frequency hopping spread spectrum
DESCRIPTION
Frequency Hopping Spread Spectrum Technique is widely used in Communications.TRANSCRIPT
Frequency Hopping Spread Spectrum
(FH-SS)
~BY~
HARSHIT GUPTA
The term – “Spread Spectrum”
IN TELECOMMUNICATION AND RADIO COMMUNICATION, SPREAD SPECTRUM TECHNIQUES ARE METHODS BY WHICH A SIGNAL GENERATED WITH A PARTICULAR BANDWIDTH IS DELIBERATELY SPREAD IN THE FREQUENCY DOMAIN, RESULTING IN A SIGNAL WITH A WIDER BANDWIDTH.
….SAYS WIKIPEDIA
“Spread Spectrum” – In Simple Words
A MODULATION TECHNIQUE WHEREBY A MODULATED WAVEFORM IS MODULATED SECOND TIME IN SUCH A WAY SO AS TO GENERATE AN EXPANDED BANDWIDTH (WIDEBAND) SIGNAL, THAT DOES NOT SIGNIFICANTLY INTERFERE WITH OTHER SIGNALS.
Need of Spread Spectrum TechniqueTO PROVIDE EFFICIENT UTILIZATION OF
BANDWIDTH AND POWER.TO REJECT INTERFERENCE.TO ESTABLISH SECURE COMMUNICATION.
Spread Spectrum – “Illustration”
Types Of Spread Spectrum
DIRECT SEQUENCE SPREAD SPECTRUM TECHNIQUE (DS-SS)
FREQUENCY HOP SPREAD SPECTRUM TECHNIQUE (FH-SS)
CARRIER SERVICE MULTIPLE ACCESS SPREAD SPECTRUM (CSMA)
TIME HOPINGHYBRID SPREAD SPECTRUM
Insight Into – “FH-SS”THE AVAILABLE CHANNEL BANDWIDTH IS DIVIDED
INTO A LARGE NUMBER.ARRANGED IN CONTINOUS FRQUENCY SLOTS.TRANSMITTED SIGNAL OCCUPIES ONE OR MORE
OF THE AVAILABLE FRQUENCY SLOT.FREQUENCY SLOTS ARE SELECTED “PSEUDO
RANDOMLY”BASED ON THE OUTPUT OF THE PN GENERATOR.
FH-SS – “Illustration”
…an another illustration
FH-SS – “Block Diagram”
Pseudo Noise Generator
USED TO SPREAD THE BANDWIDTH OF THE MODULATED SIGNAL TO THE LARGER TRANSMISSION BANDWIDTH.
Types of FH-SS
THERE ARE TWO TYPES OF FREQUENCY HOPPING:
1. SLOW FREQUENCY HOPPING SPREAD SPECTRUM
2. FAST FREQUENCY HOPPING SPREAD SPECTRUM
Difference between Slow & Fast FH-SS
- FREQUENCY SHIFT TIME
- DURATION OF SIGNAL ELEMENT
SLOW FAST
In this case one or more data bits are transmitted within one Hop.
One data bit is divided over multiple Hops.
Coherent data detection is possible.
Coherent signal detection is difficult, and seldom used.
Error controlling can be done No Error controlling
Advantages IMPROVED INTERFERENCE REJECTIONCODE DIVISION MULTIPLEXING FOR CDMASECURE COMMUNICATIONHIGH RESOLUTION RANGING INCREASED CAPACITY AND SPECTRAL EFFICIENCYLOWER COST OF IMPLEMENTATIONREADILY AVAILABLE IC COMPONENTS
FH-SS – “Uses” IN MILITARY COMMUNICATION SYSTEMS.
- UNAUTHORISED RECEIVERS CANNOT DETECT MESSAGE.
- MILITARY RADIOS USES CRYPTOGRAPHIC TECHNIQUES TO GENERATE THE
CHANNEL SEQUENCE.
- TRANSMISSION SECURITY KEY (TRANSEC) IN SATELLITE COMMUNICATION IN LOCAL AREA NETWORKS (LAN)
Thank You Very Much
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