$($a$)($i$)$ Describe direct sequence spread spectrum $($DSSS$)$ technique as used in wireless communication.

$($ii$)$ State two communication technologies which apply the spread spectrum technique in $($i$).$

$(6$ marks$)$

$($b$)$ Table $2$ shows different wireless modulation schemes. Complete the table.

$(6$ marks$)$

Table $2$

$\backslash$table$[[\backslash$table$[[$Modulation$],[$scheme$]],\backslash$table$[[$Code bits per$],[$sub carrier$]],\backslash$table$[[$Data$],[$rate$]],\backslash$table$[[$Baud$],[$rate$]]],[$BPSK$,,54,],[$QPSK$,,216,],[16-$QAM,,$864,]]$

$($c$)$ A GSM $800MHz$ digital cellular network has the following parameters:

Two way bandwidth $=25MHz$

$RF$ channel spacing $=400$kII.

Number of users per RF channel $=16$

Number of TDMA control channel per cell $=6$

Area of a cell $=8k{m}^2$

Total coverage area $=8000k{m}^2$

Determine the:

$($i$)$ number of RF channels;

$($ii$)$ TDM channels;

$($iii$)$ TDM traffic channels per cell;

$($iv$)$ number of cells.

$(8$ marks$)$