Difference between revisions of "Quadrature Phase Shift Keying"
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−  +  The '''Quadrature Phase Shift Keying''' or '''QPSK''' is a [[Modulation Scheme]] where the [[Phase]] of the modulated signal is shifted depending on the incoming bitstream by an angle of 135°, 45°, +45° or +135°. Thus 4 states (a twodigit binary symbol) can get expressed in every transition: 

−  [[Image:Qpsk.jpgQPSK in 
+  [[Image:Qpsk.jpgQPSK Sample points in the Phase Plot]] 
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+  The resulting waveform looks like if it would be assembled of several sine wave segments from 4 phaseshifted base sine signals. 

+  
+  [[Image:Principle_QPSK.jpgpicture of a sine signal with shifted phase]] 

In order to minimize the used [[Bandwidth]] allocated on the [[Transponder]] the outgoing signal is usually filtered using digital lowpass [[FIR Filter]]s with smooth rolloff so that the highorder noise of the sudden state changes gets removed. 
In order to minimize the used [[Bandwidth]] allocated on the [[Transponder]] the outgoing signal is usually filtered using digital lowpass [[FIR Filter]]s with smooth rolloff so that the highorder noise of the sudden state changes gets removed. 

+  
+  ''here we may show the smoothed version of the sine sigal with shifted phase. Maybe also the spectrum diagrams?'' 

+  
+  
+  ''Has anybody the standard number of the paper that specifies usage of QPSK in DVBS handy? Any more useful information in there?'' 

+  
+  ''a few words about allocated bandwidth and noise sensitivity of QPSK modulated signals would be great.'' 

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+  [[Category:Technology]] 
Latest revision as of 22:16, 2 April 2005
The Quadrature Phase Shift Keying or QPSK is a Modulation Scheme where the Phase of the modulated signal is shifted depending on the incoming bitstream by an angle of 135°, 45°, +45° or +135°. Thus 4 states (a twodigit binary symbol) can get expressed in every transition:
The resulting waveform looks like if it would be assembled of several sine wave segments from 4 phaseshifted base sine signals.
In order to minimize the used Bandwidth allocated on the Transponder the outgoing signal is usually filtered using digital lowpass FIR Filters with smooth rolloff so that the highorder noise of the sudden state changes gets removed.
here we may show the smoothed version of the sine sigal with shifted phase. Maybe also the spectrum diagrams?
Has anybody the standard number of the paper that specifies usage of QPSK in DVBS handy? Any more useful information in there?
a few words about allocated bandwidth and noise sensitivity of QPSK modulated signals would be great.