563489578934

(
(
Sec. 5–9 Binary Modulated Bandpass Signaling 355
where m(t) has a peak value of A = 12 so that s(t) has an average normalized power of A 2 c>2.
The PSD for the corresponding OOK signal is then obtained by substituting Eq. (5–72) into
Eq. (5–2b). The result is shown for positive frequencies in Fig. 5–20a, where R = 1T b is the
bit rate. The null-to-null bandwidth is B T = 2R, and the absolute bandwidth is B T = . Also,
the transmission bandwidth of the OOK signal is B T = 2B, where B is the baseband bandwidth,
since OOK is AM-type signaling.
If raised cosine-rolloff filtering is used (to conserve bandwidth), the absolute bandwidth
of the filtered binary signal is related to the bit rate R by Eq. (3–74), where D = R for binary
digital signaling. Thus, the absolute baseband bandwidth is
q
B = 1 2 (1 + r)R
(5–73)
where r is the rolloff factor of the filter. This gives an absolute transmission bandwidth of
B T = (1 + r)R
for OOK signaling with raised cosine-rolloff filtering.
(5–74)
2
A c
Weight =
8
2
A c
8R
(
sin (∏( f f c )/R
∏( f f c )/R
2
f c 2R
f c
f c 2R
f
(a) OOK
2R
2
A c
4R
(
sin (∏( f f c )/R
∏( f f c )/R
2
f c 2R f c f c 2R
2R
(b) BPSK (see Fig 5–15 for a more detailed spectral plot)
Figure 5–20 PSD of bandpass digital signals (positive frequencies shown).