4 ms·

To be clear, what's happening here is people are accustomed to using "bandwidth" to mean bits/second but bandwidth has a much more specific meaning in the RF wo

To be clear, what's happening here is people are accustomed to using "bandwidth" to mean bits/second but bandwidth has a much more specific meaning in the RF world, akin to calling Ethernet "SSH". Bandwidth is the actual number of kilo/mega/gigahertz the signal occupies on the spectrum and is largely a function of symbol rate, but the actual data rate has many more variables.

lxgr 3y ago
I’m aware of the distinction and I’m using the terms accordingly. More bandwidth does not help you get a better data rate if you’re power limited. In the case of satellite communications you basically always are, and bidirectionally so when it’s to mobile/battery-powered devices.
- AnarchismIsCool 3y ago
  Yeah, I posted to clarify for the person you replied to and other non-rf people. You obviously know what's going on but you used a lot of language I figured should be defined for anyone who comes across this.
  - lxgr 3y ago
    Ah, sorry, I mixed you up with GP then and thought you were disagreeing with the "power-limited regime" statement!
- cycomanic 3y ago
  That is in fact incorrect. Capacity scales as Blog2(1+SNR) so increasing bandwidth at the same power (which would decrease SNR linearly assuming AWGN) will result in increased capacity. Although pratically you can do that only so far, because you're going to be limited by the bandwidth of your receiver.
  - lxgr 3y ago
    It’s only theoretically incorrect. Practically, satellite communications are power-limited and accordingly will always be so close to the noise floor (i.e. S/N << 1) that the logarithm can be approximated with a constant and the bandwidth dependency is negligible and drops out of the equation. It only matters in the bandwidth-limited regime, i.e. for S/N >> 1.
    - CraigJPerry 3y ago
      This thread is why I like HN. Thanks for sharing the insights both.
      - lxgr 3y ago
        Please take all of this with a grain of salt! It's quite possible that the limiting factor here is already spectral efficiency and not power; I don't know the link budgets involved and am mainly basing this on the very low observed data rates of systems I'm familiar with. I don't have the exact S/N numbers for these systems, and there might well be some potential gain that's not being exploited for reasons of spectral efficiency (after all, these systems want to serve multiple phones at least somewhat efficiently). The spectrum is limited in any case, both by receiver capabilities and the fact that it's a very scarce resource in useful frequency ranges.

lxgr 3y ago

I’m aware of the distinction and I’m using the terms accordingly. More bandwidth does not help you get a better data rate if you’re power limited. In the case of satellite communications you basically always are, and bidirectionally so when it’s to mobile/battery-powered devices.

AnarchismIsCool 3y ago
Yeah, I posted to clarify for the person you replied to and other non-rf people. You obviously know what's going on but you used a lot of language I figured should be defined for anyone who comes across this.
- lxgr 3y ago
  Ah, sorry, I mixed you up with GP then and thought you were disagreeing with the "power-limited regime" statement!
cycomanic 3y ago
That is in fact incorrect. Capacity scales as Blog2(1+SNR) so increasing bandwidth at the same power (which would decrease SNR linearly assuming AWGN) will result in increased capacity. Although pratically you can do that only so far, because you're going to be limited by the bandwidth of your receiver.
- lxgr 3y ago
  It’s only theoretically incorrect. Practically, satellite communications are power-limited and accordingly will always be so close to the noise floor (i.e. S/N << 1) that the logarithm can be approximated with a constant and the bandwidth dependency is negligible and drops out of the equation. It only matters in the bandwidth-limited regime, i.e. for S/N >> 1.
  - CraigJPerry 3y ago
    This thread is why I like HN. Thanks for sharing the insights both.
    - lxgr 3y ago
      Please take all of this with a grain of salt! It's quite possible that the limiting factor here is already spectral efficiency and not power; I don't know the link budgets involved and am mainly basing this on the very low observed data rates of systems I'm familiar with. I don't have the exact S/N numbers for these systems, and there might well be some potential gain that's not being exploited for reasons of spectral efficiency (after all, these systems want to serve multiple phones at least somewhat efficiently). The spectrum is limited in any case, both by receiver capabilities and the fact that it's a very scarce resource in useful frequency ranges.