We live in a world of wireless communications, from the early days of radio to new digital television, Wi-Fi and the latest 4G (soon to be 5G) connected smart devices.
But there are limits to this wireless world. With the prediction of 12 billion mobile-connected devices by 2021 and a projected sevenfold increase in wireless traffic, the search is on for any new method of wireless connectivity.
One solution could be right before our very eyes, if only we could see it.
Current wireless connections
All wireless applications – such as mobile communications, Wi-Fi, broadcasting, and sensing – rely on some form of electromagnetic radiation.
The difference between these applications is simply the frequency of the signal (the carrier frequency) used in the electromagnetic radiation.
For example, current mobile phones sold as 3G and 4G operate in the lower microwave frequency bands (850MHz, 1.8GHz, 2-2.5GHz). A wireless local area network such as Wi-Fi operates in the 2.4GHz and 5GHz bands, whereas digital terrestrial television operates at 600-620MHz.
The spectrum of electromagnetic radiation covers a very broad range of frequencies and some of these are selected for specific applications.
These frequency regions are highly contested and valuable resources for wireless applications.
Running out of spectrum
Our current spectrum use in the lower microwave region will soon be heavily congested, even exhausted. It would be difficult to squeeze any more spare spectrum for any wireless application.
To carry an information content on to one of these frequencies, the frequency bands need sufficient bandwidth – the amount of information that can be transmitted – to meet future requirements. At the lower end of the spectrum, there are insufficient bandwidths to meet speeds exceeding gigabits per second.
At the higher end of the spectrum, ionising radiation such as x-rays and gamma rays cannot be used because of safety issues.
Despite current 4G wireless standard promising more shared capacity (1Gb/s), the projected demand and traffic volume already pushes the existing infrastructure to its ultimate limit. The future promise of 5G communication only adds to the problem.
A major rethink of the current wireless technologies is needed to meet these challenging requirements.
Let there be light!
The wireless transmission of optical signals has emerged as a viable option. It offers advantages not possible with current wireless technologies.
Optical wireless promises greater speed, higher throughput, and potentially lower energy consumption. Leveraging on existing optical wired infrastructures (namely optical fibre cables and networks), optical wireless connectivity can provide a seamless high capacity to end-users.
An example would be using optical wireless connectivity inside buildings to complement fibre-to-the-home deployments.
Optical wireless networks would be immune to electromagnetic interference and so could be deployed in radio frequency (RF) sensitive environments. You’ve probably seen those warning signs asking you not to use your mobile phone in hospitals, aircraft and other areas where equipment is sensitive to interference.
Optical wireless communications can be divided into visible light and infrared systems.
And let there be sight
A common issue with both is that devices need to be in the line of sight, as any physical obstruction can result in the loss of transmission. You may have experienced this issue when attempting to change a channel on TV if someone or something gets in the way of your remote.
Visible light communication (VLC) relies on LEDs that are also used for lighting. For example, by flashing LED lights located in the ceiling of a room at a rate much higher than can be discerned by the human eye, information can be conveyed to detectors around the room.
The major limitation of VLC is the limited bandwidth of commercially available white LED (~100 of MHz) that limits the transmission speeds.
Infrared communication systems have ample bandwidth with the potential of transmission tens of Gb/s per user. Despite the major advantage over VLC, the need for line-of-sight has seen this technology under-developed. Until now.
To overcome this we have demonstrated an infrared-based optical wireless communication link that can support a user on the move. By using a pair of access points with some spatial separation, any blockage of beams can be easily overcome as users hop from beam to beam freely.
Optical wireless systems can be built to make sure there is a secure wireless transmission. Using efficient wireless protocols it’s possible to transmit data without any delay and to allow users to move within a building while enjoying high speed wireless coverage.
Optical wireless in action
We will in future be using a range of devices, such as virtual reality (VR) and augmented reality (AR) devices, that all require superfast wireless connections.
For example, these new user interfaces are poised to make a big difference to the way museums and galleries will operate in the future. Currently, most of these platforms are linked via wired connections. But wireless interfaces will make them more easy to be used in applications.
The uptake of optical wireless as a viable communications technology can also drive further possibilities of using low-cost optical wireless transceivers to substitute expensive optical fibre rollout in rural and regional broadband contexts.
The integrated transceivers for infrared optical wireless communications are still under development and more effort is needed to speed up such integration efforts. But the researcher teams here and abroad are trying to make advances in the way such systems can be used in realistic scenarios.
Authors: Thas Ampalavanapillai Nirmalathas, Director - Networked Society Institute and Professor of Electrical and Electronic Engineering, University of Melbourne