DIGITAL SPREAD SPECTRUM SYSTEMS

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DIGITAL SPREAD SPECTRUM SYSTEMS
ENG-737 Hardware Demo

• Wright State University
• James P. Stephens

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BASIC SPREAD SPECTRUM SYSTEM CONFIGURATION
Transmitter
Receiver
DBM
DBM
FM Receiver
FM Exciter
RF Preamp
X
Amp/Filter
X
Audio
Audio
PN Code Generator
Synchronous Oscillator
PN Code Generator
Embedded Reference
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AFIT BUILT DSSS THEORY OF OPERATION
TRANSMITTER
So(t)
FM Exciter
Audio
DBM
FM Osc
BPF
X
Amp
X3
X3
X4
ST1(t)
ST2(t)
12.388 MHz
111.5 MHz
PN Code Gen
Divide by 40
bT(t)
2.7875 MHz
Detailed DSSS System Block Diagram
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AFIT BUILT DSSS THEORY OF OPERATION
RECEIVER
SI(t)
DBM
SR1(t)
SR2(t)
X
FM Receiver
Audio
Preamp
446.0 MHz
bR(t)
PN Code Gen
Divide by 40
Synchronous Oscillator
Tune
2.7875 MHz
111.5 MHz
Detailed DSSS System Block Diagram
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DIRECT SQUENCE BPSK SPECTRAL CHARACTERISTICS
Rc 2.7875 MHz Tc 0.3587 ?s N 255 BW 5.575
MHz 1/NTc 10.93 kHz

• PSD Sin (x)/x2
• Spectral line spacing 1/NTc
• Null-to-Null BW 2 1/Tc
• Number of spectral lines N

0 to 1st Null
40
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EFFECT OF HELICAL BANDPASS FILTER
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SPECTRAL CHARACTERISTICS
Rc 2.7875 MHz Tc 0.3587 ?s N 255 BW 5.575
MHz 1/NTc 10.93 kHz

• Sin (x)/x2
• Spectral lines 1/NTc
• Null-to-Null BW 2 1/Tc
• Number of spectral lines N

40
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CODE GENERATOR

PN Code Output
SYNC
Sync output generates a single pulse at the code
period rate (NTc)