DIGITAL SPREAD SPECTRUM SYSTEMS

DIGITAL SPREAD SPECTRUM SYSTEMS ENG-737 Hardware Demo Wright State University James P. Stephens

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

AFIT BUILT DSSS THEORY OF OPERATION TRANSMITTER So(t) FM Exciter Audio DBM FM Osc BPF X Amp X4 X3 X3 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

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 Tune Synchronous Oscillator 2.7875 MHz 111.5 MHz Detailed DSSS System Block Diagram

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)/x}2 • Spectral line spacing = 1/NTc • Null-to-Null BW = 2 * 1/Tc • Number of spectral lines = N 0 to 1st Null 40

EFFECT OF HELICAL BANDPASS FILTER

SPECTRAL CHARACTERISTICS Rc = 2.7875 MHz Tc = 0.3587 s N = 255 BW = 5.575 MHz 1/NTc = 10.93 kHz • {Sin (x)/x}2 • Spectral lines – 1/NTc • Null-to-Null BW – 2 * 1/Tc • Number of spectral lines = N 40

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

DIGITAL SPREAD SPECTRUM SYSTEMS