Analytical Characterization of the Operational Diversity Order in Fading Channels

We introduce and characterize the operational diversity order (ODO) in fading channels, as a proxy to the classical notion of diversity order at any arbitrary operational signal-to-noise ratio (SNR). Thanks to this definition, relevant insights are brought up in a number of cases: 1) We quantify that in dominant line-of-sight scenarios an increased diversity order is attainable compared to that achieved asymptotically, even in the single-antenna case; 2) this effect is attenuated, but still visible, in the presence of an additional dominant specular component; 3) the decay slope in Rayleigh product channels increases very slowly, never fully achieving unitary slope for a finite SNR.