 stop there. There's 16-PSK, 64-PSK, and, hey, why not 10192-PSK? Input bits Output waveform Acos(Wet+0°) Acos(wot+270°) Figure 5.17 4-PSK modulation Next stop, the FSK modulators, short for frequency shift-keying modulators. As the name suggests, here we stuff the information bits into the frequency. We'll look at the simplest first, which is BFSK (binary FSK). Here, if bit 0 goes into the modulator, it sends out Acos((W +4 +0). If bit 1 goes in, then out comes Acos((W W1 + 0). The 'W0 is the frequency offset used to represent a 0, and w is the frequency offset used to repre- sent a 1. You can see an illustration of the BFSK modulator in action in Figure 5.18. Table 5.5 provides a summary of this BFSK modulator. Next up, 4-FSK. Here, two bits are input to the modulator at the same time, and the 4-FSK modulator outputs one of four possible waveforms. Take a look at Table 5.5, where you can see all the 4-FSK modulator action. Of course, those "bigger-is-better" guys also introduced 8-FSK, 16-FSK, and SO on same great idea, just a bigger table to describe it. Chapter Five Input bits Output waveform Figure 5.18 BFSK modulation Output waveform Input bits Output waveform (shorthand) so(t)=Acos((@+4Wo)t),iTSt<(i+1)T = s(t)=Acos((@+4w)t),iTSt<(i+1)T 4-FSK so(t)=Acos((@+4()t), iTSt<(i+1)T s,(t)=Acos((@+4())t),iTSt<(i+1)T Acos((@+w)t).(t-iT) S2(t)=Acos((W+4W2)t), iTSt<(i+1)T iT<t<(i+1)T Table 5.5 FSK modulator QAM modulators (short for quadrature amplitude modulation modulators) take incom- ing bits and pop out waveforms of the usual form s(t) = Acos(at+0) . What makes QAM modulators unique is that the input bits are stored in both the amplitude (A) and the phase (0) of the output waveform. I know this is going to seem rather short, but I'm going to stop talking about QAM for now. I'll provide more details a little later, after I've had a chance to tell you about orthonormal basis. Getting It from Here to There: Modulators and Demodulators Example 5.2 Sketch the output of a 4-ASK and 4-PSK system when the input bits are 0