Antenna selection and reassignment in multiple radio access technology (RAT) communication systems with unlicensed spectrum is disclosed. Aspects include a user equipment (UE) monitoring for a channel reserving signal in each frame from multiple transmission sources. If no channel reserving signal is detected, then the UE reassigns one or more of the antennas previously assigned to the transmission sources with no activity detected. Additional aspects include base stations that determine a clear channel assessment (CCA) status for each of unlicensed carrier designated for transmission to a UE. The base station will transmit a receive antenna usage adjustment signal to the UE based on the determined CCA status.