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Sec. 5–9 Binary Modulated Bandpass Signaling 357
cos (v c t), must be provided. This is usually obtained from a PLL circuit (studied in Sec. 4–14),
where the PLL is locked onto a discrete carrier term (see Fig. 5–20a) of the OOK signal.
For optimum detection of OOK—that is, to obtain the lowest BER when the input OOK
signal is corrupted by additive white Gaussian noise (AWGN)—product detection with
matched filter processing is required. This is shown in Fig. 5–21c, where waveforms at
various points of the circuit are illustrated for the case of receiving an OOK signal that corresponds
to the binary data stream 1101. Details about the operation, the performance, and the
realization of the matched filter are given in Sec. 6–8. Note that the matched filter also
requires a clocking signal that is used to reset the integrator at the beginning of each bit interval
and to clock the sample-and-hold circuit at the end of each bit interval. This clock signal
is provided by a bit synchronizer circuit (studied in Chapter 4).
The optimum coherent OOK detector of Fig. 5–21c is more costly to implement than
the noncoherent OOK detector of Fig. 5–21a. If the input noise is small, the noncoherent
receiver may be the best solution, considering both cost and noise performance. The trade-off
in BER performance between optimum coherent detection and nonoptimun noncoherent
detection is studied in Sec. 7–6.
Binary Phase-Shift Keying
The Binary phase-shift keying BPSK signal is represented by
s(t) = A c cos [v c t + D p m(t)]
(5–75a)
where m(t) is a polar baseband data signal. For convenience, let m(t) have peak values of ;1
and a rectangular pulse shape.
We now show that BPSK is also a form of AM-type signaling. Expanding Eq. (5–75a),
we get
s(t) = A c cos(D p m(t)) cosv c t - A c sin(D p m(t)) sin v c t
Recalling that m(t) has values of ;1 and that cos (x) and sin (x) are even and odd functions
of x, we see that the representation of the BPSK signal reduces to
s(t) = (A c cos D p ) cos v c t - (A c sin D p ) m (t) sin v c t
t
pilot carrier term
t
data term
(5–75b)
The level of the pilot carrier term is set by the value of the peak deviation, ∆u = D p
.
For digital angle-modulated signals, the digital modulation index h is defined by
h = 2¢u
p
(5–76)
where 2∆u is the maximum peak-to-peak phase deviation (radians) during the time required
to send one symbol, T s . For binary signaling, the symbol time is equal to the bit time (T s = T b ).
The level of the pilot carrier term is set by the value of the peak deviation, which is
∆u = D p for m(t) = ;1. If D p is small, the pilot carrier term has a relatively large amplitude
compared to the data term; consequently, there is very little power in the data term