S-72.245 Transmission Methods in Telecommunication Systems (4 cr)

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S-72.245 Transmission Methods in
Telecommunication Systems (4 cr)

• Review

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PLL based frequency synthesizer
Reference signal fin is locked for instance to
the fundamental frequency of a crystal oscillator
By adjusting the divider different frequencies
can be produced whose phase is locked into fin
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Detecting DSB using PLL-principle

• An important application for PLLs is in
  synchronization of receiver local oscillator in
  synchronous detection
• In the Costas PLL (below) two phase
  discriminators are used to
• cancel out DSB modulation x(t) in the driving
  signal
• synchronize the output frequency to the center
  frequency of the DSB spectra (the suppressed
  carrier)
• to detect the DSB signal

PD phase detector (multiplyLPF)
Costas PLL detector for DSB
LPF yields constant (zero) output when loop is
locked to carrier
Loop drives phase error to zero
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PAM Power Spectral Density (PSD)

• PSD for PAM can be determined by using a general
  expression
• For uncorrelated message bitsand
  thereforeon the other hand
  and

Amplitude autocorrelation
Total power
DC power
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PAM Power Spectral Density (PSD)

• PSD for PAM can be determined by using a general
  expression
• For uncorrelated message bitsand
  thereforeon the other hand
  and

Amplitude autocorrelation
Total power
DC power
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Example

• For unipolar binary RZ signal
• Assume source bits are equally alike and
  independent, thus

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Equalization Removing Residual ISI

• Consider a tapped delay line equalizer with
• Search for the tap gains cN such that the output
  equals zero at sample intervals D except at the
  decision instant when it should be unity. The
  output is (think for instance paths c-N, cN or
  c0)that is sampled at
  yielding

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Tapped Delay Line Matrix Representation

• At the instant of decision
• That leads into (2N1)x(2N1) matrix where (2N1)
  tap coefficients can be solved

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Example of Equalization

• Read the distorted pulse values into matrix from
  fig. (a)and the solution is

Question what does thesezeros help because they
dont exist at the sampling instant?
Zero forced values
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Monitoring Transmission Quality by Eye Diagram
Required minimum bandwidth isNyqvists
sampling theorem
Given an ideal LPF with the bandwidth B it is
possible to transmit independent symbols at the
rate