b$.$Explain the difference between amplitude$-$shift keying $($ASK$)$ and phase$-$shift keying $($PSK$)$ modulations with the aid of suitable diagrams.

$(4$ marks$)$

c$.$

i$.$Explain what is meant by Gray encoding and provide an advantage of Gray codes over binary codes.

$(2$ marks$)$

ii$.$Consider the $16-$PSK signal constellation. Use the Gray encoding technique to provide a labelled $16-$PSK constellation diagram. Ensure each point is labelled with a suitable code.