NARROWBAND.PPT

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NARROWBAND NOISE
Presented by Tanvir Rashid Chowdhury
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NARROWBANDING

• Narrowbanding refers to public safety and
  industrial/business land mobile radio systems
  migrating from 25 kHz efficiency technology to at
  least 12.5 kHz efficiency technology.
  Narrowbanding is also referred to as VHF/UHF
  narrowbanding because the frequency bands
  impacted by narrowbanding are in the VHF/UHF
  ranges.

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Purpose of Narrowbanding

• The 150-174 MHz and 421-512 MHz frequency bands
  are congested with limited frequency availability
  for implementation of new systems or expansion of
  existing systems.
• Narrowbanding to at least 12.5 kHz efficiency
  technology will enable licensees to operate more
  efficiently, either with narrower channel
  bandwidths or an increased number of voice paths
  or higher data rate per channel.

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Narrowband Noise Representation

• In most communication systems, we are often
  dealing with band-pass filtering of signals.
  Wideband noise will be shaped into band limited
  noise. If the bandwidth of the band limited noise
  is relatively small compared to the carrier
  frequency, we refer to this as narrowband noise.

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How to generate narrowband noise from wideband
noise?

• We can derive the power spectral density Gn(f)
  and the auto-correlation function Rnn(t) of the
  narrowband noise and use them to analyse the
  performance of linear systems. In practice, we
  often deal with mixing (multiplication), which is
  a non-linear operation, and the system analysis
  becomes difficult. In such a case, it is useful
  to express the narrowband noise as
• n(t) x(t) cos 2pfct - y(t) sin 2pfct

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-EXAMPLE-

• Given that the power spectral density of a
  narrowband Gaussian noise of variance s2 and
  power N is-
• (a) Power spectral density of narrowband Gaussian
  noise n(t)
• where fc is the carrier frequency within the
  band occupied by the noise, then the power
  spectral densities of the quadrature components
  of the noise are
• (b) Power spectral
• density of x(t) and y(t)

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• The processes of frequency translation may be
  used to change a "wideband" signal into a
• "narrowband" signal which may well be more
• conveniently processed.
• The terms "wideband" and "narrowband" are being
  used here to refer not to an absolute range of
  frequencies but rather to the fractional change
  in frequency from one band edge to the other.

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THANKYOU ?