  In this letter, a C-RAN-type cluster-head-driven uplink model for
multiple-antenna Unmanned Aerial Vehicles (UAV) relaying schemes, which enables
joint Maximum Likelihood (ML) symbol detection in the UAV cluster-head and the
selection of UAV sources to communicate with each other aided by UAV-based
relays, {is presented. In this context,} a relay selection technique, named
Cluster-Head-Driven Best-Link (CHD-Best-Link), that employs cluster-head
buffers and physical-layer network coding, {is devised}. Then, a recursive
maximum minimum distance relay selection strategy that exploits time-correlated
channels and equips the CHD-Best-Link scheme is developed. Simulations
illustrate that CHD-Best-Link has superior average delay and bit error rate
performances to that of previous schemes.
