4 ms·

The frequencies are what I was curious about as well. To have a half mile range at relatively low powers it would need to be a low frequency band. I'm guessing

by sinak 8y ago

The frequencies are what I was curious about as well. To have a half mile range at relatively low powers it would need to be a low frequency band. I'm guessing they haven't bought licenses from the FCC, so my bet is that they're using the 900 MHz ISM band. There's only 26 MHz of spectrum in that band, which isn't much, particularly for a mesh setup that won't be particularly spectrally efficient. Even with a high 30 dB signal to noise ratio, the Shannon channel capacity in a 26 MHz band is 50 Mbps. MIMO helps a bit, but even in ideal real-world conditions you'll likely have at most 50 Mbps to share between all the users connected to a node. Spread that across a few users/mesh hops, throw in some packet retransmissions and noise, and it's not nearly enough to compete with LTE networks at any meaningful user density. Incentivizing users to create as many nodes as possible is a good idea, as that allows lower power transmissions and better frequency reuse. It's still a huge struggle to get anywhere near commercial wireless speeds, particularly in areas where there are fewer nodes and a higher density of users.

syedkarim 8y ago
They mention on Reddit that they are using 900 MHz. https://www.reddit.com/r/VolkFi/comments/b1u7o3/spectrum/ https://www.reddit.com/r/VolkFi/comments/b1u7o3/spectrum/
ac29 8y ago
I work with 900MHz radios and infrastructure, here's my thoughts: > The frequencies are what I'm confused by as well. To have a half mile range at relatively low powers it would need to be a low frequency band. > I'm guessing they haven't bought licenses from the FCC, so my bet is that they're using the 900 MHz ISM band. Seems likely, and probably even works in controlled tests over relatively short distances. 900MHz meshing radios certainly exist, like this one (no affiliation with them, haven't used the product): https://www.rajant.com/products/breadcrumb-wireless-nodes/lx-series/ https://www.rajant.com/products/breadcrumb-wireless-nodes/lx... >Even with a high 30 dB signal to noise ratio, the Shannon channel capacity in a 26 MHz band is 50 Mbps. Impossible in urban areas without highly directional antennas (which aren't small). The effective noise floor in most even semi-developed areas I've worked in is ~-100 to -80dBm - it can be a struggle even with expensive radios and fixed infrastructure. 30dB SNR just isn't going to happen over any appreciable amount of range on this sort of device (a high gain parabolic dish? sure). Using all 26MHz of the spectrum with an omni directional antenna (again, as would be required) also isn't going to happen except over relatively short distances. 900MHz is good technology, and can get robust, long distance links with the right infrastructure (I most work on 1-10mi links). The limitations on a pocket sized device with a pocket sized antenna mean this is unlikely to work @ 900MHz- especially in their fantasized scenarios of being in areas with no cell phone coverage (cell carriers have access to better bands, and far better infrastructure).
- angel_j 8y ago
  What if you used the noise as the carrier wave for the signal? Like, if in an urban area you have a "stable" probability distribution of noise, modulate that.
  - Robin_Message 8y ago
    You're being downvited because, whilst this is a clever sounding idea, unfortunately it doesn't work like that. The noise is random, so you can't modulate it because you can't predict what it will be. A probability distribution isn't enough; say you want to modulate by XORing with a random, uniformly distributed stream of zeros and ones. Knowing that distribution doesn't enable the receiver to extract the data. (Fun fact: GPS signals are under the noise floor, but detectable because they are encoded with a predictable pseudorandom carrier which can be found even in the noise.)
    - angel_j 8y ago
      Could you... modulate the amplitude of the PD?
      - lapinot 8y ago
        Amplitude is about power, that what you want to minimize. If you can affect the amplitude of the noise, that means your signal has high amplitude: you have a high signal-to-noise ratio (SNR) and you already have won.
    - eleitl 8y ago
      Do you know why digital pulse radios never happened?
- athrowaway3z 8y ago
  > cell carriers have access to better bands, and far better infrastructure What would be the best band for this kind of infrastructure? ( Disregarding any existing FCC licenses )
gandalfian 8y ago
My real world wifi experience. Domestic 2.4ghz wifi ap with a directional antenna plugged in, 600m direct line of sight across valley to neighbours netgear ap with stock antenna, assumed in his window. Internet achieved. Wifi ap, stock antenna in my house window, looking unobstructed over field, I get wifi internet on my phone about 200m out. Indoors in my stone walled house wifi is perhaps 10-15m. So half a mile range or 600m is almost true in a marketing sense though a bit dishonest in a real world usage sense.
ansible 8y ago
> I'm guessing they haven't bought licenses from the FCC, so my bet is that they're using the 900 MHz ISM band. No FCC filings for this device yet that I found. I guess we'll have to see.

by sinak 8y ago

syedkarim 8y ago

They mention on Reddit that they are using 900 MHz. https://www.reddit.com/r/VolkFi/comments/b1u7o3/spectrum/ https://www.reddit.com/r/VolkFi/comments/b1u7o3/spectrum/

ac29 8y ago

I work with 900MHz radios and infrastructure, here's my thoughts: > The frequencies are what I'm confused by as well. To have a half mile range at relatively low powers it would need to be a low frequency band. > I'm guessing they haven't bought licenses from the FCC, so my bet is that they're using the 900 MHz ISM band. Seems likely, and probably even works in controlled tests over relatively short distances. 900MHz meshing radios certainly exist, like this one (no affiliation with them, haven't used the product): https://www.rajant.com/products/breadcrumb-wireless-nodes/lx-series/ https://www.rajant.com/products/breadcrumb-wireless-nodes/lx... >Even with a high 30 dB signal to noise ratio, the Shannon channel capacity in a 26 MHz band is 50 Mbps. Impossible in urban areas without highly directional antennas (which aren't small). The effective noise floor in most even semi-developed areas I've worked in is ~-100 to -80dBm - it can be a struggle even with expensive radios and fixed infrastructure. 30dB SNR just isn't going to happen over any appreciable amount of range on this sort of device (a high gain parabolic dish? sure). Using all 26MHz of the spectrum with an omni directional antenna (again, as would be required) also isn't going to happen except over relatively short distances. 900MHz is good technology, and can get robust, long distance links with the right infrastructure (I most work on 1-10mi links). The limitations on a pocket sized device with a pocket sized antenna mean this is unlikely to work @ 900MHz- especially in their fantasized scenarios of being in areas with no cell phone coverage (cell carriers have access to better bands, and far better infrastructure).

angel_j 8y ago
What if you used the noise as the carrier wave for the signal? Like, if in an urban area you have a "stable" probability distribution of noise, modulate that.
- Robin_Message 8y ago
  You're being downvited because, whilst this is a clever sounding idea, unfortunately it doesn't work like that. The noise is random, so you can't modulate it because you can't predict what it will be. A probability distribution isn't enough; say you want to modulate by XORing with a random, uniformly distributed stream of zeros and ones. Knowing that distribution doesn't enable the receiver to extract the data. (Fun fact: GPS signals are under the noise floor, but detectable because they are encoded with a predictable pseudorandom carrier which can be found even in the noise.)
  - angel_j 8y ago
    Could you... modulate the amplitude of the PD?
    - lapinot 8y ago
      Amplitude is about power, that what you want to minimize. If you can affect the amplitude of the noise, that means your signal has high amplitude: you have a high signal-to-noise ratio (SNR) and you already have won.
  - eleitl 8y ago
    Do you know why digital pulse radios never happened?
athrowaway3z 8y ago
> cell carriers have access to better bands, and far better infrastructure What would be the best band for this kind of infrastructure? ( Disregarding any existing FCC licenses )

gandalfian 8y ago

My real world wifi experience. Domestic 2.4ghz wifi ap with a directional antenna plugged in, 600m direct line of sight across valley to neighbours netgear ap with stock antenna, assumed in his window. Internet achieved. Wifi ap, stock antenna in my house window, looking unobstructed over field, I get wifi internet on my phone about 200m out. Indoors in my stone walled house wifi is perhaps 10-15m. So half a mile range or 600m is almost true in a marketing sense though a bit dishonest in a real world usage sense.

ansible 8y ago

> I'm guessing they haven't bought licenses from the FCC, so my bet is that they're using the 900 MHz ISM band. No FCC filings for this device yet that I found. I guess we'll have to see.