9 ms·

Newb question: since they are both electromagnetic radiation, how does Li-Fi get up to 100x faster than Wi-Fi? Are the light transmitters and sensors that much

Newb question: since they are both electromagnetic radiation, how does Li-Fi get up to 100x faster than Wi-Fi? Are the light transmitters and sensors that much faster? Or perhaps is it able to use a wider band of frequencies? I'm also so curious how this ends up working in practice. Even using infrared, would it interfere with things like baby monitors in night mode? The Wikipedia article says it can be tuned to be less intense than humans can perceive, but I'm curious if that's true in practice. (Granted, babies don't typically need Internet access while they are sleeping, but maybe the monitor itself does.)

embwbam 3y ago
You can encode a lot more information in higher frequencies. But each frequency has different things that are opaque to it, and travel different distances before dropping off. Wi-Fi is already “really low frequency, really low intensity infrared light”, so I suspect the article is correct when it says we won’t notice it.
- cdumler 3y ago
  Correct. The reason why microwaves can cook food isn't the fact that it is a microwave frequency. Microwaves ovens cook by flipping the polarity back and forth. The frequency emitted is the same resonant frequency as water molecules, so the water molecules attempt to align constantly to the ever changing polarity. Movement is heat; thus, the water heats the food.
  - oehtXRwMkIs 3y ago
    I've heard the resonance with water explanation is a common misconception: https://physics.stackexchange.com/questions/150128/how-do-microwaves-heat-moisture-free-items https://physics.stackexchange.com/questions/150128/how-do-mi...
    - rolph 3y ago
      more of an oversimplification. polar bonds interact with EM field of microwave oven. water is one of many thousands of compounds having polar bonds
      - oehtXRwMkIs 3y ago
        That doesn't sound like resonance to me, which is about constructive interference and natural frequencies. So more of an inaccuracy I think.
  - pfedak 3y ago
    To set the record straight for the above comment - - it's true that there isn't a precise frequency needed for microwave ovens to heat food - however, "polarity flipping" is just a description of electromagnetic radiation itself, and shooting enough EM radiation at food in a frequency range it absorbs will heat it up via dielectric heating - microwaves have no relationship to any specific resonant frequency of water - the vibration frequencies are orders of magnitude higher https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water#Vibrational_spectrum https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_... while rotation response inherently does not have a peak - otherwise, yes, the motion of (polar) molecules induced by an electric field is indeed the mechanism of dielectric heating
- NotYourLawyer 3y ago
  > Wi-Fi is already “really low frequency, really low intensity infrared light” No, infrared by definition starts around 300 GHz and goes up from there.
  - embwbam 3y ago
    Sorry. I was just going by the literal reading of the infra (under) red.
admax88qqq 3y ago
I don't know anything about LiFi, but for EM radiation in general, the higher the frequency, the higher the theoretical maximum bandwidth. https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore... Wifi is 2.6 Ghz or 5Ghz, visible red light is 430 terahertz. Or it sounds like LiFi is just pulsing the lights on an off, in which case the Nyquist Rate that was invented for telegrams is a better analogy https://en.wikipedia.org/wiki/Nyquist_rate https://en.wikipedia.org/wiki/Nyquist_rate
- rbanffy 3y ago
  Just imagine what we'll be able to do with Gamma data transmissions ;-) I like to explain to my kids that it's all colors - we are transparent to some (such as X-rays) the same way some fish are mostly transparent to the light we can see and walls are transparent to the radios we use in Wi-Fi, and also that both snakes and bees can see light in colors we can't (snakes see IR, bees see UV).
  - noobface 3y ago
    Face melting speed.
- sinak 3y ago
  I think you're misreading Shannon's Law. It's not that the higher the frequency the greater the max bandwidth. It's the higher the bandwidth the more data you can put through.
  - OnACoffeeBreak 3y ago
    I am agreeing with you and providing more info: https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore... Maximum channel capacity depends on signal bandwidth and SNR.
- makeworld 3y ago
  > the higher the frequency, the higher the theoretical maximum bandwidth. This is not true and is unrelated to Shannon's theorem. Shannon's theorem shows us that wider bandwidths allow for larger bit rates. At higher frequencies our bandwidths can be bigger. For example a band from 1 to 2 terahertz is 1 terahertz wide, which is 1000 times larger than a band from 1 to 2 gigahertz (1 gigahertz wide). The total bandwidth available (including multiple channels) for 2.4 GHz Wi-Fi is about 100 MHz. The total space available for this new standard is 800 to 1000 nm [0], which is 450 THz. That's 4.5 million times wider than Wi-Fi. That is why you get higher bit rates with this new standard, AKA more throughput, or more "bandwidth", when the term is used to mean data rate. [0]: https://standards.ieee.org/ieee/802.11bb/10823/ https://standards.ieee.org/ieee/802.11bb/10823/
jbperry 3y ago
My understanding is they went with 800 to 1000 nm (infrared), or ~ 375 to 300 THz. I'm not sure as to the total combined bandwidth of all of WiFi 6 or 7, but 75,000 GHz band gives them a lot to play with.
Tade0 3y ago
> Even using infrared, would it interfere with things like baby monitors in night mode? If you're referring to the infrared LEDs that illuminate the baby, their light is not polarized, while light used for communication is, so a polarizing filter in the receiver can filter out such noise.
- Shadowmist 3y ago
  Baby monitors with night vision usually have a small set of tiny infrared lights so that they can see. Adding additional infrared to the room will help the monitor to see better.
  - DropInIn 3y ago
    Given how they are calibrated I don't think so.... More likely the image would be getting constantly washed out, right?
    - anyoneamous 3y ago
      Depending on how fast the extra IR light is pulsing, it might end up looking like your baby is sleeping through a rave - which would be entertaining enough to be passed off as a feature rather than a bug.
      - DropInIn 3y ago
        "Between 3-30 hertz (flashes per second) are the common rates to trigger seizures but this varies from person to person. While some people are sensitive at frequencies up to 60 hertz, sensitivity under 3 hertz is not common" https://epilepsysociety.org.uk/about-epilepsy/epileptic-seizures/seizure-triggers/photosensitive-epilepsy https://epilepsysociety.org.uk/about-epilepsy/epileptic-seiz... This came immediately to mind which when comorbid with infrared sensitivity is likely to trigger people without any apparent cause to third party observers.... People forget that the average human barely see jack sht compared to the remarkable exceptions of our species, let alone that such exceptions often have disabling/uncommon conditions comorbid with thier remarkable capabilities.
bloggie 3y ago
I think Li-Fi is more comparable to Ethernet instead of Wi-Fi, not because the fundamentals are very different but because of the link budgets available. If you think of an ethernet line as a pipe carrying data, then a collimated laser can be thought of in a similar way - most of the energy that you transmit is going to make it to the destination, and that is not the case with Wi-Fi, even with very high gain antennas. This allows for different modulation schemes and thus higher throughput. Copper ethernet is now capable of 1.6 Tbps [1] and Li-Fi doesn't seem so very fast compared to that; however keep in mind this is comparing only physical layers. Demonstrations of optical laser links of hundreds of Gbps over hundreds of kilometers have taken place [2] using COTS optical ethernet transceivers and special output stages providing precise collimation and pointing. [1] https://en.wikipedia.org/wiki/Ethernet_physical_layer#1.6_Tbit/s https://en.wikipedia.org/wiki/Ethernet_physical_layer#1.6_Tb... [2] https://ntrs.nasa.gov/api/citations/20210026855/downloads/spie2022-tbird-v1.pdf https://ntrs.nasa.gov/api/citations/20210026855/downloads/sp... For your second question, I'm not sure how baby monitors work but the proposed wavelengths are unlicenced and there are little if any rules for how to deal with interference. There are rules for eye safety of laser which limits the maximum energy that can be delivered to the output. Generally as Li-Fi gets more common we will have to learn to deal with interference as it arrives. For example, Lidar systems (older, noncoherent ones) interfere with one another and are even susceptible to interferece from IR motion detectors and such, but these aspects have to be considered during design.
bmacho 3y ago
> Newb question: since they are both electromagnetic radiation, how does Li-Fi get up to 100x faster than Wi-Fi? They specified that they wanted to be 100x faster, and they added parallel channels, until they reached that goal. No, really, this is the real reason. It is entirely nonsensical to ask for a physical reason, because different channels are just different.
- cowl 3y ago
  well the physical reason is that the band available at the visible light spectrum allows you to add that much channels in parallel. You can't do that at 2.4GHz

embwbam 3y ago

You can encode a lot more information in higher frequencies. But each frequency has different things that are opaque to it, and travel different distances before dropping off. Wi-Fi is already “really low frequency, really low intensity infrared light”, so I suspect the article is correct when it says we won’t notice it.

cdumler 3y ago
Correct. The reason why microwaves can cook food isn't the fact that it is a microwave frequency. Microwaves ovens cook by flipping the polarity back and forth. The frequency emitted is the same resonant frequency as water molecules, so the water molecules attempt to align constantly to the ever changing polarity. Movement is heat; thus, the water heats the food.
- oehtXRwMkIs 3y ago
  I've heard the resonance with water explanation is a common misconception: https://physics.stackexchange.com/questions/150128/how-do-microwaves-heat-moisture-free-items https://physics.stackexchange.com/questions/150128/how-do-mi...
  - rolph 3y ago
    more of an oversimplification. polar bonds interact with EM field of microwave oven. water is one of many thousands of compounds having polar bonds
    - oehtXRwMkIs 3y ago
      That doesn't sound like resonance to me, which is about constructive interference and natural frequencies. So more of an inaccuracy I think.
- pfedak 3y ago
  To set the record straight for the above comment - - it's true that there isn't a precise frequency needed for microwave ovens to heat food - however, "polarity flipping" is just a description of electromagnetic radiation itself, and shooting enough EM radiation at food in a frequency range it absorbs will heat it up via dielectric heating - microwaves have no relationship to any specific resonant frequency of water - the vibration frequencies are orders of magnitude higher https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water#Vibrational_spectrum https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_... while rotation response inherently does not have a peak - otherwise, yes, the motion of (polar) molecules induced by an electric field is indeed the mechanism of dielectric heating
NotYourLawyer 3y ago
> Wi-Fi is already “really low frequency, really low intensity infrared light” No, infrared by definition starts around 300 GHz and goes up from there.
- embwbam 3y ago
  Sorry. I was just going by the literal reading of the infra (under) red.

admax88qqq 3y ago

I don't know anything about LiFi, but for EM radiation in general, the higher the frequency, the higher the theoretical maximum bandwidth. https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore... Wifi is 2.6 Ghz or 5Ghz, visible red light is 430 terahertz. Or it sounds like LiFi is just pulsing the lights on an off, in which case the Nyquist Rate that was invented for telegrams is a better analogy https://en.wikipedia.org/wiki/Nyquist_rate https://en.wikipedia.org/wiki/Nyquist_rate

rbanffy 3y ago
Just imagine what we'll be able to do with Gamma data transmissions ;-) I like to explain to my kids that it's all colors - we are transparent to some (such as X-rays) the same way some fish are mostly transparent to the light we can see and walls are transparent to the radios we use in Wi-Fi, and also that both snakes and bees can see light in colors we can't (snakes see IR, bees see UV).
- noobface 3y ago
  Face melting speed.
sinak 3y ago
I think you're misreading Shannon's Law. It's not that the higher the frequency the greater the max bandwidth. It's the higher the bandwidth the more data you can put through.
- OnACoffeeBreak 3y ago
  I am agreeing with you and providing more info: https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore... Maximum channel capacity depends on signal bandwidth and SNR.
makeworld 3y ago
> the higher the frequency, the higher the theoretical maximum bandwidth. This is not true and is unrelated to Shannon's theorem. Shannon's theorem shows us that wider bandwidths allow for larger bit rates. At higher frequencies our bandwidths can be bigger. For example a band from 1 to 2 terahertz is 1 terahertz wide, which is 1000 times larger than a band from 1 to 2 gigahertz (1 gigahertz wide). The total bandwidth available (including multiple channels) for 2.4 GHz Wi-Fi is about 100 MHz. The total space available for this new standard is 800 to 1000 nm [0], which is 450 THz. That's 4.5 million times wider than Wi-Fi. That is why you get higher bit rates with this new standard, AKA more throughput, or more "bandwidth", when the term is used to mean data rate. [0]: https://standards.ieee.org/ieee/802.11bb/10823/ https://standards.ieee.org/ieee/802.11bb/10823/

jbperry 3y ago

My understanding is they went with 800 to 1000 nm (infrared), or ~ 375 to 300 THz. I'm not sure as to the total combined bandwidth of all of WiFi 6 or 7, but 75,000 GHz band gives them a lot to play with.

Tade0 3y ago

> Even using infrared, would it interfere with things like baby monitors in night mode? If you're referring to the infrared LEDs that illuminate the baby, their light is not polarized, while light used for communication is, so a polarizing filter in the receiver can filter out such noise.

Shadowmist 3y ago
Baby monitors with night vision usually have a small set of tiny infrared lights so that they can see. Adding additional infrared to the room will help the monitor to see better.
- DropInIn 3y ago
  Given how they are calibrated I don't think so.... More likely the image would be getting constantly washed out, right?
  - anyoneamous 3y ago
    Depending on how fast the extra IR light is pulsing, it might end up looking like your baby is sleeping through a rave - which would be entertaining enough to be passed off as a feature rather than a bug.
    - DropInIn 3y ago
      "Between 3-30 hertz (flashes per second) are the common rates to trigger seizures but this varies from person to person. While some people are sensitive at frequencies up to 60 hertz, sensitivity under 3 hertz is not common" https://epilepsysociety.org.uk/about-epilepsy/epileptic-seizures/seizure-triggers/photosensitive-epilepsy https://epilepsysociety.org.uk/about-epilepsy/epileptic-seiz... This came immediately to mind which when comorbid with infrared sensitivity is likely to trigger people without any apparent cause to third party observers.... People forget that the average human barely see jack sht compared to the remarkable exceptions of our species, let alone that such exceptions often have disabling/uncommon conditions comorbid with thier remarkable capabilities.

bloggie 3y ago

I think Li-Fi is more comparable to Ethernet instead of Wi-Fi, not because the fundamentals are very different but because of the link budgets available. If you think of an ethernet line as a pipe carrying data, then a collimated laser can be thought of in a similar way - most of the energy that you transmit is going to make it to the destination, and that is not the case with Wi-Fi, even with very high gain antennas. This allows for different modulation schemes and thus higher throughput. Copper ethernet is now capable of 1.6 Tbps [1] and Li-Fi doesn't seem so very fast compared to that; however keep in mind this is comparing only physical layers. Demonstrations of optical laser links of hundreds of Gbps over hundreds of kilometers have taken place [2] using COTS optical ethernet transceivers and special output stages providing precise collimation and pointing. [1] https://en.wikipedia.org/wiki/Ethernet_physical_layer#1.6_Tbit/s https://en.wikipedia.org/wiki/Ethernet_physical_layer#1.6_Tb... [2] https://ntrs.nasa.gov/api/citations/20210026855/downloads/spie2022-tbird-v1.pdf https://ntrs.nasa.gov/api/citations/20210026855/downloads/sp... For your second question, I'm not sure how baby monitors work but the proposed wavelengths are unlicenced and there are little if any rules for how to deal with interference. There are rules for eye safety of laser which limits the maximum energy that can be delivered to the output. Generally as Li-Fi gets more common we will have to learn to deal with interference as it arrives. For example, Lidar systems (older, noncoherent ones) interfere with one another and are even susceptible to interferece from IR motion detectors and such, but these aspects have to be considered during design.

bmacho 3y ago

> Newb question: since they are both electromagnetic radiation, how does Li-Fi get up to 100x faster than Wi-Fi? They specified that they wanted to be 100x faster, and they added parallel channels, until they reached that goal. No, really, this is the real reason. It is entirely nonsensical to ask for a physical reason, because different channels are just different.

cowl 3y ago
well the physical reason is that the band available at the visible light spectrum allows you to add that much channels in parallel. You can't do that at 2.4GHz