 stroll into a BPSK modulator. Table 5.4 (look at the top part marked BPSK) summarizes the BPSK idea in a neat fashion. Chapter Five Input bits Output waveform Acos(Wet+0°) Acos(wot+180) Acos(Wct+0°) Figure 5.16 BPSK modulator Output waveform Input bits Output waveform (shorthand form) so(t) = Acos (@ t+0°), iT<t<(i+1)T A cos s,(t) = iT<t<<i+1)T Acos(Wt+180)(t-iT) 4-PSK so(t) = A A cos s,(t) = A COS (w.t+90°), iT<t<(i+1)T Acos(Wt+90).(t-iT) 52(t) = A COS (wt+180°), iT<t<(i+1)T Acos(Wt+180).(t-iT) S3(t)=Acos(Wt+270),iTSt<(i+1)T = Acos(wt+270).(t-iT) 8-PSK so(t) =Acos(Wt+0),iTSt<(i+1)T = s((t) = COS (w.t+45°), iTSt<(i+1)T 52(t) = A COS (@gt+90°), iT<t<(i+1)T 53(t) = A COS (w.t+135°), iT<t<(i+1)T 54(t) = A \ COS (wt+180), iTSt<(i+1)T 55(t) = A COS (wt+225°), iT<t<(i+1)T sa(t) = A COS (wt+270°), iT<t<(i+1)T Table 5.4 PSK explained Getting It from Here to There: Modulators and Demodulators Next up is 4-PSK. Here, the modulator works on two bits at a time. For every two bits that come into the modulator, the modulator outputs a different waveform. Con- sider this. The incoming bits are 0011. The modulator first gets hold of the bit pair 00 and it maps this into Acos(w,t+0). Next, it grabs the bit pair 11, mulls it over, and pops out Acos(@,++270°) You can see all the action in Figure 5.17. Table 5.4 (the part marked 4-PSK) summarizes the workings of 4-PSK. As you can see here, for each input bit pair, you get a different waveform output. It's very common for 4-PSK to be called by the name quadrature PSK (that's QPSK for short). Next, you've got 8-PSK. It's that "bigger is better" philosophy, again. (Gotta be careful with that one-it'll get you in trouble, as we'll see later on.) At any rate, in 8- PSK, three bits are input at the same time, and the modulator thinks it over, and pops out one of eight possible waveforms. Take a look at the bottom of Table 5.4. For every possible set of three incoming bits, a different waveform is output, and these wave- forms differ from one another in phase. Of course, you don't have to