use threads;
use Net::...

my $ssh = ...;
$ssh->scp_put($firmware[$antenna_type],'/tmp/fwupdate.bin');

async {
    print "Upgrading firmware, this will take about 3 minutes.\n";
    my $chan = $ssh->channel();
    $chan->exec("/sbin/fwupdate -m\n");
    $chan->close;
}->detach;

...