Exploiting Coherence Time Variations for Opportunistic Blind Interference Alignment

The observed coherence times associated with different wireless transmitters at any given user may vary at different rates. We demonstrate how these variations can be exploited for interference management. More precisely, we propose a new opportunistic blind interference alignment (BIA) strategy in the context of K -user interference channels that exploits these variations in coherence times and provides significant data rate gains. We first provide a proof-of-concept setup in which the information about coherence time variations is available non-causally to the transmitters, and we demonstrate how transmitters and receivers can perform pre-coding and post-processing, respectively, to align a considerable part of the interference signal power. We note that in this non-causal scenario, no channel state information is available to the transmitters, and we make no specific assumption on the channel distributions. We take the key ideas of this scenario and consider a K -user interference channel in which the direct links vary at a higher pace compared to the cross links. This assumption is motivated by considering mobile users, or by using our proposed transmit antenna for stationary or low-mobility users. We show how to eliminate the need for non-causal knowledge of coherence time variations, and still provide significant capacity gains.