Define FDMA $($Frequency Division Multiple Access$)$ and briefly explain how it differ from TDMA.

b$)$ What is the advantage of using FDMA and how does it handle simultaneous communication by multiple users

c$)$ Briefly explain how frequency spectrum divided in FDMA and define frequency channel in FDMA.

d$)$ In a second$-$generation cellular communication system, the available bandwidth is $25$ MHz$.$ The system adopts

Frequency Division Multiple Access $($FDMA$)$ with a channel spacing of $50$ kHz$.$ Calculate the multiple access

spectral efficiency for FDMA in this system.