Spread spectrum is a communication technique that spreads a narrow band signal over a wide range of frequencies, enhancing resistance to interference and jamming. Key methods include direct sequence, frequency hopping, and hybrid techniques. It has applications in cellular telephony, GPS, and secure military communication.

1. PresenterDeepak Chandra Pant
ECE - Third Year
1

2. Spread Spectrum
 What is Spectrum…?
 Spread Spectrum is a communication technique that
spreads a narrow band communication signal over a wide
range of frequencies for transmission and de-spreads it into
the original data bandwidth at the receiver.
 Processing Gain (N) = Bss/B
2

3. Narrowband vs Spread Spectrum
P
o
w
e
r
3

4. Conditions for Spread Spectrum System
 Modulated Signal Bandwidth >> Message Signal
Bandwidth
 A same code called pseudonoise sequence must be
used at the transmitter as well as at receiver in order to
recover the message.
4

5. Characteristics of Spread Spectrum
 Hard to interference
 Resistant to jamming
 Hard to intercept
 Multiple access capability
5

6. Techniques for Spread Spectrum
 Direct Sequence Spread Spectrum (DS/SS)
 Frequency Hopping Spread Spectrum (FH/SS)
 Hybrid Spread Spectrum
6

7. Direct Sequence Spread Spectrum
(DS/SS)
7

8. Signals at the DS/SS Generator
Pseudorandom Code
(Barker Sequence)
1 0 1 1 0 1 1 1 0 0 0 1 0 1 1 0 1 1 1 0 0 0
10110111000
Original Data
1
One Bit
0
One Bit
Spread Data
0 1 0 0 1 0 0 0 1 1 1 1 0 1 1 0 1 1 1 0 0 0
Six 0s = 1
Six 1s = 0
8

9. Frequency Hopping Spread Spectrum
(FH/SS)
9

10. Frequency Hopping Schemes
Fast Frequency Hopping
Slow Frequency Hopping
10

11. Hybrid Spread Spectrum
 Combination of DS/SS and FH/SS
11

12.  Advantages:
 Resists interferences
 Anti jamming effect
 Can share same band of frequency with other users
 Privacy due to Pseudorandom Code
 Disadvantages:
 Bandwidth Inefficient
 Complex Implementation
 Near – Far Problem
12

13. Application’s of Spread Spectrum
 Cellular Telephony
 Global Positioning System (GPS)
 Wireless local area network
 Secure communication in military
13

14. THANK YOU…
14