Fast Frequency Hopping & Slow Frequency Hopping Spread-final for the Day
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Transcript of Fast Frequency Hopping & Slow Frequency Hopping Spread-final for the Day
FAST FREQUENCY HOPPING & SLOW
FREQUENCY HOPPING SPREAD SPECTRUM
YASHNA SHARMAPOOJA MISHRA
M TECH(JOP), IIT DELHI
CONTENTSCONTENTS
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 INTRODUCTIONFHSS-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 FHSSTHE 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 TYPES OF FREQUENCY HOPPINGHOPPING
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 FAST HOPPING-PARAMETERS USED IN MATLAB USED IN MATLAB PROGRAMMINGPROGRAMMING
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 FAST FREQUENCY HOPPINGHOPPING
0 500 1000 1500 2000 2500 3000
-1
0
1
X: 2403Y: -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: 2403Y: -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
FREQUENCY SPECTRUMFREQUENCY 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: 19.92Y: 0.06642
Power spectral density(BPSK SIGNAL)
Frequency (Hz)
0 100 200 300 400 500 6000
1
2
3
4
5
6
7
X: 119.5Y: 0.03645
Power spectral density(FHSS)
Frequency (Hz)
0 100 200 300 400 500 6000
10
20
30
40
50
60
X: 19.92Y: 0.06642
Power spectral density(BPSK SIGNAL)
Frequency (Hz)
0 100 200 300 400 500 6000
1
2
3
4
5
6
7
X: 119.5Y: 0.03645
Power spectral density(FHSS)
Frequency (Hz)
BPSK BPSK SIGNALSIGNAL
FHSS FHSS SIGNALSIGNAL
DEHOPPING & DEHOPPING & DEMODULATIONDEMODULATION
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
FAS
T 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
LATE
D IN
TER
ME
DIA
TE
DEHOPPED SIGNAL
0 500 1000 1500 2000 2500 3000-1
-0.5
0
0.5
1
TIME UNITS
DE
MO
DU
LATE
D D
ATA
(UN
EN
VE
LOP
ED
)
0 500 1000 1500 2000 2500 3000
-1
0
1
Original Bit Sequence
0 500 1000 1500 2000 2500 3000
-1
0
1
BFSK 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
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 WHY FAST FREQUENCY HOPPPING?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 SLOW HOPPING- PARAMETERS USED IN MATLAB USED IN MATLAB PROGRAMMING 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
Tb ˂ Tc
Hopping Rate ˂ Data Rate= SLOW FREQUENCY HOPPING
SLOW FREQUENCY SLOW FREQUENCY HOPPINGHOPPING
0 500 1000 1500 2000 2500 3000
-1
0
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
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
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 DEHOPPING AND DEMODULATIONDEMODULATION
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
-101
Original Bit Sequence
0 500 1000 1500 2000 2500 3000
-101
BFSK Modulated Signal
0 500 1000 1500 2000 2500 3000
-101
Spread Signal with 6 frequencies
0 500 1000 1500 2000 2500 3000
-101
Frequency Hopped Spread Spectrum Signal
ADVANTAGES AND LIMITATIONS ADVANTAGES AND LIMITATIONS OF USING SLOW FREQUENCY OF USING SLOW FREQUENCY
HOPPINGHOPPING
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 YOUTHANK YOU
A LOOK AT THE A LOOK AT THE MODULATION PROCESSMODULATION PROCESS
FREQUENCFREQUENCY Y
SYNTHESISYNTHESIZERZER
HOPPING HOPPING CODE CODE
GENERATGENERATOROR
BPSK MODULATED DATATO ANTENNA
GENERATION OF THE HOPPING SEQUENCE
IF
RF
LO
A LOOK AT THE A LOOK AT THE DEMODULATION PROCESSDEMODULATION PROCESS
FREQUENCFREQUENCY Y
SYNTHESISYNTHESIZERZER
HOPPING HOPPING CODE CODE
GENERATGENERATOROR
IF
LO
BAND BAND PASS PASS
FILTERFILTER
IF IF FILTERFILTER
RF
FREQ. FREQ. DISCRIMINATDISCRIMINAT
OROR
DEMODULATED DATA