1. Spread Spectrum
CEN 220/CIS 192 Advanced Data Communications and Networking
Data and Computer Communications, W. Stallings 9/E, Chapter 9

2. 2
Spread Spectrum
“All creative people want to do the unexpected.”
—Ecstasy and Me: My Life as a Woman,
Hedy Lamarr

3. 3
Spread Spectrum

4. 4
Pseudorandom Numbers

5. 5
General Model of Spread Spectrum System

6. 6
Spread Spectrum Advantages
Immunity from noise and multipath distortion
Can hide / encrypt signals
Several users can share same higher bandwidth with little
interference

CDM/CDMA Mobile telephones

7. 7
Frequency Hopping Spread Spectrum
(FHSS)

8. 8
Frequency Hopping Example

9. 9
FHSS (Transmitter)
Frequency Hopping Spread Spectrum (FHSS)

10. 10
FHSS (Receiver)
Frequency Hopping Spread Spectrum (FHSS)

11. 11
Slow and Fast FHSS
Commonly 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

12. 12
Slow MFSK FHSS

13. 13
Fast MFSK FHSS

14. 14
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

15. 15
Direct Sequence Spread Spectrum Example

16. 16
Direct Sequence Spread Spectrum System

17. 17
DSSS Example Using BPSK

18. 18
Approximate
Spectrum of
DSSS Signal

19. 19
Code Division Multiple Access (CDMA)

20. 20
CDMA Example

21. 21
CDMA
Example

22. 22
CDMA for DSSS

23. 23
Summary
Concept of spread spectrum
FHSS

FHSS using MFSK
DSSS

DSSS using BPSK
Code Division Multiple Access

CDMA for Direct Sequence Spread Spectrum