Improving optical wireless networks

FSO is a licence-free optical wireless networking technology, having numerous advantages over conventional radio frequency systems. Nevertheless, atmospheric effects cause performance losses over link distances greater than 1 km.

The EU-funded 'Free-space optical systems for next generation communication networks' (FOCUS) project studied cooperative (relay-assisted) FSO for long range links. The work aimed to address FSO performance shortcomings using efficient physical layer solutions tailored to the characteristics of particular FSO channels. Turkey's Ozyegin University administered the project between September 2010 and August 2014.

Research into relay-assisted FSO systems with intensity modulation/direct detection (IM/DD) yielded various relaying architectures. The team investigated the fundamental performance bounds of proposed relay-assisted systems using tools from communication and information theories and demonstrated significant performance gains through relaying. The project also produced optimal relay placement strategies for additional performance improvements.

The EU team further studied coherent FSO systems which are more difficult to implement in practice, but provide more flexibility and further performance enhancements with respect to IM/DD counterparts. Finally, the team proposed and analysed a relay-assisted quantum key distribution scheme, which improves performance over long distances.

Overall, the FOCUS project helped to overcome limitations of FSO systems. The performance improvements helped with development of reliable, fast and secure long-range FSO communication systems.