Spread SpectrumCEN 220/CIS 192 Advanced Data Communications and NetworkingData and Computer Communications, W. Stallings 9/E, Chapter 9

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Spread Spectrum“All creative people want to do the unexpected.”

—Ecstasy and Me: My Life as a Woman,

Hedy Lamarr

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Spread Spectrum

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Pseudorandom Numbers

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General Model of Spread Spectrum System

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Spread Spectrum AdvantagesImmunity from noise and multipath distortion

Can hide / encrypt signals

Several users can share same higher bandwidth with little interference

CDM/CDMA Mobile telephones

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Frequency Hopping Spread Spectrum (FHSS)

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Frequency Hopping Example

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FHSS (Transmitter)

Frequency Hopping Spread Spectrum (FHSS)

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FHSS (Receiver)

Frequency Hopping Spread Spectrum (FHSS)

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Slow and Fast FHSSCommonly use multiple fsk (mfsk)

Have frequency shifted every tc seconds

Duration of signal element is ts seconds

Slow fhss has tc ts

Fast fhss has tc < ts

FHSS quite resistant to noise or jamming with fast FHSS giving better performance

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Slow MFSK FHSS

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Fast MFSK FHSS

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Direct Sequence Spread Spectrum (DSSS)Each bit is represented by multiple bits using a spreading code

This spreads signal across a wider frequency band

Has performance similar to FHSS

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Direct Sequence Spread Spectrum Example

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Direct Sequence Spread Spectrum System

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DSSS Example Using BPSK

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ApproximateSpectrum of DSSS Signal

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Code Division Multiple Access (CDMA)

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CDMA Example

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CDMA Example

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CDMA for DSSS

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SummaryConcept of spread spectrum

FHSS FHSS using MFSK

DSSS DSSS using BPSK

Code Division Multiple Access CDMA for Direct Sequence Spread Spectrum