263,728 research outputs found
Maximally Flexible Assignment of Orthogonal Variable Spreading Factor Codes for Multi-Rate Traffic
In universal terrestrial radio access (UTRA) systems, orthogonal variable spreading factor (OVSF) codes are used to support different transmission rates for different users. In this paper, we first define the flexibility index to measure the capability of an assignable code set in supporting multirate traffic classes. Based on this index, two single-code assignment schemes, nonrearrangeable and rearrangeable compact assignments, are proposed. Both schemes can offer maximal flexibility for the resulting code tree after each code assignment. We then present an analytical model and derive the call blocking probability, system throughput and fairness index. Analytical and simulation results show that the proposed schemes are efficient, stable and fair
On deformed double current algebras for simple Lie algebras
We prove the equivalence of two presentations of deformed double current
algebras associated to a complex simple Lie algebra, the first one obtained via
a degeneration of affine Yangians while the other one naturally appeared in the
construction of the elliptic Casimir connection. We also construct a specific
central element of these algebras and, in type A, show that they contain a very
large center for certain values of their parameters.Comment: 40 page
Optimal asymptotic cloning machines
We pose the question whether the asymptotic equivalence between quantum
cloning and quantum state estimation, valid at the single-clone level, still
holds when all clones are examined globally. We conjecture that the answer is
affirmative and present a large amount of evidence supporting our conjecture,
developing techniques to derive optimal asymptotic cloners and proving their
equivalence with estimation in virtually all scenarios considered in the
literature. Our analysis covers the case of arbitrary finite sets of states,
arbitrary families of coherent states, arbitrary phase- and
multiphase-covariant sets of states, and two-qubit maximally entangled states.
In all these examples we observe that the optimal asymptotic fidelity enjoys a
universality property, as its scaling does not depend on the specific details
of the set of input states, but only on the number of parameters needed to
specify them.Comment: 27 + 9 pages, corrected one observation about cloning of maximally
entangled state
Delay distributions of slotted ALOHA and CSMA
We derive the closed-form delay distributions of slotted ALOHA and nonpersistent carrier sense multiple access (CSMA) protocols under steady state. Three retransmission policies are analyzed. We find that under a binary exponential backoff retransmission policy, finite average delay and finite delay variance can be guaranteed for G<2S and G<4S/3, respectively, where G is the channel traffic and S is the channel throughput. As an example, in slotted ALOHA, S<(ln2)/2 and S<3(ln4-ln3)/4 are the operating ranges for finite first and second delay moments. In addition, the blocking probability and delay performance as a function of r/sub max/ (maximum number of retransmissions allowed) is also derived
A Remark on Soliton Equation of Mean Curvature Flow
In this short note, we consider self-similar immersions of the Graphic Mean Curvature Flow of higher co-dimension. We
show that the following is true: Let be
a graph solution to the soliton equation
Assume . Then there exists a
unique smooth function such that
and for any real number , where Comment: 6 page
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