When we use smartphones or tablet PCs to surf the internet, check emails, share pictures, engage in social networking, or store information in a cloud, we make use of wireless communications technology.
Traditionally, all the information we move around with these devices is transmitted using radio frequency spectrum. The more data we generate, the more radio frequency spectrum we need.
It is forecast that by the year 2015, we will transmit six exabytes -- six billion, billion bytes -- every month through wireless networks. This is a ten-fold increase on the amount of data we send now.
In order to meet this increased demand, we need either 10 times more radio frequency spectrum for commercial wireless networks, or we have to make the existing radio frequency spectrum 10 times more efficient.
The first is impossible -- most of the available radio frequency spectrum is already used. The second option is difficult to achieve, as existing wireless technology is very sophisticated, and it has been shown that further improvements are often offset by unmanageable complexity.
Therefore, we are heading to a saturation point in terms of how efficiently we can use the radio frequency spectrum. The only way out of this is to find new ways to transmit data wirelessly. Fortunately, the electromagnetic spectrum not only incorporates the radio frequency spectrum, but also includes the visible light spectrum, the best know transmitter of which is the sun.
In the past we used incandescent light bulbs in our homes and offices. This technology is more than 100-years-old and, as such, is hugely inefficient. In the past decade, there have been massive developments in the use of light emitting diodes (LEDs). Since LEDs are far more energy efficient than incandescent bulbs, they are at the heart of the latest generation of lights. In fact, research by my team at the University of Edinburgh has shown that, if all the world's incandescent light bulbs were replaced by LED, the energy saved would be equivalent to that produced by more than 100 nuclear power stations.
However, this is not the only advantage of LEDs. These lights are semiconductor devices similar to transistors, which are commonly found in devices such as TVs, laptops or smartphones. Like transistors, LEDs can be switched on and off very quickly.
We have harnessed this feature to develop novel techniques that enable ordinary LED light bulbs to wirelessly transmit data at speeds many times faster than WiFi routers. We have named the new technology Li-Fi (light fidelity) which we now commercialize via the university spin-out company VLC Ltd.
In our lab, under ambient light conditions, we are able to achieve data speeds of 130 megabits per second. If all light bulbs were able to do this, it would create a simple, energy-efficient solution to the lack of available radio frequency spectrum for future wireless broadband communication. The new Li-Fi technology utilizes existing infrastructures and as a result the installation costs are minimal, let alone the reduced cost of the technology as it does not require an antenna.
On top of this, there are other advantages to this technology. Light does not penetrate walls, and so internet signals cannot be intercepted outside the room in which they are transmitted, which enhances security. Light also travels through water, and so short-range underwater communication is possible. For instance, divers could share pictures, or remotely operated vehicles could exchange information.
Light is inherently safe and can be used in places where radio frequency communication is often deemed problematic, such as in aircraft cabins or hospitals. So visible light communication not only has the potential to solve the problem of lack of spectrum space, but can also enable novel applications.
In the not-too-distant future, a day in the life of an average person, whom we'll call Sally, could look like this:
- When Sally switches on the light in the morning, she gets the latest news flashed on her smartphone. From the breakfast table she sends a few emails through the table light.
- Sally gets into her car and drives to work. On the way, a cat crosses the street and she has to brake hard. Her LED backlights tell the car behind to slow down even before the driver has a chance to brake -- an accident is avoided.
- Sally stops in front of a traffic light that operates using LEDs. While showing red, the traffic light is able to send a signal to switch off the engine in Sally's car, reducing CO2 emissions. The traffic light also communicates with the navigator inside the car, and helps Sally avoid a traffic jam ahead.
- In the office, Sally's fast internet access is provided through the LED ceiling lights. She has internet access in all meeting rooms, but no-one on the street outside can intercept the signals.
- After work she decides to go to an art gallery to pass the time until she meets Tom, her new boyfriend, for a date at a restaurant downtown. The LED spotlights in the gallery illuminate the pictures and provide information about them.
- Sally leaves the art gallery and, on the way downtown, she passes some shops. LED lights in the shop windows broadcast offers. She buys a pair of shoes on sale.
- The restaurant is in a large shopping mall. Sally's navigation system guides her there. Inside the mall, LED ceiling lights take over the task of guiding her to the restaurant.
- Once inside the restaurant, LED table lights beam the menu card onto Sally's smart-phone. She enjoys her meal and leaves a recommendation on the restaurant's home page, using the connection from the same table light.
- By the time Sally leaves the restaurant it is dark. She is in a good mood after her date. On the way back to her car, she leaves a little message at a street light, which acts as a local message board, saying "Sally loves Tom" -- just as in the past she might have carved the same into a tree.
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