Li-Fi to replace Wi-Fi? Sounds like Sci-Fi or bullcrap - Page 1
Forum section: electronics / general

author: AshrafE
author_rank: Newbie
timestamp: February 26, 2018, 07:42:13 am
content: Hi,Came across this article posted on LinkedIn. Just sounds too good to be true.https://www.linkedin.com/groups/23006/23006-6356836195850424320?midToken=AQGVufgP_ioCLA&trk=eml-b2_anet_digest_of_digests-hero-11-discussion%7Esubject&trkEmail=eml-b2_anet_digest_of_digests-hero-11-discussion%7Esubject-null-fut9b%7Eje2mgx0h%7Exp-null-communities%7Egroup%7Ediscussion&lipi=urn%3Ali%3Apage%3Aemail_b2_anet_digest_of_digests%3B4bEpKV%2BeRgqWc7FVPtniBg%3D%3DCheers.

author: ataradov
author_rank: Super Contributor
timestamp: February 26, 2018, 08:14:15 am
content: That thing has been around for a while, but I don't think any has ever seen an independent review of a practical implementation.It surfaces every trade show cycle, gets press resales published in sketchy places, like engadged, and then slowly gets quiet, until the next trade show.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 02, 2018, 06:05:40 am
content: I see it as more of a supplement than a replacement for Wifi, and there apparently are still a bunch of challenges to overcome.BTW, before Wifi, some hobbyists have figured out how to send Ethernet over laser pointers.

author: David Hess
author_rank: Super Contributor
timestamp: March 02, 2018, 12:45:16 pm
content: I would be satisfied with an updated IRDA standard for portable devices like cameras to exchange information with desktops. It would be more secure and could be more reliable than WiFi, Bluetooth, and similar radio standards. I live in perpetual fear of breaking the micro USB connector on my camera or wearing out the SD card slot and WiFi for cameras just sucks.

author: Marco
author_rank: Super Contributor
timestamp: March 02, 2018, 12:57:51 pm
content: Li-Fi can't replace WiFi, but it might make mm wave superfluous for communication in consumer applications. They both compete in the same space, but light has some advantages.The concept developed by University of Eindhoven is interesting. Central optical emitter, bunch of cheap fibre through the house with passive access points (download only, wifi for upload).

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 02, 2018, 04:13:40 pm
content: Quote from: Marco on March 02, 2018, 12:57:51 pmMost communications are two way. With no upload, the clients can't make any requests so they can't initiate any sort of transfer! The only thing you could do might be imaging drives or something, but it would be in UDP with no corrections. So if a fly goes across your emitter, everything gets corrupted!You could use it with wifi to have two-way, but then again...why? You would be limited to the infrared range anyway.

author: Marco
author_rank: Super Contributor
timestamp: March 02, 2018, 05:13:27 pm
content: It's for asymmetrical bandwidth applications. Mbps upload through wifi, Gbps download through lifi.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 02, 2018, 05:27:43 pm
content: Quote from: Marco on March 02, 2018, 05:13:27 pmIf you need infrared for whatever reason, then why not use a regular two-way infrared connection?

author: Marco
author_rank: Super Contributor
timestamp: March 02, 2018, 06:38:20 pm
content: Because you can passively turn a coherent collimated beam from a fibre into a wide beam to cover the room, but you can't passively turn light from a device in the room into a coherent collimated beam to send through the fibre in the other direction.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 02, 2018, 06:54:04 pm
content: Quote from: Marco on March 02, 2018, 06:38:20 pmWhich is exactly why their system is pointless!

author: Marco
author_rank: Super Contributor
timestamp: March 02, 2018, 07:15:28 pm
content: It's an elegant and potentially low cost way to provide 10+ Gbps downstream bandwidth wirelessly throughout a home.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 02, 2018, 08:13:54 pm
content: Quote from: Marco on March 02, 2018, 07:15:28 pmYou sound like a shill at this point. Time to crush your bubble with a hydraulic press.802.11ac has been invented as gigabit wifi. Without the need to run fiber optics everywhere, and is two way by default.https://en.wikipedia.org/wiki/IEEE_802.11acPlus, no home would ever need a 10Gb connection, let alone a single device! That's the speed of a main fiber for a small building!

author: Brumby
author_rank: Unknown
timestamp: March 03, 2018, 02:22:30 am
content: Quote from: Cyberdragon on March 02, 2018, 08:13:54 pmHow long before this statement falls down?2 years ...? 5 years ...?

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 03, 2018, 03:01:03 am
content: Quote from: Brumby on March 03, 2018, 02:22:30 amRight now if you count wireless VR. That's obviously LAN rather than WAN but the wireless solution doesn't care.

author: Brumby
author_rank: Unknown
timestamp: March 03, 2018, 03:14:49 am
content: I was thinking about two words in particular: "home", but especially "need".Capability is a different thing.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 03, 2018, 03:27:15 am
content: Quote from: Brumby on March 03, 2018, 02:22:30 amRight, I forgot about all the IOT loving hipsters hogging bandwidth with their privacy destroying advertisement machines.Or if you're a mad scientist with a Watson supercomputer in your house. But those VR systems have their own interlinks, they don't use the wifi (because they eat bandwidth).But the point is that a one way LOS infrared system is still useless, when you have to have wifi anyway just to make it work!

author: Brumby
author_rank: Unknown
timestamp: March 03, 2018, 03:44:11 am
content: I was thinking more along the lines of multiple 8K (or higher) video streaming ... and perhaps more bandwidth hungry websites and other such things .... but, yeah, I suppose the IOT realm will be a part of it.I don't know why - but I just had a random thought that led me to look up "id":"The id acts according to the "pleasure principle"—the psychic force that motivates the tendency to seek immediate gratification of any impulse"Then the "Internet Of Things" fell in place after that - and the resultant word just struck a chord.

author: Marco
author_rank: Super Contributor
timestamp: March 03, 2018, 04:44:17 am
content: Quote from: Cyberdragon on March 02, 2018, 08:13:54 pmI wouldn't have been so repetitive if you hadn't been so obtuse. There was a method to what you consider madness, as we have now established.Quote5GHz still has reach and thus contention issues in urban environments, and they are an order of magnitude apart in potential bandwidth ... not a 1:1 replacement.QuoteStill need to put routers everywhere and run wire between them, not like there's anything left of that gigabit potential after a single wall.QuoteThat's the meat of the issue, it's certainly the rock mm wave ran ashore on ... but maybe VR takes off, never know, humans are fickle.LiFi has advantages over mm wave, no multipath fading, low cost to put multiple emitters in a room, etc.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 03, 2018, 05:57:44 am
content: You can't talk about reach with an infrared LOS system, unless it uses a direct laser beam. But even then you would have to contend with walls, coffee cups, paper airplains, wandering pets, and anything else that could inadvertantly block the sensor.Quote from: Marco on March 03, 2018, 04:44:17 amYou just said yourself you need to run wifi to make this work anyway since it's send only. So you would need to run TWO systems of wiring for ONE interlink.Gig wifi is not "blocked by a single wall", it's been in use since 2011 and has had no such problems. Plus, an optical system would be blocked by a fly landing on the sensor! And you would only need one access point per room for wifi since it's not LOS, and is two way.VR would only be a local interlink, between two devices (the computer/console and the headset) not throughout a house. But even then, it's VR, so you'd be moving, the detriment of any LOS system.

author: Marco
author_rank: Super Contributor
timestamp: March 03, 2018, 07:07:19 am
content: Quote from: Cyberdragon on March 03, 2018, 05:57:44 amWhether it's purely LOS or detectable after some bounce/refraction/diffusion depends on noise margins, much like mm wave.QuoteYou need high density access points to get near the throughput potential of 802.11ac, but lifi wouldn't need to get near that potential, because upload requirements are almost always far lower.It's like you're unaware that there is quite a large industry out there trying to push mm wave systems ... doesn't necessarily need to succeed, but it does allow me to appeal to authority.

author: BrianHG
author_rank: Super Contributor
timestamp: March 04, 2018, 08:14:02 pm
content: This will be the future of WiFi :http://www.newelectronics.co.uk/electronics-news/full-duplex-radio-ics-transmit-and-receive-at-the-same-frequency/75059/The document underestimates the speed increases. A whole lot of handshaking & overhead will be lost once you sync 2 radios on the same frequency where both sides transmits continuously simultaneously, not to mention looking for clean alternate open channels.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 04, 2018, 09:09:23 pm
content: Quote from: Marco on March 03, 2018, 07:07:19 amYou only need two points to get at least 1 gig speed for 802.11ac. And again, that's one system, not entirely two different and seperate systems that have to work together.I never said infrared was entirely useless, it has specialized applications. I just think it's a stupid idea for residential or office use.

author: helius
author_rank: Super Contributor
timestamp: March 04, 2018, 09:22:31 pm
content: Infrared was originally part of the 802.11 standard in 1997. Along with FHSS, it was dropped from the next revision of the standard in 1999.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 04, 2018, 10:24:02 pm
content: Quote from: BrianHG on March 04, 2018, 08:14:02 pmI'm not sure why they didn't think of it the day dual band Wifi became commonplace. Negotiate with the device to transmit on one band while receiving with the other, full duplex.

author: Marco
author_rank: Super Contributor
timestamp: March 04, 2018, 11:27:17 pm
content: How do they distinguish a signal from a weak reflection? Only way I see to do full duplex on the "same" frequency is using part of the constellations for transmit and the rest for receive, but that doesn't double the bandwidth.PS. oh, it learns the multipath response during the preamble .... that's smart. The hand shaking is kind of an essential part of what makes it work, CSMA isn't going away either.

author: BrianHG
author_rank: Super Contributor
timestamp: March 04, 2018, 11:37:15 pm
content: Quote from: NiHaoMike on March 04, 2018, 10:24:02 pmWhen transmitting, you cannot receive on the same frequency at the same time. The outgoing signal is 100 trillion times stronger than the receive signal making it impossible. Don't get confused, our current WiFi do transmit and receive on the same frequencies, it's just that on side transmits, the other side shuts down the transmitter to listen, then, they swap. This is called Half-duplex. It only looks full to the PCs since this is going on so rapidly.Prior to this IC, only military radar with reciprocal antennas, where they had special structures on the antenna so that the out-going signal was not seen by the receiving antenna in the same scanning dish. By strategically designing the structure so that the RX part of the antenna was positioned not to see the XT output (signal was canceled out by the orientation and shape of the structure), yet still be in the same focal point of the dish antenna making the radar as accurate as possible. It was the physical antenna which allowed the powerful transmit outgoing signal to always be on, yet, the RX antenna would not see that signal at all, just the super-weak reflections coming back.

author: BrianHG
author_rank: Super Contributor
timestamp: March 04, 2018, 11:43:17 pm
content: Another advance in full duplex, this one explains how it was done they cancelled out that 100 trillion times stronger transmit while receiving at the same time:https://phys.org/news/2017-03-two-way-radio-chip.htmlIt's coming....

author: Marco
author_rank: Super Contributor
timestamp: March 05, 2018, 01:52:01 am
content: With highly asymmetric data the impact will be unlikely to reach 2x or higher total throughput though. In fact I doubt it's even worth the headaches in cellular, where contention isn't an issue, the dynamic range and distances higher and the IC's already being complex enough as is.

author: BrianHG
author_rank: Super Contributor
timestamp: March 05, 2018, 01:55:59 am
content: Quote from: Marco on March 04, 2018, 11:27:17 pm.

author: BrianHG
author_rank: Super Contributor
timestamp: March 05, 2018, 02:04:06 am
content: Quote from: Marco on March 05, 2018, 01:52:01 amTry continuous realtime flow control and error correction without waiting for larger blocks to be transferred to attain speed. It will get closer to Ethernet performance. As for complexity, that's a load of BS. Take a look at a modern cell phone CPU, even a bottom end one, it roasts the complexity of even this radio chip. In the future, complexity and sophistication is going up, everything is not stooping at today's level, and we will call what we have today the definitive end of our radio technology.

author: Marco
author_rank: Super Contributor
timestamp: March 05, 2018, 02:14:02 am
content: Quote from: BrianHG on March 05, 2018, 01:55:59 amIt uses the pre-amble as a ping to measure and be able to correct for the reflections, which it corrects for digitally after solving the 100 trillion problem in analogue.

author: David Hess
author_rank: Super Contributor
timestamp: March 05, 2018, 02:21:34 am
content: Quote from: BrianHG on March 04, 2018, 11:43:17 pmI remember looking into this 20+ years ago. The problem then was the shot noise from any active elements outside the path between the sampling point and cancelling point was greater than the received signal. It worked fine if the received signal strength was large compared to the transmitter noise but that is a pretty big restriction.This problem applies even if frequency-division multiplexing is used which explains why transmitters require passive filtering on their output whether they meet distortion requirements or not. If transmit and receive are in the same band, then it is not sufficient to have only high Q bandpass filtering on only the receiver because it will pass the shot noise from the transmitter.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 05, 2018, 04:44:50 am
content: Quote from: BrianHG on March 04, 2018, 11:37:15 pmWhy can't, for example, the AP transmit on 5GHz and the client transmit on 2.4GHz? Kind of like what drone pilots do for remote control with real time video.

author: BrianHG
author_rank: Super Contributor
timestamp: March 05, 2018, 06:35:03 am
content: Quote from: NiHaoMike on March 05, 2018, 04:44:50 amYou get more throughput when both transmit on the higher bandwidth channels. And, why not have both transmit and receive on both bands simultaneously is you want 4x speed. Though, with the allowed power for consumer devices, you might get better distance or bandwidth on one band versus the other. Also, what if one band is occupied by other devices. At least, if your sender is already transmitting, you can send data back on the same channel without eating up a second band which may have other traffic. Freeing up channels means lest wasted bandwidth/congestion. I know my WiFi suffers from all the other new routers my neighbors have installed recently. I also know going from my laptop to my main WiFi router is twice as fast as the other direction on channel 2, yet, on channel 1, this difference in UL/DL performance is swapped. With this new tech, the fastest channel I choose will be identical in both directions.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 05, 2018, 07:04:02 am
content: Quote from: BrianHG on March 05, 2018, 06:35:03 amWhat about when latency is the priority rather than bandwidth? I also think that for most real world bulk traffic that is mostly in one direction, putting the reverse traffic on a different band would improve overall performance.

author: BrianHG
author_rank: Super Contributor
timestamp: March 05, 2018, 07:38:43 am
content: Quote from: NiHaoMike on March 05, 2018, 07:04:02 amYou obviously ignored to the 2 linked document I posted. The whole purpose of the FULL DUPLEX chip is when it transmits, it can receive external broadcasts on the same frequency coming from the other side while it's transmitting on the exact same frequency as the FULL DUPLEX radio on the other side is doing the exact same thing at the same time.Question, do you know understand meaning of full duplex communication? This new IC isn't emulating full duplex by rapidly switching between transmit and receive, this is what we have now. This full duplex radio IC is doing it for real.There would be no purpose in developing such an IC if we already had it. Right now we have half duplex and it sucks. Just using 2 different bands means either wasting bandwidth, having to use 2 very spaced apart bands, one which might not have the same speed at different distances and may have different speeds. Also, if since both sides are always transmitting at the same frequency at the same time, you know your channel is clear both ways. With full duplex, not switching delays since you can transmit while receiving right on the exact same frequency.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 05, 2018, 08:06:54 am
content: Doing full duplex across two separate bands is far easier to implement. I would like to see how that single band full duplex chip really performs in the real world. As a related example, MU-MIMO sounds good on paper but doesn't always work well in the real world.

author: BrianHG
author_rank: Super Contributor
timestamp: March 05, 2018, 06:35:50 pm
content: Quote from: NiHaoMike on March 05, 2018, 08:06:54 amOk, yes, this is a legitimate concern.

author: f4eru
author_rank: Super Contributor
timestamp: March 10, 2018, 09:25:50 am
content: QuoteNot a very convincing system...Won't do more than 2-3 meters, at most, then you're submerged in your TX noise.Also, for "hand shaking" don't shake your hands nearby, you'll change the multipath propagation, and the handshake has to happen again.

author: Marco
author_rank: Super Contributor
timestamp: March 10, 2018, 09:48:54 am
content: Isn't there a preamble for every frame?

author: borjam
author_rank: Unknown
timestamp: March 19, 2018, 09:06:11 am
content: The problem with the 2.4 and 5.8 GHz bands is, of course, interference. It's especially strong in high density dwellings such as appartment buildings.The 60 GHz (802.11ad) band would be a good candidate because it won't cross a wall, which means neighbor interference will be non existant. Even windows will attenuate it a lot. The problem, of course, you would need an access point per room. But that means clean spectrum for everyone.As for lasers, I remember that in the early 90's there was a product called Terabeam that transmitted 10 Mbps Ethernet using lasers. It worked pretty well although it had a weakness, the lasers had to be replaced periodically.I am now trying a 60 GHz link (Mikrotik Wireless Wire) just to cross a street (20 - 30 metres) and the performance is incredible. Almost the same as digging a trench and laying a fibre. And it's not expensive, less than €200 a pair. Using a phased array with some degree of beam forming you don't even need to aim them very carefully. just use a rule of thumb.

author: Marco
author_rank: Super Contributor
timestamp: March 19, 2018, 12:06:18 pm
content: Millimeter wave is almost as pure line of sight as light. Indoor it doesn't really have any advantage to light, outdoor it's better with fog.