broecker-Prestel theorem

The Broecker-Prestel local-global principle characterizes weak isotropy of quadratic forms over a formally real field in terms of weak isotropy over the henselizations and isotropy over the real closures of that field. A hermitian analogue of this principle is presented for algebras of index at most two. An improved result is also presented for algebras with a decomposable involution, algebras of pythagorean index at most two, and algebras over SAP and ED fields.

math.RA↗

arXiv2011

Space-time block codes from nonassociative division algebras

Associative division algebras are a rich source of fully diverse space-time block codes (STBCs). In this paper the systematic construction of fully diverse STBCs from nonassociative algebras is discussed. As examples, families of fully diverse $2\times 2$, $2\times 4$ multiblock and $4\x 4$ STBCs are designed, employing nonassociative quaternion division algebras.

cs.IT↗

arXiv2011

Quadratic Forms and Space-Time Block Codes from Generalized Quaternion and Biquaternion Algebras

In the context of space-time block codes (STBCs), the theory of generalized quaternion and biquaternion algebras (i.e., tensor products of two quaternion algebras) over arbitrary base fields is presented, as well as quadratic form theoretic criteria to check if such algebras are division algebras. For base fields relevant to STBCs, these criteria are exploited, via Springer's theorem, to construct several explicit infinite families of (bi-)quaternion division algebras. These are used to obtain new $2\x 2$ and $4\x 4$ STBCs.

cs.IT↗