Wireless optical communication

How does it work?

In telecommunications, the notion ‘optical communication’ is usually understood as optical fibre communication. Optical fibres provide light waves with good propagation and allow communication over long distances and at high speeds. But that’s not the only way to communicate using light, because it can also be done wirelessly, when modulated beams of light propagate directly through the air (or space).

We call this Free Space Optical Communication (FSO or FSOC). The transmitting device (Tx) converts electrical signals into pulses of light and sends them into space (with a wide cone or narrow beam, depending on the intended use), and the receiving device (Rx) converts the incoming light back into electrical signals. In practice, it would be good for the transmitter and receiver to be one device (and the two beams of light can fly opposite each other without affecting each other).



Free Space Optical Communication has quite a few advantages allowing for new usages:

  • Very high transmission speeds can be achieved. Today’s solutions reach bandwidths of 10 Gb/s.
  • It allows for communication over distances of kilometers (and even thousands of kilometers in space) with relatively low energy consumption.
  • It is more difficult to eavesdrop than radio communications, because you have to be physically in the path of the light. This has its benefits especially in closed spaces, as it does not penetrate walls (which can be a disadvantage in other usages)
  • The link can be set up easily and quickly.
  • You don’t need any licenses or officially assigned frequencies for this, as it is the case with radio communications

But it must be admitted that it also has some significant drawbacks:

  • The light beam can be obscured by something e.g., a passing bird. So you need to plan the distribution of nodes in a way to minimize this risk.
  • Rain, fog or snow can temporarily significantly reduce throughput or even prevent transmission (this problem does not exist indoors).
  • The transmitter must be very well aimed at the receiver. The greater the distance, the more difficult this is to achieve, especially if mounted on flexible mast-like structures. For longer distances or mobile heads, the beam needs to be controlled adaptively, which involves more complication of the heads. Or you can use a wider beam and accept the greater power consumption. This makes mobile usages difficult.
  • The receiver can be easily blinded dazzled. And this can be done with a completely legal equipment (while, for example, radio jamming is not legal).

What do we do with FSO?

Wireless optical communication is the main axis of the Perfect project. The project is carried out by a consortium consisting of the Heinrich Hertz Institute, VI Systems, Warsaw University of Technology and EXATEL. The main objective is to develop a new type of semiconductor laser that will be particularly well suited for optical communications due to its speed of operation and the profile of the generated beam. This will be achieved through the design of a structure consisting of many small cells, each of which is an independent laser, and proper control of them ensures optimal beam parameters. The construction of the laser is handled primarily by HHI and VI Systems, while Warsaw University of Technology will test the solution on a laboratory scale.

EXATEL’s role is to develop communication protocols that enable efficient and secure communication for selected target products using optical communication. In more complex scenarios, network building using SDN solutions developed by EXATEL may also be applicable in other projects.

However, to do this, such promising usage must first be identified and validated, and as  can be seen in the frame, despite the many advantages of optical communications, its drawbacks may limit these usages. So you have to find niches where the disadvantages are not so severe or are balanced by the advantages. And it can be done. For example, there are places where radio use must be restricted (i.e., Wi-Fi), or places where large electromagnetic interference even makes the use of it impossible. This is where optics could be a great solution (wires as well, but it is not always a good choice). An optical alternative to Wi-Fi also comes to light – a Li-Fi (from light).

A technology demonstrator will be built for the selected most promising usage, which will enable the verification of product assumptions and checking how optical communications performs in reality, under various conditions.

Author: Wojciech Gołębiowski, Research and Development Project Manager, EXATEL