Coherence Diversity DoF in MIMO Relays: Generalization, Transmission Schemes, and Multi-Relay Strategies

This paper studies the MIMO relay with nonidentical link coherence times, a condition known as coherence diversity. This happens in practice when a node or the scatterers surrounding it have different mobility compared with the conditions at or around other nodes. In this paper, coherence diversity in relays is studied under link coherence intervals with arbitrary (unequal) length and alignment. Second, a new transmission scheme under coherence diversity is proposed in which the relay transmission is given a duty cycle based on the balance between the gain versus the channel training costs in the relay-destination link. Finally, we investigate multiple parallel relays operating under non-identical coherence intervals, propose transmission strategies, and calculate degrees of freedom.