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- Oliver Henkel
- IEEE Transactions on Information Theory
- 2005

Applying the Riemann geometric machinery of volume estimates in terms of curvature, bounds for the minimal distance of packings/codes in the Grassmann and Stiefel manifolds will be derived and analyzed. In the context of space-time block codes this leads to a monotonically increasing minimal distance lower bound as a function of the block length. This… (More)

- Oliver Henkel
- 2001

This work investigates some global questions about cosmological spacetimes with two dimensional spherical, plane and hyperbolic symmetry containing matter. The result is, that these spacetimes admit a global foliation by prescribed mean curvature surfaces, which extends at least towards a crushing singularity. The time function of the foliation is… (More)

- Aydin Sezgin, Eduard A. Jorswieck, Oliver Henkel, Stephanie Pereira, Arogyaswami Paulraj
- IEEE Transactions on Signal Processing
- 2008

Recently, the statistical properties of the equivalent channel representation of a multiple-input-multiple output (MIMO) system employing code rate one quasi-orthogonal space-time block codes (QSTBC), which are constructed by using orthogonal space-time block codes (OSTBC) as building elements, was characterized. Based on these characterizations we analyze… (More)

- Oliver Henkel
- IEEE Trans. Information Theory
- 2006

In this work, the geometric relation between space time block code design for the coherent channel and its noncoherent counterpart is exploited to get an analogue of the information theoretic inequality I(X;S) I((X;H);S) in terms of diversity. It provides a lower bound on the performance of non-coherent codes when used in coherent scenarios. This leads in… (More)

- Oliver Henkel
- ICASSP
- 2005

In this work, the natural geometric relation between the space time block code design if the channel is unknown at the receiver and its counterpart design if the receiver knows the channel is exploited, to establish an estimate on the corresponding diversities. This leads to a decomposition of code designs and splits the design problem into two complexity… (More)

- Oliver Henkel
- Proceedings. International Symposium on…
- 2005

A new design method for high rate, fully diverse ('spherical') space frequency codes for MIMO-OFDM systems is proposed, which works for arbitrary numbers of antennas and subcarriers. The construction exploits a differential geometric connection between spherical codes and space time codes. The former are well studied e.g. in the context of optimal sequence… (More)

- Oliver Henkel
- GLOBECOM
- 2006

A new class of space time codes with high performance is presented. The code design utilizes tailor-made permutation codes, which are known to have large minimal distances as spherical codes. A geometric connection between spherical and space time codes has been used to translate them into the final space time codes. Simulations demonstrate that the… (More)

- Aydin Sezgin, Oliver Henkel
- IEEE Transactions on Signal Processing
- 2007

It is well known that the Alamouti scheme is the only space-time code from orthogonal designs achieving the capacity of a multiple-input multiple-output (MIMO) wireless communication system with n<sub>T</sub>=2 transmit antennas and n<sub>R</sub>=1 receive antenna. In this paper, we propose the n-times stacked Alamouti scheme for n<sub>T</sub>=2n transmit… (More)

- Oliver Henkel
- 2001

A theorem about local in time existence of spacelike foliations with prescribed mean curvature in cosmological spacetimes will be proved. The time function of the foliation is geometrically defined and fixes the diffeomorphism invariance inherent in general foliations of spacetimes. Moreover, in contrast to the situation of the more special constant mean… (More)

- Oliver Henkel
- 2004

This second part is devoted to the investigation of global properties of Prescribed Mean Curvature (PMC) foliations in cosmological spacetimes with local U(1)× U(1) symmetry and matter described by the Vlasov equation. It turns out, that these spacetimes admit a global foliation by PMC surfaces, as well, but the techniques to achieve this goal are more… (More)