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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