Multi-User MIMO Communications
In cellular networks, the spatial degrees of freedom offered by several antennas at the base station allow serving multiple users simultaneously by transferring data to and from the users. The resulting transmit and receive strategies, referred to as multi-user MIMO, potentially lead to significant gains in throughput since several data streams can be transmitted simultaneously. This gain is called multiplexing gain and does also appear in point-to-point MIMO settings. In particular, we work on multi-user MIMO in the context of massive MIMO, i.e., setups where the base station has a very large number of antennas and is able to serve a high number of users to fully exploit the multiplexing gains.
In these large-scale systems, a lot of challenges need to be solved, e.g., analyzing the achievable performance of massive MIMO systems based on physical models, reducing the computational complexity, or acquiring channel state information. The massive MIMO setup becomes even more challenging when considering frequency-division-duplex (FDD) mode, where uplink-downlink
channel reciprocity does not hold as compared to time-division-duplex systems. Therefore, we work on designing transmit strategies for the downlink of FDD systems, that not only aim to mitigate the inter-user interference
but also account for the contaminated channel state information available at the base station. Specifically, we investigate the application of rate splitting multiple access in combination with statistical precoding techniques
and its ability to enhance the system throughput.