Measuring the impact of outdated channel state information in interference alignment techniques

Interference alignment has been proposed as a transmission technique to cancel the interference for the K-user interference channel at high signal-to-noise ratio. In the case of multiple-input multiple-output (MIMO)-transmission the interference can be aligned in a subspace of the receiver antennas. In this work we investigate the impact of outdated channel state information (CSI) due to temporal channel variations on the performance of interference alignment. Experimental transmissions of real-time precoded signals from an indoor and outdoor MIMO testbed exhibit performance degradation due to outdated CSI. Furthermore, a model is proposed and evaluated that describes the temporal channel fluctuations based on these measurements.