Adaptive Reliable Receivers for Optical Wireless communication (ARROW)

The gradual shrinkage of cell sizes in mobile cellular networks and applying frequency reuse techniques has been the main approach to cope with the exponential growth of capacity demands over the last few decades. However, the outdoor deployment of 5G cells will require a large-scale expansion of the backhaul network. The most preferred backhaul solution is based on highly reliable and high-speed fibre optic links; however, their use is limited to a fraction of the current backhaul network because of overwhelming installation costs. Free space optical (FSO) communication is an attractive alternative solution that provides high-capacity but cost-effective wireless backhaul connectivity without interfering with radio frequency (RF) communication systems. However, despite decades of technological advances, FSO links still suffer from availability issues in the form of occasional long outages in adverse weather conditions. This is because classical high-speed FSO receivers such as avalanche photodiodes (APDs) may totally fail under low visibility weather conditions. The important question is, therefore, whether we can build high-speed atmospheric optical communication links that can reliably operate over all weather conditions while providing data rates beyond their RF counterparts.

ARROW aims to address the question above by combining classical and quantum optical receptions to allow for adaptive operation of FSO receivers within a wide range of sensitivity levels while keeping high-speed communication. However, highly sensitive quantum detectors such as single photon avalanche diodes (SPADs) are not practically suitable for terrestrial FSO links as they can easily saturate at typically high irradiance levels experienced at such links while their bandwidth is limited by effects such as dead time. ARROW's hybrid receiver employs an APD along with a large array of SPADs integrated into a single chip. The large size of array effectively relaxes the saturation issue of the SPAD-based detector while allowing for spectrally efficient modulations that can significantly improve its achievable data rate.

ARROW receivers will combine the functionality of the classical and quantum detectors using hard and soft optical switching and efficient digital signal processing to support adaptive operation based on the slow varying weather condition. In order to design efficient switching and signal processing, we will develop an accurate but tractable theoretical model that describes the hybrid channel in terms of different atmospheric effects (e.g., visibility and background light level) and their interaction with the hybrid receiver's characteristics (e.g., SPAD dead time, detectors field of view, and optical splitting ratio). Based on this model, a number of optical frontend designs and advanced modulation and joint coding schemes will be proposed to enhance both data rate and reliability of the receiver. Finally, the adaptive functionalities of the hybrid receiver will be experimentally demonstrated and validated. ARROW FSO receivers are expected to provide carrier grade availability for a wide range of practical link geometries and geographical locations.

Economic impacts:

The fixed and mobile data traffics in the UK are set to increase, respectively, at rates of 100% every two years and 25% to 42% per year. ARROW will lay an important foundation to support the efficient expansion of UK's digital communication infrastructure by developing high-speed alternative solutions based on the emerging but affordable optical wireless technology. ARROW receivers are attractive solutions for both terrestrial (e.g., backhaul and broadband connectivity) and satellite-to-ground applications where atmospheric effects can be limiting.

ARROW will potentially impact photonics, and telecommunication industries within the manufacturing sector by providing new designs and applications that can be well adopted inline with the large expansion of 5G networks nationally and internationally. Our partnership with ST Microelectronics will help us to accelerate such impacts by translating the research conducted in the project into higher technology readiness levels and ultimately generating economic impact through licensing or spin-out formations.

A recent research reports that increased broadband speeds alone could add £17 billion to UK output by 2024, which strongly suggests that a commercial success of ARROW can deliver potential economical impacts on many small and large industries particularly within the service sector that rely on digital economy. This would include the banking system, streaming service providers, social media service providers, cloud computing providers, online retailers, etc.

Societal Impacts:

With the advent of Internet of things, the dependence of our daily life to the quality and robustness of Internet connections become more apparent. Another important societal issue that we are facing today is the migration of a significant portion of daily social interactions into social media. This amplifies the expectations of the general public for ubiquitous data connectivity with high levels of quality of service. Therefore, ARROW can potentially impact the society and the general public by contributing to the improvement of mobile and broadband networks as our today's day-to-day activities, more than ever, depend on data connectivity. In general, the project promotes the use of light as a natural and economical medium for carrying data supporting high-speed, ubiquitous, and secure data connectivity, which would be of wide societal interest.

Impacts on the professional community:

ARROW's impacts will be further extended by contributing into the development of expert researchers/engineers in the emerging field of optical wireless communication. In particular, the project will be an important step in the professional development of the research associate and PhD students who would be involved in this project. Furthermore, ARROW will disseminate knowledge to the wide community of engineers working in telecommunications, optoelectronics, photonics and quantum technology. This knowledge will be in the form of fundamental theoretical models, novel designs and experimental data.