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Published byMorgan Stone Modified over 6 years ago
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S-72.245 Transmission Methods in Telecommunication Systems (4 cr)
Review
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PLL based frequency synthesizer
VCO Filt. Phase detector Divide by 10 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 (=multiply+LPF) 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 bits and therefore on 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 bits and therefore on 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 (2N+1)x(2N+1) matrix where (2N+1) 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 these zeros help because they don’t exist at the sampling instant? Zero forced values
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Monitoring Transmission Quality by Eye Diagram
Required minimum bandwidth is Nyqvist’s sampling theorem: Given an ideal LPF with the bandwidth B it is possible to transmit independent symbols at the rate:
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