The shift to optical – part II

This is a second part to the post ‘the shift to optical’ where I look at the current state and future trend for device interconnect technologies and see if there is a trend towards optical technologies.

The proliferation of devices that can display rich media has been causing data bottle neck problems.  Harald Haas recently highlighted the congestion on radio networks and how this is expected to get worse.  When the wireless network capacity is limited or unreliable we often reach for a cabled solution, e.g. a fixed line telephone, an Ethernet cable, or a USB interconnect.  There have been significant improvements in cabled systems over the years. The same is true of wireless systems although the data rates have always lagged behind.

visible light communicationWired interconnect can transfer large data files (e.g. video) quickly, but it would be much nicer if this could all be done wirelessly.  The good news is that there are wireless technologies around the corner that promise very high transfer speeds.

In the table below I have highlighted 3 wired interconnect technologies that are at the top end of what is on the market today. i.e. FireWire, USB 3.0 and Thunderbolt.  All of these use wires rather than optical fibres although Thunderbolt considered fibre but reverted to conductors in order to carry power.



Data density


FireWire 800 800 Mbps *****
USB 3.0 5 Gbps *****
Thunderbolt 2x 10 Gbps *****

Wireless (current)

Wi-Fi – IEEE 802.11n 150 Mbps *
Bluetooth 3 Mbps *
IrDA 4 Mbps ***

Wireless (future)

WiGig 2 Gbps **
Giga-IR 1 Gbps ***
Li-Fi >1Gbps ****

The table also contains the current wireless technologies that can be used for transferring data between devices today, i.e. Wi-Fi, Bluetooth and IrDA.  Only Wi-Fi currently offers very high data rates. The IEEE 802.11.n in most implementations provides up to 150Mbit/s (in theory the standard can go to 600Mbit/s) although in practice you receive considerably less than this. Note that one out of three of these is an optical technology.

Then looking ahead the table has 3 future wireless technologies; WiGig, GigaIR and Li-Fi. Note that 2 out of three of these technologies are optical.  Prior to WiGig, the new IEEE standard at 5GHz promises up to 1Gbit/s in the future, although at MWC I saw a rate of 200Mbit/s over a short distance being proudly demonstrated by one of the leading players using a prototype system. WiGig has claims of up to 7Gbit/s but in practice we might expect maybe 1.2Gbit/s or perhaps 2Gbit/s .  GigaIR is being developed by the Infrared Data Association (IrDA) and is aiming for 1Gbit/s.  Li-Fi is close to1Gbit/s in lab demonstrators using commercial light bulbs with the promise of much greater rates with higher bandwidth LEDs.

We usually compare communications technology by looking at their maximum data rates.  However, this provides a maximum under ideal conditions (short distances with no interference). Data rates can diminish quite rapidly under normal non-ideal conditions for some technologies. Radio based communication in particular suffers if several radio interferers operate in the same band in the same area.  This spectral congestion is rapidly increasing with the proliferation of wireless radio systems.  Data density (measured in bps per unit of area) is a much more useful way to compare these technologies. So the table also includes a relative measure of data density for each technology.


Extremely high data densities can be achieved with wired systems since there is little cross-talk interference between cables. The next in line are the optical wireless systems since the interference is directional and is well contained. Li-Fi has the best data density since the optical output from the LED light bulbs may greatly exceed that of infra-red.  WiGig is short range and requires complex antenna configurations to maintain directionality.  Another interesting comparison will be that of cost.  The optical systems use direct modulation of the light carrier and so are simple to implement, whereas WiGig requires additional radio and antenna circuits.

Wired systems shifted to optical technology to deliver very high data rates.  The indicators are that wireless systems will be following a similar trend.

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The shift to optical

We have seen long-haul communications cables move from copper to optical, we are seeing point to point wireless links starting to shift from microwave to free space optics. Short wired interconnects are also move towards optical links, and now VLC is continuing this trend with short range wireless.

So why has there been a shift towards optical technologies compared to copper conductors and wireless radio? While the reasons appear to be complex and varied, they do boil down to two key factors; cost and performance.

Free Space Optical linkLong-haul fibre took a long time to be fully adopted.  Initially in the late 1980s and early 1990s there was good supply of new fibre capacity and a lack of demand but then the Internet came along and changed that.  Point-to-point links between buildings have traditionally been microwave, but there is now a growing shift towards free-space optical (FSO) links giving Gbit/s capacities using lasers.

Plastic Optical FibreIn the local loop and interconnect we have seen low-cost plastic optical fibre (POF) interconnects widely used, initially for audio interconnects and now being widely proposed for future home networks.

If we now consider the problem we have today; there is massive demand for wireless data and the excess capacity using radio has dried up.  In the early 1990s optical fibre was technology led until the Internet. The current demand for wireless capacity is insatiable and creates a market led demand for alternative wireless technologies.  Looking at the contenders for short-range wireless in the Gbit/s range we seem to have 3 contenders; WiGig, GigaIR and of course VLC, or Li-Fi as we can now call it. You will notice that two out of these three are optical technologies.  The trend continues!

In a second article I will look at these technologies in a little more detail.

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PureVLC at Mobile World Congress

MWC 3×3

I spent 3 days at MWC with 3 objectives.

  • Launch the pureVLC brand
  • Get a snapshot of the current mobile landscape
  • Gauge how receptive the mobile industry is to Li-Fi.

PureVLC ™ is launched

Choose LiFiOn Monday we launched, or rather introduced, our new brand for the spin-out company, PureVLC ™. There was no ceremony and the idea of doing a press launch at MWC we knew was silly.  The media had much more interest in what the Google CEO or Facebook CTO had to say, not to mention major new products launches from the likes of Microsoft.  Instead we simply adopted the new name and style on Monday morning.  Most of 60,000 delegates wore dark suits and so we did get noticed in canary yellow polo shirts.

Mobile Landscape

MWC 2012 AndroidThere seems to be a lot of posturing for supremacy by the big boys.  Eric Schmitt saying he wants Android ‘in every pocket’.  Apple made the headlines by simply not being there.  Smart phones are dominant, apps are everywhere at the show and there was a lot of talk about the Internet of Things, although I suspect some were just applying a sexier name to last years M2M technology.


I could not get any data over the MWC Wi-Fi network so I tweeted away about the need for Li-Fi (using a slow cellular connection).  Wi-Fi was totally choked and several people told me how it was worse than last year, and asked why things seem to be going backwards. But, let’s pause on that note – why would it be much worse – surely there was no less infrastructure and I expect they made some upgrades.  Of course the answer lies in the fact that the demand has risen much faster than the technology improvements. We were all trying to email, tweet and post pictures live on social media, MWC themselves were sending emails with links to graphic filled web pages. Some delegates could be observed with iPhone in one hand and Blackberry in the other.


So we were discussing Li-Fi technology with people – the fact that the Wi-Fi was choked helped get the point across and we encountered much less resistance than expected.  I did observe that many people already knew something about the technology and were interested to learn more about the capabilities and status of the hardware. With one exception no one was dismissive.

MWC student protestProtests and riotsMWC protest turn violent

Student protestors had violent clashes with Police outside the MWC main gate yesterday over Spain’s austerity measures.  The main gate was closed, as were all roads around Plaça d’Espanya as armed police in heavy riot gear clashed with protestors.

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LEDs used to map Wi-Fi

The article “Immaterials: Light painting WiFi” by Einar Sneve Martinussen was published about a year ago and I confess I have only just stumbled across this.  It is an excellent piece of art meets engineering where LEDs and long image exposure times are used to visually map out Wi-Fi signal strength.

LEDs map out Wi-Fi in OsloI found the piece interesting in itself but also because it makes an interesting comparison between Wi-Fi and Li-Fi.  With Wi-Fi, to get the best data rate you must seek out the best signal strength – which is invisible. With Li-Fi it is obvious where the best data rate can be achieved – just find a spot which is well lit.


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Mobile World Congress, asking for more spectrum?

Mobile World Congress 2012I will soon be heading to Mobile World Congress (MWC) in Barcelona.  I am looking forward to a programme of meetings with some of the key mobile players and talking to them about visible light communications.

Redefining Mobile at MWC 2012The theme for MWC 2012 is redefining mobile. The overview states that “mobiles now serve as our books, health monitors, payment transfer devices, social connectors and tour guides. Mobile technology is embedded in our cars, homes, appliances, governments and utilities …”  and I think we cannot deny that this is true.

Looking through the programme and exhibition catalogue I can see a lot of exciting things happening although it is an evolution and nothing I see strikes me as radical.  Smarter smart phones, cleverer new apps, ever smaller infrastructure, better augmented reality, faster mobile cloud computing, and much more besides.  The event clearly reinforces the reasons for the growing use of wireless data – for everything mobile.

Forecast headlines like “Model Forecasts Unmet Mobile Data Demand Will Rise From 4.52 GB/day/km2 in 2011 to 72 GB/day/ km2 in 2016” and articles such as “Solving the Snowballing Wireless Data Problem” are being published on a regular basis.  So you might think that the spectrum shortage and capacity issues would be near the top of the industry’s agenda at MWC.  Well, the last seminar on the last day of the GSMA programme does deal with the topic in terms of spectrum availability under the title “Spectrum – It’s everybody’s business”. The overview states “Mobile is at the heart of a $1.2 trillion Oliver Twist asks for moreindustry…. Spectrum is the oxygen that sustains this ecosystem and with data demands rising, you need to support ‘the ask’ for future spectrum. This seminar will explain amongst other topics, why it is important to complement ‘the ask’ for future spectrum and how to advocate for additional spectrum to your respective governments.”  So there you have one solution from the mobile industry. Ask your government for more spectrum – please, can I have more?

Charles Dickens (200 today) famously wrote about a boy who was encouraged to ask for more, with some limited success I recall!

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Li-Fi it is then!

Harald Haas coined the “Li-Fi” term in his TED Global talk last year. It seems to have resonated well and the term has begun to be used generally to describe high speed optical wireless communications.

I confess, I was not a fan of the term from day one.  To me, the name suggested a direct alternative to Wi-Fi and I felt it might send out the wrong message about VLC.  In the same way as Wi-Fi can be viewed as complimentary to cellular data, I view VLC as an assistant to Wi-Fi in areas where very high data rates are required in a localised area.

The term Li-Fi has just appeared on the front cover of February’s Wired magazine and was added to Wired’s Jargon Watch.

February 2012 Wired Magazine Li-FiThis week it has been used widely in an article on visible light communication in The Economist “Tripping the light fantastic”.  The superb illustration by Dave Simonds even has the Li-Fi name emblazoned on the light bulb.

The Economist Li-Fi My old elevator pitch on VLC always had to be short since my office is just on the second floor. It went along the lines of “we turn light bulbs into Wi-Fi”  This was sometimes interpreted as we stick a wireless radio module into the bulb so I often had to explain what this really meant.  However, I have found with the term Li-Fi people seem to get the concept quicker.  They identify it as similar to Wi-Fi but obviously with a twist.  “Li” standing for “light” when explained gets the difference across and importantly is easily remembered.

Li-Fi appears to be heading towards common parlance, so Li-Fi it is then!

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LEDs powered by Ethernet

Back in October I posted a blog item on Power over Ethernet (PoE).  I am briefly revisiting this because Raffaele Soloperto of Allnet sent me this excellent picture.

Power over Ethernet Switch for Visible Light CommunicationPoE is ideal for VLC since the power and data signals are all carried over a single cable.  The power required for powerful LED lamps has been decreasing over the years, and at the same time the power that can by provided by PoE has increased.  Allnet have demonstrated beautifully that now it is practical to power LEDs directly from an Ethernet switch.

It seems that one of my New Year predictions for VLC has just got one step closer.

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Casio announces VLC prototype

Casio exhibited their Visible Light Communication system at the Consumer Electronic Show (CES) in Las Vegas this week.

I was not at CES so this post is based on a number of reports I have obtained from various sources about their VLC prototype.  Also, here is the link to their official press release about the prototype.

Casio use the smart phone display to transmit the data which can be captured on the smart phone’s camera.  A VLC App is required on both the transmitting and the receiving smart phone devices.  The transmitting device sends the data by displaying a large spot on the screen which rapidly changes colour.  The receiving device’s camera is pointed towards the spot on the display and the images are processed to decode the information.  I am told that it takes a few seconds to transmit the equivalent of a short message or tweet.

Casio Visible Light CommunicationsAccording to Nobuo Iizuka, a research manager at Casio, the spots need to be 1cm in diameter for every meter of transmission distance.  This means that a small spot could be added to TV commercial adverts, or to electronic billboards to transmit a URL.  Several transmit devices can be used simultaneously if they are all within the view of the camera.  I did hear about a few operational issues in practice with sunlight, reflections and shadows.

Clearly there are a number of applications that could use this.  I do know that my Edinburgh University colleagues have also developed low data rate VLC receivers using standard smart phones.  What Casio have done additionally is to use the smart phone display as the transmitter.

I think the important point to note is; if useful applications can be developed based on low data rate VLC systems with unmodified smart phones, then logically even more useful applications can be created if the smart phone has its sensors adapted for much higher data rates.

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Five VLC predictions for 2012

Gordon Povey predicts the future!Gordon Povey looks into his crystal ball and makes some interesting predictions about visible light communication in 2012.

I believe that 2012 will prove to be a turning point for optical wireless communications and VLC commercialisation.  In 2011 we saw the green shoots of an industry emerge and this year I expect we will see the delivery of something real.  Here are my predictions:

  1. The IEEE 802.15.7 standard will be improved during 2012 and OFDM modulation schemes adopted to provide higher data rates.  The dimming schemes will also be improved to maintain data throughput in heavily dimmed conditions.  Colour shift keying (CSK) modulation schemes are unlikely to evolve during 2012 since most LEDs currently being deployed are single colour types and not RGB.  If this standard does evolve during 2012, I believe that VLC products will start to become IEEE compliant in 2013.
  2. Smart phone based positioning products using LED lamps or modulated displays will be piloted in the market.  ByteLight and Casio ones to watch in this space.
  3. Early products for Wi-Fi spectrum relief will also be piloted during 2012.  I believe these will be complementary to Wi-Fi to ease congestion, rather than a replacement technology.  VLC Ltd will definitely be active in this space and I believe we will see competition from Japan and Germany.
  4. I think we might see a low-cost product using LEDs indicator lamps for device-to-device communications.  This will be at a low data rate possibly using the LED as both transmitter and receiver in a half-duplex mode.  As I mentioned in an earlier post this could emerge in a toy, or could even be in an electronic door lock.
  5. I am not expecting any Power over Ethernet (PoE) VLC products this year but I will predict that a PoE based LED lamp type of product might make the market as a forerunner to this.

The only certain thing about predictions is that they rarely turn out to be accurate. I am, however, confident that some of this will come true.  It will be interesting to review the situation again in December 2012.

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VLC; a review of 2011

Looking back over 2011 there is evidence that a Visible Light Communication industry now exists.

At the end of 2010 we saw the IEEE 802.15.7 standard being published and LVX System made the press with what was claimed to be the first commercial VLC system.  So, the first seeds appeared to be sown.  While the IEEE standard has not really developed further, and LVX have gone very quiet, there are other green shoots emerging that suggests the birth of an industry.

In early February I attended the Smart Lighting Engineering Research Center’s Academia – Industry Day at the Boston University and it was clear that there was growing academic and industry interest in the VLC area.

The European Omega Project concluded in March of 2011 and produced a number of working demonstrations of VLC including high data rate systems.

In July Harald Haas delivered his TED Global presentation and for the first time it seems that a general public audience grasped the importance of this technology when he demonstrated HD video transmitted from a desk lamp.

HHI VLC image

Image source: Heinrich Hertz Institute

During the year we have seen the emergence of ByteLight and VLC components from Outstanding Technologies. The Heinrich Hertz Institute have made a number of announcements. The first report on VLC was published by GBI Research, the LiFi Consortium was launched.

In December the second IEEE Workshop on Optical Wireless Communications Workshop was held at Globecom in Houston and prompted some lively debates.  At the panel session is seemed to be widely agreed that an industry is emerging and 2012 will be an exciting year for Visible Light Communications.

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