Visible Light Communication

It’s been a while since last time, you might be wondering what’s next with communication infrastructure. It’s light this time. It recently has appeared as buzz word Visible Light Communication all across online media channels.

How light can transmit information

Visible light can be guided through an optic fiber which is for instance connected to your home PC. However, when you switch on a light bulb, you immediately see that light can propagate also through free space. The term VLC (Visible Light Communication; sometimes also called Li-Fi) refers to the latter, while FSO (Free Space Communication) refers to invisible light communication.

Information transmission requires a certain amount of spectral bandwidth (Hz). A certain pure color – let’s say blue – has a very narrow bandwidth but poses a high carrier frequency where enough sideband spectrum is available – green is far away. The carrier frequency is modulated by an RF source which contains the information. Modulation causes the light source to change its intensity, either continuously or on/off. The modulation frequency is very high for broadband communication and the flicker not visible by the human eye.

Differences to RF transmission

If light is blocked between transmitter and receiver, there is no communication, except when using a white reflecting surface amplifying indirect light. It therefore cannot be tapped from outside. It doesn’t interfere with RF spectrum and contains much more bandwidth capacity than the RF range. It’s cheap and doesn’t consume much energy.

Visible light has been existing even before life developed (in fact, it was even a prerequisite for life). It is therefore safe to say that VLC is not dangerously interfering with biologic matter. But be advised that if you are encountered by millions of illuminated LED’s, you might not feel at ease with this light smog.

It will not disrupt everything

The VLC market gained traction in 2013 and is forecasted to grow heavily and become a $6b market in 2018. Oh I forgot to mention that even 1782 b.c. there was a VLC market, or haven’t you ever seen a bonfire? There are several commercial industry solutions that allow data rates up to 1 Gbit/s per color. Also, VLC is currently being standardized within IEEE.

Even though technology has become available, even though it can ease the spectrum demand in the RF range and even though LED’s are anyway implemented in electronic devices, there are intrinsic properties that simply prevents from becoming an ubiquitous technology. Weak light sources will heavily rely on a line of sight, which for mobile things is generally not given. Also, daylight means heavy noise and thus limited data rate. It will rather coexist with other transmission technologies like the RF and THz spectrum, even combined with them as triple-stack solution in order to increase bandwidth. However, be assured that indoor and outdoor light sources (household devices, car lights, street lights, …) might exchange information with each other – or with the mobile device you’re carrying with you.

So, don’t switch off the light