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Hi guys

I read that Spread Spectrum is a technique that spreads a narrowband communication signal over a wide range of frenquencies for transmission. A signal is a spread spectrum when the bandwidth is much wider that what is required.

in the case of FHSS, does the term "wider bandwidth" means the range from 2.402 --> 2.480 band (79 MHz)
OR
the carrier frenquency bandwidth (1 MHz to 5 MHz in the case of FHSS) ???


I understood it in 2 ways:

THE FIRST:
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For FHSS, instead of using just one frequency, FHSS changes frequency when dwell time expires. The frequencies pattern is predefined. So, instead of using 1 fixed frequency, FHSS can use up to 75 frequencies and restart the pattern again. This is the meaning of wider bandwidth here=the use of a number of frequencies, not just 1.

For DSSS, wider bandwidth means that 1 bit is presented by 11 chips (by XORing the initial bit with the Pseudorandom Number). So we are sending 11 times the desired data. This is the meaning of wider bandwidth here.



THE SECOND:
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wider bandwidth means, wider carrier bandwidth.. not 2.402 to 2.480, but carrier frequency bandwidth for 5 MHz of these 79 MHz (not the 79 MHz by themselves, but the sub carriers that are composed of 5MHz each, with 15 different hop (carrier) note that 15*5=75 ).

For examle, for FHSS, at t=5, lets say the frequency is at 2.417, this means that it can accept signals from 2.415 to 2.419 = 5 MHz of frequency bandwidth, which means less power is required because hitting anything from 2.414 to 2.419 is good, unlike narrowband, where u HAVE TO hit the exact frequency, which means more accurate, which means more power.

Same applies for DSSS and OFDM, which are both Spread Spectrum, but they don't hop at all, they stay on a given frequency band (about 5 MHz) centered on a given frequency (ex 2.422). So, these 5 MHz "acceptance" is the Spread Spectrum, where systems can accept anything between 2.420 and 2.424...

I just wantto know, how is Spread Spectrum in FHSS and DSSS and OFDM.. I mean, where is it applied in every1 of these technologies?

I am a bit confused of the meaning of "increase in bandwidth means less power required for the same transmission of info" ?

Can you please tell me where I was right?
Thanks a lot.

it looks like you are correct with your first interpretation. in all honesty I tried to break your explanation and find holes where you could be wrong, but there weren't any.

excellent explanation :D


I do still have issues with the DSSS explanation of spread spectrum however, so if a mod could shed a little light, I would appreciate it.

my issue: what is it that makes DSSS spread spectrum? is it using 11 channels or stuffing more bandwidth into a channel to lower the power output needed... I'm confused :D