  Multiple-input multiple-output (MIMO) technology has significantly impacted
wireless communication, by providing extraordinary performance gains. However,
a minimum inter-antenna space constraint in MIMO systems does not allow its
integration in devices with limited space. In this context, the concept of
fluid antenna systems (FASs) appears to be a potent solution, where there is no
such restriction. In this paper, we investigate the average level crossing rate
(LCR) of such FASs. Specifically, we derive closed-form analytical expressions
of the LCR of such systems and extensive Monte-Carlo simulations validate the
proposed analytical framework. Moreover, we also demonstrate that under certain
conditions, the LCR obtained coincides with that of a conventional selection
combining-based receiver. Finally, the numerical results also provide insights
regarding the selection of appropriate parameters that enhance the system
performance.
