$5\mathrm{.}7$ If a baseband binary message with a bit rate $\backslash ($ R$\_\{$b$\}=100\backslash$mathrm$\{$kbps$\}\backslash )$ is modulated by an RF carrier using BPSK$,$ answer the following:

$($a$)$ Find the range of values required for the rms delay spread of the channel such that the received signal is a flat$-$fading signal.

$($b$)$ If the modulation carrier frequency is $5\mathrm{.}8$ GHz $,$ what is the coherence time of the channel, assuming a vehicle speed of $30$ miles per hour?

$($c$)$ For your answer in $($b$),$ is the channel "fast" or "slow" fading?

$($d$)$ Given your answer in $($b$),$ how many bits are sent while the channel appears "static"?

$($e$)$ A CDMA Rake receiver is able to exploit multipath when the channel is $($circle all that apply$)$

$($a$)$ flat;

$($b$)$ slow;

$($c$)$ fast;

$($d$)$ frequency selective