Frequently asked questions received about Li-Fi technology.
- Isn’t LiFi just another name for VLC (visible light communications)?
The starting point for the technologies are similar in that they both consist of links formed by a solid state emitting device and a photo sensitive receiver. VLC tends to refer to a point to point light communication link, usually over a fixed link with known and carefully controlled characteristics that is unidirectional and operated at low or moderate data rates. LiFi is more about having a network infrastructure of transceivers that can form ad-hoc connections on demand to clusters of devices, that is integrated to work in tandem with r.f. services, and supports from moderate to high to ultra-high data rates.
- Isn’t this just a line of sight technology?
It is not necessary to have line of sight between the transmitter and the receiver. Any light path that exists between the transmitter and receiver can in principle support a LiFi link, including via reflections from a wall, ceiling or floor, so long as the power budget is arranged to cope with losses due to the diffusion.
- What kinds of devices will use this technology?
At the current state of art, LiFi communication has been demonstrated between dedicated transceiver units. In future, a LiFi capability will be integrated into many devices, including those where Wi-Fi or Bluetooth is currently used, and in many more where these technologies would not be suitable. Ultimately it can be anticipated that nearly all electronic devices will have LiFi compatibility.
- But you won’t be able to link to a device such as a mobile phone if it is in your pocket?
It is not necessary for a LiFi link to be always active since it works alongside other systems. In general, the times when high data rate transfers are required, are inevitably exactly the times the device is open to be accessed by a user, and adjacent to a light within the local environment. So, more often than not, a LiFi signal will be available when it is most required.
- What happens when something blocks the beam temporarily?
It is possible that a transmitting light beam will be blocked in the course of events. Again though, it is not necessary for a LiFi link to solely support data transfers. It is already the case that devices seamlessly transfer between a range of communication protocols, including 2G, 3G, LTE and Wi-Fi. In a similar way, LiFi would integrate with the available stack of physical communication links, and when available be used by preference to offload from other domains.
- Will my lights flicker?
No, not visibly. LiFi uses very high frequencies, in general greater than 1MHz and these are well above the rates where the eye can distinguish any flicker.
- What happens when the lights are off?
LiFi provides for a very sensitive communication link, with a very advantageous signal to noise ratio. Counter-intuitively, this means that an LED light can be turned down all the way to the point where it appears off to the naked eye, while still transmitting data that is able to be picked up by a compatible receiver.
- Does LiFi provide a one-way link, so it’s for download only?
No. We have already demonstrated bi-directional links between a fixed access point and a user terminal. There are various technological approaches to providing this, including the use of different wavelength ranges, or different communication protocols for the uplink and the downlink.
- Are there any health risks?
In common with all existing lights, including LED light bulbs, the transmitters used for LiFi need to conform, by design, to national and international light hazard regulations. Having achieved that standard however, there are no particular additional health hazards, and potentially far fewer than are thought to be associated with r.f. transmitters.
- This all sounds very futuristic, when will I be able to buy a device in my high street?
The first LiFi devices are only just appearing commercially, and are now being trialled in a large variety of applications. It will be some time before LiFi is widely available as a generic communication link in all consumer devices, but starting this year there is a steady growth in the roll-out of products, initially targeted at very specific applications areas for business and commerce.
- Won’t security be an issue when signals leak through windows?
When LiFi is widely deployed in urban interiors, it may be possible for there to be a leakage of signal through a window, but it will be much easier to take advantage of the inherent security properties of light, in that it does not pass through many common building materials, unlike r.f. signals, which in general will readily pass through walls (clue – draw the curtains!).
- Won’t the different lights in a room interfere with each other so that the receiver is confused?
Most LED lighting is fundamentally directional. The competition between adjacent lights is not so much of a problem as might be imagined. Typical lighting situations have been closely modelled at the University of Edinburgh, and it has been shown that it is easily possible to position lighting to achieve both good illumination coverage, and clean LiFi reception.
- Who invented LiFi?
The term ‘LiFi’ was coined by Professor Harald Haas during his 2011 TED talk. The basis of light communication can be traced back to ancient historical roots but, in terms of the modern age, can perhaps be said to have started with Alexander Graham Bell’s photo-phone. In recent times, VLC was pioneered by Nakagawa and others, while the extension of VLC into a LiFi that includes the very latest communication algorithms and full networking capability, was initiated by Professor Haas, starting in 2001 and eventually being realised as the full LiFi concept as described here. Many groups are now active in developing LiFi technology, with the University of Edinburgh holding a key portfolio of underlying LiFi intellectual property.
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