Correlation Diversity in MIMO Broadcast and Coherence Diversty in the MIMO Relay Channel

Abstract

The links in wireless networks may have non-identical spatial correlation or coherence times when nodes have different scatters around them or they have unequal mobility. This phenomenon can occur in massive MIMO and high-mobility scenarios. This dissertation investigates the multiuser broadcast channel when the links have non-identical spatial correlations and relay channel with unequal coherence times. It is found that exploiting the disparity in these different fading conditions for multiple users can lead to gains over techniques that do not take advantage of this disparity. For the MIMO broadcast channel with non-identical spatial transmit correlation, we broaden the scope of transmit correlation diversity to the case of partially and fully overlapping eigenspaces and introduce techniques to harvest these generalized gains. We derive achievable degrees of freedom regions and achievable rate regions and then extend the degrees of freedom results to the K-user case by analyzing the interference graph that characterizes the overlapping structure of the eigenspaces. For the massive MIMO experiencing different spatial transmit correlation, we propose a strategy combining product superposition and beamforming that applies to any configuration of transmit correlation eigenspaces, leveraging of the statistical characteristics of massive MIMO channels to reconcile the incompatibility of product superposition and beamforming. To demonstrate the characteristics of this technique, we calculate the sum rate of K-user downlink under two correlation models. For the MIMO relay with non-identical link coherence times, we calculate the achievable degrees of freedom under this condition. Product superposition technique is employed at the source which allows a more efficient usage of degrees of freedom when the relay and the destination have different training requirements. Analysis is provided and varying configurations of coherence times are studied, including unaligned coherence blocks and arbitrary length of coherence times.