Unitary precoding for MIMO interference networks

For MIMO interference networks, uncertainty in the spatial structure of interfering signals is a major source of performance degradation. In this work, we promote the use of linear unitary precoding, as it can be designed such that downlink transmission becomes more robust. Optimizing linear unitary precoding is a combinatorial and nonconvex problem, thus no efficient methods to compute global optimal solutions are available. Therefore, methods with reasonable complexity and acceptable performance are desired and have been investigated in research literature as well as for practical implementation. Contrary to existing work on unitary precoding, which considers receivers with a single antenna, we target scenarios with multiple receive antennas. We introduce and discuss a low-complexity method for successive user and precoder selection to enable unitary precoding for multi-antenna receivers. In addition to interference robustness, our novel method has several advantages for potential implementations, concerning the channel feedback and computation of optimal receive filters. Initial results by numerical simulations indicate that our approach has the potential to outperform existing methods.