4 ms·
Hopefully its not pedantic or unwelcome of me to make the distinction between spread-spectrum and frequency hopping. With frequency hopping only one frequency
by nonrandomstring 3y ago
Hopefully its not pedantic or unwelcome of me to make the distinction
between spread-spectrum and frequency hopping.
With frequency hopping only one frequency is used at once, and they're
selected according to a sequence that matches a shared PRNG. As I
understand it, that's what Bluetooth and some Wifi links do. They
switch between discrete bands very fast.
Spread spectrum is a little different. During modulation, as with FM a
series of side bands spread out. Normally we would limit these as
they're considered "interference". But with the right modulator you
can spread (and indeed encrypt at the RF link level) information into
some bands but not others. Although all sidebands are present, to an
observer who can't tell which ones carry the data at any moment, it
makes no sense to even try demodulating the signal.
Neither solutions are much use if you need to communicate back because
triangulation alone is enough to find you.
Curious if this tallys with your understanding, its over a decade
since I had anything to so with this sort of thing. The best summary I
recall was in Ross Anderson's "Security Engineering" book (first ed.)
- deleted 3y ago[deleted]
- stoneman24 3y agoNo, it’s fine by me. I believe that it was thought that the combination of frequency hopping and spread spectrum would make it difficult to monitor and jam ( other than very wide band jamming). My application was rapidly moving so triangulation would be difficult. If I understand the capabilities of modern Software Defined Radio systems, then they can monitor many different frequencies at the same time which might defeat those old systems. It’s been a long time since I read up on the current ideas and capabilities.
- nonrandomstring 3y ago> If I understand the capabilities of modern Software Defined Radio systems, then they can monitor many different frequencies at the same time Haven't been keeping up with it as much as I should, but that's very interesting.
- NovemberWhiskey 3y ago>Hopefully its not pedantic or unwelcome of me to make the distinction between spread-spectrum and frequency hopping Spread spectrum refers to any technique where a narrowband signal is deliberately spread to occupy a larger bandwidth. Frequency-hopping is an example of a spread spectrum technique; they're not different things. Direct-sequence spread spectrum (which is what I think you're describing) is also a spread spectrum technique. There are also other techniques; the most popular one is probably the chirp spread spectrum as used in LoRA.
- nonrandomstring 3y agoThanks for the clarification NW