Hi Abdel,
mostly silence call/blank voice was due to transmsion problem not in radio part and defined as normal call.
if the problem occured due to transmisiion problem, try to conduct verticality check in Abis and Ater. check every single port/slots which have problem. u can query and localize problem from BSC log in ftp data.
after u do it, u can localize which port or slot which have problem, then do troubleshooting with instalation team…
might help.