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• EVALUATION OF THE FUNCTIONAL ELEMENTS INFLUENCE ON THE PARAMETERS OF THE QKD SYSTEM BASED ON B92 PROTOCOL

  К.Е. Rumyantsev, P.D. Mironova, H.H. Shakir

  2022-11-01

  Abstract ▼

  The influence of the parameters of functional elements on the energy, time and probabilistic
  characteristics of the quantum key distribution system (QKD) based on the B92 protocol is studied.
  The dependences of the probability of writing correct and erroneous bits into a raw quantum
  key sequence are plotted for various lengths of a fiber-optic communication line (FOCL) and the
  use of various lasers (EML-laser; DFB-laser; VCSEL-laser and FP-laser) and photodetector
  modules (id201; id210; id220; id230). Thus, changes in the probability of writing a correct bit into
  a raw quantum key sequence are much more significant than changes in the probability of writing
  an erroneous bit (50.9 times versus 3.3 times with FWHM=80 pm and a change in the length of
  the FOCL from 10 to 100 km). This is due to the fact that with an increase in the length of the
  FOCL, the probability of the absence of registration at the receiving station of photons or dark
  current pulses (DCP) sharply increases. Numerical material indicates a direct proportional dependence
  of the probability of writing an erroneous bit on the frequency of generation of noise
  pulses of single-photon avalanche photodiodes (SAPD). So, with an increase in the frequency of
  occurrence of DCP by 60 times (from 100 to 6000 Hz), the probability of recording an erroneous
  bit also increases by 60 times (for example, with a FOCL length of 100 km – 6.39 versus 383.3).
  It has been established that the root-mean-square deviation of the photon delay time is directly proportional to the length of the FOCL and the width of the laser spectrum. With a spectrum width
  of FWHM=10 pm and an increase in the FOCL length from 10 to 100 km (by a factor of 10), the
  standard deviation of the photon delay time also increases by a factor of 10 (from 4.16 to 41.6 ps).
  To achieve the best performance of the QKD system as a whole, it is advisable to use a laser with
  a minimum width of the radiation spectrum, for example, an EML-laser. However, EML-lasers are
  considered the most complex and expensive of all the considered types of lasers, so the use of
  EML-lasers significantly increases the cost of the entire QKD system.

• NON-PARAMETRIC METHOD FOR DETECTING BREAKDOWN OF TIME SERIES USING THE RANDOM WALKS THEORY MECHANISM

  G. F. Filaretov , Z. Bouchaala

  2020-11-22

  Abstract ▼

  The task of the on-line detection of a sudden change in the probability properties of a time series
  is considered, which is usually interpreted as the detecting task of change point the characteristics
  (breakdown) in the observed stochastic process. The actuality of the development of research on this
  topic is noted, which is due to the emergence of ever new applied problems where methods and algorithms
  for breakdown detecting can be successfully used - in particular, when creating monitoring systems
  in industry, ecology, medicine, etc. Two main varieties of methods for breakdown detecting are
  discussed: parametric and nonparametric. It is noted that, although nonparametric methods, ceteris
  paribus, are inferior to parametric methods in terms of efficiency (the speed of breakdown detecting),
  they also have a number of advantages, without requiring, in particular, for their application detailed
  information about the probabilistic properties of the controlled process. This is fundamentally important
  for building monitoring systems, when detailed information about these properties may either be completely
  absent and then it is necessary to conduct a rather laborious preliminary study of it, or to be
  unreliable. An original sequential nonparametric algorithm for detecting discord is proposed based on
  the implementation of the random walk mechanism or, more specifically, using the theory of success
  runs. The operating principle of the control algorithm is explained and its description is given. The results
  of the study of the basic statistical characteristics of the algorithm, including the determination of
  its effectiveness, and results of comparison with known parametric methods, are given. The area of possible
  practical use of the proposed algorithm is highlighted, where its effectiveness remains quite high.
  The prospects of using the proposed algorithm as part of the software and algorithmic support of monitoring
  systems for various purposes are noted.