$($b$)$ A $900MHz$ digital cellular network has the following characteristics:

up$-$link of $925-945MHz$

R$-$F channel spacing $=400kHz$

number of time slots per R$.$F channel $=8$

Determine the:

$($i$)$ channel bandwidth;

$($ii$)$ number of up$-$link RF channels;

$($iii$)$ total number of up$-$link TDM channels.

$(7$ marks$)$