Steerable Light Antenna for Enhanced QoS Cell-Free LiFi Networks – SAFELiFi

LiFi is seen as a relevant connectivity solution to cope with the traffic explosion expected with 5G and even more with 6G. LiFi systems currently used for indoor network access, for example in offices, are based on the concept of cells generated by access points (APs) installed in the ceiling. By deploying multiple APs, continuous coverage of an entire room can be provided, with data rates of up to 100 Mbps per cell for some products. However, this LiFi network topology is subject to many constraints. For example, specific interference management and handover mechanisms between APs are required to ensure continuous communication to users on the move. These mechanisms require the transmission of a significant amount of signalling data in addition to the payload data, which limits the throughput and latency dedicated to the users and therefore reduces the quality of service (QoS). Furthermore, one user's data can be listened to by another user in the same cell, which, although less likely than in the case of radio communications, poses security problems.

To solve these problems, the SAFELiFi project proposes to develop a cell-free LiFi system. Each AP would be equipped with steerable light antennas capable of tracking users' movements in real time in order to provide them with a focused, directional optical signal. The optical links thus established between APs and users would then maintain a very high signal-to-noise ratio and be less prone to interference, thus considerably improving QoS. Furthermore, due to their directionality, these links would be very difficult to capture by a hostile device and therefore extremely secure in a physical sense.

To achieve such a system, six fundamental building blocks will have to be developed: 1) a localisation and tracking algorithm; 2) a steerable hardware platform, which will track the served users based on the information from the localisation algorithm; 3) an optimised optoelectronic header dedicated to the transmission and reception of high-speed optical signals over several wavelengths; 4) an optimised physical layer with, in particular, a modulation optimised for high signal-to-noise conditions; 5) a handover/horizontal load balancing mechanism to distribute traffic between APs and to manage AP changes when a user is mobile and 6) a handover/vertical load balancing mechanism to distribute traffic between LiFi network and radio network (e.g. WiFi network) and to switch from one technology to the other if necessary (e.g. to switch to the WiFi network if the LiFi link is blocked by an obstacle).

The final objective of the project is to set up a demonstrator consisting of four APs and four users, but which will then be easily scalable. Each link between the AP and the user would achieve a throughput of 2 Gbps with a latency of 1 ms. In addition, several links could be aggregated at the user level (e.g. by wavelength multiplexing or via several APs), so that a user would have a throughput of 5 Gbps available. To achieve this objective, the SAFELiFi project will last 42 months and will involve two PhD students and an engineer, in addition to several permanent LISV staff, including Bastien BECHADERGUE who will be the coordinator.