Terabit Bidirectional Multi-user Optical Wireless System (TOWS) for 6G LiFi

Given the unprecedented demand for mobile capacity beyond that available from the RF spectrum, it is natural to consider the infrared and visible light spectrum for future terrestrial wireless systems. Wireless systems using these parts of the electromagnetic spectrum could be classified as nmWave wireless communications system in relation to mmWave radio systems and both are being standardised in current 5G systems. TOWS, therefore, will provide a technically logical pathway to ensure that wireless systems are future-proof and that they can deliver the capacities that future data intensive services such as high definition (HD) video streaming, augmented reality, virtual reality and mixed reality will demand. Light based wireless communication systems will not be in competition with RF communications, but instead these systems follow a trend that has been witnessed in cellular communications over the last 30 years. Light based wireless communications simply adds new capacity - the available spectrum is 2600 times the RF spectrum. 6G and beyond promise increased wireless capacity to accommodate this growth in traffic in an increasingly congested spectrum, however action is required now to ensure UK leadership of the fast moving 6G field. Optical wireless (OW) opens new spectral bands with a bandwidth exceeding 540 THz using simple sources and detectors and can be simpler than cellular and WiFi with a significantly larger spectrum. It is the best choice of spectrum beyond millimetre waves, where unlike the THz spectrum (the other possible choice), OW avoids complex sources and detectors and has good indoor channel conditions. Optical signals, when used indoors, are confined to the environment in which they originate, which offers added security at the physical layer and the ability to re-use wavelengths in adjacent rooms, thus radically increasing capacity. Our vision is to develop and experimentally demonstrate multiuser Terabit/s optical wireless systems that offer capacities at least two orders of magnitude higher than the current planned 5G optical and radio wireless systems, with a roadmap to wireless systems that can offer up to four orders of magnitude higher capacity. There are four features of the proposed system which make possible such unprecedented capacities to enable this disruptive advance. Firstly, unlike visible light communications (VLC), we will exploit the infrared spectrum, this providing a solution to the light dimming problem associated with VLC, eliminating uplink VLC glare and thus supporting bidirectional communications. Secondly, to make possible much greater transmission capacities and multi-user, multi-cell operation, we will introduce a new type of LED-like steerable laser diode array, which does not suffer from the speckle impairments of conventional laser diodes while ensuring ultrahigh speed performance. Thirdly, with the added capacity, we will develop native OW multi-user systems to share the resources, these being adaptively directional to allow full coverage with reduced user and inter-cell interference and finally incorporate RF systems to allow seamless transition and facilitate overall network control, in essence to introduce software defined radio to optical wireless. This means that OW multi-user systems can readily be designed to allow very high aggregate capacities as beams can be controlled in a compact manner. We will develop advanced inter-cell coding and handover for our optical multi-user systems, this also allowing seamless handover with radio systems when required such as for resilience. We believe that this work, though challenging, is feasible as it will leverage existing skills and research within the consortium, which includes excellence in OW link design, advanced coding and modulation, optimised algorithms for front-haul and back-haul networking, expertise in surface emitting laser design and single photon avalanche detectors for ultra-sensitive detection.