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Sec. 5–13 Spread Spectrum Systems 391<br />

BPSK modulator<br />

BPSK modulator<br />

DS spreader<br />

BPSK-DS<br />

spread spectrum<br />

signal<br />

m(t)<br />

A c cos c t<br />

c(t)<br />

s (t)=<br />

A c m(t)<br />

c(t) cos ( c t)<br />

T b<br />

p m (f)<br />

t<br />

Carrier<br />

oscillator<br />

f c<br />

Spreading<br />

code<br />

generator<br />

R b<br />

2<br />

(a) BPSK-DS-SS Transmitter<br />

f<br />

Pseudo noise code<br />

c(t)<br />

Modulo 2 adder<br />

c(t)<br />

1<br />

3<br />

r 1<br />

r<br />

t<br />

T 0 =NT c<br />

Clock<br />

R-2 r -1<br />

R c /N<br />

T c<br />

R c<br />

p c (f)<br />

(b) Spreading Code Generator<br />

f<br />

r(t)=s(t)+n(t)<br />

DS spreader<br />

v 1 (t)<br />

BPSK demodulator<br />

v 2 (t)<br />

Low-pass filter<br />

Detected<br />

modulation<br />

m(t)+n 3 (t)<br />

c(t)<br />

Spreading code<br />

generator<br />

Oscillator<br />

2 cos c t<br />

|H(f)|<br />

1.0<br />

R b R b<br />

f<br />

(c) BPSK-DS-SS Receiver<br />

Figure 5–39<br />

Direct sequence spread spectrum system (DS-SS).

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