Degrees of Freedom of Multi-hop MIMO Broadcast Networks with Delayed CSIT

TL;DR

This paper investigates the maximum sum degrees of freedom in multi-hop MIMO broadcast networks with delayed channel state information, revealing how feedback scenarios and network parameters influence capacity.

Contribution

It provides the first characterization of the optimal sum DoF for multi-layer relay-aided MIMO networks with delayed CSIT under practical feedback assumptions.

Findings

Optimal sum DoF is K/(1+1/2+...+1/K) with full-layer feedback.

Achievable sum DoF is 4/3 for K=2 and 3/2 for K>=3 with hop-limited feedback.

Sum DoF depends only on K, not on the number of layers N.

Abstract

We study the sum degrees of freedom (DoF) of a class of multi-layer relay-aided MIMO broadcast networks with delayed channel state information at transmitters (CSIT). In the assumed network a K-antenna source intends to communicate to K single-antenna destinations, with the help of N-2 layers of K full-duplex single-antenna relays. We consider two practical delayed CSIT feedback scenarios. If the source can obtain the CSI feedback signals from all layers, we prove the optimal sum DoF of the network to be K/(1+1/2+...+1/K). If the CSI feedback is only within each hop, we show that when K=2 the optimal sum DoF is 4/3, and when K >= 3 the sum DoF 3/2 is achievable. Our results reveal that the sum DoF performance in the considered class of N-layer MIMO broadcast networks with delayed CSIT may depend not on N, the number of layers in the network, but only on K, the number of antennas/terminals in each layer.