Intelligent Reflecting Surface Systems

While the fifth-generation (5G) wireless network is still being under deployment, researchers all around the world already work on upcoming beyond 5G networks, such as the sixth-generation (6G) wireless network. In 6G networks, the requirements to the system are even more demanding as compared to 5G networks, i.e., ultra-high data rates, global coverage and connectivity, as well as extremely high reliability and ultra-low latency. A promising technology, which is able to significantly improve the performance of wireless communication networks and meets the described requirements are intelligent reflecting surface (IRS) systems.

An IRS system is a planar surface, which consists of a large number of low-cost passive reflecting units. Each of the passive reflecting units is capable of manipulating the amplitude and/or the phase to the incident signal independently. Thus, IRS systems are key enablers to reconfigure the radio propagation environment in wireless networks. In essence, with the help of IRS systems the wireless link performance can be enhanced and smart and controllable wireless environments can be realized.

We work on algorithms to jointly optimize the phases at the IRS together with the precoder at the base station. The additional elements at the IRS pose new challenges to the system optimization as they have to fulfill certain requirements (e.g. passivity). Furthermore, the channel estimation phase is more complicated as the additional channels to and from the IRS have to be estimated as well. This has to be done at the base station because the IRS has no RF chains but can only reflect the incoming wavefronts. Another aspect is therefore to find efficient channel estimation algorithms for this new scenario, especially with the goal of minimizing the number of needed pilot symbols.