i am not sure if antenna hopping is something that is standardized in 3GPP. Therefore, antenna hopping might mean different things for different vendors…
anyway, here is how it works for ALU:
a TRX transmits one TDMA frame through one antenna, and the next one through the other antenna.
This is a feature that works only with twinTRX.
The benefit is that each timeslot is sent over two different antenna, alternatively, so that helps fighting fast fading. Radio coverage is increased.