Improved Interference Alignment Performance for MIMO OFDM Systems by Multimode MIMO Antennas

This contribution presents an improved Interference Alignment (IA) method for arbitrary MIMOOFDM communication systems by exploiting spatial degrees of freedom of sophisticated multimode MIMO antennas. It is widely known that IA needs sufficient orthogonality between all the multi-user channels which is in typical indoor environments often not given due to insufficient spatial diversity. A significant improvement of the IA system performance has been achieved by using multimode MIMO antennas instead of classical and idealized omni-directional antennas. Such multimode MIMO antennas are capable to switch between different modes of the radiation patterns which significantly reduces the relevant channel coherence. Simulations of an indoor multi-user environment are carried out by a deterministic MIMO-OFDM channel model based on hybrid Electro Magnetic (EM) ray-tracing for being as close as possible to reality. Moreover, hardware implementation aspects are discussed as well demonstrating the feasibility of the overall IA based MIMO OFDM system.