413x0g2 - CCSDS

CCSDS REPORT CONCERNING BANDWIDTH-EFFICIENT MODULATIONSFIR filter because an analog VCO is used, but a numerically controlled oscillator can be usedinstead. Moreover, a quadrature modulator may be used instead of the VCO, as in figure 3-3.BitSourceBit toLevelnTbb na nN bb n a nZ -1 (-1) n+1x(t)VCOz(t)D/Az[n]g[n]Figure 3-9: The FM-1 Implementation of the Precoded GMSK TransmitterAnother quadrature modulator (IQ-L1) can be designed, based on the Laurent decompositionof the GMSK signal complex envelope (see figure 3-11):~ x ( t)≈ A+cn=−∞∞jA∞∑∑[ bcn=−∞2n[ bC ( t − 2nT02n+10s) − bC ( t − 2nTs2n+1 2n− T ) − bsbb2n−12nbC ( t − 2nT1b2n−12n−2)]C ( t − 2nT1s− Twhere C 0 (t) and C 1 (t) are shown in figure 3-10 for BT s =0.5 and BT s =0.25.ss)]t/T s t/T sFigure 3-10: Pulses C0(t) and C1(t) with BT s =0.25 (left) and BT s =0.5 (right)CCSDS 413.0-G-2 Page 3-7 October 2009