User Manual DDS200 Digital Demodulation System 070-9952-00

Manual OperationExamples of ApplicationThis section is divided into the following subsections:Application and Interpretation of Constellation Diagram page 2–62Explanation of Calculated Parameters, Formulasand Limit Values page 2–68Selection of Integration Time for BER Measurements page 2–79BER Measurements with External Equipment page 2–80BER as a function of C/N, Calculation of Further Parameters page 2–82Assignment and Functions of Parallel and SerialMPEG-2 Outputs page 2–85Analog and Digital Cascading of Two DigitalDemodulation Systems page 2–88Application and Interpretation of Constellation Diagram. In this subsection, thebasic causes of specific modulation errors are described with the aid of simulatedconstellation diagrams. Using simulated data is instructive, especially because itallows different effects to be demonstrated separately. In the examples shownbelow, the following basic settings were used:A maximum possible DVB data transmission rate of 6.92 MSPS (megasymbols per second) or 41.73 Mbit/s (with 64QAM)Cosine roll-off filtering with roll-off factor r = 0.15PRBS (pseudo random binary sequence) data stream; no codingIn practice, there is always a combination of various modulation errors that maybe difficult to separate and identify. To this end, the DDS200 Digital DemodulationSystem evaluates the measured constellation diagram using mathematicaland statistical methods and furnishes a quantitative representation of results(refer to Explanation of Calculated Parameters, Formulas and Limit Values onpage 2–68).All constellation diagrams shown are based on 64QAM modulation. The effectsof the modulation errors shown, however, apply to all other orders of QAM.2–62 DDS200 Digital Demodulation System User Manual