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Browsing by Subject "Input-output"

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    Fast and accurate algorithm for the computation of complex linear canonical transforms
    (Optical Society of America, 2010-08-05) Koç A.; Özaktaş, Haldun M.; Hesselink, L.
    A fast and accurate algorithm is developed for the numerical computation of the family of complex linear canonical transforms (CLCTs), which represent the input-output relationship of complex quadratic-phase systems. Allowing the linear canonical transform parameters to be complex numbers makes it possible to represent paraxial optical systems that involve complex parameters. These include lossy systems such as Gaussian apertures, Gaussian ducts, or complex graded-index media, as well as lossless thin lenses and sections of free space and any arbitrary combinations of them. Complex-ordered fractional Fourier transforms (CFRTs) are a special case of CLCTs, and therefore a fast and accurate algorithm to compute CFRTs is included as a special case of the presented algorithm. The algorithm is based on decomposition of an arbitrary CLCT matrix into real and complex chirp multiplications and Fourier transforms. The samples of the output are obtained from the samples of the input in ∼N log N time, where N is the number of input samples. A space-bandwidth product tracking formalism is developed to ensure that the number of samples is information-theoretically sufficient to reconstruct the continuous transform, but not unnecessarily redundant.
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    An improvement of the deletion channel capacity upper bound
    (IEEE, 2013-10) Rahmati, M.; Duman, Tolga M.
    In this paper, we offer an alternative look at channels with deletion errors by considering equivalent models for deletion channels by 'fragmenting' the input sequence where different subsequences travel through different channels. The resulting output symbols are combined appropriately to come up with an equivalent input-output representation of the original channel which allows for derivation of new upper bounds on the channel capacity. Considering a random fragmentation processes applied to binary deletion channels, we prove an inequality relation among the capacities of the original binary deletion channel and the introduced binary deletion subchannels. This inequality enables us to provide an improved upper bound on the capacity of the i.i.d. deletion channels, i.e., C(d) ≤ 0.4143(1 - d) for d ≥ 0.65. We also consider a deterministic fragmentation process suitable for the study of non-binary deletion channels which results in improved capacity upper bounds. © 2013 IEEE.
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    PID controller design for fractional-order systems with time delays
    (Elsevier, 2011-11-22) Özbay, Hitay; Bonnet, C.; Fioravanti, A.R.
    Classical proper PID controllers are designed for linear time invariant plants whose transfer functions are rational functions of sα, where 0<α<1, and s is the Laplace transform variable. Effect of inputoutput time delay on the range of allowable controller parameters is investigated. The allowable PID controller parameters are determined from a small gain type of argument used earlier for finite dimensional plants.

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