$1$a$).$In a cellular system with $7-$cell cluster, $168$ voice channels are available. Determine the assignment of voice channels to each cell$/$ sector if:$-$

$($a$).$ Omnidirectional antennas are used at cell site, $($b$)3-$sector $120$ directional antennas are used at cell site, $($c$)6-$sector $60$ directional antennas are used at cell site.

$1.$b$)$ Mr$.$ Phunkshuk Wangdu is travelling from Dimna Hill Top to NIT Jamshedpur. Consider that up to Mango, his mobile phone is under the base station located at Mango and after that the phone is under the base station located at Bistupur. Execute ground reflection model for radio propagation when, $($a$)$ Mr$.$ Wangdu is at Dimna Hill $($b$)$ Mr$.$ Wangdu is in NIT Jamshedpur.