Figure 13

The dashed lines with circle markers denote the asymptote for the system if the expectation for ${\left({\mathit{\sigma }}_{\mathit{z}}^{\mathbf{2}}\mathbf{/}\mathbf{2}\right)}^{\mathbf{-}{\mathit{N}}_{\mathit{r}}}$ is obtained via simulations. The solid lines with square markers denote the asymptote when (32) is used. Moving from the rightmost to the leftmost pairs of curves, each pair corresponds to an incremental increase in N _r from 2 to 6. The system is using two transmit antennas and has an overall spectral efficiency of 5 bits/s/Hz.