Interference Alignment over a Combination of Space and Frequency

Time or frequency extensions are integral in most information theoretic studies of interference alignment (IA), but a large majority of the more practically oriented studies have focused on narrowband space-only schemes. As wideband systems are now common, it is natural to investigate IA for frequency extended multiple antenna systems where precoding is performed over a combination of space and frequency dimensions. For this setting, we derive a necessary condition on IA feasibility using the properness framework and investigate the sum rate performance using simulations. Applying frequency extensions to multiple antenna systems allows for some additional users to be served interference-free, but our numerical results with synthetic channels indicate a practically more important improvement in terms of a power gain. Emulating a particular scenario using channel measurements, with real-world path losses and channel correlations, we see similar performance gains.