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Crosslinking in parallel
A crosslink is a double link established between the two entries of an edge in an adjacency list representation of a graph. Crosslinks play important roles in several parallel algorithms as they provide constant time access between the two entries of an edge; the existence of crosslinks is usually assumed. We consider the problem of establishing crosslinks in a crosslink-less adjacency list for graphs that belong to a class of graphs called the linearly contractible graphs, and show that cross-links can be established optimally in O(log n log*n) time using a CREW PRAM and optimally in O(log n) time using a CRCW PRAM for such graphs
Modulation Diversity for Spatial Modulation Using Complex Interleaved Orthogonal Design
In this paper, we propose modulation diversity techniques for Spatial
Modulation (SM) system using Complex Interleaved Orthogonal Design (CIOD) meant
for two transmit antennas. Specifically, we show that by using the CIOD for two
transmit antenna system, the standard SM scheme, where only one transmit
antenna is activated in any symbol duration, can achieve a transmit diversity
order of two. We show with our simulation results that the proposed schemes
offer transmit diversity order of two, and hence, give a better Symbol Error
Rate performance than the SM scheme with transmit diversity order of one.Comment: 7 page
A Fast Eigen Solution for Homogeneous Quadratic Minimization with at most Three Constraints
We propose an eigenvalue based technique to solve the Homogeneous Quadratic
Constrained Quadratic Programming problem (HQCQP) with at most 3 constraints
which arise in many signal processing problems. Semi-Definite Relaxation (SDR)
is the only known approach and is computationally intensive. We study the
performance of the proposed fast eigen approach through simulations in the
context of MIMO relays and show that the solution converges to the solution
obtained using the SDR approach with significant reduction in complexity.Comment: 15 pages, The same content without appendices is accepted and is to
be published in IEEE Signal Processing Letter
Structured Dispersion Matrices From Division Algebra Codes for Space-Time Shift Keying
We propose a novel method of constructing Dispersion Matrices (DM) for Coherent Space-Time Shift Keying (CSTSK) relying on arbitrary PSK signal sets by exploiting codes from division algebras. We show that classic codes from Cyclic Division Algebras (CDA) may be interpreted as DMs conceived for PSK signal sets. Hence various benefits of CDA codes such as their ability to achieve full diversity are inherited by CSTSK. We demonstrate that the proposed CDA based DMs are capable of achieving a lower symbol error ratio than the existing DMs generated using the capacity as their optimization objective function for both perfect and imperfect channel estimation
A No-go theorem for de Sitter compactifications?
A general framework for studying compactifications in supergravity and string
theories was introduced by Candelas, Horowitz, Strominger and Witten. This was
further generalised to take into account the warp factor by de Wit, Smit and
Hari Dass. Though the prime focus of the latter was to find solutions with
nontrivial warp factors (shown not to exist under a variety of circumstances),
it was shown there that de Sitter compactifications are generically
disfavoured. In this note we place these results in the context of a revived
interest in de Sitter spacetimes .Comment: 11 pages in LATEX. Contribution to the "First IUCAA meeting on the
Interface of Gravitational and Quantum Realms", Pune, Dec 2001. To appear in
Modern Physics Letters
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