As demand for mobile capacity continues apace, wireless communications using the radio frequency (RF) spectrum have been required to accommodate ever-increasing amounts of data, presenting challenges for future capacity, especially for the uplink from the device to the access point. However, if supplementary spectra could be identified and harnessed, these offer the potential to expand existing bandwidth and support higher levels of connectivity.  Thus, the TOWS project proposed a solution to the growing demand for data-intensive services such as high definition (HD) video, augmented reality (AR) and virtual reality (VR).

Objectives

The vision of TOWS was to:

• Develop and experimentally demonstrate multiuser terabit-per-second optical wireless systems that offer capacities of at least two orders of magnitude higher than the current, planned 5G optical and radio wireless systems
• Accompany with a roadmap to wireless systems that can offer up to four orders of magnitude higher capacity
• Help ensure UK leadership of the fast moving 6G field, by developing technologies that can increase wireless capacity to accommodate future growth in traffic in an increasingly congested spectrum

Methodology

Work was under taken to exploit the infrared spectrum, a form of optical wireless communications (OWC), by creating a new, light-based wireless system that complements, and operates in parallel to, Wi-Fi and cellular networks, and supports bi-directional communication.  To achieve this, a novel, scalable grid-of-beam (GoB) multi-user access point (AP) architecture, using vertical cavity surface emitting laser (VCSEL) arrays, was designed, to enable wide-coverage and ultra-high-speed, multi-user connectivity based on narrow laser beams with data rates > 10 Gb/s per beam.

Major LRDC contributions within TOWS comprised:

• Advanced beam clustering schemes to effectively share communication resources and allow full-beam coverage, by coordinating inter-beam interference and eliminating inter-cluster interference, leading to enhanced energy efficiency and network resilience
• Advanced, wide field-of-view receiver architectures based on imaging/non-imaging optics and high-speed photodiode arrays to provide laser-grade connectivity with seamless coverage
• A terabit-capacity back-haul system using VCSEL arrays, robust to misalignment errors, to support aggregate data rates generated by each access point
• Efficient algorithms for the eye safety analysis of VCSEL arrays with optics, which is a crucial aspect of the system design.

As well as:

• Providing a holistic and rigorous comparison between optical wireless and Terahertz (THz) wireless technologies under a unified framework for future-proof applications
• Evaluating and developing technology demonstrators, including a 70 Gb/s VCSEL-based OWC link and real-time transmission of ultra- HD video through VCSEL-based optical wireless links.

Impact

Trials of the resulting indoor, terabit-per-second, multi-user wireless system demonstrated that it can leverage the availability of 2,600 times more unregulated spectrum compared to current RF technologies and achieve a 100 times the capacity of 5G systems, as well as provide a roadmap for developing the wireless systems of the future.

Key academic partners: the Universities of Cambridge, Edinburgh and Bath, and Kings College London (also Lead Research Organisation), working in close conjunction with major industry partners: the BBC, Airbus Germany and Microsoft. An additional 23 partners from academia and industry made up the full consortium.

The TOWS project was funded by the EPSRC for a duration of 2.5 years and completed in March 2025.