101624956 Fast Frequency Hopping Slow Frequency Hopping Spread Final for the Day

FAST FREQUENCY

HOPPING & SLOW

FREQUENCY HOPPING

SPREAD SPECTRUM YASHNA SHARMA

POOJA MISHRA

M TECH(JOP), IIT DELHI

CONTENTS

INTRODUCTION TO FHSS

FAST AND SLOW FREQUENCY HOPPING

THE NEED FOR FHSS

MATLAB SIMULATION OF FAST FHSS MODULATOR & DEMODULATOR

MATLAB SIMULATION OF SLOW FHSS MODULATOR & DEMODULATOR

ADVANTAGES AND DISADVANTAGES

APPLICATIONS OF FHSS AND SHSS

FHSS-AN INTRODUCTION

FREQUENCY HOPPED: Regular Hopping of

Frequencies, at hop rates more , less or equal

to the data rate of the modulated signal.

SPREAD SPECTRUM: Spreading of the

Modulated Signal with another modulation

technique, to increase the bandwidth but

reduce the Power Spectral Density

THE NEED FOR FHSS

Single Frequency Systems are vulnerable to

jamming, interference, and multipath problems

Repeated switching of frequencies during

transmission according to specified techniques

will minimize sensitivity of the system to

jamming and interference

Power Spectral Density Reduces as

Bandwidth Increases, thus Signals get Hidden

to Spurious Recievers.

TYPES OF FREQUENCY

HOPPING

THE FREQUENCY

HOPPING RATE IS

MORE THAN THE

DATA RATE,I.E,

THERE ARE

MULTIPLE

FREQUENCIES

REPRESENTING ONE

BIT OF INFORMATION

THE FREQUENCY

HOPPING RATE IS

LESS THAN THE

DATA RATE,I.E,

THERE MAY BE

MULTIPLE BITS

REPRESENTED BY

ONE FREQUENCY

FAST HOPPING-PARAMETERS

USED IN MATLAB PROGRAMMING

Initially we have a BPSK System to modulate the data. The Bandwidth of the BPSK Signal is 2fb

We use 6 Frequencies for the Hopping Process

The time periods are:

Tb(Data Time Period)= 300

Tc(Period for which one Frequency Lasts)=120

Tb>Tc Hopping Rate> Data Rate= FAST FREQUENCY

HOPPING

FAST FREQUENCY

HOPPING

0 500 1000 1500 2000 2500 3000

-1

0

1

X: 2403

Y: -1

Original Bit Sequence

0 500 1000 1500 2000 2500 3000

-1

0

1

BPSK Modulated Signal

0 500 1000 1500 2000 2500 3000

-1

0

1

Spread Signal with 6 frequencies

0 500 1000 1500 2000 2500 3000

-1

0

1

Frequency Hopped Spread Spectrum Signal

0 500 1000 1500 2000 2500 3000

-1

0

1

X: 2403

Y: -1


0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1


FREQUENCY SPECTRUM

0 500 1000 1500 2000 2500 3000-1.5

-1

-0.5

0

0.5

1

1.5 Frequency Hopped Spread Spectrum signal and its FFT

0 500 1000 1500 2000 2500 30000

50

100

150

200

BANDWIDTH

0 100 200 300 400 500 6000

10

20

30

40

50

60

X: 19.92

Y: 0.06642

Power spectral density(BPSK SIGNAL)

Frequency (Hz)

0 100 200 300 400 500 6000

1

2

3

4

5

6

7

X: 119.5

Y: 0.03645

Power spectral density(FHSS)

Frequency (Hz)

0 100 200 300 400 500 6000

10

20

30

40

50

60

X: 19.92

Y: 0.06642

Power spectral density(BPSK SIGNAL)

Frequency (Hz)

0 100 200 300 400 500 6000

1

2

3

4

5

6

7

X: 119.5

Y: 0.03645

Power spectral density(FHSS)

Frequency (Hz)

BPSK

SIGNAL

FHSS

SIGNAL

DEHOPPING &

DEMODULATION

500 1000 1500 2000 2500 3000

-1

-0.5

0

0.5

1

OR

IGIN

AL

DA

TA

TIME UNITS

ORIGINAL BIT STREAM

0 500 1000 1500 2000 2500 3000-1

-0.5

0

0.5

1

TIME UNITS

FA

ST

FH

SS

SIG

NA

L

FHSS SIGNAL

0 500 1000 1500 2000 2500 3000-1

-0.5

0

0.5

1

TIME UNITS

DE

MO

DU

LA

TE

D I

NT

ER

ME

DIA

TE

DEHOPPED SIGNAL

0 500 1000 1500 2000 2500 3000-1

-0.5

0

0.5

1

TIME UNITS

DE

MO

DU

LA

TE

D D

AT

A(U

NE

NV

EL

OP

ED

)

0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1

BFSK Modulated Signal

0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1


FHSS WITH FSK-THE ACTUAL METHOD

0 500 1000 1500 2000 2500 3000-1.5

-1

-0.5

0

0.5

1

1.5 Frequency Hopped Spread Spectrum signal and its FFT

0 500 1000 1500 2000 2500 30000

100

200

300

WHY FAST FREQUENCY

HOPPPING?

Increased Resistance to

Jamming/Interference due to multiple hops

Resistance to Multipath Fading by providing

Diversity

L= Tsymbol/ Thop ; Order of Diversity

Low probability of Intercept: Used for

assuring security

SLOW HOPPING- PARAMETERS

USED IN MATLAB PROGRAMMING

Initially we have a BPSK System to modulate the data. The bandwidth of the BPSK Signal is 2fb

We use 6 Frequencies for the Hopping Process.

The time periods are:

Tb(Data Time Period)= 60

Tc(Period for which one Frequency Lasts)=120

Hopping Rate Data Rate= SLOW FREQUENCY HOPPING

SLOW FREQUENCY HOPPING

0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1


BANDWIDTH

0 100 200 300 400 500 6000

10

20

30Power spectral density(BPSK SIGNAL)

Frequency (Hz)

0 100 200 300 400 500 6000

2

4

6

8Power spectral density(FHSS)

Frequency (Hz)

DEHOPPING AND

DEMODULATION

500 1000 1500 2000 2500 3000

-1

-0.5

0

0.5

1

0 500 1000 1500 2000 2500 3000-1

-0.5

0

0.5

1

0 500 1000 1500 2000 2500 3000-1

-0.5

0

0.5

1

0 500 1000 1500 2000 2500 3000-1

-0.5

0

0.5

1

Original bit sequence

Demodulated

signal

Dehopped

signal

Slow FHSS signal

Time units Time

units

Time units Time units

0 500 1000 1500 2000 2500 3000-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1

BFSK Modulated Signal

0 500 1000 1500 2000 2500 3000

-1

0

1


0 500 1000 1500 2000 2500 3000

-1

0

1


ADVANTAGES AND LIMITATIONS OF

USING SLOW FREQUENCY HOPPING

FHSS provides only 3Mbps capacity but it is a very robust technology with little influence from noises, reflections and from other radio stations.

Coherent data detection is easily possible through slow frequency hopping.

It is also useful in burst error control coding to restore loss of bits in one hop.

SFH uses a less expensive synthesizer with a worst near far rejection and it also need for more powerful error correction scheme.

APPLICATIONS OF FHSS

It is useful in cellular deployments for fixed Broadband Wireless Access.

Bluetooth radio also uses FHSS operating in the 2.4 GHz band, with a dwell time of 0.625ms (1,600 hops per second).The amount of time spent on each hop is known as dwell time.

This can be explained further as:

When DSSS executes a transmission, it is using 22 MHz for the duration of the transmitted frame.

When FHSS executes a transmission, it is using 1 MHz for the duration of the transmitted frame.

APPLICATIONS(Continue)

Thus the chances of having Bluetooth hitting the 22 MHz band used by DSSS are higher than the

chances of it hitting the 1 MHz band used by

FHSS.

It is also used in radar systems.

It means the hop rate is an integer multiple of the

pulse repetition rate i.e., the pulse carrier

frequency will change or hop several times during

the transmission of one pulse.

REFERENCES

Sami A. Mostafa, FREQUENCY HOPPING TRANSCEIVER SYSTEM WITH APPLICATION TO

RADAR

Filol, Riley ,An Interpolated Frequency-Hopping Spread-Spectrum Transceiver

Berder, Bouder, Identification of Frequency Hopping Communications

Zoran Spasojevic, John Burns, Performance Comparison Of Frequency Hopping And Direct

Sequence Spread Spectrum Systems In The 2.4 GHz

Range

Rapport, Wireless Communication, Second Edition

Schiller, Mobile Communications, Second Edition

THANK

YOU

A LOOK AT THE MODULATION

PROCESS

FREQUENC

Y

SYNTHESIZ

ER

HOPPING

CODE

GENERATO

R

BPSK MODULATED DATA

TO ANTENNA

GENERATION OF THE

HOPPING SEQUENCE

I

F

RF

LO

A LOOK AT THE

DEMODULATION PROCESS

FREQUENC

Y

SYNTHESIZ

ER

HOPPING

CODE

GENERATO

R

I

F LO

BAND PASS

FILTER IF

FILTER RF

FREQ.

DISCRIMINATO

R

DEMODULATED DATA

Documents

101624956 Fast Frequency Hopping Slow Frequency Hopping Spread Final for the Day