GP 1.30 (0553)

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• GP 1.30 (0553)
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• NARROW BAND NOISE ATTENUATION FOR FMCW SOUNDING
•  
• Alexey A. Kolchev,
• Andrey O. Shiriy
• Mari State University
• Lenin sq., 1 Yoshkar-Ola,
• Mari El, Russia
• E-mail kolchevaa_at_ mail.ru
•  

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• Abstract
• The way of the attenuation of the narrow band
  noise on an output of the chirpsounder receiver
  is out forward. Detection of the noise is based
  on difference of noise statistical
  characteristics and a receiver signal after
  compression in frequency area. Attenuation of the
  signal element struck with the concentrated
  handicap, is carried out on the basis of
  criterion of gross blunders detection in
  experimental measurements. Results of numerical
  and natural experiments are presented according
  to efficiency of the offered method.

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• Introduction
• The processing of a LFM signal of the
  chirpsounder by a method of compression in
  frequency area consists in multiplication of the
  received signal to a heterodyne signal,
  complex-conjugated to a transmitted signal. As a
  result of demodulation the noise concentrated in
  frequency area becomes pulse noise, allowing to
  use specific methods of pulse noise reduction.
• The operation of the noise reduction system will
  be effective at significant excess of noise
  energy over energy of a signal 1. Therefore the
  signal on an output of the receiver can be
  considered within the framework of a mix model of
  two distributions with different dispersions.
• Identification of distribution form has been
  realized on the basis of estimations use of the
  kurtosis and entropy factor .
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• Basic Equations
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• De-chirped signal from the receiver A(t) is
  represented by the sum of two symmetric
  distributions with various dispersions
• where - f(xs ) distribution density of a
  signal A(t) f1(xs1 ) - distribution density of
  a chirp signal sum and wide band noise f2(xs 2
  ) - distribution density of a narrow band noise
  h1,h2 - densities of distribution in general set
  s 2, s 12 , s 2 2 - corresponding dispersions
• (s 12 ltlt s 2 2 and h1 gt h2 ). For allocation of
  the concentrated handicap the signal A(t) was
  broken on K elements. Estimations of a standard
  deviation s k were found for each element of a
  signal.

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• The factor of entropy under the histogram of
  distribution s k is calculated as
• where
• h width of a column histogram, n volume of
  sample, m number of column histogram, nj -
  number of sample in j- column of a histogram.
• If samples of a signal element of two-modal
  distribution was considered, it speaks about the
  existence noise and attenuation of this element
  is made.
• The indication of the sample belonging to the
  noise is the big distance of this sample from
  distribution center. The importance of difference
  between samples is estimated on the base of
  criterion finding of the blunders in experimental
  measurements justified for a great number of
  distribution laws 2. If inequality
• is carried out for the value of s k , where E -
  factor of an excess, there are no grounds to
  consider this value to be distinguished
  considerably from s s . If the inequality for
  some element is not carried out and
• s kgt s s , this element of a signal is
  attenuated.
• Efficiency of attenuation procedure was estimated
  on value of size n10lg (P1/P2) (P1 the
  attitude signal / noise after attenuation, P2
  the initial attitude signal / noise).

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• Applications to Observations
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• The data received in experiments were used for
  the analysis, carried out on radiolines
  Inskip(England) - Nizhny Novgorod and Irkutsk -
  Nizhny Novgorod.
• On fig. 1 the fragment of ionogram before (?) and
  after (?) applications of noise attenuation
  procedure is given.
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• Separate oscilogramma and spectra of a signal
  before (a,?) and after (c, d) attenuation of the
  noise are shown on fig.2. Application of
  procedure attenuation enables to allocate a
  signal on frequency of 700 Hz which cannot be
  allocated in an initial spectrum.
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• Thus application of the offered technique is
  especially effective at a small signal on a
  background of significant noise. Application of
  estimations of the kurtosis and factor of entropy
  for identification of the form distribution has
  increased probability of correct noise detection
  from 76 up to 95 .
• The factor of correlation between n and the
  entropy factor in the carried out experiments is
  equal -0,8, i.e. the increase in energy of noise
  leads to reduction of the entropy factor.
• Conclusion
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• Application of the offered method of the narrow
  band noise attenuation will allow to increase
  reliability of ionosphere parameters definition,
  at work low-power FMCW ionosonde, in research of
  a high order signal mode and weak round-the-world
  signals.
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• References
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• 1 Goldberg A.P. Complex rejection of the narrow
  band noise (in Russia) Radiotekhnica, Moscow.
  1978, no.4, pp.3-9.
• 2 Novitskij P.V., Zograf I.A. Errors estimation
  of measurements results (in Russia) , Leningrad.
  Energoatomizdat. 1991. 304p.
•