413x0g2 - CCSDS

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CCSDS REPORT CONCERNING BANDWIDTH-EFFICIENT MODULATIONSI-channel NRZsymbol streamδ(t-kT ChS )SRRCLPFOSCto RF amplifierQ-channel NRZsymbol streamδ(t-kT ChS )Half ChannelSymbol DelaySRRCLPF90°Figure 3-27: Nyquist Pulse-Shaped SRRC OQPSK Modulator Based onTheoretical EquationFigure 3-28: Simulated Spectrum of Nyquist Pulse-Shaped SRRC (α=0.5) OQPSK atOutput of Saturated SSPACCSDS 413.0-G-2 Page 3-21 October 2009
CCSDS REPORT CONCERNING BANDWIDTH-EFFICIENT MODULATIONS3.2.2.3.3 Baseband Filtered OQPSK with Other Filter TypesAs indicated above, Butterworth and/or SRRC filters are not necessarily optimum for use inbaseband filtered OQPSK systems. While it would be impossible to document theperformance of all possible filters, the performance of Bessel-filtered OQPSK is addressed inthe following subsection as an example.3.2.2.3.3.1 Baseband Filtered OQPSK with Bessel FilterThis subsection describes a 6 th order BT s = 0.5 Bessel filter. The magnitude and phaseresponse of the filter are plotted in figure 3-29. The simulated power spectral density forboth the I/Q and PM implementations of baseband filtered OQPSK with the Bessel filter arepresented in figure 3-30. The PSD is measured at the output of a saturated power amplifierto demonstrate the ability of the spacecraft using this modulation to meet the requirements ofthe SFCG emissions mask. The characteristics of the power amplifier are provided inannex B.0Bessel Filter Magnitude ResponseBessel Filter Phase Response (Linear Comp Removed)12-10-20-3096Magnitude in dB-40-50-60-70-80Phase degrees30-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-3-6-90-9-100-5 -4 -3 -2 -1 0 1 2 3 4 5F/Rs-12F/RsFigure 3-29: Magnitude and Phase Response of 6th Order BT s = 0.5 Bessel FilterCCSDS 413.0-G-2 Page 3-22 October 2009
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