7 April 2018

Difference between DSSS and FHSS

DSSS and FHSS both are spread spectrum techniques. There is some difference between spreading the data into the wider bandwidth. FHSS using frequency hopping while DSSS using pseudo noise to modify the phase of the signal. So in this article, you can check some difference between these two spread spectrum. 

Difference :
  • Over the complete bandwidth of the spread spectrum signal, the data sequence is spread in DSSS but in FHSS the data sequence is spread over small frequency slots of the spread spectrum signal.
  • Cost is more in DSSS compare to FHSS.
  • DSSS is relative distance and the system, FHSS is less affected by distance change.
  • DSSS used the BPSK method and FHSS used many FSK methods.
  • The acquisition time of  DSSS is long while in short in case of FHSS.
  • Dwell time is 400 ms in FHSS but in DSSS has no dwell time. 
  • Used density is less in DSSS but in more in FHSS.
  • Chip rate Rc = 1 /  Tc in DSSS and Chip rate for FHSS is Rc = max (Rh,Rs).
  • Interoperability is high in DSSS while low in FHSS. 
  • DSSS changes the phase wheres FHSS changes the frequency being used. 
  • FHSS is easier to synchronize than DSSS.
  • DSSS used in positioning systems while FHSS is not.
  • DSSS delivers capacity up to 11 Mbps but in FHSS supports up to 3 Mbps.
  • DSSS is a very sensitive technology while FHSS is a robust one. 
  • DSSS ideal for point to point applications while in FHSS can be used in point to multi-point deployment with better performance. 
  • DSSS systems use a carrier that remains fixed to a specific frequency band while FHSS systems use a radio carrier that 'hops' from frequency to frequency in a pattern known as transmitter and receiver. 
  • Frequencies are randomized in case of FHSS but in constant in case of DSSS. 
  • Data is constant is the case of FHSS while randomize in case of DSSS.
  • FHSS spreads the signal by hopping with a bandwidth of 83 MHz while in using DSSS spreads the signal by adding redundant with a bandwidth of 22 MHz.
  • DSSS prone to errors but at a low level as compared to FHSS system. FHSS produces strong bursty errors. 
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