1. Prof. Neeraj Bhargava
Pramod Singh Rathore
Department of Computer Science
School of Engineering & System Sciences,
MDS, University Ajmer, Rajasthan, India
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2. •The Spread Spectrum Technology (S.S.T) is a technique
used for transmitting radio or telecommunications
signals.
•It is Wideband radio Technology use in requiring High
Security.
• These techniques are used for a variety of reasons,
including the establishment of secure communications,
increasing resistance to natural Interference , Noise
and Jamming.
•It use an Hopping Modulation Technique for Signal
Transmission.
4. The main advantage of spread spectrum
communication technique is to prevent
“INTERFERENCE” whether it is intentional or
unintentional.
The signals modulated with these techniques are
hard to interfere and cannot be jammed. An intruder
with no official access is never allowed to crack them.
Hence, these techniques are used for military
purposesas per its Security Reasons.
There is Pseudo-Noise Sequence used for
Transmitting Signal.
5. Basically there are 4 Spread Spectrum Techniques i.e:-
Direct Sequence Spread Spectrum (D.S.S.S)
Frequency Hopped Spread Spectrum (F.H.S.S)
Time Hopped Spread Spectrum (T.H.S.S)
Pulse Hopped Spread Spectrum (P.H.S.S)
6. Direct Sequence Spread Spectrum (D.S.S.S)
It is an popular technique adopted by CDMA & 3G wireless
communication.
Data signal is multiplied by spreading code and resulting
signal occupies a much higher frequency band.
Spreading code is Pseudo-random sequence.
Whenever a user wants to send data using this DSSS
technique, each and every bit of the user data is multiplied by
a secret code, called as chipping code.
7. Spreading Information with Pseudo random sequence.
“This chipping code is nothing but the spreading code which is multiplied
with the original message and transmitted. The receiver uses the same
code to retrieve the original message.”
8. Frequency Hopped Spread Spectrum (F.H.S.S)
It is a technique use by Bluetooth and other
critical military communication system for
Security & simplicity.
The user signal first to be Digitized before
modulating itself.
The frequencies of the data are hopped from
one to another in order to provide a secure
transmission.
9. In a frequency-hopping spread spectrum (FHSS) system, the
transmitted signal is spread across multiple channels, as shown in
Figure below.
In the example of Figure , the full bandwidth is divided into 8
channels, centered at f1 through f8. The signal "hops" between them
in the following sequence: f5, f8, f3, f6, f1, f7, f4, f2.
10. FHSS DSSS / CDMA
Multiple frequencies are used Single frequency is used
Hard to find the user’s
frequency at any instant of time
User frequency, once allotted is
always the same
Frequency reuse is allowed Frequency reuse is not allowed
Sender need not wait Sender has to wait if the
spectrum is busy
Power strength of the signal is
high
Power strength of the signal is
low
Stronger and penetrates
through the obstacles
It is weaker compared to FHSS
It is never affected by
interference
It can be affected by
interference
It is cheaper It is expensive
This is the commonly used
technique
This technique is not frequently
used
11. Reduced Crosstalk Interference
Better Voice Quality/Data and less Noise
Inherent Security
Longer Operation Distances
Hard to Intercept
Harder to Jammed
12. Spread Spectrum promises several benefits such
as higher capacity and ability to resist multipath
propagation.
Spread Spectrum signal are difficult to intercept
for an unauthorized person, they are easily
hidden.
For an unauthorized person it is difficult to even
detect their presence in many cases.
