Frequency Hopping Spread
Spectrum System
Frequency Hopping Spread Spectrum System (FHSS) is a method of transmitting radio signals
by rapidly switching a carrier among man frequency channels, using a pseudorandom sequence known
to both transmitter and receiver.
Transmitter
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Receiver
When using Frequency Hopping, the carrier frequency is 'hopping' according to a known sequence (of length). In this way the bandwidth is also increased.
Frequency Hopping Techniques:
Slow Frequency Hopping (SFH)
In this case one or more data bits are transmitted within one Frequency Hop. An advantage is that coherent data detection is possible. A disadvantage is that if one frequency hop channel is jammed, one or more data bits are lost. So we are forced to use error correcting codes.
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Fast Frequency Hopping (FFH)
In this technique one data bit is divided over more Frequency Hops. Now error correcting codes are not needed. An other advantage is that diversity can be applied. Every frequency hop a decision is made whether a -1 or a 1 is transmitted, at the end of each data bit a majority decision is made. The applied modulation technique should be FSK or MFSK.
Frequency shifted every Tc seconds
• Duration of signal element is Ts seconds
• Slow FHSS has Tc ≥ Ts
• Fast FHSS has Tc < Ts
Time-hopping spread spectrum (THSS)
Time-Hopping in communications, a type of spread spectrum technology in which the carrier is turned on and off by the pseudorandom code sequence.
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Hybrid System: DS/(F)FH
The DS/FFH Spread Spectrum technique is a combination of direct-sequence and frequencyhopping.
One data bit is divided over frequency-hop channels (carrier frequencies). In each frequency-hop channel one complete PN-code of length is added to the data signal
Using the FFH scheme in stead of the SFH scheme causes the bandwidth to increase, this increase
however is neglectable with regard to the enormous bandwidth already in use.
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by rapidly switching a carrier among man frequency channels, using a pseudorandom sequence known
to both transmitter and receiver.
Transmitter
VISIT OUR FACEBOOK PAGE
Receiver
When using Frequency Hopping, the carrier frequency is 'hopping' according to a known sequence (of length). In this way the bandwidth is also increased.
Slow Frequency Hopping (SFH)
In this case one or more data bits are transmitted within one Frequency Hop. An advantage is that coherent data detection is possible. A disadvantage is that if one frequency hop channel is jammed, one or more data bits are lost. So we are forced to use error correcting codes.
In this technique one data bit is divided over more Frequency Hops. Now error correcting codes are not needed. An other advantage is that diversity can be applied. Every frequency hop a decision is made whether a -1 or a 1 is transmitted, at the end of each data bit a majority decision is made. The applied modulation technique should be FSK or MFSK.
Frequency shifted every Tc seconds
• Duration of signal element is Ts seconds
• Slow FHSS has Tc ≥ Ts
• Fast FHSS has Tc < Ts
The DS/FFH Spread Spectrum technique is a combination of direct-sequence and frequencyhopping.
One data bit is divided over frequency-hop channels (carrier frequencies). In each frequency-hop channel one complete PN-code of length is added to the data signal
Using the FFH scheme in stead of the SFH scheme causes the bandwidth to increase, this increase
however is neglectable with regard to the enormous bandwidth already in use.
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Fast Frequency Hopping (FFH)In this technique one data bit is divided over more Frequency Hops. Now error correcting codes are not needed. An other advantage is that diversity can be applied. Every frequency hop a decision is made whether a -1 or a 1 is transmitted, at the end of each data bit a majority decision is made. The applied modulation technique should be FSK or MFSK.
Frequency shifted every Tc seconds
• Duration of signal element is Ts seconds
• Slow FHSS has Tc ≥ Ts
• Fast FHSS has Tc < Ts
Time-hopping spread spectrum (THSS)
Time-Hopping in communications, a type of spread spectrum technology in which the carrier is turned on and off by the pseudorandom code sequence.
VISIT OUR FACEBOOK PAGE
Hybrid System: DS/(F)FH
The DS/FFH Spread Spectrum technique is a combination of direct-sequence and frequencyhopping.
One data bit is divided over frequency-hop channels (carrier frequencies). In each frequency-hop channel one complete PN-code of length is added to the data signal
Using the FFH scheme in stead of the SFH scheme causes the bandwidth to increase, this increase
however is neglectable with regard to the enormous bandwidth already in use.
VISIT OUR FACEBOOK PAGE
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