wireless connection do not reconnect

Guys,

I am still new to the wireless technology. I am workin as consultant in
aproject to deploy wireless mobile Panasonic ToughBook using HSDPA sim card,
utilising telco's Radius server. The dialer is Mobilink by Novatel configured
in NDIS mode.
we have been experiencing intermittent issues, where by some times when you
are in black spot, you lose coverage but the dialler does not appear to
reconnect. in some cases until Hot shut down on the machine.The Dialler is
configured UMTS only 850 + GPRS 900/1800. I have tried to enable the windows
logs i.e eapol etc, but got no idea how to interpret them.

Can anyone help me me on :

1) what is the prob?
2) How the best way I can tell the Root Cause