5,400 research outputs found
Frequency permutation arrays
Motivated by recent interest in permutation arrays, we introduce and
investigate the more general concept of frequency permutation arrays (FPAs). An
FPA of length n=m lambda and distance d is a set T of multipermutations on a
multiset of m symbols, each repeated with frequency lambda, such that the
Hamming distance between any distinct x,y in T is at least d. Such arrays have
potential applications in powerline communication. In this paper, we establish
basic properties of FPAs, and provide direct constructions for FPAs using a
range of combinatorial objects, including polynomials over finite fields,
combinatorial designs, and codes. We also provide recursive constructions, and
give bounds for the maximum size of such arrays.Comment: To appear in Journal of Combinatorial Design
Resolvable designs with large blocks
Resolvable designs with two blocks per replicate are studied from an
optimality perspective. Because in practice the number of replicates is
typically less than the number of treatments, arguments can be based on the
dual of the information matrix and consequently given in terms of block
concurrences. Equalizing block concurrences for given block sizes is often, but
not always, the best strategy. Sufficient conditions are established for
various strong optimalities and a detailed study of E-optimality is offered,
including a characterization of the E-optimal class. Optimal designs are found
to correspond to balanced arrays and an affine-like generalization.Comment: Published at http://dx.doi.org/10.1214/009053606000001253 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Low-complexity LSMR equalisation of FrFT-based multicarrier systems in doubly dispersive channels
The discrete fractional Fourier transform (FrFT) has been suggested to enhance performance over DFT-based multicarrier systems when transmitting over doubly-dispersive channels. In this paper, we propose a novel low-complexity equaliser for inter-symbol and inter-carrier interference arising in such multicarrier transmission system. Due to a lower spreading in the FrFT-domain compared to the DFTchannel matrix as compared to the DFT domain, the equaliser cam approximate the fractional-domain channel matrix by a band matrix. Further, we utilise the least squares minres (LSMR) algorithm in the calculation of the equalisation, which exhibits attractive numerical properties and low complexity. Simulation results demonstrate the superior performance of the proposed LSMR equaliser over benchmark schemes
Accurate Telescope Mount Positioning with MEMS Accelerometers
This paper describes the advantages and challenges of applying
microelectromechanical accelerometer systems (MEMS accelerometers) in order to
attain precise, accurate and stateless positioning of telescope mounts. This
provides a completely independent method from other forms of electronic,
optical, mechanical or magnetic feedback or real-time astrometry. Our goal is
to reach the sub-arcminute range which is well smaller than the field-of-view
of conventional imaging telescope systems. Here we present how this
sub-arcminute accuracy can be achieved with very cheap MEMS sensors and we also
detail how our procedures can be extended in order to attain even finer
measurements. In addition, our paper discusses how can a complete system design
be implemented in order to be a part of a telescope control system.Comment: Accepted for publication in PASP, 12 page
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