Figure $3\mathrm{.}12$ from Block $1$ shows the bit error rate performance in terms of signal$-$to$-$noise ratio per bit

i$.$Explain why is the metric used, instead of S$/$N ratio, for digital transmissions communication.

ii$.$Find $($in dB$)$ the required at for PSK constellations BPSK$,8$PSK and $16-$PSK that are shown in Figure $3\mathrm{.}12$ from Block $1$

iii.What is the advantage of $8-$PSK versus BPSK$?$

iv$.$Explain why the bit error rate is increased for $8-$PSK from BPSK$.$