Explain, giving an example, the concept of "spatial reuse of frequencies".

$(5$ marks$)$ b$.$ Explain $($in one sentence$)"$co$-$channel interference". Where in a cell might cochannel

interference be worst? Explain $($in one sentence$).$

$(5$ marks$)$ c$.$ Explain $($in one sentence$)$ why multi$-$path propagation can lead to signal loss,

and give a brief example.

$(5$ marks$)$ d$.$ A city of size $28$ km$2$ is to be covered by a digital cellular phone network. The

spectrum re$-$use cluster size is $7$ cells, and each cell has area $1$ km$2$

$.$ Assume that

the cells perfectly fit the city size without overlap. If the system bandwidth is

$49$ MHz$,$ and FDM is used where each user is allocated $25$ kHz including

guardband, how many users can simultaneously make calls in the system? How

many can simultaneously make calls per cell?

$(5$ marks$)$ e$.$ The GSM system uses TDM to transmit data. Eight users share a TDM frame of

duration $4\mathrm{.}615$ milliseconds $($ms$),$ where each user transmits a $148-$bit data

frame. There is a guard time of $0\mathrm{.}030$ ms$.$ What is the peak bit rate of the user?